Stress Degradation Studies on Azithromycin and Development of a Validated Stability-Indicating TLC-Densitometric Method with HPLC/Electrospray Ionization-MS Analysis of Degradation Products

Abstract

Abstract The purpose of this work was to develop a sensitive stability-indicating TLC-densitometric method for determination of azithromycin (AZ) in the presence of its impurities E, I, and L, and to study the stability of AZ under different stress conditions. The method was developed on TLC aluminum plates precoated with silica gel F254 using the mobile phase methanol–acetone–ammonia 25% (2 + 13 + 0.1, v/v/v), which gives compact zones for AZ (Rf = 0.39) and impurities E, I, and L (Rf = 0.54, 0.20, and 0.05, respectively). Densitometric analysis of AZ and its impurities was carried out at 483 nm after spraying with sulfuric acid–ethanol (1 + 4, v/v) and heating at 100 ° C for 5 min. The linear regression analysis data for the calibration plots showed good linear relationships with r = 0.9941 for AZ, 0.9987 for impurity E, 0.9989 for impurity I, and 0.9984 for impurity L. AZ was subjected to acidic and alkaline hydrolysis, oxidation, and reduction stress. The drug underwent degradation under these conditions. The degradation products were well-resolved from the pure drug, with significantly different Rf values. A plausible degradation pathway of AZ was established by HPLC/electrospray ionization-MS analysis of the products.