Formulary
Pyrimethamine: Indications, Dosing, Side Effects and Interactions
Pyrimethamine clinical drug profile including indications, dosing, side effects, cautions and interactions.
MedNext Academy | 3 min read
Pyrimethamine: Indications, Dosing, Side Effects and Interactions
Pyrimethamine clinical drug profile including indications, dosing, side effects, cautions and interactions.
Indications and dose
**Toxoplasmosis in pregnancy (in combination with sulfadiazine and folinic acid)**
- **Adult** (By Mouth): 50 mg once daily until delivery.
**Toxoplasmosis in pregnancy (in combination with sulfadiazine and folinic acid) for pyrimethamine**
- **Child 12-17 years** (By mouth): 50 mg once daily until delivery.
**Congenital toxoplasmosis (in combination with sulfadiazine and folinic acid) for pyrimethamine**
- **Neonate** (By mouth): 1 mg/kg twice daily for 2 days, then 1 mg/kg once daily for 6 months, then 1 mg/kg 3 times a week for 6 months.
Cautions
History of seizures-avoid large loading doses; predisposition to folate deficiency
Side effects
Common or very common Anaemia; diarrhoea; dizziness; headache; leucopenia; nausea; skin reactions; thrombocytopenia; vomiting Uncommon Fever Rare or very rare Abdominal pain; oral ulceration; pancytopenia; pneumonia eosinophilic; seizure
Interactions
**Severe interactions:**
- Cases of fatal bone marrow aplasia have been associated with the administration of daunorubicin, cytosine arabinoside and pyrimethamine to individuals suffering from acute myeloid leukaemia.
**Other interactions (7):**
- Folate inhibitors, agents associated with myelosuppression Daraprim, by its mode of action, may further depress folate metabolism in patients receiving treatment with other folate inhibitors, or...
- Megaloblastic anaemia has been reported occasionally in individuals who took pyrimethamine concurrently with a trimethoprim/sulphonamide combination.
- Methotrexate Convulsions have occurred after concurrent administration of methotrexate and pyrimethamine to children with central nervous system leukaemia.
- Other antimalarial drugs Seizures have occasionally been reported when pyrimethamine was used in combination with other antimalarial drugs.
- Lorazepam The concurrent administration of lorazepam and Daraprim may induce hepatotoxicity .
- Antacid salts, kaolin In vitro data suggest that antacid salts and the anti-diarrhoeal agent kaolin reduce the absorption of pyrimethamine.
Pregnancy
Toxoplasmosis in pregnancy (in combination with sulfadiazine and folinic acid) for pyrimethamine By mouth Adult 50 mg once daily until delivery.
Breast feeding
Significant amount in milk-avoid administration of other folate antagonists to infant. Avoid breast-feeding during toxoplasmosis treatment.
Hepatic impairment
Manufacturer advises caution (limited information available). Dose adjustments Manufacturer advises consider dose reduction.
Renal impairment
Manufacturer advises caution.
Medicinal forms
Suspension
Clinical governance
**Author:** MedNext Clinical Team. **Clinical reviewer:** Dr Shameer Deen, MBBS, MS, MRCS. **Sources:** BNF, Indian Pharmacopoeia, CIMS India. **Correction:** Report errors at support@mednext.academy.
Inside MedNext for this topic
- 411 MedNext-authored chapters
- 80,000+ MCQ bank
- 15 study modes
- Growing visual cheat sheets
Study modes
- Notes
- MCQ
- Audio
- Video
- Visual
- 3D Anatomy
- Trace
- Flashcards
- Mnemonics
- Image Bank
- Clinical
- Microscopy
- Audio QBank
- Cadaver
- Book Match
Continue reading
Subject HubPharmacology Hub
All pharmacology resources in one place.
Drug SchedulesIndian Drug Schedules
Schedule H, H1, X and G classifications.
FormularyBrowse all drugs
Search 1,850+ drug profiles.
Study Pyrimethamine in the MedNext app
Challenge yourself with targeted pharmacology MCQs on this drug class. Every explanation links back to the chapter that teaches the concept.
Start drug challengeExplore the full formulary

