Indications
Isoniazid is used to treat tuberculosis (TB) of the lungs and other parts of the body, always together with other TB medicines for active disease. It is also used on its own to prevent TB in people who have latent (sleeping) TB infection or who are at high risk after close contact with someone with TB.
How It Works
Isoniazid stops TB bacteria from building their cell wall, which kills actively growing bacteria. Using it with other TB medicines prevents the bacteria from becoming resistant.
Dosage and Administration
Adults: usually 5 mg per kg of body weight once a day, commonly 300 mg a day, as part of the treatment plan set by the doctor or TB programme. Children: by body weight, as prescribed.
- Take on an empty stomach, at least 30 minutes before or 2 hours after food, at the same time each day.
- Pyridoxine (vitamin B6) is usually given with it to prevent nerve problems.
- Complete the full course, often 6 months or longer for active TB, even when you feel better. Stopping early can make TB come back and become resistant.
Interactions
Isoniazid can raise the levels of Phenytoin, Carbamazepine and some other medicines, so doses may need adjusting. Taking it with Rifampicin, Paracetamol in high doses or alcohol increases the risk of liver damage. Antacids containing aluminium reduce its absorption; take them at least 1 hour apart. Foods rich in tyramine or histamine, such as aged cheese and some fish like tuna, can cause flushing, headache, fast heartbeat and sweating.
Contraindications
- Allergy to Isoniazid.
- Active or acute liver disease.
- Previous liver damage or severe reaction caused by Isoniazid.
Side Effects
Common: nausea, loss of appetite, stomach upset, tingling or numbness in the hands and feet, and mild rise in liver enzymes. Less common: rash, fever, joint pain, dizziness.
Get urgent medical help if you have yellowing of the skin or eyes, dark urine, pain in the upper abdomen, vomiting that does not stop or unusual tiredness (signs of liver damage); a severe skin rash with blisters or peeling; fits; confusion; or blurred vision.
Pregnancy and Lactation
Isoniazid is considered safe in pregnancy and is used to treat TB in pregnant women, together with Pyridoxine. It can be taken while breastfeeding; the baby may also need Pyridoxine, so follow the doctor’s advice.
Precautions and Warnings
Your doctor may check liver blood tests, especially if you are older, drink alcohol, have hepatitis or HIV, or are pregnant or recently delivered. Avoid alcohol during treatment. People with diabetes, kidney disease, malnutrition, alcohol problems or HIV are at higher risk of nerve problems. Tell your doctor if you have epilepsy or a mental health condition.
Overdose
Isoniazid overdose is very dangerous and can cause vomiting, slurred speech, fits, coma and serious acid build-up in the blood within a few hours. Go to hospital immediately, even if the person seems well.
Therapeutic Class
Antituberculosis medicine.
Storage
Store below 30°C in a dry place, away from light and out of the reach of children.
Prepared by the Oshud Alo team from standard drug references. For information only; always follow your doctor's advice.