<s>[INST] context: Isoniazid (lsonicotinic acid hydrazide, H) Isoniazid is the antitubercular drug parexcellence, and an essential component of all antitubercular regimens, unless the patient is not able to tolerate it or bacilli are resistant. lt is primarily tuberculocidal. Fast multiplying organisms are rapidly killed, but quiescent ones are only inhibited. It acts on extracellular as well as on intracellular TB (bacilli present within macrophages); is equally active in acidic and alkaline medium. It is one of the cheapest antitubercular drugs. However, most atypical mycobacteria are not inhibited by INH. The most plausible mechanism of action of INH is inhibition of synthesis of mycolic acids which are unique fatty acid component of mycobacterial cell wall. This may explain the high selectivity of INH for mycobacteria (it is not active against any other microorganism). The lipid content of mycobacteria exposed to INH is reduced. A gene labelled inh A which encodes for a fatty acid synthase enzyme is the target of INH action. Adverse effects INH is well tolerated by most patients. Peripheral neuritis and a variety of neurological manifestations (paresthesias, numbness, mental disturbances, rarely convulsions) are the most impoant dose-dependent toxic effects. These are due to interference with utilization of pyridoxine and its increased excretion in urine Pyridoxine given prophylactically (10 mg / day) prevents the neurotoxicity even with higher doses, but routine use is not mandatory. INH neurotoxicity is treated by pyridoxine lOO mg/day. Hepatitis, a major adverse effect of iNH, is rare in children, but more common in older people and in alcoholics. It is due to dose-related damage to liver cells and is reversible on stopping the drug. Other side effects are rashes, fever, acne and ahralgia. ESSENTIALS OF MEDICAL PHARMACOLOGY K.D.TRIPATHI SIXTH EDITION PAGE NO:740,741 [/INST] question: ATT most commonly implicated in causing peripheral neuropathy is: | options: A: Rifampicin B: Pyrazinamide C: INH D: Ethambutol | answer: C </s>