Omed: The potential for metabolic interactions between Omeprazole and other drugs is very limited. However, as Omeprazole inhibits hepatic microsomal drug metabolism (cytochrome P450 enzyme system), the elimination of other drugs that require hepatic metabolism via the cytochrome P450 system or that are highly extracted by the liver may be decreased during concurrent use with Omeprazole. This effect may result in delayed elimination, increased blood concentrations of diazepam, phenytoin and anticoagulants such as warfarin (monitoring of blood concentrations, or prothrombin time for anticoagulants, is recommended as a guide to dosage adjustment may be necessary during Omeprazole therapy).
Omeprazole, by increasing gastric pH, has the potential to affect the bioavailability of any medication for which absorption is pH-dependent and also Omeprazole may prevent the degradation of acid labile drug. Therefore, concurrent use of itraconazole and Ketoconazole with Omeprazole may result in reduced absorption of these drugs.
Omeprazole has no influence on any other relevant isoforms of CYP, as shown by the lack of metabolic interaction with substrates for CYP1A2 (caffeine, phenacetin, theophylline), CYP2C6 (S-warfarin, piroxicam, phenacetin, theophylline), CYP2D6 (metoprolol, propranolol), CYP2E1 (ethanol), and CYP3A (cyclosporine, lidocaine, quinidine, estradiol, erythromycin, budesonide).
Omed 20: The following drugs should not be used: atazanavir, cilostazol, cyclosporine, diazepam, disulfiram, phenytoin, voriconazole, warfarin, ampicillin, azole antifungals (e.g. ketoconazole), iron supplements.