ISONIAZID = H oral

Last updated: June 2021

Therapeutic action

• First line antituberculosis antibacterial (bactericidal activity)

Indications

• Tuberculosis, in combination with other antituberculosis antibacterials
• Latent tuberculosis, as monotherapy or in combination with rifampicin or rifapentine

Forms and strengths

• 100 mg and 300 mg tablets
• 50 mg and 100 mg dispersible tablets

Dosage

Tuberculosis, latent tuberculosis as monotherapy or in combination with daily rifampicin

• Child under 30 kg: 10 mg/kg (7 to 15 mg/kg) once daily, on an empty stomach
• Child 30 kg and over and adult: 5 mg/kg (4 to 6 mg/kg) once daily, on an empty stomach

Do not exceed 300 mg daily.

Latent tuberculosis in combination with weekly rifapentine

• Child under 30 kg and over 2 years: 20 to 30 mg/kg once weekly, on an empty stomach
• Child 30 kg and over and adult: 900 mg once weekly, on an empty stomach

Latent tuberculosis in combination with daily rifapentine

• Child 13 years and over and adult: 300 mg once daily, on an empty stomach

Duration

• Tuberculosis and latent tuberculosis as monotherapy: according to protocol
• Latent tuberculosis in combination with daily rifampicin or weekly rifapentine: 3 months
• Latent tuberculosis in combination with daily rifapentine: 1 month

Contra-indications, adverse effects, precautions

• Do not administer to patients with severe hepatic impairment.
• May cause:
  • peripheral neuropathy, especially in malnourished, alcoholic, diabetic, HIV-infected patients; pregnant and breast-feeding women and patients with renal impairment;
  • hepatotoxicity, especially in alcoholic patients or patients with chronic hepatic disease or receiving rifampicin, or over 35 years;
  • hypersensitivity reactions, psychotic reactions, seizures and depression.
• Monitor liver function in patients with known hepatic disease.
• If signs of hepatotoxicity (e.g. jaundice) develop, isoniazid should be discontinued until symptoms resolve.
• Administer with caution and closely monitor patients taking phenytoin, carbamazepine, benzodiazepines (risk of toxicity), warfarin (risk of bleeding).
• Administer pyridoxine (vitamin B₆) in patients at risk of peripheral neuropathy (child: 5 to 10 mg once daily; adult: 10 mg once daily).
• Pregnancy: no contra-indication. Administer pyridoxine to the mother (10 mg once daily).
• Breast-feeding: no contra-indication;. Administer pyridoxine to the mother (10 mg once daily) and the infant (5 mg once daily).

Remarks

• For patients sensitive to first-line antituberculosis treatment, isoniazid is given as part of a fixed dose combination.
• Also comes in fixed dose combination containing 300 mg of rifapentine/300 mg of isoniazid for the treatment of latent tuberculosis in children over 14 years and adults.

Storage