This is a Phase I trial to evaluate Pharmacokinetics, Pharmacodynamics and Safety of Isosorbide Mononitrate gel for usage in participants with anal fissure and healthy volunteers. Three doses will be used in patients with anal fissure (0.5%, 1.0% or 2.0%) and healthy volunteers will receive 2.0% dose. All treatment will last 7 days.

This is a Phase I, open-label, parallel trial to evaluate Pharmacokinetics, Pharmacodynamics and Safety of Isosorbide Mononitrate gel for usage in participants with anal fissure and healthy volunteers. Investigational product will be randomly assigned as follows: * healthy volunteers will receive 2g (2.0%) of investigational product at a single dose, and will undergo a washout period of 7 days; subsequently, they will receive 2g of investigational product once daily, for 7 consecutive days; * participants with anal fissure will receive 2g of investigational product, either at 0.5%, 1.0% or 2.0%, at a single dose, and will undergo a washout period of 7 days; subsequently, they will receive 2g of investigational product, either at 0.5%, 1.0% or 2.0%, once daily, for 7 consecutive days.