[Bioavailability of new nifedipine preparations in man. 1. Pharmacokinetics of nifedipine in the form of sustained-release tablets].

Following a single dose of a 20 mg nifedipine retard-tablet (Pidilat retard or a marketed formulation) to 12 healthy volunteers in a randomized, two-fold cross-over trial the nifedipine plasma levels were quantitatively determined by gas chromatography up to 24 h p.a. The relative bioavailabilities and important pharmacokinetic parameters were calculated and then statistically evaluated for significant differences between the preparations. Approx. 2 h after dosing, peak concentrations of 13 to 74 ng/ml were reached, the minimal therapeutic plasma level of 10-15 ng/ml was - in general - upheld for 10 respectively 8 h. Terminal elimination half-lives were calculated to be 5 and 8 h, respectively. An extrapolation with the obtained data for the expected steady state plasma levels after a twice-a-day dosing showed that the above mentioned therapeutically relevant plasma levels of the unchanged drug are in general achieved for most of the dosage interval. The strong inter- and intraindividual variations of blood levels after nifedipine application, which have already been described by numerous other authors, could also be observed in this study.