Isoniazid for latent tuberculosis

This leaflet is for parents and carers about how to use this medicine in children. Our information may differ from that provided by the manufacturers, because their information usually relates to adults. Read this leaflet carefully. Keep it somewhere safe so that you can read it again.

It is essential that your child takes all their medicines daily, as explained by the doctor, and continues until the doctor tells you to stop.

Name of medicine

Isoniazid (EYE-soe-NYE-a-zid)

Why is it important for my child to take Isoniazid?

Your child is likely to be infected with the bacteria that can cause TB, but at the moment this is not making them ill (i.e. it is latent or hidden or dormant). It is important that your child takes isoniazid to stop them becoming ill from the active form of TB (TB disease). The bacteria that cause TB are hard to kill, and infected children are more likely to develop TB disease than infected adults, and are also more likely to become seriously unwell. Your child will have to take isoniazid for at least 3-6 months.

If your child has a problem with their liver, it is important to talk about this with your doctor before they prescribe the medicine.

You must continue to give the medicine until your doctor tells you to stop. If you stop too soon, or your child does not take the medicine as your doctor has told you to, the bacteria may not be killed and TB disease may develop. It is also possible that the bacteria will become resistant to Isoniazid, which means that they will no longer work. This may mean that other stronger drugs will have to be used, or that if TB disease does develop, it will be much harder to treat.

What is Isoniazid available as?

Tablets: 50 mg, 100 mg; these contain lactose

Liquid medicine can be ordered specially from your pharmacist

When should I give Isoniazid

Isoniazid is usually given once each day. This is usually in the morning.

Give the medicine at about the same time(s) each day so that this becomes part of your child’s daily routine, which will help you to remember.

How much should I give?

Your doctor will work out the amount of Isoniazid (the dose) that is right for your child. The dose will be shown on the medicine label.

It is important that you follow your doctor’s instructions about how much to give.

How should I give Isoniazid?


  • Tablets should be swallowed with a glass of water, squash or juice. Your child should not chew the tablets.
  • You can crush the tablet and mix it with a small amount of soft food such as yogurt, honey, or mashed potato. Make sure your child swallows it straight away, without chewing.

Liquid medicine

  • Shake the medicine well. Measure out the right amount using an oral syringe or a medicine spoon. You can get these from your pharmacist. Do not use a kitchen teaspoon as it will not give the right amount.

You need to give Isoniazid to your child when their stomach is empty. Give it 30 minutes before a meal or 2 hours after a meal.

When should the medicine start working?

The medicine will start working straight away, although you will not see any difference in your child because isoniazid is being given to prevent them becoming seriously unwell with TB disease. However, they must continue to take the medicine every day until the doctor tells you to stop treatment. This will be for at least 3-6 months

What if my child is sick (vomits)?

  • If your child is sick less than 30 minutes after having a dose of Isoniazid, give them the same dose again.
  • If your child is sick more than 30 minutes after having a dose of Isoniazid, do not give them another dose. Wait until the next normal dose.

If your child is sick again, seek advice from your family doctor, nurse, pharmacist, or hospital. They will decide what to do based on your child’s condition and the specific medicine involved.

What if I forget to give it?

Give the missed dose when you remember during the day, as long as this is at least 12 hours before the next dose of Isoniazid is due.

Never give a double dose of Isoniazid.

What if I give too much?

If you think you may have given your child too much Isoniazid, contact your doctor or local NHS services (details at end of leaflet). Have the medicine or packaging with you if you telephone for advice.

Are there any possible side effects?

We use medicines to make our children better, but sometimes they have other effects that we don’t want (side effects).

Side effects you must do something about

If your child develops a rash, swelling of the face, lips, tongue or throat, or has difficulty breathing or swallowing, they may be allergic to Isoniazid. Contact your doctor or take your child to hospital straight away.

If your child feels sick (nausea) or is sick (vomits) for more than 24 hours, or gets a yellowish tinge to the skin or whites of the eyes, contact your doctor straight away, as there may be a problem with your child’s liver. Do not give any more Isoniazid.

If your child seems to be getting more infections than usual (e.g. bad colds, chest or skin infections, stomach upsets), or they seem to bruise more easily or bleeding doesn’t stop as quickly as you would expect, contact your a doctor straight away, as there may be a problem with your child’s blood.

If your child has problems with their sight (vision), has difficulty telling colours apart or develops eye pain, contact your doctor straight away.

Other side-effects you need to know about

Your child may get the following symptoms when they first start taking isoniazid.

  • they may feel sick (nausea) or be sick (vomit). Giving the medicine with some food or milk may help. They may also get constipation (difficulty doing a poo) or have difficulty passing urine (doing a wee).
  • they may get tingling or numbness in the hands or feet and may feel dizzy or light-headed. Encourage them to stand up slowly and to sit or lie down if they feel dizzy or light-headed.
  • they may have a dry mouth. Eating citrus fruits (e.g. oranges) and taking sips of water may help.

These symptoms should wear off as your child’s body gets used to the medicine. If they are still a problem after a week or so, contact your doctor or TB nurse for advice:

  • Your child may have swelling in the breast area, or their breasts may increase in size. If this happens, contact your doctor. These changes will reverse when they stop taking the medicine.

  • If your child feels thirsty all the time and needs to pass urine (wee) very often, contact your doctor, as they may have high blood sugar.

There may sometimes be other side effects that are not listed above. If you notice anything unusual and are concerned, contact your doctor. You can report any suspected side effects to a UK safety scheme at

Can other medicines be given at the same time as Isoniazid?

  • You can give your child medicines that contain paracetamol or ibuprofen, unless your doctor has told you not to.
  • Isoniazid should not be taken with some medicines. Tell your doctor or pharmacist about any other medicines your child is taking before giving Isoniazid.
  • Check with your doctor or pharmacist before giving any other medicines to your child. This includes herbal and complementary medicines.

Is there anything else I need to know about this medicine?

Keep all your clinic appointments, as your doctor or TB nurse needs to check how your child is doing.

It is important that your child has their TB medicines every day.

The oral contraceptive pill does not work properly during treatment with Isoniazid, so your daughter should use other forms of contraception if she is sexually active, and for 4-8 weeks after finishing the course.

Your doctor or TB nurse will take blood samples before your child starts Isoniazid and regularly while they are taking it. This is to make sure that their liver is working properly, and that Isoniazid has not affected it.

General advice about medicines

  • Try to give medicines at about the same times each day, to help you remember.
  • Only give this medicine to your child. Never give it to anyone else, even if their condition appears to be the same, as this could do harm.
  • Make sure that you always have enough medicine. Order a new prescription at least 2 weeks before you will run out.
  • Make sure that the medicines you have at home have not reached the ‘best before’ or ‘use by’ date on the packaging. Give old medicines to your pharmacist to dispose of.
  • If you are not sure a medicine is working, contact your doctor but continue to give the medicine as usual in the meantime. Do not give extra doses, as you may do harm.

If you think someone else may have taken the medicine by accident, contact your doctor straight away.

Where should I keep this medicine?

  • Keep the medicine in a cupboard, away from heat and direct sunlight.
  • It does not need to be kept in the fridge.
  • Make sure that children cannot see or reach the medicine.
  • Keep the medicine in the container it came in.

Who to contact for more information?

Your child’s doctor, pharmacist or nurse will be able to give you more information about Isoniazid and about other medicines used to treat TB.

England: NHS 111

Tel 111

Scotland: NHS 24

Northern Ireland: NI Direct

Wales: NHS Direct

Tel 111 (free) or 0845 46 47 (2p per minute)

British Lung Foundation

Copyright disclaimer

Version [1]. © NPPG, RCPCH and WellChild, all rights reserved. Review by November 2016.

The primary source for the information in this leaflet is the British National Formulary for Children. For details on any other sources used for this leaflet, please contact us through our website,

We take great care to make sure that the information in this leaflet is correct and up-to-date. However, medicines can be used in different ways for different patients. It is important that you ask the advice of your doctor or pharmacist if you are not sure about something. This leaflet is about the use of these medicines in the UK, and may not apply to other countries. The Royal College of Paediatrics and Child Health (RCPCH), the Neonatal and Paediatric Pharmacists Group (NPPG), WellChild and the contributors and editors cannot be held responsible for the accuracy of information, omissions of information, or any actions that may be taken as a consequence of reading this leaflet.