A Cochrane review (abstract , review [Abstract]) included 8 studies with a total of 194 patients. Three papers compared the effects of anticholinergic drugs with placebo, and a meta-analysis of these results demonstrated no statistically significant benefit of the use of anticholinergic drugs over placebo in any of the outcome measures used. Two studies compared the addition of an anticholinergic drug to a beta-2 agonist with the beta-2 agonist alone. Both trials failed to show any significant benefit from the long term use of combined anticholinergics with beta-2 agonists compared with beta-2 agonists alone.
Comment: The quality of evidence is downgraded by study quality (inadequate or unclear allocation concealment) and by imprecise results (few patients and wide confidence intervals).
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