1 May 2026Oral drugs
Pyrimethamine oral
Pyrimethamine guidance for toxoplasmosis and isosporiasis in immunodeficient patients, with folate-deficiency precautions.
Prescription under medical supervision
This guide page is for structured reference only and does not replace a clinician, pharmacist, or emergency review. Dose choice, route choice, interactions, and safety decisions still need professional judgment.
Therapeutic action
Antiprotozoal.
Indications
- Treatment and secondary prophylaxis of toxoplasmosis in immunodeficient patients, in combination with sulfadiazine or clindamycin.
- Primary prophylaxis of toxoplasmosis in immunodeficient patients, in combination with dapsone only if co-trimoxazole cannot be used.
- Second-line treatment of isosporiasis in immunodeficient patients only if co-trimoxazole cannot be used.
Forms and strengths
- 25 mg tablet.
Dose and duration
Treatment of toxoplasmosis
- Adult: 2 doses of 100 mg on D1, then 75 to 100 mg once daily for at least 6 weeks.
Secondary prophylaxis of toxoplasmosis
- Adult: 25 to 50 mg once daily, as long as necessary.
Primary prophylaxis of toxoplasmosis
- Adult: 50 to 75 mg once weekly, as long as necessary.
Treatment of isosporiasis
- Adult: 50 to 75 mg once daily for 10 days.
Contra-indications, adverse effects, precautions
- Do not administer to patients with severe renal or hepatic impairment.
- May cause gastrointestinal disturbances, seizures, leucopenia, thrombocytopenia, and megaloblastic anaemia due to folic acid deficiency.
- Administer calcium folinate to prevent folic acid deficiency.
- Avoid if possible combination with other folate antagonists such as co-trimoxazole and methotrexate.
- Monitor combination with zidovudine because of the increased risk of zidovudine-associated haematotoxicity.
- Pregnancy: contraindicated during the first trimester.
- Breast-feeding: no contra-indication; however avoid concomitant administration of other folate antagonists.
Source
MSF Essential drugs practical guidelines (January 2026)
This page reproduces the structured reference information for this batch while leaving out the Storage and Remarks sections.
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