Drug Interactions between Allegra-D 12 Hour and neratinib

GENERALLY AVOID: Grapefruit, grapefruit juice, grapefruit hybrids, pomelos, star-fruit, and Seville oranges may increase the plasma concentrations of neratinib. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in these fruits. Inhibition of hepatic CYP450 3A4 may also contribute. In a study consisting of 24 healthy subjects, neratinib peak plasma concentration (Cmax) and systemic exposure (AUC) increased by 3.2- and 4.8-fold, respectively, when a single 240 mg oral dose of neratinib was administered with the potent CYP450 3A4 inhibitor ketoconazole (400 mg once daily for 5 days). Also, mean apparent oral clearance of neratinib decreased by approximately 75% and mean elimination half-life increased by 54%. The interaction has not been studied with these fruits. In general, for example, 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 neratinib may increase adverse effects such as diarrhea, nausea, vomiting, abdominal pain, stomatitis, anorexia, and hepatotoxicity.

Food with a high fat content enhances the oral bioavailability of neratinib. In healthy volunteers, administration of neratinib 240 mg with a high-fat meal (approximately 55% fat; 31% carbohydrate; 14% protein) increased neratinib peak plasma concentration (Cmax) and systemic exposure (AUC) by 1.7- and 2.2-fold, respectively, compared to administration under fasting conditions. By contrast, a standard breakfast (approximately 50% carbohydrate; 35% fat; 15% protein) increased the Cmax and AUC of neratinib by 1.2- and 1.1-fold, respectively.

MANAGEMENT: The manufacturer recommends administering neratinib with food at approximately the same time every day. Patients should avoid consumption of grapefruit, grapefruit juice, grapefruit hybrids, pomelos, star-fruit, and Seville oranges during treatment with neratinib.

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GENERALLY AVOID: Coadministration with large amounts of certain fruit juices, including grapefruit, orange and apple, may decrease the oral bioavailability of fexofenadine. The proposed mechanism is inhibition of drug efflux via intestinal organic anion transporting polypeptides (e.g., P-glycoprotein), of which fexofenadine is a substrate. In a five-way crossover study with 10 healthy volunteers, 1/4-strength grapefruit juice, grapefruit juice, orange juice and apple juice (300 mL with drug administration and 150 mL every 1/2 hour for up to 3 hours, total volume 1.2 L) reduced the mean area under the plasma concentration-time curve (AUC) of a 120 mg dose of fexofenadine by 23%, 67%, 72% and 77%, respectively, compared to water. Mean peak plasma concentration (Cmax) was similarly affected. The clinical significance of these changes is unknown. However, results from studies using histamine-induced skin wheals and flares found that the size of wheal and flare was significantly larger when fexofenadine was administered with either grapefruit or orange juices compared to water.

MANAGEMENT: To maximize plasma levels and therapeutic effects, fexofenadine should be taken with water. In addition, patients should refrain from consuming large amounts of grapefruit, orange, or apple juice.

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MONITOR: Coadministration of two or more sympathomimetic agents may increase the risk of adverse effects such as nervousness, irritability, and increased heart rate. Central nervous system (CNS) stimulants, particularly amphetamines, can potentiate the adrenergic response to vasopressors and other sympathomimetic agents. Additive increases in blood pressure and heart rate may occur due to enhanced peripheral sympathetic activity.

MANAGEMENT: Caution is advised if two or more sympathomimetic agents are coadministered. Pulse and blood pressure should be closely monitored.

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