[Clinical and pharmacokinetic comparison of 2 oral preparations of nifedipine: 10 mg capsules and 20 mg delayed-release tablets].

The effects and pharmacokinetic parameters of two oral formulations of nifedipine, 10 mg capsule (Adaltat) and 20 mg slow release tablet (Adalat a.p.). With the 10 mg capsule nifedipine was rapidly absorbed, reaching a maximum concentration of 120 +/- 39 ng/ml in 0.52 +/- 0.07 h, and also rapidly eliminated with an apparent halflife of 5.51 +/- 0.64 h. A fall in blood pressure and a raise in heart rate, that significantly correlated with plasma levels, were observed. 83% of the subjects reported headache, that was probably due to the sudden increase in plasma levels. With the 20 mg slow release tablet nifedipine absorption was slower, reaching a maximum concentration of 39 +/- 7 ng/ml in 1.82 +/- 0.43 h, and the apparent half-life (16.89 +/- 3.14 h) was longer than with the capsule. A fall in blood pressure was observed that significantly correlated with plasma levels; however, there was no significant correlation between these and changes in heart rate. Only 17% of the subjects reported headache. Pharmacokinetic data indicate that, in most subjects, nifedipine therapeutics plasma levels (over 15 ng/ml) can be maintained with the administration of a 20 mg slow release tablet every 12 hours. This, joined to the reduction in side effects, suggest that this formulation is the adequate alternative in chronic treatments with nifedipine, such as arterial hypertension.