A 58-year-old man with gout is started on a new medication. Eight weeks later, he develops fever, malaise, and a pruritic, erythematous maculopapular (morbilliform) rash that began on the face and upper trunk and has become widespread. He has facial edema and tender cervical and axillary lymphadenopathy. Laboratory studies show leukocytosis with marked eosinophilia and elevated AST/ALT. Which of the following is the most likely diagnosis?