Twelve hour (trough) plasma nifedipine concentrations during chronic treatment with nifedipine retard.

Variation in plasma nifedipine concentrations have been reported and one study has suggested the existence of a subpopulation of poor metabolisers of this drug. We have studied the variability of 12 h plasma nifedipine concentrations in 64 hypertensive patients on long-term nifedipine Retard 20 mg twice daily. A slightly skewed unimodal distribution with a modal concentration of 15 to 30 ng/ml was obtained. No relationship between 12-h plasma levels and debrisoquine hydroxylation phenotype was found.