A 52-year-old man complains of unpleasant sensations during swallowing and erosions on the oral mucosa. The disease onset was over a month ago. Objectively, on the normal mucosa of the soft palate, cheeks, and gums there are bright red erosions with the remains of erupted vesicles. The mucosa easily sloughs off. The Nikolsky's sign is positive. What medicines must be prescribed for the treatment first?