What is the appropriate cefazolin dose and route for an adult with normal renal function?

Cefazolin Dosing and Route for Adults with Normal Renal Function

For adults with normal renal function, cefazolin 2 g IV administered as a slow infusion is the standard dose for most indications, including surgical prophylaxis and treatment of moderate-to-severe infections. 1, 2

Standard Dosing by Indication

Surgical Prophylaxis (Most Common Use)

• Standard dose: Cefazolin 2 g IV slow infusion given 30–60 minutes before skin incision 1
• Route: Intravenous only for prophylaxis 1
• Timing is critical: The dose must be completed before incision to ensure adequate tissue concentrations at the moment of bacterial exposure 2

Intra-operative Re-dosing

• Re-dose with 1 g IV if the procedure exceeds 4 hours to maintain therapeutic levels throughout prolonged surgery 3, 1, 2
• If the initial dose was given more than 60 minutes before incision and surgery is delayed beyond one hour, repeat the full 2 g dose 1

Treatment Dosing (Non-Prophylactic)

For moderate-to-severe infections:

• Cefazolin 500 mg to 1 g IV every 6–8 hours 2

For severe, life-threatening infections (endocarditis, septicemia):

• Cefazolin 1–1.5 g IV every 6 hours 2
• For endocarditis specifically, the guideline-recommended dose is 6 g per 24 hours IV divided into 3 equally divided doses (2 g every 8 hours) for 6 weeks 3

For mild infections (susceptible gram-positive cocci):

• Cefazolin 250–500 mg IV every 8 hours 2

For uncomplicated urinary tract infections:

• Cefazolin 1 g IV every 12 hours 2

Procedure-Specific Prophylaxis Dosing

Cardiac Surgery

• Cefazolin 2 g IV pre-operatively plus 1 g added directly to the cardiopulmonary bypass priming solution 1
• Re-dose 1 g IV at 4 hours if surgery continues 1

Orthopedic Surgery with Prosthetic Material

• Cefazolin 2 g IV slow infusion as a single dose 3, 1
• Re-dose 1 g if duration exceeds 4 hours 3
• Limited to the operative period (maximum 24 hours post-operatively) 3

Bariatric Surgery

• Higher dosing required: Cefazolin 4 g IV over 30 minutes for gastric band procedures 1
• Re-dose 2 g IV if surgery exceeds 4 hours 1

Route of Administration

Intravenous is the standard and preferred route for both prophylaxis and treatment in hospitalized patients 1, 2

• IV push: Can be given over 5 minutes for rapid administration 4
• IV infusion: Slow infusion over 30 minutes is preferred to minimize adverse reactions 1
• Intramuscular: The FDA label permits IM administration for treatment dosing, but IV is strongly preferred for surgical prophylaxis 2
• Subcutaneous: Recent research suggests SC administration is feasible with 74.8% bioavailability, but this is not yet standard practice and requires further validation 5

Critical Duration Limits

Prophylaxis must be stopped no later than 24 hours post-operatively 3, 1, 2

• Extending beyond 24 hours constitutes treatment rather than prophylaxis and increases antimicrobial resistance risk 1
• The presence of surgical drains does not justify extending prophylaxis duration 6, 1

Common Pitfalls to Avoid

Timing Errors

• Do not give cefazolin too early: If administered more than 60 minutes before incision and surgery is delayed, you must re-dose the full amount 1
• Do not give it too late: The infusion must be completed before the surgical incision 2

Dosing Errors in Obesity

• Standard 2 g dose is adequate for most obese patients (BMI 40–50 kg/m²) for procedures lasting less than 5 hours 4, 7
• Weight-based dosing (e.g., 3 g) is not supported by pharmacokinetic principles because cefazolin is hydrophilic and does not penetrate adipose tissue regardless of dose 7
• The 2 g dose achieves peak serum concentrations of approximately 185 mcg/mL, providing at least 6 hours of protection above the MIC for common SSI pathogens 7

Duration Errors

• Never continue prophylaxis beyond 24 hours based on patient anxiety, ICU stay, or presence of drains 1
• For cardiac and prosthetic joint surgery, some older guidelines suggested 3–5 days of prophylaxis, but current evidence limits this to 24 hours maximum 2

Re-dosing Errors

• Do not re-dose before 4 hours unless there is massive blood loss or the initial dose was mistimed 1
• Do not forget to re-dose if the procedure genuinely exceeds 4 hours 3, 1

Alternative Regimens for β-Lactam Allergy

If documented β-lactam allergy:

• Vancomycin 30 mg/kg IV (actual body weight) infused over 120 minutes, completing at least 30 minutes before incision 1
• Maximum vancomycin infusion rate: ≤1000 mg/h to prevent Red-Man syndrome 1
• Alternative: Clindamycin 900 mg IV slow infusion as a single dose 3, 1