CRD Summary: This review concluded that the use of tiotropium was beneficial in treatment of patients with moderate-to-severe stable chronic obstructive pulmonary disease. Previous evidence in favour of the superiority of tiotropium over long-acting beta-agonists was also supported. As the results may not be generalisable and potential bias was possible, these conclusions may not be reliable.

[Parallel or crossover randomised controlled trials (RCTs) comparing inhaled tiotropium bromide with placebo, inhaled ipratropium bromide or inhaled long-acting beta-agonists (e.g. salmeterol) were eligible for inclusion.]

CRD Commentary: This research question was well defined and the inclusion criteria were clear with regard to participants, intervention, outcomes and study design. The authors searched for published and unpublished studies with no language restrictions, reducing the possibility of publication and language bias. Study selection was performed independently by two reviewers reducing the possibility of reviewer bias and error. However, the processes by which data were extracted and validity was assessed were not clearly reported, so although it appeared that similar steps were taken, it was not certain. Validity of the primary studies was assessed appropriately. The clinical characteristics of the study population were quite similar. Statistical heterogeneity also assessed and investigated where present. There may be issues regarding generalisability, as the majority of patients were male. Also, patients were double counted, which increased the sample size and might have biased the results. Due to the potential for bias, the authors' conclusions may not be reliable.