Drug Interaction Report

ADJUST DOSING INTERVAL: Limited data suggest that some antacids may decrease the oral bioavailability of rifampin. The mechanisms include decreased dissolution of rifampin in the presence of increased gastric pH and/or aluminum chelation with rifampin. The clinical significance has not been established.

MANAGEMENT: Rifampin should be administered at least 1 hour before antacids. Monitoring for altered therapeutic effect is advisable.

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.

ADJUST DOSING INTERVAL: Didanosine bioavailability is decreased when administered with food. Loss of efficacy may result.

MANAGEMENT: Didanosine should be administered in the fasting state, at least 30 minutes before or more than 2 hours after eating.