US Pharm. 2011;36(3):46-47.
Method of Preparation: Calculate the required quantity of each ingredient for the total amount to be prepared. Accurately weigh or measure each ingredient. Add the benzyl alcohol to about 85 mL of the alcohol. Add the melaleuca oil and mix until dissolved. Sprinkle the hydroxypropyl cellulose on the mixture slowly, while stirring. Cover mixture and let stand to complete gelling. Add sufficient alcohol to final volume and mix well. Package and label.
Use: This preparation has been used for the topical treatment of acne.
Packaging: Package in tight, light-resistant containers.1
Labeling: Keep out of the reach of children. Use only as directed. For external use only.
Stability: A beyond-use date of up to 6 months may be used for this preparation.1
Quality Control: Quality-control assessment can include theoretical volume compared with actual volume, specific gravity (SG), color, appearance, feel, rheologic properties, and physical observations.2
Discussion: Tea tree oil (melaleuca oil, Australian tea tree oil) is an essential oil that is obtained by steam distillation from the foliage and terminal branchlets of Melaleuca alternifolia, M linariifolia, M dissitiflora, and other Melaleuca species. It occurs as a clear, mobile, colorless to pale-yellow liquid with a characteristic odor with nutmeg associations and possibly citrus or floral undertones. It is soluble in 80% alcohol. Tea tree oil should be stored in well-filled, airtight containers at room temperature and should be protected from light. It has bactericidal and fungicidal properties and is used topically to treat various skin disorders; it also is used in aromatherapy.3,4
Benzyl alcohol (C7H8O, MW 108.14) is an antimicrobial preservative, disinfectant, and solvent. It is commonly used in concentrations up to 2% in pharmaceutical formulations as an antimicrobial preservative. Benzyl alcohol is a clear, colorless, oily liquid with a faint, aromatic odor and a sharp, burning taste. It has an SG of about 1.045, a boiling point of 204.7°C, and a freezing point of –15°C. It is soluble 1 g in 25 mL of water at 25°C and is miscible with ethanol. Benzyl alcohol will slowly oxidize in air to benzaldehyde and benzoic acid; its aqueous solutions may be sterilized by filtration or autoclaving. It may be stored in metal or glass containers; plastic should not be used, with the exception of polypropylene containers coated with inert fluorinated polymers such as Teflon. Benzyl alcohol should be stored in an airtight container and protected from light. It is incompatible with oxidizing agents and strong acids, and it can accelerate auto-oxidation of fats.5
Hydroxypropyl cellulose is a white to slightly yellow-colored, odorless and tasteless powder. It is widely used in oral and topical pharmaceutical formulations. The pH of a 1% w/v aqueous solution is in the range of pH 5.0 to 8.5. Hydroxypropyl cellulose is soluble 1 in 2 parts water, 1 in 2.5 parts ethanol, and 1 in 5 parts propylene glycol, but is practically insoluble in glycerin and oils. It has some incompatibility problems with substituted phenol derivatives, such as methylparaben and propylparaben.6
Alcohol (ethyl alcohol, ethanol, grain alcohol, C2H5OH, MW 46.07) is a clear, colorless, mobile and volatile liquid with a slight, characteristic odor and a burning taste. It is used as an antimicrobial preservative (>10% concentration), disinfectant (60%-90% concentration), and solvent in injectable and oral liquids (variable concentration), and as a solvent in topical products (60%-90% concentration). Alcohol USP refers to 95% ethanol; dehydrated alcohol refers to 99.5% alcohol. The SG of alcohol is between 0.812 and 0.816, and its boiling point is 78.15°C. Alcohol is miscible with chloroform, glycerin, and water, and its solutions may be sterilized by autoclaving or filtration. It should be stored in a cool place. Alcohol is incompatible with oxidizing materials in acidic conditions, and with alkalies it may darken in color. When alcohol is added to aqueous solutions of organic salts or acacia, the substances may precipitate. Alcohol is incompatible with aluminum containers, and it may interact with some drugs.7
REFERENCES
1. USP Pharmacists’ Pharmacopeia. 2nd ed. Rockville, MD: US Pharmacopeial Convention, Inc; 2008:775-779,797-831.
2. Allen LV Jr. Standard operating procedure for performing physical quality assessment of ointments/creams/gels. IJPC. 1998;2:308-309.
3. Sweetman SC, ed. Martindale: The Complete Drug Reference. 37th ed. London, England: Pharmaceutical Press; 2009:1463-1464, 2338.
4. O’Neil MJ, ed. The Merck Index. 14th ed. Whitehouse Station, NJ: Merck & Co, Inc; 2006:1562.
5. Storey RA. Benzyl alcohol. In: Raymond CR, Sheskey PJ, Quinn ME, eds. Handbook of Pharmaceutical Excipients. 6th ed. London, England: Pharmaceutical Press; 2009:64-66.
6. Kabir MS, Reo JP. Hydroxypropyl cellulose. In: Rowe RC, Sheskey PJ, Quinn ME, eds. Handbook of Pharmaceutical Excipients. 6th ed. London, England: Pharmaceutical Press; 2009:317-322.
7. Quinn ME. Alcohol. In: Rowe RC, Sheskey PJ, Quinn ME, eds. Handbook of Pharmaceutical Excipients. 6th ed. London, England: Pharmaceutical Press; 2009:17-19.
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