Drug Interaction Report

MONITOR: Coadministration with inducers of CYP450 3A4 may decrease the plasma concentrations of ibrutinib, which is primarily metabolized by the isoenzyme. Preliminary pharmacokinetic data from an ongoing dedicated drug interaction trial and simulations using physiologically based pharmacokinetic models indicate that rifampin, a potent CYP450 3A4 inducer, can decrease ibrutinib peak plasma concentration (Cmax) and systemic exposure (AUC) by more than 10-fold. Pharmacokinetic modeling also suggests that a moderate CYP450 3A4 inducer such as efavirenz may decrease the AUC of ibrutinib up to 3-fold.

MANAGEMENT: The potential for diminished therapeutic effects of ibrutinib should be considered when prescribed in combination with CYP450 3A4 inducers. Patients should be closely monitored, and the dosage of ibrutinib adjusted as necessary in accordance with product labeling.

GENERALLY AVOID: Coadministration with grapefruit, grapefruit juice, or Seville oranges may significantly increase the plasma concentrations of ibrutinib. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. Pharmacokinetic modeling suggests that other moderate CYP450 3A4 inhibitors such as diltiazem and erythromycin may increase ibrutinib systemic exposure (AUC) by 6- to 9-fold under fasting condition. The safety and efficacy of these exposures are unknown. The highest ibrutinib dose evaluated in clinical trials was 12.5 mg/kg (actual doses of 840 to 1400 mg) given for 28 days, which yielded single dose AUC values that were approximately 50% greater than steady-state exposures seen at the highest indicated dose of 560 mg.

ADJUST DOSING INTERVAL: Food increases the oral bioavailability of ibrutinib. The mechanism of interaction is unknown. According to the product labeling, administration with food increases ibrutinib exposure approximately 2-fold compared to administration after overnight fasting.

MANAGEMENT: Patients treated with ibrutinib should avoid consumption of Seville oranges, grapefruit, grapefruit juice, and any supplement containing grapefruit extract. Ibrutinib should be taken once daily at approximately the same time each day.

MONITOR: Isolated case reports have suggested that the ingestion of alcohol during griseofulvin therapy may rarely cause disulfiram-like reactions, flushing, tachycardia, or increased effects of alcohol. The mechanism is unknown.

MANAGEMENT: Patients should be advised of the possibility of increased adverse effects or a disulfiram-like reaction.