Rationale Given the known effectiveness of tiotropium in chronic obstructive pulmonary disease (COPD) and the significant benefit observed in COPD patients with concomitant features of asthma, it is relevant to investigate whether patients included in the recent large trials of tiotropium in asthma can be confidently considered to have asthma alone.

Methods Baseline characteristics were analysed for patients enrolled in two replicate Phase III, randomised, double-blind, placebo-controlled, parallel-group studies of tiotropium in asthma patients symptomatic despite treatment with inhaled corticosteroids plus long-acting beta agonists (Kerstjens et al. NEJM 2012). The entry criteria were: age 18–75 years; asthma diagnosed before the age of 40 years; =5-year history of asthma; score of =1.5 in the Asthma Control Questionnaire (ACQ) 7; and life-long non-smokers or ex-smokers (<10 pack-years). Patients were also required to have persistent airflow limitation. Asthma diagnosis was confirmed in line with current Global Initiative for Asthma guidelines. Patients with a diagnosis of COPD or other lung disease were excluded from the studies.

Results 912 patients were enrolled: 456 received add-on treatment with tiotropium and 456 received placebo. Mean age of the study population was 53.0 years; 37.6% of patients were aged =50 years. Mean age at diagnosis of asthma was 22.7 (range 0–44) years. Median duration of asthma was 28.0 (range 5–72) years, with 76.5% of patients having asthma for =20 years before enrolment. The majority of patients (75.9%) were life-long non-smokers; 24.1% were ex-smokers with a median number of pack-years of only 5.0. Mean ACQ score was 2.6 (range 1–5). Mean immunoglobulin E was 1210 µmol/L. The mean ( ± SD) bronchodilator response to salbutamol was 217 ± 217 mL.

Conclusions The age of onset, duration of symptoms, lack of smoking, allergic status and bronchodilator response provide reasonable certainty that the patients enrolled in these studies had asthma and not COPD. Features compatible with COPD were thus more likely to reflect the effects of long-standing severe persistent asthma than the alternative diagnosis, and the efficacy demonstrated by tiotropium to represent improvement of asthma.