A 61-year-old man with HIV and a CD4 count of 428 cells/mm³ is seen in clinic for evaluation of a new rash, and a clinical diagnosis of secondary syphilis is strongly suspected. On further questioning, he also reports new, intermittent severe headaches. A lumbar puncture is performed, and cerebrospinal (CSF) examination reveals a white blood cell count of 19 cells/mm³ and elevated protein of 55 mg/dL. A serum syphilis enzyme immunoassay (EIA) is positive, a serum Venereal Disease Research Laboratory (VDRL) test is positive with a titer of 1:128, and the CSF VDRL test is positive. He has no medication allergies.