New specific antimuscarinic for overactive bladder

PHARMACOLOGY
Darifenacin is a selective muscarinic M₃ receptor antagonist that blocks the stimulation of the M₃ receptors. These are the receptors primarily responsible for controlling detrusor contractions.

CLINICAL STUDIES
The efficacy of darifenacin was assessed in four double-blind, Phase III, randomised, controlled studies in male and female patients with symptoms of overactive bladder.

A pooled analysis of three of the Phase III studies involving 1059 patients, each randomised to receive darifenacin 7.5mg or 15mg once daily, or placebo for 12 weeks was conducted.¹ The primary endpoint was reduction in incontinence episodes versus placebo.

Following 12 weeks of treatment, darifenacin 7.5mg once daily and 15mg once daily significantly reduced the median number of incontinence episodes per week compared to placebo. Also, both the 7.5mg and 15mg treatment groups showed significant decreases in the frequency and severity of urgency, voiding frequency and number of significant leaks (incontinence episodes resulting in a change of clothing or pads) compared to placebo. There was a significant dose response trend evident between the two darifenacin treatment groups. The treatment effect between males and females was similar.

Overall, darifenacin was well tolerated across all studies. The most common adverse effects were dry mouth, headache, abdominal pain, dyspepsia and nausea.

1. Chapple C, Steers W, Norton P et al. A pooled analysis of three phase III studies to investigate the efficacy, tolerability and safety of darifenacin, a muscarinic M3 selective receptor antagonist, in the treatment of overactive bladder. BJU International 2005:95(7); 993-1001.

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