A 65-year-old woman presents to the emergency department with a 3-day history of fever, sore throat, and severe malaise, followed by a painful skin rash that started on her face and trunk and is now spreading to her extremities. She reports burning in her eyes and pain when swallowing. Ten days ago, she was prescribed trimethoprim-sulfamethoxazole for an uncomplicated urinary tract infection. She has no other significant past medical history and takes no other medications. She is afebrile with a temperature of 102.2°F (39.0°C). Her blood pressure is 110/70 mmHg, her heart rate is 125 bpm, and her respiratory rate is 20 breaths per minute.