The new H+/K+ -ATPase inhibitor pantoprazole is extensively metabolized by the liver. As substituted benzimidazoles can interact with the cytochrome P450 system, the influence of pantoprazole on the steady-state pharmacokinetics of the calcium antagonist nifedipine was investigated. Nifedipine is widely used in the treatment of cardiovascular diseases and is mainly metabolized in the liver by CYP3A4. Additionally possible influence of gastric pH on the absorption of nifedipine is discussed. Twenty-four healthy volunteers (13 m/11 f) completed a randomized crossover study. As test they received orally 40 mg pantoprazole s.i.d. for 10 days and concomitantly 20 mg nifedipine sustained release (SR) b.i.d. from day 6 to 10. During the reference period 20 mg nifedipine SR were dosed b.i.d. for 5 days. Nifedipine and pantoprazole serum concentrations were measured over one dosing interval on the last day of each period. Lack of pharmacokinetic interaction was handled as an equivalence problem. The 90%-confidence intervals (CI) of the ratios of the primary characteristics AUC and Cmax of nifedipine were entirely within the equivalence range of 0.8 - 1.25. Hence no influence of pantoprazole on the pharmacokinetics of nifedipine was concluded, either by competition with the CYP3A4 or by the reduction of gastric acid secretion. As secondary criterion nifedipine had no relevant influence on the pantoprazole pharmacokinetic characteristics. All treatments were safe and well tolerated. No dose adjustment is required during concomitant treatment with nifedipine and pantoprazole.