Drug Interaction Report

GENERALLY AVOID: Coadministration with potent inducers of CYP450 2C19 and/or 3A4 may significantly decrease the plasma concentrations of omeprazole, which is primarily metabolized by these isoenzymes. In a study consisting of 12 healthy male subjects, administration of omeprazole in combination with St John's wort (300 mg three times daily for 14 days) decreased omeprazole peak plasma concentration (Cmax) and systemic exposure (AUC) in CYP450 2C19 poor metabolizers by 37.5% and 37.9%, respectively, and in extensive metabolizers by 49.6 % and 43.9%, respectively. The interaction is likely to also occur with esomeprazole, an enantiomer of omeprazole.

MANAGEMENT: The concomitant use of omeprazole or esomeprazole with St. John's wort or rifampin should generally be avoided.

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.