Interaction
May reduce effectivity of hormonal contraceptives. Reduced absorption w/ antacids. May decrease plasma concentrations of antivirals (e.g. atazanavir, darunavir, fosamprenavir), atovaquone w/ rifampicin. Rifampicin may reduce serum levels of anticonvulsants (e.g. phenytoin), antiarrhythmics (e.g. disopyramide), oral anticoagulants, antifungals (e.g. ketoconazole), barbiturates, ?-blockers, Ca channel blockers (e.g. diltiazem), chloramphenicol, clarithromycin, corticosteroids, ciclosporin, cardiac glycosides, clofibrate, dapsone, diazepam, doxycycline, fluoroquinolones (e.g. ciprofloxacin), haloperidol, oral hypoglycemic agents (sulfonylureas), levothyroxine, methadone, narcotic analgesics, progestins, quinine, tacrolimus, theophylline, TCAs (e.g. amitriptyline, nortriptyline) and zidovudine. Increased risk of hepatotoxicity w/ halothane. Isoniazid may inhibit the metabolism of anticonvulsants (e.g. carbamazepine, phenytoin), benzodiazepines (e.g. diazepam), haloperidol, ketoconazole, theophylline, and warfarin. May enhance the CNS effects of meperidine, cycloserine, and disulfiram w/ isoniazid. Loss of glucose control in patients on oral hypoglycaemics w/ isoniazid. Potentially Fatal: Concurrent treatment w/ saquinavir/ritonavir combination may result to severe hepatoxicity.