Reviewed on 6/6/2022

What Is Pyrimethamine and How Does It Work?

Pyrimethamine is a prescription medication used to treat the symptoms of Toxoplasmosis.

  • Pyrimethamine is available under the following different brand names: Daraprim

What Are Dosages of Pyrimethamine?

Adult and pediatric dosage


  • 25mg


Adult dosage

  • 50-75 mg once a day orally for 1-3 weeks, THEN
  • 25-37.5 mg once a day orally for 4-5 weeks

Pediatric dosage

  • Children above 2 Months Old

Congenital Toxoplasmosis

  • Loading dose: 2 mg/kg/day divided every 12 hours orally for 2 days  
  • Maintenance.: First 2-6 months old: 1 mg/kg orally once a day for 2-6 months old; THEN remainder of 12 months old; 1 mg/kg orally 3 times/week


  • Loading dose: 2 mg/kg/day divided every 12 hours orally for 3 days
  • Maintenance: 1 mg/kg orally once a day for 4 weeks
  • Children below 2 months old: Safety and efficacy not established

Dosage Considerations – Should be Given as Follows: 

  • See “Dosages”

What Are Side Effects Associated with Using Pyrimethamine?

Common side effects of Pyrimethamine include:

Serious side effects of Pyrimethamine include:

  • hives,
  • difficulty breathing,
  • swelling of the face, lips, tongue, or throat,
  • sore throat,
  • swelling in the tongue,
  • pale skin,
  • easy bruising,
  • purple spots under your skin,
  • skin rash (no matter how mild),
  • blood in the urine,
  • fever,
  • cold or flu symptoms,
  • new or worsening cough,
  • irregular heartbeats,
  • unusual tiredness,
  • mood changes,
  • feeling sick or unwell,
  • mouth sores,
  • stomach discomfort,
  • loss of appetite,
  • burning in the eyes,
  • skin pain, and
  • a red or purple skin rash that spreads 

Rare side effects of Pyrimethamine include:

  • none 

This is not a complete list of side effects and other serious side effects or health problems that may occur as a result of the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may report side effects or health problems to FDA at 1-800-FDA-1088.


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What Other Drugs Interact with Pyrimethamine?

If your medical doctor is using this medicine to treat your pain, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider, or pharmacist first.

This information does not contain all possible interactions or adverse effects. Visit the RxList Drug Interaction Checker for any drug interactions. Therefore, before using this product, tell your doctor or pharmacist about all your products. Keep a list of all your medications with you and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions or concerns.

What Are Warnings and Precautions for Pyrimethamine?


  • Hypersensitivity
  • Megaloblastic or folate-deficiency anemia

Effects of drug abuse

  • None

Short-Term Effects

  • See “What Are Side Effects Associated with Using Pyrimethamine?”

Long-Term Effects

  • See “What Are Side Effects Associated with Using Pyrimethamine?”


  • Use with caution in patients with G6PD deficiency
  • Use with caution in hepatic/renal impairment and history of seizure disorders
  • Dosage of pyrimethamine required for treatment of toxoplasmosis. has a narrow therapeutic window; if signs of folate deficiency develop, reduce dosage or discontinue the drug according to the response of the patient; folinic acid (leucovorin) should be administered in a dosage of 5 to 15 mg daily (orally, Intravenous, or Intramuscular) until normal hematopoiesis restored
  • Megaloblastic anemia, leukopenia, thrombocytopenia, neutropenia, and pancytopenia were reported with high doses; monitor CBC and platelets twice weekly in patients receiving high dose therapy
  • Use caution in patients with possible folate deficiency, including pregnancy, malabsorption syndrome, and alcoholism
  • Administer with leucovorin, especially at high doses, to prevent hematologic complications, due to pyrimethamine-induced folic acid deficiency; continue leucovorin during therapy and for 1 week after discontinuing therapy

Pregnancy & Lactation

  • Use with caution if the benefits outweigh the risks during pregnancy.
  • Lactation
    • Enters breast milk, do not nurse


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