Drug Interaction Report

GENERALLY AVOID: Coadministration with potent inducers of CYP450 3A4 may significantly decrease the plasma concentrations of sorafenib. According to the prescribing information, sorafenib undergoes oxidative metabolism by hepatic CYP450 3A4 as well as glucuronidation by UGT1A9. When a single 400 mg oral dose of sorafenib was administered to healthy volunteers following treatment with the potent CYP450 3A4 inducer rifampin at a dosage of 600 mg once daily for 5 days, mean sorafenib systemic exposure (AUC) decreased by 37% compared to sorafenib administered alone. In another study conducted in 9 patients with advanced hepatocellular carcinoma initiating treatment with sorafenib 400 mg once daily or twice daily, addition of the potent CYP450 3A4 inducer enzalutamide at 160 mg daily starting on day 8 of sorafenib therapy reportedly led to a 60% reduction in mean AUC and 59% reduction in mean peak plasma concentration (Cmax) of sorafenib. The clinical significance of this interaction has not been established, but reduced therapeutic efficacy of sorafenib may occur. In addition, some of the known potent inducers of CYP450 3A4 such as apalutamide, encorafenib, and enzalutamide can cause QT interval prolongation and may have additive effects with sorafenib, resulting in increased risk of ventricular arrhythmias including torsade de pointes and sudden death.

MANAGEMENT: Concomitant use of sorafenib with potent CYP450 3A4 inducers should be avoided when possible.

GENERALLY AVOID: Concurrent use of rifampin in patients who ingest alcohol daily may result in an increased incidence of hepatotoxicity. The increase in hepatotoxicity may be due to an additive risk as both alcohol and rifampin are individually associated with this adverse reaction. However, the exact mechanism has not been established.

ADJUST DOSING INTERVAL: Administration with food may reduce oral rifampin absorption, increasing the risk of therapeutic failure or resistance. In a randomized, four-period crossover phase I study of 14 healthy male and female volunteers, the pharmacokinetics of single dose rifampin 600 mg were evaluated under fasting conditions and with a high-fat meal. Researchers observed that administration of rifampin with a high-fat meal reduced rifampin peak plasma concentration (Cmax) by 36%, nearly doubled the time to reach peak plasma concentration (Tmax) but reduced overall exposure (AUC) by only 6%.

MANAGEMENT: The manufacturer of oral forms of rifampin recommends administration on an empty stomach, 30 minutes before or 2 hours after meals. Patients should be encouraged to avoid alcohol or strictly limit their intake. Patients who use alcohol and rifampin concurrently or have a history of alcohol use disorder may require additional monitoring of their liver function during treatment with rifampin.

ADJUST DOSING INTERVAL: Food may reduce the oral absorption and bioavailability of sorafenib. According to the product labeling, sorafenib bioavailability was reduced by 29% when administered with a high-fat meal compared to administration in the fasted state. When given with a moderate-fat meal, bioavailability was similar to that in the fasted state.

MANAGEMENT: To ensure maximal and consistent oral absorption, sorafenib should be taken at least one hour before or two hours after eating.