In a crossover design, Kerstjens et al randomized 100 patients with uncontrolled severe asthma (despite high dose inhaled corticosteroid and long-acting beta agonist) to also receive tiotropium 5 mcg, tiotropium 10 mcg, and placebo (in random order) for 8 weeks each.
Tiotropium improved peak FEV1 at both doses (increase of 139-170 mL, the primary endpoint). There were no detectable differences in meaningful clinical outcomes (asthma-related health status or asthma symptoms). Patients taking the high dose of tiotropium complained of dry mouth.
The study, and its lead author, are supported by Boehringer Ingelheim and Pfizer. Add this to Peters et al's showing noninferiority of tiotropium to long-acting beta-agonist in 210 patients in a randomized trial in N Engl J Med in 2010 (critiques). Spiriva is not expected to gain a new FDA indication for asthma for at least the next 2 years.