In an HIV-positive patient with multiple ring-enhancing brain lesions and edema, which treatment is the choice?

• A. Acyclovir
• B. Rifampin
• C. Sulfadiazine and Pyrimethamine
• D. Fluconazole

Answer: (C)

When an HIV-positive patient has multiple ring-enhancing brain lesions with edema, toxoplasma encephalitis from reactivation is high on the list. The treatment targets the parasite’s folate synthesis: pyrimethamine inhibits dihydrofolate reductase in Toxoplasma, and sulfadiazine blocks dihydropteroate synthase, effectively stopping the parasite’s ability to make nucleotides needed for replication. Folinic acid (leucovorin) is added to lessen bone marrow toxicity in the patient. This combination is the standard approach to toxoplasma encephalitis in AIDS.

Other drugs listed don’t treat toxoplasma: acyclovir targets herpesviruses, rifampin targets mycobacteria, and fluconazole targets fungi, none of which explain the presentation.