CYP3A4 inducers may decrease levels/effects eg aminoglutethimide, carbamazepine, nafcillin, nevirapine, atazanavir, nelfinavir, phenobarbital, phenytoin, lamotrigine, rifamycins, griseofulvin and ritonavir; ampicillin, tetracycline and other antibiotics may reduce efficacy; oestrogens may antagonise anticoagulant effect of coumarins; may inhibit metabolism of prednisolone and ciclosporin; may reduce clearance of alprazolam, chlordiazepoxide, diazepam; may increase clearance of lorazepam, oxazepam, temazepam.