Evaluation of hplc and spectrophotometric methods used for the determination of nifedipine and its degradation products

Nifedipine is a calcium channel blocking dihydropyridine derivative, which undergoes a photochemical conversion to the corresponding pyridine derivative when exposed to normal U.V. light. The photooxidation leads to a remarkable decrease of its pharmacological activity. In this study, an evaluation of the chromatographic and spectrophotometric methods for the determination of both nifedipine and its oxidised form was carried out. The spectrophotometric method based on simultaneous determination, the molar absorptivities of both components at 237, 280, and 360 nm were calculated. The method involves the measurement of the absorbance value at two wavelengths and the calculation of the concentration of two components in the mixture by solving for two simultaneous equations. In the second method, we used HPLC to determine the nifedipine and its degradation products. A statistical comparison between both methods was carried out. The results of the analysis of commercial drug formulations, obtained by both methods, agrees quite well with the current USP and BP procedures.