A 40-year-old man with known HIV infection is admitted to the hospital with right arm weakness and difficulty with speech. He was diagnosed with HIV infection eight years ago. He has not been adherent with either anti-retroviral treatment or trimethoprim-sulfamethoxazole prophylaxis therapy for several months prior to admission. His most recent CD4 count obtained 12 months ago was 150/µL. He does not smoke, drink alcohol, or use intravenous drugs.
His BMI is 26 kg/m². After a thorough evaluation, a diagnosis of central nervous system toxoplasmosis was established. He was given intravenous fluids and therapy was initiated with sulfadiazine and pyrimethamine.
Which of the following additional medications should be given to this patient?

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11ec193a_96ef_1079_853d_4f38bac094c3_MD0002_00 This patient presents with toxoplasmosis, which is usually treated with pyrimethamine in conjunction with a sulfonamide (sulfadiazine) to improve eradication of the tachyzoite form of Toxoplasma gondii. Patients unable to tolerate sulfadiazine may take clindamycin (preferred), atovaquone, or azithromycin in its place. Pyrimethamine (similar to methotrexate and trimethoprim) is a folic acid antagonist and inhibits dihydrofolate reductase. This inhibition also blocks rapidly dividing cells and manifests first as bone marrow suppression. Leucovorin is a reduced folic acid that bypasses the blocked enzyme and has equivalent activity to folic acid. Leucovorin should be administered concomitantly with pyrimethamine to prevent hematologic complications (i.e., leukopenia, megaloblastic anemia, and thrombocytopenia). (Choice A) Filgrastim (human granulocyte colony-stimulating factor) increases neutrophil counts. It is typically used with cytotoxic therapy and also in patients who fail leucovorin therapy. (Choice C) While nausea and vomiting are common side effects of pyrimethamine, they are generally not severe enough to warrant prophylactic anti-nausea medications such as ondansetron. (Choice D) Although patients with toxoplasmosis may present with or have seizures during the course of their illness, anticonvulsants are usually not given routinely to patients unless they have a prior history of seizures. Also, the addition of phenytoin to pyrimethamine may cause potential drug interactions and increase pyrimethamine's toxicity risk. (Choice E) Trimethoprim-sulfamethoxazole (TMP-SMX) is fairly efficacious for toxoplasmosis; but it is considered a second-line regimen to pyrimethamine and sulfadiazine, especially in settings where these drugs are not available. In addition, patients treated with sulfadiazine do not require additional TMP-SMX for Pneumocystis pneumonia prophylaxis. Educational objective: Pyrimethamine (in conjunction with sulfadiazine) is the preferred treatment for toxoplasmosis in HIV patients. Pyrimethamine causes bone marrow suppression and leucovorin should be used in conjunction to decrease the risk of hematologic complications. __________ References: Role of clindamycin in the treatment of acute toxoplasmosis of the central nervous system. (http://www.ncbi.nlm.nih.gov/pubmed/2060525) Comparison of two medications in central nervous system toxoplasmosis in patients with AIDS. (http://www.ncbi.nlm.nih.gov/pubmed/1428784)

A 40-Year-Old Man with Known HIV Infection Is Admitted to the Hospital