Interactions with the hepatic cytochrome P-450 microsomal enzyme system, as evidenced by statistically significant changes in pharmacokinetic parameters, have been described with some H2-receptor antagonists. Omeprazole is the first of a new class of antisecretory agents inhibiting gastric secretion by blocking hydrogen potassium ATPase. Omeprazole contains a benzimidazole moiety and thus has the potential to interact with the cytochrome P-450 enzyme group. In vitro, in vivo and human clinical studies have assessed whether such an interaction occurs, and the potential clinical consequences, in patients receiving omeprazole therapy. In vitro studies have demonstrated that omeprazole influences O-deethylation and N- demethylation in liver microsomes and the clearance and elimination half-life of antipyrine in isolated perfused liver preparations. Overall, the studies reviewed suggest that omeprazole has a differential affinity toward specific cytochrome P-450 isozymes. In vivo animal studies have demonstrated that omeprazole prolongs pentobarbital sleep times and half-life and decreases [14C]-aminopyrine elimination. Human clinical studies have not demonstrated the 'all or none' effect of omeprazole on cytochrome P-450-mediated drug interactions, as is seen with cimetidine. These studies confirm in vitro findings that omeprazole is a differential inhibitor of drug metabolism: interactions have been demonstrated with the model drugs aminopyrine and antipyrine, and the therapeutic drugs diazepam, phenytoin, and warfarin but not with theophylline or propranolol. Although caution should be exercised when initiating omeprazole therapy in patients taking concomitant diazepam, warfarin, and phenytoin, clinically significant drug interactions appear unlikely

Due to the prevalence of both gastrointestinal and cardiovascular diseases, it is likely that patients may be coprescribed gastric parietal cell proton pump inhibitors and beta-adrenergic antagonists. Therefore, the objectives of this phase I study were to assess the potential effects of the coadministration of lansoprazole on the pharmacokinetics of propranolol and to evaluate the safety of propranolol with concomitant lansoprazole dosing. In a double-blind fashion, 18 healthy male nonsmokers were initially randomized to receive either 60 mg oral lansoprazole, each morning for 7 days, or an identical placebo (period 1). On day 7, all subjects were concomitantly administered oral propranolol, 80 mg. After a minimum of 1 week following the last dose of either lansoprazole or placebo, subjects were crossed over to the opposite treatment for another 7 days (period 2). Subjects were again administered oral propranolol on day 7. During both treatment periods, blood samples for the determination of plasma propranolol and 4-hydroxy-propranolol were obtained just before the dose and at 0.5, 1, 2, 3, 4, 6, 8 12, 16, 20, and 24 hours postdose. Plasma propranolol and 4-hydroxy-propranolol concentrations were determined by using HPLC with fluorescence detection. The Cmax, tmax, AUC0-infinity, and t1/2 values for propranolol, as well as the AUC0-infinity for 4-hydroxy-propranolol, were calculated and compared between the lansoprazole and placebo regimens. The mean age of the 15 subjects who successfully completed the study was 31 years (range: 24-38 years), and their average weight was 174.8 pounds (range: 145-203 pounds). There were no statistically significant differences between the lansoprazole and placebo regimens for the propranolol Cmax, tmax, AUC0-infinity, and t1/2 values. Also, there were no statistically significant differences between regimens for the 4-OH-propranolol AUC0-infinity. Safety evaluations, which included adverse events, vital signs, clinical laboratory determinations, ECG, and physical examinations, revealed no unexpected clinically significant findings and did not suggest a drug-drug interaction. In conclusion, lansoprazole does not significantly alter the pharmacokinetics of propranolol, suggesting that it does not interact with the CY

The new H+/K+ ATPase inhibitor pantoprazole, a substituted benzimidazole, is metabolized by the hepatic cytochrome P450 enzymes 2C19 or 3A4 and subsequently undergoes phase II metabolism. The widely used beta 1-adrenoreceptor-blocking agent metoprolol is metabolized via CYP2D6. The influence of pantoprazole on the pharmacokinetics of an orally administered zero order kinetics formulation (ZOK) of metoprolol was the objective of this study. Eighteen volunteers (9 female, 9 male, age 20-44 years) completed the randomized, double-blind crossover study. Each subject received either 95 mg metoprolol and placebo (reference (R)) or 95 mg metoprolol and 40 mg pantoprazole (test (T)) as oral doses (sid) for 5 consecutive days. On day 5 of each period serum concentrations of R- and S-metoprolol were determined and a treadmill ergometry was performed. The primary pharmacokinetic characteristics for extent and rate of absorption were AUC(0-24h) and % PTF, respectively. To assess the pharmacodynamic effect of metoprolol the excess area under the effect vs. time curve was calculated for heart rate during ergometry (AUCexHR). Point estimate and 90% confidence limits (CI) for the ratios of population medians of T and R were given. The respective point estimates (90% CI) of the ratios of both primary and secondary characteristics were entirely within the equivalence range of 0.80 and 1.25 for both enantiomers of metoprolol. Moreover, equivalence could be shown for the pharmacodynamic characteristic AUCexHR. Hence, it was concluded that pantoprazole does not interact with metoprolol pharmacokinetics or pharmacodynamics. Therefore, no dose adjustment of metoprolol during therapy with pantoprazole is necessary

Propranolol is widely used in clinical practice and is frequently administered along with other drugs. The co-administration of propranolol and other drugs may result in either propranolol-induced changes in the disposition of other drugs or in effects of the other drugs on the pharmacokinetics of propranolol. These changes may be due to alteration in absorption, metabolism or to haemodynamic effects such as altered liver blood flow. Understanding the pharmacokinetics of propranolol is important to the rational interpretation of the effects of other drugs on propranolol´s disposition. The absorption, protein binding and metabolism of propranolol may all be affected by the co-administration of other drugs. Induction of propranolol´s metabolism by halofenate, phenytoin, phenobarbitone, rifampicin and alcohol have all been implicated in altering propranolol clearance, while inhibition of hepatic drug metabolising enzymes by chlorpromazine and cimetidine appear to reduce propranolol clearance. Propranolol may also affect the metabolism of other drugs such as antipyrine, chlorpromazine, theophylline and thyroid hormones. Suggestions that propranolol may alter quinidine´s elimination have not been substantiated. By reducing liver blood flow propranolol may reduce the systemic clearance of other high extraction drugs such as lignocaine

In a randomised double-blind cross-over study, 8 normal subjects received propranolol 80 mg twice daily with omeprazole 20 mg or identical placebo each morning. Propranolol kinetics were measured on day 8 of both treatment periods. Areas under the propranolol concentration/time curves were not significantly increased by omeprazole treatment: off treatment mean 787.6, on treatment 802.5 ng-1.ml.h. Maximum and minimum steady-state propranolol concentrations were similarily unaffected. Omeprazole also failed to increase the clinical effect of propranolol, as assessed by exercise tests on Day 8 of treatment. We conclude that omeprazole in the dose likely to be used for peptic ulcer has no significant effect on the kinetics or action of propranolol