Presurgical antibiotics are indicated for specific types of surgical procedures and in individual patients with risk factors for infection. However, antimicrobials are not indicated in all surgical patients and can add unnecessary cost, lead to adverse drug reactions, and encourage the selection of resistant bacteria.

Cases for Which Antimicrobials are Not Indicated

Uncontaminated, short surgical procedures (< 1 hour in duration), to include ovariohysterectomy, castration, skin mass removal, and some splenectomies, do not require antibiotic prophylaxis. In one study of 122 dogs undergoing short-duration, clean surgical procedures, there was no difference in the rate of infection in those animals given ampicillin compared to those given placebo (Vasseur 1985).

Cases for Which Antimicrobials are Indicated

Surgical Sites with Expected Contamination

Contaminated surgery sites, to include procedures that enter the GI, lower urogenital, oropharyngeal, or respiratory tracts, warrant prophylactic antibiotics. Examples include gastrotomy, enterotomy, subtotal colectomy, urethrostomy, vaginoplasty, oral tumor removal, palate surgery, dental surgeries, and laryngeal or tracheal surgery. Surgical sites that are difficult to decontaminate, such as the eye, also warrant antibiotic prophylaxis. A protocol of 0.5% ofloxacin drops (q 6 h the day before surgery, and 3 times the hour before surgery) and topical irrigation of the conjunctiva with 1% povidone-iodine before surgery significantly reduces conjunctival bacterial numbers in human patients (Mino de Kaspar 2008).

Surgical Procedures of Prolonged Duration

Prolonged anesthesia alone has been correlated with an increased risk of infection in dogs and cats (Beal 2000). This may be due to hypothermia, hypotension, and decreased tissue perfusion (Vassuer 1988; Brown 1997). Procedures greater than 60–90 minutes warrant antimicrobials; in a Swiss study of 1010 surgeries in dogs and cats, infection risk doubled for every 70 minutes of surgery (Eugster 2004). For elective orthopedic surgeries in dogs, antibiotic prophylaxis has been shown to decrease the rate of postoperative infection compared to placebo (Whittem 1999). Preventing infection in orthopedic procedures is particularly important, since infection at the site of bone healing can have disastrous consequences.

Preexisting Infection at the Surgical Site

If surgery is not urgent, preexisting infection should be cleared prior to the procedure, if possible. If the infection is longstanding or recurrent, tissue should be submitted for aerobic and anaerobic cultures prior to perioperative antibiotic treatment. If devitalized tissue is present, it should be debrided appropriately, since antibiotics will not penetrate tissue without adequate blood flow. Topical antibiotics, which are inactivated in the presence of necrotic debris, are also not useful in such instances.

Devitalized or Desiccated Tissue

Preoperative (or intraoperative) tissue trauma and desiccation increase the risk of postsurgical infection. In one study, antimicrobials were not necessary in preventing infection in surgeries performed by experienced veterinary surgeons, but did reduce the incidence of infections in surgeries performed by inexperienced students (Vasseur 1988). For practicing veterinarians, it makes more sense to focus on good surgical technique than to rely on antimicrobials to compensate for poor tissue handling.

Immunocompromised Patients

Immunodeficient human patients have a higher risk of surgical infections and poor wound healing. By analogy, dogs and cats with neutropenia, as well as cats with FeLV or FIV infection, may benefit from antimicrobial prophylaxis prior to surgery. This is particularly important for procedures for which the gastrointestinal tract, lower urogenital, or upper respiratory tract are entered. Bactericidal antibiotics provide a theoretical advantage in immunocompromised patients. Human diabetics also have a higher risk of surgical infections. However, since humans with diabetes, unlike dogs and cats, develop peripheral vascular disease, this increased risk may not translate to veterinary patients. In hyperadrenocorticism, no published studies have compared surgical infection rates in dogs with controlled versus uncontrolled disease. However, delayed wound healing and incision dehiscence are common surgical complications of both spontaneous and iatrogenic hyperadrenocorticism. Whenever possible, hyperadrenocorticism should be treated and managed before elective surgeries.

Timing of Antimicrobial Prophylaxis

The following recommendations are the standard of care in humans (National Surgical Infection Prevention Project):

1.  Parenteral antimicrobials within one hour before incision;

2.  Re-dosing every 1–2 elimination half-lives during prolonged procedures; and

3.  Discontinuation of prophylactic antimicrobials after wound closure.

Antimicrobial Selection

Orthopedic Procedures

Coverage should be targeted at skin flora (i.e., Staph. pseudintermedius) that may cause deeper wound contamination. Cefazolin is effective in preventing infection after orthopedic procedures in dogs, when given at 20 mg/kg at induction, followed by 20 mg/kg IV every 90 minutes thereafter until wound closure (Whittem 1999). The same study demonstrated that penicillin G was also effective, compared to placebo, in this setting. However, cefazolin and related first-generation cephalosporins remain the standard for orthopedic prophylaxis because of their spectrum against many beta-lactamase-producing Staph.

Dental Procedures

Treatment of preexisting infection prior to definitive dental procedures may decrease tissue inflammation and bleeding at the time of oral surgery. Amoxicillin-clavulanate and clindamycin are effective against Gram-positive and anaerobic gingival flora in dogs and cats. For routine dental cleaning without significant preexisting infection, antibiotic prophylaxis is probably not indicated in most patients since "healthy animals are able to overcome (transient) bacteremia without the use of systemic antibiotics" (American Veterinary Dental College 2005). Antibiotics prior to dental prophylaxis are only recommended for human patients with joint prostheses or conditions that predispose to endocarditis (artificial heart valves, prior endocarditis, or cardiac transplant; ada.org). For these high-risk patients, antibiotics are given one hour prior to the dental; additional antibiotics after the procedure are not indicated. Note: the use of long-acting injectables such as Convenia is not appropriate for short-term prophylaxis of bacteremia during dental procedures and is only indicated if there is residual infection that requires specific treatment.

Gastric, Biliary, and Small Intestinal Surgery

Treatment prior to incision is the key to efficacy. Coverage should be aimed primarily at anaerobes and routine Gram-negative enterics such as E. coli. Ampicillin or cefazolin are reasonable choices, given within 30 minutes prior to incision. For soft-tissue surgeries, a bolus dose of 20 mg/kg cefazolin given IV at the time of surgery in experimental dogs was shown to provide adequate tissue drug concentrations for 3–6 hours (Rosin 1993).

Colonic Surgery

Surgery involving the colon carries a relatively high risk of surgical site infection and bacterial peritonitis. In humans, the standard of care for colorectal surgery is both oral and intravenous antibiotic prophylaxis, with coverage for anaerobes and Gram-negative enterics. Typical regimens include oral neomycin and erythromycin given in divided doses the day before surgery, followed by ampicillin-sulbactam, cefotetan, or metronidazole/cefazolin, given IV one hour prior to incision (Nelson 2009), with no additional antimicrobials beyond wound closure. If surgery is urgent, cefotetan (a broad-spectrum second-generation cephalosporin) can be administered at induction and for 24 hours after surgery. Although mechanical irrigation prior to colonic procedures is widely used in both human and veterinary patients, it has shown no benefit in reducing postoperative complications in humans. Notably, mechanical irrigation has actually been associated with an increased risk of abdominal infections in colorectal surgeries in humans, possibly due to mucosal inflammation and loss of colonic mucus (Bucher 2005, 2006).

Bladder Surgery

Prophylactic antibiotics do not reduce the incidence of wound infections after routine bladder surgery in humans. In immunocompromised patients (e.g., patients on chemotherapy, with Cushing's, or with neutropenia), a single dose of a cephalosporin or fluoroquinolone is recommended prior to cystotomy.

For stable patients with documented or suspected preexisting urinary tract infections, there are two options prior to bladder surgery:

1.  Culture urine, and treat infection for a week or more prior to elective surgery, or

2.  Obtain cultures at surgery (no prophylaxis), and treat based on results.

If postoperative urinary catheterization is necessary, minimize the duration; urinary infection rates in dogs increase by about 1.3X per day of catheterization (Bubenik 2007), and intermittent clean catheterization may be preferred over indwelling catheter, if possible, in male dogs (Bubenik 2008). Use scrupulous clean technique and always use a closed collection system. Treat with antimicrobials only if lower urinary tract signs develop, with bacteriuria. To distinguish between postoperative hematuria and an active bacterial cystitis post-cystotomy, collect a midstream voided sample and request a quantitative culture; > 10,000 cfu/ml is significant growth in midstream voided urine.

Other prophylactic measures to prevent perioperative infections