A 62-year-old man is hospitalized for elective coronary artery bypass graft surgery. The patient had been having worsening exertional angina and was found to have 3-vessel coronary artery disease. His other medical conditions include hypertension, type 2 diabetes mellitus, and hyperlipidemia. He has had no infections and has not used antibiotics recently. The patient has a history of severe penicillin allergy causing anaphylactic shock. Blood pressure is 128/72 mm Hg and pulse is 78/min. The lungs are clear on auscultation and heart sounds are normal. Preoperative blood cell counts, serum chemistry, and coagulation studies are within normal limits. Which of the following is the most appropriate preoperative prophylactic antibiotic for this patient?
Antibiotics for SSI prevention | |||
Wound classification | Procedure examples | Typical contaminants | Antibiotic prophylaxis |
Clean* | Cardiac, neurological, orthopedic, vascular | Skin flora: Streptococcus, Staphylococcus aureus & coagulase-negative staphylococci | 1st-line: cefazolin Alternatives: vancomycin, clindamycin |
Clean-contaminated** | Gastrointestinal, genitourinary, gynecologic/obstetric, head & neck, thoracic | Skin flora, gram-negative bacilli, enterococci & endogenous flora of the viscus | Based on surgical site, broader coverage often indicated |
*Uninfected, uninflamed, the viscus is not entered. **Viscus (eg, alimentary, genitourinary, respiratory systems) is entered under controlled conditions. SSI = surgical site infection. | |||
In addition to preoperative antiseptic skin preparation and sterile surgical technique, prophylactic antibiotics can help reduce surgical site infections (SSIs). Administered prior to incision, prophylactic antibiotics reduce the microorganism burden at the surgical site and are indicated when there is a high risk of infection (eg, traumatic wounds) or when infection would cause significant morbidity/mortality (eg, mediastinitis after cardiac surgery).
The specific antibiotic is chosen based on several factors, including the type of surgical wound and its expected degree of microbial contamination:
Cardiac procedures are typically considered clean, and most associated SSIs are due to skin flora. Therefore, only gram-positive skin flora (eg, Streptococcus, Staphylococcus aureus, coagulase-negative Staphylococcus) coverage is required. First- and second-generation cephalosporins (eg, cefazolin) typically provide good prophylactic coverage. However, this patient has a history of a severe IgE-mediated allergic reaction (ie, anaphylactic shock) to penicillin, with which first- and second-generation cephalosporins have structural similarities (ie, shared allergenic epitopes). Therefore, an alternative antibiotic (eg, vancomycin, clindamycin) with good gram-positive coverage should be selected.
(Choice A) Azithromycin has a broad spectrum of activity against many gram-positive and some gram-negative bacteria including atypical bacteria (eg, Mycoplasma, Legionella); it is commonly used for treatment of community-acquired pneumonia. It has inferior coverage against Staphylococcus and is not typically used for SSI prophylaxis.
(Choices B and C) Ciprofloxacin has antimicrobial activity against aerobic, enteric, gram-negative bacilli and is used for prophylaxis in some genitourinary procedures. Metronidazole has antimicrobial activity against anaerobes (eg, Bacteroides, Clostridium) and protozoa (eg, Trichomonas vaginalis) and is used as part of a prophylaxis regimen in some gastrointestinal, gynecologic, and genitourinary procedures. However, neither antibiotic provides adequate coverage against typical gram-positive skin flora for this cardiac procedure.
(Choice D) Piperacillin-tazobactam has antimicrobial activity against gram-positive, gram-negative, and anaerobic bacteria including Pseudomonas aeruginosa; it is commonly used in broad-spectrum, empiric coverage for severe infections. However, such broad coverage is unnecessary (following principles of antimicrobial stewardship) for prophylaxis against a narrower spectrum of gram-positive skin flora. In addition, piperacillin-tazobactam should be avoided given this patient's severe penicillin allergy.
Educational objective:
Prophylactic antibiotics reduce surgical site infections and are indicated when there is a high risk of infection or when infection would lead to significant morbidity/mortality. Patients undergoing clean procedures (ie, without infection or viscus entry) should receive coverage against gram-positive skin flora, ideally with a first- or second-generation cephalosporin (eg, cefazolin) or, alternatively, with vancomycin or clindamycin.