Isoniazid is used alone or in combination with other drugs to treat tuberculosis. It is also used to prevent tuberculosis in individuals who came into contact with the bacteria that causes it.


What is Isoniazid?

Isoniazid works by actively killing tuberculosis bacteria. 


How should Isoniazid be taken?

Isoniazid can be taken in the form of tablets (including sustained-release), capsules or syrup. Typically, one dose per day is recommended on an empty stomach (1 hour before or 2 hours after a meal). If it is used to treat stomach disorders, it can be taken with a small portion of food.


Tuberculosis bacteria may remain quiescent without replicating for longer periods. For this reason, treatment should be prolonged and isoniazid should be taken for 6 to 12 months. 


Side effects associated with Isoniazid

Isoniazid can cause severe liver damage and in some cases, it can be fatal. Therefore, it is important to tell your doctor if:


  • You have (or have suffered from) liver disease
  • You are an alcoholic
  • You abuse drugs
  • You have symptoms such as extreme tiredness, weakness, lack of energy, loss of appetite, upset stomach, vomiting, dark urine and jaundice


Among the other possible side effects of isoniazid include the following:


  • Diarrhea
  • Impaired vision


You should contact your doctor immediately if you experience:


  • Eye pain
  • Numbness or tingling in hands and feet
  • Skin rash
  • Fever
  • Swollen glands
  • Sore throat
  • Bleeding or bruising
  • Abdominal pain or tenderness to the touch


Contraindications and warnings associated with the use of Isoniazid

During treatment with isoniazid, alcohol should not be consumed. 


Before starting treatment with isoniazid, it is important to tell your doctor if: 


  • You have any allergies to the active substance, its excipients or any other drugs or food
  • You are taking any other medications, herbal remedies or supplements. Mentioning in particular: acetaminophen, antacids, carbamazepine, disulfiram, ketoconazole, phenytoin, theophylline, valproic acid and vitamins
  • You are suffering (or have suffered) from kidney disease, diabetes or peripheral neuropathies
  • You have an HIV infection
  • You are pregnant or breast-feeding