Drug Interaction Report

MONITOR: Coadministration with inducers of CYP450 3A4 may decrease the plasma concentrations of mirtazapine, which is partially metabolized by the isoenzyme. In healthy study subjects, administration of mirtazapine (30 mg once daily) with the potent CYP450 3A4 inducer carbamazepine (400 mg twice daily) decreased mean steady-state mirtazapine peak plasma concentration (Cmax) and systemic exposure (AUC) by approximately 40% and 60%, respectively, compared to administration with placebo. In another study consisting of patients with unipolar depression receiving mirtazapine 45 mg daily, the addition of carbamazepine reportedly decreased mirtazapine plasma concentrations by approximately 47% after 3 weeks. Likewise, when mirtazapine 30 mg once daily was given with phenytoin 200 mg once daily in healthy, nonsmoking male volunteers, steady-state mirtazapine Cmax and AUC decreased by 33% and 47%, respectively, compared to mirtazapine given alone. Mirtazapine had no significant effect on the pharmacokinetics of either carbamazepine or phenytoin.

MANAGEMENT: The possibility of diminished therapeutic response to mirtazapine should be considered during coadministration with CYP450 3A4 inducers, particularly potent ones like carbamazepine, enzalutamide, lumacaftor, mitotane, phenobarbital, phenytoin, rifampin, and St. John's wort. Pharmacologic response to mirtazapine should be monitored more closely whenever a CYP450 3A4 inducer is added to or withdrawn from therapy, and the dosage adjusted as necessary.

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.

GENERALLY AVOID: Alcohol may potentiate some of the pharmacologic effects of CNS-active agents. Use in combination may result in additive central nervous system depression and/or impairment of judgment, thinking, and psychomotor skills.

MANAGEMENT: Patients receiving CNS-active agents should be warned of this interaction and advised to avoid or limit consumption of alcohol. Ambulatory patients should be counseled to avoid hazardous activities requiring complete mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.