Drug Interaction Report

ADJUST DOSE: Coadministration with gemfibrozil may increase the plasma concentrations of drugs that are substrates of the organic anion transporting polypeptide (OATP) 1B1 transporter. The mechanism is decreased clearance due to inhibition of OATP 1B1-mediated hepatic uptake by gemfibrozil and its metabolite, gemfibrozil 1-O-beta-glucuronide. The clinical relevance of this interaction is unknown.

MANAGEMENT: A dosage reduction of OATP 1B1 substrates may be required when used with gemfibrozil. Clinical and laboratory monitoring may be appropriate for some drugs whenever gemfibrozil is added to or withdrawn from therapy.

GENERALLY AVOID: Concurrent use of rifampin in patients who ingest alcohol daily may result in an increased incidence of hepatotoxicity. The increase in hepatotoxicity may be due to an additive risk as both alcohol and rifampin are individually associated with this adverse reaction. However, the exact mechanism has not been established.

ADJUST DOSING INTERVAL: Administration with food may reduce oral rifampin absorption, increasing the risk of therapeutic failure or resistance. In a randomized, four-period crossover phase I study of 14 healthy male and female volunteers, the pharmacokinetics of single dose rifampin 600 mg were evaluated under fasting conditions and with a high-fat meal. Researchers observed that administration of rifampin with a high-fat meal reduced rifampin peak plasma concentration (Cmax) by 36%, nearly doubled the time to reach peak plasma concentration (Tmax) but reduced overall exposure (AUC) by only 6%.

MANAGEMENT: The manufacturer of oral forms of rifampin recommends administration on an empty stomach, 30 minutes before or 2 hours after meals. Patients should be encouraged to avoid alcohol or strictly limit their intake. Patients who use alcohol and rifampin concurrently or have a history of alcohol use disorder may require additional monitoring of their liver function during treatment with rifampin.