Singapore Drugs Database

Indication

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

Mechanism of Action

Pyrazinamide diffuses into M. tuberculosis, where the enzyme pyrazinamidase converts pyrazinamide to the active form pyrazinoic acid. Under acidic conditions, the pyrazinoic acid that slowly leaks out converts to the protonated conjugate acid, which is thought to diffuse easily back into the bacilli and accumulate. The net effect is that more pyrazinoic acid accumulates inside the bacillus at acid pH than at neutral pH. Pyrazinoic acid was thought to inhibit the enzyme fatty acid synthase (FAS) I, which is required by the bacterium to synthesise fatty acids. However, this theory was thought to have been discounted (PMID: 11914348). However, further studies reproduced the results of FAS I inhibition as the putative mechanism first in whole cell assay of replicating M. tuberculosis bacilli which have shown that pyrazinoic acid and its ester inhibit the synthesis of fatty acids (PMID: 17101678). This study was followed by in vitro assay of tuberculous FAS I enzyme that tested the activity with pyrazinamide, pyrazinoic acid and several classes of pyrazinamide analogs. Pyrazinamide and its analogs inhibited the activity of purified FAS I (PMID: 17485499). It has also been suggested that the accumulation of pyrazinoic acid disrupts membrane potential and interferes with energy production, necessary for survival of M. tuberculosis at an acidic site of infection. Pyrazinoic acid has also been shown to bind to the ribosomal protein S1 (RpsA) and inhibit trans-translation. This may explain the ability of the drug to kill dormant mycobacteria (PMID: 21835980).

Pharmacokinetics

Absorption

Rapidly and well absorbed from the gastrointestinal tract.

Distribution

Metabolism

Hepatic.

Elimination

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.

Active Ingredient/Synonyms

2-carbamylpyrazine | 2-pyrazinecarboxamide | Aldinamide | Pirazinamida | Pirazinamide | Pyrazinamid | Pyrazinamida | Pyrazinamide | Pyrazinamidum | Pyrazine carboxamide | pyrazine-2-carboxamide | Pyrazineamide | Pyrazinecarboxamide | Pyrazinoic acid amide | Pyrizinamide | Pyrazinamide |