Study is looking at the development of tolerance to methacholine following regular use of ipratropium bromide in mild asthmatics.

This study is being conducted people with well controlled (mild) asthma to determine if ipratropium bromide taken three times daily for six days (i.e. 2 puffs in the morning, 2 puffs in the afternoon and 2 puffs in the evening) followed by a final dose on the morning of day 7 reduces the effectiveness of this medication on blocking the effect of methacholine challenge.

Inclusion Criteria:

• airway responsiveness to methacholine
• adequate baseline lung function
• no respiratory infection or exposure to stimuli that may alter response to methacholine within 4 weeks

Exclusion Criteria:

• pregnancy
• current smoker
• requirement for medications other than salbutamol that will interfere with airway response to methacholine