Hypothesis: The endothelin-1 receptor antagonist, bosentan when added to the treatment of
asthma patients who are symptomatic despite the use of controller therapy will improve asthma
symptoms and physiology.
Twenty patients with a diagnosis of asthma, between the ages of 21 and 70 who are symptomatic
despite the use of at least one controller medication will be randomized to either placebo or
active medication for an 8 week period (initial 4 weeks is at 1/2 of final dose as per
package insert and FDA approval). Measures of lung function and symptoms will be recorded.
Patients will then cross over, so that patients initially on placebo will receive active drug
for 8 weeks and those initially on active drug will receive placebo. The same endpoints will
be measured. The acute bronchodilator effects of the drug will also be tested on the first
day of therapy at the full therapeutic dose.