Which antibiotic regimen is recommended for prophylaxis of endometritis in a woman undergoing cesarean delivery?

Prophylactic Antibiotic Regimen for Cesarean Section

None of the options listed (A-D) represent the current standard of care; the correct answer is cefazolin 2g IV given 30-60 minutes before skin incision, with azithromycin added for women in labor or with ruptured membranes. 1

Why the Listed Options Are Incorrect

Option A: Gentamicin + Ceftriaxone

• This combination is NOT a first-line recommendation in major obstetric guidelines for cesarean prophylaxis. 1
• Gentamicin plus ceftriaxone is reserved for treatment of established infections or as an alternative regimen in patients with documented penicillin/cephalosporin allergies. 1
• This regimen does not align with ACOG's evidence-based recommendations for routine prophylaxis. 1

Option B: Metronidazole Alone

• Metronidazole monotherapy is inadequate because it provides only anaerobic coverage and lacks activity against the aerobic gram-positive organisms (particularly skin flora like Staphylococcus) that commonly cause surgical site infections. 2
• Metronidazole is used as an adjunct to cefazolin in specific high-risk scenarios (e.g., suspected chorioamnionitis), never as sole prophylaxis. 1

Option C: No Antibiotics

• This is unequivocally wrong. Prophylactic antibiotics reduce postcesarean endometritis by approximately 43% when given pre-incision (RR 0.57,95% CI 0.36-0.90). 3
• The combination of cefazolin plus azithromycin reduced endometritis rates from 16.4% to 1.3% in a large cohort study. 4

Option D: Amoxicillin Alone

• Amoxicillin is not recommended as the primary prophylactic agent. 1
• First-generation cephalosporins (cefazolin) are preferred due to superior efficacy, better pharmacokinetics, and broader coverage of skin and vaginal flora. 1

The Correct Evidence-Based Regimen

Standard Prophylaxis (All Cesarean Deliveries)

• Cefazolin 2g IV as a single dose, administered 30-60 minutes before skin incision. 1
• This represents high-quality evidence with a strong recommendation grade from ACOG. 1
• Timing is critical: pre-incision administration is superior to post-cord-clamping dosing for reducing infectious morbidity. 1, 3

Enhanced Prophylaxis (High-Risk Patients)

• Add azithromycin 500mg IV to cefazolin for women who are in labor or have ruptured membranes. 1, 4
• This dual-agent regimen provides superior protection against postoperative endometritis compared to cefazolin alone, reducing rates to approximately 1.3%. 4
• The addition of azithromycin addresses the increased bacterial burden and broader spectrum of organisms in the setting of labor or membrane rupture. 1

Penicillin/Cephalosporin Allergy

• Clindamycin 900mg IV plus gentamicin 5mg/kg IV provides both gram-positive and anaerobic coverage in allergic patients. 1
• Administer clindamycin as a slow IV infusion to avoid infusion-related reactions. 1

Key Clinical Pearls

Timing Matters

• Antibiotics must be given 30-60 minutes before skin incision, not after cord clamping. 1
• Pre-incision dosing significantly reduces endometritis compared to post-cord-clamping administration. 3

Single Dose Is Sufficient

• No additional doses are needed if the procedure duration is less than 4 hours. 1
• Multiple-dose regimens offer no added benefit over single-dose prophylaxis (OR 0.92,95% CI 0.70-1.23). 5

Antibiotic Spectrum

• First-generation cephalosporins (cefazolin) and ampicillin have similar efficacy (OR 1.27,95% CI 0.84-1.93). 5
• Broader-spectrum second- or third-generation agents provide no additional benefit for routine prophylaxis (OR 1.21,95% CI 0.97-1.51). 5

If forced to choose from the options provided, none are correct. The evidence unequivocally supports cefazolin (not listed) as the standard of care. 1, 4, 5, 3