US Pharm. 2010;35(12):86-87.
Method of Preparation: Calculate the quantity of each ingredient for the amount to be prepared. Accurately weigh or measure each ingredient. Combine the glyceryl stearate, cetyl alcohol, petrolatum, and mineral oil, and heat the mixture to about 60°C to 70°C. Dissolve the urea in about 40 mL of purified water. Mix the terbinafine, Carbopol 940, and xanthan gum with the propylene glycol. Incorporate the propylene glycol solution into the urea solution; mix well and heat to about 60°C to 70°C. Combine the two mixtures and mix while agitating to form an emulsion. Add the trolamine; while the mixture is cooling, add sufficient purified water to final weight and mix well. Package and label.
Use: This preparation has been used in the treatment of fungal infections.
Packaging: Package in tight, light-resistant containers.
Labeling: For external use only. Keep out of the reach of children. Discard after ____ [time period].
Stability: A beyond-use date of up to 30 days may be used for this preparation.1
Quality Control: Quality-control assessment can include theoretical weight compared with actual weight, specific gravity (SG), active drug assay, color, texture-surface, texture-spatula spread, appearance, feel, rheologic properties, and physical observations.2
Discussion: Terbinafine (Lamisil, C21H25N, MW 291.43) is an allylamine derivative with broad-spectrum antifungal activity. It occurs as a white or off-white powder that is very slightly or slightly soluble in water and freely soluble in dehydrated alcohol. It is used topically in the treatment of tinea corporis, tinea cruris, and tinea pedis.3
Urea (carbamide, ureum, carbonic acid diamide, NH2CONH2, MW 60.06) occurs as colorless, transparent, slightly hygroscopic, odorless or almost odorless, prismatic crystals or as white crystalline powder or pellets. It is very soluble in water and is soluble 1 g in 10 mL to 12 mL of alcohol and 1 g in 1 mL of boiling alcohol.3
Carbopol 940 is a synthetic, high-molecular-weight (HMW) polymer that occurs as a white-colored, fluffy, acidic, hygroscopic powder with a slight characteristic odor. It is soluble in water and, after neutralization, in 95% ethanol and glycerin.4
Glyceryl stearate (C21H42O4, MW 358.6) occurs as a white to cream-colored, waxlike solid in the form of beads, flakes, or powder. It is waxy to the touch and has a slight fatty odor and taste. The commercial products occur as mixtures of glyceryl monostearate and glyceryl monopalmitate.4
Cetyl alcohol (C16H34O, MW 242.44) occurs as waxy, white flakes, granules, cubes, or castings. It has a faint characteristic odor and a bland taste. Cetyl alcohol is freely soluble in 95% ethanol and ether, and it is practically insoluble in water. It is miscible when melted with fats, liquid and solid paraffins, or isopropyl myristate.4
Propylene glycol (C3H8O2) occurs as a clear, colorless, viscous, practically odorless liquid with a sweet taste somewhat resembling glycerin. It has an SG of 1.038 g/mL and is miscible with acetone, 95% ethanol, glycerin, and water. It is not miscible with fixed oils or light mineral oil. Propylene glycol is used as a humectant and solvent in this preparation. Since it is hygroscopic, propylene glycol should be stored in tight containers and protected from light.4
Xanthan gum (corn sugar gum) is an HMW polysaccharide gum with a molecular weight of approximately 2 ´ 106. Xanthan gum occurs as a cream or white-colored, odorless, free-flowing, fine powder. It is soluble in cold or warm water, but practically insoluble in ethanol and ether.4
Trolamine (TEA) is an alkalizing and emulsifying agent. It occurs as a variable mixture of alkanolamines and is a clear, colorless to pale yellow-colored, viscous liquid with a slight ammoniacal odor. Trolamine has an SG of about 1.120 to 1.128 g/mL. It is miscible with water and 95% ethanol.4
White petrolatum (white petroleum jelly, white soft paraffin) is a white-colored, translucent, soft, unctuous mass that is inert, odorless, and tasteless. It has an SG of about 0.815 to 0.880. White petrolatum is practically insoluble in ethanol, glycerin, and water, but is soluble in most fixed and volatile oils.4
Mineral oil (heavy mineral oil, liquid paraffin, liquid petrolatum, paraffin oil, white mineral oil) is a transparent, colorless, viscous liquid that is practically tasteless and odorless when cold; when warm, it has a faint odor. It has an SG of 0.845 to 0.905. Mineral oil is practically insoluble in 95% ethanol, glycerin, and water.4
REFERENCES
1. USP Pharmacists' Pharmacopeia. 2nd ed. Rockville, MD: U.S. Pharmacopeial Convention, Inc; 2008:775-779.
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. 36th ed. London, England: Pharmaceutical Press; 2009:546-547,1620.
4. Rowe RC, Sheskey PJ, Quinn ME, eds. Handbook of Pharmaceutical Excipients. 6th ed. London, England: Pharmaceutical Press; 2009:110-114,155-156,290-293,
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