Increased Risk of Bleeding with Topical Metronidazole in a Postoperative Wound after Anal Fistula and Hemorrhoid Surgery: A Propensity Score-Matched Case–Control Study

Background: Topical metronidazole (TM) is commonly used in many infective conditions and postoperative wounds including after anorectal surgery. TM was prescribed in patients operated for benign anorectal conditions (anal fistula and hemorrhoids) to hasten wound healing. After the initiation of this protocol, the incidence of postoperative wound bleeding seemed to increase. There are no data in the literature suggesting that topical metronidazole increases the risk of bleeding. Objective: Analysis of the association of TM with an increased risk of bleeding in postoperative anorectal wounds. Design: This was an observational and a retrospective study. Propensity score matching was performed. Setting: This study was conducted at a specialized center for anorectal disorders in postoperative patients suffering from anal fistula and hemorrhoids. Materials: The incidence of postoperative bleeding in the patients in whom TM was used (study group) was retrospectively compared with the patients operated one year before this period in whom TM was not used (control group). Sample size: There were 35 patients in the study group and 181 patients in the control group. Main outcome measures: The incidence of bleeding and the number of bleeding episodes were evaluated. Results: The incidence of bleeding was significantly higher in the study group as compared to the control group (8/35 (22.8%) vs. 8/181 (4.4%), respectively, p = 0.0011). In most cases, bleeding was controlled with conservative measures. The number of bleeding episodes was also significantly higher in the study group (14 vs. 11, respectively, p = 0.0001). The number of patients requiring operative intervention was also higher in the study group (2/35—5.7%) as compared to the control group (1/181—0.56%), but this was not statistically significant (p = 0.069). Conclusions: The study highlighted that application of topical metronidazole in postoperative anorectal wounds increased the risk of bleeding. Most of the bleeding episodes were controlled with conservative measures but they caused considerable patient anxiety and apprehension.