What are the antibiotics of choice for prophylaxis in a post-coronary artery bypass graft (CABG) patient, particularly those with a history of methicillin-resistant Staphylococcus aureus (MRSA) or penicillin allergy?

Antibiotic Prophylaxis for Post-CABG Patients

For standard post-CABG patients without MRSA risk factors, use cefazolin 2g IV plus 1g in the cardiopulmonary bypass priming solution, with a single 1g re-injection at the 4th hour intraoperatively if the procedure is prolonged, limited to the operative period only (maximum 24 hours). 1, 2

Standard Prophylaxis Protocol

First-line antibiotic choice:

• Cefazolin is the preferred agent, administered as 2g IV at induction plus 1g added to the bypass priming solution 1
• Re-inject 1g at the 4th hour if surgery duration exceeds 4 hours 1
• Alternative first-generation cephalosporins include cefamandole or cefuroxime (1.5g IV + 0.75g in priming, with re-injection of 0.75g every 2 hours intraoperatively) 1

Critical timing considerations:

• Administer the first dose within 60 minutes before surgical incision, ideally 30 minutes prior 1, 2
• The infusion must be completed before incision to achieve adequate tissue levels 1, 2

Duration of prophylaxis:

• Limit antibiotic prophylaxis strictly to the operative period 1, 2
• Maximum duration is 24 hours postoperatively 1, 2
• Never extend prophylaxis beyond 24-48 hours, even in the presence of surgical drains 1
• Do not prescribe antibiotics for drain, probe, or catheter removal 1

MRSA Risk Factors and Vancomycin Use

Vancomycin is specifically indicated for patients with:

• Documented or suspected MRSA colonization 1
• Beta-lactam (penicillin/cephalosporin) allergy 1
• Reoperation in a patient hospitalized in a unit with high MRSA prevalence 1
• Recent broad-spectrum antibiotic therapy 1, 3

Vancomycin dosing protocol:

• Dose: 30 mg/kg administered over 120 minutes 1
• The 120-minute infusion must end at the latest at the beginning of the intervention, ideally 30 minutes before incision 1
• Single dose only for prophylaxis 1
• Pretreat with diphenhydramine to prevent hypotension during infusion 3

Evidence Supporting Vancomycin in High-Risk Settings

Superiority of vancomycin in specific contexts:

• A randomized trial demonstrated vancomycin resulted in significantly lower surgical wound infection rates (3.7%) compared to cefazolin (12.3%) and cefamandole (11.5%) in cardiac surgery (p=0.05) 3
• No thoracic wound infections occurred in cardiac operations with vancomycin prophylaxis (p=0.04) 3
• Mean postoperative hospitalization was shortest with vancomycin (10.1 days vs 12.9 days with cefazolin, p<0.01) 3
• Vancomycin provides superior protection against methicillin-resistant coagulase-negative staphylococci and enterococci, which are common pathogens in prosthetic valve and vascular graft infections 3

Penicillin Allergy Management

For non-anaphylactic penicillin allergies:

• First-generation cephalosporins (cefazolin 6g/day or cefotaxime 6g/day IV in 3 doses) can be used safely 1
• Cross-reactivity between penicillins and cephalosporins is low in non-immediate hypersensitivity reactions 1

For immediate/anaphylactic penicillin allergies:

• Vancomycin 30 mg/kg over 120 minutes is mandatory 1
• Cephalosporins are absolutely contraindicated in patients with urticaria, angioedema, bronchospasm, or anaphylaxis to penicillins 4

Common Pitfalls to Avoid

Critical errors in prophylaxis:

• Never continue antibiotics beyond 24 hours "because drains are still in place" - this is explicitly not recommended and increases resistance without benefit 1
• Do not use vancomycin routinely in all patients - reserve it for specific indications to prevent resistance 1
• Avoid inadequate vancomycin infusion time - the full 120-minute infusion is essential to prevent hypotension and ensure adequate tissue levels 1, 3
• Do not give prophylactic antibiotics at drain removal - there is no evidence supporting this practice 1

Target organisms:

• Primary pathogens are S. aureus, S. epidermidis, and select gram-negative bacteria 2, 5
• In MRSA-endemic institutions, consider vancomycin for all prosthetic valve replacements and vascular graft implantations 3