Drug Interactions between chlorpheniramine / dihydrocodeine / phenylephrine and lonafarnib

GENERALLY AVOID: Grapefruit juice may increase the plasma concentrations of lonafarnib. 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 a single 50 mg oral dose of lonafarnib was administered following pretreatment with the potent CYP450 3A4 inhibitor ketoconazole (200 mg once daily for 5 days) in healthy study subjects, lonafarnib peak plasma concentration (Cmax) and systemic exposure (AUC) increased by 270% and 425%, respectively, compared to lonafarnib administered alone. 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 lonafarnib may increase the risk and/or severity of adverse effects such as nausea, vomiting, diarrhea, anorexia, electrolyte disturbances, liver enzyme elevations, myelosuppression, infection, and hypertension.

ADJUST DOSING INTERVAL: Food does not have clinically relevant effects on the oral bioavailability of lonafarnib. When a single 75 mg oral dose of lonafarnib was administered with a high-fat meal (952 calories; approximately 43% from fat) in healthy subjects, lonafarnib Cmax and AUC decreased by 55% and 29%, respectively, compared to administration under fasted conditions. When administered with a low-fat meal (421 calories; approximately 12% from fat), lonafarnib Cmax decreased by 25% and AUC decreased by 21% relative to fasting. However, administration with food may help improve gastrointestinal tolerance to lonafarnib, which may commonly cause nausea, vomiting, diarrhea, and abdominal pain.

MANAGEMENT: Lonafarnib should be administered with the morning and evening meals and an adequate amount of water. Patients should avoid consumption of grapefruit or grapefruit juice and Seville oranges (also known as bitter or sour oranges).during treatment with lonafarnib.

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

MANAGEMENT: Patients receiving CNS-active agents should be warned of this interaction and advised to avoid or limit consumption of alcohol. Ambulatory patients should be counseled to avoid hazardous activities requiring complete mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

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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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