Isoniazid is an antibiotic. It is used together with other medicines to treat an infection in the lungs or other parts of the body known as tuberculosis (TB).
This medicine may also be given on its own or together with other medicines as a preventive therapy of TB in high-risk individuals.
Take Isoniazid exactly as directed by your doctor or according to the instructions on the label. Do not take more or less than instructed by your doctor.
Take this medicine on an empty stomach, at least 30 minutes before or 2 hours after a meal. Try to take it at the same time each day.
Isoniazid is available as a tablet or as an oral solution.
Swallow the tablets whole with a glass of water.
If you are taking an oral solution, shake the bottle well before you take it to ensure that the liquid is evenly mixed. Use the measuring spoon or cup provided to measure your dose.
The dose of this medicine will be decided by your doctor. Your doctor will advise you on the treatment timeframe depending on the type and severity of your infection.
Take Isoniazid at regular intervals. Do not skip any doses. You must complete the entire course of this medicine. If you don't, the infection will not be properly controlled.
Take the missed dose as soon as you remember. If it is almost time for your next dose, skip the missed dose and return to your normal dosing schedule.
DO NOT double a dose under any circumstances.
If you often forget to take your medicine, let your doctor and pharmacist know.
Do not take Isoniazid if you ever had an allergic reaction (e.g. rashes, breathlessness, swollen eyes) to this medicine.
Alert your doctor if you have the following conditions:
- history of liver disease or side effects due to isoniazid
- serious liver disease
as Isoniazid may not be suitable for you.
Inform your doctor if you have the following conditions:
- diabetes
- HIV infection
- epilepsy (fits or seizures)
- mental illness
- poor nutritional status e.g. malnourished
- porphyria (an inherited disorder that causes skin or nervous system abnormalities)
- neuropathy (nerve damage that causes tingling, numbness, and pain)
- long-term liver disease
- severe kidney disease
Let your doctor know if you are pregnant or breastfeeding.
Be sure to check with your doctor or pharmacist before giving Isoniazid to a child. Children may be more sensitive to the side effects.
Notify your doctor if you consume large amounts of alcohol or if you are a frequent drinker.
If you are going to have certain laboratory tests (e.g. urine tests), inform your doctor that you are taking this medicine.
Individuals who are known as slow acetylators or inactivators of Isoniazid may experience enhanced side effects. If you know you have this gene type, inform your doctor.
Why is it important to keep my appointments with the doctor?
Keep your appointments with your doctor. Your doctor needs to monitor your condition and check your response to the medication regularly.
- Routine tests (e.g. liver and kidney function, sputum culture, eye examination) may be done before and during your treatment with this medicine. Your doctor will advise you about how often you need to have these tests.
- Regular monitoring for signs and symptoms of liver problems may also be needed.
What must I do to prevent spreading TB to other people?
TB is spread through the air, especially when you cough, sneeze or laugh. Always cover your mouth when you cough, sneeze or laugh. If you use tissue paper, seal it in a plastic bag before you throw it away. If you need to be around people for a long time, be sure to wear a mask that covers your mouth and nose to minimise the risk of passing the disease to other people.
You may still be able to infect others while undergoing treatment for TB. Your doctor may tell you to stay at home to avoid passing the disease to other people. You may need to sleep in a bedroom separate from your family members.
Be sure to finish the course of medication according to your doctor's instructions.
Isoniazid may cause any of the following side effects: dizziness with sensations of spinning, constipation, nausea, vomiting, dry mouth, and difficulty when urinating.
Some side effects may need immediate medical help. Alert your doctor quickly if you experience any of the following:
- rashes, breathlessness, swelling of the face, eyes or mouth
- yellowing of the skin or eyes, abdominal pain, dark coloured urine, swelling in the legs and ankles
- tingling, numbness, and pain of the hands or feet
- blurring or loss of vision, eye pain
- unusual bleeding or bruising
- frequent and persistent sore throat with fever
- unusual tiredness or weakness
- fits or seizures
- hallucination (seeing, hearing or feeling things that are not existent)
Inform your doctor if any of these side effects do not go away or are severe, or if you experience other side effects.
Inform your doctor if you are taking any of these medicines:
- medicines for epilepsy (fits or seizures) e.g. phenytoin, carbamazepine, primidone
- medicines for sleep disorder e.g. triazolam, diazepam
- medicines to treat fungal infection e.g. itraconazole, ketoconazole
- medicines for HIV infection e.g. stavudine, zalcitabine
- levodopa (medicine for Parkinson’s disease)
- theophylline (asthma medicine)
- prednisolone (anti-inflammatory medicine)
This list does not include all medicines that may interact with Isoniazid.
This medicine should not be taken with aluminium-containing antacids as these could reduce the absorption of Isoniazid. If you must take antacids, take this medicine at least 1 hour before taking the antacid.
Always notify your doctor and pharmacist if you are taking any other medicines, including herbal tonics such as traditional Chinese medicines, supplements and medicines that you buy without a prescription.
Avoid alcohol and other drinks that contain tyramine such as red wine and beer.
Avoid foods that are rich in tyramine, such as cheese, sausages, soya beans, fava beans, broad beans and pickled foods like sauerkraut. Ask your doctor or dietitian about the types of food you should avoid.
Store in a cool, dry place away from the reach of children. Protect from light.
The tablet must also be protected from moisture.
Medicines must not be used past the expiry date.
Sign Out
