title: The dose response of the internal anal sphincter to topical application of glyceryl trinitrate ointment.
abstract: BACKGROUND
  Glyceryl trinitrate (GTN) ointment has been used for the treatment of chronic anal fissure based on the assumed pathophysiology that the fissure is due to internal anal sphincter hypertonia and that GTN causes relaxation.
  
  
  METHODS
  48 patients, with a diagnosis of haemorrhoids, underwent 24 h anal manometry following application of different concentrations (placebo, 0.1%, 0.2%, 0.4%) of GTN ointment.
  
  
  RESULTS
  We have found that there was a progressive relaxation with increasing doses (placebo -8.8%, 0.1% GTN -21.9%, 0.2% GTN -27.2%, 0.4% GTN -33.1%). One way ANOVA showed this progression was significant (P=0.020), with the difference lying between placebo and 0.4% GTN (Tukey multiple comparisons, P=0.017). Only 3 patients experienced headaches and these were split evenly between the treatment arms.
  
  
  CONCLUSIONS
  The internal anal sphincter has a dose related response to GTN and when dose application is strictly applied higher doses may be used without an increase in side-effects.
authors.affiliation: The University of Hull, Academic Surgical Unit, Castle Hill Hospital, Cottingham, East Yorkshire, UK.
authors.forename: J D
authors.initials: JD
authors.lastname: Cundall
authors.forename: J
authors.initials: J
authors.lastname: Gunn
authors.forename: J R
authors.initials: JR
authors.lastname: Easterbrook
authors.forename: J V
authors.initials: JV
authors.lastname: Tilsed
authors.forename: G S
authors.initials: GS
authors.lastname: Duthie