Drug Interactions between Phyrago and rufinamide

GENERALLY AVOID: Grapefruit and grapefruit juice may significantly increase the plasma concentrations of dasatinib. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall induced by certain compounds present in grapefruit. Because grapefruit juice inhibits primarily intestinal rather than hepatic CYP450 3A4, the magnitude of interaction is greatest for those drugs that undergo significant presystemic metabolism by CYP450 3A4 (i.e., drugs with low oral bioavailability). 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. Pharmacokinetic interactions involving grapefruit juice are also subject to a high degree of interpatient variability, thus the extent to which a given patient may be affected is difficult to predict. Because dasatinib prolongs the QT interval, high plasma levels of dasatinib may increase the risk of ventricular arrhythmias such as torsade de pointes and sudden death.

MANAGEMENT: Patients treated with dasatinib should avoid consumption of grapefruit, grapefruit juice, and any supplement containing grapefruit extract. Some authorities recommend close monitoring for toxicity (e.g., myelosuppression, bleeding complications, fluid retention, bradycardia or other conduction disturbances) and a reduction of dasatinib dosage to a range of 20 to 40 mg daily should be considered if there are no alternatives and concomitant use with a potent CYP450 3A4 inhibitor is necessary.

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GENERALLY AVOID: Alcohol may potentiate some of the pharmacologic effects of rufinamide. Use in combination may result in additive central nervous system depression and/or impairment of judgment, thinking, and psychomotor skills.

ADJUST DOSING INTERVAL: Food enhances the oral absorption and bioavailability of rufinamide. In healthy volunteers, administration of a single 400 mg dose of rufinamide with food resulted in an approximately 56% increase in mean peak plasma concentration (Cmax) and a 34% increase in systemic exposure (AUC) compared to administration during a fasting state.

MANAGEMENT: To ensure maximal oral absorption, it is preferable to administer rufinamide with food. Patients receiving rufinamide should be advised to avoid consumption of alcohol. Ambulatory patients should be counseled to avoid hazardous activities requiring complete mental alertness and motor coordination until they know how rufinamide affects them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

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