Isoniazid

It is more effective against Myco. tuberculosis than both streptomycin and PAS. It is well absorbed from the alimentary tract and is distributed throughout the body water, penetrating easily into the cerebrospinal fluid. It should always be given in cases where there is special risk of meningitis. Isoniazid enters milk in about the same concentration as in the blood. It interferes with pyridoxine metabolism and induces pyridoxine deficiency.

Indications

Tuberculosis

Dosage

Adults: 300 mg daily in 1-3 doses. Children: 10-20 mg/kg body wt. in 1-3 doses.Max dose; 300-500mg daily.

Contra-Indications

Drug induced hepatic diseases.

Special Precautions

Chronic alcoholism,Epilepsy, Hepatitis. When Isoniazid is used alone drug resistance develops in all cases within 5 months, hence a combination with other anti-tubercular drugs is advised. Paediatrics: Reduced dose necessary. Pregnancy: Safety not established. Lactation: The drug passes into breast milk. Elderly: Increased likelihood of adverse effects.

Side Effects

Peripheral neuropathy and, more rarely, anaemia and pellagra. Mental disturbances convulsions, incoordination, encephalopathy, alcohol intolerance and a variety of allergic effects. Preventable with administrations of vit. B-6 (Pyridoxine) 50-100 mg orally/day.

Drug Interactions

Increases effect of phenytoin. Cause hyperpyrexia, tremor and death with alcohol. Servere hepatitis with rifampicin. Increases effect of carbamazepine. Prednisolone decreases INH level.Antagonises hypoglycaemic action of insulin.Efficacy increased by PAS