Drug Interactions between glycerol phenylbutyrate 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).

ADJUST DOSING INTERVAL: Food may decrease the rate and extent of the oral absorption of selumetinib. When a single 75 mg dose of selumetinib (1.5 times the approved maximum recommended dose) was administered with a high-fat meal (1000 calories; 50% fat) in healthy adults, mean Cmax and AUC of selumetinib decreased by 50% and 16%, respectively, and time to reach peak concentration (Tmax) was delayed by approximately 1.5 hours compared to administration in the fasted state. When a single 50 mg dose of selumetinib was administered with a low-fat meal (400 calories; 25% fat) in healthy adults, selumetinib Cmax and AUC decreased by 60% and 38%, respectively, and Tmax was delayed by approximately 0.9 hours.

MANAGEMENT: Selumetinib should be administered on an empty stomach at least 1 hour before or 2 hours after a meal. Patients should avoid consumption of grapefruit, grapefruit juice, or supplements that contain grapefruit during treatment with selumetinib.

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