Isonicid (Isoniazid)

Isoniazid is an antitubercular agent used in the treatment of Mycobacterium tuberculosis infection.

• Active tuberculosis: used as part of initial phase therapy to kill replicating bacilli and reduce disease burden.
• Latent tuberculosis infection: administered alone or with rifampin to prevent progression to active disease.
• Tuberculosis prophylaxis in high‑risk contacts: reduces the risk of developing active TB after exposure.
• TB prevention in HIV‑positive individuals: lowers the incidence of active tuberculosis in immunocompromised patients.

• Isoniazid inhibits the synthesis of mycolic acids, essential fatty acids that form a critical component of the mycobacterial cell wall. By blocking the enzyme InhA, it prevents the formation of the lipid-rich outer layer, leading to cell lysis and death of actively dividing Mycobacterium tuberculosis organisms.

Isoniazid may cause a range of adverse reactions, from mild to severe.

Common Side Effects

• Nausea: mild to moderate stomach upset.
• Loss of appetite: reduced desire to eat.
• Peripheral neuropathy: tingling or numbness in extremities.
• Rash: skin irritation or mild eruption.
• Elevated liver enzymes: mild, often asymptomatic.

Serious or Rare Side Effects

• Hepatotoxicity: significant liver injury, jaundice, or hepatitis.
• Severe allergic reactions (anaphylaxis): difficulty breathing, swelling, or hives.
• Sideroblastic anemia: impaired red blood cell production.
• Stevens‑Johnson syndrome: severe skin blistering.
• Drug‑induced lupus: joint pain and fever.

Before prescribing Isonicid, clinicians should consider several safety measures.

• Liver function monitoring: assess baseline and periodic LFTs due to risk of hepatotoxicity.
• Alcohol consumption: avoid or limit as it increases liver toxicity.
• Vitamin B6 supplementation: consider pyridoxine to prevent peripheral neuropathy.
• Pregnancy: use only if benefit outweighs risk; data are limited.
• Renal impairment: dose adjustment may be needed in severe renal dysfunction.
• Store at room temperature: keep in original container, protect from moisture and heat.

Isoniazid can interact with several medicines, requiring attention to avoid reduced efficacy or increased toxicity.

Major Interactions (Avoid)

• Rifampin: induces hepatic enzymes, lowering isoniazid plasma levels.
• Phenytoin: increases metabolism, reducing therapeutic effect.
• Alcohol: additive hepatotoxic risk.

Moderate Interactions (Monitor Closely)

• Acetaminophen: concurrent use may raise liver enzyme levels.
• Nevirapine: monitor liver function during combined therapy.
• Macrolide antibiotics (e.g., erythromycin): may increase isoniazid concentrations.