Isoniazid

How does it work?

Isoniazid is an antibiotic that is used to kill the bacteria that cause tuberculosis (TB). It's exact mechanism of action is unknown but it is thought to prevent the bacteria from making components called mycolic acids which are needed to form cell walls. It also seems to combine with an enzyme which interferes with the cell metabolism of the bacteria. As a result of the disruption in it's metabolism and without a cell wall the bacteria die. There are two stages in the treatment of tuberculosis. In the first two months after infection (the initial phase), treatment is aimed at killing as many bacteria as possible. Therefore several anti-TB drugs with different mechanisms of action are used in combination. After this time some of the medications are stopped and the others are continued for a further four months (continuation phase) to kill any remaining bacteria. Isoniazid is used in both stages of treatment. The bacteria that cause TB are difficult to treat. By using medications in combination, the bacteria can be targeted in different ways and hence treatment is more likely to be effective than a single medicine alone. In addition, using different medications make it less likely that bacteria will develop resistance to treatment.

What is it used for?

Treatment of tuberculosis in combination with other drugs

Warning!

Your liver functioning should be monitored while you are taking this medicine. Symptoms that may suggest a liver problem include persistent nausea and vomiting, abdominal pain, or the development of jaundice (a yellow colouring to the skin and the whites of the eyes). Consult your doctor if you experience any of these symptoms.

As isoniazid can cause peripheral neuropathy (peripheral neuritis) as a side effect, pyridoxine (Vitamin B6) is often prescribed to help prevent this.

Use with caution in

Alcoholism

Decreased kidney function

Decreased liver function

Epilepsy

History of psychotic illness

Slow liver metabolism (slow acetylator status)

Not to be used in

Life long inherited blood diseases which can cause a variety of symptoms, including mental health problems (porphyrias)

Liver disease caused by the medication

This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy. If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and Breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

This medicine should be used with caution during pregnancy, and only if the expected benefit to the mother is greater than any possible risk to the foetus. Seek medical advice from your doctor.

This medicine should be used with caution by breastfeeding mothers, and only if the expected benefit to the mother is greater than any possible risk to the baby. Seek medical advice from your doctor.

Label warnings

Do not stop taking this medication except on your doctor's advice.

Take this medication half to one hour before food.

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