Antibiotic therapy for prevention of fistula in-ano after incision and drainage of simple perianal abscess: A randomized single blind clinical trial.

Background: Much controversy exists regarding the role of antibiotics in the development of fistula in-ano after incision and drainage. We evaluated the role of postoperative antibiotics in the prevention of fistula in-ano after incision and drainage of perianal abscess.

Methods: In a randomized single blind clinical trial study, 307 patients were randomly selected from those referring for incision and drainage of perianal abscess at Shahid Faghihi Hospital, Shiraz, Iran, during September 2013 to September 2014. Patients were allocated randomly either to receive 7 days of oral metronidazole and ciprofloxacin in addition to their standard care or to only receive standard care without any antibiotics after they were discharged from the hospital. Patients were followed for 3 months and final results were evaluated. The study was registered at the clinical trial registry (www.irct.ir; Irct201311049936n7).

Results: Seven patients were lost to follow-up. Those who used prophylactic antibiotics (n = 155) had significantly lower rates of fistula formation compared with those who did not use any medication (n = 144; P < .001). Men had higher rates of fistula formation (P = .002). Patients who used more cigarettes had higher rates of fistula development (P = .001). In the univariate analysis, only postoperative antibiotic use showed a protective role against fistula formation (odds ratio = 0.426; confidence interval, 0.206-0.881). In the regression analysis postoperative antibiotic use remained protective against fistula development (odds ratio = 0.371; confidence interval, 0.196-0.703), furthermore male sex presented as a risk factor for developing fistula in-ano (odds ratio = 3.11; confidence interval, 1.31-7.38).

Conclusion: Postoperative prophylactic antibiotic therapy including ciprofloxacin and metronidazole play an important role in preventing fistula in-ano formation. Considering the complications of fistula in-ano formation and the minor side effects of antibiotic therapy, based on our results, a 7-10 course of postoperative antibiotics is advised after incision and drainage of perianal abscess.