A 44-year-old woman with type 2 diabetes is brought to the emergency department with a 2-day history of lethargy, fever, nausea, and vomiting. She reports a diarrheal illness that started 4 days before the onset of fever. She also has Crohn's disease that is being treated with glucocorticoid therapy.
The patient's temperature is 38.9°C, her heart rate is 105 beats per minute, and her blood pressure is 100/68 mm Hg. Nuchal rigidity, photophobia, and phonophobia are noted. On neurologic examination, she appears to have left-sided facial palsy, left abducens nerve palsy, ataxia, and dysmetria. She reports diminished sensation on the right side of her body.
CT of the head is obtained (figure). Testing of the cerebrospinal fluid reveals a normal glucose level, no erythrocytes, a leukocyte count of 63 per mm3 with mononuclear predominance, and a protein level of 62 mg/dL (reference range, 15–45). A Gram's stain of the cerebrospinal fluid is negative.
Which one of the following medical regimens is most appropriate for this patient?