A Cochrane review included 19 studies. Participants had either neurogenic or idiopathic overactive bladder with or without stress incontinence. Comparison interventions included no intervention, placebo, lifestyle modification, bladder retraining, pharmacological treatments, surgery, bladder instillation techniques, neuromodulation and different types, doses, and injection techniques of botulinum toxin. Lower doses of botulinum toxin (100 to 150 U) appeared to have beneficial effects, but larger doses (300 U) may have been more effective and longer lasting, but with more side effects. All studies followed participants after a single intravesical injection of BTX, except in one study the participants were reinjected every six months. The length of predetermined follow up varied from six weeks in to 24 months in.
For the most part, studies reported superiority of botulinum toxin A to placebo in such outcomes as incontinence episodes, bladder capacity, maximum detrusor pressure, and quality of life. Low doses of botulinum toxin (100 U to150 U) appeared to have beneficial effects, but higher doses (300 U) may have been more effective. As the great majority of participants in the studies reviewed had neurogenic overactive bladder, the results may not be generalisable to patients with idiopathic overactive bladder.
Comment: The quality of evidence is downgraded by imprecise results (limited study size for each comparison) and by inconsistency (heterogeneity in interventions and outcomes).