Increased clearance w/ enzyme inducers (eg, barbiturates, bosentan, carbamazepine, phenytoin, primidone, rifampicin, & HIV medication ritonavir, nevirapine & efavirenz & possibly also felbamate, griseofulvin, oxcarbazepine, topiramate & products containing the St. John's Wort). Increased or decreased conc w/ HIV PIs & NNRTIs including HCV inhibitors. Decreased clearance w/ strong CYP3A4 inhibitors eg, ketoconazole, etoricoxib. Increased plasma & tissue conc of ciclosporin. Decreased plasma & tissue conc of lamotrigine. Increased plasma conc of CYP1A2 substrates eg, theophylline (weak increases), tizanidine (moderate increases).