Cefazolin Dosing for GBS Prophylaxis
For GBS prophylaxis in penicillin-allergic pregnant women without high-risk allergy features, administer cefazolin 2 g IV as the initial dose, followed by 1 g IV every 8 hours until delivery. 1
Dosing Regimen
- Initial loading dose: 2 g IV 1, 2, 3
- Maintenance dose: 1 g IV every 8 hours until delivery 1, 2, 3
- The first dose should ideally be administered at least 2 hours before delivery to achieve maximum preventive effect, as effectiveness increases from 71% to 89% when given ≥2 hours before delivery 4
When Cefazolin is Indicated
- Cefazolin is the preferred alternative for penicillin-allergic pregnant women who do NOT have a history of anaphylaxis, angioedema, respiratory distress, or urticaria following penicillin or cephalosporin administration 1
- This recommendation is based on pharmacologic data showing cefazolin achieves effective intraamniotic concentrations 1
- Research confirms that cefazolin concentrations exceed the MIC₉₀ for GBS in nearly all maternal, fetal, and amniotic fluid samples when using this dosing regimen 5
Critical Contraindications
Do NOT use cefazolin in patients with high-risk penicillin allergy features including: 1
- History of anaphylaxis
- History of angioedema
- History of respiratory distress or urticaria following penicillin or cephalosporin administration
- Approximately 10% of penicillin-allergic patients also have immediate hypersensitivity to cephalosporins 2
Alternative Agents for High-Risk Allergies
For patients at high risk for anaphylaxis: 1, 3
- Clindamycin 900 mg IV every 8 hours (if GBS isolate is susceptible to both clindamycin and erythromycin)
- Vancomycin 1 g IV every 12 hours (if susceptibility testing unavailable or isolate is resistant)
Pharmacokinetic Evidence Supporting This Dosing
- Population pharmacokinetic modeling demonstrates that the standard 2 g loading dose followed by 1 g every 8 hours provides adequate maternal and umbilical cord exposure for up to 12 hours 6
- At delivery, maternal and arterial umbilical cord unbound cefazolin concentrations exceeded the target of 1 mg/L in 95.8% and 91.7% of cases respectively 6
- All GBS isolates remain universally susceptible to cefazolin, supporting its continued use 7
Common Pitfalls to Avoid
- Never use cefazolin in patients with documented high-risk penicillin allergy - approximately 10% will cross-react 2
- Do not underdose - the 2 g loading dose is essential to achieve rapid therapeutic levels 1
- Do not extend the dosing interval beyond 8 hours - this is longer than typical cefazolin dosing due to pregnancy-related pharmacokinetic changes 1
- Verify allergy history - many reported penicillin allergies are not true IgE-mediated reactions, and patients may be candidates for penicillin rather than cefazolin 2