Refractoriness to inhaled mannitol 3 hours after allergen challenge

Background: A positive response to indirect airway challenges (eg, mannitol) that cause release of mast cell mediators causes refractoriness to a repeat exposure to the same or different indirect stimulus that lasts for at least several hours. Allergen challenge causes increased response to methacholine measured at 3 hours. Objective: To compare allergen-induced changes in airway response to methacholine and mannitol 3 hours after completion of an allergen challenge. Methods: Ten atopic patients with asthma completed a randomized clinical trial. The provocation concentration of methacholine causing a 20% decrease in forced expiratory volume in 1 second (FEV1) was measured 24 hours before and 3 hours after a standard allergen challenge. The provocation dose of mannitol causing a 15% decrease in FEV1 was also measured 24 hours before and 3 hours after allergen challenge. The allergen challenges were separated by 7 to 14 days. Results: The allergen-induced early responses, expressed as the maximum (SD) percent decrease in FEV1, were 29.7% (11.1%) and 27.8% (7.6%) on the methacholine and mannitol days, respectively. Airway response to methacholine increased significantly after allergen challenge (P = .02). By contrast, the airway response to mannitol was reduced by almost a doubling dose (P = .02) after allergen. Conclusion: Three hours after allergen challenge at a time when the airways are more responsive to methacholine, there is a significant refractoriness to the indirect stimulus mannitol. (C) 2013 American College of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.