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n a large-scale, randomized, placebo-controlled clinical trial, patients treated with transdermal oxybutynin (Oxytrol™) achieved statistically significant reductions in symptoms of overactive bladder, and an incidence of anticholinergic side effects comparable to those observed in the placebo group. The study, involving patients at 40 medical centers in the United States, was conducted by the Transdermal Oxybutynin Study Group headed by G. Willy Davila, MD, Chairman of the Department of Gynecology at Cleveland Clinic Florida. Dr. Davila reported the findings at the 22nd Annual Scientific Meeting of the American Urogynecologic Society in Chicago on October 26, 2001.
       In this study, 520 patients were randomized to receive a placebo patch or patches delivering either 1.3mg/day, 2.6mg/day, or 3.9mg/day of the active drug. The patches were applied twice weekly for 12 weeks, followed by a 12-week open-label, dose titration phase. More than 90 percent of the patients were women, and more than 90 percent were Caucasian; the average age was about 61 years.
       The 3.9mg/day transdermal oxybutynin group had significantly greater improvements compared with placebo (p < 0.05) in the median number of incontinence episodes per week, median change in micturition (urination) frequency per day, increase in urine volume per urination, and scores on incontinence questionnaires.
       Itching (pruritus) at the patch site was the most common adverse event, reported in 16.8 percent of patients in the 3.9mg/day group. Dry mouth occurred in 9.6 percent of patients in the 3.9mg/day transdermal oxybutynin group and in 8.3 percent of those receiving placebo. Seventy-three patients withdrew at the end of the double-blind phase (including active group and placebo patients); 53 (approximately 10 percent) of them due to adverse events. The vast majority of the eligible patients at the end of the randomization phase (92%) entered into the 12-week open-label extension, of which 87 percent completed. At the end of the open-label extension, further decreases in incontinent episodes were seen for all active groups.
       One theory for the observed reduction in anticholinergic side effects is the novel delivery system. Transdermal oxybutynin bypasses presystemic liver and gastrointestinal metabolism, resulting in a decreased production of a metabolite suspected to cause uncomfortable side effects, such as dry mouth.
       Watson Pharmaceuticals’ new drug application for transdermal oxybutynin is currently under review at the Food and Drug Administration.