Utility of Oxidation–Reduction Reaction for the Spectrophotometric Determination of Azithromycin

Two simple, rapid, accurate, sensitive and economical visible spectrophotometric (direct, indirect) methods (A and B) for the determination of azithromycin (AZT) in bulk sample and in dosage forms are described. The first method (A) is based on the oxidation of the drug by ammonium metavanadate in sulfuric acid medium and the absorbance is measured at 750 nm. The absorbance concentration plot is linear over the range (0.3-29.7 μg/ml). The second method (B) is based on oxidation of AZT by iodine solution in acidic medium, and determination of the unreacted oxidant by measuring the decrease in absorbance using methylene blue dye (MB) at a suitable λmax (662 nm), respectively. Regression analysis of Beer's law plots showed good correlation in the concentration ranges (0.4-36.1 μg/ml). The quality control/assurance parameters such as limits of detection (LOD), quantification (LOQ), molar absorptivity and Sandelle’s sensitivity values are also reported. The accuracy and precision of the methods were studied on intra-day and inter-day basis. No interference was observed from common pharmaceutical additives. The methods are used successfully to assay AZT in its pharmaceutical dosage forms viz. tablets, capsules and spiked human plasma.