Isoniazid Macleods Pharma Uk (Isoniazid)

Isoniazid is an antitubercular drug that targets Mycobacterium tuberculosis in both active disease and latent infection.

• Active tuberculosis: helps eradicate the bacterial load and achieve cure when combined with standard multidrug therapy.
• Latent tuberculosis infection prophylaxis: reduces the risk of progression to active disease in individuals with a positive tuberculin test or recent exposure.
• Post‑exposure prophylaxis: provides preventive treatment for close contacts of confirmed TB cases.

• After oral absorption, isoniazid is activated by the mycobacterial enzyme catalase‑peroxidase (KatG). The activated form inhibits the synthesis of mycolic acids, essential components of the mycobacterial cell wall, leading to cell wall disruption and bacterial death.

Isoniazid may cause a range of adverse reactions, from mild to severe. Monitoring and patient education are essential.

Common Side Effects

• Nausea: mild to moderate stomach upset.
• Vomiting: occasional episodes, especially early in therapy.
• Loss of appetite: reduced desire to eat.
• Peripheral neuropathy (mild): tingling or numbness, often preventable with pyridoxine.
• Rash: mild skin irritation or erythema.
• Elevated liver enzymes: asymptomatic laboratory finding.

Serious or Rare Side Effects

• Hepatotoxicity: clinically significant liver injury, jaundice, or hepatitis.
• Severe peripheral neuropathy: persistent numbness or weakness requiring medical attention.
• SIADH (syndrome of inappropriate antidiuretic hormone secretion): hyponatremia with neurological symptoms.
• Anaphylaxis: acute allergic reaction with airway compromise.
• Stevens‑Johnson syndrome: severe skin and mucous membrane involvement.
• Hemolytic anemia (in G6PD deficiency): rapid drop in red blood cells.

Isoniazid requires careful assessment of patient risk factors and regular monitoring.

• Pregnancy: Category B; use under medical supervision after weighing benefits and risks.
• Liver disease: monitor hepatic function tests before and during therapy.
• Alcohol consumption: avoid excessive intake to reduce hepatotoxic risk.
• Peripheral neuropathy: supplement with pyridoxine (vitamin B6) to prevent nerve damage.
• Drug resistance: ensure susceptibility testing before initiating monotherapy.
• Storage: Store below 25°C: keep in the original container, protect from moisture and direct sunlight.

Isoniazid interacts with several medicines that can alter its efficacy or increase toxicity.

Major Interactions (Avoid)

• Rifampicin: antagonistic effect that reduces isoniazid efficacy.
• Pyrazinamide: combined use heightens risk of hepatotoxicity.
• Alcohol: synergistic liver injury potential.
• Carbamazepine: induces metabolism, lowering isoniazid levels.
• Methotrexate: may increase methotrexate toxicity.

Moderate Interactions (Monitor Closely)

• Phenytoin: may increase isoniazid clearance, requiring dose review.
• Warfarin: can alter INR, necessitating closer anticoagulation monitoring.
• Clozapine: increased plasma concentrations, watch for sedation.
• Zidovudine: potential for enhanced neurotoxicity, monitor neurologic status.