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Generic Name: pyrimethamine (PIR i METH a meen)
Brand Name: Daraprim

What is pyrimethamine?

Pyrimethamine is an antiparasite medicine that helps prevent parasites from growing and reproducing in the body.

Pyrimethamine is used together with other medicines to treat or prevent certain types of malaria. However, pyrimethamine is generally not preferred as a medicine to prevent malaria while traveling.

Pyrimethamine is also used to treat toxoplasmosis, an infection caused by the Toxoplasma parasite.

Pyrimethamine may also be used for purposes not listed in this medication guide.

What is the most important information I should know about pyrimethamine?

You should not use pyrimethamine if you have a blood cell disorder called megaloblastic anemia that has been caused by folate deficiency.

What should I discuss with my healthcare provider before taking pyrimethamine?

You should not use pyrimethamine if you are allergic to it, or if you have:

  • a blood cell disorder called megaloblastic anemia that has been caused by folate (folic acid) deficiency.

To make sure pyrimethamine is safe for you, tell your doctor if you have:

  • seizures (especially if you take phenytoin);

  • liver disease;

  • kidney disease;

  • a history of alcoholism;

  • if you are pregnant; or

  • if you are malnourished.

FDA pregnancy category C. It is not known whether pyrimethamine will harm an unborn baby. Tell your doctor if you are pregnant, and avoid becoming pregnant while taking this medicine.

In some cases, pyrimethamine is given to pregnant women to treat toxoplasmosis. Talk with your doctor about the risks and benefits of using this medicine if you are pregnant.

Pyrimethamine can pass into breast milk and may harm a nursing baby. You should not breast-feed while using this medicine.

How should I take pyrimethamine?

Follow all directions on your prescription label. Your doctor may occasionally change your dose to make sure you get the best results. Do not take this medicine in larger or smaller amounts or for longer than recommended.

The pyrimethamine dose for treating toxoplasmosis is much higher than the dose for malaria. Follow your doctor's dosing instructions very carefully.

Your dosage and the length of time you take pyrimethamine will depend on the reason you are taking this medicine. In some cases, pyrimethamine is taken for several weeks.

Take with food if pyrimethamine upsets your stomach or affects your appetite.

While using pyrimethamine, you may need frequent blood tests.

Store at room temperature away from moisture, heat, and light.

What happens if I miss a dose?

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of pyrimethamine can be fatal, especially to a child.

Overdose symptoms may include stomach pain, severe vomiting, coughing up blood or vomit that looks like coffee grounds, feeling anxious or excited, seizure (convulsions), and weak or shallow breathing (breathing may stop).

What should I avoid while taking pyrimethamine?

Follow your doctor's instructions about any restrictions on food, beverages, or activity.

Pyrimethamine side effects

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Stop using pyrimethamine and call your doctor at once if you have:

  • sore throat, swelling in your tongue;

  • pale skin, easy bruising, purple spots under your skin;

  • the first sign of any skin rash, no matter how mild;

  • blood in your urine;

  • new or worsening cough, fever, trouble breathing;

  • irregular heartbeats; or

  • severe skin reaction--fever, sore throat, swelling in your face or tongue, burning in your eyes, skin pain, followed by a red or purple skin rash that spreads (especially in the face or upper body) and causes blistering and peeling.

Common side effects may include:

  • vomiting; or

  • loss of appetite.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

See also: Side effects (in more detail)

Pyrimethamine dosing information

Usual Adult Dose for Malaria Prophylaxis:

25 mg orally once a week. Prophylaxis should begin one week prior to departure and continue for at least 6 to 10 weeks following exposure.

Usual Adult Dose for Toxoplasmosis:

Initially: 50 to 75 mg orally once a day with 1 to 4 g of a sulfonamide (e.g., sulfadoxine, sulfadiazine). Continue for 1 to 3 weeks, depending on response and tolerance. Dosage for each drug may then be reduced by one-half and continued for an additional 4 or 5 weeks. Patients receiving pyrimethamine should also receive folinic acid.

Usual Adult Dose for Toxoplasmosis -- Prophylaxis:

1 mg/kg or 15 mg/m2 (max 25 mg) orally every day plus folinic acid (leucovorin) 5 mg orally every 3 days plus sulfadiazine 85 to 120 mg/kg/day divided into 2 to 4 oral doses. Clindamycin 20 to 30 mg/kg/day may be used in place of sulfadiazine as an alternative regimen.

Usual Adult Dose for Pneumocystis Pneumonia Prophylaxis:

50 to 75 mg orally once a week. Pyrimethamine is used in combination with dapsone and leucovorin. This is considered an alternative regimen for patients who do not tolerate trimethoprim-sulfamethoxazole.

Usual Pediatric Dose for Malaria Prophylaxis:

Less than 4 years: 6.25 mg orally once a week.

4 to 10 years: 12.5 mg orally once a week.

Usual Pediatric Dose for Toxoplasmosis:

Newborns and infants:
Initial: 2 mg/kg/day orally divided every 12 hours for 2 days, then 1 mg/kg/day once daily given with sulfadiazine for the first 6 months; next 6 months: 1 mg/kg/day 3 times per week with sulfadiazine; oral folinic acid 5 to 10 mg 3 times per week should be administered to prevent hematological toxicity.

1 to 12 years: 2 mg/kg/day divided every 12 hours for 3 days followed by 1 mg/kg/day (maximum 25 mg/day) once daily or divided twice daily for 4 weeks given with sulfadiazine; oral folinic acid 5 to 10 mg 3 times per week should be administered to prevent hematological toxicity.

What other drugs will affect pyrimethamine?

Other drugs may interact with pyrimethamine, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell each of your health care providers about all medicines you use now and any medicine you start or stop using.

Where can I get more information?

  • Your pharmacist can provide more information about pyrimethamine.
  • Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.
  • Disclaimer: Every effort has been made to ensure that the information provided by Cerner Multum, Inc. ('Multum') is accurate, up-to-date, and complete, but no guarantee is made to that effect. Drug information contained herein may be time sensitive. Multum information has been compiled for use by healthcare practitioners and consumers in the United States and therefore Multum does not warrant that uses outside of the United States are appropriate, unless specifically indicated otherwise. Multum's drug information does not endorse drugs, diagnose patients or recommend therapy. Multum's drug information is an informational resource designed to assist licensed healthcare practitioners in caring for their patients and/or to serve consumers viewing this service as a supplement to, and not a substitute for, the expertise, skill, knowledge and judgment of healthcare practitioners. The absence of a warning for a given drug or drug combination in no way should be construed to indicate that the drug or drug combination is safe, effective or appropriate for any given patient. Multum does not assume any responsibility for any aspect of healthcare administered with the aid of information Multum provides. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the drugs you are taking, check with your doctor, nurse or pharmacist.

Copyright 1996-2012 Cerner Multum, Inc. Version: 5.01.

Date modified: April 03, 2017
Last reviewed: July 10, 2014