PHILADELPHIA — Antibiotic prophylaxis “absolutely, positively” lowers the risk of wound infection in patients undergoing elective colon and rectal surgery, Richard L. Nelson, M.D., said at the annual meeting of the American Society of Colon and Rectal Surgeons.
“It's unethical to do an operation in the abdomen or open colon without antibiotic prophylaxis,” he said, based on the results of a metaanalysis of 103 randomized, controlled trials of antibiotic prophylaxis that were published during 1980–2004. The studies all involved abdominal, colorectal surgery, and the primary end point of the studies was the incidence of abdominal surgical wound infections.
The literature search done by Dr. Nelson and his associates initially identified 180 published reports of randomized, controlled trials that assessed the efficacy of antibiotic prophylaxis. The studies involved 49 different antibiotics and nearly 30,000 patients. The investigators eliminated 77 of the studies from the analysis because they included too many variables that produced results that could not be evaluated, leaving 103 studies included in the final analysis.
The metaanalysis documented several other conclusions about antibiotic prophylaxis, said Dr. Nelson, chief of the division of colon and rectal surgery at the University of Illinois Medical Center in Chicago:
▸ Virtually any antibiotic will work, but prophylaxis is most effective if it covers both aerobic and anaerobic species. Compared with placebo, aerobic coverage cut the risk of wound infection by 59%, and drugs effective against anaerobic species reduced wound infections by 45%.
▸ Adequate prophylaxis is achieved with a single dose that's administered within 2 hours of the start of surgery. Additional antibiotic doses confer no additional protection regardless of how long the surgery takes. In the metaanalysis, 18 studies compared one dose against more than one, and the two strategies produced virtually identical wound infection rates. Despite this, in the 103 studies, 45% of patients received antibiotics more than 48 hours after surgery was finished, and the overall, average duration of prophylaxis was 57 hours.
▸ Oral and intravenous formulations are equally effective, but the combination is even better.
A pairing of oral and intravenous formulations was better than any intravenous drug alone and any oral drug alone. But the study results were unable to clearly show the ideal time to administer the two formulations of antibiotics relative to each other.