Isoniazid
Prescription neededTB medicines
Comes as:Tablet
Usual adult dose
Dose is set by your doctor as part of TB treatment, usually 5 mg per kg (about 300 mg for adults) once a day on an empty stomach. Vitamin B6 (pyridoxine) is often given with it. Never stop TB treatment early.
Your doctor may give you a different dose. Children's doses depend on weight.
Side effects
Common
- nausea
- tingling or numbness of hands and feet (prevented by vitamin B6)
Serious — get help
Stop taking it and see a doctor straight away if you notice:
- yellow eyes or skin
- dark urine
- severe stomach pain or vomiting (liver damage)
- seizures
- severe skin rash
Do not take it, or take care, if
- Active liver disease
- Previous liver damage from isoniazid
- Heavy alcohol use (use with caution)
- Epilepsy (use with caution)
Interactions
Medicines that can react with this one.
Serious2 medicinesDo not take these together unless your doctor says so.
- Carbamazepine
Raises carbamazepine levels, and the combination raises the risk of liver damage.
- Phenytoin
Isoniazid raises phenytoin levels and can cause toxicity; levels should be checked.
Minor2 medicinesUsually not a problem, but tell your doctor.
- Aluminium hydroxide + Magnesium hydroxide
Antacids reduce absorption; take isoniazid at least 1 hour before them.
- Pyridoxine
Pyridoxine is usually given with isoniazid on purpose to prevent nerve damage; this is a helpful combination.