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.

ADJUST DOSING INTERVAL: Consumption of food has led to a 27% decrease in the bioavailability of orally administered tacrolimus.

MANAGEMENT: Tacrolimus should be administered at least one hour before or two hours after meals.

GENERALLY AVOID: Grapefruit juice has been reported to increase tacrolimus trough concentrations. Data are limited, but inhibition of the CYP450 enzyme system appears to be involved.

MANAGEMENT: The clinician may want to recommend that the patient avoid ingesting large amounts of grapefruit juice while taking tacrolimus.