Xifaxan Drug Interactions

There is no experience regarding administration of rifaximin to subjects who are taking another rifamycin antibacterial agent to treat a systemic bacterial infection. Due to the lack of data and the potential for severe disruption of gut flora with unknown consequences, rifaximin should not be administered concomitantly with other rifamycins.
Due to the negligible gastrointestinal absorption of orally administered rifaximin (<1%), the systemic drug interaction potential is low.
In vitro data show that rifaximin is a weak inducer of the CYP3A4 isoenzyme of the P-450 cytochrome. Drug-drug interaction studies investigating the clinical interaction between rifaximin and drugs metabolised by the human cytochrome P-450 isoenzymes demonstrated that Rifaximin did not significantly affect the pharmacokinetics of midazolam or an oral contraceptive containing ethinyl estradiol and norgestimate. Therefore, clinical interactions with drugs metabolised by these isoenzymes are not expected.
The potential for drug-drug interactions to occur at the level of gut transporter systems has not been evaluated and cannot be ruled out. No drug interaction studies investigating the concomitant intake of rifaximin and other drugs that might be used during an episode of traveller’s diarrhoea (eg, loperamide, charcoal) are available. Patients should take rifaximin at least 2 hrs after the administration of charcoal.