Drug Interaction Report

GENERALLY AVOID: Coadministration with potent inducers of CYP450 3A4 and/or P-glycoprotein may significantly decrease the plasma concentrations and pharmacologic effects of sirolimus. The mechanism probably involves reduced absorption as well as accelerated clearance of sirolimus due to induction of both intestinal P-glycoprotein drug efflux transporter and hepatic/intestinal CYP450 3A4 isoenzymes. In a study of 14 healthy volunteers, a potent inducer of CYP450 3A4 and P-gp, rifampin (600 mg daily for 14 days) increased the oral clearance of sirolimus (20 mg single dose) by 5.5-fold, representing mean decreases in peak blood concentration (Cmax) and area under the concentration-time curve (AUC) of 71% and 82%, respectively.

MANAGEMENT: Given the risk of organ rejection associated with inadequate immunosuppressant levels, the use of sirolimus with potent inducers of CYP450 3A4 and/or P-gp is not recommended. Alternative therapeutic agents with less enzyme induction potential should be considered.

GENERALLY AVOID: Coadministration with potent or moderate inhibitors of CYP450 3A4 may significantly increase the plasma concentrations of encorafenib, which is primarily metabolized by the isoenzyme. When a single 50 mg dose of encorafenib (equivalent to 0.1 times the recommended dose) was administered with posaconazole, a potent CYP450 3A4 inhibitor, encorafenib peak plasma concentration (Cmax) increased by 68% and systemic exposure (AUC) increased by 3-fold. When the same dose of encorafenib was administered with diltiazem, a moderate CYP450 3A4 inhibitor, encorafenib Cmax increased by 45% and AUC increased by 2-fold. Increased exposure to encorafenib may increase the risk of serious and life-threatening adverse effects such as hemorrhage, uveitis, QT prolongation, hepatotoxicity, dermatologic reactions, and new malignancies.

MANAGEMENT: Concomitant use of encorafenib with grapefruit or grapefruit juice should generally be avoided. If coadministration is required, the manufacturer recommends reducing the encorafenib dose to one-third of the dose used prior to addition of a potent CYP450 3A4 inhibitor or one-half of the dose used prior to addition of a moderate CYP450 3A4 inhibitor. After the inhibitor has been discontinued for 3 to 5 elimination half-lives, the encorafenib dose that was taken prior to initiating the inhibitor may be resumed.

ADJUST DOSING INTERVAL: Consumption of food can decrease the rate and extent of gastrointestinal absorption of sirolimus. Also, the consumption of grapefruit juice may result in increased sirolimus trough concentrations.

MANAGEMENT: Experts recommend that this drug be taken either at least one hour prior to eating or consistently with or without food to avoid variations in sirolimus blood levels. The manufacturer recommends against using grapefruit juice for dilution of sirolimus doses. Patients should be monitored for clinical and laboratory evidence of altered immunosuppressant effects.