We did a prespecified analysis of the ADRB2 polymorphisms Arg16Gly and Gln27Glu within the 1 year randomised , double-blind , double-dummy , parallel-group Prevention Of Exacerbations with Tiotropium in COPD ( POET-COPD ) trial , comparing the effects of treatment with tiotropium or salmeterol on exacerbations in 7376 patients with COPD .