Drug Interaction Report

MONITOR: Coadministration with moderate inhibitors of CYP450 3A4 may increase the plasma concentrations of alfuzosin, which is primarily metabolized by the isoenzyme. Hypotension, syncope, QT prolongation, and priapism may occur. In one study, repeated oral administration of 240 mg/day of diltiazem, a moderate CYP450 3A4 inhibitor, with 7.5 mg/day (2.5 mg three times daily) of alfuzosin increased alfuzosin peak plasma concentration (Cmax) and systemic exposure (AUC) by 50% and 30%, respectively, and increased diltiazem Cmax and AUC each by 40%. No changes in blood pressure were observed in this study.

MANAGEMENT: Caution is advised if alfuzosin is prescribed in combination with moderate CYP450 3A4 inhibitors. Pharmacologic response to alfuzosin should be monitored more closely whenever a CYP450 3A4 inhibitor is added to or withdrawn from therapy, and the alfuzosin dosage adjusted as necessary. Patients should be advised to avoid rising abruptly from a sitting or recumbent position and to notify their physician if they experience dizziness, lightheadedness, orthostasis, syncope, or tachycardia. Taking alfuzosin at bedtime may minimize the occurrence of orthostatic effects. Patients should also avoid driving or operating hazardous machinery until they know how the medication affects them.

ADJUST DOSING INTERVAL: Administration of alfuzosin with food enhances oral bioavailability. According to the manufacturer, extent of absorption is 50% higher when administered under fed conditions compared to fasting conditions.

MANAGEMENT: To ensure maximal oral absorption, alfuzosin should be administered with or immediately after a meal.