indication

For the initial treatment of active tuberculosis in adults and children when combined with other antituberculous agents.

pharmacology

Pyrazinamide kills or stops the growth of certain bacteria that cause tuberculosis (TB). It is used with other drugs to treat tuberculosis. It is a highly specific agent and is active only against Mycobacterium tuberculosis. In vitro and in vivo, the drug is active only at a slightly acid pH. Pyrazinamie gets activated to Pyrazinoic acid in the bacilli where it interferes with fatty acid synthase FAS I. This interferes with the bacteriums ability to synthesize new fatty acids, required for growth and replication.

mechanism of action

Pyrazinamide is an important sterilizing prodrug that shortens tuberculosis (TB) therapy. However, the mechanism of action of pyrazinamide is poorly understood because of its unusual properties. In literature it has been written that the pyrazinoic acid (POA), the active moiety of pyrazinamide, disrupted membrane energetics and inhibited membrane transport function at acid pH in Mycobacterium tuberculosis. The antimycobacterial activity appears to partly depend on conversion of the drug to POA. Susceptible strains of M. tuberculosis produce pyrazinamidase, an enzyme that deaminates pyrazinamide to POA, and the vitro susceptibility of a given strain of the organism appears to correspond to its pyrazinamidase activity. Experimental evidence suggests that pyrazinamide diffuses into M. tuberculosis in a passive manner, is converted into POA by pyrazinamidase, and because of an inefficient efflux system, accumulates in huge amounts in the bacterial cytoplasm. The accumulation of POA lowers the intracellular pH to a suboptimal level that is likely to inactivate a vital target enzyme such as fatty acid synthase. Recent studies (2007) demonstrated that pyrazinamide and its analogs inhibit the activity of purified FAS I.

toxicity

Side effects include liver injury, arthralgias, anorexia, nausea and vomiting, dysuria,malaise and fever, sideroblastic anemia, adverse effects on the blood clotting mechanism or vascular integrity, and hypersensitivity reactions such as urticaria, pruritis and skin rashes.

biotransformation

Hepatic.

absorption

Rapidly and well absorbed from the gastrointestinal tract.

half life

9-10 hours (normal conditions)

route of elimination

Approximately 70% of an oral dose is excreted in the urine, mainly by glomerular filtration within 24 hours