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Your public health nurse or health care provider has told you that you have a positive TB skin test. This means you have come in contact with the tuberculosis germ (bacteria) at some time in the past.

Your body has built a “wall” around the bacteria. The bacteria has gone “to sleep” (dormant) and isn’t making your body sick. You can’t make anyone else sick. Your chest x-ray shows that you don’t have active TB disease.

You Have Latent TB Infection:

  • Your health care provider has prescribed an antibiotic called Isoniazid (INH), which will go through the wall and kill the bacteria.
  • This medication must be taken daily for a minimum of 6 months, usually 9 months.
  • You should have a blood test before starting this medication.
  • This medication is free from the Windsor-Essex County Health Unit.

Isoniazid (INH)

Take Your Medicine:

  • Every day, don’t miss a day. Use the dosette (pill box) that is given to you.
  • On an empty stomach (1 hour before or 2 to 3 hours after eating).

Important to Know

  • You can’t drink alcohol while taking this medicine because it can hurt the liver.
  • You must finish all of the medication. If you miss taking your meds or stop before 6 months, your body may build a resistance to the antibiotic.
  • You may have to have blood work done before you start the medicine and during treatment.

What happens if I forget to take my medicine?

If you remember later that day: take your medicine as soon as you remember.

If you forget until the day after: take 1 dose only, never take 2 doses.

Side Effects 

INH is safe. Most people can take this medication without having problems. Liver problems are the most serious. Tell your doctor if you have liver disease, are taking any other medication, or drink alcohol. Older people will be more sensitive to this medication.

Call your health care provider if you are experiencing any of these symptoms:

  • Loss of appetite, nausea, vomiting, fatigue, or weakness for more than 3 days.
  • Brown or very dark urine.
  • Yellow skin or eyes.
  • Fever for more than 3 days.
  • Abdominal tenderness, especially right upper abdominal discomfort.

Other side effects could include:

  • Change in vision. You would need to see an eye specialist.
  • Headache.
  • Numbness and tingling in the hands and feet occurs rarely. Your health care provider may prescribe pyridoxine (vitamin B6) to prevent this from happening.
  • Rash and/or itching.

If you have side effects that may be from the medication and can’t contact your health care provider immediately, stop your medication until you’ve had a medical evaluation.

I MUST remember...

  • To take pills on an empty stomach.
  • To take my medicine at the same time every day.
  • To use my dosette and keep it in a safe place.
  • Not to drink alcohol.
  • To see my health care provider if I have any problems.
  • Not to take the pain medicine acetaminophen (Tylenol or another brand).
  • To come back and get more medication before it is all gone.
  • To check with my health care provider or pharmacist before taking any new medication.

Public Health Agency of Canada (2013). Canadian Tuberculosis Standards (7th Edition). Ontario Ministy of Health and Long Term Care (2006). Tuberculosis protocol. Toronto, ON : Author.

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Last modified: 
Monday, March 6, 2023 - 11:15am