Isoniazid for the treatment of tuberculosis

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Isoniazid for the treatment of tuberculosis

This leaflet is about the use of isoniazid for the treatment of tuberculosis (TB for short). Your child will have to take up to four medicines for at least 6 months to cure their TB.

A separate information leaflet about the use of isoniazid for the prevention of TB is available on www.medicinesforchildren.org.uk/isoniazid-latent-tuberculosis.

Information-Standard-logoThis leaflet has been written specifically about the use of this medicine in children. The information may differ from that provided by the manufacturer. Please read this leaflet carefully. Keep it somewhere safe so that you can read it again.

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

Name of drug


Why is it important for my child to take this medicine?

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. 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, milk or juice 30-60 minutes before food. Your child should not chew the tablets. The tablets can be crushed and mixed with a small amount of soft food such as yogurt, jam or mashed potato. Make sure your child swallows it straight away, without chewing.

Liquid medicine: Measure out the right amount using a medicine spoon or oral syringe. 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, you do not need to give them another dose. Wait until the next normal dose.

If your child is sick again, seek advice from your GP, your TB nurse, a 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 (111 in England and Scotland; 0845 4647 in Wales). 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 or is sick (vomits) for more than 24 hours, or their skin or eyes gets a yellow tinge, 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 doctor straight away, as there may be a problem with your child’s blood.

  • If your child seems to have or complains about problems with their sight (vision) or they have colour blindness or 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 taking sips of water may help.
  • If your child feels thirsty all the time and has go to the toilet often, contact your doctor, as they may have high blood sugar.
  • Your child may have swelling in the breast area, or breasts may increase in size. This can happen with boys or girls. If this happens, contact your doctor. These changes will reverse when the course of treatment is finished.

Can other medicines be given at the same time?

  • 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 many common medicines that you get on prescription. Tell your doctor about all medicines your child is taking before starting isoniazid.
  • Check with your doctor or pharmacist before giving any other medicines to your child. This includes herbal or 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 isoniazid?

  • Your doctor will take blood samples before your child starts taking isoniazid and regularly while they are taking it. This is to make sure it has not affected your child’s liver.

It is vital that you keep all your clinic appointments, as your doctor or nurse needs to monitor your child.

It is important that your child takes their TB medicines every day and does not stop taking them until instructed.

General advice about medicines

  • 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.

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

  • 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 medicine you have at home has not reached the ‘best before’ or ‘use by’ date on the packaging. Give old medicines to your pharmacist to dispose of.

Where I should keep this medicine?

  • Keep the medicines 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 other medicines used to treat TB.

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