Common Cefazolin (Ancef) Dosing
For adults with normal renal function, cefazolin is dosed at 1-2 grams every 8 hours for moderate to severe infections, with doses ranging from 500 mg to 1 gram every 6-8 hours depending on infection severity. 1
Adult Dosing by Indication
Treatment Dosing (Normal Renal Function)
- Moderate to severe infections: 500 mg to 1 gram IV every 6-8 hours 1
- Mild infections (susceptible gram-positive cocci): 250-500 mg IV every 8 hours 1
- Severe/life-threatening infections (endocarditis, septicemia): 1-1.5 grams IV every 6 hours 1
- Uncomplicated UTI: 1 gram IV every 12 hours 1
- Pneumococcal pneumonia: 500 mg IV every 12 hours 1
- MSSA infections (skin/soft tissue): 1 gram IV every 8 hours 2, 3
- MSSA pneumonia: 150 mg/kg/day divided every 8 hours 4
In rare cases of extremely severe infections, doses up to 12 grams daily have been used 1.
Surgical Prophylaxis
- Preoperative: 2 grams IV given 30-60 minutes before incision (3 grams if ≥120 kg) 1
- Intraoperative redosing: 1 gram IV every 2-4 hours for prolonged procedures 1
- Postoperative: 500 mg to 1 gram IV every 6-8 hours for 24 hours 1
- High-risk surgery (cardiac, prosthetic joints): May continue 3-5 days postoperatively 1
The timing is critical—the preoperative dose must be given 30-60 minutes before incision to ensure adequate tissue levels at the time of surgical exposure 1.
Pediatric Dosing
Treatment (Normal Renal Function)
- Mild to moderate infections: 25-50 mg/kg/day divided every 6-8 hours 1
- Severe infections: Up to 100 mg/kg/day (maximum 45 mg/lb/day) 1
- MSSA pneumonia: 150 mg/kg/day divided every 8 hours 4
Important caveat: Cefazolin is not recommended for premature infants and neonates due to lack of safety data 1.
Renal Impairment Dosing
Adults
After an initial full loading dose appropriate to infection severity 1:
- CrCl ≥55 mL/min (SCr ≤1.5 mg/dL): Full dose, no adjustment needed 1
- CrCl 35-54 mL/min (SCr 1.6-3.0 mg/dL): Full dose but extend interval to at least every 8 hours 1
- CrCl 11-34 mL/min (SCr 3.1-4.5 mg/dL): 50% of usual dose every 12 hours 1
- CrCl ≤10 mL/min (SCr ≥4.6 mg/dL): 50% of usual dose every 18-24 hours 1
The serum half-life extends from 1.6-2.2 hours in normal function to approximately 42 hours in anephric patients 5, 6.
Pediatric Renal Impairment
After an initial loading dose 1:
- CrCl 40-70 mL/min: 60% of normal daily dose divided every 12 hours 1
- CrCl 20-40 mL/min: 25% of normal daily dose divided every 12 hours 1
- CrCl 5-20 mL/min: 10% of normal daily dose every 24 hours 1
Key Clinical Pearls
Obesity considerations: Standard weight-based dosing may be inadequate in patients with obesity, particularly for achieving therapeutic concentrations in subcutaneous adipose tissue 7. For surgical prophylaxis in patients ≥120 kg, use 3 grams preoperatively 1, 8.
CNS infections: For MSSA meningitis, high-dose continuous infusion (6-12 g/day) or intermittent dosing of 2 grams every 6 hours may be required to achieve adequate CSF concentrations, as the CSF:plasma ratio is only approximately 0.0525 9, 10.
Dialysis: Cefazolin is removed by hemodialysis; supplemental dosing post-dialysis is necessary 6, 11. The elimination rate constant correlates linearly with creatinine clearance (Ke = 0.022 + 0.0028 × CrCl) 12.
Always give a loading dose in renal impairment—the loading dose is not affected by renal function, only maintenance dosing 1.