A pilot study of the effects of sildenafil on stool characteristics, colon transit, anal sphincter function, and rectal sensation in healthy men

Dig Dis Sci. 2005 Jun;50(6):1005-11. doi: 10.1007/s10620-005-2695-5.


Nitric oxide is an important mediator of gut smooth muscle relaxation and visceral sensation. Sildenafil results in stimulation of the nitric oxide-cyclic GMP pathway. We sought to determine the effects of daily sildenafil administration on colorectal function. Over a 4-week period, sildenafil was administered during weeks 2 and 3. Stool frequency and consistency were assessed daily. Anorectal manometry, rectal sensation, and colon transit testing were performed at the end of weeks 1 and 3. Ten healthy men were studied. No significant differences in segmental or total colon transit time were noted; however, significant changes in stool frequency and trends toward decreased stool consistency were noted during sildenafil use. A trend toward reduced resting anal sphincter pressure was seen after sildenafil. Rectal volumes to first sensation and desire to defecate were significantly increased after sildenafil on test day 2 only. Additionally, volumes to desire to defecate and maximal tolerable volume were significantly increased before sildenafil on test day 2 compared to before sildenafil on test day 1. We conclude that daily administration of sildenafil is well tolerated and results in alterations in colorectal function.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Anal Canal
  • Colon / drug effects
  • Defecation / drug effects*
  • Feces
  • Gastrointestinal Transit / drug effects*
  • Humans
  • Intestine, Large / drug effects*
  • Male
  • Manometry
  • Middle Aged
  • Nitric Oxide / metabolism
  • Phosphodiesterase Inhibitors / pharmacology*
  • Pilot Projects
  • Piperazines / pharmacology*
  • Purines
  • Rectum / drug effects
  • Sensation / drug effects
  • Sildenafil Citrate
  • Sulfones


  • Phosphodiesterase Inhibitors
  • Piperazines
  • Purines
  • Sulfones
  • Nitric Oxide
  • Sildenafil Citrate