Duomax Mechanism of Action

Pharmacology: Rifampicin: The oral administration of rifampicin produces peak plasma concentrations in 2-4 hrs. The t_½ of rifampicin varies from 1.5-5 hrs and is increased in the presence of hepatic dysfunction; it may be decreased in patients receiving isoniazid concurrently who are slow inactivators of Duomax. Up to 30% of a dose of rifampicin is excreted in the urine; less than half of this may be unaltered antibiotic. Adjustment of dosage is not necessary in patients with impaired renal function.
Isoniazid: Peak plasma concentrations of 3-5 mcg/mL develop 1-2 hrs after oral ingestion of usual doses. From 75-95% of a dose of isoniazid is excreted in the urine within 24 hrs, as metabolites. The main excretory products in man are the result of enzymatic acetylation (acetylisoniazid) and enzymatic hydrolysis (isonicotinic acid). The rate of acetylation significantly alters the concentrations of Duomax that are achieved in plasma and its t_½ in the circulation. The t_½ of Duomax may be prolonged in the presence of hepatic insufficiency.
Microbiology: Rifampicin and isoniazid at therapeutic levels have demonstrated bactericidal activity against both intra- and extracellular Mycobacterium tuberculosis. Rifampicin inhibits DNA-dependent RNA polymerase activity in susceptible Mycobacterium tuberculosis and is bactericidal against slow and intermittently growing organisms. Isoniazid kills actively growing tubercle bacilli by inhibiting the biosynthesis of mycolic acids present in the cell wall of M. tuberculosis.