The doses of tiotropium and olodaterol used in these studies were based on previously published dose–response studies of this drug combination [21, 22]. In the latter, although a dose response for lung function was observed with increasing doses of tiotropium added to a fixed dose of olodaterol, the increase with tiotropium 2.5 µg when added to olodaterol was smaller than the increase with 5 µg when added to olodaterol [21, 22]. Overall, based on the results of the current studies and TIOSPIR, the optimum dose of tiotropium is considered to be 5 µg, both as monotherapy and in combination with olodaterol.