## Empiric Coverage of Surgical Site Infection (SSI) ### Clinical Context Postoperative SSI in abdominal surgery typically involves polymicrobial flora including gram-positive cocci (Staphylococcus aureus), gram-negative bacilli (E. coli, Klebsiella), and anaerobes (Bacteroides, Clostridium). ### Drug of Choice Rationale **Key Point:** Ceftriaxone + Metronidazole is the preferred empiric regimen for established abdominal SSI because it provides: - Broad gram-negative coverage (ceftriaxone) - Anaerobic coverage (metronidazole) - Excellent tissue penetration into wound and peritoneal cavity ### Comparison of Options | Agent | Coverage | Use Case | Limitation | |-------|----------|----------|-------------| | Cefazolin | Gram-positive, some gram-negative | Prophylaxis only | Inadequate anaerobic coverage for established SSI | | Ceftriaxone + Metronidazole | Gram-positive, gram-negative, anaerobes | Empiric treatment of established SSI | Gold standard | | Penicillin G | Gram-positive, anaerobes | Outdated | Poor gram-negative coverage | | Fluoroquinolone monotherapy | Gram-negative, limited gram-positive | Oral step-down only | Inadequate anaerobic and gram-positive coverage | ### High-Yield Facts **High-Yield:** Cefazolin is appropriate for *surgical prophylaxis* (given preoperatively), but once SSI is established and culture results are pending, broader empiric coverage is mandatory. **Clinical Pearl:** The addition of metronidazole is critical because anaerobic organisms are common in abdominal SSI and cephalosporins alone do not reliably cover them. **Mnemonic:** **ABCD of SSI coverage** — **A**naerobes (metronidazole), **B**road gram-negative (cephalosporin), **C**ephalosporin choice (3rd generation), **D**epth of tissue penetration.
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