Antimicrobial Therapy in Surgical Infections

Antimicrobial Prophylaxis - Pre-emptive Strike!

• Goal: Prevent SSIs; achieve bactericidal tissue levels before incision. Not for active infection.
• Timing - CRITICAL:

  ⭐ Prophylactic antibiotics should be administered within 60 minutes (or 120 minutes for vancomycin/fluoroquinolones) before surgical incision.

• Duration:
  • Usually single pre-op dose.
  • Discontinue within 24 hours post-op (most cases). Prolonged use ↑ resistance.
• Selection Principles:
  • Targets likely pathogens for specific surgery.
  • Consider patient allergies & local antibiogram.
  • Cefazolin (1st/2nd gen ceph): Standard for many clean/clean-contaminated procedures.
  • Vancomycin: MRSA risk / severe β-lactam allergy.
  • Anaerobic cover (e.g., Metronidazole): For colorectal, appendiceal, some GYN surgeries.
• Indications (Wound Class):
  • Clean-contaminated (Class II).
  • Contaminated (Class III) - prophylaxis blends with empiric therapy.
  • Clean (Class I) if:
    • Prosthetic implant (joint, valve, graft).
    • High-risk patient (e.g., immunocompromised, diabetes).
• Intraoperative Redosing:
  • Surgery duration >2 drug half-lives (e.g., >3-4 hrs for Cefazolin).
  • Major blood loss (>1500 mL).

Empiric & Definitive Therapy - Battle Plan!

• Empiric Therapy (Initial Broad Attack):
  • ASAP for severe infections (sepsis, necrotizing fasciitis).
  • Broad-spectrum: Covers Gram (+), Gram (-), anaerobes.
    • Consider: Local antibiogram, infection site, host factors (immune status, allergies).
    • Common choices: Piperacillin-tazobactam, carbapenems; add Vancomycin if MRSA suspected.
  • Reassess response & cultures at 48-72 hours.
• Definitive Therapy (Precision Strike):
  • Tailor to Culture & Sensitivity (C&S) results.
  • De-escalate: Narrowest effective spectrum, IV to PO switch.
  • Duration: Varies by infection type/severity & resolution (e.g., uncomplicated cellulitis 5-7 days; intra-abdominal 4-7 days post-source control).
• Source Control: The Decisive Action!

  ⭐ Source control (e.g., drainage of abscess, debridement of necrotic tissue, removal of infected device) is paramount in managing surgical infections, often more critical than antibiotic choice alone.

Special Scenarios & Resistance - Tough Cases!

• Necrotizing Soft Tissue Infections (NSTI):

  • Urgent, wide surgical debridement = cornerstone.
  • Empiric Rx: Broad-spectrum (e.g., Piperacillin-Tazobactam + Clindamycin + Vancomycin/Linezolid).
  • Clindamycin: ↓ toxin production (Strep/Staph).
  • 

  ⭐ The LRINEC score (Laboratory Risk Indicator for Necrotizing Fasciitis) ≥ 6 suggests NSTI, prompting urgent surgical exploration.

• Sepsis & Septic Shock in Surgical Patients:

  • Hour-1 Bundle: Cultures, broad-spectrum IV antibiotics, IV fluids, vasopressors if MAP < 65 mmHg.
  • Source control is critical.
  • De-escalate therapy based on culture results.

• Infections in Immunocompromised Host:

  • Higher risk: opportunistic pathogens (fungi, atypical bacteria).
  • Empiric therapy: broader coverage (e.g., anti-pseudomonal + MRSA + antifungal if high risk).
  • Consider G-CSF for neutropenia.

• Managing Antibiotic Resistance:

  • MRSA: Vancomycin, Linezolid, Daptomycin.
  • VRE: Linezolid, Daptomycin.
  • ESBL Producers: Carbapenems (Imipenem, Meropenem).
  • CRE (Carbapenem-Resistant Enterobacteriaceae): Colistin, Tigecycline, newer combos (e.g., Ceftazidime-avibactam).

  💡 Tailor to local antibiogram & C/S; practice antibiotic stewardship.

High‑Yield Points - ⚡ Biggest Takeaways

• Empirical therapy targets likely pathogens based on site and local antibiogram.
• Give prophylactic antibiotics 30-60 minutes before incision; re-dose for long surgeries/blood loss.
• Cefazolin is a common choice for surgical prophylaxis.
• For colorectal surgery, add anaerobic coverage (e.g., metronidazole).
• Use Vancomycin or clindamycin for beta-lactam allergic patients.
• Prophylaxis duration: single dose or ≤ 24 hours post-op.
• Source control (drainage, debridement) is paramount, often more critical than antibiotics_._