Bioavailability of nifedipine from different oral dosage forms in healthy volunteers

The absolute and relative bioavailability of nifedipine (1) from different formulations administered as single oral doses in healthy volunteers was determined. Serum concentrations of 1 were measured by GC. The absolute bioavailability of 1 was 53% because of presystemic metabolism. The bioavailability of Adalat (Bayer) tablets, Nifedipina (Terapia) and Corinfar (VEB Arzneimittelwerk Dresden) sugar-coated tablets was 93%, 92% and 86% (respectively) as compared with Adalat capsules. The AUC were not significantly different. The Cmax and tmax values were different, indicating that the absorption of 1 showed differences in first-order rate constants of dissolution in the above mentioned order. Despite the differences among the formulations studied, each preparation may have its merits. In a multiple dose regimen of 20 mg 1 (Nifedipina, Terapia) t.i.d., minimal therapeutic drug levels were achieved and maintained during steady state, from the 1st d of treatment.