Recommended Dosing Intervals for Ancef (Cefazolin) IV
The recommended dosing interval for Ancef (Cefazolin) IV is every 8 hours for most standard indications, with adjustments based on renal function and specific infection types. 1
Standard Adult Dosing Intervals
- For moderate to severe infections: Administer 500 mg to 1 gram every 6 to 8 hours 1
- For mild infections caused by susceptible gram-positive cocci: 250 mg to 500 mg every 8 hours 1
- For severe, life-threatening infections (e.g., endocarditis, septicemia): 1 gram to 1.5 grams every 6 hours 1
- For acute, uncomplicated urinary tract infections: 1 gram every 12 hours 1
- For pneumococcal pneumonia: 500 mg every 12 hours 1
Pediatric Dosing Intervals
- For most mild to moderately severe infections: Total daily dosage of 25 to 50 mg/kg divided into 3 or 4 equal doses (every 8 hours or every 6 hours) 1
- For severe infections: Total daily dosage may be increased to 100 mg/kg divided every 8 hours 1
- For staphylococcal infections (including methicillin-susceptible S. aureus): 150 mg/kg/day divided every 8 hours 2
- For infective endocarditis: 100 mg/kg/day IV divided every 8 hours (maximum 12 g daily) 2
Dosing Interval Adjustments for Renal Impairment
- For patients with creatinine clearance ≥55 mL/min or serum creatinine ≤1.5 mg%: Standard intervals (every 6-8 hours) 1
- For patients with creatinine clearance 35-54 mL/min or serum creatinine 1.6-3.0 mg%: At least every 8 hours 1
- For patients with creatinine clearance 11-34 mL/min or serum creatinine 3.1-4.5 mg%: Every 12 hours (with half the usual dose) 1
- For patients with creatinine clearance ≤10 mL/min or serum creatinine ≥4.6 mg%: Every 18-24 hours (with half the usual dose) 1
Special Considerations
- For perioperative prophylaxis: 1 gram IV administered 30-60 minutes prior to surgery, with additional doses of 500 mg to 1 gram every 6-8 hours for 24 hours postoperatively 1
- For lengthy surgical procedures (≥2 hours): Additional intraoperative doses of 500 mg to 1 gram 1
- For surgery where infection may be particularly devastating (e.g., open-heart surgery, prosthetic arthroplasty): Consider extending prophylactic administration for 3-5 days 1
Pharmacokinetic Considerations
- The 8-hour interval for standard dosing aligns with cefazolin's half-life of approximately 2 hours in patients with normal renal function 3
- Time-dependent antibiotics like cefazolin require maintaining concentrations above the MIC for optimal bactericidal effect 4
- Loading doses are particularly important in critically ill patients to achieve therapeutic concentrations quickly, regardless of renal function 4
Important Caveats
- Always administer a proper loading dose before implementing adjusted maintenance dosing schedules in patients with renal impairment 1
- For CNS infections, maintain the every 8-hour interval even at high doses (100 mg/kg/day) to ensure adequate penetration 5
- Therapeutic drug monitoring may be beneficial in critically ill patients to ensure optimal dosing 4
- Pain is minimal after intramuscular injection, and thrombophlebitis is rare with IV administration 6