A 10-year-old girl presented with a two-day history of headache. A fever, dry cough, and maculopapular rash developed one day after the headache began. The rash first appeared on the face and spread to her entire body. The patient had no pruritus or pain. She had loss of appetite but no nausea, vomiting, diarrhea, constipation, or recent travel. She had been taking trimethoprim/sulfamethoxazole for nine days to treat a urinary tract infection. She was taking clonidine and risperidone (Risperdal) for attention-deficit/hyperactivity disorder. She had no known drug allergies and was up to date on immunizations.

On physical examination, the patient had a fever of 101.4°F (38.6°C). An erythematous, non-blanching, maculopapular rash in a morbilliform pattern was noted on the face, trunk, back, and upper and lower extremities bilaterally, sparing the palms and feet (Figure 1 and Figure 2). Mild conjunctival injection was observed in both eyes, with normal pharyngeal and tonsillar mucosa.

Question

Based on the patient’s history and physical examination findings, which one of the following is the most likely diagnosis?