Isoniazid is one of several medicines that you will need to take to treat tuberculosis (TB).
It is important that you take the tablets regularly every day.
The ideal time to take the tablets is half an hour before breakfast.
|Type of medicine||An antituberculosis medicine|
|Used for||Tuberculosis (TB)|
|Also called||Rifinah® (isoniazid with rifampicin); Rifater® (isoniazid with rifampicin and pyrazinamide); Voractiv®, Rimstar® (isoniazid with rifampicin, pyrazinamide and ethambutol)|
Isoniazid is used to treat tuberculosis (TB). TB is a bacterial infection which mostly affects the lungs, but which can affect any part of your body. It is treatable with a course of medicines which usually lasts for six months in total. You will need to take several medicines to treat TB - isoniazid is just one of the medicines prescribed.
Isoniazid is usually prescribed as a tablet which contains a combination of two, three or four medicines to treat TB. The brand names of these are Rifinah®, Rifater®, Rimstar® and Voractiv®. You may be prescribed one or more of these brands at different times in your treatment. Taking combination medicines like these helps to reduce the total number of tablets you need to take each day.
Although isoniazid is a very effective medicine, it can sometimes cause damage to peripheral nerves (such as numbness and tingling sensations in the hands and feet). If you are considered to be at risk of this, your doctor will prescribe you a vitamin supplement of pyridoxine to prevent it.
Before taking isoniazid
Some medicines are not suitable for people with certain conditions, and sometimes a medicine may only be used if extra care is taken. For these reasons, before you start taking isoniazid it is important that your doctor knows:
- If you are pregnant, trying for a baby or breastfeeding. Although isoniazid is not known to be harmful in pregnancy, it is important that you tell your doctor, as you may need to be given a vitamin supplement.
- If you have any problems with the way your kidneys work, or the way your liver works.
- If you have epilepsy or diabetes.
- If you have ever had a mental health problem called psychosis.
- If you drink a lot of alcohol, or if you do not eat a sufficient amount.
- If you are HIV-positive.
- If you know you have slow acetylator status. This means that your body may process isoniazid more slowly, leading to an increased risk of side-effects.
- If you have a rare inherited blood condition called porphyria.
- If you are taking any other medicines. This includes any medicines you are taking which are available to buy without a prescription, as well as herbal and complementary medicines.
- If you have ever had an allergic reaction to a medicine.
How to take isoniazid
- Before you start treatment, read the manufacturer's printed information leaflet from inside the pack. It will give you more information about the brand of tablets you have been given and will provide you with a full list of the side-effects which you may experience.
- It is important that you take the medicines to treat TB exactly as your doctor tells you to. You will be asked to take isoniazid every day. Your doctor will explain to you how many tablets to take each day, and this information will be printed on the label of the pack of tablets to remind you. If when you collect your supply of tablets you are unclear about how to take them, ask your pharmacist to explain.
- The ideal time to take your tablets each day is half an hour before breakfast. If you forget, then take the tablets two hours after breakfast or wait until half an hour before your next meal. This is because isoniazid is absorbed better when your stomach is empty.
Getting the most from your treatment
- It is important that you keep your regular appointments with your doctor. This is so your doctor can check on your progress. Your doctor will want you to have blood tests from time to time during treatment to make sure that your liver stays healthy.
- Continue to take the tablets regularly unless your doctor tells you to stop. This is because it is important for you to complete the treatment course so that the infection does not come back. If for any reason you stop taking the tablets (such as if you think you may be developing side-effects - see also below) then you must let your doctor know about it straightaway so that you can be given alternative treatment.
- If you buy any medicines, check with a pharmacist first that they are suitable for you to take with isoniazid. Some antacid preparations can reduce the amount of the medicine that your body absorbs.
- Some foods may interact with isoniazid. Try to avoid eating foods containing histamine or tyramine. Examples include tuna fish, fermented or pickled products, strong cheeses, cured meats and red wine.
- You should try to avoid drinking alcohol whilst taking isoniazid, as the combination could harm your liver.
- Isoniazid may stop the oral typhoid vaccine from working. If you are having any vaccinations, make sure the person treating you knows that you are taking this medicine.
- If you are having an operation or any dental treatment, tell the person carrying out the treatment which medicines you are taking.
Can isoniazid cause problems?
Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains the most common ones associated with isoniazid. You will find a full list in the manufacturer's information leaflet supplied with your medicine. Unwanted effects often improve as your body adjusts to a new medicine, but speak with your doctor or pharmacist if any become troublesome.
|Common isoniazid side-effects||What can I do if I experience this?|
|Tingling feelings, muscle weakness||Let your doctor know as soon as possible|
|Dizziness||If affected do not drive and do not use tools or machines until you feel better|
|Feeling sick (nausea) or being sick (vomiting)||Stick to simple meals - avoid rich or spicy food. Drink plenty of liquid to replace any lost fluids|
|Dry mouth||Try chewing sugar-free gum or sucking sugar-free sweets|
|High temperature (fever), skin rash, hearing problems, mood changes, difficulty passing urine||If any of these become troublesome, speak with your doctor|
Important: isoniazid on rare occasions causes liver problems. The symptoms include persistent sickness (nausea and vomiting), feeling very weak and yellowing of the skin and whites of the eyes (jaundice). If this happens to you, speak with your doctor or go to your local accident and emergency department straightaway.
If you experience any other symptoms which you think may be due to this medicine, speak with your doctor or pharmacist for advice.
How to store isoniazid
- Keep all medicines out of the reach and sight of children.
- Store in a cool, dry place, away from direct heat and light.
Important information about all medicines
Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine go to the accident and emergency department of your local hospital. Take the container with you, even if it is empty.
This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.
Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.
If you have any questions about this medicine ask your pharmacist.
Further reading and references
Manufacturer's PIL, Isoniazid 50 mg and 100 mg Tablets; RPH Pharmaceuticals AB, The electronic Medicines Compendium. Dated January 2019.
Manufacturer's PIL, Rifater® Tablets; Sanofi, The electronic Medicines Compendium. Dated July 2019.
Manufacturer's PIL, Rifinah® 150/100 mg Tablets; Sanofi, The electronic Medicines Compendium. Dated July 2019.
British National Formulary, 79th Edition (Mar 2020); British Medical Association and Royal Pharmaceutical Society of Great Britain, London.