Intravesical capsaicin and resiniferatoxin therapy: spicing up the ways to treat the overactive bladder.

Pharmacological treatment of the overactive bladder relies on partially blocking the efferent parasympathetic innervation to the detrusor with anticholinergic drugs. However, often these drugs have troublesome side effects and doses are insufficient to restore continence in patients with detrusor instability. We present the background, basic and clinical research with intravesical instillation of capsaicin and resiniferatoxin as treatments for the overactive bladder. Capsaicin, the main pungent ingredient in hot peppers of the genus Capsicum, is a specific neurotoxin that desensitizes C fiber afferent neurons which may be responsible for signals that trigger detrusor overactivity. In the last 6 years studies have demonstrated encouraging improvement in lower urinary tract symptoms with minimal long-term complications. Most of these studies have also demonstrated that the acute pain and irritation associated with capsaicin are major deterrents to widespread use. Therefore, resiniferatoxin, an ultra-potent analogue of capsaicin which appears to have similar efficacy but less acute side effects, may be more useful. Intravesical capsaicin and resiniferatoxin are novel and promising treatments for the overactive bladder, with profound basic and clinical implications.