Isozid (Isoniazid)

Isoniazid is used in the treatment and prevention of tuberculosis, a bacterial infection caused by Mycobacterium tuberculosis.

• Pulmonary tuberculosis: eradicates Mycobacterium tuberculosis in the lungs, contributing to cure.
• Extrapulmonary tuberculosis: eliminates bacteria in sites such as lymph nodes, bones, or meninges as part of combination therapy.
• Latent tuberculosis infection: provides prophylactic therapy to prevent progression to active disease.

• Isoniazid is a prodrug that is activated by the mycobacterial KatG catalase‑peroxidase enzyme. Once activated, it inhibits the synthesis of mycolic acids, essential components of the mycobacterial cell wall, leading to disruption of cell wall integrity and bacterial death.

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

Common Side Effects

• Nausea: mild gastrointestinal upset occurring early in therapy.
• Vomiting: occasional emesis, usually transient.
• Peripheral neuropathy: tingling or numbness, often mitigated with pyridoxine.
• Elevated liver enzymes: mild, asymptomatic increases detectable on routine labs.

Serious or Rare Side Effects

• Hepatotoxicity: clinically significant liver injury, jaundice, or hepatitis.
• Severe hypersensitivity: rash, fever, and eosinophilia indicating possible allergic reaction.
• Stevens‑Johnson syndrome: rare but potentially life‑threatening skin eruption.

Before initiating therapy, clinicians should assess patient risk factors and monitor for adverse events.

• Liver function monitoring: obtain baseline and periodic liver enzyme tests, especially in patients with pre‑existing hepatic disease.
• Vitamin B6 supplementation: provide pyridoxine to reduce risk of peripheral neuropathy.
• Hypersensitivity assessment: discontinue if signs of severe allergic reaction appear.
• Renal impairment caution: adjust dosing in severe renal dysfunction as recommended by the prescriber.
• Pregnancy and lactation review: evaluate risk‑benefit ratio before use.
• Store at room temperature: keep in the original container, protect from moisture and light.

Isoniazid interacts with several drugs that may alter its efficacy or increase toxicity.

Major Interactions (Avoid)

• Rifampicin co‑administration: reduces isoniazid plasma concentrations, compromising effectiveness.
• Carbamazepine use: increases risk of hepatotoxicity when combined with isoniazid.
• Alcohol consumption: synergistic hepatic injury risk; avoid concurrent use.

Moderate Interactions (Monitor Closely)

• Phenytoin: may affect isoniazid metabolism; monitor liver function.
• Other hepatotoxic agents (e.g., pyrazinamide, methotrexate): require regular hepatic monitoring.
• Pyridoxine supplementation: may alter neuropathy risk; adjust dose as needed.