Grapefruit juice can significantly increase blood levels of certain anti-arrhythmic drugs by inhibiting their metabolism, potentially leading to enhanced therapeutic effects or toxicity.
Interaction affects CYP3A4-metabolized anti-arrhythmics (e.g., amiodarone, dronedarone, verapamil); not all class members are impacted equally.
Even small amounts of grapefruit juice (e.g., 8 oz) can inhibit CYP3A4 for up to 24 hours.
Consult prescriber before consuming grapefruit; therapeutic drug monitoring recommended for high-risk patients.
No interaction with non-CYP3A4 substrates like lidocaine or beta-blockers (e.g., metoprolol).
Grapefruit juice contains furanocoumarins that inhibit the cytochrome P450 3A4 (CYP3A4) enzyme in the intestines and liver, reducing the first-pass metabolism of CYP3A4 substrate anti-arrhythmics such as amiodarone, dronedarone, and verapamil, resulting in elevated plasma concentrations.
Increased risk of adverse effects including QT prolongation, arrhythmias, bradycardia, hypotension, and potential proarrhythmic events; severity varies by specific drug (e.g., major interaction with amiodarone).
Advise patients to avoid grapefruit juice and products containing it while on affected anti-arrhythmics; monitor drug levels and ECG if interaction occurs; consider alternative citrus juices like orange juice.
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