Increased CNS depression with alcohol, opioids, barbiturates, other sedatives and anaesthetics. Increased respiratory depression with opiates, phenobarbital, other benzodiazepines. Plasma concentrations increased by CYP3A4 inhibitors such as cimetidine, erythromycin, clarithromycin, diltiazem, verapamil, ketoconazole and itraconazole, antiretroviral agents, quinupristin with dalfopristin. Midazolam concentration decreased by phenytoin, carbamazepine, phenobarbital, rifampicin. Halothane, thiopental requirements may be reduced during concurrent use.