Conclusions: The TIOSPIR® spirometry substudy showed that tiotropium Respimat® 5 μg was noninferior to tiotropium HandiHaler® 18 μg for trough FEV 1 , but Respimat® 2.5 μg was not. Tiotropium Respimat® 5 μg provides similar bronchodilator efficacy to tiotropium HandiHaler® 18 μg with comparable rates of FEV 1 decline. The rate of FEV 1 decline varied based on disease severity, with a steeper rate of decline observed in patients with moderate airway obstruction.Trial registrationNCT01126437. (Source: Respiratory Research)