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Pharmacology & Pharmacy

Abstract:

Roxithromycin is a 14-membered semisynthetic macrolide antibiotic, formerly known as RU 28965 or 9- {O- [(2-methoxyethoxy)methyl]oxime} -erythromycin. In the European Pharmacopoeia, chromatography using C18 reversed phase 5μm is described for the determination of related substances and assay. The method should be able to separate nine related substances (impurities A to I). The applicability of this system was tested out on different C18 columns. The retention times of all the compounds available, the resolution between N-demethylroxithromycin and roxithromycin and the symmetry factor for the main compound were measured. Two base deactivated columns gave the best symmetry factor, good resolution and the highest theoretical plate number. They gave also separation between roxithromycin and its methoxy homologue (impurity G), which is the most difficult pair to separate. Parameters such as pH, buffer concentration, temperature and amount organic modifier were optimised using Drylab.