Study for the Treatment of Chronic Idiopathic Urticaria With High Doses of AERIUS (Desloratadine) (Study P04849)

Inclusion Criteria: * Subjects must satisfy the following criteria before being enrolled/randomized into the study. * Subject must demonstrate willingness to participate in the study. * Subject must be 18 to 75 years of age, of either gender, and any race. * Subject must have had this episode of chronic idiopathic urticaria for at least 6 weeks or more, and has been dosing with a "2nd generation antihistamine (AH)" for 2 weeks or longer, and * Subject's current episode of urticaria is sufficiently symptomatic at the Screening Visit to qualify for this study, in the opinion of the investigator. * Subject has a Baseline Week (entry period) UAS between 10 and 30 inclusive. * Patient must understand and be willing to assess and record symptom scores. * Has voluntarily signed a written informed consent. * Subjects must confirm that all prior medication washout times have been observed. * Subject must confirm that he/she is practicing adequate contraception: Female volunteers of childbearing potential (including women who are less than 1 year postmenopausal and women who will be sexually active during the study) must agree to use a medically accepted method of contraception or be surgically sterilized prior to screening, while receiving protocol-specified medication, and for 30 days after stopping the medication. Women who are postmenopausal for \>1 year (i.e., women who have experienced 12 consecutive months of amenorrhea) will be exempted from the use of contraception during the study. Nonsterile or premenopausal female subjects must be using a medically accepted method of birth control, ie, double-barrier method (eg, male or female condom and spermicide), oral contraceptive, Depo-Provera, NuvaRing, contraceptive transdermal patch, etc, for female subjects of childbearing potential prior to screening and during the study. Women of childbearing potential should be counseled in the appropriate use of birth control while in the study. Vasectomy or tubal ligation is considered a single barrier. Women who are not currently sexually active must agree and consent to use one of the above-mentioned methods if they become sexually active while participating in the study. * If subject is a female volunteer of childbearing potential, she must have a negative urine pregnancy test at Screening/Visit 1. * Subjects must be free of any clinically relevant disease other than chronic idiopathic urticaria (CIU) that would, in the principal investigator's and/or sponsor's opinion, interfere with the conduct of the study or study evaluations. * Subjects must be able to adhere to the dosing and visit schedules and agree to record symptom severity scores, medication times, concomitant medications, and adverse events (AEs) accurately and consistently in a daily diary. Exclusion Criteria: * Is a female who is pregnant, or intends to become pregnant during the study. * Is nursing, or intends to be nursing during the study or within 90 days after study completion. * Has not observed the designated washout periods for any of the prohibited medications. * Has used any investigational product within 30 days prior to enrollment. * Have any of the following clinical conditions: * Symptomatic seasonal or perennial allergic rhinitis. * Asthma not controlled by short-acting beta-2 agonists used as necessary. * The presence of permanent severe diseases, especially those affecting the immune system, except urticaria. * The presence of a permanent gastrointestinal condition which may influence the oral therapy (chronic diarrhea diseases, congenital malformations or surgical mutilations of gastrointestinal tract). * History of/or presence of epilepsy, significant neurological disorders, cerebrovascular attacks or ischemia. * History of/or presence of myocardial infarction or cardiac arrhythmia which requires drug therapy. * Evidence of/or a history of significant renal disease. * Evidence of/or a history of significant hepatic disease. * Presence of cancer which requires chemotherapy or radiation therapy. * Presence of glaucoma. * Presence of urinary bladder neck obstruction with emptying difficulties. * Presence of acute urticaria . * Body mass index (BMI) \> 35 * Has any clinically significant deviation from the appropriate reference range in the physical examination, or other clinical evaluation that, in the investigator's judgment, may interfere with the study evaluation or affect subject safety. * Is in a situation or condition that, in the opinion of the investigator, may interfere with optimal participation in the study. * Is participating in any other clinical study(ies). * Is on the staff, affiliated with, or a family member of the staff personnel directly involved with this study. * Is allergic to or has a history of hypersensitivity to the study drug (desloratadine), to any of its excipients, or to loratadine. * Has the rare hereditary problem of galactose intolerance, the Lapp lactase deficiency, or glucose-galactose malabsorption.