SAN FRANCISCO — Almost half of patients on flexible-dosing schedules of extended-release oxybutynin for urge incontinence chose a dose of more than 10 mg/day, the level employed in two fixed-dose trials of the medication, Peter K. Sand, M.D., and Scott A. MacDiarmid, M.D., reported in a poster presentation at the annual meeting of the American College of Obstetricians and Gynecologists.
In a combined analysis of 368 patients from three clinical trials employing flexible dosing schedules of 5–30 mg/day, 47% of participants chose a final dose of 15, 20, 25, or 30 mg/day.
At all selected final doses of oxybutynin, 77%–83% of the patients reportedly achieved a reduction of at least 70% in the number of urge incontinence episodes, according to Dr. Sand of Northwestern University, Chicago, and Dr. MacDiarmid of Wake Forest University, Winston-Salem, N.C.
At final doses of 5 mg to 25 mg/day, patients achieved a reduction of about 85% in the number of urge incontinence levels.
But at 30 mg/day, the reduction in episodes was only 61%.
Given that the incidence of dry mouth (the most common side effect) was similar to that in the other groups, the investigators suggested that the finding of relatively low efficacy in the highest dose may be due to a relative insensitivity to anticholinergics among some of the patients.
Overall, 23.1% had moderate or severe dry mouth, but only 5 (or 1.4%) withdrew from their trial for this reason.
Ortho-McNeil Pharmaceutical Inc. sponsored the analysis.