The pathophysiology of faecal spotting in obese subjects during treatment with orlistat.

Author(s): Fox M, Thumshirn M, Menne D, Stutz B, Fried M, Schwizer W

Affiliation(s): Department of Gastroenterology and Hepatology, University Hospital of Zurich, Zurich, Switzerland Menne Biomed, Tubingen, Germany.

Publication date & source: 2004-02-01, Aliment Pharmacol Ther., 19(3):311-21.

Publication type: Clinical Trial; Randomized Controlled Trial

BACKGROUND: The intermittent loss of oil or liquid faeces ('spotting') is an adverse effect that occurs in obese patients during treatment with the lipase inhibitor orlistat; the pathophysiology is unknown. AIM: To investigate the effects of orlistat on anorectal sensorimotor function and continence. METHODS: Obese subjects susceptible to spotting were identified by an unblind trial of orlistat. Obese spotters (n = 15) and non-spotters (n = 16) completed a randomized, double-blind, cross-over trial of orlistat and placebo. Anorectal function was assessed by rectal barostat and anal manometry, together with a novel stool substitute retention test, a quantitative measurement of faecal continence. RESULTS: Orlistat increased stool volume and raised faecal fat and water. Treatment had no effect on anorectal motor function, but rectal sensation was reduced; on retention testing, the volume retained was increased. Subjects susceptible to spotting had lower rectal compliance, heightened rectal sensitivity and weaker resting sphincter pressure than non-spotters. On retention testing, gross continence was maintained; however, spotters lost small volumes of rectal contents during rectal filling. CONCLUSION: Treatment with orlistat has no direct adverse effects on anorectal function or continence. Spotting occurs during treatment with orlistat when patients with sub-clinical anorectal dysfunction are exposed to increased stool volume and altered stool composition.