Fistula-in-ano: do antibiotics make a difference?

The objective of this study was to evaluate the hypothesis that antibiotics in conjunction with drainage of anorectal abscesses will reduce the incidence of fistulae formation. The impact of age and associated comorbidity on the formation of fistulae were also evaluated.

Patients with a diagnosis of anorectal abscesses were identified from the database of a single colorectal practice. Demographic data, comorbidity, antibiotic usage, and fistulae formation were collected from review of patient's charts and phone contact. Statistical analysis was performed with the two-sided Fisher's exact and Wald's chi-square tests.

Fifty-six patients with complete data were analyzed. The overall fistulae formation rate was 32%. Of all patients, 45% received a course of broad-spectrum antibiotics at the time of drainage and 48% of patients had associated comorbidity. Although trends were evident, there were no statistical significant associations between fistulae formation and age, comorbidity, and antibiotics.

Although not statistically significant, there was a trend that antibiotics and age >45 years may be protective against the formation of fistulae. Similarly, the data suggest that the presence of comorbidity may increase the risk of fistula formation. We are encouraged by this result and propose to conduct a larger randomized prospective study.