NEW YORK (Reuters Health) – A dose-ranging study of onabotulinumtoxinA, better known as Botox, injected into the detrusor muscle for the treatment of refractory overactive bladder indicates that a dose of 100 U provides the best symptom relief with the least effect on post-void residual urine volume.

That result, from a phase II multicenter randomized trial, is reported by Dr. Roger Dmochowski of Vanderbilt University in Nashville, Tennessee, and colleagues in the December issue of the Journal of Urology, issued online October 18.

Several trials have studied the treatment of overactive bladder using intradetrusor injections of botulinum toxin A (now designated onabotulinumtoxinA to distinguish it from other formulations with different unit strengths). The current study was designed to examine the dose-response relationship in order to establish the best balance between efficacy and safety.

The team randomly assigned 313 patients with idiopathic overactive bladder to a double-blind single treatment with placebo or onabotulinumtoxinA at doses of 50, 11359, 150, 200 or 300 U. After 12 weeks, the reduction in weekly urinary urgency incontinence (UUI) episodes in the six treatment groups was -17.4, -20.7, -18.4, -23.0, -19.6 and -19.4, respectively.

Although those numbers did not indicate a clear dose response,