A 52-year-old woman with a 15-year history of plaque psoriasis now presents with sudden onset of widespread erythema, pustules, and fever (38.5°C). Her BSA involvement has increased to 80%. Recent medication history includes initiation of a beta-blocker for hypertension 2 weeks ago. Laboratory findings show elevated WBC (13,500/μL) and normal renal function. What is the most appropriate next step in management?