A 72-year-old woman from Delhi presents with a 2-month history of recurrent tense bullae on her lower legs and abdomen. She reports mild pruritus. Skin examination reveals several intact bullae with surrounding urticarial plaques. Direct immunofluorescence shows linear IgG and C3 deposition along the basement membrane zone. Indirect immunofluorescence (serum) is positive for circulating IgG antibodies. The patient is otherwise healthy with no significant past medical history. What is the most appropriate initial pharmacological management?