What is pyrimethamine?
Pyrimethamine is an antiparasitic prescription medicine approved by the U.S. Food and Drug Administration (FDA) for the treatment of Toxoplasma gondii infection (toxoplasmosis). Pyrimethamine is usually used together with a sulfonamide (sulfa medicine) to treat toxoplasmosis.
Toxoplasmosis of the brain (also called Toxoplasma gondii encephalitis) 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.
How is pyrimethamine 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 pyrimethamine in people with HIV to:
- Toxoplasma gondii encephalitis
- Cystoisosporiasis (also called isosporiasis)
- Pneumocystis pneumonia (PCP) from occurring the first time and from recurring
- Toxoplasma gondii encephalitis from occurring the first time and from recurring
- Cystoisosporiasis from recurring
The recommended uses may not always be consistent with FDA-approved uses of pyrimethamine. See the Adult and Pediatric Guidelines for complete information on recommended uses of pyrimethamine in adults and children with HIV. Pyrimethamine may have other recommended uses not listed above.
What should I tell my health care provider before taking pyrimethamine?
Before taking pyrimethamine, tell your health care provider:
- If you are allergic to pyrimethamine, sulfonamides (sulfa medicines), or any other medicines.
- About any medical conditions you have or have had, including kidney or liver problems and folate deficiency (low levels of folic acid in the blood).
- About anything that could affect your ability to take medicines, such as difficulty swallowing or remembering to take pills.
- If you are pregnant or plan to become pregnant. Pyrimethamine should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Talk to your health care provider about the risks and benefits of taking pyrimethamine 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 pyrimethamine 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. Pyrimethamine may affect the way other medicines or products work, and other medicines or products may affect how pyrimethamine works. Ask your health care provider if there are interactions between pyrimethamine and the other medicines you take.
Ask your health care provider about possible side effects from pyrimethamine. Your health care provider will tell you what to do if you have side effects.
How should I take pyrimethamine?
Take pyrimethamine according to your health care provider’s instructions. Your health care provider will tell you how much pyrimethamine to take and when to take it. Before you start pyrimethamine and each time you get a refill, read any printed information that comes with your medicine.
How should pyrimethamine be stored?
- Store pyrimethamine tablets in a dry place between 59°F and 77°F (15°C to 25°C). Protect pyrimethamine tablets from light.
- Keep pyrimethamine in the container that it came in and keep the container tightly closed.
- Do not use pyrimethamine if the original seal over the container opening is broken or missing.
- Throw away pyrimethamine that is no longer needed or expired (out of date). Follow FDA guidelines on how to safely dispose of unused medicine.
- Keep pyrimethamine and all medicines out of reach of children.
Where can I find more information about pyrimethamine?
- Recommendations on the HIV-related uses of pyrimethamine, 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): Tablet.
- Pyrimethamine-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: November 16, 2022