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 can be an opportunistic infection (OI) of HIV. An OI is an infection that occurs more frequently or is more severe in people with weakened immune systems—such as people with HIV—than in people with healthy immune systems. To learn more about OIs, read the HIVinfo What is an Opportunistic Infection? fact sheet.
To learn how HIV and TB are connected, read the HIVinfo HIV and Tuberculosis (TB) fact sheet. The fact sheet includes information on the difference between latent TB infection (LTBI) and active TB disease.
How is isoniazid used in people with HIV?
The Guidelines for the Prevention and Treatment of Opportunistic Infections in Adults and Adolescents with HIV and the Guidelines for the Prevention and Treatment of Opportunistic Infections in Children with and Exposed to HIV include recommendations on the uses of isoniazid to treat:
- Latent TB infection in people with HIV to prevent the infection from advancing to active TB disease
- Active TB disease in people with HIV
The recommended uses may not always be consistent with FDA-approved uses of isoniazid. See the Adult and Pediatric Opportunistic Infection Guidelines for complete information on recommended uses of isoniazid in adults and children with HIV. Isoniazid may have other recommended uses not listed above.
What should I tell my health care provider before using isoniazid?
Before using 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, including:
- Liver problems
- Kidney problems
- Nervous system problems, such as peripheral neuropathy
- Malnourishment (nutrient deficiency)
- History of severe side effects to isoniazid, such as fever, chills, or arthritis
- If you drink alcohol daily or use illicit injectable drugs.
- About anything that could affect your ability to take medicines, such as difficulty swallowing tablets, difficulty remembering to take tablets or scheduled doses, or any health conditions that may prevent you from getting an injection (shot).
- If you are pregnant or plan to become pregnant. Talk to your health care provider about the risks and benefits of using isoniazid during pregnancy. The Guidelines for the Prevention and Treatment of Opportunistic Infections in Adults and Adolescents with HIV may include other recommendations on the use of isoniazid during pregnancy. Please refer to these guidelines for additional information.
- If you are breast/chestfeeding or plan to breast/chestfeed. For people with HIV in the United States, the Guideline recommends speaking with your health care provider to discuss options for feeding your baby. People with suppressed viral load have a less than 1% chance of transmitting HIV to their baby via their own milk.
- 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 use isoniazid?
Use isoniazid according to your health care provider’s instructions. Your health care provider will tell you how much isoniazid to use and when to use 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 room temperature, 68°F to 77°F (20°C to 25°C), and protect them from light. The solution may crystallize (become solid) 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, 68°F to 77°F (20°C to 25°C).
- Store isoniazid tablets at room temperature, 68°F to 77°F (20°C to 25°C), and protect them from moisture and light.
- Keep isoniazid in the container that it came in and keep the container tightly closed.
- Do not use isoniazid if the original seal over the container opening 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?
- Recommendations on the HIV-related uses of isoniazid, from the Guidelines for the Prevention and Treatment of Opportunistic Infections in Adults and Adolescents with HIV and the Guidelines for the Prevention and Treatment of Opportunistic Infections in Children with and Exposed to HIV.
- This Patient Version drug summary is based on the following FDA label(s): Injection (solution); Oral solution; Tablet.
- The American Hospital Formulary Service (AHFS) Patient Medication Information for isoniazid available from MedlinePlus.
- Isoniazid-related research studies, from ClinicalTrials.gov. (The ClinicalTrials.gov search can be modified so that you can get results that better match your interests. To learn more about the ClinicalTrials.gov search features, please see How to Search.)
Last Reviewed: May 15, 2023