- Concomitant treatment with known cytochrome P450-3A4 inhibitors (e.g cimetidine, anti-HIV protease inhibitors e.g. ritonavir, azole anti-mycotics eg. Ketoconazole, digoxin, quinidine, tacrolimus) or inducers such as anti-epileptic drugs (eg. phenytoin, carbamazepine and phenobarbitone) or rifampicin