STUDY OF THE STABILITY OF ERYTHROMYCIN IN A HYDROPHILIC CREME BASIS BY LIQUID-CHROMATOGRAPHY

The stability of the macrolide antibiotic erythromycin, incorporated a t a 2% m/m concentration in a hydrophilic creme basis containing 2% m/ m of chlorocresol, was monitored over a period of 2 months using liqui d chromatography as the analytical method. Extracts of the creme were analysed using wide-pore poly(styrene-divinylbenzene) PLRP-S 1000 Angs trom as the stationary phase and a mixture of 2-methyl-2-propanol-acet onitrile-potassium phosphate buffer (pH 11.0; 0.02 M)-water (165:30:50 :755, v/v/v/v) as the mobile phase. The method showed good selectivity towards chlorocresol, erythromycin A, its related substances and degr adation products. As the pH of the creme containing erythromycin was 8 .6, alkaline degradation products were expected to be formed. The pres ence of pseudoerythromycin A enol ether was observed after storage of the creme for 1 week at a temperature of 25 degrees C. After 1 month t he content of erythromycin was still more than 95%. (C) 1998 Elsevier Science B.V. All rights reserved.