[The role of glyceryl trinitrate in the treatment of anal fissure].

Anal fissure is a small linear tear in the lining of the distal anal canal below the dentate line. Treatment is aimed at reducing internal sphincter spasm. This can be achieved with surgery (lateral internal sphincterotomy) or pharmacological sphincterotomy applying topical medication, which relaxes the sphincter muscle. Glyceryl trinitrate is the most widely used topical agent. This is a nitric oxide donor which reduces the increased anal canal pressure caused by the hypertonic internal anal sphincter, improving anodermal blood flow. Although headache is a frequent side-effect, it is usually transient and glyceryl trinitrate does not seem to have any long-term adverse effects.