Omeprazole-associated digoxin toxicity.

Omeprazole is a commonly prescribed inhibitor of the gastric proton pump and has numerous indications in the treatment of gastrointestinal diseases. It is primarily metabolized through the CYP2C19 enzyme, a member of the P450 mixed-function oxidase group, although a minor pathway of metabolism is through CYP3A4, another P450 enzyme. Digoxin is primarily metabolized outside the P450 system, but a minor pathway of metabolism is by CYP3A4. To our knowledge, this is the first known case of digoxin toxicity associated with omeprazole. The possible pathways for such an interaction are reviewed, including increased stomach absorption, p-glycoprotein activity and interactions in the P450 system.