Efficacy and Safety of Concomitant Montelukast Sodium and Levocetirizine Dihydrochloride in Perennial Allergic Rhinitis (PAR) Patients

Inclusion Criteria: * Patients with at least 2 years history of PAR prior to the study * Positive results of skin prick test * Patients who provided a signed written informed consent form * Patients who are able and willing to complete subject diaries * Patients who agree to maintain consistency in their surroundings throughout the study period * At Visit, 2 patients whose symptom scores recorded in the subject diary meet all of the followings during the last one week of baseline period A.Daily mean of 6 points or above for Daytime Nasal Symptom Score (maximum 12 points) B.Daily mean of 1.8 points or above for Daytime Nasal Obstruction Symptom Score (maximum 3 points) Exclusion Criteria: * Patients also with non-allergic rhinitis with different causes. * Patients with severe asthma who meet the followings. * Presence of nasal polyps or any clinically important nasal anomaly. * History of acute • chronic sinusitis within 30 days of Visit 1 * History of intranasal / eye surgeries within 3 months of Visit 1 * Initiation of immunotherapy or dose modification within 1 month prior to Visit 1 * Upper respiratory infections including cold and systemic infections within 3 weeks of Visit 1. * Chronic use of tricyclic antidepressants, beta agonists, bronchodilators, etc. that may affect the efficacy of study drug * At Visit 2, patients who recorded Daytime Nasal Symptom Scores for fewer than 4 days in the subject diary during the last one week of baseline period