Background The Minimal Clinically Important Difference (MCID) for pharmacotherapy for the endurance shuttle walking test (ESWT) has been reported by Pepin et al.¹ Two performance measures, change in time (45– 85 s), and percentage change from baseline (13–15%) are investigated here.

Objective To review endurance outputs in two exercise studies combined in this post-hoc analysis, and compare two different measures of performance MCID, exercise time in seconds and as a percentage change.

Methods The effect of umeclidinium (UMEC 62.5 mcg)/vilanterol (VI 25 mcg), VI (25 mcg) and UMEC (62.5 mcg) compared with placebo on exercise endurance, using the ESWT across two 12-week cross-over studies enrolling hyperinflated COPD patients (FRC >120%) was investigated. All ESWTs were performed at 80% VO₂ max derived from a baseline incremental SWT. ESWT time (in seconds) and% change from baseline were reported and compared at Day 2 and 84, 3 h post-dose. Analysis was performed using a repeated measures model with covariates of study, period walking speed, mean walking speed, period, treatment, visit, smoking status, centre group, visit by period walking speed, visit by mean walking speed and visit by treatment interactions.

Results Baseline exercise endurance times (EET) and on-treatment change from baseline as seconds and percentage are presented in Table 1. UMEC/VI showed mean changes (95% CI) from placebo at Day 2 of 53.0s (33.4, 72.6) and 18.4% (10.1, 26.8) both p < 0.001 and at Day 84 of 43.7s (15.5, 72.0) p = 0.002 and 16.4% (4.8, 27.9) p = 0.005. Adverse events were similar between treatments.

Conclusions UMEC/VI was associated with improvements in both measures of exercise endurance, as were UMEC and VI to a lesser magnitude. An improvement greater than the MCID for percentage change from baseline was observed for UMEC/VI vs placebo at both timepoints, whereas for change from baseline EET only the Day 2 analysis vs placebo showed a result greater than the MCID. MCID as percentage change from baseline may be a more meaningful measure of response to bronchodilators than MCID in seconds because it reflects a patient’s baseline exercise tolerance. No additional safety concerns were identified.

Funding GSK Clinicaltrials.gov: NCT01328444, NCT01323660

Reference 1 Pepin V, et al. Thorax 2011;66(2):115–20