This will be a multicenter, parallel group, randomized, double-blind, active controlled, Phase III clinical study of cetirizine injection, 10 mg/mL, compared to diphenhydramine injection, 50 mg/mL (Benadryl or generic equivalent), in approximately 256 patients (1:1 ratio) with acute urticaria requiring treatment in Emergency Departments, hospitals, Urgent Care Centers, Allergy Clinics, and etc.