Drug Interaction Report

ADJUST DOSE: Coadministration with inhibitors of P-glycoprotein (P-gp) may increase the plasma concentrations of afatinib, which is a substrate of the efflux transporter. In study subjects, oral administration of the P-gp inhibitor ritonavir (200 mg twice daily) one hour before afatinib dosing resulted in a 48% increase in afatinib systemic exposure. There was no change in afatinib exposure when ritonavir was administered simultaneously with, or 6 hours after, the afatinib dose.

MANAGEMENT: Caution is advised if afatinib is used in combination with P-gp inhibitors. Patients should be monitored for potentially increased adverse effects such as diarrhea, which may lead to dehydration with or without renal impairment; cutaneous reactions including rash, erythema, and bullous, blistering, or exfoliating lesions; interstitial lung disease such as lung infiltration, pneumonitis, acute respiratory distress syndrome, and allergic alveolitis; hepatotoxicity, which may be life-threatening or fatal; keratitis characterized by acute or worsening eye inflammation, lacrimation, light sensitivity, blurred vision, eye pain, red eye, and/or ulceration; and left ventricular dysfunction. The manufacturer recommends reducing the daily dose of afatinib by 10 mg if not tolerated. The previous dose may be resumed after discontinuation of the P-gp inhibitor as tolerated.

ADJUST DOSING INTERVAL: Adagrasib can cause concentration-dependent, prolongation of the QT interval. Theoretically, coadministration with grapefruit juice before adagrasib has reached steady-state may significantly increase the plasma concentrations of adagrasib, which is primarily metabolized by CYP450 3A4. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. Inhibition of hepatic CYP450 3A4 may also contribute. The interaction has not been studied with grapefruit juice but has been reported for the potent CYP450 3A4 inhibitor, itraconazole. In a clinical drug interaction study, adagrasib peak plasma concentration (Cmax) and systemic exposure (AUC) were increased by 2.4-fold and 4-fold, respectively following concomitant use of a single dose of adagrasib (200 mg) with itraconazole. No clinically significant differences in the pharmacokinetics of adagrasib at steady state were predicted when used concomitantly with itraconazole. In general, the effect of grapefruit juice is concentration-, dose- and preparation-dependent, and can vary widely among brands. Certain preparations of grapefruit juice (e.g., high dose, double strength) have sometimes demonstrated potent inhibition of CYP450 3A4, while other preparations (e.g., low dose, single strength) have typically demonstrated moderate inhibition. Increased exposure to adagrasib may increase the risk of adverse effects such as QT prolongation, diarrhea, fatigue, musculoskeletal pain, hepatotoxicity, and renal impairment.

Adagrasib pharmacokinetics were not significantly affected when administered with a high-fat meal.

MANAGEMENT: Although clinical data are lacking, it may be advisable to avoid the consumption of grapefruit or grapefruit juice until adagrasib concentrations have reached steady state (after approximately 8 days). Patients should be advised to seek prompt medical attention if they experience symptoms that could indicate the occurrence of torsade de pointes such as dizziness, lightheadedness, fainting, palpitation, irregular heart rhythm, shortness of breath, or syncope. Adagrasib may be administered with or without food.

ADJUST DOSING INTERVAL: Food may reduce the oral bioavailability of afatinib. According to the product labeling, administration of afatinib with a high-fat meal decreased peak plasma concentration (Cmax) by 50% and systemic exposure (AUC) by 39% compared to administration in the fasted state.

MANAGEMENT: Afatinib should be taken at least 1 hour before or 2 hours after a meal.