AlternativeWith folinic acid
Pyrimethamine + Sulfadiazine
Antifolate + sulfonamide antiprotozoal
Treats confirmed fetal toxoplasmosis (≥18/40 with positive amnio).
Oral
First-line for
- Confirmed fetal toxoplasmosis (PCR-positive amnio, ≥18/40)
- Severe maternal toxoplasmosis
Mechanism
Pyrimethamine blocks dihydrofolate reductase; sulfadiazine blocks dihydropteroate synthase — synergistic anti-T. gondii.
“Spiramycin first, switch to PSF if fetus infected”
- Maternal seroconversion → spiramycin
- Amnio PCR+ at ≥18/40 → switch to pyr+sulfa+folinic
Dosing
- Pyrimethamine
- 50 mg OD
- Sulfadiazine
- 3 g/day in divided doses
- Folinic acid
- 10–25 mg OD
Contraindications
- AbsoluteT1 — pyrimethamine teratogenic (folate antagonist)
- AbsoluteSulpha allergy
- CautionG6PD — haemolysis
Side effects
- Pancytopenia (folate antagonism)
- Rash, Stevens–Johnson
- Crystalluria
Fetal & maternal notes
- • Use only ≥18/40 + folinic acid rescue
- • Spiramycin is the T1/T2 maternal-only treatment
Key interactions
Methotrexate
AvoidAdditive marrow toxicity
Sulfonylureas
CautionHypoglycaemia
Warfarin
Caution↑ INR
Clinical pearls
- 💡 Always co-prescribe folinic (NOT folic) acid
- 💡 Counsel re: maternal blood counts weekly
Content last reviewed: REPLACE_ME (e.g. 2026-07)
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