A21. The use of antibiotics in surgery and ways of administration.

The major role of antibiotics in surgery is as prophylaxis against postoperative infections. Proper use allows for reduction of incidence of infection, but overuse stimulates development of resistance. The decision to use antibiotic prophylaxis and the choice of antibiotics depend on the procedure and regional differences, and usually follows local guidelines. The bacteria are usually commensal (originate from the patient’s own flora, mostly the skin or GI tract), and so antibiotics should cover these florae.

Generally, prophylaxis is indicated if there is a high risk of infection, or if the risk of infection is low but infection would cause especially severe consequences (like for implantation of foreign material), or if the patient is immunosuppressed.

Perioperative antibiotic prophylaxis is only effective if there is sufficient tissue concentration of the antibiotics during the whole operation. Antibiotics given IV should therefore be given max 1 hour before the operation. IV beta lactams should be administered < 30 minutes before the operation. Antibiotics with short half-life may need to be administered multiple times during longer operations. Antibiotics administered p.o. must be given at least 2 hours before surgery to allow for tissue concentrations to reach sufficient levels.

Generally, prophylaxis given before (and sometimes during) surgery, and is stopped as the surgical procedure finishes. Exceptions include implantation of foreign material or certain risk factors, in which case prophylaxis should be continued for up to 24 hours. Duration > 24 hours has no proven beneficial effect.

Types of surgery

We can classify procedures according to their cleanliness:

Classification	Description	Examples	Approximate risk of surgical site infection
Clean	Elective surgery where hollow organs won’t be opened	Breast lumpectomy Inguinal hernia surgery	< 2%
Clean-contaminated	Elective surgery where hollow organs will be opened without significant spillage	Elective cholecystectomy Uncomplicated appendectomy	< 10%
Contaminated	Surgery with spillage of GI content or infected urine, or traumatic injury < 4 hours old	Elective bowel operations Complicated appendectomy Fresh traumatic skin wounds	20%
Dirty	Active purulent infection at the surgical site, or traumatic injury > 4 hours old, or traumatic perforation of viscera	Surgery of abscesses Bowel perforation Older traumatic wounds	40%

Choice of antibiotic

Cefazolin is the most commonly used drug for surgical prophylaxis overall, especially for clean and clean-contaminated procedures. It has activity against most organisms which commonly cause postoperative infection, it has a desirable duration of action, is safe, and cheap. Vancomycin is an alternative if the risk for MRSA is high or there is cephalosporin allergy.

For clean-contaminated and contaminated head and neck procedures, co-amoxiclav or clindamycin may be used.

For clean-contaminated and contaminated abdominal procedures, third generation cephalosporin + metronidazole may be used.

These recommendations are Hungarian and are different from country to country, so always follow local guidelines.

Types of surgery

Choice of antibiotic

Other measures to decrease incidence of infection