Drug Interaction Report

MONITOR: Based on in vitro data, coadministration with enasidenib may increase the plasma concentrations of drugs that are substrates of the transporters, organic anion transporting polypeptides (OATP) 1B1/1B3 and breast cancer resistance protein (BCRP). The proposed mechanism is decreased clearance due to enasidenib -mediated inhibition of OATP1B1/1B3 and BCRP transporters. There are no clinical data regarding the use of enasidenib with these substrates.

MANAGEMENT: Caution is advised when enasidenib is used concurrently with medications that are substrates of OATP 1B1/1B3 and/or BCRP, particularly those with a narrow therapeutic range. Dosage adjustments as well as clinical and laboratory monitoring may be appropriate for some drugs whenever enasidenib is added to or withdrawn from therapy.

GENERALLY AVOID: Grapefruit juice may increase the plasma concentrations of lapatinib. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits.

ADJUST DOSING INTERVAL: Food can significantly increase the oral bioavailability of lapatinib. According to the manufacturer, lapatinib peak plasma concentration (Cmax) was approximately 2.5- and 3-fold higher and systemic exposure (AUC) 3- and 4-fold higher when administered with a low fat meal (5% fat; 500 calories) or with a high-fat meal (50% fat; 1000 calories), respectively, compared to fasting. Dividing the daily dose also resulted in an approximately 2-fold higher systemic exposure at steady state compared to the same total dose administered once daily.

MANAGEMENT: Patients treated with lapatinib should preferably avoid the consumption of grapefruit or grapefruit juice. The manufacturer recommends that lapatinib be administered at least one hour before or one hour after a meal. The lapatinib dose is administered once daily and should not be divided.