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Drug Class: Commonly Known As: Category:
Antitubercular Adult, Children

Isoniazid - What is it for

Isoniazid is an antibiotic that is commonly used together with other medications for the treatment of tuberculosis (TB).

Tuberculosis is an infection caused by the bacterium Mycobacterium tuberculosis. You can get infected by breathing in droplets containing this bacterium that are sprayed into the air when an infected person coughs or sneezes.

There are two types of tuberculosis:

  1. Active TB
  • An infection with M. tuberculosis could present with symptoms. It is possible to spread the infection when you have active tuberculosis that is not treated.
  • Common signs and symptoms include coughing for more than three weeks, may be coughing up blood, fever, night sweats, loss of appetite, weight loss, pain in the chest.
  • Your doctor may do an X-ray of your chest to observe for any unusual signs in your lungs, or a phlegm test to check for the presence of the tuberculosis bacteria under the microscope.
  • Usually treated with a combination of the following four medications: Rifampicin, Isoniazid, Ethambutol and Pyrazinamide. These medications can work together to kill the tuberculosis bacteria.

      2.   Latent TB

  • An infection with tuberculosis bacteria but with NO symptoms.
  • If you have latent TB, you cannot spread it to another person.
  • Usually treated with either Isoniazid or Rifampicin.

You might have to take the medication for six to nine months. For active tuberculosis, the first two months usually consists of a combination of the four medications stated above, and the remaining four to seven months is completed using the two medications, Rifampicin and Isoniazid. Do not miss any dose of medication. This may lead to a relapse or worsening of tuberculosis, or a condition with a more resistant form of tuberculosis. In such cases, a longer duration of treatment or use of stronger medications may be needed.

Depending on your condition, you may need to attend Directly Observed Therapy (DOT) sessions to help you complete your course of treatment. DOT refers to a healthcare worker or trained volunteer supervising the patient taking each dose of tuberculosis medications. The number of DOT sessions can range from once a day to three times a week.

Isoniazid - Side Effects, Precautions, and Contraindications

What side effects can Isoniazid cause?

You may experience numbness or tingling sensations on your hands and feet.

  • Continue taking your medication and inform your doctor at your next visit. Your doctor may advise you to take Pyridoxine (Vitamin B6) to prevent or lessen this side effect.

If you experience any of these symptoms, you should stop your medication and seek immediate medical attention:

  • Drug allergy symptoms such as swollen face/eyes/lips/tongue, difficulty in breathing, itchy skin rashes over your whole body
  • Signs of liver issues such as dark coloured urine or light coloured stools, nausea and vomiting that does not go away, loss of appetite, stomach pain, yellowing of your eyes or skin
  • Fever, chills, feeling tired or weak (flu-like symptoms)
  • Unexplained bruising or bleeding

There are some tests that are required to better monitor and manage possible side effects from treatment of tuberculosis. These include:

  • Regular blood tests, especially to monitor your liver function

Before taking Isoniazid , what precautions must I follow?

​Before starting TB treatment, inform your healthcare professional if:

  • You are allergic to this medication or any of the other ingredients of this medication.
  • You have pre-existing medical conditions such as kidney and/or liver problems, gout.
  • You consume alcohol regularly.
  • You intend to become pregnant (conceive) or breastfeed while taking this medication.
  • You are pregnant or breastfeeding.
  • If you have active TB, you should stay at home for the first two weeks of your treatment. This is to prevent spreading the bacteria to others, as you are more likely to be able to infect others during this period. If you have close, regular contact with family members or friends, encourage them to visit a doctor to test for TB.
  • If you need to leave the house, wear a surgical mask in public spaces and avoid crowded places. Avoid close contact with anyone who may have low immunity (including elderly, young children, pregnant women).
  • After taking at least two weeks of effective treatment, you are generally considered non-infectious, meaning less likely to infect others, provided that you continue with the rest of the treatment.
  • If you have latent TB, seeing a doctor early and receiving treatment can help to prevent your loved ones from getting active TB in the future.

What food or medicine must I avoid when I take Isoniazid ?

  • ​Avoid alcohol as it may increase the risk of liver problems.
  • It is important that you inform your healthcare provider if you are taking other medications – including those for current medical conditions, chronic medications, oral contraceptives (birth control pills), over-the-counter medications, supplements and traditional/herbal remedies – as they may interact with TB medications.

Isoniazid - Dosage and How to Use

How should Isoniazid be used?

  • Do not stop taking your medication without checking with your healthcare professional.
  • This medication should be taken at least 30 minutes before food, on an empty stomach. However, if you are having stomach discomfort, you can take them after food instead.
  • Take your medication at the same time every day to maintain the same amount of medication in your body.
  • In children, the medication may be made into a mixture with water before taking.

What should I do if I miss a dose?

  • If you forget to take a dose, take it as soon as you remember. Then take your next dose at the usual time. Do not take two doses to make up for the missed dose.
  • It is important to complete the entire course of medication, even when you start feeling better during the treatment. This ensures that the tuberculosis bacteria in your body is fully killed.

What should I do if I overdose?

Isoniazid - Handling

How should I handle Isoniazid safely?

Isoniazid - Storage

How should I store Isoniazid ?

;#Keep away from children;#Keep in a cool, dry place, away from direct sunlight;#

How should I dispose of Isoniazid safely?

​Pack this medication into a black trash bag and seal it tightly before throwing into the rubbish chute or bin.

Isoniazid - Additional Information

  • Updated on 8/31/2019 12:00:00 AM
  • Article contributed by PSS National Medication Information Workgroup PSS National Medication Information Workgroup
The information provided is not intended as medical advice. Terms of use. Information provided by SingHealth


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