Purpose: We have evaluated the clinical and urodynamic effects of intravesical instillation of resiniferatoxin in patients with idiopathic detrusor instability refractory to anticholinergics. Materials and Methods: There were 30 women, median age 56 years old with detrusor instability for over 6 months and a history of anticholinergic use with no response or intolerable collateral effects. A 50 nM solution of resiniferatoxin was prepared for intravesical instillation. All patients were evaluated for urinary symptoms, as well as for urodynamic assessments before and 30 days after instillation. Tolerability was analyzed during the instillation. Results: A clinical improvement was observed in 30% of the patients with urinary urgency and in 33% of the patients with urge-incontinence. The mean maximum cystometric capacity before application was 303.9 ± 78.9 and after application 341 ± 84.6. No significant difference was observed (p = 0.585). The mean maximum amplitude of the contractions diminished from 47.86 ± 29.64 to 38.72 ± 30.77 (p = 0.002). Conclusions: Resiniferatoxin, in this concentration, proved to be useful in a small percentage of patients regarding clinical detrusor instability. Maximum amplitude of the involuntary contractions was significantly reduced and in 33% patients the involuntary contractions disappeared. Further studies with different concentrations are recommended.3015358Abrams, P., Blaivas, J.G., Stanton, S.L., Andersen, J.T., The standardisation of terminology of lower urinary tract function (1988) Scand. J. Urol. Nephrol. Suppl., 114, pp. 5-19. , The International Continence Society Committee on Standardisation of TerminologyDe Groat, W.C., A neurological basis for the overactive bladder (1997) Urology, 50 (SUPPL. 6A), pp. 36-52O'Reilly, B., Kosaka, A.H., Knight, G.F., Chang, T.K., Ford, A.P., Rymer, J.M., P2X receptors and their role in female idiopathic detrusor instability (2002) J. Urol., 167, pp. 157-164Brading, A.F., A myogenic basis for the overactive bladder (1997) Urology, 50 (SUPPL. 6A), pp. 57-67Chapple, C.R., Muscarinic receptor antagonists in the treatment of overactive bladder (2000) Urology, 55 (SUPPL. 5A), pp. 33-46Szallasi, A., Blumberg, P.M., Resiniferatoxin and analogs provide novel insights into the pharmacology of the vanilloid receptor (1990) Life Sci., 47, pp. 1399-1408Silva, C., Ribeiro, M.J., Cruz, F., The effect of intravesical resiniferatoxin in patients with idiopathic detrusor instability suggests that involuntary detrusor contractions are triggered by C-fiber input (2002) J. Urol., 168, pp. 575-579Szallasi, A., Conte, B., Goso, C., Blumber, P.M., Manzini, S., Vanilloid receptors in the urinary bladder: Regional distribution, localization on sensory nerves, and species-related differences (1993) Naunyn Schmiedebergs Arch. Pharmacol. [Multi], 347, p. 624Yokoyama, O., Komatsu, K., Kodama, K., Yotsuyanagi, S., Niikura, S., Namiki, M., Diagnostic value of intravesical lidocaine for overactive bladder (2000) J. Urol., 164, pp. 340-343Lazzeri, M., Beneforti, P., Turini, D., Urodynamic effects of intravesical resiniferatoxin in humans: Preliminary results in stable and unstable detrusor (1997) J. Urol., 158, pp. 2093-2096Cruz, F., Guimarães, M., Silva, C., Reis, M., Supression of bladder hyperreflexia by intravesical resiniferatoxin (1997) Lancet, 350, pp. 640-641Hayes, P., Meadows, H.J., Gunthorpe, M.J., Harries, M.H., Duckworth, D.M., Cairns, W., Cloning and functional expressions of a human orthologue of rat vanilloid receptor-1 (2000) Pain, 88, pp. 205-215Steers, W.D., Rat: Overview and innervation (1994) Neurourol. Urodyn., 13, pp. 97-118Avelino, A., Cruz, C., Nagy, I., Cruz, F., Vanilloid receptor 1 expression in the rat urinary tract (2002) Neuroscience, 109, pp. 787-798