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AIDSinfo Drug Database

AIDSinfo Drug Database

Drugs by class



Isoniazid  Audio icon

Other Names: INH
Drug Class: Opportunistic Infections and Coinfections

Chemical Image:
Click image to enlarge
Molecular Weight: 137.1413

What is isoniazid?

Isoniazid is an antibacterial prescription medicine approved by the U.S. Food and Drug Administration (FDA) for the prevention and treatment of tuberculosis (TB). TB is an opportunistic infection. An opportunistic infection is an infection that occurs more frequently or is more severe in people with weakened immune systems—such as those infected with HIV—than in people with healthy immune systems.

The Guidelines for the Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents, prepared by the Centers for Disease Control and Prevention (CDC), the National Institutes of Health (NIH), and the HIV Medicine Association of the Infectious Diseases Society of America (IDSA-HIVMA), includes recommendations on the HIV-related use of isoniazid to treat:

  • Latent TB infection to prevent the infection from advancing to active TB disease.
  • Active TB disease.
The above list may not include all of the HIV-related uses of isoniazid recommended in the Guidelines for the Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents. Some recommended uses, such as uses in certain rare circumstances, may have been omitted.

What should I tell my health care provider before taking isoniazid?

Before taking isoniazid, tell your health care provider:

  • If you are allergic to isoniazid or any other medicines.
  • About any medical conditions you have or have had, for example, diabetes or liver problems.
  • About anything that could affect your ability to take medicines, such as difficulty swallowing, difficulty remembering to take pills, or any health conditions that may prevent your use of intravenous medicines.
  • If you are pregnant or plan to become pregnant. Isoniazid should be used as a treatment for active tuberculosis during pregnancy because the benefit justifies the potential risk to the fetus. The benefit of preventive therapy also should be weighed against a possible risk to the fetus. Talk to your health care provider about possible risks with taking isoniazid when pregnant.
  • If you are breastfeeding or plan to breastfeed. Do not breastfeed if you are infected with HIV.
  • About other prescription and nonprescription medicines, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Isoniazid may affect the way other medicines or products work, and other medicines or products may affect how isoniazid works. Ask your health care provider if there are interactions between isoniazid and the other medicines you take.

Ask your health care provider about possible side effects from isoniazid. Your health care provider will tell you what to do if you have side effects.

How should I take isoniazid?

Take isoniazid according to your health care provider’s instructions. Your health care provider will tell you how much isoniazid to take and when to take it. Before you start isoniazid and each time you get a refill, read any printed information that comes with your medicine.

How should isoniazid be stored?

  • Store vials of isoniazid injection solution at 68°F to 77°F (20°C to 25°C) and protect them from light. The solution may crystallize at low temperatures. If this occurs, warm the vial to room temperature before use to redissolve the crystals.
  • Store isoniazid oral solution at room temperature, 59°F to 86°F (15°C to 30°C). (An oral solution is a mixture of a medicine and a liquid that can be taken by mouth.) 
  • Store isoniazid tablets at 68°F to 77°F (20°C to 25°C) and protect them from moisture and light.
  • Do not use isoniazid if the original seal on the medicine container is broken or missing.
  • Throw away isoniazid that is no longer needed or expired (out of date). Follow FDA guidelines on how to safely dispose of unused medicine.     
  • Keep isoniazid and all medicines out of reach of children.

Where can I find more information about isoniazid?

More information about isoniazid is available:

The above Patient Version drug summary is based on the following FDA label(s): Injection (solution); Oral solution; Tablet.

Last Reviewed: February 19, 2015

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