Drug Interactions between avapritinib and Pyrelle HB

GENERALLY AVOID: Grapefruit juice may increase the plasma concentrations of avapritinib. 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. Based on pharmacokinetic modeling, administration of avapritinib (300 mg once daily) in combination with the potent CYP450 3A4 inhibitor itraconazole (200 mg once daily) is predicted to increase avapritinib systemic exposure (AUC) by 600% at steady state, while administration with the moderate CYP450 3A4 inhibitor fluconazole (200 mg once daily) is predicted to increase avapritinib systemic exposure (AUC) by 210% at steady state. 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 avapritinib may increase the risk and/or severity of serious adverse effects such as intracranial hemorrhage, cognitive impairment, mood disorders, hallucinations, edema, and decreases in hemoglobin, leukocytes, neutrophils, and platelets.

ADJUST DOSING INTERVAL: Food may increase the oral absorption of avapritinib. When avapritinib was administered with a high-calorie, high-fat meal (approximately 909 calories; 58 g carbohydrate, 56 g fat, 43 g protein), avapritinib Cmax and AUC increased by 59% and 29%, respectively, compared to administration in the fasted state.

MANAGEMENT: Avapritinib should be administered on an empty stomach at least 1 hour before or 2 hours after a meal. Patients should avoid consumption of grapefruit and grapefruit juice during treatment with avapritinib.

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GENERALLY AVOID: Concurrent acute use of barbiturates and ethanol may result in additive CNS effects, including impaired coordination, sedation, and death. Tolerance of these agents may occur with chronic use. The mechanism is related to inhibition of microsomal enzymes acutely and induction of hepatic microsomal enzymes chronically.

MANAGEMENT: The combination of ethanol and barbiturates should be avoided.

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GENERALLY AVOID: Use of anticholinergic agents with alcohol may result in sufficient impairment of attention so as to render driving and operating machinery more hazardous. In addition, the potential for abuse may be increased with the combination. The mechanism of interaction is not established but may involve additive depressant effects on the central nervous system. No effect of oral propantheline or atropine on blood alcohol levels was observed in healthy volunteers when administered before ingestion of a standard ethanol load. However, one study found impairment of attention in subjects given atropine 0.5 mg or glycopyrrolate 1 mg in combination with alcohol.

MANAGEMENT: Alcohol should generally be avoided during therapy with anticholinergic agents. Patients should be counseled to avoid activities requiring mental alertness until they know how these agents affect them.

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