Study on the Related Substances and Mechanism of Degradation of Reference Listed Drug and Self-prepared Formulation of Roxithromycin

OBJECTIVE To compare the impurity spectrum and impurity level between self-prepared formulation and reference listed drug, and explore the mechanism of degradation of roxithromycin. METHODS The related substances of self-prepared formulation and reference listed drug were investigated by HPLC. The structure of related substances of two preparations were auxiliary confirmed on the basis of 11 known impurities, which were located by detecting the EP system suitability standard using LC-MS. The forced degradation experiments of self-prepared formulation and reference listed drug were carried out, including comparing the main degradation pathways by HPLC and preliminarily identifying the structure of degradation impurities using LC-MS. RESULTS The main impurities in the reference listed drug were impurity F, impurity G, impurity H, impurity I. The maximum impurity was impurity G and the content was 0.439%. Impurity C, impurity D, impurity H, impurity I, impurity J had been detected in the self-prepared formulation. The maximum impurity was impurity C and the content was 0.196%. The reference listed drug was stable under alkaline degradation, thermal degradation and photolytic degradation. The impurity B and impurity D were mainly produced under acid degradation. The impurity produced under oxidative degradation failed to locate in the 11 known impurities, by determing molecular weight presumably speculated N-oxide of roxithromycin. The mechanism of degradation of self-prepared formulation and reference listed drug were similar, such as the main degradation pathways and the impurities produced by the main degradation pathways. There was no significant change in the related substances of the two preparations in accelerated tests. CONCLUSION The differences between the domestic and imported active pharmaceutical ingredient lead to the differences of impurity spectrum between self-prepared formulation and reference listed drug. The impurity level of self-prepared formulation is surprisingly lower than reference listed drug. The main degradation pathways of roxithromycin are hydrolysis, isomerization and oxidation of N, respectively producing impurity B, impurity D and N-oxide(m/z=853.531 8).