A 38-year-old man with a history of tuberculosis presents to the hospital with a 7-day history of fever, widespread painful blistering eruption, and oral ulceration. He started anti-tuberculous therapy (isoniazid, rifampicin, pyrazinamide, ethambutol) 10 days ago. On examination, he has extensive erythematous patches and plaques with large flaccid bullae on his chest, abdomen, and thighs. Nikolsky sign is positive. Mucous membranes are extensively denuded. Skin biopsy shows near-total epidermal necrosis with minimal inflammatory infiltrate. Estimated body surface area involvement is 35%. What is the most appropriate next step in management?