Bioavailability and pharmacokinetics of nifedipine administered by different routes in healthy volunteers.

Absolute bioavailability (F) of 10 mg nifedipine capsules was studied in six adult healthy male volunteers. The drug was given swallowed and sublingual and the results compared with data obtained when the drug was administered intravenously (0.015 mg/k). The pharmacokinetic profile of nifedipine was performed from venous blood samples obtained over a period of 8 hours, with a specific gas chromatographic assay. Besides bioavailability (F), also were calculated the peak plasma concentration (Cmax), the time to reach Cmax, (tmax), the clearance of the drug (CL), the apparent volume of distribution (V1), the elimination half-life (t1/2 beta), and the area under the curve (AUC). The F value was 44.5 + 7.5% and 48.7 + 8.3% for the swallowed and sublingual routes respectively; however, during the sublingual administration the mean Cmax was larger (92.9 +/- ng/ml), and mean tmax greater (1 h), than the data obtained following the swallowed administration (134.1 +/- 17.7 ng/ml and 0.5 h respectively; p less than 0.05). When nifedipine was administered intravenously the mean t1/2 beta was 2.063 +/- 0.24 h, the mean CL was 0.234 + 0.017 l/h.kg, and the mean V1 was 0.278 + 0.027 l/kg; these data did nat show the great individual variability reported by other authors. Due to the mean AUC, less than 450 ng.h/ml, the group of volunteers of this trial could be classified as rapid metabolizers. Finally, there was a significant linear correlation between nifedipine plasma concentrations and the changes observed in the heart rate blood pressure (r = 0.85; p less than 0.05).