Isoniazid

Isoniazid, marketed under other names including isonicotinylhydrazide (INH) and Hydra, is an antibiotic used as a first-line agent in 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 strains like M. kansasii and M. xenopi. Isoniazid is an organic compound that is available in tablet, syrup, and injectable forms.

The most common side effect seen with isoniazid use is an increase in liver enzymes; however it is usually harmless. Uncommon side effects include numbness in the arms or legs and liver inflammation. Isoniazid has a boxed warning on the risk of liver toxicity and thus liver function should be monitored carefully on all patients receiving isoniazid. The proposed mechanism of action is the blocking of the formation of mycolic acid, which is an essential part of the mycobacterial cell wall. Disruption of the cell wall results in cell death and isoniazid can fight colonization at both the intracellular and extracellular level.