A 52-year-old woman with a 15-year history of plaque psoriasis now presents with acute onset of diffuse erythema, pustules, and scaling affecting >80% of body surface area, along with fever (38.5°C), chills, and malaise. She reports recent abrupt withdrawal of systemic corticosteroids that she had been taking for unrelated asthma. Laboratory investigations show: WBC 12,500/μL, CRP 8.2 mg/dL, albumin 2.8 g/dL. What is the most appropriate immediate next step in management?