A neonate receiving standard therapy for congenital toxoplasmosis develops progressive neutropenia on routine blood counts during the first month of treatment. Which drug is responsible and which supplement prevents this complication?
- A Pyrimethamine; supplement with folinic acid ✓
- B Sulfadiazine; supplement with folic acid
- C Spiramycin; supplement with vitamin B12
- D Pyrimethamine; supplement with folic acid
Correct answer: A. Pyrimethamine; supplement with folinic acid
Explanation
Pyrimethamine is a dihydrofolate reductase inhibitor and its dose-limiting toxicity is bone marrow suppression, especially neutropenia and thrombocytopenia. Folinic acid bypasses the blocked pathway and must be co-administered throughout the year of therapy. Plain folic acid is a poor substitute because folate reductase inhibitors do not act on reduced folate, making option D wrong. Sulfadiazine more typically causes crystalluria and rash, and spiramycin is used only for maternal treatment.
Reference: Nelson Textbook of Pediatrics, 21st ed.
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