What is the recommended dosing regimen for intravenous (IV) vancomycin and cefazolin in patients with suspected or confirmed bacterial infections, particularly in hospital or surgical settings, considering individual medical history, including allergies and impaired renal function?

IV Vancomycin and Cefazolin Dosing for Surgical Prophylaxis

First-Line Recommendation

Cefazolin 2g IV is the preferred first-line agent for surgical prophylaxis in most procedures, with vancomycin 30 mg/kg IV (infused over 120 minutes) reserved specifically for documented beta-lactam allergy, known MRSA colonization, or high-MRSA prevalence settings. 1, 2, 3

---

Cefazolin Dosing Protocol

Standard Dosing

• Initial dose: 2g IV administered within 60 minutes before surgical incision, ideally 30 minutes prior 1
• Redosing: 1g IV if procedure duration exceeds 4 hours 1, 4
• Maximum duration: Limited to operative period, not exceeding 24 hours postoperatively 1, 4

Procedure-Specific Applications

• Cardiac surgery: 2g IV + 1g in cardiopulmonary bypass priming solution, with 1g redose at 4th hour intraoperatively 1
• Vascular surgery: 2g IV slow injection as single dose (redose 1g if duration >4 hours) 1
• Orthopedic prosthesis: 2g IV slow injection, redose 1g if duration >4 hours, limited to operative period (24 hours maximum) 1
• Surgical site infections (trunk/extremity): 0.5-1g every 8 hours IV for treatment (not prophylaxis) 1

---

Vancomycin Dosing Protocol

Weight-Based Dosing (Critical)

• Dose: 30 mg/kg IV based on actual body weight, NOT ideal body weight 2, 3
• For a 68 kg patient: approximately 2040 mg (can round to 2000 mg) 2
• Never use fixed 1-gram doses - this systematically underdoses patients >67 kg 3

Infusion Timing Requirements

• Infusion duration: 120 minutes (2 hours) to minimize Red Man syndrome and hypotension 1, 2, 3
• Must complete infusion at latest by surgical incision, ideally 30 minutes before incision 1, 2, 3
• This extended timing is critical - vancomycin requires 120 minutes versus cefazolin's 60 minutes 3

Specific Indications for Vancomycin

Vancomycin should ONLY be used when:

• Documented beta-lactam (penicillin/cephalosporin) allergy 1, 2, 3
• Known or suspected MRSA colonization 1, 2, 3
• Reoperation in unit with MRSA ecology 1, 2
• Recent broad-spectrum antibiotic therapy 1, 2

Procedure-Specific Vancomycin Dosing

• Cardiac surgery (beta-lactam allergy): 30 mg/kg over 120 minutes as single dose 1, 3
• Orthopedic surgery (beta-lactam allergy/MRSA): 30 mg/kg over 120 minutes 3
• Nosocomial/prosthetic valve endocarditis: 60 mg/kg/day divided every 6 hours (up to 2g) for treatment, not prophylaxis 1

Duration of Prophylaxis

• Single perioperative dose for most surgical procedures 2
• Never extend beyond 24 hours postoperatively, and absolutely never beyond 48 hours 2
• Prolonged administration increases resistance without improving outcomes 2, 3

---

Critical Pitfalls to Avoid

Vancomycin-Specific Errors

• Do NOT use vancomycin as routine first-line prophylaxis - it is inferior to cefazolin against methicillin-susceptible S. aureus and streptococci 3, 5
• Do NOT start vancomycin infusion <120 minutes before incision - inadequate tissue penetration will result 2, 3
• Do NOT use fixed 1g vancomycin doses - this underdoses the majority of patients 3
• Do NOT continue prophylaxis beyond 24 hours - increases resistance risk without benefit 2, 3

Cefazolin-Specific Errors

• Do NOT extend cefazolin beyond operative period - maximum 24 hours 1, 4
• Do NOT forget redosing if procedure exceeds 4 hours 1

Allergy Verification

• Confirm reported penicillin allergies preoperatively - second-line antibiotics increase surgical site infection odds by 50% 3
• Many reported "allergies" are not true IgE-mediated reactions and can safely receive cephalosporins 3

---

Renal Dysfunction Considerations

Vancomycin Adjustments

• Patients with renal dysfunction require dose adjustments and closer monitoring 2
• Routine trough monitoring NOT required for single prophylactic dose 2
• If vancomycin continued beyond prophylaxis for treatment, monitor trough before 4th or 5th dose 2
• Teicoplanin may be considered as alternative in high-risk AKI patients, though less nephrotoxic effect (RR 0.66) 6

Cefazolin Adjustments

• Standard dosing typically safe, but consider dose reduction in severe renal impairment (CrCl <10 mL/min) based on general medicine knowledge

---

Comparative Efficacy Evidence

When Vancomycin May Be Superior

• One RCT in cardiac/vascular surgery showed vancomycin had lower surgical wound infection rate (3.7%) versus cefazolin (12.3%) and cefamandole (11.5%), p=0.05 5
• No thoracic wound infections in cardiac operations with vancomycin (p=0.04) 5
• However, this was in a high-MRSA prevalence setting 5

When Cefazolin Remains Preferred

• Neurosurgical prophylaxis showed no significant difference in SSI rates between cefazolin (2.2%) and vancomycin (4.1%), OR 1.59, p=0.49 7
• Cefazolin has lower toxicity profile and better specificity for skin commensals 7
• Vancomycin should be reserved for specific indications, not routine use 3, 7

---

Monitoring and Safety

Vancomycin Adverse Events

• Hypotension during infusion: Occurs despite 1-hour infusion; slow rate and pretreat with diphenhydramine if needed 5
• Red Man syndrome: Reduced by 120-minute infusion protocol (RR 0.21 versus faster infusion) 2, 6
• Nephrotoxicity: Lower risk than historical data suggest, but still monitor in high-risk patients 6
• Cutaneous rash: Less frequent than with other agents (RR 0.57) 6

Cefazolin Adverse Events

• Generally well-tolerated with minimal adverse effects 1
• Hypersensitivity reactions possible in true beta-lactam allergy 1