A 48-year-old man presents with a 2-day history of a pruritic rash. He has no prior history of dermatologic disease. Four days ago, he had an upper respiratory infection that resolved with acetaminophen and over-the-counter cold medication. His medical history is significant for type 1 diabetes mellitus well controlled with insulin. He was diagnosed with hypertension 3 weeks ago and started on captopril at that time. Vital signs are within normal limits. Physical examination reveals multiple blanching, nontender erythematous lesions over the waistline, trunk, and forearms; a representative lesion on the right forearm is shown in the image. There is no lymphadenopathy or hepatosplenomegaly. Which of the following is the most likely explanation for this patient’s skin findings?