Capsaicin is an extract from red pepper and exerts a selective action on certain sensory nerves, most notably those involved in reflex contractions of the bladder after SCI.
One RCT (n=23) (Giannantoni et al. 2002) and one pre-post study (n=7) (Igawa et al. 2003) evaluated the effect of capsaicin. Capsaicin exerts a selective action on those sensory nerves involved in reflex contractions of the bladder after SCI. In their pre-post study, Igawa et al. (2003) demonstrated that intravesical capsaicin decreased episodes of AD in patients with SCI during catheterization, thereby suggesting the therapeutic potential of intravesical capsaicin for both AD and detrusor hyperreflexia in SCI patients (Igawa et al. 2003). Giannantoni et al. (2002) in a high quality RCT (PEDro=6) used an analogue of capsaicin (resiniferatoxin RXT) that is more than 1,000 times more potent in desensitizing C-fiber bladder afferents and found reduced episodes of AD (Giannantoni et al. 2002). In addition, investigators found that intravesical administration of resiniferatoxin was superior to that of intravesical capsaicin in terms of urodynamic results and clinical benefits in SCI patients within 60 days of treatment and did not cause the inflammatory side effects associated with capsaicin. Long-term effects of capsaicin or resiniferatoxin on AD, however, have not been evaluated.
There is level 4 evidence (from 1 pre-post study: Igawa et el. 2003) that intravesical capsaicin is effective for reducing episodes of AD in SCI.
There is level 1 evidence (from 2 RCTs: Kim et al. 2003; Giannantoni et al. 2002) that intravesical resiniferatoxin is effective for reducing episodes of AD in patients with SCI.
There is level 1 evidence (from 1 RCT: Giannantoni et al. 2002) that intravesical resiniferatoxin is more effective than intravesical capsaicin.