Background: Clemastine (1 mg) is currently available over-the-counter for the treatment of allergic rhinitis.
Objective: To evaluate the efficacy of half the standard dose of clemastine (0.5 mg) in inhibiting the nasal response to allergen and the cutaneous response to histamine.
Methods: Double-blind, placebo-controlled, crossover study of 20 allergic subjects out of season. The subjects received placebo or clemastine administered one, four, and six hours before the challenges. Filter paper discs were used both to challenge the nasal mucosa with diluent and allergen and collect generated secretions. Sneezes, secretion weights, nasal and ocular symptoms, and albumin levels in nasal secretions were monitored for the nasal challenge. Intradermal skin testing was performed with diluent followed by histamine and the wheal and flare reactions were measured.
Results: There was a significant reduction in the number of sneezes after clemastine administered one, four, and six hours prior to challenge compared with placebo (P < .01). Clemastine administered four and six hours before challenge reduced sneezing significantly more than clemastine administered one hour before challenge (P < .05). Antigen-induced increases in secretion weights and symptoms of rhinorrhea were significantly reduced compared with placebo only when clemastine was administered four and six hours prior to challenge (P < .05). Pretreatment with clemastine had no significant inhibitory effects on other nasal symptoms or on albumin levels in nasal secretions, an objective index of increased vascular permeability. Pretreatment with clemastine did not inhibit the histamine-induced wheal skin reaction but showed a tendency, when administered six hours prior to the intradermal challenge, to reduce the flare reaction induced by the lowest dose of histamine (P = .05).
Conclusions: The data show that clemastine, given at half the usual dose four and six hours prior to allergen challenge, provides relief for sneezing and rhinorrhea and suggests that this dose might be useful in the treatment of allergic rhinitis.