A 27-year-old woman presents with a 3-month history of recurrent itchy “welts” on her trunk and proximal extremities. The lesions are well-circumscribed, raised, erythematous plaques that appear spontaneously 2–3 times per day and resolve within 6–8 hours without bruising or scarring. She denies fevers, weight loss, and joint pain. She recently stopped taking ibuprofen because it seemed to worsen the outbreaks. Physical examination shows several edematous, blanching wheals with excoriations. Which of the following is the most appropriate first-line pharmacotherapy for this condition?

(Assume she has no history of anaphylaxis and is not taking ACE inhibitors.)