US Pharm. 2010;35(9):64-65.
Method of Preparation: Calculate the quantity of each ingredient for the amount to be prepared. Accurately weigh or measure each ingredient. Mix the purified water, propylene glycol (PG), benzyl alcohol, and isopropyl alcohol in a suitable container. Individually, add the menthol, butylated hydroxytoluene (BHT), and capsicum oleoresin, mixing until dissolved after each addition. Add the piroxicam and diisopropylamine; stir until dissolved.
Separately, mix the methyl salicylate with the polysorbate 80. Slowly, sift the hydroxypropyl cellulose (HPC) and stir to form a uniform slurry. Add this oil phase to the aqueous phase and mix well. Homogenize if necessary. Check the pH and, if necessary, adjust with the citric acid.
Use: This preparation has been used in the treatment of mild-to-moderate sore muscle and joint pain.
Packaging: Package in tight, light-resistant containers.
Labeling: Keep out of the reach of children. Discard after ____ [time period]. For external use only.
Stability: A beyond-use date of up to 6 months may be used for this preparation, which is commercially available in some countries.1
Quality Control: Quality-control assessment can include theoretical weight compared with actual weight, pH, specific gravity (SG), active drug assay, color, texture-surface, texture-spatula spread, appearance, feel, rheologic properties, and physical observation.2
Discussion: Piroxicam (Feldene, C15H13N3O4S, MW 331.35, ) is a nonsteroidal anti-inflammatory agent with analgesic and antipyretic effects. It occurs as an off-white to light tan or light yellow odorless powder. Feldene is very slightly soluble in water and slightly soluble in alcohol.1
Methyl salicylate (C8H8O3, MW 152.15) occurs as a colorless, yellowish, or reddish liquid with the characteristic odor and taste of wintergreen. It is slightly soluble in water and soluble in alcohol and glacial acetic acid.3
Menthol (C10H20O, MW 156.27) occurs as colorless hexagonal crystals, usually needle-like or in fused masses, or as a crystalline powder. It has a pleasant, peppermint-like odor. It is slightly soluble in water and highly soluble in alcohol.4
Capsicum oleoresin is an alcoholic extract of the dried, ripe fruits of Capsicum annum var. minimum and small fruited varieties of Capiscum frutescens (family Solanaceae). It contains not less than 8.0% of total capsaicins. Capsicum oleoresin occurs as a dark red oily liquid that is soluble in alcohol, acetone, and ether and in volatile oils.3
HPC is a white to slightly yellow-colored odorless, tasteless powder. It is soluble 1 part in 2 parts water, 2.5 parts ethanol, and 5 parts PG, but practically insoluble in glycerin and oils.4
Polysorbate 80 (Tween 80, polyoxyethylene 20 sorbitan monooleate, C64H124O26, MW 1310) occurs as a yellow oily liquid with a characteristic odor and a warm, somewhat bitter taste. It has an SG of 1.06-1.09.4
PG (C3H8O2) occurs as a clear, colorless, viscous, practically odorless liquid with a sweet taste and an SG of 1.038 g/mL. It is miscible with acetone, 95% ethanol, glycerin, and water.4
BHT is an antioxidant. It occurs as a white or pale yellow crystalline solid or powder with a faint characteristic odor. It is practically insoluble in water, glycerin, and PG, but freely soluble in ethanol.4
Benzyl alcohol (C7H8O, MW 108.14) is an antimicrobial preservative, disinfectant, and solvent. Benzyl alcohol is a clear, colorless, oily liquid that has a faint aromatic odor and a sharp, burning taste. It is soluble 1 g in 25 mL water and is miscible with ethanol.4
Diisopropylamine (C6H15N, MW 101.19) occurs as a liquid with a characteristic odor. It is strongly alkaline, with a density of 0.722, and is soluble in water and alcohol. Diisopropylamine is used for pH adjustment.5
Citric acid (citric acid monohydrate, C6H8O7.H2O) occurs as colorless or translucent crystals or as a white crystalline, efflorescent powder that is odorless and has a strong, tart, acidic taste. One gram is soluble in less than 1 mL water and 1.5 mL ethanol.4
Isopropyl alcohol (isopropanol) is a clear, colorless, mobile, volatile flammable liquid with a characteristic odor resembling a mixture of ethanol and acetone, with a bitter taste. It has an SG of 0.786 and is miscible with ethanol, glycerin, and water; it is soluble in acetone and insoluble in salt solutions.4
REFERENCES
1. USP Pharmacists' Pharmacopeia. 2nd ed. Rockville, MD: US Pharmacopeial Convention, Inc; 2008:284,775-779,797-831,1454.
2. Allen LV Jr. Standard operating procedure for performing physical quality assessment of ointments/creams/gels. IJPC. 1998;2:308-309.
3. Reynolds JEF, ed. Martindale: The Extra Pharmacopoeia. 30th ed. London, England: Pharmaceutical Press; 1993:24,1349.
4. Rowe RC, Sheskey PJ, Quinn ME, eds. Handbook of Pharmaceutical Excipients. 6th ed. London, England: Pharmaceutical Press; 2009:64-66,75-76,181-183,317-
5. O'Neil MJ, ed. The Merck Index. 14th ed. Whitehouse Station, NJ: Merck & Co, Inc; 2006:542.
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