Isoniazid

Isoniazid is indicated for the treatment of all forms of tuberculosis in which organisms are susceptible.

Isoniazid inhibits the synthesis of mycoloic acids in susceptible bacteria which results in loss of acid-fastness and disruption of bacterial cell wall. At therapeutic levels, it is bacteriocidal against actively growing intracellular and extracellular Mycobacterium tuberculosis organisms.

Adult: 

• Active tuberculosis: 5 mg/kg/day. Max: 300 mg/day or 15 mg/kg up to 900 mg/day, 2 or 3 times wkly.
• Latent tuberculosis: 300 mg/day for 6 mth. Nontuberculous mycobacterial infections 5 mg/kg/day for at least 12 mth of culture-negative sputum. Max: 300 mg/day.

Child: 10-15 mg/kg/day, max 300 mg/day q 12-24 hourly

With directly observed biweekly therapy, dosage is 20-30 mg/kg, max 900 mg/dose twice weekly

Inhibit the hepatic metabolism of antiepileptics (e.g. carbamazepine, ethosuximide, primidone, phenytoin), benzodiazepines (e.g. diazepam, triazolam), chlorzoxazone, theophylline, disulfiram, sometimes leading to increased toxicity. Increased metabolism of enflurane, resulting in potentially nephrotoxic levels of fluoride. Increased concentrations and enhanced effects or toxicity of clofazimine, cycloserine and warfarin. Reduced absorption with Al-containing antacids. Increased risk of peripheral neuropathy with zalcitabine and stavudine.

Acute liver disease or history of hepatic damage during INH therapy; hypersensitivity.

Peripheral neuropathy (dose-related incidence, 10-20% incidence with 10 mg/kg/d), Loss of appetite, Nausea, Vomiting, Stomach pain, Weakness 1-10%, Dizziness, Slurred speech, Lethargy, Progressive liver damage (increases with age; 2.3% in pts > 50 yo), Hyperreflexia, Agranulocytosis, Anemia, Megaloblastic anemia, Thrombocytopenia, Systemic lupus erythematosus, Seizure

Pregnancy Category C. Animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks

Lactation: distributed into milk but safe for nursing infants

Renal or hepatic impairment; convulsive disorders; history of psychosis; patients at risk of neuropathy or pyridoxine deficiency eg, diabetic, alcoholic, malnourished, uraemic, infected with HIV. Careful monitoring of hepatic function is necessary for black and hispanic women. Check hepatic function before and during treatment. Pregnancy and lactation.

Anti-Tubercular Chemotherapeutics