Decreased efficacy w/ phenytoin, phenobarb, primidone, bosentan, carbamazepine, rifampicin, oxcarbazepine, rifabutin, topiramate, felbamate, griseofulvin, ritonavir, nelfinavir, efavirenz & St. John's wort. Increased or decreased plasma conc w/ HIV PIs eg, nelfinavir, NNRTIs eg, nevirapine &/or HCV medicinal products eg, boceprevir, telaprevir. Increased serum conc w/ strong CYP3A4 inhibitors eg, ketoconazole, itraconazole, clarithromycin or moderate CYP3A4 inhibitors eg, fluconazole, diltiazem, erythromycin. Reduced steroid absorption & efficacy w/ medical charcoal. Increased plasma & tissue conc of ciclosporin. Decreased plasma & tissue conc of lamotrigine.