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Oral versus systemic antibiotic prophylaxis in elective colon surgery: a randomized study and meta-analysis send a message from the 1990s.

OBJECTIVES
To compare the efficacy of combined oral and systemic antibiotics (combined) versus systemic antibiotics (systemic) alone in preventing surgical site infection in elective surgery of the colon, and to perform a meta-analysis of randomized studies comparing combined versus systemic antibiotics in elective colon surgery.


DESIGN
A double-blind, placebo-controlled, randomized clinical trial.


SETTING
The Queen Elizabeth Hospital, Montreal, a university-affiliated community hospital.


PARTICIPANTS
Two hundred and fifteen patients scheduled to undergo elective surgery of the colon.


INTERVENTIONS
Patients were randomized to receive neomycin and metronidazole orally (109 patients) or identical placebos (106 patients) on the final preoperative day. All were given amikacin and metronidazole intravenously just before operation. Thirteen randomized series comparing combined and systemic antibiotic prophylaxis in elective colon surgery were identified for meta-analysis.


OUTCOME MEASURES
Rates of postoperative surgical site infections: risk differences, risk ratios (RRs) and 95% confidence intervals (CIs); organisms found in the colon and wound fat at surgery, and in infected wounds.


RESULTS
Three patients in the systemic group, and 5 in the combined group were excluded. Wound infections occurred in 5 patients in the combined group but in 17 in the systemic group (p < 0.01, RR = 0.29, 95% CI 0.11-0.75). Bacteria isolated from wound infections and wound fat were similar to those found in the colon. They were more frequent in the colon in the systemic group (p < 0.001) and occurred in wound fat in the systemic group twice as often as in the combined group (p < 0.001). By stepwise logistic regression, the presence of bacteria in wound fat at surgery was the strongest predictor of postoperative wound infection (p < 0.002). In the meta-analysis, the summary weighted risk difference in surgical site infections between groups (d(w)) and the summary RR both favoured combined prophylaxis (d(w) = 0.56, 95% CI 0.26-0.86; RR = 0.51, 95% CI 0.24-0.78; p < 0.001).


CONCLUSIONS
In elective surgery of the colon combined oral and systemic antibiotics are superior to systemic antibiotics in preventing surgical site infections. Orally administered antibiotics add value by reducing bacterial loading of the colon and wound fat contamination, both associated with postoperative wound infection. Meta-analysis of randomized clinical trials reported from 1975 to 1995 supports these conclusions.