Primary Endpoint The time to meaningful change in diary-based clinical symptoms as measured by the Urticaria Activity Score from baseline (Wk -7 to Day -1) to the date at which an MID (5 point change in weekly UAS 7) or achievement of > 50% reduction in daily symptom score for 3 days if in the first week. The UAS score, which is the sum of pruritus and hives, will be used to calculate the UAS7. The UAS7 score obtained 1 week prior to randomization will be used as the baseline.