A 28-year-old woman from Delhi presents to the emergency department with a 5-day history of high-grade fever, severe oral pain, and difficulty swallowing. On examination, she has extensive erosions of the lips, buccal mucosa, and pharynx with blood-stained crusts. She also has a widespread erythematous rash on her trunk and extremities with target lesions and flaccid blisters. She reports taking trimethoprim-sulfamethoxazole for a urinary tract infection 10 days ago. Her temperature is 39.2°C, heart rate 110/min, and blood pressure 98/62 mmHg. Laboratory investigations show WBC 8,500/μL, hemoglobin 11.2 g/dL, and serum creatinine 1.8 mg/dL. What is the most appropriate immediate management for this patient?