Drugs Used In Tuberculosis - Isoniazid

• First line anti tubercular agent
• Highly effective and most widely used
• Orally effective and cheapest
• Effective in both acidic as well as alkaline environment
• Effective against both intracellular and extracellular bacilli
• Has tuberculocidal action

• Inhibits the biosynthesis of Mycolic acid which is an essential component of the mycobacterial cell wall.

• Orally administered and well absorbed from the gastrointestinal tract
• Widely distributed across all the body cavities,tissues and fluids.
• Attains high concentrations in the CSF.
• Metabolised by acetylation in the liver and excreted in urine.
• Rate of acetylation is under genetic control i.e Slow acetylators and rapid acetylators.

• Peripheral Neuritis
• More common among the slow acetylators.
• Due to structural similarities with Pyridoxine (Vitamin B6), Isoniazid, competetively interferes with its utilization and increases its excretion.
• Pyridoxine 10mg is added routinely for prophylaxis
• To treat peripheral neuritis induced by Isoniazid toxicity, Pyridoxine, 100mg per day is advised.
• Hepatitis
• More common in rapid acetylators.
• Hydrazine is a metabolite of Isoniazid produced in the liver which is implicated in hepatotoxicity.
• More common among the elderly and chronic alcoholics.
• Reversible on stopping therapy.
• Gastointestinal disturbance, skin rashes,drug fever, arthralgia, psychosis and rarely convulsions may also occur.

Category: Pharmacology Notes