Isoniazid

Isoniazid is a first-line antituberculous medication used in the prevention and treatment of tuberculosis. It is often prescribed under the name INH. The chemical name is isonicotinyl hydrazine or isonicotinic acid hydrazide.

It is available in tablet, syrup, and injectable forms (given via intramuscular injection), available world-wide, inexpensive to produce, and is generally well tolerated.

Mechanism of action

Isoniazid inhibits the mycolic acid cell wall synthesis via oxygen-dependant pathways, such as the catalase-peroxidase reaction. It reaches therapeutic concentrations is serum, cerebrospinal fluid (CSF), and within caseous granulomas.

Isoniazid is metabolized in the liver via acetylation and hydrolysis. Metabolites are excreted in the urine. Doses do not usually have to be adjusted in case of renal failure.

Isoniazid is bactericidal to mycobacteria that are sensitive to it, and is bacteriostatic if the mycobacterium is resistant.

Side effects

The most common side effect of isoniazid is peripheral neuropathy, which is due to vitamin B6 depletion. The incidence of peripheral neuropathy can be decreased by co-administration of vitamin B6.