Determination of nifedipine in human plasma and its use in bioequivalence study

A sensitive atmospheric pressure chemical ionization liquid chromatographic–mass spectrometric (APCI–LC–MS) assay with positive ion mode has been developed for the determination of nifedipine in human plasma. In this method, nifedipine was extracted from human plasma using diethyl ether with dimethoxanate as the internal standard. Analysis was achieved on a BDS C18 column with methanol–H2O (66:34, v/v) as the mobile phase. Sustained-release nifedipine tablets from DiSha (test, Weihai, China) and from GuoFeng (reference, Qingdao, China) were evaluated following a single 20 mg oral dose to 20 healthy volunteers. Bioequivalence between the products was determined by calculating 90% confidence intervals (90% CI) for the ratio of Cmax, AUC0–t and AUC0–∞ values for the test and reference products, using logarithmic transformed data. The 90% confidence intervals for the ratio of Cmax (86.6–105.2%), AUC0–t (97.8–110.9%) and AUC0–∞ (96.5–110.4%) values for the test and reference products are within the interval (80.0–125.0% for AUC, and 70–143% for Cmax), proposed by State of Food and Drug Administration [SFDA, 2005. Guidance for Bioavailability and Bioequivalence Studies for Chemical Drug Products in Human Being. China, p. 19]. It was concluded that the two sustained-release nifedipine tablets are bioequivalent in their rate and extent of absorption and, thus, may be used interchangeably.