What is the recommended duration of antibiotic prophylaxis for coronary artery bypass grafting (CABG), comparing single dose versus 24-hour dose regimens?

Antibiotic Prophylaxis Duration for CABG Surgery: Single Dose vs 24-Hour Regimen

For coronary artery bypass grafting (CABG) surgery, a 24-hour multiple-dose cefazolin regimen (2g initial dose plus 1g every 8 hours for 24 hours) is superior to single-dose prophylaxis and should be the standard of care. 1

Evidence Supporting 24-Hour Prophylaxis

The most definitive evidence comes from a prospective randomized trial of 838 CABG patients that directly compared single-dose versus 24-hour cefazolin prophylaxis 1:

• Single-dose cefazolin resulted in significantly higher surgical site infection (SSI) rates: 8.3% versus 3.6% with 24-hour dosing (P = 0.004) 1
• This represents more than a 2-fold increase in infection risk with single-dose prophylaxis 1
• No differences in mortality or hospital length of stay were observed between groups 1
• Gram-positive cocci accounted for 86% of SSIs in both groups 1

Recommended Dosing Protocol for CABG

The optimal regimen for cardiac surgery includes: 2, 3

• Preoperative dose: 2g cefazolin IV slow infusion, administered 30-60 minutes before surgical incision 2, 3
• Cardiopulmonary bypass priming: Add 1g cefazolin directly to the bypass priming solution 2
• Intraoperative redosing: 1g cefazolin at the 4th hour if surgery continues beyond 4 hours 2, 4
• Postoperative continuation: 1g cefazolin every 8 hours for 24 hours postoperatively 4, 1
• Maximum duration: Do not extend beyond 24 hours 5, 2, 3

Reconciling Conflicting Evidence

While general surgical guidelines state that single-dose prophylaxis is adequate for most procedures 5, cardiac surgery represents a specific exception where 24-hour prophylaxis is justified 5, 2. The 2019 European guidelines explicitly note that "post-procedural doses of intravenous antibiotics (up to 24 hours) may be required in defined circumstances, such as some cardiac and vascular surgeries" 5.

Critical distinction: The observational study by Mertz et al. 6 that found no benefit to prolonged prophylaxis (>48 hours) actually supports limiting duration to ≤48 hours, not advocating for single-dose prophylaxis. That study compared <48 hours versus >48 hours, finding that extending beyond 48 hours increased antibiotic resistance without reducing SSI 6. This reinforces the 24-hour maximum recommendation, not single-dose use.

Alternative Cephalosporin Regimens

Second-generation cephalosporins are acceptable alternatives: 5, 2, 7

• Cefuroxime: 1.5g IV initial dose plus 0.75g in bypass priming, with 0.75g redosing every 2 hours intraoperatively, continued every 12 hours for 24 hours 5, 2, 7
• Cefamandole: 1.5g IV initial dose plus 0.75g in bypass priming, with similar redosing schedule 5, 2, 7
• A randomized trial of 337 cardiac surgery patients found cefuroxime and cefamandole had fewer wound infections than cefazolin (5% and 6% versus 9%, P<0.05) 7
• Single-dose cefuroxime has been studied and found effective in some cohorts 8, though the strongest evidence supports 24-hour dosing 1

Beta-Lactam Allergy Alternatives

For patients with documented beta-lactam allergy: 5, 2, 9

• Vancomycin: 30 mg/kg infused over 120 minutes as a single dose 5, 2, 9
• The infusion must be completed at the latest by the beginning of surgery, ideally 30 minutes before incision 5, 2, 9
• Reserve vancomycin only for: documented beta-lactam allergy, known MRSA colonization, reoperation in units with MRSA ecology, or recent antibiotic therapy 5, 2, 9

Critical Pitfalls to Avoid

Timing errors: 2, 3

• Do not delay the preoperative dose—it must be given 30-60 minutes before incision to ensure adequate tissue levels 2, 3
• For vancomycin, the 120-minute infusion time requires even earlier administration 5, 2

Duration errors: 5, 2, 6

• Never extend prophylaxis beyond 24 hours for CABG 5, 2
• Prolonging beyond 48 hours increases antibiotic resistance (adjusted OR 1.6, P<0.05) without reducing SSI 6
• The presence of surgical drains does not justify extending prophylaxis 2

Dosing errors: 2, 4

• Do not forget the 1g cefazolin added to cardiopulmonary bypass priming solution 2
• Do not miss intraoperative redosing for procedures exceeding 4 hours 2, 4
• Obese patients ≥120 kg require higher doses 5

Cohort Studies Summary

The key cohort study comparing regimens: 1

• Prospective randomized trial, 838 patients undergoing elective CABG or valve surgery 1
• Single-dose (n=419): 2g cefazolin preoperatively only 1
• 24-hour regimen (n=419): 2g initial dose, then 1g every 8 hours for 24 hours 1
• 12-month follow-up with blinded outcome assessment 1
• Result: 8.3% SSI with single-dose versus 3.6% with 24-hour regimen (P=0.004) 1

Supporting observational evidence: 6

• 4-year cohort of 2,641 CABG patients comparing <48 hours versus >48 hours prophylaxis 6
• No benefit to extending beyond 48 hours; increased resistance with prolonged use 6
• Confirms 24-hour duration is appropriate maximum 6