The bioavailability and pharmacokinetics of slow release nifedipine during chronic dosing in volunteers.

Eight healthy volunteers received slow release nifedipine 20 mg 12 hourly, for six doses. A nifedipine pharmacokinetic profile was performed after the fifth dosing interval using 12 sampling times over 12 h. A specific high pressure liquid chromatography (h.p.l.c.) nifedipine assay was used. Six of the volunteers subsequently received an i.v. infusion of 3.5 mg of nifedipine after an identical period (five dosing intervals) of chronic oral dosing with slow release nifedipine 20 mg 12 hourly. An identical pharmacokinetic profile was performed after the infusion. Bioavailability, clearance (CL), apparent volume of distribution (V), apparent half life (t1/2) and area under the curve (AUC) were calculated. The geometric mean apparent t1/2 for the slow release preparation was 6.3 +/- 2.0 h. In the six volunteers, the mean bioavailability was 46% (range 29-86%), the mean CL was 588.0 +/- 67.1 ml min-1, the mean apparent V was 160.1 +/- 61.7 l. The pharmacokinetics of slow release nifedipine during chronic dosing appear similar to those derived from single dose studies.