Topical phenylephrine increases anal sphincter resting pressure

Background: Phenylephrine is an alpha(1)-adrenergic agonist which causes co ntraction of human internal anal sphincter muscle in vitro. Its intra-arter ial administration in animals has been shown to increase resting sphincter pressure in vivo. In this study the effect of topical application of phenyl ephrine on resting anal pressure in healthy human volunteers was investigat ed. Methods: Twelve healthy volunteers had measurements of maximum resting sphi ncter pressure (MRP) and anodermal blood flow taken before and after topica l application of increasing concentrations of phenylephrine gel to the anus . To determine the duration of effect of the agent, readings were taken thr oughout the day after a single application. Results: There was a dose-dependent rise in the resting anal sphincter pres sure, with a small 8 per cent rise after 5 per cent phenylephrine (P = 0.01 2) and a larger 33 per cent rise with 10 per cent phenylephrine (mean(s.d.) MRP 85(12) cmH(2)O before versus 127(12) cmH(2)O after treatment, P < 0.00 01). Thereafter no additional response was noted with higher concentrations of phenylephrine. The median duration of action of a single application of 10 per cent phenylephrine was 7 (range from 6 to more than 8) h. Conclusion: Topical application of 10 per cent phenylephrine gel to the anu s produces a significant rise in the resting anal sphincter pressure in hea lthy human volunteers. This represents a potential novel therapeutic approa ch to the treatment of passive faecal incontinence associated with a low re sting anal sphincter pressure.