Drug Interactions between pexidartinib and Proben-C

GENERALLY AVOID: Coadministration with grapefruit juice may increase the serum concentrations of colchicine. Clinical toxicity including myopathy, neuropathy, multiorgan failure, and pancytopenia may occur. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism and P-glycoprotein efflux in the gut wall by certain compounds present in grapefruits. A published case report describes an eight-year-old patient with familial Mediterranean fever who developed acute clinical colchicine intoxication after ingesting approximately one liter of grapefruit juice per day for two months prior to hospital admission while being treated with colchicine 2 mg/day. Her condition progressed to circulatory shock and multiorgan failure, but she recovered with supportive therapy after 24 days in the hospital. In a study of 21 healthy volunteers, administration of 240 mL grapefruit juice twice a day for 4 days was found to have no significant effect on the pharmacokinetics of a single 0.6 mg dose of colchicine. However, significant interactions have been reported with other CYP450 3A4 inhibitors such as clarithromycin, diltiazem, erythromycin, ketoconazole, ritonavir, and verapamil.

MANAGEMENT: Patients treated with colchicine should be advised to avoid the consumption of grapefruit and grapefruit juice, and to contact their physician if they experience symptoms of colchicine toxicity such as abdominal pain, nausea, vomiting, diarrhea, fatigue, myalgia, asthenia, hyporeflexia, paresthesia, and numbness.

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ADJUST DOSING INTERVAL: The presence of food may increase the absorption and toxicity of pexidartinib. Administration of pexidartinib with a high-fat meal increased peak plasma concentration (Cmax) and systemic exposure (AUC) by 100% and prolonged the time to reach peak plasma concentration (Tmax) by 2.5 hours.

GENERALLY AVOID: Grapefruit or grapefruit juice may increase the plasma concentration and risk of adverse effects of pexidartinib, including potentially fatal hepatotoxicity. The mechanism is inhibition of CYP450 3A4-mediated metabolism of pexidartinib by certain compounds present in grapefruits. Concomitant administration of itraconazole, a strong CYP450 3A4 inhibitor, increased pexidartinib peak plasma concentration (Cmax) and systemic exposure (AUC) by 48% and 70%, respectively.

MANAGEMENT: Pexidartinib should be administered on an empty stomach, at least one hour before or two hours after a meal or snack. Consumption of grapefruit or grapefruit juice should generally be avoided during pexidartinib therapy. If concomitant use is unavoidable, the dose of pexidartinib should be reduced according to the manufacturer's recommendations. If concomitant use of grapefruit or grapefruit juice is discontinued, the dose of pexidartinib may be increased (after 3 plasma half-lives of a strong CYP450 3A4 inhibitor) to the dose that was used prior to consumption of grapefruit or grapefruit juice.

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