Drug Interaction Report

ADJUST DOSE: Coadministration with moderate inhibitors of CYP450 3A4 may significantly increase the plasma concentrations of ibrutinib, which is primarily metabolized by the isoenzyme. In 18 healthy volunteers administered a single 120 mg dose of ibrutinib alone on day 1 and a single 40 mg dose of ibrutinib on day 7 in combination with ketoconazole 400 mg daily on days 4 thru 9, there was a 29-fold increase in dose-normalized ibrutinib peak plasma concentration (Cmax) and 24-fold increase in dose-normalized systemic exposure (AUC) during treatment with ketoconazole compared to administration alone. Pharmacokinetic modeling suggests that moderate CYP450 3A4 inhibitors such as diltiazem and erythromycin may increase the AUC of ibrutinib 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.

MANAGEMENT: The dosage of ibrutinib should be adjusted according to the indication in the product labeling whenever it is used in combination with a moderate CYP450 3A4 inhibitor such as amprenavir, aprepitant, atazanavir, ciprofloxacin, crizotinib, darunavir, diltiazem, dronedarone, erythromycin, fluconazole, fosamprenavir, fosaprepitant, imatinib, or verapamil. All patients should be closely monitored for signs of ibrutinib toxicity such as myelosuppression, bleeding, infection, and renal impairment.

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.

ADJUST DOSING INTERVAL: Food may reduce the systemic bioavailability of amprenavir from fosamprenavir oral suspension. The mechanism of interaction has not been described. According to the product labeling, administration of fosamprenavir oral suspension (1400 mg single dose) with a high-fat meal (967 kcal, 67 g fat, 33 g protein, 58 g carbohydrate) reduced amprenavir peak plasma concentration (Cmax) by 46% and systemic exposure (AUC) by 28% compared to administration in a fasted state. The time to reach peak plasma level (Tmax) was delayed by 0.72 hours. In contrast, the same high-fat meal did not affect the pharmacokinetics of amprenavir from fosamprenavir tablets.

MANAGEMENT: Fosamprenavir suspension should be administered on an empty stomach in adults, but with food in pediatric patients to aid palatability and compliance. If emesis occurs within 30 minutes after dosing the suspension, the dose should be repeated. Fosamprenavir tablets may be taken with or without food.