For toxoplasmic encephalitis, which drug combination is used as treatment?

• A. Sulfadiazine and pyrimethamine
• B. Trimethoprim-sulfamethoxazole
• C. Metronidazole and clindamycin
• D. Dapsone and pyrimethamine

Answer: (A)

Treat toxoplasmic encephalitis by blocking folate synthesis at two steps, which works synergistically to stop parasite replication. Pyrimethamine inhibits dihydrofolate reductase, while sulfadiazine inhibits dihydropteroate synthase; together they deprive the parasite of tetrahydrofolate needed for DNA synthesis. To protect the patient from pyrimethamine-induced bone marrow suppression, folinic acid (leucovorin) is added. This combination—pyrimethamine with sulfadiazine, plus leucovorin—is the standard first-line therapy. Alternatives like trimethoprim-sulfamethoxazole can be used if sulfadiazine is not tolerable, but the classic regimen is sulfadiazine plus pyrimethamine.