Dermatitis Herpetiformis & Linear IgA Disease — Topic Test

A 6-year-old boy presents with a tense, itchy eruption around the mouth and on the limbs. Clinical examination shows large tense bullae arranged in a rosette around central crusts on the lower abdomen and a few sausage-shaped blisters on the hands, the so-called string-of-pearls pattern, with no mucosal involvement. Direct immunofluorescence shows linear IgA deposition along the basement membrane zone. What is the drug of choice?