Design and validation of chromatographic and spectrophotometric stability indicating methods for determination of amlodipine besylate and esomeprazole magnesium

Abstract

The objectives of this study were both to develop, optimize and validate spectrophotometric and chromatographic methods for the analysis of amlodipine besylate and esomeprazole magnesium in pharmaceutical formulations in presence of their degradation products and to study their stability under various conditions. The spectrophotometric method for amlodipine was based on either its solubility enhancement using different hydrotropic agents including potassium acetate, ammonium acetate and nicotineamide, or on its formation of ion-pair complex with methyl orange at pH 3.5, showing percentage recovery ranges of 99.74 – 100.04 and 99.82 – 101.05, respectively. For esomeprazole magnesium, the method, however, was based either on its reaction with alizarin red s to form a deep brown complex, or on its formation of ion-pair complex with eriochrome black T at pH 3, showing percentage recoveries ranges of 99.53 – 100.45 and 99.57- 100.52, respectively. These recovery results indicated that both developed spectrophotometric methods for each drug were highly accurate. The development of the liquid chromatographic methods for each drug, however, was based on the application of the factorial design approach, and they were all performed at ambient temperature; for amlodipine besylate, the mobile phase used was composed of either of acetonitrile and water (60:40 v/v) in presence of 0.1% triehylamine or of 20 mM potassium dihydrogen phosphate, flowing at a rate of either 1.0 or 1.5 ml/min, through column C18 column (containing 5µm- size particle) of dimensions 250× 4.5 mm or 150× 4.6 mm, respectively at wavelength either 362 or 212 nm, giving recovery percentage of either 99.96 – 100.54 or 99.76 – 101.13, respectively. For esomeprazole magnesium, the mobile phase used was composed of water and either methanol (60:40) or ethanol (45:55), flowing at the same flow rate of 1.0 ml/min for both methods, through either column C12 (150× 4.5 mm) or column C18 column (150× 4.6 mm), both containing 5µm-size particles, respectively at 302 nm wavelength for both methods, and giving percentage recovery range of 99.90 – 100.26 and 99.43 – 100.78, respectively. These recovery results for both developed chromatographic methods for each drug were also highly accurate. It was found that stability of both drugs was affected by several factors including hydrolysis, heat, and sunlight. The kinetic study of the effect of sunlight, thermal hydrolysis, hydrolysis in alkaline medium and effect of heat on the stability of amlodipine besylate revealed that the reaction was zero, second, zero and first order, respectively. That of the effect of sunlight, thermal hydrolysis, hydrolysis in acidic medium and heat on the stability of esomeprazole magnesium revealed that the reaction was zero, zero, first and zero order, respectively.