Environmental Exposure Unit Study of Cetirizine Hydrochloride in Japanese Cedar Pollinosis

Background: Cedar pollinosis is a widespread seasonal allergy that is unique to Japan. Environmental exposure units (EEU) assist in the development of effective therapeutic and preventive measures because outdoor studies are limited by seasonal variation in pollen exposure. Objectives: We constructed an EEU to conduct a randomized cross-over double-blind placebo-controlled study of the effi cacy of cetirizine (Zyrtec), a second-generation antihistamine. Methods: The spatial and temporal homogeneity of pollen distribution in the EEU was evaluated by counting the number of pollen grains on petroleum-jelly–smeared glass slides and by real-time pollen monitors. In the clinical study, 20 volunteers with known cedar pollinosis were exposed to pollen for 5 hours, randomly allocated to receive either cetirizine hydrochloride or placebo 30 minutes after exposure. Symptoms and the degree of somnolence were recorded every 30 minutes for 5.5 hours. As a measure of psychomotor performance, the Uchida–Kraepelin test was used to determine work quantity and error rate. Results: The cedar pollen grains were scattered evenly in the exposure room. In the clinical study, symptom scores were elevated in both groups, showing signifi cant symptom induction 30 minutes after exposure. Test drugs were administered 30 minutes after exposure, and 1 hour later patients in the cetirizine hydrochloride group experienced a signifi cant decrease in sneezing, nose-blowing frequency, and nasal congestion compared with the placebo group. There were no signifi cant differences between the 2 groups in terms of subjective somnolence or objective psychomotor performance. Conclusion: The fi rst EEU in Japan was used successfully to evaluate cetirizine as a treatment for cedar pollinosis. The results confi rmed those from studies in other countries, except for the degree of somnolence, which increased in both groups and may have been related to postprandial sleepiness.