Isoniazid

Isoniazid, also known as isonicotinylhydrazide (or INH), is an organic compound that is the first-line medication in prevention and treatment of tuberculosis.

Isoniazid is a prodrug and must be activated by a bacterial catalase-peroxidase enzyme that in mycobacterium tuberculosis is called KatG. KatG couples the isonicotinic acyl with NADH (M6056) > 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.

Isoniazid is bactericidal to rapidly dividing mycobacteria, but is bacteriostatic if the mycobacteria are slow-growing. It inhibits the P450 system and hence acts as a source of free radicals.

Synonyms: INH; Isonicotinic acid hydrazide; Isonicotinic hydrazide ; 4-Pyridinecarboxylic acid hydrazide; 4-(Hydrazinocarbonyl)pyridine

Isoniazid is often used together with Rifampicin (M3144) >.