Effectiveness of higher doses of botulinum toxin to induce healing in patients with chronic anal fissures

Background. Botulinum toxin induces healing in patients with idiopathic anal fissures. Methods. One hundred-fifty patients with posterior anal fissures were treated with botulinum toxin injected in the internal anal sphincter on each side of the anterior midline. Subjects were randomized into 2 treatment groups based on the number of units of botulinum toxin injected. Patients in group I were treated with 20 units of botulinum toxin and, if the fissure persisted, were retreated with 30 units. Patients in group II were treated with 30 units and retreated with 50 units, if the fissure persisted. Results. The 2 groups were comparable in age, gender distribution, duration of symptoms, resting pressure, and maximum voluntary pressure at anorectal manometry. One month after the injection, examinations revealed complete healing in 55 patients (73%) from group I and 65 patients (87%) from group II (P = .04). Five patients from group II reported a mild incontinence of flatus that lasted 2 weeks after the treatment and disappeared spontaneously. The values of the resting anal pressure (P = .3) and the maximum voluntary pressure (P = .2) did not differ between the 2 groups. At 2 months' evaluation, a healing scar was found in 67 patients (89%) from group I and 72 patients (96%) from group II. A relapse of the fissure was observed in 6 patients (8%) from group I who had a healing scar at 1 month, and 2 other patients never healed. A persistent fissure was present in 3 patients from group II who had no other symptoms. Conclusions. Botulinum toxin injected into the internal anal sphincter is effective in managing anal fissures and avoiding permanent complications. All patients were treated with the active drug and healed after 1 or 2 successive treatments. The results also confirm that higher doses account for a higher success rate, with little increase in complications or side effects, which is probably related to the diffusion of the toxin to the external sphincter.