RecruitingPhase 2Drug trialAn Outpatient Study of the Efficacy of ARS-2 in Patients With Chronic Spontaneous UrticariaThis is a Phase 2b, outpatient, single-dose, randomized, double blind, placebo-controlled, three period crossover study that will consist of a screening period and three blinded treatment periods. Subjects enrolled will have CSU with a history of moderate to severe acute exacerbations (or flares).