Isoniazid for treatment of 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


Why is it important for my child to take Isoniazid?

The bacteria that cause TB are hard to kill. Your child will have to take up to four medicines for at least 6 months in order to cure their TB. Isoniazid is one of these key medicines.

Your child may not necessarily have symptoms from the TB infection. Any symptoms should start to improve soon after starting treatment. You must continue to give the medicines until your doctor tells you to stop. If you stop too soon, or your child does not take the medicines as your doctor has told you to, the bacteria may not be killed and the TB may come back.
It is also possible that the bacteria will become ‘resistant’ to (no longer be killed by) the first drugs, which means that they will no longer work. This may mean that other stronger drugs will have to be used, or the TB will no longer be treatable

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 a day, alongside other TB medicines, 30-60 minutes before food. This is usually in the morning.

Give the medicine at about the same time 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.

Give 30-60 minutes before food.

When should the medicine start working?

Your child will start to feel better about 2 weeks after taking the TB medicines and they should have fewer symptoms. However, they must continue to take the medicines every day until the doctor says to stop treatment. This will usually be for at least 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?

If you forget to give your child a dose, give it as soon as possible on the same day.

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 gets a blotchy red rash anywhere on the body, blisters in the mouth, or a fever (temperature of 39°C or higher), contact your doctor straight away or take your child to hospital, as they may be allergic to isoniazid.

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

  • When your child first starts taking isoniazid, they may feel sick, be sick (vomit) or get constipation. They may also have difficulty passing urine (doing a wee), get tingling or numbness in the hands or feet and may feel dizzy. These effects should wear off after a few days. If they are still a problem after a week, contact your doctor.
  • Your child may have a dry mouth. Eating citrus fruits (e.g. oranges) and sipping water may help.

  • 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.

  • 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.

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.
  • There is a small risk that the oral contraceptive pill will 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.

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.

  • Isoniazid may also be used to prevent TB (also called chemoprophylaxis).

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 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 [2]. © NPPG, RCPCH and WellChild, all rights reserved. Review by January 2018.

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.