Drug Interaction Report

MONITOR: Coadministration with inhibitors of P-glycoprotein (P-gp) may increase the plasma concentrations of mitoxantrone, which is a substrate of the efflux transporter also known as ABCB1 or MDR1. The interaction has been studied with cyclosporine, a potent P-gp inhibitor. In a pharmacokinetic study of 38 children with de novo acute myeloid leukemia, mitoxantrone 6 mg/m2 administered daily in combination with cyclosporine resulted in a 42% decrease in mean mitoxantrone clearance and 12% increase in systemic exposure (AUC) compared to mitoxantrone 10 mg/m2 administered daily without cyclosporine. There were no differences in the rates of stomatitis or infection between the two groups, but an increased incidence of hyperbilirubinemia was observed in the cyclosporine group, which rapidly reversed upon conclusion of treatment. Therefore, it appears a 40% dose reduction of mitoxantrone given with cyclosporine produced statistically similar systemic exposure and toxicity as mitoxantrone given alone.

MANAGEMENT: Caution is advised if mitoxantrone is prescribed in combination with a P-gp inhibitor. Patients should be closely monitored for increased adverse effects including cardiotoxicity and myelosuppression.

GENERALLY AVOID: Grapefruit juice may increase the plasma concentrations of dronedarone. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. According to the product labeling, administration with grapefruit juice resulted in a 2.5-fold increase in dronedarone peak plasma concentration and a 3-fold increase in systemic exposure. Because dronedarone is associated with concentration-dependent prolongation of the QT interval, increased levels may potentiate the risk of ventricular arrhythmias such as torsade de pointes and sudden death.

ADJUST DOSING INTERVAL: Food increases the oral bioavailability of dronedarone. The mechanism of interaction is unknown. According to the product labeling, the absolute bioavailability of dronedarone increases from about 4% when administered in the fasted state to approximately 15% when administered with a high-fat meal.

MANAGEMENT: Patients treated with dronedarone should avoid consumption of grapefruit, grapefruit juice, and any supplement containing grapefruit extract. Dronedarone should be taken twice daily with the morning and evening meals.