Review Question - QID 109820

A 61-year-old man presents to the emergency department because he has developed blisters at multiple locations on his body. He says that the blisters appeared several days ago after a day of hiking in the mountains with his colleagues. When asked about potential triggering events, he says that he recently had an infection and was treated with antibiotics but he cannot recall the name of the drug that he took. In addition, he accidentally confused his medication with one of his wife's blood thinner pills several days before the blisters appeared. On examination, the blisters are flesh-colored, raised, and widespread on his skin but do not involve his mucosal surfaces. The blisters are tense to palpation and do not separate with rubbing. Pathology of the vesicles show that they continue under the level of the epidermis. Which of the following is the most likely cause of this patient's blistering?