Isoniazid - High dose (Hh)

Update: November 2022

Forms and strengths

• 300 mg and 100 mg tablets
• 100 mg and 50 mg dispersible tablets, to be dispersed in 10 ml water

Dosage

• Child under 30 kg: 15 to 20 mg/kg once daily
• Child 30 kg and over and adult: 10 to 15 mg/kg once daily
• Maximum dose: 600 mg daily

Alternatively, 50 mg dispersible tablets may be used instead of ½ tablets of 100 mg.

Contra-indications, adverse effects, precautions

• Do not administer to patients with severe hepatic impairment.
• May cause:
  • peripheral neuropathy;
  • hepatotoxicity;
  • hypersensitivity reactions, arthragias, optic neuritis, psychotic reactions, seizures and depression.
• Monitor closely:
  • pregnant and breastfeeding women; patients with renal impairment, diabetes, malnutrition or HIV infection (increased risk of neuropathy);
  • patients with alcohol dependence (increased risk of neuropathy and hepatotoxicity);
  • patients with chronic hepatic disease or taking rifampicin or ≥ 35 years (increased risk of hepatotoxicity);
  • patients taking antiseizure medications, benzodiazepines (risk of toxicity), warfarin (risk of bleeding). Dose adjustment may be required.
• Avoid or monitor combination with cycloserine or terizidone and thionamides (increased risk of neurotoxicity).
• For the management of adverse effects, see Appendix 17.
• Administer concomitantly pyridoxine (vitamin B₆): child: 1 to 2 mg/kg (usual range: 10 to 50 mg) once daily; adult: 100 mg once daily.
• Pregnancy and breastfeeding: no contra-indication. Administer pyridoxine to the mother (as above). Observe the breast-fed neonate or infant for adverse effects and supplement it with pyridoxine (1 to 2 mg/kg once daily).

Monitoring

• Symptomatic monitoring.
• Liver function.

Patient instructions

• Take without food.
• Dispersible tablets should be dispersed in 10 ml water.
• Avoid alcohol during treatment.

Storage