01Why Antibiotic Prophylaxis Matters
- Surgical site infection is the most common postoperative adverse event
- Medicare no longer reimburses for certain SSIs (mediastinitis post-cardiac, post-bariatric, some ortho)
- Best practice combines:
- Sterility (surgeon, instruments, drapes)
- Skin prep (clipping > shaving; let antiseptic dry)
- Timely antibiotic prophylaxis
02Timing of Prophylaxis
- Within 60 minutes before surgical incision (ideally 15–45 min) for adequate serum and tissue levels
- Exceptions: IV vancomycin and ciprofloxacin — slower infusion → start ~1 h before incision
- If tourniquet is used → give entire dose before inflation
- Exceptions when pre-incision dosing is NOT done:
- Active ongoing antibiotic therapy
- Surgeon declined
- Surgery may not require antibiotics
- Delay until specimen sent for culture
Time-to-incision relationship: rates of SSI increase steeply when antibiotics are given > 60 min before, or after incision.
03Wound Classification (CDC/NHSN)
| Class | SSI rate | Examples |
|---|---|---|
| Clean | 1.3–2.9% | Uninfected; respiratory/GI/GU not entered. Skin flora (CoNS, MSSA/MRSA, strep) |
| Clean-contaminated | 2.4–7.7% | Respiratory/GI/GU entered, controlled. Skin flora + gram-negatives, Enterococci |
| Contaminated | 6.4–15.2% | Fresh accidental wounds; major sterility breaks; gross GI spillage |
| Dirty / infected | 7.1–40% | Old traumatic wounds; existing clinical infection or perforated viscera |
04Selected Antibiotic Choices (Stanford 2017)
| Surgery | Preferred | β-lactam allergy |
|---|---|---|
| Cardiac / vascular / thoracic / device implant / general / neuro / ortho / plastics | Cefazolin | Vancomycin (preferred) or clindamycin |
| Cardiac w/ prosthetic material | Cefazolin + Vancomycin | Vancomycin |
| Gastroduodenal | Cefazolin | Vancomycin + Gentamicin |
| Biliary | Cefazolin | Metronidazole + Levofloxacin |
| Colorectal / appendectomy | Cefazolin + Metronidazole | Metronidazole + Levofloxacin |
| OB-GYN / hysterectomy / C-section | Cefazolin | Clindamycin + Gentamicin |
| Urology (clean) | Cefazolin | Gentamicin + Clindamycin |
| Urology (clean-contam w/ ileal conduit) | Cefoxitin | Metronidazole + Levofloxacin |
| Head & neck clean | Cefazolin | Clindamycin |
| H&N w/ oral mucosa breach | Cefazolin + Metronidazole | Clindamycin |
05Dosing & Re-dosing
| Antibiotic | Dose | Re-dose interval |
|---|---|---|
| Cefazolin | < 120 kg: 2 g; > 120 kg: 3 g | 4 h |
| Cefoxitin | 2 g | 2 h |
| Cefuroxime | 1.5 g | 4 h |
| Ceftriaxone | 2 g | No re-dose (long half-life) |
| Vancomycin | 15 mg/kg (max 2 g) | No re-dose if < 6 h |
| Clindamycin | 900 mg | 6 h |
| Metronidazole | 500 mg | 6 h (long half-life) |
| Gentamicin | 5 mg/kg | No re-dose typically |
| Ciprofloxacin | 400 mg | No re-dose |
| Ampicillin-sulbactam | 3 g | 2 h |
| Piperacillin-tazobactam | 3.375 g | 2 h |
Re-dose triggers: elapsed time exceeded; blood loss > 1500 mL; massive fluid resuscitation.
06Antibiotics That Augment Neuromuscular Blockade
- Aminoglycosides (gentamicin, neomycin, streptomycin) — most significant
- Polymyxins
- Tetracyclines (mild)
- Clindamycin (mild)
- Lincomycin
Clindamycin is sometimes tested as NOT augmenting NMB significantly (compared to aminoglycosides) — ITE trap.
07β-Lactam (Penicillin) Allergy
- True IgE-mediated penicillin allergy is rare (< 10% of self-reported).
- Cross-reactivity of penicillin to cephalosporins ~1% (much lower than the historical 10% number).
- Cefazolin and other cephalosporins are generally safe in patients with non-severe penicillin reactions (rash, GI).
- Avoid cephalosporins only with documented severe reactions: anaphylaxis, Stevens-Johnson, TEN, DRESS, interstitial nephritis, hemolytic anemia.
- When unclear → vancomycin or clindamycin per institutional protocol.