Drug Interaction Report

CONTRAINDICATED: Coadministration with potent inhibitors of CYP450 3A4 may significantly increase the plasma concentrations of ranolazine, which is primarily metabolized by the isoenzyme. 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. In pharmacokinetic studies, plasma levels of ranolazine (1000 mg twice a day) were increased 3.2-fold by the potent CYP450 3A4 inhibitor, ketoconazole (200 mg twice a day), and 1.8- to 2.3-fold by the moderately potent inhibitor diltiazem (180 to 360 mg/day). Plasma levels of ranolazine (750 mg twice a day) were increased about 2-fold by the CYP450 3A4 and P-glycoprotein inhibitor, verapamil (120 mg three times a day).

MANAGEMENT: Concomitant use of ranolazine with potent CYP450 3A4 inhibitors is considered contraindicated. Some authorities consider concomitant administration of ranolazine and itraconazole to be contraindicated during and for 2 weeks after treatment with itraconazole.

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.

ADJUST DOSING INTERVAL: Administration of atazanavir with food enhances oral bioavailability and reduces pharmacokinetic variability. According to the manufacturer, administration with a light meal increased the peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of a single 400 mg dose of atazanavir by 57% and 70%, respectively, relative to the fasting state. Administration with a high-fat meal resulted in a mean increase of 35% in atazanavir AUC and no change in Cmax compared to fasting. The coefficient of variation of AUC and Cmax decreased by approximately one-half when given with either a light or high-fat meal compared to the fasting state.

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