Drug Interaction Report

MONITOR: Coadministration with inducers of CYP450 3A4 may decrease the plasma concentrations of vemurafenib, which has been shown in vitro to be a substrate of the isoenzyme. According to the product labeling, administration of a single 960 mg dose of vemurafenib with the potent CYP450 3A4 inducer rifampin at a dosage of 600 mg once daily resulted in a 40% decrease in vemurafenib systemic exposure (AUC) relative to vemurafenib administered alone, with no effect on peak plasma concentration (Cmax). The extent to which other, less potent CYP450 3A4 inducers may affect vemurafenib is unknown.

MANAGEMENT: The potential for diminished pharmacologic effects of vemurafenib should be considered during coadministration with CYP450 3A4 inducers. Alternative treatments or a dose adjustment of vemurafenib may be required if an interaction is suspected.

MONITOR: Isolated case reports have suggested that the ingestion of alcohol during griseofulvin therapy may rarely cause disulfiram-like reactions, flushing, tachycardia, or increased effects of alcohol. The mechanism is unknown.

MANAGEMENT: Patients should be advised of the possibility of increased adverse effects or a disulfiram-like reaction.