Isoniazid was introduced for the treatment of tuberculosis early in 1952. It is an extremely potent antituberculosis agent both in vitro and in vivo. It is bacteriostatic in vitro in concentrations as low as 0.05γ per cc. and inhibits BCG. in a concentration of 0.02.
Its toxicity in man is relatively low in dosage up to 5 mg/kg. of body weight. The toxic effects include constipation, difficulty in micturition, increased reflexes, and dizziness. Impairment of renal function may result in the retention of toxic concentrations in the body. Also, in epileptics caution is urged. Chronic toxicity results in anorexia, loss of weight, ataxia, tremors, convulsions, and jaundice. At postmortem examination, there is hepatic fatty degeneration and renal tubule degeneration.
After an oral dose of 3 mg. per kg., a plasma concentration of 1.3 to 3.4γ per cc. is reached. One-half to three-quarters of the ingested dose is excreted in the