PROPHYLAXIS

17. Should systemic antibiotic prophylaxis be used in elective colon resection?

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Yes, beyond any statistical shadow of a doubt. At least two dozen clinical trials have been carried out using placebo controls against a variety of antibiotics, principally those active against at least the anaerobic-predominant flora, and nearly all have shown a reduction in infectious complications in the antibiotic group. Never again should this point need repeating, and no patient should be placed at risk when systemic antibiotic prophylaxis has been established as the standard of care. No new clinical trials against placebo in this group of patients with known risk can be performed ethically given the confirmed risk reduction.
Other risk groups (e.g., cesarean section after membrane rupture) besides patients undergoing colon resection have been standardized by trials in large patient populations and have shown similar risk reduction. The benefit of prophylaxis has been demonstrated. In other groups of patients that cannot be standardized because of unusual contamination factors or unique factors of host resistance impairment, guidelines for rational prophylaxis should follow similar principles.

18. Are two prophylactic doses better than one in preventing infection? Are three doses better still?

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Only one dose of prophylactic antibiotic can be proved, beyond statistical or clinical doubt, to be efficacious-the dose in systemic circulation at the time of the inoculum. Whether the dose needs to be repeated one or more times during the 24 hours after the inoculum depends on the blood levels of the drug, which are largely a function of protein binding and clearance rate. We also know for sure that 10 days of the same prophylactic drug that is efficacious if given immediately before the inoculum results in a higher risk of infection than no antibiotic at all.
KEY POINTS: PREOPERATIVE ANTIBIOTIC PROPHYLAXIS

1. Timing of administration is the most important factor.
2. Dose 30 minutes before incision so that antibiotic is circulating before the inoculum.
3. No evidence supports continuation of prophylaxis beyond 24 hours.

19. What factors determine the timing of antibiotic administration under the criteria of prophylaxis?

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The one immutable principle has been set out above-the most important element in timing of prophylaxis is that the drug be circulating before the inoculum. When should it stop? When the reduction in infection risk is no longer provable and before continued use will defeat the prophylactic purpose (as explained above). To summarize with an arbitrary rule of thumb: there is no justification for prophylactic antibiotic 24 hours after the inoculum of an invasive procedure.

What does this rule imply? Should we not continue prophylaxis for weeks to cover the presence of a prosthetic hip joint? Presumably, the prosthetic hip will be in the patient for many years-but surely you do not argue that the antibiotic should continue on a daily basis as long as the hip is in place! What is “prophylaxed” is not the prosthetic hip but the procedure of implantation. And it is not only implantation that poses a risk to the patient with a prosthesis-so does hemorrhoidectomy done years later, for which prophylaxis is made mandatory by the presence of the hip prosthesis.
The prosthetic or rheumatic heart valve is a risk, but the indication for the use of prophylactic antibiotics is an invasive procedure-a root canal is an example in which an inoculum is unavoidable. Operations are covered by prophylactic antibiotics; the conditions that are risk factors during the operation are not.

20. To be safe, why not administer prophylactic antibiotics to all patients undergoing any kind of operation?

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Can you give me the indication for a prophylactic antibiotic in a patient undergoing a clean elective surgical procedure that implants no prosthesis, such as hernia repair?
“Sure,” one of my brighter students once responded, “the patient who has a serious impairment in host response, such as acute granulocytic leukemia in blast crisis.”
I responded, “Why on earth are you fixing his hernia? That is a clean error [hopefully not a clean kill] in surgical judgment that has nothing to do with antibiotics at all. A patient with that degree of host impairment does not undergo an elective surgical procedure.”
Rule of thumb: If you can provide the indication for a prophylactic antibiotic to cover a clean elective nonprosthetic operation for a patient, you have provided the contraindication for the operation.