Isoniazid, also known as isonicotinylhydrazide (INH), is an antibiotic used as a first-line agent for the prevention and treatment of both latent and active tuberculosis. It is effective against mycobacteria, particularly Mycobacterium tuberculosis. It is also active against some atypical types of mycobacteria, such as M. kansasii and M. xenopi. Isoniazid is an organic compound that is available in tablet, syrup, and injectable forms.

Isoniazid is an antibacterial agent used primarily as a tuberculostatic. Target: Antibacterial Isoniazid is a prodrug and must be activated by a bacterial catalase-peroxidase enzyme that in M. tuberculosis is called KatG. KatG couples the isonicotinic acyl with NADH to form isonicotinic acyl-NADH complex. This complex binds tightly to the enoyl-acyl carrier protein reductase known as InhA, thereby blocking the natural enoyl-AcpM substrate and the action of fatty acid synthase. This process inhibits the synthesis of mycolic acid, required for the mycobacterial cell wall. A range of radicals are produced by KatG activation of isoniazid,  which has also been shown to be important in the action of another antimycobacterial prodrug PA-824. Isoniazid is bactericidal to rapidly dividing mycobacteria, but is bacteriostatic if the mycobacteria are slow-growing.

1.Antituberculosis It inhibits and kills Mycobacterium tuberculosis. Its biomembrane permeability is good. Because of its good curative effect, low toxicity, low cost, and convenience for oral administration, it is listed as the first choice antituberculosis drug.
2.Antidepressant Isoniazid is also the first antidepressant drug, but it exits the market because of its hepatotoxicity.
3.Antibacterial Isoniazid is highly selective for Mycobacterium tuberculosis, strong antibacterial activity, bacteria have bactericidal effect.