Relative molecular mass. 44.01
Chemical name. Nitrous oxide; CAS Reg. No. 10024-97-2.
Other name. Nitrous oxide.
Description. A colourless gas; odourless.
Solubility. One volume dissolves in about 1.5 volumes of water at a pressure of 101.3 kPa and a temperature of 20 °C.
Category. Inhalational anaesthetic gas.
Storage. Dinitrogen oxide should be kept as compressed gas or liquid at very low temperatures, in appropriate containers complying with the safety regulations of the national authority. Valves or taps should not be lubricated with oil or grease.
Labelling. An ISO standard1 requires that cylinders containing Dinitrogen oxide intended for medical use should bear the name of the contents in legible and permanent characters and, preferably, also the molecular formula N2O.
1 International Standard 32. Gas cylinders for medical use - marking for identification content. International Organization for Standardization, Switzerland, 1977.
Additional information. In the analysis of medicinal gases certain tests are not intended for hospital pharmacists. They are applicable solely by laboratories equipped with specialized apparatus.
Requirements
Dinitrogen oxide contains not less than 98.0% v/v of N2O in the gaseous phase, when sampled at 15 °C.
Note: If the analysis is performed on a cylinder, keep the cylinder of the gas to be examined at room temperature for at least 6 hours before carrying out the tests. Keep the cylinder in the vertical position with the outlet valve uppermost.
The test for carbon monoxide should be carried out on the first portion of gas drawn from the container and the tests for nitrogen monoxide and nitrogen dioxide immediately thereafter.
Identity tests
• Either test A alone or tests B, C, and D may be applied.
A. Carry out the examination as described under 1.7 Spectrophotometry in the infrared region. The infrared absorption spectrum is concordant with the reference spectrum of dinitrogen oxide.
B. Place a glowing splinter of wood into the gas; the splinter bursts into flame.
C. Shake the gas with alkaline pyrogallol TS; it is not absorbed and the solution does not become brown (distinction from oxygen).
D. Mix the gas with an equal volume of nitrogen monoxide R; no red fumes are produced (distinction from oxygen).
Carbon monoxide
• Either test A, test B, or test C may be applied.
• The tests should be carried out on the first portion of gas released from the container.
A. The apparatus (Fig. 6) consists of the following parts connected in series:
- a U-tube (U1) containing desiccant silica gel R impregnated with chromium trioxide R;
- a wash bottle (F1) containing 100 ml of potassium hydroxide (~400 g/l) TS;
- a U-tube (U2) containing pellets of potassium hydroxide R;
- a U-tube (U3) containing phosphorus pentoxide R dispersed on previously granulated, fused pumice;
- a U-tube (U4) containing 30 g of recrystallized iodine pentoxide R in granules, previously dried at 200 °C and kept at a temperature of 120°C (T) during the test. The iodine pentoxide is packed in the tube in 1-cm columns separated by 1-cm columns of glass wool to give an effective length of 5 cm;
- a reaction tube (F2) containing 2.0 ml of potassium iodide (160 g/l) TS and 0.15 ml of starch TS.
Flush the apparatus with 5.0 litres of argon R. If necessary, discharge the blue colour in tube F2 containing potassium iodide (160 g/l) TS by adding a sufficient volume of freshly prepared sodium thiosulfate (0.002 mol/l) VS. Continue flushing with argon R until not more than 0.045 ml of sodium thiosulfate (0.002 mol/l) VS is required after the passage of 5.0 litres of argon R. Pass 5.0 litres of the test gas from the container through the apparatus. Flush the last traces of liberated iodine into the reaction tube by passing 1.0 litre of argon R through the apparatus. Titrate the liberated iodine with sodium thiosulfate (0.002 mol/l) VS. Repeat the procedure using 5.0 litres of argon R.
Figure 6.
Apparatus for the determination of carbon monoxide in medicinal gases
Measurements in mm.
Reproduced with the permission of the European Pharmacopoeia Commission, European Directorate for the Quality of Medicines, Council of Europe.
The difference between the volumes of sodium thiosulfate (0.002 mol/l) VS used in the titrations is not more than 0.25 ml (5μl/l).
B. Carry out the test as described under 1.14.5 Gas chromatography, using a stainless steel column (2m × 4mm) packed with a 0.5-nm molecular sieve (e.g. X13, obtainable from a commercial source). Maintain the column at 80 °C, and the injection port and the detector at room temperature. Use helium R as the carrier gas at a flow rate of 60 ml per minute, and a helium ionization detector.
Use the following gases: (1) the test gas; and (2) a mixture containing 5μl of carbon monoxide R in 1 litre of dinitrogen oxide R as the reference gas.
Inject a suitable volume of both gases (1) and (2). Adjust the volume, as well as the conditions specified above, to produce a peak response for carbon monoxide obtained with the reference gas (2) that gives a height of not less than 5% on the recorder.
Measure the areas of the peak responses obtained in the chromatograms from injections 1 and 2 and calculate the content of carbon monoxide in the test gas (1) by comparing with the peak response for carbon monoxide obtained from the reference gas (2); not more than 5μl/l.
C. Determine the content using a carbon monoxide detector tube. Pass the required volume of the test gas through the tube, the calibration of which is verified according to the manufacturer's instructions.
The gas supply is connected to a pressure regulator and needle valve. Connect the flexible tubing fitted with a Y-piece to the valve and adjust the flow of the test gas to purge the tubing to an appropriate flow. Fit the carbon monoxide detector tube to the metering pump according to the manufacturer's instructions. Connect the open end of the tube to the short leg of the tubing and pump a suitable volume of the test gas through the tube. Read the value corresponding to the length of the coloured layer or the intensity of the colour on the graduated scale; not more than 5μl/l.
Note: For the following tests - Nitrogen monoxide and nitrogen dioxide, Carbon dioxide Test A, Halogens and hydrogen sulfide, and Acidity and alkalinity - pass the gas to be tested through the appropriate reagent contained in a hermetically closed flat-bottomed glass cylinder, with dimensions such that 50ml of liquid reaches a height of 12-14 cm, that is fitted with (a) a delivery tube terminated by a capillary 1 mm in internal diameter and placed within 2mm of the bottom of the cylinder; and (b) an outlet tube.
Prepare the reference solutions in identical cylinders.
Nitrogen monoxide and nitrogen dioxide
• Either test A or test B may be applied.
• This test should be performed after release of the 5.0 litres of gas as described above under "Carbon monoxide, test A".
A. Pass the test gas through two of the cylinders connected in series as described above under "Carbon monoxide, test A". To obtain the liquid phase invert the gas cylinder; the liquid vaporizes on leaving the valve.
To 50 ml of water add 1.2 ml of sulfuric acid (~1760 g/l) TS and dilute with sufficient water to produce 100 ml. To 15 ml of this solution add 375mg of potassium permanganate R, mix, and transfer to the first cylinder (solution A).
Dissolve 1 g of sulfanilic acid R in a mixture of 180 ml of water and 10ml of glacial acetic acid R (solution 1). Separately dissolve 0.2g of N-(1- naphthyl)ethylenediamine hydrochloride R in a mixture of 4 ml of glacial acetic acid R and 5 ml of water, heat gently, and dilute to 200 ml with water (solution 2). Mix 1 volume of solution 2 with 9 volumes of solution 1 and transfer 20 ml of this mixture to the second cylinder (solution B).
Connect the outlet tube of the first cylinder to the delivery tube of the second cylinder containing solution B. Pass 2.5 litres of the test gas through the reagents at a rate of 15.0 litres per hour.
Prepare a reference solution by adding 0.25 ml of a solution containing 61.6μg/ml of sodium nitrite R in water to 20 ml of solution B as prepared above. Allow the test solution and reference solution to stand for 10 minutes.
Examine the gaseous and the liquid phases separately.
For both gaseous and liquid phases, any red colour produced from the solution of the test gas is not more intense than that from the reference solution (2μl/l of NO + NO2).
B. Determine the content using a nitrogen monoxide and nitrogen dioxide detector tube. Pass the required volume of the test gas through the tube, the calibration of which is verified according to the manufacturer's instructions.
The gas supply is connected to a pressure regulator and needle valve. Connect the flexible tubing fitted with a Y-piece to the valve and adjust the flow of the test gas to purge the tubing to an appropriate flow. Fit the nitrogen monoxide and nitrogen dioxide detector tube to the metering pump following the manufacturer's instructions. Connect the open end of the tube to the short leg of the tubing and pump a suitable volume of the test gas through the tube. Read the value corresponding to the length of the coloured layer or the intensity of the colour on the graduated scale; not more than 2μl/l.
Carbon dioxide
• Either test A, test B, or test C may be applied.
A. Pass 1.0 litre of the test gas through 50 ml of a clear solution of barium hydroxide (0.15 mol/l) VS. Similarly prepare a reference solution by adding 1.0 ml of a 1.1 mg/ml solution of sodium hydrogen carbonate R in carbondioxide- free water R to 50 ml of barium hydroxide (0.15 mol/l) VS.
Any turbidity in the solution after the passage of the the test gas is not more intense than that of the reference solution (300μl/l).
B. Carry out the test as described under 1.14.5 Gas chromatography, using a stainless steel column (3.5m × 2mm) packed with ethylvinyl-benzenedivinylbenzene copolymer. Maintain the column at 40 °C and the detector at 90 °C. Use helium R as the carrier gas at a flow rate of 15 ml per minute, and a thermal conductivity detector.
Use the following gases: (1) the test gas; and (2) a mixture containing 300μg of carbon dioxide R in 1 litre of dinitrogen oxide R as the reference gas.
Inject a suitable volume of both gases (1) and (2). Adjust the volume, as well as the conditions specified above, to obtain a peak response for carbon dioxide obtained with the reference gas (2) of a height of not less than 35% on the recorder.
Measure the areas of the peak responses obtained in the chromatograms from the injections of gases 1 and 2 and calculate the content of carbon dioxide in the test gas (1) by comparing with the peak response for carbon dioxide obtained from the reference gas (2); not more than 300μl of CO2 per litre.
C. Determine the content using a carbon dioxide detector tube. Pass the required volume of the test gas through the tube, the calibration of which is verified according to the manufacturer's instructions.
The gas supply is connected to a suitable pressure regulator and needle valve. Connect the flexible tubing fitted with a Y-piece to the valve and adjust the flow of the test gas to purge the tubing to an appropriate flow. Fit the carbon dioxide detector tube to the metering pump according to the manufacturer's instructions. Connect the open end of the tube to the short leg of the tubing and pump a suitable volume of the test gas through the tube. Read the value corresponding to the length of the coloured layer or the intensity of the colour on the graduated scale; not more than 300μl/l.
Halogens and hydrogen sulfide. Pass 20.0 litres of the test gas through a mixture of 1 ml of silver nitrate (40 g/l) TS and 49 ml of water at a flow rate not exceeding 15 litres per hour.
Prepare the reference solution as follows: to 1.0 ml of silver nitrate (40 g/l) TS add 40 ml of chloride standard (5μg/ml) TS and 0.15 ml of nitric acid (~130 g/l) TS, dilute to 50 ml with water, and allow to stand protected from light for 5 minutes. For the blank solution, repeat the procedure passing the test gas through 50 ml of water.
Compare a 100-mm layer of the solution as described under 1.11 Colour of liquids.
The solution of the test gas does not darken when compared with the blank. Any opalescence is not more intense than that of the reference solution (10μg Cl per litre of dinitrogen oxide).
Water
• Either test A or test B may be applied.
A. The apparatus consists of either an electrolytic hygrometer as described below, an appropriate humidity detector tube, or a capacity hygrometer.
The measuring cell consists of a thin film of phosphoric anhydride placed between two coiled platinum wires which act as electrodes. The water vapour in Dinitrogen oxide is absorbed by the phosphoric anhydride to form phosphoric acid which acts as an electrical conductor.
Before introducing the test gas into the device, allow the gas to stabilize at room temperature and make sure that the temperature is constant throughout the apparatus. Apply a continuous voltage across the electrodes to produce electrolysis of the water and regeneration of phosphoric anhydride. Measure the resulting electric current, which is proportional to the water content in the test gas. (This is a self-calibrating system that obeys Faraday's law.)
Calculate the content of water; not more than 60μg/l.
B. Determine the content using a water vapour detector tube. Pass the required volume of the test gas through the tube, the calibration of which is verified according to the manufacturer's instructions.
The gas supply is connected to a suitable pressure regulator and needle valve. Connect the flexible tubing fitted with a Y-piece to the valve and adjust the flow of the test gas to purge the tubing to an appropriate flow. Fit the water vapour detector tube to the metering pump according to the manufacturer's instructions. Connect the open end of the tube to the short leg of the tubing and pump a suitable volume of the test gas through the tube. Read the value corresponding to the length of the coloured layer or the intensity of the colour on the graduated scale; not more than 60μl/l.
Acidity and alkalinity. Pass 2.0 litres of the test gas through a mixture of 0.10 ml of hydrochloric acid (0.01 mol/l) VS and 50 ml of carbon-dioxide-free water R.
For reference solution 1, use 50 ml of carbon-dioxide-free water R. For reference solution 2, use a mixture of 0.20 ml of hydrochloric acid (0.01 mol/l) VS and 50ml of carbon-dioxide-free water R.
To each solution add 0.1 ml of methyl red/ethanol TS; the intensity of the colour in the test gas solution is between that of reference solutions 1 and 2.
Assay. Determine as described under 1.14.5 Gas chromatography, using a stainless steel column (2m × 2mm) packed with silica gel for chromatography R (250-355μm). Maintain the column at 60 °C and the detector at 130°C. Use helium R as the carrier gas at a flow rate of 50 ml per minute, and a thermal conductivity detector.
Use the following gases: (1) the test gas; and (2) dinitrogen oxide R as the reference gas.
Inject a suitable volume of both gases (1) and (2). Adjust the volume, as well as the conditions specified above, to produce a peak response for dinitrogen oxide obtained with reference gas (2) that gives a height of not less than 35% on the recorder.
Measure the areas of the peak responses obtained in the chromatograms from the injections of gases (1) and (2), and calculate the percentage content of dinitrogen oxide.
Saturday, 22 August 2009
Monographs: Pharmaceutical substances: Dinatrii edetas - Disodium edetate
C10H14N2Na2O8,2H2O
Relative molecular mass. 372.2
Chemical name. Disodium dihydrogen (ethylenedinitrilo)tetraacetate dihydrate; N,N'-1,2-ethanediylbis[N-(carboxymethyl)glycine] disodium salt, dihydrate; CAS Reg. No. 6381-92-6.
Other name. Edetate disodium.
Description. A white, crystalline powder; odourless.
Solubility. Soluble in water; slightly soluble in ethanol (~750 g/l) TS; practically insoluble in ether R.
Category. Stabilizer; chelating agent.
Storage. Disodium edetate should be kept in a well-closed container.
Additional information. Solutions of disodium edetate should not come into contact with metal.
Requirements
Disodium edetate contains not less than 98.5% and not more than the equivalent of 101.0% of C10H14N2Na2O8,2H2O.
Identity tests
• Either test A alone or tests B, C, and D may be applied.
A. Carry out the examination as described under 1.7 Spectrophotometry in the infrared region. The infrared absorption spectrum is concordant with the spectrum obtained from disodium edetate R or with the reference spectrum of disodium edetate.
B. To 3 drops of ferric chloride (25 g/l) TS add 3 drops of ammonium thiocyanate (75 g/l) TS; to the deep red solution produced add 0.05 g of Disodium edetate; the colour is discharged, leaving a yellowish solution. (Keep this solution for test D.)
C. Dissolve 2 g in 25 ml of water, add 2 ml of lead nitrate (100 g/l) TS, shake, and add 6 ml of potassium iodide (80 g/l) TS; no yellow precipitate is observed.
D. To the solution from test B, add ammonia (~100 g/l) TS, drop by drop, until an alkaline reaction is obtained with pH-indicator paper R. Add 5 ml of ammonium oxalate (25 g/l) TS; no precipitate is produced (distinction from sodium calcium edetate).
Heavy metals. Use 1.0 g for the preparation of the test solution as described under 2.2.3 Limit test for heavy metals, Procedure 3; determine the heavy metals content according to Method A; not more than 20 μg/g.
pH value. pH of a 0.05 g/ml solution, 4.0-5.5.
Assay. Dissolve 0.5 g, accurately weighed, in sufficient water to produce 300 ml. Add 2 g of methenamine R and 2 ml of hydrochloric acid (~70 g/l) TS. Titrate with lead nitrate (0.1 mol/l) VS to which 50 mg of xylenol orange indicator mixture R has been added.
Each ml of lead nitrate (0.1 mol/l) VS is equivalent to 37.22 mg of C10H14N2Na2O8,2H2O.
Saturday, 1 August 2009
Silicone Excipients in Drug Development
A versatile ingredient works in excipient applications
By Gerald K. Schalau II and Katherine L. Ulman
Silicones have a range of applications in the pharmaceutical industry, from active ingredients in antacids to tubing used in drug processing. They also are used as excipients in topical pharmaceutical creams, ointments and lotions. These applications depend on the versatility and distinctive physicochemical and performance properties of silicone fluids, gums, and gels, which can offer combinations of formulating solutions not available with other ingredients. Low surface tension, improved aesthetics, substantivity, high permeability, nonstaining properties, and the ability to protect and deliver active ingredients allow contract manufacturers expanded formulating opportunities to meet the evolving needs of their customers.
 |
An Expanding Role for Silicones
As the functional properties of excipients become more critical to the performance of pharmaceutical products — for example, their impact on bioavailability of drugs — contract manufacturers can benefit from considering excipients with versatility to fill a number of roles. Although silicones can function as active ingredients, they are more often used as excipients. Examples include siliconization (lubrication of syringe barrels, pistons, needles or stoppers), skin adhesives in transdermal patches (based on their adaptability for drug permeability), volatile or nonvolatile agents to improve spreading and aesthetic properties, or carriers for active ingredients. With silicone excipients, a key factor for success is selecting from a range of materials to provide specific functionalities and performance characteristics throughout the shelf life of the drug product.
The use of silicones to improve a pharmaceutical application or its aesthetics might be considered a form of technology transfer from the personal care industry. Silicones have been incorporated into skin care products since the early 1950s, and today at least 50% of newly launched skin care products contain at least one silicone. However, many silicones also have been used in healthcare applications, as evidenced by the number of silicone materials listed on the FDA’s inactive ingredient list. The silicones used in healthcare applications are among the most extensively tested materials for safety, and they are known to provide a pleasant silky, nongreasy and dry feel on skin.
Aiding Patient Compliance
The sensory properties of silicone excipients can be important factors in assisting patients who do not comply with treatment regimens because their prescribed medications have poor aesthetics. Poor patient compliance and its impact on treatment failure is a growing concern. A recent publication estimated the economic impact in the U.S. at $100 billion annually due to excessive use of healthcare resources in response to medication noncompliance1. Because of its chronic nature and the need for topical treatments, psoriasis has been a focus of the dermatology community in an effort to understand the causes of medication noncompliance. It has been reported that more than one-third of psoriatic patients are not compliant with their prescribed medication2.
Another study of psoriatic patients links medication compliance and successful patient outcomes3. The vehicle-related factor that the “medication felt unpleasant” was rated as important, while the “medication stained clothing” factor and the convenience of application (“application was time-consuming”) factor were rated as some of the most important issues. The authors stated, “Choosing a fast-drying vehicle that is easy to apply may improve usage in patients concerned about inconvenience of application.” Of note, the authors indicated that compliance did not vary with prescribed application frequency (once- versus twice-daily application), nor was there a significant difference between high-potency steroid use compared to medium and low-potency steroids.
Versatile Options
Whether selection of excipients focuses primarily on patient compliance or on other functional issues, the distinctive chemical and structural characteristics of silicones play a significant role. The silicones used in healthcare applications are typically based on the polydimethylsiloxane (PDMS) polymer, with its silicon-oxygen backbone and attached methyl pendants. Based on the requirements of individual applications, chain length, cross-linking or substitution by various functional groups can result in a variety of useful materials. Among the most important silicone forms in healthcare applications are volatile and nonvolatile silicone fluids, waxes, emulsifiers, or polymer blends such as elastomers and gums.
Volatile silicone fluids are used in a variety of personal care applications because of their easy spreading, fast evaporation rates, nonstaining properties, smooth and nongreasy feel, noncooling and nonstinging characteristics, and their safety profile. The chemical characteristics of these high purity fluids also make them useful in topical pharmaceutical products. They are compatible with a broad range of lipophilic products such as mineral oil, petrolatum, esters, and lipophilic sun filters, and can be incorporated into the oil phase of emulsions and easily dispersed into hydrogels. Some volatile silicones can be used as volatile excipients in spray pump systems for topical applications. Their low surface tension improves skin coverage and may increase bioavailability of active ingredients, while the low heat of vaporization allows films to dry quickly.
Nonvolatile silicone fluids offer high water repellency through nonocclusive films, good lubrication characteristics and low surface tension for improved spreading. They can also provide substantivity and lubrication, while reducing tackiness and residue on the skin.
As hydrophobic lubricants, nonvolatile silicone fluids can serve as emollients to improve the aesthetics of lotions and creams, and as excipients in transdermal drug delivery systems. At use levels of 1% to 30%, some silicone fluids, depending upon viscosity, appear as active ingredients with skin protectant claims. These products fit the description of “a drug product that temporarily protects injured or exposed skin or mucous membrane surfaces from harmful or annoying stimuli, and may help provide relief to such surfaces,” as described in the FDA skin protectant monograph4.
Figure 1 illustrates the use of two viscosities of PDMS delivered at 5% from an isododecane carrier and measured on the skin using a wash-off simulator. After three washes, results show the higher viscosity material has a higher level of substantivity.
Figure 1: Substantivity of 5% PDMS in isododecane on skin after three washings. |
Silicone elastomer blends, a mixture of fluid and cross-linked nonfunctional silicone elastomer, can also be used to improve the substantivity of topical pharmaceutical formulations. They provide a more matte appearance on the skin compared to silicone fluids and leave a drier and more powdery feel — an effect that is enhanced by their ability to absorb oil and sebum. In formulations, they can act as rheology modifiers to offer distinctive sensory and textural effects, and recent studies show they can function as carriers for the release of active ingredients5. They also offer enhanced delivery and stabilization of volatile or unstable ingredients such as vitamins and pharmaceutical actives. Silicone elastomers can aid in the formation of emulsions or anhydrous gels, and they are optimum thickeners for silicone-based formulations. Upon application, their shear-thinning properties translate to smooth, even application for good coverage, and a “rebuild” of viscosity to remain substantive on the skin.
Figure 2 shows results of sensory evaluations of two ointments, one containing 100% petrolatum, and the other containing 70% petrolatum, 15% volatile silicone and 15% silicone elastomer. The ointment containing silicone was easier to spread and less tacky before and after application than the 100% petrolatum ointment. After application, a perceptible film was present on the skin for both formulations, but the silicone-containing ointment was less greasy, silkier and more slippery (showing better lubrication) than the ointment containing petrolatum. The perception of higher wetness for the silicone formulation was attributed to its lower oiliness.
| Figure 2: Sensory evaluation (paired comparison) of an all-petrolatum ointment versus an ointment containing petrolatum and silicones. Percentages indicate level of confidence, and the ratings for absorption were based on panelists’ perceptions, not biological skin absorption.  |
The addition of silicones to petrolatum resulted in a net improvement in the sensory profile of the ointment. This improvement is important in the case of ointments, which traditionally are linked to poor patient compliance due to their lack of spreadability and their tacky and greasy feel.
Silicone gums are high molecular weight silicone polymers that may be linear or branched and can be delivered onto the skin in volatile or nonvolatile silicone fluids. Like nonvolatile silicone fluids, these materials can enhance film cohesion on the skin, for greater substantivity and prolonged effectiveness of active ingredients. Improved substantivity of UV sunscreens on the skin has been demonstrated in the presence of very high molecular weight (Mw = 700,000) silicone gums6.
Silicone gums have been shown to improve substantivity of ketoprofen, a nonsteroidal anti-inflammatory drug, on skin when dispensed from a volatile-based silicone spray7. After eight hours, the presence of ketoprofen was detected on the skin surface using formulations containing a silicone gum, while ketoprofen was no longer detected in the control after six hours. It is not clear if the improved substantivity was a result of improved abrasion resistance or whether the gum had an influence on the skin penetration rate by acting as a reservoir to delay penetration. Abrasion resistance was certainly improved. Consecutive attempts to remove the film with adhesive tape immediately after spraying indicated the presence of silicone gum made removal more difficult, and drug-loaded films were even more resistant to removal7.
Silicone gums are very substantive on their own.In one evaluation, more than 25% of the silicone gum tested remained on the skin after eight hours7. Improved substantivity was observed even when very low concentrations of silicone gum (1% to 3% by weight) were used, thus providing a low viscosity formulation that could easily be applied by spraying, and which would not unreasonably increase drying time7.
Silicone waxes improve the aesthetic properties of topical pharmaceutical formulations, allowing application of very thin occlusive to semi-occlusive films that are neither too oily, tacky, nor dry. While silicones such as these are used for their biocompatibility and aesthetic benefits, studies also suggest they may improve the bioavailability of active ingredients over less occlusive formulations. Silicone waxes can also be used to impart moisturization, reduce tackiness and increase the viscosity of emulsions, and they have good compatibility with organic ingredients. Figure 3 shows the thickening effect of a silicone wax on three emulsion types.
Figure 3: Viscosity of emulsions with and without silicone wax. |
While PDMS materials are highly permeable to moisture, some silicones such as stearoxytrimethylsilane wax display occlusive properties while still maintaining the silky feel usually associated with silicones. The following listcompares the occlusivity of oil-in-water petrolatum and stearoxytrimethylsilane wax emulsions on gelatin membranes.
Comparison of Oil-in-Water Emulsion Occlusivity
Oily Ingredient / Occlusivity (%)
Petrolatum Emulsion:93.4
Petrolatum/Silicone Wax, 50:50 Emulsion:84.7
Silicone Wax Emulsion:72.9
Silicone emulsifiers are designed for preparation of water-in-oil and water-in-silicone emulsions with excellent stability, flexibility and aesthetics. They are completely soluble in the water phase and dispersible in water solutions, but soluble in detergent systems. The presence of electrolytes (e.g., NaCl, or MgSO4 at 0.7% to 2%) helps reduce the interfacial surface and so reduce particle size, while increasing viscosity, stability and freeze resistance. At levels of 1% to 3%, silicone emulsifiers deliver the benefits of skin protection and water resistance, and they allow formulation of creams and lotions at room temperature, resulting in lower processing costs and faster processing times.
Product Registration Support
When selecting a silicone excipient, the source of the excipients may be in question, and compendial monographs do not exist to describe all potential silicone excipients. It may be preferable to select excipients that are manufactured, packaged, or tested in a dedicated facility that is registered and inspected by the FDA, or similar agencies in other geographies, that apply appropriate GMPs or similar standards for the intended healthcare applications.
Many of the silicone chemistries discussed in this article have already been used in such applications and are listed on the FDA’s Inactive Ingredient List. Using materials on this list may expedite product registration times and reduce costs. The flexibility of silicone excipient options can also be enhanced by selecting a supplier who can provide documentation to help expedite and simplify the regulatory approval process and support customer requests. Filings with global authorities may include Drug Master Files (in the U.S.) and Technical Files (in Europe) or similar filings in other geographies. Other assistance may include Letters of Authorization that provide customer access to Drug Master Files without disclosing proprietary information, while FDA inspection reports can show how well suppliers are conforming to regulatory requirements.
Access to filings of this type can expedite the regulatory application process. In addition, if a contract manufacturer has access to toxicologists and toxicological data via its excipient supplier, the process of determining suitability of silicone excipients for specific applications can go more smoothly. In effect, the expertise of the supplier can help serve as a screening process for potential excipients.
As a complement to regulatory support, availability of formulation expertise to illustrate prototype formulations in a variety of product forms can help contract manufacturers screen multiple formulations without the need to develop them from scratch. This may in turn support their customers by speeding the process for getting products to market.
Silicones have a history of more than 50 years of safety and efficiency in healthcare-related applications, and polydimethylsiloxanes are globally recognized both for their proven biocompatibility as well as for being one of the most tested materials for their safety.
As excipients, many of the unique properties of PDMS have been capitalized upon in controlled release drug delivery systems due to their chemical stability, high level of purity, ease of use and high permeability to many active drugs. Because of their distinctive physicochemical properties, silicones are especially suitable for providing aesthetics and bioavailability of actives for topical formulations.
References
1 R. Balkrishnan, C.L. Carroll, F.T. Camancho and S.R. Feldman, J. Am. Acad. Dermatol., 49, 651-4 (2003).
2 P.C. van de Kerkhof, D. de Hoop, J. De Korte, S.A. Cobelens, and M.V. Kuipers, Dermatology, 200, 292-8 (2000).
3 C.L. Carroll, S.R. Feldman, F.T. Camancho and R. Balkrishnan, Br. J. Dermatol., 151, 895-7 (2004).
4 Skin Protectant Drug Products for Over-the-Counter Human Use; Final Monograph, FDA Monograph 21 CRF Part 347, June 4, 2003.
5 A. Etienne and L. Aguadisch, EP 0 475 664 (1992).
6 G. Chandra and H. Klimisch, J. Soc. Cosmet Chem., 37:2 73 (1986).
7 L. Aguadisch et al., EP 0 966 972 (1999)
Silicone Excipients in Drug Development
A versatile ingredient works in excipient applications
By Gerald K. Schalau II and Katherine L. Ulman
Silicones have a range of applications in the pharmaceutical industry, from active ingredients in antacids to tubing used in drug processing. They also are used as excipients in topical pharmaceutical creams, ointments and lotions. These applications depend on the versatility and distinctive physicochemical and performance properties of silicone fluids, gums, and gels, which can offer combinations of formulating solutions not available with other ingredients. Low surface tension, improved aesthetics, substantivity, high permeability, nonstaining properties, and the ability to protect and deliver active ingredients allow contract manufacturers expanded formulating opportunities to meet the evolving needs of their customers.
|
An Expanding Role for Silicones
As the functional properties of excipients become more critical to the performance of pharmaceutical products — for example, their impact on bioavailability of drugs — contract manufacturers can benefit from considering excipients with versatility to fill a number of roles. Although silicones can function as active ingredients, they are more often used as excipients. Examples include siliconization (lubrication of syringe barrels, pistons, needles or stoppers), skin adhesives in transdermal patches (based on their adaptability for drug permeability), volatile or nonvolatile agents to improve spreading and aesthetic properties, or carriers for active ingredients. With silicone excipients, a key factor for success is selecting from a range of materials to provide specific functionalities and performance characteristics throughout the shelf life of the drug product.
The use of silicones to improve a pharmaceutical application or its aesthetics might be considered a form of technology transfer from the personal care industry. Silicones have been incorporated into skin care products since the early 1950s, and today at least 50% of newly launched skin care products contain at least one silicone. However, many silicones also have been used in healthcare applications, as evidenced by the number of silicone materials listed on the FDA’s inactive ingredient list. The silicones used in healthcare applications are among the most extensively tested materials for safety, and they are known to provide a pleasant silky, nongreasy and dry feel on skin.
Aiding Patient Compliance
The sensory properties of silicone excipients can be important factors in assisting patients who do not comply with treatment regimens because their prescribed medications have poor aesthetics. Poor patient compliance and its impact on treatment failure is a growing concern. A recent publication estimated the economic impact in the U.S. at $100 billion annually due to excessive use of healthcare resources in response to medication noncompliance1. Because of its chronic nature and the need for topical treatments, psoriasis has been a focus of the dermatology community in an effort to understand the causes of medication noncompliance. It has been reported that more than one-third of psoriatic patients are not compliant with their prescribed medication2.
Another study of psoriatic patients links medication compliance and successful patient outcomes3. The vehicle-related factor that the “medication felt unpleasant” was rated as important, while the “medication stained clothing” factor and the convenience of application (“application was time-consuming”) factor were rated as some of the most important issues. The authors stated, “Choosing a fast-drying vehicle that is easy to apply may improve usage in patients concerned about inconvenience of application.” Of note, the authors indicated that compliance did not vary with prescribed application frequency (once- versus twice-daily application), nor was there a significant difference between high-potency steroid use compared to medium and low-potency steroids.
Versatile Options
Whether selection of excipients focuses primarily on patient compliance or on other functional issues, the distinctive chemical and structural characteristics of silicones play a significant role. The silicones used in healthcare applications are typically based on the polydimethylsiloxane (PDMS) polymer, with its silicon-oxygen backbone and attached methyl pendants. Based on the requirements of individual applications, chain length, cross-linking or substitution by various functional groups can result in a variety of useful materials. Among the most important silicone forms in healthcare applications are volatile and nonvolatile silicone fluids, waxes, emulsifiers, or polymer blends such as elastomers and gums.
Volatile silicone fluids are used in a variety of personal care applications because of their easy spreading, fast evaporation rates, nonstaining properties, smooth and nongreasy feel, noncooling and nonstinging characteristics, and their safety profile. The chemical characteristics of these high purity fluids also make them useful in topical pharmaceutical products. They are compatible with a broad range of lipophilic products such as mineral oil, petrolatum, esters, and lipophilic sun filters, and can be incorporated into the oil phase of emulsions and easily dispersed into hydrogels. Some volatile silicones can be used as volatile excipients in spray pump systems for topical applications. Their low surface tension improves skin coverage and may increase bioavailability of active ingredients, while the low heat of vaporization allows films to dry quickly.
Nonvolatile silicone fluids offer high water repellency through nonocclusive films, good lubrication characteristics and low surface tension for improved spreading. They can also provide substantivity and lubrication, while reducing tackiness and residue on the skin.
As hydrophobic lubricants, nonvolatile silicone fluids can serve as emollients to improve the aesthetics of lotions and creams, and as excipients in transdermal drug delivery systems. At use levels of 1% to 30%, some silicone fluids, depending upon viscosity, appear as active ingredients with skin protectant claims. These products fit the description of “a drug product that temporarily protects injured or exposed skin or mucous membrane surfaces from harmful or annoying stimuli, and may help provide relief to such surfaces,” as described in the FDA skin protectant monograph4.
Figure 1 illustrates the use of two viscosities of PDMS delivered at 5% from an isododecane carrier and measured on the skin using a wash-off simulator. After three washes, results show the higher viscosity material has a higher level of substantivity.
| Figure 1: Substantivity of 5% PDMS in isododecane on skin after three washings. |
Silicone elastomer blends, a mixture of fluid and cross-linked nonfunctional silicone elastomer, can also be used to improve the substantivity of topical pharmaceutical formulations. They provide a more matte appearance on the skin compared to silicone fluids and leave a drier and more powdery feel — an effect that is enhanced by their ability to absorb oil and sebum. In formulations, they can act as rheology modifiers to offer distinctive sensory and textural effects, and recent studies show they can function as carriers for the release of active ingredients5. They also offer enhanced delivery and stabilization of volatile or unstable ingredients such as vitamins and pharmaceutical actives. Silicone elastomers can aid in the formation of emulsions or anhydrous gels, and they are optimum thickeners for silicone-based formulations. Upon application, their shear-thinning properties translate to smooth, even application for good coverage, and a “rebuild” of viscosity to remain substantive on the skin.
Figure 2 shows results of sensory evaluations of two ointments, one containing 100% petrolatum, and the other containing 70% petrolatum, 15% volatile silicone and 15% silicone elastomer. The ointment containing silicone was easier to spread and less tacky before and after application than the 100% petrolatum ointment. After application, a perceptible film was present on the skin for both formulations, but the silicone-containing ointment was less greasy, silkier and more slippery (showing better lubrication) than the ointment containing petrolatum. The perception of higher wetness for the silicone formulation was attributed to its lower oiliness.
| Figure 2: Sensory evaluation (paired comparison) of an all-petrolatum ointment versus an ointment containing petrolatum and silicones. Percentages indicate level of confidence, and the ratings for absorption were based on panelists’ perceptions, not biological skin absorption. |
The addition of silicones to petrolatum resulted in a net improvement in the sensory profile of the ointment. This improvement is important in the case of ointments, which traditionally are linked to poor patient compliance due to their lack of spreadability and their tacky and greasy feel.
Silicone gums are high molecular weight silicone polymers that may be linear or branched and can be delivered onto the skin in volatile or nonvolatile silicone fluids. Like nonvolatile silicone fluids, these materials can enhance film cohesion on the skin, for greater substantivity and prolonged effectiveness of active ingredients. Improved substantivity of UV sunscreens on the skin has been demonstrated in the presence of very high molecular weight (Mw = 700,000) silicone gums6.
Silicone gums have been shown to improve substantivity of ketoprofen, a nonsteroidal anti-inflammatory drug, on skin when dispensed from a volatile-based silicone spray7. After eight hours, the presence of ketoprofen was detected on the skin surface using formulations containing a silicone gum, while ketoprofen was no longer detected in the control after six hours. It is not clear if the improved substantivity was a result of improved abrasion resistance or whether the gum had an influence on the skin penetration rate by acting as a reservoir to delay penetration. Abrasion resistance was certainly improved. Consecutive attempts to remove the film with adhesive tape immediately after spraying indicated the presence of silicone gum made removal more difficult, and drug-loaded films were even more resistant to removal7.
Silicone gums are very substantive on their own.In one evaluation, more than 25% of the silicone gum tested remained on the skin after eight hours7. Improved substantivity was observed even when very low concentrations of silicone gum (1% to 3% by weight) were used, thus providing a low viscosity formulation that could easily be applied by spraying, and which would not unreasonably increase drying time7.
Silicone waxes improve the aesthetic properties of topical pharmaceutical formulations, allowing application of very thin occlusive to semi-occlusive films that are neither too oily, tacky, nor dry. While silicones such as these are used for their biocompatibility and aesthetic benefits, studies also suggest they may improve the bioavailability of active ingredients over less occlusive formulations. Silicone waxes can also be used to impart moisturization, reduce tackiness and increase the viscosity of emulsions, and they have good compatibility with organic ingredients. Figure 3 shows the thickening effect of a silicone wax on three emulsion types.
| Figure 3: Viscosity of emulsions with and without silicone wax. |
While PDMS materials are highly permeable to moisture, some silicones such as stearoxytrimethylsilane wax display occlusive properties while still maintaining the silky feel usually associated with silicones. The following listcompares the occlusivity of oil-in-water petrolatum and stearoxytrimethylsilane wax emulsions on gelatin membranes.
Comparison of Oil-in-Water Emulsion Occlusivity
Oily Ingredient / Occlusivity (%)
Petrolatum Emulsion:93.4
Petrolatum/Silicone Wax, 50:50 Emulsion:84.7
Silicone Wax Emulsion:72.9
Silicone emulsifiers are designed for preparation of water-in-oil and water-in-silicone emulsions with excellent stability, flexibility and aesthetics. They are completely soluble in the water phase and dispersible in water solutions, but soluble in detergent systems. The presence of electrolytes (e.g., NaCl, or MgSO4 at 0.7% to 2%) helps reduce the interfacial surface and so reduce particle size, while increasing viscosity, stability and freeze resistance. At levels of 1% to 3%, silicone emulsifiers deliver the benefits of skin protection and water resistance, and they allow formulation of creams and lotions at room temperature, resulting in lower processing costs and faster processing times.
Product Registration Support
When selecting a silicone excipient, the source of the excipients may be in question, and compendial monographs do not exist to describe all potential silicone excipients. It may be preferable to select excipients that are manufactured, packaged, or tested in a dedicated facility that is registered and inspected by the FDA, or similar agencies in other geographies, that apply appropriate GMPs or similar standards for the intended healthcare applications.
Many of the silicone chemistries discussed in this article have already been used in such applications and are listed on the FDA’s Inactive Ingredient List. Using materials on this list may expedite product registration times and reduce costs. The flexibility of silicone excipient options can also be enhanced by selecting a supplier who can provide documentation to help expedite and simplify the regulatory approval process and support customer requests. Filings with global authorities may include Drug Master Files (in the U.S.) and Technical Files (in Europe) or similar filings in other geographies. Other assistance may include Letters of Authorization that provide customer access to Drug Master Files without disclosing proprietary information, while FDA inspection reports can show how well suppliers are conforming to regulatory requirements.
Access to filings of this type can expedite the regulatory application process. In addition, if a contract manufacturer has access to toxicologists and toxicological data via its excipient supplier, the process of determining suitability of silicone excipients for specific applications can go more smoothly. In effect, the expertise of the supplier can help serve as a screening process for potential excipients.
As a complement to regulatory support, availability of formulation expertise to illustrate prototype formulations in a variety of product forms can help contract manufacturers screen multiple formulations without the need to develop them from scratch. This may in turn support their customers by speeding the process for getting products to market.
Silicones have a history of more than 50 years of safety and efficiency in healthcare-related applications, and polydimethylsiloxanes are globally recognized both for their proven biocompatibility as well as for being one of the most tested materials for their safety.
As excipients, many of the unique properties of PDMS have been capitalized upon in controlled release drug delivery systems due to their chemical stability, high level of purity, ease of use and high permeability to many active drugs. Because of their distinctive physicochemical properties, silicones are especially suitable for providing aesthetics and bioavailability of actives for topical formulations.
References
1 R. Balkrishnan, C.L. Carroll, F.T. Camancho and S.R. Feldman, J. Am. Acad. Dermatol., 49, 651-4 (2003).
2 P.C. van de Kerkhof, D. de Hoop, J. De Korte, S.A. Cobelens, and M.V. Kuipers, Dermatology, 200, 292-8 (2000).
3 C.L. Carroll, S.R. Feldman, F.T. Camancho and R. Balkrishnan, Br. J. Dermatol., 151, 895-7 (2004).
4 Skin Protectant Drug Products for Over-the-Counter Human Use; Final Monograph, FDA Monograph 21 CRF Part 347, June 4, 2003.
5 A. Etienne and L. Aguadisch, EP 0 475 664 (1992).
6 G. Chandra and H. Klimisch, J. Soc. Cosmet Chem., 37:2 73 (1986).
7 L. Aguadisch et al., EP 0 966 972 (1999)
Monographs: Pharmaceutical substances: Diphenoxylati hydrochloridum - Diphenoxylate hydrochloride
Molecular formula. C30H32N2O2,HCl
Relative molecular mass. 489.1
Graphic formula.
Chemical name. Ethyl 1-(3-cyano-3,3-diphenylpropyl)-4-phenylisonipecotate monohydrochloride; ethyl 1-(3-cyano-3,3-diphenylpropyl)-4-phenyl-4-piperidinecarboxylate monohydrochloride; CAS Reg. No. 3810-80-8.
Description. A white or almost white, crystalline powder; odourless.
Solubility. Sparingly soluble in water, acetone R and ethanol (~750 g/l) TS; practically insoluble in ether R.
Category. Antidiarrhoeal drug.
Storage. Diphenoxylate hydrochloride should be kept in a well-closed container.
Requirements
Definition. Diphenoxylate hydrochloride contains not less than 98.0% and not more than 101.0% of C30H32N2O2,HCl, calculated with reference to the dried substance.
Identity tests
• Either tests A and E or tests B, C, D and E may be applied.
A. Carry out the examination as described under 1.7 Spectrophotometry in the infrared region. The infrared absorption spectrum is concordant with the spectrum obtained from diphenoxylate hydrochloride RS or with the reference spectrum of diphenoxylate hydrochloride.
B. The absorption spectrum of a 0.50 mg/ml solution in a mixture of 1 volume of hydrochloric acid (1 mol/l) VS and 99 volumes of methanol R, when observed between 230 nm and 350 nm, exhibits maxima at about 252 nm, 258 nm, and 265 nm; the absorbances of a 1-cm layer at these wavelengths are about 0.55, 0.65 and 0.50, respectively.
C. Dissolve 25 mg in 5 ml of water and add 0.1 ml of potassio-mercuric iodide TS; a cream-coloured precipitate is produced.
D. Melting temperature, about 223 °C.
E. A 20 mg/ml solution yields reaction B described under 2.1 General identification tests as characteristic of chlorides.
Sulfated ash. Not more than 1.0 mg/g.
Loss on drying. Dry to constant weight at 105°C; it loses not more than 5.0 mg/g.
Related substances. Carry out the test as described under 1.14.1 Thin-layer chromatography, using silica gel R1 as the coating substance and a mixture of 92 volumes of chloroform R, 3 volumes of methanol R, and 5 volumes of glacial acetic acid R as the mobile phase. Apply separately to the plate 10 μl of each of 2 solutions in chloroform R containing (A) 50 mg of the test substance per ml and (B) 0.50 mg of the test substance per ml. After removing the plate from the chromatographic chamber, allow it to dry in air, expose it to the vapour of iodine, and examine the chromatogram in daylight. Any spot obtained with solution A, other than the principal spot, is not more intense than that obtained with solution B.
Assay. Dissolve about 0.4 g, accurately weighed, in 40 ml of glacial acetic acid R1, add 10 ml of mercuric acetate/acetic acid TS and titrate with perchloric acid (0.1 mol/l) VS as described under 2.6 Non-aqueous titration. Method A. Each ml of perchloric acid (0.1 mol/l) VS is equivalent to 48.91 mg of C30H32N2O2,HCl.
Monographs: Pharmaceutical substances: Dinitrogenii oxidum - Dinitrogen oxide
N2O
Relative molecular mass. 44.01
Chemical name. Nitrous oxide; CAS Reg. No. 10024-97-2.
Other name. Nitrous oxide.
Description. A colourless gas; odourless.
Solubility. One volume dissolves in about 1.5 volumes of water at a pressure of 101.3 kPa and a temperature of 20 °C.
Category. Inhalational anaesthetic gas.
Storage. Dinitrogen oxide should be kept as compressed gas or liquid at very low temperatures, in appropriate containers complying with the safety regulations of the national authority. Valves or taps should not be lubricated with oil or grease.
Labelling. An ISO standard1 requires that cylinders containing Dinitrogen oxide intended for medical use should bear the name of the contents in legible and permanent characters and, preferably, also the molecular formula N2O.
1 International Standard 32. Gas cylinders for medical use - marking for identification content. International Organization for Standardization, Switzerland, 1977.
Additional information. In the analysis of medicinal gases certain tests are not intended for hospital pharmacists. They are applicable solely by laboratories equipped with specialized apparatus.
Requirements
Dinitrogen oxide contains not less than 98.0% v/v of N2O in the gaseous phase, when sampled at 15 °C.
Note: If the analysis is performed on a cylinder, keep the cylinder of the gas to be examined at room temperature for at least 6 hours before carrying out the tests. Keep the cylinder in the vertical position with the outlet valve uppermost.
The test for carbon monoxide should be carried out on the first portion of gas drawn from the container and the tests for nitrogen monoxide and nitrogen dioxide immediately thereafter.
Identity tests
• Either test A alone or tests B, C, and D may be applied.
A. Carry out the examination as described under 1.7 Spectrophotometry in the infrared region. The infrared absorption spectrum is concordant with the reference spectrum of dinitrogen oxide.
B. Place a glowing splinter of wood into the gas; the splinter bursts into flame.
C. Shake the gas with alkaline pyrogallol TS; it is not absorbed and the solution does not become brown (distinction from oxygen).
D. Mix the gas with an equal volume of nitrogen monoxide R; no red fumes are produced (distinction from oxygen).
Carbon monoxide
• Either test A, test B, or test C may be applied.
• The tests should be carried out on the first portion of gas released from the container.
A. The apparatus (Fig. 6) consists of the following parts connected in series:
- a U-tube (U1) containing desiccant silica gel R impregnated with chromium trioxide R;
- a wash bottle (F1) containing 100 ml of potassium hydroxide (~400 g/l) TS;
- a U-tube (U2) containing pellets of potassium hydroxide R;
- a U-tube (U3) containing phosphorus pentoxide R dispersed on previously granulated, fused pumice;
- a U-tube (U4) containing 30 g of recrystallized iodine pentoxide R in granules, previously dried at 200 °C and kept at a temperature of 120°C (T) during the test. The iodine pentoxide is packed in the tube in 1-cm columns separated by 1-cm columns of glass wool to give an effective length of 5 cm;
- a reaction tube (F2) containing 2.0 ml of potassium iodide (160 g/l) TS and 0.15 ml of starch TS.
Flush the apparatus with 5.0 litres of argon R. If necessary, discharge the blue colour in tube F2 containing potassium iodide (160 g/l) TS by adding a sufficient volume of freshly prepared sodium thiosulfate (0.002 mol/l) VS. Continue flushing with argon R until not more than 0.045 ml of sodium thiosulfate (0.002 mol/l) VS is required after the passage of 5.0 litres of argon R. Pass 5.0 litres of the test gas from the container through the apparatus. Flush the last traces of liberated iodine into the reaction tube by passing 1.0 litre of argon R through the apparatus. Titrate the liberated iodine with sodium thiosulfate (0.002 mol/l) VS. Repeat the procedure using 5.0 litres of argon R.
Figure 6. | Apparatus for the determination of carbon monoxide in medicinal gases |
Measurements in mm. |
Reproduced with the permission of the European Pharmacopoeia Commission, European Directorate for the Quality of Medicines, Council of Europe.
The difference between the volumes of sodium thiosulfate (0.002 mol/l) VS used in the titrations is not more than 0.25 ml (5μl/l).
B. Carry out the test as described under 1.14.5 Gas chromatography, using a stainless steel column (2m × 4mm) packed with a 0.5-nm molecular sieve (e.g. X13, obtainable from a commercial source). Maintain the column at 80 °C, and the injection port and the detector at room temperature. Use helium R as the carrier gas at a flow rate of 60 ml per minute, and a helium ionization detector.
Use the following gases: (1) the test gas; and (2) a mixture containing 5μl of carbon monoxide R in 1 litre of dinitrogen oxide R as the reference gas.
Inject a suitable volume of both gases (1) and (2). Adjust the volume, as well as the conditions specified above, to produce a peak response for carbon monoxide obtained with the reference gas (2) that gives a height of not less than 5% on the recorder.
Measure the areas of the peak responses obtained in the chromatograms from injections 1 and 2 and calculate the content of carbon monoxide in the test gas (1) by comparing with the peak response for carbon monoxide obtained from the reference gas (2); not more than 5μl/l.
C. Determine the content using a carbon monoxide detector tube. Pass the required volume of the test gas through the tube, the calibration of which is verified according to the manufacturer's instructions.
The gas supply is connected to a pressure regulator and needle valve. Connect the flexible tubing fitted with a Y-piece to the valve and adjust the flow of the test gas to purge the tubing to an appropriate flow. Fit the carbon monoxide detector tube to the metering pump according to the manufacturer's instructions. Connect the open end of the tube to the short leg of the tubing and pump a suitable volume of the test gas through the tube. Read the value corresponding to the length of the coloured layer or the intensity of the colour on the graduated scale; not more than 5μl/l.
Note: For the following tests - Nitrogen monoxide and nitrogen dioxide, Carbon dioxide Test A, Halogens and hydrogen sulfide, and Acidity and alkalinity - pass the gas to be tested through the appropriate reagent contained in a hermetically closed flat-bottomed glass cylinder, with dimensions such that 50ml of liquid reaches a height of 12-14 cm, that is fitted with (a) a delivery tube terminated by a capillary 1 mm in internal diameter and placed within 2mm of the bottom of the cylinder; and (b) an outlet tube.
Prepare the reference solutions in identical cylinders.
Nitrogen monoxide and nitrogen dioxide
• Either test A or test B may be applied.
• This test should be performed after release of the 5.0 litres of gas as described above under "Carbon monoxide, test A".
A. Pass the test gas through two of the cylinders connected in series as described above under "Carbon monoxide, test A". To obtain the liquid phase invert the gas cylinder; the liquid vaporizes on leaving the valve.
To 50 ml of water add 1.2 ml of sulfuric acid (~1760 g/l) TS and dilute with sufficient water to produce 100 ml. To 15 ml of this solution add 375mg of potassium permanganate R, mix, and transfer to the first cylinder (solution A).
Dissolve 1 g of sulfanilic acid R in a mixture of 180 ml of water and 10ml of glacial acetic acid R (solution 1). Separately dissolve 0.2g of N-(1- naphthyl)ethylenediamine hydrochloride R in a mixture of 4 ml of glacial acetic acid R and 5 ml of water, heat gently, and dilute to 200 ml with water (solution 2). Mix 1 volume of solution 2 with 9 volumes of solution 1 and transfer 20 ml of this mixture to the second cylinder (solution B).
Connect the outlet tube of the first cylinder to the delivery tube of the second cylinder containing solution B. Pass 2.5 litres of the test gas through the reagents at a rate of 15.0 litres per hour.
Prepare a reference solution by adding 0.25 ml of a solution containing 61.6μg/ml of sodium nitrite R in water to 20 ml of solution B as prepared above. Allow the test solution and reference solution to stand for 10 minutes.
Examine the gaseous and the liquid phases separately.
For both gaseous and liquid phases, any red colour produced from the solution of the test gas is not more intense than that from the reference solution (2μl/l of NO + NO2).
B. Determine the content using a nitrogen monoxide and nitrogen dioxide detector tube. Pass the required volume of the test gas through the tube, the calibration of which is verified according to the manufacturer's instructions.
The gas supply is connected to a pressure regulator and needle valve. Connect the flexible tubing fitted with a Y-piece to the valve and adjust the flow of the test gas to purge the tubing to an appropriate flow. Fit the nitrogen monoxide and nitrogen dioxide detector tube to the metering pump following the manufacturer's instructions. Connect the open end of the tube to the short leg of the tubing and pump a suitable volume of the test gas through the tube. Read the value corresponding to the length of the coloured layer or the intensity of the colour on the graduated scale; not more than 2μl/l.
Carbon dioxide
• Either test A, test B, or test C may be applied.
A. Pass 1.0 litre of the test gas through 50 ml of a clear solution of barium hydroxide (0.15 mol/l) VS. Similarly prepare a reference solution by adding 1.0 ml of a 1.1 mg/ml solution of sodium hydrogen carbonate R in carbondioxide- free water R to 50 ml of barium hydroxide (0.15 mol/l) VS.
Any turbidity in the solution after the passage of the the test gas is not more intense than that of the reference solution (300μl/l).
B. Carry out the test as described under 1.14.5 Gas chromatography, using a stainless steel column (3.5m × 2mm) packed with ethylvinyl-benzenedivinylbenzene copolymer. Maintain the column at 40 °C and the detector at 90 °C. Use helium R as the carrier gas at a flow rate of 15 ml per minute, and a thermal conductivity detector.
Use the following gases: (1) the test gas; and (2) a mixture containing 300μg of carbon dioxide R in 1 litre of dinitrogen oxide R as the reference gas.
Inject a suitable volume of both gases (1) and (2). Adjust the volume, as well as the conditions specified above, to obtain a peak response for carbon dioxide obtained with the reference gas (2) of a height of not less than 35% on the recorder.
Measure the areas of the peak responses obtained in the chromatograms from the injections of gases 1 and 2 and calculate the content of carbon dioxide in the test gas (1) by comparing with the peak response for carbon dioxide obtained from the reference gas (2); not more than 300μl of CO2 per litre.
C. Determine the content using a carbon dioxide detector tube. Pass the required volume of the test gas through the tube, the calibration of which is verified according to the manufacturer's instructions.
The gas supply is connected to a suitable pressure regulator and needle valve. Connect the flexible tubing fitted with a Y-piece to the valve and adjust the flow of the test gas to purge the tubing to an appropriate flow. Fit the carbon dioxide detector tube to the metering pump according to the manufacturer's instructions. Connect the open end of the tube to the short leg of the tubing and pump a suitable volume of the test gas through the tube. Read the value corresponding to the length of the coloured layer or the intensity of the colour on the graduated scale; not more than 300μl/l.
Halogens and hydrogen sulfide. Pass 20.0 litres of the test gas through a mixture of 1 ml of silver nitrate (40 g/l) TS and 49 ml of water at a flow rate not exceeding 15 litres per hour.
Prepare the reference solution as follows: to 1.0 ml of silver nitrate (40 g/l) TS add 40 ml of chloride standard (5μg/ml) TS and 0.15 ml of nitric acid (~130 g/l) TS, dilute to 50 ml with water, and allow to stand protected from light for 5 minutes. For the blank solution, repeat the procedure passing the test gas through 50 ml of water.
Compare a 100-mm layer of the solution as described under 1.11 Colour of liquids.
The solution of the test gas does not darken when compared with the blank. Any opalescence is not more intense than that of the reference solution (10μg Cl per litre of dinitrogen oxide).
Water
• Either test A or test B may be applied.
A. The apparatus consists of either an electrolytic hygrometer as described below, an appropriate humidity detector tube, or a capacity hygrometer.
The measuring cell consists of a thin film of phosphoric anhydride placed between two coiled platinum wires which act as electrodes. The water vapour in Dinitrogen oxide is absorbed by the phosphoric anhydride to form phosphoric acid which acts as an electrical conductor.
Before introducing the test gas into the device, allow the gas to stabilize at room temperature and make sure that the temperature is constant throughout the apparatus. Apply a continuous voltage across the electrodes to produce electrolysis of the water and regeneration of phosphoric anhydride. Measure the resulting electric current, which is proportional to the water content in the test gas. (This is a self-calibrating system that obeys Faraday's law.)
Calculate the content of water; not more than 60μg/l.
B. Determine the content using a water vapour detector tube. Pass the required volume of the test gas through the tube, the calibration of which is verified according to the manufacturer's instructions.
The gas supply is connected to a suitable pressure regulator and needle valve. Connect the flexible tubing fitted with a Y-piece to the valve and adjust the flow of the test gas to purge the tubing to an appropriate flow. Fit the water vapour detector tube to the metering pump according to the manufacturer's instructions. Connect the open end of the tube to the short leg of the tubing and pump a suitable volume of the test gas through the tube. Read the value corresponding to the length of the coloured layer or the intensity of the colour on the graduated scale; not more than 60μl/l.
Acidity and alkalinity. Pass 2.0 litres of the test gas through a mixture of 0.10 ml of hydrochloric acid (0.01 mol/l) VS and 50 ml of carbon-dioxide-free water R.
For reference solution 1, use 50 ml of carbon-dioxide-free water R. For reference solution 2, use a mixture of 0.20 ml of hydrochloric acid (0.01 mol/l) VS and 50ml of carbon-dioxide-free water R.
To each solution add 0.1 ml of methyl red/ethanol TS; the intensity of the colour in the test gas solution is between that of reference solutions 1 and 2.
Assay. Determine as described under 1.14.5 Gas chromatography, using a stainless steel column (2m × 2mm) packed with silica gel for chromatography R (250-355μm). Maintain the column at 60 °C and the detector at 130°C. Use helium R as the carrier gas at a flow rate of 50 ml per minute, and a thermal conductivity detector.
Use the following gases: (1) the test gas; and (2) dinitrogen oxide R as the reference gas.
Inject a suitable volume of both gases (1) and (2). Adjust the volume, as well as the conditions specified above, to produce a peak response for dinitrogen oxide obtained with reference gas (2) that gives a height of not less than 35% on the recorder.
Measure the areas of the peak responses obtained in the chromatograms from the injections of gases (1) and (2), and calculate the percentage content of dinitrogen oxide.
Monographs: Pharmaceutical substances: Dinatrii edetas - Disodium edetate
C10H14N2Na2O8,2H2O
Relative molecular mass. 372.2
Chemical name. Disodium dihydrogen (ethylenedinitrilo)tetraacetate dihydrate; N,N'-1,2-ethanediylbis[N-(carboxymethyl)glycine] disodium salt, dihydrate; CAS Reg. No. 6381-92-6.
Other name. Edetate disodium.
Description. A white, crystalline powder; odourless.
Solubility. Soluble in water; slightly soluble in ethanol (~750 g/l) TS; practically insoluble in ether R.
Category. Stabilizer; chelating agent.
Storage. Disodium edetate should be kept in a well-closed container.
Additional information. Solutions of disodium edetate should not come into contact with metal.
Requirements
Disodium edetate contains not less than 98.5% and not more than the equivalent of 101.0% of C10H14N2Na2O8,2H2O.
Identity tests
• Either test A alone or tests B, C, and D may be applied.
A. Carry out the examination as described under 1.7 Spectrophotometry in the infrared region. The infrared absorption spectrum is concordant with the spectrum obtained from disodium edetate R or with the reference spectrum of disodium edetate.
B. To 3 drops of ferric chloride (25 g/l) TS add 3 drops of ammonium thiocyanate (75 g/l) TS; to the deep red solution produced add 0.05 g of Disodium edetate; the colour is discharged, leaving a yellowish solution. (Keep this solution for test D.)
C. Dissolve 2 g in 25 ml of water, add 2 ml of lead nitrate (100 g/l) TS, shake, and add 6 ml of potassium iodide (80 g/l) TS; no yellow precipitate is observed.
D. To the solution from test B, add ammonia (~100 g/l) TS, drop by drop, until an alkaline reaction is obtained with pH-indicator paper R. Add 5 ml of ammonium oxalate (25 g/l) TS; no precipitate is produced (distinction from sodium calcium edetate).
Heavy metals. Use 1.0 g for the preparation of the test solution as described under 2.2.3 Limit test for heavy metals, Procedure 3; determine the heavy metals content according to Method A; not more than 20 μg/g.
pH value. pH of a 0.05 g/ml solution, 4.0-5.5.
Assay. Dissolve 0.5 g, accurately weighed, in sufficient water to produce 300 ml. Add 2 g of methenamine R and 2 ml of hydrochloric acid (~70 g/l) TS. Titrate with lead nitrate (0.1 mol/l) VS to which 50 mg of xylenol orange indicator mixture R has been added.
Each ml of lead nitrate (0.1 mol/l) VS is equivalent to 37.22 mg of C10H14N2Na2O8,2H2O.
Relative molecular mass. 372.2
Chemical name. Disodium dihydrogen (ethylenedinitrilo)tetraacetate dihydrate; N,N'-1,2-ethanediylbis[N-(carboxymethyl)glycine] disodium salt, dihydrate; CAS Reg. No. 6381-92-6.
Other name. Edetate disodium.
Description. A white, crystalline powder; odourless.
Solubility. Soluble in water; slightly soluble in ethanol (~750 g/l) TS; practically insoluble in ether R.
Category. Stabilizer; chelating agent.
Storage. Disodium edetate should be kept in a well-closed container.
Additional information. Solutions of disodium edetate should not come into contact with metal.
Requirements
Disodium edetate contains not less than 98.5% and not more than the equivalent of 101.0% of C10H14N2Na2O8,2H2O.
Identity tests
• Either test A alone or tests B, C, and D may be applied.
A. Carry out the examination as described under 1.7 Spectrophotometry in the infrared region. The infrared absorption spectrum is concordant with the spectrum obtained from disodium edetate R or with the reference spectrum of disodium edetate.
B. To 3 drops of ferric chloride (25 g/l) TS add 3 drops of ammonium thiocyanate (75 g/l) TS; to the deep red solution produced add 0.05 g of Disodium edetate; the colour is discharged, leaving a yellowish solution. (Keep this solution for test D.)
C. Dissolve 2 g in 25 ml of water, add 2 ml of lead nitrate (100 g/l) TS, shake, and add 6 ml of potassium iodide (80 g/l) TS; no yellow precipitate is observed.
D. To the solution from test B, add ammonia (~100 g/l) TS, drop by drop, until an alkaline reaction is obtained with pH-indicator paper R. Add 5 ml of ammonium oxalate (25 g/l) TS; no precipitate is produced (distinction from sodium calcium edetate).
Heavy metals. Use 1.0 g for the preparation of the test solution as described under 2.2.3 Limit test for heavy metals, Procedure 3; determine the heavy metals content according to Method A; not more than 20 μg/g.
pH value. pH of a 0.05 g/ml solution, 4.0-5.5.
Assay. Dissolve 0.5 g, accurately weighed, in sufficient water to produce 300 ml. Add 2 g of methenamine R and 2 ml of hydrochloric acid (~70 g/l) TS. Titrate with lead nitrate (0.1 mol/l) VS to which 50 mg of xylenol orange indicator mixture R has been added.
Each ml of lead nitrate (0.1 mol/l) VS is equivalent to 37.22 mg of C10H14N2Na2O8,2H2O.
Monographs: Pharmaceutical substances: Dimercaprolum - Dimercaprol
Molecular formula. C3H8OS2
Relative molecular mass. 124.2
Graphic formula.
Chemical name. 2,3-Dimercapto-1-propanol; CAS Reg. No. 59-52-9.
Description. A clear, colourless or slightly yellow liquid, with an unpleasant, mercaptan-like odour.
Miscibility. Miscible with 20 parts of water; miscible with ethanol (~750 g/l) TS and methanol R.
Category. Antidote for arsenic, gold, and mercury poisoning.
Storage. Dimercaprol should be kept in a small, well-filled and tightly closed container, protected from light, and stored at a temperature not exceeding 5°C.
Requirements
Definition. Dimercaprol contains not less than 98.5% w/w and not more than 101.5% w/w of C3H8OS2.
Identity tests
A. Mix 0.05 ml of cobalt(II) chloride (30 g/l) TS with 5 ml of water and add 0.05 ml of the test liquid; a yellow-brown colour is produced.
B. Dissolve 0.1 ml in 4 ml of water and add a few drops of lead acetate (80 g/l) TS; a yellow precipitate is formed.
Refractive index. .
Relative density. .
Halides. Dissolve 2.0 g in 25 ml of potassium hydroxide/ethanol TS1 and heat under a reflux condenser for 2 hours. Evaporate the ethanol in a current of warm air, add 20 ml of water, and cool. Add a mixture of 10 ml of hydrogen peroxide (~330 g/l) TS and 40 ml of water, boil gently for 10 minutes, cool, and filter rapidly. Add 10 ml of nitric acid (~130 g/l) TS and 5 ml of silver nitrate (0.1 mol/l) VS and titrate with ammonium thiocyanate (0.1 mol/l) VS, using ferric ammonium sulfate (45 g/l) TS as indicator. Repeat the operation without the test liquid being examined. The difference between the titrations does not exceed 1.0 ml.
pH value. pH of a 0.5 g/ml solution in carbon-dioxide-free water R, 4.6-6.8.
Assay. Dissolve about 0.12 g, accurately weighed, in 20 ml of hydrochloric acid (0.1 mol/l) VS and titrate rapidly with iodine (0.05 mol/l) VS, using starch TS as indicator. Repeat the operation without the test liquid being examined and make any necessary corrections. Each ml of iodine (0.05 mol/l) VS is equivalent to 6.211 mg of C3H8OS2.
Additional requirement for Dimercaprol for parenteral use
Relative molecular mass. 124.2
Graphic formula.
Chemical name. 2,3-Dimercapto-1-propanol; CAS Reg. No. 59-52-9.
Description. A clear, colourless or slightly yellow liquid, with an unpleasant, mercaptan-like odour.
Miscibility. Miscible with 20 parts of water; miscible with ethanol (~750 g/l) TS and methanol R.
Category. Antidote for arsenic, gold, and mercury poisoning.
Storage. Dimercaprol should be kept in a small, well-filled and tightly closed container, protected from light, and stored at a temperature not exceeding 5°C.
Requirements
Definition. Dimercaprol contains not less than 98.5% w/w and not more than 101.5% w/w of C3H8OS2.
Identity tests
A. Mix 0.05 ml of cobalt(II) chloride (30 g/l) TS with 5 ml of water and add 0.05 ml of the test liquid; a yellow-brown colour is produced.
B. Dissolve 0.1 ml in 4 ml of water and add a few drops of lead acetate (80 g/l) TS; a yellow precipitate is formed.
Refractive index. .
Relative density. .
Halides. Dissolve 2.0 g in 25 ml of potassium hydroxide/ethanol TS1 and heat under a reflux condenser for 2 hours. Evaporate the ethanol in a current of warm air, add 20 ml of water, and cool. Add a mixture of 10 ml of hydrogen peroxide (~330 g/l) TS and 40 ml of water, boil gently for 10 minutes, cool, and filter rapidly. Add 10 ml of nitric acid (~130 g/l) TS and 5 ml of silver nitrate (0.1 mol/l) VS and titrate with ammonium thiocyanate (0.1 mol/l) VS, using ferric ammonium sulfate (45 g/l) TS as indicator. Repeat the operation without the test liquid being examined. The difference between the titrations does not exceed 1.0 ml.
pH value. pH of a 0.5 g/ml solution in carbon-dioxide-free water R, 4.6-6.8.
Assay. Dissolve about 0.12 g, accurately weighed, in 20 ml of hydrochloric acid (0.1 mol/l) VS and titrate rapidly with iodine (0.05 mol/l) VS, using starch TS as indicator. Repeat the operation without the test liquid being examined and make any necessary corrections. Each ml of iodine (0.05 mol/l) VS is equivalent to 6.211 mg of C3H8OS2.
Additional requirement for Dimercaprol for parenteral use
Monographs: Pharmaceutical substances: Diloxanidi furoas - Diloxanide furoate
Molecular formula. C14H11Cl2NO4
Relative molecular mass. 328.2
Graphic formula.
Chemical name.
2,2-Dichloro-4'-hydroxy-N-methylacetanilide 2-furoate (ester); 4-[(dichloroacetyl)methylamino]phenyl 2-furancarboxylate; 2,2-dichloro-N-(4-hydroxyphenyl)-N-methylacetamide 2-furoate; CAS Reg. No. 3736-81-0.
Description. A white or almost white, crystalline powder; odourless.
Solubility. Very slightly soluble in water; soluble in 100 parts of ethanol (~750 g/l) TS and in 130 parts of ether R.
Category. Antiamoebic drug.
Storage. Diloxanide furoate should be kept in a well-closed container, protected from light.
Requirements
Definition. Diloxanide furoate contains not less than 98.0% and not more than 102.0% of C14H11Cl2NO4, calculated with reference to the dried substance.
Identity tests
• Either test A alone or tests B and C may be applied.
A. Carry out the examination as described under 1.7 Spectrophotometry in the infrared region. The infrared absorption spectrum is concordant with the spectrum obtained from diloxanide furoate RS or with the reference spectrum of diloxanide furoate.
B. The absorption spectrum of a 7.0 μg/ml solution in ethanol (~750 g/l) TS, when observed between 240 nm and 350 nm, exhibits a maximum at about 258 nm; the absorbance of a 1-cm layer at this wavelength is about 0.49.
C. Carry out the combustion as described under 2.4 Oxygen flask method, using 20 mg of the test substance and 10 ml of sodium hydroxide (1 mol/l) VS as the absorbing liquid. When the process is complete, acidify with nitric acid (~130 g/l) TS; the solution yields reaction A, described under 2.1 General identification tests as characteristic of chlorides.
Melting range. 114-116 °C.
Sulfated ash. Not more than 1.0 mg/g.
Loss on drying. Dry to constant weight at 105°C; it loses not more than 5.0 mg/g.
Free acidity. Shake 3.0 g with 50 ml of carbon-dioxide-free water R, filter and wash the residue with 3 quantities, each of 20 ml of carbon-dioxide-free water R. Titrate the combined filtrate and washings with sodium hydroxide (0.1 mol/l) VS, phenolphthalein/ethanol TS being used as indicator; not more than 1.3 ml is required.
Related substances. Carry out the test as described under 1.14.1 Thin-layer chromatography, using silica gel R2 as the coating substance and a mixture of 24 volumes of dichloromethane R and 1 volume of methanol R as the mobile phase. Apply separately to the plate 5 μl of each of 2 solutions in chloroform R containing (A) 0.10 g of the test substance per ml and (B) 2.5 mg of the test substance per ml. After removing the plate from the chromatographic chamber, allow it to dry in air and examine the chromatogram in ultraviolet light (254 nm). Any spot obtained with solution A, other than the principal spot, is not more intense than that obtained with solution B.
Assay. Dissolve about 0.3 g, accurately weighed, in 50 ml of anhydrous pyridine R and titrate with tetrabutylammonium hydroxide (0.1 mol/l) VS determining the end-point potentiometrically as described under 2.6 Non-aqueous titration, Method B. Each ml of tetrabutylammonium hydroxide (0.1 mol/l) VS is equivalent to 32.82 mg of C14H11Cl2NO4.
Monographs: Pharmaceutical substances: Digitoxinum - Digitoxin
Molecular formula. C41H64O13
Relative molecular mass. 765.0
Graphic formula.
Chemical name.
3β-[(O-2,6-Dideoxy-β-D-ribo-hexopyranosyl-(1→4)-O-2,6-dideoxy-β-D-ribo-hexopyranosyl-(1→4)-2,6-dideoxy-β-D-ribo-hexopyranosyl)-oxy]-14-hydroxy-5β-card-20(22)-enolide; CAS Reg. No. 71-63-6.
Description. A white or almost white, microcrystalline powder; odourless.
Solubility. Practically insoluble in water; slightly soluble in ethanol (~750 g/l) TS.
Category. Cardiotonic.
Storage. Digitoxin should be kept in a well-closed container, protected from light.
Additional information. CAUTION: Digitoxin is extremely poisonous and should be handled with care.
Requirements
Definition. Digitoxin contains not less than 95.0% and not more than 105.0% of C41H64O13, calculated with reference to the dried substance.
Identity tests
• Either tests A, B and D or tests B, C and D may be applied.
A. Carry out the examination as described under 1.7 Spectrophotometry in the infrared region. The infrared absorption spectrum is concordant with the spectrum obtained from digitoxin RS or with the reference spectrum of digitoxin.
B. Carry out the test as described under 1.14.1 Thin-layer chromatography, using kieselguhr R1 as the coating substance and a mixture of 10 volumes of formamide R and 90 volumes of acetone R to impregnate the plate, dipping it about 5 mm beneath the surface of the liquid. After the solvent has reached a height of at least 15 cm, remove the plate from the chromatographic chamber and allow to stand for at least 5 minutes. Use the impregnated plate within 2 hours, carrying out the chromatography in the same direction as the impregnation. As the mobile phase, use a mixture of 50 volumes of xylene R, 50 volumes of ethylmethylketone R and 4 volumes of formamide R. Apply separately to the plate 3 μl of each of 2 solutions (A) of the test substance, and (B) of digitoxin RS, each prepared by dissolving 50 mg in a mixture of equal volumes of chloroform R and methanol R to produce 10 ml and then diluting 1 ml to 5 ml with methanol R. Develop the plate for a distance of 12 cm. After removing the plate from the chromatographic chamber, allow it to dry at 115 °C for 20 minutes, cool, spray with a mixture of 15 volumes of a solution of 25 g of trichloroacetic acid R in 100 ml of ethanol (~750 g/l) TS and 1 volume of a freshly prepared 30 mg/ml solution of tosylchloramide sodium R, and then heat the plate at 115°C for 5 minutes. Allow to cool, and examine the chromatogram in daylight and in ultraviolet light (365 nm). The principal spot obtained with solution A corresponds in position, appearance, and intensity with that obtained with solution B.
C. Dissolve 1 mg in 1 ml of ethanol (~750 g/l) TS by heating gently. Cool the solution and add 1 ml of dinitrobenzene/ethanol TS and 1 ml of potassium hydroxide (1 mol/l) VS; a violet colour develops and then fades.
D. Dissolve 1 mg in 2 ml of a solution prepared by mixing 0.5 ml of ferric chloride (25 g/l) TS and 100 ml of glacial acetic acid R; cautiously add 1 ml of sulfuric acid (~1760 g/l) TS to form a lower layer; a brown ring, but no red colour, is produced at the junction of the two liquids, and after some time the acetic acid layer acquires a blue colour (distinction from allied glycosides).
Specific optical rotation. Use a 10 mg/ml solution in chloroform R and calculate with reference to the dried substance;
Sulfated ash. Not more than 1.0 mg/g.
Loss on drying. Dry to constant weight at 105°C; it loses not more than 20 mg/g.
Gitoxin. Dissolve about 5 mg, accurately weighed, in 1 ml of methanol R and dilute to 25 ml with a mixture of equal volumes of hydrochloric acid (~250 g/l) TS and glycerol R. Allow to stand for 1 hour. The absorbance of a 1-cm layer of this solution at 352 nm, when measured against a solvent cell containing a mixture of equal volumes of hydrochloric acid (~250 g/l) TS and glycerol R, is not more than 0.28 (preferably use 2-cm cells for the measurement and calculate the absorbance of a 1-cm layer); the gitoxin content is about 50 mg/g.
Assay. Dissolve about 0.05 g, accurately weighed, in sufficient methanol R to produce 25 ml; dilute 5.0 ml of this solution to 100 ml with methanol R. Place 5.0 ml of the dilute solution to be tested in a 25-ml volumetric flask, add 15 ml of alkaline trinitrophenol TS, and dilute to 25 ml with methanol R. Set aside for 30 minutes, protected from light, and measure the absorbance in a 1-cm layer at the maximum at about 490 nm against a solvent cell containing a solution prepared by diluting 15 ml of alkaline trinitrophenol TS to 25 ml with methanol R. Calculate the amount of C41H64O13 in the substance being tested by comparison with digitoxin RS, similarly and concurrently examined.
Additional requirements for Digitoxin for parenteral use
Complies with the monograph for "Parenteral preparations".
Bacterial endotoxins. Carry out the test as described under 3.4 Test for bacterial endotoxins; contains not more than 111.0 IU of endotoxin RS per mg.
Monographs: Pharmaceutical substances: Digitoxinum - Digitoxin
Molecular formula. C41H64O13
Relative molecular mass. 765.0
Graphic formula.
Chemical name.
3β-[(O-2,6-Dideoxy-β-D-ribo-hexopyranosyl-(1→4)-O-2,6-dideoxy-β-D-ribo-hexopyranosyl-(1→4)-2,6-dideoxy-β-D-ribo-hexopyranosyl)-oxy]-14-hydroxy-5β-card-20(22)-enolide; CAS Reg. No. 71-63-6.
Description. A white or almost white, microcrystalline powder; odourless.
Solubility. Practically insoluble in water; slightly soluble in ethanol (~750 g/l) TS.
Category. Cardiotonic.
Storage. Digitoxin should be kept in a well-closed container, protected from light.
Additional information. CAUTION: Digitoxin is extremely poisonous and should be handled with care.
Requirements
Definition. Digitoxin contains not less than 95.0% and not more than 105.0% of C41H64O13, calculated with reference to the dried substance.
Identity tests
• Either tests A, B and D or tests B, C and D may be applied.
A. Carry out the examination as described under 1.7 Spectrophotometry in the infrared region. The infrared absorption spectrum is concordant with the spectrum obtained from digitoxin RS or with the reference spectrum of digitoxin.
B. Carry out the test as described under 1.14.1 Thin-layer chromatography, using kieselguhr R1 as the coating substance and a mixture of 10 volumes of formamide R and 90 volumes of acetone R to impregnate the plate, dipping it about 5 mm beneath the surface of the liquid. After the solvent has reached a height of at least 15 cm, remove the plate from the chromatographic chamber and allow to stand for at least 5 minutes. Use the impregnated plate within 2 hours, carrying out the chromatography in the same direction as the impregnation. As the mobile phase, use a mixture of 50 volumes of xylene R, 50 volumes of ethylmethylketone R and 4 volumes of formamide R. Apply separately to the plate 3 μl of each of 2 solutions (A) of the test substance, and (B) of digitoxin RS, each prepared by dissolving 50 mg in a mixture of equal volumes of chloroform R and methanol R to produce 10 ml and then diluting 1 ml to 5 ml with methanol R. Develop the plate for a distance of 12 cm. After removing the plate from the chromatographic chamber, allow it to dry at 115 °C for 20 minutes, cool, spray with a mixture of 15 volumes of a solution of 25 g of trichloroacetic acid R in 100 ml of ethanol (~750 g/l) TS and 1 volume of a freshly prepared 30 mg/ml solution of tosylchloramide sodium R, and then heat the plate at 115°C for 5 minutes. Allow to cool, and examine the chromatogram in daylight and in ultraviolet light (365 nm). The principal spot obtained with solution A corresponds in position, appearance, and intensity with that obtained with solution B.
C. Dissolve 1 mg in 1 ml of ethanol (~750 g/l) TS by heating gently. Cool the solution and add 1 ml of dinitrobenzene/ethanol TS and 1 ml of potassium hydroxide (1 mol/l) VS; a violet colour develops and then fades.
D. Dissolve 1 mg in 2 ml of a solution prepared by mixing 0.5 ml of ferric chloride (25 g/l) TS and 100 ml of glacial acetic acid R; cautiously add 1 ml of sulfuric acid (~1760 g/l) TS to form a lower layer; a brown ring, but no red colour, is produced at the junction of the two liquids, and after some time the acetic acid layer acquires a blue colour (distinction from allied glycosides).
Specific optical rotation. Use a 10 mg/ml solution in chloroform R and calculate with reference to the dried substance;
Sulfated ash. Not more than 1.0 mg/g.
Loss on drying. Dry to constant weight at 105°C; it loses not more than 20 mg/g.
Gitoxin. Dissolve about 5 mg, accurately weighed, in 1 ml of methanol R and dilute to 25 ml with a mixture of equal volumes of hydrochloric acid (~250 g/l) TS and glycerol R. Allow to stand for 1 hour. The absorbance of a 1-cm layer of this solution at 352 nm, when measured against a solvent cell containing a mixture of equal volumes of hydrochloric acid (~250 g/l) TS and glycerol R, is not more than 0.28 (preferably use 2-cm cells for the measurement and calculate the absorbance of a 1-cm layer); the gitoxin content is about 50 mg/g.
Assay. Dissolve about 0.05 g, accurately weighed, in sufficient methanol R to produce 25 ml; dilute 5.0 ml of this solution to 100 ml with methanol R. Place 5.0 ml of the dilute solution to be tested in a 25-ml volumetric flask, add 15 ml of alkaline trinitrophenol TS, and dilute to 25 ml with methanol R. Set aside for 30 minutes, protected from light, and measure the absorbance in a 1-cm layer at the maximum at about 490 nm against a solvent cell containing a solution prepared by diluting 15 ml of alkaline trinitrophenol TS to 25 ml with methanol R. Calculate the amount of C41H64O13 in the substance being tested by comparison with digitoxin RS, similarly and concurrently examined.
Additional requirements for Digitoxin for parenteral use
Complies with the monograph for "Parenteral preparations".
Bacterial endotoxins. Carry out the test as described under 3.4 Test for bacterial endotoxins; contains not more than 111.0 IU of endotoxin RS per mg.
Friday, 31 July 2009
CMC Process testing
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The development of a pharmaceutical product requires a broad spectrum of scientific expertise to lead it through the complex pathway from discovery through characterization of quality, efficacy and safety, which are the hallmarks of a successful drug product. A company must be highly proactive in setting targets for appraising and selecting a compound that has the highest probability of success. In addition, the compound and its therapeutic use must be consistent with the research and marketing goals of the company in order to leverage existing resources and experience. To ensure scientific and commercial success, it is critical to understand the drug development process (Figure 1) and the myriad tasks and milestones that are vital to a comprehensive development plan.
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Although the primary purpose of a well-designed pathway is to assure an efficient process for providing new, high quality and effective drugs for patients, it is also essential to effectively maximize the return on investment. In this context, some primary drivers contributing to maximizing return on investment include the cost of development, market price, product life cycle and competition (Table 1). Each step along the path from discovery to commercialization is important. However, if material cannot be manufactured, the drug development process cannot proceed. As a result, an effective chemistry, manufacturing and controls (CMC) process plays an integral role in the success of a therapeutic compound.
CMC Process
The ability to assure, over time, the physical and chemical properties of an active pharmaceutical ingredient, drug product or nutraceutical is critical for regulatory approval and therapeutic success. The CMC process is necessary for an efficient and comprehensive development strategy. The major challenges for the manufacturing and control component of drug development is to assure the chemical and physical properties of the compound and product are monitored at all critical phases of the pathway. This process matches the scientific and analytical tasks to the manufacturing and commercialization strategy (Table 2).
In recent years, the International Conference on Harmon-isation of Technical Requirements for Registration of Pharma-ceuticals for Human Use (ICH) has adopted scientific standards for quality control monitoring. These standards are the basis of most regulatory guidelines, including those published by the FDA. Key steps on the path include pharmaceutical analysis and stability studies that are required to determine and assure the identity, potency and purity of ingredients, as well as those formulated products. Stability testing facilitates the establishment of recommended storage conditions, determination of retest periods and definition of acceptable shelf life. These data play a key role in determining labeling requirements, as well as in the development and monitoring process.
A Continuous Process
Stability testing is performed on drug substances and products at various stages of product development (Table 3). In early stages, accelerated stability testing (at relatively high temperatures and/or humidities) is used as a "worst case" evaluation to determine what types of degradation products may be found after long-term storage. In preformulation studies, interactions between excipients and the drug substance are studied under stress conditions to access compatibility.
The design of a complete stability testing program for a drug or nutraceutical product is based upon an understanding of the behavior, properties and stability of the drug substance or active ingredient and the experience gained from preformulation studies and early clinical formulations. Products are analyzed at specific intervals to evaluate a variety of parameters, such as the identity of the active ingredient, potency, measurement of degradation products, dissolution time, physical properties and appearance. Samples from production lots of approved products are retained for stability testing and for comparison testing in the case of product failure. Testing of retained samples alongside returned samples is key to ascertaining whether the product failure was manufacturing or storage related.
The objective of analytical testing during preclinical evaluation and Phase I clinical development is to evaluate the stability of the investigational formulations used in initial clinical trials, to obtain information needed to develop a final formulation, and to select the most appropriate container and closure (e.g., compatibility studies of potential interactive effects between a drug substance and other components). Information from the experiments listed in Table 3 under Discovery to Phase I is summarized in the Investigational New Drug application (IND) with the initiation of Phase I clinical trials. When the delivery mechanism of the drug is an integral part of creating the therapeutic effect and must be used in the Phase I trials, formulation data, container closure data and corresponding short-term accelerated stability data should be included in the IND prior to Phase I trials.
Analysis studies on formulations should be underway by the end of Phase II and the stability protocol for study of both the drug substance and drug product should be defined. This will help assure that analytical chemistry data generated during Phase III are appropriate for submission. Prior to Phase I, stability of the drug substance and the formulation to be used must be evaluated. Impurities from the manufacturing and degradants that form are quantitated and tracked to ensure safety prior to moving into the Phase I clinical trials and continuity of material used for laboratory safety testing and clinical trials.
Stability testing done during Phase III studies focuses on testing final formulations in the proposed packaging produced at the manufacturing site. It is recommended that the stability protocol is defined prior to the initiation of Phase III studies. In this regard, consideration should be given to establish appropriate linkage between the non-clinical and clinical batches of the drug substance and drug product and those of the primary stability batches in support of the proposed expiration dating period. Factors to be considered include the source, quality and purity of various components of the drug product, manufacturing process and production facility for the drug substance and the drug product, as well as use of same containers. Data obtained on tests done under controlled conditions replicating conditions recommended for long-term storage and slightly elevated temperatures are used to determine a product's shelf life and expiration dates. In some cases, comprehensive stability testing must also be conducted after approval (Table 4).
A Focus on Stability
The stability of a product may be defined as the extent to which a product retains, within specified limits, throughout its period of storage and use, the same properties and characteristics possessed at the time of its packaging. Stability testing provides evidence on how the quality of a drug substance or drug product varies with time under the influence of a variety of environmental factors such as temperature, humidity and light. These studies are designed to determine if a drug substance will remain within specifications during its shelf life if stored under recommended storage conditions.
Stability testing focuses on the chemical (i.e., integrity, potency, degradation) and physical properties (e.g., appearance, hardness, particle size, solubility) of active pharmaceutical ingredients (API) and products (Table 5). In addition, microbiological testing is done to ensure the substance and product maintain their resistance to microbial and bacterial growth. Assuring the physical/chemical properties and effectiveness properties of a pharmaceutical is critical for labeling and marketing purposes. A wide range of testing is used to evaluate and verify the identity, potency and availability of the API in the product (Table 6). Stability testing is done at all phases of the development, production and marketing process for quality control and monitoring purposes. A wide scope of analytical methodologies is used, including high-performance liquid, gas and thin-layer chromatography (HPLC, GC, TLC) as well as IR and LC/mass spectrometry.
Stability testing requires the use of specialized environmental chambers that can simulate long-term storage conditions. The stress conditions in the chambers include heat, humidity and light. These chambers enable researchers to evaluate product stability based on real-time, accelerated and long-term protocols and are available in both walk-in and reach-in styles. Chambers are engineered and qualified to ensure uniform exposure of the stress conditions to all material in the chamber. Early in the development of the drug product, purposeful degradation studies are done as a means to predict possible degradation pathways of an API. This information is used in the validation of stability indicating analytical methods and in pre-formulation studies. Degradation studies include stress conditions such as heat, oxidative, light, acidic conditions, basic conditions and heat/humidity.
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Physical-Chemical Properties
The physical-chemical properties of the substance are analyzed to verify the identity/structure of the drug substance or product API. Many of these tests require specialized instrumentation and laboratory expertise. In addition, the organoleptic properties—including appearance, hardness and moisture—are evaluated. For quality control purposes, the potency, availability and microbial quality are monitored. All of these factors are key ingredients in stability evaluations.
Testing to assure that products meet specifications for the presence of degradation and impurities are usually intensive chromatographic separations with detection down to the 0.01% levels. Typically, impurities and degradation products that are 0.1% and above need to be evaluated for identity and chemical structure. The level of the impurities allowed depends on the toxicity of the impurity and the daily dose levels of the drug.
Identity information on the stability of a drug substance under defined storage conditions is an integral part of the systematic approach to stability evaluation. Stress testing helps to determine the intrinsic stability characteristics of a molecule by establishing degradation pathways to identify the likely degradation products and to validate the stability indicating power of the analytical procedures used.
Microbiological
Along with chemical and physical testing, a number of microbiological tests must be performed based on the dosage form. For sterile products, the microbiological tests performed include sterility, bioburden and bacterial endotoxins. These tests must be validated to show that the compendial tests are suitable. For example, to validate sterility, the test for bacteriostasis and fungistasis (BF) is performed at time of set down. The BF test ensures that any BF activity does not adversely affect the reliability of the sterility test. Bioburden requires validation to show that the test article will not adversely affect the growth of positive controls.
Non-sterile products have different testing requirements depending on if preservatives are used. Orally administered suspensions or liquids with a preservative are evaluated for microbial limits, total yeasts and molds and antimicrobial preservative effectiveness test. The variations of container closure systems will determine the frequency of testing during the stability study. For example, the sterility of a formulation in a sealed glass ampule need not be tested after sterility is established. For most container closure systems, microbiological testing is performed initially, at 12 months and annually thereafter. For accelerated conditions, testing is minimally performed at end of the storage time.
Stress Testing
The severe conditions encountered during distribution are covered by stress testing of definitive batches of the drug substance. Stress testing provides data on forced decomposition products and mechanisms. These studies establish the inherent stability characteristics of the molecule (e.g., degradation pathways) and lead to identification of degradation products and support the suitability of the proposed analytical procedures. The detailed nature of the studies will depend on the individual drug substance and type of drug product.
Testing is carried out on a single batch of a drug substance and includes the effects of temperatures in 10°C increments above the accelerated temperature test condition and humidity, where appropriate (e.g., 75 % or greater). In addition, one must evaluate oxidation and photolysis on the drug substance, plus its susceptibility to hydrolysis across a wide range of pH values when in solution or suspension.
Photostability (i.e., light) testing is an integral part of stress testing. Some degradation pathways can be complex and, under forced conditions, decomposition products may be observed that are unlikely to be formed under accelerated or long-term testing. This information is useful in developing and validating suitable analytical methods, but may not be necessary to examine specifically for all degradation products if it has been demonstrated that in practice these are not formed. Information obtained from photostability is key in choosing appropriate container/closure systems.
Dosage Form/Delivery System Requirements
The route of administration and delivery system used are key components to the successful development of new drugs and therapies. In addition, these choices have a significant impact on the scientific and regulatory aspects of a stability protocol. The diversity of testing needed for all dosage forms and delivery systems requires a broad range of expertise and methodologies.
In general, all dosage forms are evaluated for appearance, assay and degradation products. Additional tests (i.e., potency) are needed for specific dosage forms. For example, sterility is needed for sterile products but not for tablets or capsules. In addition, not every test will be performed at each time point.
The evaluation of inhalation powders includes aerodynamic particle size distribution of the emitted dose, microscopic evaluation, microbial limit, moisture content, foreign particulates, content uniformity of the emitted dose and number of medication doses per device that meets content uniformity of the emitted dose (metered dose products). The unique characteristics of metered-dose and dry-powder inhalers can affect the product's efficacy as well as the ability of the product to deliver reproducible doses. These factors must be considered during development with respect to formulation, stability, manufacturing, container and closure system and quality control (Table 7).
Stability data for products supplied in closed-end tubes should support the maximum anticipated use period after the tube seal is punctured, allowing product contact with the cap. Ointments, pastes, gels and creams in large containers, including tubes, should be assayed by sampling at the surface, top, middle and bottom of the container. In addition, tubes should be sampled near the crimp.
Evaluation of ophthalmic or optic products (e.g., creams, ointments, solutions and suspensions) includes sterility, particulate matter and extractables. Evaluation of nonmetered topical aerosols includes appearance, assay, degradation products, pressure, weight loss, net weight dispensed, delivery rate, microbial limits, spray pattern, water content and particle size distribution (for suspensions).
Studies of drugs for injection (i.e., parenterals) include monitoring for appearance, clarity, color, reconstitution time and residual moisture content. The stability of drug for injection products must also be evaluated after reconstitution, according to the recommended labeling. Small volume parenterals (SVPs) are a wide range of injection products (e.g., drugs for injection, drugs for injectable suspension and drugs for injectable emulsion). Large volume parenterals (LVPs) studies include evaluation of product stability following exposure to at least the maximum specified process lethality. Interaction of administration sets and dispensing devices are considered to ensure that absorption and adsorption during dwell time do not occur. In veterinary applications, some LVPs are designed for multiple use. These products are evaluated for stability after opening with part of the content removed. The "in-use" studies last from seven days to four weeks.
The functionality and integrity of parenterals in prefilled syringe delivery systems needs to be evaluated throughout the expiration dating period with regard to factors, such as the applied extrusion force, syringeability, pressure rating and leakage. Continued assurance of sterility for products is by a variety of means, including evaluation of the container and closure integrity.
Specific parameters to be examined for reconstituted drug products include appearance, clarity, color, pH, assay (i.e., potency), preservative, degradation products/aggregates, sterility, pyrogenicity and particulate matter. Studies for drug injectable suspension and drug for injectable suspension also include particle size distribution, redispersibility and rheological properties. The studies for drug injectable emulsion products also include phase separation, viscosity and mean size and distribution of dispersed phase globules.
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Package Extraction and Migration
A widely overlooked factor in pharmaceutical analysis testing is the determination of potential impurities resulting from migration from packaging components. This includes testing for nitrosamine residue testing as well as both quantitative and qualitative techniques for nitrosamines and olefin polymers used in packages and closures. The 1998 draft stability guidance recommends performing extractable studies on the container/closure (C/C) system using sensitive and quantitative methods even if the C/C system meets compendial suitability tests. Concern over extractables/leachables from the C/C system depends on the route of administration and the likelihood of a packaging component-dosage form interaction. For example, routes of adminstration such as inhalation aerosals and injectables are of highest concern, whereas orally administered solid dosage forms are of lower priority.
An Integral Component
Although stability is an integral component of a CMC program, a comprehensive testing regimen includes a broad scope of analytical evaluations. The importance of assuring the physical and chemical properties throughout the development and commercialization of a compound is key to effectively managing resources and costs. The inclusion of a well-designed chemistry, manufacturing and controls process in the development pathway can help alleviate devastating pitfalls and facilitate a cost-effective process.
References
1. U.S. Department of Health and Human Services, "Guidance for Industry: Q1A Stability Testing of New Drug Substances and Products." Food and Drug Administration, August 2001.
2. International Conference on Harmonisation of Technical Requirements for Registration of Pharamceuticals for Human Use (ICH), "Stability Testing of New Drug Substances and Products (ICH Q1A)." ICH, September 1993.
3. Gallanger, Maxine M.; A Comparative Analysis of International Regulations and Guidances presented at PDA Scientific Forum: The Extractables Puzzle, November 2001
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