Inhaled clemastine, an H1 antihistamine inhibits airway narrowing caused by aerosols of non-isotonic saline.

Asthmatic subjects were challenged with aerosols of hyper- and hypotonic saline 15 min (Group A) and 90 min (Group B) after inhaling clemastine. Measurements were made of forced expiratory volume in one second (FEV1) before and after medication and after challenge. When the FEV1 values (% predicted) were compared on the active and placebo days they were higher 15 min after clemastine (p less than 0.05) for both challenges and higher 90 min after clemastine inhalation (p less than 0.05) for the hypertonic challenge. The % fall in FEV1 was compared after the same concentration of saline aerosol had been given on both active and placebo days. In Group A the % fall in FEV1 on the clemastine day was reduced after challenge with hypertonic (p less than 0.02) and hypotonic (p less than 0.03) aerosol. In Group B there was a reduction in the % fall in FEV1 on the clemastine day only after hypertonic challenge (p less than 0.04). The protective effect afforded by clemastine was unrelated to change in baseline lung function. We conclude that histamine is an important mediator of the airway response to non-isotonic aerosols and suggest that the aerosol route of administration may be useful for delivering antihistamines.