May decrease effectiveness w/ phenytoin, phenobarb, primidone, bosentan, carbamazepine, rifampicin, oxcarbazepine, rifabutin, topiramate, felbamate, griseofulvin, some HIV-PIs (eg, ritonavir, nelfinavir) & NNRTIs (eg, efavirenz) & St. John's wort; medical charcoal. May increase or decrease plasma conc w/ combinations of HIV-PIs (eg, nelfinavir) & NNRTIs (eg, nevirapine), &/or combinations w/ HCV medicinal products (eg, boceprevir, telaprevir). May increase serum conc w/ strong (eg, ketoconazole, itraconazole, clarithromycin) or moderate (eg, fluconazole, diltiazem, erythromycin) CYP3A4 inhibitors. May increase plasma conc of ciclosporine. May decrease plasma conc of lamotrigine. Reduced absorption w/ medical charcoal.