INVESTIGATION ON THE CHEMICAL-STABILITY OF ERYTHROMYCIN IN SOLUTIONS USING AN OPTIMIZATION SYSTEM

Erythromycin, an antibiotic commonly used topically in the treatment o f acne, is unstable in solution. The stability is influenced by the pH and by the presence of water. The influence of the pH on the stabilit y of erythromycin was investigated even with the use of dimethyl isoso rbide as co-solvent instead of water. The addition of zinc was attempt ed to ameliorate erythromycin stability as suggested in the literature . To investigate these three factors and their interactions, an optimi zation technique was carried out consisting of a 2(3) factorial analys is and a rotative central composite design. The erythromycin solutions were analysed with an HPLC method. The pH and the concentration of di methyl isosorbide had a significant influence on the stability of eryt hromycin but the addition of zinc was not a significant factor. Moreov er, there was a significant interaction between the pH and dimethyl is osorbide.