BACKGROUND: Dexamethasone cipecilate is a corticosteroid nasal spray whose local efficacy durability has been improved by introduction of a liposoluble functional group to its chemical structure. This study was conducted to evaluate the efficacy of once-daily treatment with this drug in patients with perennial allergic rhinitis by a challenge test with house dust antigen (Phase I clinical pharmacology study). METHODS: This study was designed as a randomised placebo-controlled double-blind study in 28 patients with perennial allergic rhinitis. Either 200 μg dexamethasone cipecilate or placebo was administered once daily for 7 days, and the antigen challenge test conducted 23 h after the dose on each day. We evaluated the efficacy primarily through assessment of suppression of immediate nasal symptoms. RESULTS: When efficacy durability was evaluated by physicians based on a general assessment of the effects of suppression of nasal symptoms, the percentage of patients with efficacy lasting for 24 h differed significantly between the dexamethasone cipecilate group (69.2%, 9 out of 13) and the placebo group (15.4%, 2 out of 13) (p = 0.015). CONCLUSIONS: Dexamethasone cipecilate was shown to be a corticosteroid having sustainable local efficacy. The results suggest that once-daily administration of dexamethasone cipecilate is effective in patients with allergic rhinitis, and that its efficacy lasts for 24 h.