Randomized Trial of Oxybutynin Extended Versus Immediate Release for Women Aged 65 and Older with Overactive Bladder: Lessons Learned from Conducting a Trial

Objective: This trial was designed to investigate the effectiveness of extended release versus immediate release oxybutynin in reducing symptoms of overactive bladder in a community-dwelling female population over the age of 65. Methods: This was a prospective randomized 12-week, open-label study. The primary outcome was number of micturitions per 24 hours, 12 weeks after treatment. The a priori sample size estimate was 60 patients per group. Results: Of the 318 women approached, only 72 women (23%) were enrolled over 34 months (33 in the immediate release group, and 39 in the extended release group). The study was stopped prematurely because of recruitment difficulties and an interim analysis revealing the need for a much larger sample than had been estimated to show a significant difference between treatments. After 12 weeks of treatment, there was no difference between the oxybutynin extended release and immediate release groups in the number of micturitions per 24 hours or in other outcomes. Conclusion: This study did not demonstrate differences between oxybutynin extended release and immediate release and in reducing symptoms of overactive bladder or quality of life, possibly because the study did not reach the necessary sample size. The difficulty in recruiting subjects for the trial likely resulted from the onerous study requirements (4 study visits required over 12 weeks) and the downtown location of the study centres: these factors would cause particular difficulties for women over age 65 with overactive bladder, for whom travelling may be a problem. Evidence is needed to guide prescribing for older patients, but designing research to obtain adequate sample sizes is difficult. Studies in older subjects should ensure that a much larger budget is allocated for recruitment than would be allocated for studies in younger subjects, that meticulous attention is paid to issues of transport and access, and that support is provided for subjects who agree to take part in research.