Drug Interactions Reported with Grapefruit Juice

Grapefruit juice ingested concurrently with several classes of drugs can profoundly influence drug effects and toxicity. Fatal interactions have been reported. Grapefruit juice inhibits cytochrome P450 3A (CYP3A) enzymes and may inhibit cytochrome P450 1A2 (CYP1A2) enzymes.2,5 This can inhibit metabolism of drugs whose metabolic fate relies upon those enzymes. Only orally administered drugs are effected. First-pass metabolism mediated by the CYP3A subfamily of enzymes is a common property shared by drugs that interact with grapefruit juice.2 Also, drugs that undergo a significant first-pass metabolism with a lower bioavailability ranging from 5% to 30% may be affected to a greater degree by grapefruit juice.2 Drugs that interact with grapefruit juice include antiepileptic agents, antimicrobial agents, benzodiazepines, calcium channel blockers, HMG-CoA reductase inhibitors, hormones, immunosuppressant agents, and others. Reported interactions are summarized.