Digoxin: Simultaneous treatment with omeprazole and digoxin in healthy subjects lead to a 10% increase in the bioavailability of digoxin as a consequence of the increased intragastric pH.
Diazepam, Phenytoin and Warfarin: Omeprazole inhibits the metabolism of drugs metabolised by the hepatic cytochrome P450 enzyme system and may increase plasma concentrations of diazepam, phenytoin, and warfarin.
Aminopyrine and Antipyrine: Administration of 60 mg daily for 2 weeks caused a 10-20% prolongation of aminopyrine and antipyrine half-life while half this dose had no significant effect. In most animal models, the effects of omeprazole on barbiturate sleeping times and antipyrine clearance are less marked than those caused by cimetidine.
Theophylline, Propranolol and 7 ethoxycoumarin de-ethylase: Omeprazole does not interfere with theophylline or propranolol metabolism. In one study, however, omeprazole was a more potent inhibitor of 7 ethoxycoumarin de-ethylase activity than cimetidine.
Metoprolol, Lidocaine, Quinidine, Amoxycillin or Antacids: There is no evidence of interaction with theophylline, propranolol, metoprolol, lidocaine, quinidine, amoxycillin or antacids, but interaction with other drugs also metabolised via cytochrome P-450 system cannot be excluded.
Combinations containing any of the following medications, depending on the amount present, may also interact with this medication.
Ampicillin esters, Iron salts or Ketoconazole: Omeprazole may increase gastrointestinal pH; concurrent use with omeprazole may result in a reduction in absorption of ampicillin esters, iron salts, or ketoconazole.
Bone marrow depressants: Concurrent use of omeprazole with these medications may increase the leukopenic and/or thrombocytopenic effects of both these medications; if concurrent use is required, close observations for toxic effects should be considered.