Probenecid and rifampicin serum levels.

Serum-levels of rifampicin were investigated in patients receiving rifampicin alone or with other antituberculosis drugs. 2 g of probenecid given 30 min before 300 mg of rifampicin did not result in raising serum levels to more than half those achieved with the standard 600 mg dose of rifampicin. Hence probenecid should not be used to reduce rifampicin dosage in antituberculosis therapy.