HomeSearch by AntimicrobialIsoniazid (INH, Laniazid, Nydrazid, Rifamate)
Antimicrobial Name: Isoniazid (INH, Laniazid, Nydrazid, Rifamate)
CAS Number: 54-85-3
Origin: Chemical/Synthetic
Functional Category: Antibiotic, Other
Molecular Weight: 137.139 g/mol
Mechanism of Action: Isoniazid (INH, Laniazid, Nydrazid, Rifamate) 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, including nitric oxide, 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 mycobacterium is slow-growing.
Chemical Formula:



Isoniazid (INH, Laniazid, Nydrazid, Rifamate), also known as isonicotinylhydrazine (INH), is an organic compound that is the first-line antituberculosis medication in prevention and treatment. It was first discovered in 1912, and later in 1951 it was found to be effective against tuberculosis. Isoniazid is never used on its own to treat active tuberculosis because resistance quickly develops. Isoniazid also has an antidepressant effect, and it was one of the first antidepressants discovered. Isoniazid can also be used in the treatment of a BCG-oma. The compound was first synthesised in the early 20th century,but its activity against tuberculosis was first reported in the early 1950s and three pharmaceutical companies attempted unsuccessfully to simultaneously patent the drug. With the introduction of isoniazid, a cure for tuberculosis was first considered reasonable. Isoniazid is available in tablet, syrup, and injectable forms (given intramuscularly or intravenously). Isoniazid is available worldwide, is inexpensive and is generally well tolerated. It is manufactured from isonicotinic acid, which is produced from 4-methylpyridine. Although isoniazid has actions that can be considered antidepressant (the so-called "psychic energizers"), it is important to point out that in contrast to closely related agents such as iproniazid which are MAOIs, isoniazid does not inhibit MAO. Keeping this in mind, it has been suggested that the MAO inhibiting action of MAOIs may be secondary to some other more fundamental explanation that can be used to rationalize their observed utility in the treatment of depression. This is particularly true in the case of hydrazides. However, this property remains undefined, although it does still seem pertinent to emphasize that isoniazid is not believed to inhibit MAO even though it does possess properties that are considered antidepressant.