Systematic review and meta-analysis: do clinical trials testing antimuscarinic agents for overactive bladder adequately measure central nervous system adverse events?

Experimental studies in healthy volunteers suggest that some antimuscarinic agents confer a risk of cognitive impairment, yet clinical trials of people with overactive bladder report only rare central nervous system (CNS) side effects. A lack of systematic measurement and reporting of CNS outcomes in clinical trials may partially explain this discrepancy. The purpose of this review and meta-analysis was to ascertain the reporting bias associated with adverse CNS events in clinical drug trials of younger and older adults with overactive bladder. Articles were identified from MEDLINE and EMBASE databases until 2010 using the search terms "clinical trial" AND (one of) "oxybutynin, tolterodine, fesoterodine, propiverine, solifenacin, darifenacin, and trospium." Eligibility criteria included original randomized trials involving adults with overactive bladder; standard doses of medication; reports of confusion, somnolence, sedation, dizziness, drowsiness, asthenia, insomnia, and vertigo; no evidence of dementia at baseline; and trials in English. Seventy-seven percent (242/314) of eligible trials identified in the search neither measured nor reported CNS outcomes. Of the remaining 23%, it was difficult to distinguish whether CNS adverse events were systematically measured or spontaneously reported. Only one of 72 trials that were retained objectively measured changes in cognitive performance (Mini-Mental State Examination). Dizziness was the most frequently reported side effect, in 3% of oxybutynin, 3.2% of propiverine, and 1.8% of tolterodine users, compared with 1.6% with placebo. Confusion was reported in fewer than 1% of cases. Age-stratified analyses of CNS outcomes from trials in adults aged 65 and older with overactive bladder were found in only eight publications. Meta-analyses were conducted with 33 randomized, double-blind, placebo-controlled trials to determine the effect of each drug and dose on different CNS outcomes. Study heterogeneity, dosing inconsistency, and reporting bias limited interpretation of the findings from the meta-analyses. More-detailed standardized measurement of age-stratified CNS outcomes in clinical trials is required to better inform patients and clinicians about CNS risks associated with antimuscarinic agents.