Cefazolin (Ancef) Dosing Frequency
No, Ancef (cefazolin) is not given IV daily—it is typically administered every 8 hours for most therapeutic indications.
Standard Dosing Intervals
The most common dosing schedule for cefazolin is every 8 hours, as supported by multiple high-quality guidelines:
- For skin and soft tissue infections caused by methicillin-susceptible Staphylococcus aureus (MSSA), cefazolin is dosed at 1 g IV every 8 hours in adults 1
- For pediatric staphylococcal infections, the recommended regimen is 33 mg/kg/dose every 8 hours 1
- For perinatal Group B Streptococcus prophylaxis, cefazolin is given as 2 g IV initial dose, then 1 g IV every 8 hours until delivery 1
- For infective endocarditis in children, dosing is 100 mg/kg/day divided every 8 hours (maximum 12 g daily) 2, 3
Once-Daily Dosing: Limited Applications
While every-8-hour dosing is standard, once-daily cefazolin is used only in specific circumstances:
- Surgical prophylaxis contexts where single-dose or limited redosing is appropriate 2
- With probenecid co-administration: Cefazolin 2000 mg IV once daily plus oral probenecid 500 mg four times daily can maintain therapeutic levels, though this is not standard practice 4
The pharmacokinetic rationale for frequent dosing is clear: cefazolin has a serum half-life of approximately 1.8 hours IV 5, and as a time-dependent beta-lactam antibiotic, it requires sustained concentrations above the minimum inhibitory concentration (MIC) for optimal bactericidal activity 6.
Common Pitfall to Avoid
Do not confuse cefazolin with ertapenem, which is genuinely dosed once daily (1 g every 24 hours) for necrotizing infections 1. This is a critical distinction, as using once-daily cefazolin without probenecid will result in subtherapeutic trough levels—serum concentrations drop to approximately 4 mcg/mL at 8 hours after a 1 g dose 5, which may be inadequate for many infections.
Alternative Dosing Strategy
For bone and joint infections, continuous infusion of cefazolin (administered over 12 hours twice daily, median 6 g/day total) has demonstrated efficacy and maintained therapeutic serum levels (median 57-63 mcg/mL) 6. However, this remains an alternative approach rather than standard practice.