Chemical formula: C₅H₅N₃O Molecular mass: 123.113 g/mol PubChem compound: 1046
Pyrazinamide exhibits tuberculostatic activity in vitro only at slightly acidic pH. The growth of tubercle bacilli within monocytes in vitro is completely inhibited by pyrazinamide at a concentration of 12.5 μg/ml.
Pyrazinamide is active only at an acid pH, and it is therefore active mainly on the tubercle bacilli located within the cell. It is these bacteria which are probably responsible for microbial persistance and thus for relapses after chemotherapy has stopped.
Pyrazinamide has low bacterial activity compared with isoniazide. It is thought that when these are used in combination, isoniazide is the key bactericidal drug, whilst pyrazinamide has a sterilising role, acting on a special bacterial population inhibited by the acid environment inside the macrophage or the walls of tuberculous cavities.
Pyrazinamide is readily absorbed from the gastrointestinal tract. Peak concentrations occur about 2 hours after an oral dose and have been reported to be 33 µg per ml after 1.5 g and 59 µg per ml after 3 g.
Serum concentrations then decline, with a plasma half-life of about 9-10 hours.
About 30% of the dose is excreted in the urine as pyrazinoic acid and 4% as unchanged pyrazinamide within 24 hours.
No relevant information.
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