Muscarinic Receptor Antagonism and Allergen Induced Airway Responses in Allergic Asthma: A Scoping Review.

Purpose: The purpose of this scoping review was to identify existing clinical and basic science knowledge surrounding the effect of muscarinic receptor antagonism on allergen-induced airway responses to inform future clinical research in this area.

Methods: Multiple advanced searches were performed using the National Library of Medicine PubMed search engine. Each search began with two terms; for example, "atropine and asthma" or "tiotropium and airway inflammation". Results were then further refined to include terms such as "allergen" or "ovalbumin (OVA)". Abstracts of refined searches were reviewed for relevance to allergic asthma and allergen-induced airway responses including the early and late asthmatic responses, airway inflammation and tissue remodelling. There was no restriction regarding publication date. Reference lists of selected papers were also reviewed for relevant publications.

Results: Nine human clinical trial publications and fourteen animal model publications were identified. In humans, single dose atropine (n=4), ipratropium (n=4) or oxitropium (n=1) administered pre-challenge produced equivocal effects on allergen-induced early asthmatic responses as reported but favored inhibition in eight of nine studies after re-analyses. Animal model investigations (n=14) showed mostly favorable results, especially with respect to airway inflammation and tissue remodelling, although two studies were negative, and one study showed a worsening in allergen induced airway inflammation following muscarinic receptor antagonism.

Conclusion: Existing human and animal model data suggest muscarinic receptor antagonism may be beneficial in preventing allergen induced airway responses in those with allergic asthma. Additional human research utilizing current standardized methodologies is required.