Lack of pharmacodynamic and pharmacokinetic interaction between pantoprazole and phenprocoumon in man

Objective: Pantoprazole is a selective proton pump inhibitor characterized by a low potential to interact with the cytochrome P450 enzymes in man. Due to the clinical importance of an interaction with anticoagulants, this study was carried out to investigate the possible influence of pantoprazole on the pharmacodynamics and pharmacokinetics of phenprocoumon. Methods: Sixteen healthy male subjects were given individually adjusted doses of phenprocoumon to reduce prothrombin time ratio (Quick method) to about 30-40% of normal within the first 5-9 days and to maintain this level. The individual maintenance doses remained unaltered from day 9 on and were administered until day 15. Additionally, on study days 11-15, pantoprazole 40 mg was given per once daily. As a pharmacodynamic parameter, the prothrombin time ratio was determined on days 9 and 10 (reference value) and on days 14 and 15 (test value), and the ratio test/reference was evaluated according to equivalence criteria. Results: The equivalence ratio (test/reference) for prothrombin time ratio was 1.02 (90% confidence interval 0.95-1.09), thus fulfilling predetermined bioequivalence criteria (0.70-1.43). The pharmacokinetic characteristics AUC(0-24h) and C-max of S(-)- and R(+)-phenprocoumon were also investigated using equivalence criteria. Equivalence ratios and confidence limits of AUC(0-24h) and of C-max of S(-)-phenprocoumon (0.93, 0.87-1.00 for AUC(0-24h); 0.95, 0.88-1.03 for C-max) and of R(+)-phenprocoumon (0.89, 0.82-0.96; 0.9, 0.83-0.98) were within the accepted range of 0.8-1.25. Conclusion: Pantoprazole does not interact with the anticoagulant phenprocoumon on a pharmacodynamic or pharmacokinetic level. Concomitant treatment was well tolerated.