Ethnic differences in the pharmacokinetics of oral nifedipine.

1. The pharmacokinetics of a single oral dose of 20 mg nifedipine, given as capsules, has been compared in five South Asian volunteers with data for 27 Caucasian volunteers. 2. The area under the plasma concentration-time curve (AUC) of nifedipine was three fold higher in South Asians (989 +/- 166 ng ml-1 h) than in Caucasians (323 +/- 116 ng ml-1 h). 3. The ratio of the AUC of nifedipine to that of the nitropyridine analogue, which is formed largely as a first pass metabolite, was significantly higher in South Asians (4.6 +/- 1.9) than in Caucasians (2.3 +/- 1.1) indicating a lower first pass metabolism in South Asians. 4. The terminal half-lives of nifedipine and the nitropyridine metabolite were significantly greater in South Asians than in Caucasians. 5. Consumption of a spicy curry diet for 3 days by Caucasians did not significantly affect the pharmacokinetics of a single oral dose of nifedipine. 6. The treatment of patients of South Asian origin with nifedipine should be initiated with lower doses than would be given to Caucasians.