Randomized double-blind study of prophylactic treatment with an antihistamine for seasonal allergic rhinitis.

Background: The efficacy of prophylactic treatment before the start of pollen dispersal for prevention of aggravation of symptoms is unclear. The aim of the present study was to examine the efficacy of prophylactic treatment with an antihistamine for seasonal allergic rhinitis (SAR) using an environmental challenge chamber (ECC).

Methods: The study was performed in a randomized double-blind manner with a 3-way crossover design. The subjects were 50 patients with SAR caused by Japanese cedar pollen who were randomized for treatment with levocetirizine hydrochloride 5 mg (Xyzal®) or placebo as follows: administration of placebo for 8 days (treatment A), single administration of levocetirizine on day 8 after placebo for 7 days (treatment B) or administration of levocetirizine for 8 days (treatment C). Efficacy in each treatment arm was evaluated based on cedar pollen exposure for 3 h on day 9 in an ECC, following 1-hour exposure on day 8. The primary endpoint was the total nasal symptom score for 12 h on day 9. Other nasal and ocular symptoms were secondary endpoints.

Results: The evaluation was performed in 45 subjects. The total nasal symptom score on day 9 was significantly lower with treatment B compared with treatment A. Treatment C did not show superior efficacy compared with treatment B.

Conclusions: Our results suggest that early intervention with levocetirizine soon after onset of symptoms may attenuate these symptoms as effectively as prophylactic treatment before pollen dispersal. These results are important from the perspective of patient convenience and reduction of medical costs.