Medication Information Leaflet

What is this medication 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.

How should I take or use this medication?

• 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 medications 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 forget to take or use this medication?

• 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 precautions should I take when taking or using this medication?

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 are some common side effects of this medication?

• 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.

What are some rare but serious side-effects that I need to seek medical advice immediately?

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

What food or medication should I avoid when I take or use this medication?

• 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.

How should I store this medication?

Store in a cool and dry place, away from direct sunlight. Keep this medication away from children. 

How do I throw away this medication safely?

Pack the medication into a bag and bring it back to the pharmacy where you received the medication from.
 

Disclaimer

Please take note that the above is not a complete list of all possible side effects. If you have any concerns about your medication or if you have other side effects that you think are caused by this medication, please consult your doctor or pharmacist.

If you take more than the recommended dose, please seek medical advice immediately. The information provided on this page does not replace information from your healthcare professional. Please consult your healthcare professional for more information.

This article is jointly developed by members of the National Medication Information workgroup. The workgroup consists of cluster partners (National Healthcare Group, National University Health System and SingHealth), community pharmacies (Guardian, Unity and Watsons) and Pharmaceutical Society of Singapore. The content does not reflect drug availability and supply information in pharmacies and healthcare institutions. You are advised to check with the respective institutions for such information.

Last reviewed on August 2019