Drug Characteristics
  • Formulation

    Tablets: 100 mg

    Injection: 25mg/ml

    Liquid 50mg/5ml unlicensed in UK, available from special order manufacturers

  • Dose

    DMAC: 300 mg orally once a day, as part of a combination regimen


    15mg/kg (max 900 mg) orally twice or three times a week for D.O.T regimens

  • Side Effects

    Peripheral neuropathy; increased LFTs and hepatic necrosis; hypersensitivity reactions; rash; nausea; anaemia and thrombocytopenia

  • Interactions

    Antacids reduce absorption; increased CNS toxicity with cycloserine; enhanced phenytoin and carbamazepine effect; additive hepatic toxicity with carbamazepine; metabolism of ketoconazole increased

    Additive toxicity with other drugs causing peripheral neuropathy e.g. stavudine, dapsone

  • Renal

    GFR (ml/min)

    20–50 Dose as in normal renal function

    10–20 Dose as in normal renal function

    <10 100–200 mg daily suggested

    Alternative dosing from Renal Handbook

    <10 200-300mg

    Patients with GFR < 10 ml/minute and slow acetylator status might require a dose reduction of about 100mg to maintain trough plasma levels at less than 1 mcg/ml

  • Hepatic

    Isoniazid should be used in caution in patients with pre-existing hepatic dysfunction.

    Monitor LFTs

    No dosage recommendations in hepatic dysfunction

  • Pregnancy

    Compatible – Maternal Benefit >> Embryo-Foetal Risk

  • Other Information