COrticosteroids in acUte uRticAria in emerGency dEpartment

Experimental: Antihistamines + placebo of cortancyl

- In emergency department : Levocetirizine 5 mg orally. Renewable once if persistence of hives at 30 minutes.~Placebo of Cortancyl : 1mg/kg (the number of tablets the patient needs to take is based on his weight and is noted on annex 4), once orally~- At home : Levocetirizine 5 mg twice daily for 7 days (D1 to D7). If persistence of hives, levocetirizine 10 mg twice daily for 7 more days (D8 to D14).~Placebo of Cortancyl 20 mg x 2 tablets = 40mg once per day for 3 days orally

Active Comparator: Association of antihistamines and cortancyl

- In emergency department : Levocetirizine 5 mg orally Renewable once if persistence of hives at 30 minutes.~Cortancyl: 1 mg/kg (the number of tablets the patient needs to take is based on his weight and is noted on annex 4), once orally.~- At home : Levocetirizine 5 mg twice daily for 7 days (D1 to D7). If persistence of hives, levocetirizine 10 mg twice daily for 7 more days (D8 to D14).~Cortancyl : 20 mg x 2 tablets = 40 mg per day for 3 days orally