Drug Interactions between repotrectinib and selumetinib

GENERALLY AVOID: Grapefruit juice may increase the plasma concentrations of selumetinib, which undergoes metabolism primarily by CYP450 3A4 and to a lesser extent by CYP450 2C19, 1A2, 2C9, 2E1 and 3A5, as well as glucuronidation by UGT1A1 and UGT1A3. 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 other CYP450 3A4 inhibitors. When coadministered with itraconazole, a potent CYP450 3A4 inhibitor, selumetinib peak plasma concentration (Cmax) and systemic exposure (AUC) increased by 19% and 49%, respectively. When coadministered with fluconazole, a potent CYP450 2C19 and moderate CYP450 3A4 inhibitor, selumetinib Cmax and AUC increased by 26% and 53%, respectively. Concomitant use of erythromycin, a moderate CYP450 3A4 inhibitor, is predicted to increase selumetinib Cmax and AUC by 23% and 41%, respectively. 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 selumetinib may increase the risk and/or severity of serious adverse effects such as cardiomyopathy (decrease in left ventricular ejection fraction by 10% or more below baseline), ocular toxicity (blurred vision, photophobia, cataracts, ocular hypertension, retinal pigment epithelial detachment, retinal vein occlusion), gastrointestinal toxicity (diarrhea, colitis), skin toxicity (dermatitis acneiform, maculopapular rash, eczema), and musculoskeletal toxicity (creatine phosphokinase elevations, myalgia, rhabdomyolysis).

MANAGEMENT: Patients should avoid consumption of grapefruit, grapefruit juice, or supplements that contain grapefruit during treatment with selumetinib.

GENERALLY AVOID: Grapefruit juice may increase the plasma concentrations and adverse effects of repotrectinib. According to prescribing information, repotrectinib is primarily metabolized by CYP450 3A4, and is also a substrate of P-gp in vitro. 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 repotrectinib and grapefruit juice but has been reported for other CYP450 3A4 inhibitors. Drug interaction studies have shown that the administration of repotrectinib with itraconazole, a potent CYP450 3A4 and P-gp inhibitor, increased the peak plasma concentration (Cmax) and systemic exposure (AUC) of repotrectinib by 1.7-fold and 5.9-fold, respectively. 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 repotrectinib may increase the risk of adverse reactions such as dizziness, fatigue, cognitive disorders, ataxia, dysgeusia, peripheral neuropathy, muscular weakness, and dyspnea as well as more serious adverse effects such as interstitial lung disease/pneumonitis, liver transaminase elevations, myalgia with creatinine phosphokinase (CPK) elevation, hyperuricemia, and skeletal fractures.

MANAGEMENT: The manufacturer advises that concomitant use of repotrectinib with grapefruit, grapefruit juice, or supplements that contain grapefruit should be avoided.

The recommended maximum number of medicines in the 'multikinase inhibitors' category to be taken concurrently is usually one. Your list includes two medicines belonging to the 'multikinase inhibitors' category:

• repotrectinib
• selumetinib

Note: In certain circumstances, the benefits of taking this combination of drugs may outweigh any risks. Always consult your healthcare provider before making changes to your medications or dosage.