The bronchial response to mannitol is attenuated by a previous methacholine test: but not vice versa

Summary Aim To examine the airway response to inhaled mannitol performed before or after a methacholine challenge test in a group of asthmatics with different levels of disease. Methods A total of 48 asthmatics, 18–73 years of age, were included in the study. Two pairs of challenges were performed in a random order on two separate days 24 h apart: either with mannitol performed first on day one, followed 1 h by methacholine, and methacholine as the first on day two, followed 1 h by mannitol or vice versa. A questionnaire-based interview was performed and lung function, exhaled nitric oxide, skin prick test, and blood eosinophil count were measured. Results A total of 44% of the asthmatics used inhaled corticosteroids and 48% were atopic. The airway response to mannitol was attenuated when mannitol was given after methacholine, compared with the response to mannitol when it was given first [log response dose ratio (RDR): 1.42 vs. 1.60 (P=0.004)], whereas the response to methacholine was unchanged in the opposite test order [log RDR: 0.81 vs. 0.96 (P=0.102)]. Conclusion Bronchial challenges with inhaled mannitol and methacholine may be performed on the same day but provocation with mannitol should be performed before methacholine.