Evaluating the Impact of Single Dose Tiotropium on Allergen-induced Early Asthmatic Response

Inclusion Criteria: * age (years) at least 18 years * no confounding health issue (i.e. no health conditions, other than asthma, that would put the participant at risk or affect data integrity as determined by the principal investigator) * baseline FEV1 ≥ 65% of predicted normal at Visit 1 * evidence of atopy to an allergen suitable for inhalation challenge following skin prick testing such as house dust mite, grass, cat or horse * fall in FEV1 of ≥ 20% at a dose of methacholine ≤ 600mcg (methacholine PD20) at Visit 1 * positive response to allergen inhalation challenge (fall in FEV1 of ≥ 15% after inhalation of allergen at a dilution 1:32 or more dillute. * absence of respiratory infection for at least 4 weeks prior to Visit 1 * absence of significant worsening of asthma that requires health care intervention or prolonged change in medication due to allergen exposure (or other trigger) for at least 4 weeks prior to Visit 1 * women of child-bearing potential shall not be pregnant or lactating * non-smoker (cigarettes, vaping); ex-smoker with \<10 pack year history allowed; cannabis use will be evaluated on a case-by-case basis * if on as needed budesonide/formoterol therapy, no reported use within 3 weeks prior to allergen challenge Exclusion Criteria: * Smoker \>10 pack year history