The purpose of this study is to demonstrate that the efficacy of Concomitant Montelukast Sodium and Levocetirizine Dihydrochloride is superior to that of Levocetirizine and Montelukast monotherapies and to compare the safety and tolerability of Concomitant Montelukast Sodium and Levocetirizine Dihydrochloride to those of Levocetirizine and Montelukast monotherapies in Perennial Allergic Rhinitis (PAR) patients.

randomized, double-blind, active-controlled, multicenter, phase 3 trial

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