The most appropriate therapy for this patient is a second-generation H1 antihistamine, such as cetirizine. He has acute urticaria, characterized by evanescent red, pruritic plaques and wheals that last less than 24 hours after a probable viral upper respiratory tract infection. Newer-generation H1 antihistamines are preferred to first-generation agents (diphenhydramine, hydroxyzine) primarily because they are long-acting and are more likely to suppress the urticaria consistently. They also do not readily cross the blood-brain barrier and therefore have less sedating and anticholinergic side effects that may be dose-limiting in some patients.
Amoxicillin can be used if there is concern for a bacterial infection, but the clinical history of nonpurulent cough, rhinitis, and self-resolution is not consistent with a bacterial infection.
Glucocorticoids, such as prednisone, are effective therapy for urticaria, but have considerable systemic side effects. Although their use may be appropriate in patients with angioedema, antihistamines are the preferred initial treatment option owing to their effectiveness and safer side-effect profile.
Ranitidine is an H2 antihistamine used primarily for gastric acid suppression and would not be appropriate antihistamine monotherapy for this patient. The combination of an H1 and H2 antihistamine is often used, particularly in patients with severe urticaria, although there is limited evidence of effectiveness of this practice.
