Drug Interaction Report

MONITOR: Coadministration with inhibitors of the P-glycoprotein (P-gp) efflux transporter may increase the oral bioavailability of ranolazine, which has been shown in vitro to be a substrate of P-gp. Ranolazine can prolong the QT interval in a dose-dependent manner, thus increased plasma levels may potentiate the risk of ventricular arrhythmias including ventricular fibrillation and torsade de pointes. However, the interaction has not been evaluated in pharmacokinetic studies. Plasma levels of ranolazine (750 mg twice a day) were increased about 2-fold by the CYP450 3A4 and P-gp inhibitor, verapamil (120 mg three times a day), although the extent to which P-gp inhibition actually contributes to the overall interaction is unknown.

MANAGEMENT: Caution is advised if ranolazine is prescribed in combination with P-gp inhibitors. Pharmacologic response to ranolazine should be monitored more closely whenever a P-gp inhibitor is added to or withdrawn from therapy, and the ranolazine dosage adjusted as necessary. Patients should be advised to seek medical attention if they experience symptoms that could indicate the occurrence of torsade de pointes such as dizziness, palpitations, or syncope.

GENERALLY AVOID: Grapefruit and grapefruit juice may significantly increase the plasma concentrations of orally administered ranolazine. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. Because ranolazine prolongs QT interval in a dose-dependent manner, high plasma levels of ranolazine may increase the risk of ventricular arrhythmias such as ventricular tachycardia, ventricular fibrillation, and torsade de pointes.

MANAGEMENT: Patients treated with ranolazine should avoid consumption of grapefruit juice and other grapefruit products if possible. Otherwise, the dosage of ranolazine should be limited to 500 mg twice a day.