Stability of topical erythromycin formulations

Abstract The stability of erythromycin, suspended in a w/o and an o/w emulsion or dissolved in an alcoholic solution and gel, was tested over a 12 week period. The influence of pH and storage temperature was evaluated. A shift in pH from 6.3 to 8.5 as well as an increase in storage temperature from 4°C to 25°C seemed to decrease the stability of erythromycin. The activity of erythromycin in emulsions with an aqueous phase of pH 8.5 had only 40% of the original activity after 1 month storage at 25°C. The alcoholic solution and gel retained more than 90% of their initial activity after 1 month storage at 25°C.