Antimicrobial chemoprophylaxis in colorectal surgery.

Infective complications are often seen in colorectal surgery. These even occur in cases of elective surgery and in patients where adequate bowel preparation has been performed and is due to the very high numbers of bacteria colonising the bowel. Several controlled clinical studies showed that antimicrobial prophylaxis is effective in preventing infective complications and the lack of prophylaxis is no longer justified. Antimicrobial prophylaxis can be oral (poorly absorbed antibiotics aimed to reduce the number of bacteria in the bowel) or systemic (aimed to reach a high tissue concentration when bacterial contamination occurs, in order to prevent colonisation) or a combination of the two. Which is to be preferred is still controversial. Systemic prophylaxis should have the following features: 1) use of a single agent with a broad spectrum of action, effective both on aerobes and anaerobes; 2) rapid I.V. administration, at the beginning of surgery; 3) good tissue penetration; 4) long half-life, in order to assure that the single dose will cover the whole duration of surgery; 5) good therapeutic ratio. The use of long half-life cephalosporins, particularly cefotetan, was shown to be highly beneficial. Prophylaxis can fail if contamination during surgery is severe, with a particularly high bacterial count. The degree of contamination of the operating field can be evaluated both by surgeon's judgment, and by tissue or peritoneal cavity lavage fluid sampling and culture. In case of severe contamination (bacterial number greater than 10(5) CFU/ml of fluid or mg of tissue) prolonging of antibiotic therapy for some days is justified. Otherwise, no evidence supports its prolongation beyond surgery.