Methylene Blue Effectiveness as Local Analgesic after Anorectal Surgery: A Literature Review.

Background: Methylene blue (MB) has been found to have unique analgesic property through temporary disruption of sensory nerve conduction. In anorectal surgery, MB is widely used as a biologic stain but the analgesic effect has never been studied. Thus, a literature review completed with critical appraisal is required to find out its efficacy.

Methods: A review has been run to find out its efficacy. Literature search proceeded in database sites, namely, PubMed, EBSCO, Cochrane, Wiley, and ProQuest using the following keywords: "anorectal" OR "hemorrhoid" OR "anal fistula" OR "anal fissure" OR "anal abscess" OR "anal pruritus" AND "methylene blue" AND "analgesic"; then the critical appraisal and its implication were discussed.

Result: There were 491 articles in full text found, and four studies met the inclusion criteria. Two studies were focused on the evaluation of VAS in hemorrhoid surgery whereas the rest were focused on the evaluation of symptom score in anal pruritus.

Conclusions: A study with level of evidence 2 on VAS showed the efficacy. The rest showed insufficient evidence due to variations of anorectal surgery and the methods and techniques of MB application. A further prospective clinical study is required.