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Home > Medicines & Drugs > Isoniazid

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Isoniazid


  • Take isoniazid 30 to 60 minutes before food.
  • Your treatment with isoniazid will usually last for up to six months, and will be part of a treatment regimen which will include other medicines.
  • Do not stop taking isoniazid unless your doctor tells you to stop.

About isoniazid

Type of medicineAntituberculosis drug
Used forUsed alongside other drugs to treat and prevent tuberculosis (TB)
Also calledRifinah® (isoniazid in combination with rifampicin)
Rifater® (isoniazid in combination with rifampicin and pyrazinamide)
Available asTablet
Injection

Tuberculosis (TB) is a bacterial infection mostly found in the lungs but which can affect any part of the body. TB is treatable with a course of medicines which usually last 6 months. Several medicines are given together to treat TB - isoniazid is one of the medicines which are used. Isoniazid works by stopping the bacteria that cause tuberculosis from growing and multiplying.

Before taking isoniazid

Before taking isoniazid make sure your doctor or pharmacist knows:

  • If you are pregnant, trying for a baby or breast-feeding.
  • If you have liver or kidney problems.
  • If you have or have previously had psychosis (a mental health problem).
  • If you know you have slow acetylator status, which means your body may process isoniazid more slowly, leading to an increased risk of side-effects.
  • If you have epilepsy or diabetes.
  • If you are alcohol dependent (drink excessively).
  • If you are malnourished (eat an insufficient diet).
  • If you are HIV positive.
  • If you have porphyria (a blood disorder).
  • If you are taking other medicines, including those available to buy without a prescription, herbal or complementary medicines.
  • If you have ever had an allergic reaction to this or any other medicine.

How to take isoniazid

  • Before beginning treatment, read the manufacturer's printed information leaflet.
  • Your doctor will want to check your liver and kidney function before you start taking isoniazid, and during your treatment.
  • It is important that you take all of the medicines you have been given to treat tuberculosis exactly as you have been directed by your doctor.
  • Try to take isoniazid at the same time each day to avoid missing any doses.
  • Take isoniazid 30 to 60 minutes before food.
  • If you forget to take a dose, take it as soon as you remember. If you do not remember until the following day, skip the missed dose. Do not take two doses together to make up for a forgotten dose.

Getting the most from your treatment

  • Your treatment with isoniazid will usually last for up to six months, and will be part of a treatment regimen which will include other medicines.
  • Do not stop taking isoniazid unless your doctor tells you to stop.
  • Keep your regular doctor's appointment so your progress can be monitored.
  • If you are having an operation or any dental treatment, tell the person carrying out the treatment which medicines you are taking.
  • If you buy any medicines, check with a pharmacist that they are safe to take with your other medicines.

Can isoniazid cause problems?

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. These usually improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following side-effects continue or become troublesome.

Possible side-effectsWhat can I do if I experience this
Feeling or being sickEat little and often. Stick to simple or bland foods – avoid very rich or spicy food.
If the sickness is severe, contact your doctor, or go to the accident and emergency department of your local hospital at once
ConstipationTry to eat a well balanced diet containing plenty of fibre, and drink 6-8 glasses of water each day
Dry mouthTry chewing sugar-free gum or sugar-free sweets

Important: If you experience jaundice (yellowing of the skin and whites of the eyes), malaise, (generally feeling unwell), severe nausea or vomiting, or a rash, speak with your doctor immediately or go to your local accident and emergency department without delay.

Isoniazid may rarely cause other side-effects. If you experience any other symptoms which you think may be due to this medicine, speak with your doctor or pharmacist.

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 has taken an overdose of this medicine, go to the accident and emergency department of your local hospital at once. 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.
  • Never 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.

References

  • British National Formulary; 61st Edition (March 2011) British Medical Association and Royal Pharmaceutical Society of Great Britain, London (link to current BNF)
Comprehensive patient resources are available at www.patient.co.uk
© EMIS 2011DocID: 3330DocRef: dils2297Last Reviewed: 3 Jun 2011Version: 22
For the planned review period see the Data Creation and Quality Control Process.
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