What is the recommended use and dosage of Cefazolin (a cephalosporin antibiotic) for treating bacterial infections?

Cefazolin: Recommended Use and Dosing

Cefazolin is a first-generation cephalosporin primarily used for surgical prophylaxis and treatment of methicillin-susceptible staphylococcal and streptococcal infections, with standard adult dosing of 1-2 grams IV every 8 hours for treatment and 2 grams IV for surgical prophylaxis.

Primary Indications

Surgical Prophylaxis

• Administer 2 grams IV slow infusion 30-60 minutes before surgical incision to ensure adequate tissue levels at the time of initial incision 1
• For lengthy procedures (≥2 hours), re-dose with 1 gram IV intraoperatively 1
• Continue 500 mg to 1 gram IV every 6-8 hours for 24 hours postoperatively 1
• For high-risk procedures (open-heart surgery, prosthetic arthroplasty), prophylaxis may extend 3-5 days post-surgery 1

Specific Surgical Applications

• Orthopedic surgery with prosthetic material: 2 grams IV slow, with 1 gram re-injection if duration exceeds 4 hours, limited to operative period (maximum 24 hours) 2
• Closed fractures requiring intrafocal osteosynthesis: Same dosing as above 2
• Post-surgical wound infections (trunk/extremity away from axilla or perineum): 0.5-1 gram every 8 hours IV 2

Treatment Dosing

Adult Dosing by Infection Severity

• Mild infections (susceptible gram-positive cocci): 250-500 mg every 8 hours 1
• Moderate to severe infections: 500 mg to 1 gram every 6-8 hours 1
• Severe, life-threatening infections (endocarditis, septicemia): 1-1.5 grams every 6 hours 1
• Acute uncomplicated UTI: 1 gram every 12 hours 1
• Pneumococcal pneumonia: 500 mg every 12 hours 1

Pediatric Dosing

• Mild to moderate infections: 25-50 mg/kg/day divided into 3-4 equal doses 1
• Severe infections: Up to 100 mg/kg/day 1
• Staphylococcal infections: 33 mg/kg/dose every 8 hours IV 2
• Not recommended in premature infants and neonates due to lack of safety data 1

Renal Dose Adjustments

Critical dosing modifications based on creatinine clearance 1:

• CrCl ≥55 mL/min or SCr ≤1.5 mg/dL: Full dose
• CrCl 35-54 mL/min or SCr 1.6-3.0 mg/dL: Full dose but restrict to at least 8-hour intervals
• CrCl 11-34 mL/min or SCr 3.1-4.5 mg/dL: Half the usual dose every 12 hours
• CrCl ≤10 mL/min or SCr ≥4.6 mg/dL: Half the usual dose every 18-24 hours

All reduced dosing applies after an appropriate initial loading dose 1

Spectrum of Activity and Critical Limitations

Effective Against

• Methicillin-susceptible Staphylococcus aureus (MSSA) 3, 4
• Streptococci including S. pyogenes 2, 4
• Escherichia coli, Klebsiella species, Proteus mirabilis 4

Complete Ineffectiveness Against

• Methicillin-resistant S. aureus (MRSA) - never use cefazolin if MRSA suspected 3
• Pseudomonas aeruginosa 3
• Poor activity against Haemophilus influenzae and Moraxella catarrhalis 3

Clinical Scenarios Where Cefazolin Should NOT Be Used

Bite Wounds

Cefazolin is NOT recommended for animal or human bite wounds because it misses critical pathogens 3:

• Animal bites: Use amoxicillin-clavulanate 875/125 mg twice daily instead (covers Pasteurella multocida and anaerobes) 3
• Human bites: Use amoxicillin-clavulanate 875/125 mg twice daily or ampicillin-sulbactam 1.5-3.0 grams IV every 6 hours (covers Eikenella corrodens and anaerobes) 3

Necrotizing Infections

For necrotizing fasciitis or aggressive polymicrobial infections, cefazolin alone is inadequate 2:

• Requires broad-spectrum coverage: vancomycin or linezolid PLUS piperacillin-tazobactam or carbapenem 2
• For axilla/perineum surgery: requires anaerobic coverage with metronidazole plus ciprofloxacin or ceftriaxone 2

Special Considerations

Obesity and Weight-Based Dosing

• Standard 2-gram prophylactic dose may be inadequate in patients ≥120 kg, though evidence is mixed 5
• Some guidelines recommend 3 grams for patients ≥120 kg, though this is based primarily on pharmacokinetic rather than clinical outcome data 5
• Trends suggest higher SSI rates with 2-gram dosing in obese patients, though not statistically significant 5

Site-Specific Pharmacokinetics

Cefazolin concentrations vary significantly by surgical site 6:

• Hip surgery achieves higher bone concentrations than knee surgery (mean difference 4 μg/g) 6
• Distal extremity sites may require higher doses due to lower tissue penetration 6

Penicillin Allergy

• Can be used in non-severe penicillin allergy 3
• Contraindicated in patients with history of anaphylaxis, angioedema, or urticaria to penicillins 3
• Alternative for severe allergy in surgical prophylaxis: clindamycin 900 mg IV or vancomycin 30 mg/kg over 120 minutes 2

Alternative Administration Route

• Subcutaneous administration (3 grams twice daily or 6 grams continuous 24-hour infusion) shows favorable pharmacokinetics with 74.8% bioavailability and improved PTA compared to IV dosing 7
• Well tolerated with slower absorption in patients with BMI ≥30 7

Common Pitfalls to Avoid

• Never use cefazolin monotherapy for infections involving axilla or perineum - requires anaerobic coverage 2
• Do not rely on cefazolin for MRSA coverage - add vancomycin if MRSA suspected 2, 3
• Avoid extending surgical prophylaxis beyond 24 hours for most procedures (except high-risk cases like prosthetic joints) 1
• Do not use for empiric treatment of necrotizing infections - requires immediate broad-spectrum therapy 2