Does Adjuvant Antibiotic Treatment After Drainage of Anorectal Abscess Prevent Development of Anal Fistulas? A Randomized, Placebo-Controlled, Double-Blind, Multicenter Study

BACKGROUND: The risk of fistula formation is a major concern after incision and drainage of an anorectal abscess. OBJECTIVE: Our objective was to the test the effects of antibiotic treatment on fistula formation after incision and drainage of anorectal abscesses. DESIGN: Randomized, placebo-controlled, double-blind study. SETTING: Multicenter trial at 3 teaching hospitals in Turkey. PATIENTS: Patients who underwent abscess drainage between September 2005 and January 2008 were evaluated for eligibility. Exclusion criteria included penicillin allergy, antimicrobial agent usage before enrolment, other infection, previous anorectal surgery, inflammatory bowel disease, suspicion of Fournier gangrene, secondary and recurrent anorectal abscesses, anal fistula at time of the surgery, immune compromised states, and pregnancy. INTERVENTION: Patients were randomly assigned to receive placebo or amoxicillin-clavulanic acid combination treatment for 10 days after abscess drainage. MAIN OUTCOME MEASURES: The primary end point was rate of anorectal fistula formation at 1-year follow-up. RESULTS: Of 334 patients assessed for eligibility, 183 entered the study (placebo, 92; antibiotics, 91). Data were available for per-protocol analysis from 151 patients (placebo, 76; antibiotics, 75) with a mean age of 37.6 years; 118 patients (78.1%) were men. Overall, 45 patients (29.8%) developed anal fistulas during 1-year follow-up. Fistula formation occurred in 17 patients (22.4%) in the placebo group and in 28 patients (37.3%) in the antibiotic group (P = .044). Risk of fistula formation was increased in patients with ischiorectal abscess (odds ratio, 7.82) or intersphincteric abscess (odds ratio, 3.35) compared with perianal abscess. CONCLUSION: Antibiotic treatment following the drainage of an anorectal abscess has no protective effect regarding risk of fistula formation.