Antibiotic Prophylaxis

What is Antibiotic Prophylaxis?

Antibiotic prophylaxis is the pre-emptive administration of antimicrobials to prevent infection in patients who are not yet infected but are at elevated risk due to planned procedures, immunocompromised states, or specific exposures. The goal is to achieve adequate tissue/serum drug concentration before bacterial contamination occurs.

Timing

Administer 30–60 min before incision. Vancomycin/fluoroquinolones: begin 120 min before. Repeat if surgery >2 half-lives or blood loss >1500 mL.

Spectrum

Target the most likely pathogens for the procedure site. Narrow-spectrum preferred. Broad empiric cover is NOT prophylaxis.

Duration

Single dose or ≤24 hours post-op for most surgical prophylaxis. Cardiac surgery: up to 48h. Longer ≠ better and increases resistance.

Core Principles (ASHP/IDSA/WHO)

Indication must be evidence-based. Not all surgeries require prophylaxis — Clean (Class I) wounds have SSI rates <2% without prophylaxis. Prophylaxis is indicated for clean-contaminated (Class II), implant/prosthesis surgery, and high-risk patients.

Correct drug at the correct dose. Weight-based dosing: Cefazolin 2g (3g if ≥120 kg). Underdosing in obese patients is the #1 modifiable failure point.

Redosing intraoperatively. Redose at 2× the half-life of the drug (Cefazolin q4h intra-op; Cefoxitin q2h). Also redose for significant blood loss (>1500 mL).

Discontinue promptly. Extended prophylaxis beyond 24h does NOT reduce SSI rates but DOES increase C. difficile risk, resistance emergence, and drug-related adverse events.

Consider local antibiogram. If institutional MRSA rates >10–20% for the specific procedure, add Vancomycin to (not replace) standard prophylaxis.

Surgical Wound Classification & SSI Risk

Class	Type	SSI Rate	Prophylaxis?	Examples
I	Clean	1–3%	Only if implant/prosthesis	Thyroidectomy, hernia (no mesh), breast biopsy
II	Clean-Contaminated	3–11%	Yes — Recommended	Cholecystectomy, hysterectomy, elective colon
III	Contaminated	10–17%	Yes → Treatment	Open fractures, GI spillage, fresh traumatic wounds
IV	Dirty/Infected	>27%	Treatment (not prophylaxis)	Abscess drainage, perforated viscus, fecal peritonitis

Surgical Prophylaxis by Procedure

ASHP/IDSA/SIS/SHEA Clinical Practice Guidelines 2013 (updated). β-lactam allergy alternatives listed.

Cardiac Surgery (CABG, Valve, Device Implant)

First Line: Cefazolin 2g IV (3g if ≥120 kg), within 60 min of incision. Redose q4h intra-op.

Penicillin Allergy: Vancomycin 15 mg/kg IV (begin 120 min before) OR Clindamycin 900 mg IV.

Duration: ≤48 hours post-op. Single dose may be adequate for low-risk.

Organisms: S. aureus, CoNS, Gram-negative bacilli.

If MRSA prevalence high: add Vancomycin to Cefazolin (do not replace). Consider mupirocin nasal decolonization + CHG bathing (NICE/WHO).

Orthopaedic (Arthroplasty, Spine, Open Fractures)

Joint Replacement/Spine with Hardware: Cefazolin 2g IV. Duration ≤24h.

Open Fractures:

Gustilo I–II: Cefazolin 2g IV q8h × 24h (some extend to 72h or until wound closure)
Gustilo III: Cefazolin + Gentamicin (or add Metronidazole for farm/soil contamination)
Gustilo IIIC (vascular injury): Add Penicillin G for Clostridial coverage

Allergy: Vancomycin or Clindamycin. For Gram-neg cover: Aztreonam or Aminoglycoside.

GI / Colorectal Surgery

Colorectal: Cefazolin 2g + Metronidazole 500 mg IV. OR Ertapenem 1g IV single dose.

Mechanical Bowel Prep + Oral Antibiotics (MBP+OA): Neomycin 1g + Erythromycin base 1g PO at 1 PM, 2 PM, 11 PM day before surgery. Strong evidence for reduced SSI when combined with IV prophylaxis (NNT ~10).

Appendectomy: Cefoxitin 2g IV single dose. OR Cefazolin + Metronidazole.

Cholecystectomy (lap, low-risk): NOT routinely recommended. Give if high-risk: acute, empyema, immunosuppressed, conversion to open.

Allergy: Clindamycin + Aminoglycoside or Aztreonam + Metronidazole.

Neurosurgery (Craniotomy, CSF Shunts)

Craniotomy: Cefazolin 2g IV. Duration ≤24h.

CSF Shunt/EVD Insertion: Cefazolin 2g IV single dose. Evidence for reduced shunt infection (OR 0.51).

Transsphenoidal: Cefazolin 2g IV ± nasal Mupirocin.

MRSA risk: Add Vancomycin. Allergy: Vancomycin or Clindamycin.

Urological Procedures

TURP / Cystoscopy with manipulation: TMP-SMX DS or Ciprofloxacin single dose (if urine sterile).

Prosthetic implant (penile, ureteral stent): Cefazolin 2g IV + Gentamicin.

Key: Always obtain pre-op urine culture. If bacteriuria, treat based on culture before elective procedure.

Obstetric & Gynecologic Surgery

Cesarean Section: Cefazolin 2g IV BEFORE skin incision (not after cord clamping — landmark change). Consider adding Azithromycin 500mg IV for unscheduled C-sections (C/SOAP trial: NNT=12 for SSI reduction).

Hysterectomy (all routes): Cefazolin 2g IV single dose.

Abortion/D&C: Doxycycline 200 mg PO pre-procedure (1st trimester surgical abortion).

Allergy: Clindamycin + Gentamicin. OR Metronidazole + Gentamicin.

Head & Neck / Clean-Contaminated

Clean-contaminated (through oral/pharyngeal mucosa): Cefazolin 2g + Metronidazole 500 mg IV. OR Ampicillin-Sulbactam 3g IV.

Duration: ≤24h post-op.

Clean head/neck (thyroid, parotid, no mucosal breach): Prophylaxis NOT indicated.

Intraoperative Redosing Reference

Drug	Half-life	Redose Interval	Standard Dose
Cefazolin	1.8h	4h	2g (3g if ≥120 kg)
Cefoxitin	0.7h	2h	2g
Cefuroxime	1.3h	4h	1.5g
Clindamycin	2.4h	6h	900 mg
Metronidazole	6–8h	Not typically needed	500 mg
Vancomycin	4–8h	Not typically redosed	15 mg/kg

Infective Endocarditis Prophylaxis

AHA/ACC 2021 Guidelines — Significantly narrowed indications from 2007 update.

Prophylaxis ONLY for Highest-Risk Cardiac Conditions

• Prosthetic cardiac valves (mechanical, bioprosthetic, or homograft)
• Previous infective endocarditis
• Cardiac transplant recipients with valvulopathy
• Unrepaired cyanotic CHD, including palliative shunts/conduits
• Repaired CHD with prosthetic material/device — first 6 months after procedure
• Repaired CHD with residual defects at/adjacent to prosthetic patch or device

Prophylaxis NO LONGER Recommended For

• Mitral valve prolapse (even with regurgitation)
• Bicuspid aortic valve
• Calcific aortic stenosis
• Rheumatic heart disease
• Hypertrophic cardiomyopathy
• All GI/GU procedures (even in high-risk cardiac patients)

Procedures Requiring Prophylaxis (in high-risk patients only)

Dental procedures involving manipulation of gingival tissue, periapical region of teeth, or perforation of oral mucosa.

Respiratory tract procedures involving incision/biopsy of respiratory mucosa (tonsillectomy, adenoidectomy, bronchoscopy with biopsy).

NOT indicated: GI endoscopy (even with biopsy), GU procedures, routine anesthetic injections through non-infected tissue.

IE Prophylaxis Regimens (30–60 min before procedure)

Situation	Drug	Adult Dose	Pediatric Dose
Oral	Amoxicillin	2g PO	50 mg/kg PO
Unable to take PO	Ampicillin OR Cefazolin/Ceftriaxone	2g IM/IV OR 1g IM/IV	50 mg/kg
PCN allergy (oral)	Cephalexin OR Azithromycin OR Doxycycline	2g / 500 mg / 100 mg PO	50 / 15 / — mg/kg
PCN allergy + unable to take PO	Cefazolin/Ceftriaxone	1g IM/IV	50 mg/kg

⚠ Cephalosporins should NOT be used in patients with history of anaphylaxis, angioedema, or urticaria to penicillins.

What is Antibiotic Prophylaxis?

Timing

Spectrum

Duration

Core Principles (ASHP/IDSA/WHO)

Surgical Wound Classification & SSI Risk

Surgical Prophylaxis by Procedure

Intraoperative Redosing Reference

Infective Endocarditis Prophylaxis

Prophylaxis ONLY for Highest-Risk Cardiac Conditions

Prophylaxis NO LONGER Recommended For

Procedures Requiring Prophylaxis (in high-risk patients only)

IE Prophylaxis Regimens (30–60 min before procedure)

Medical (Non-Surgical) Prophylaxis

SBP Prophylaxis (Cirrhosis)

Meningococcal Meningitis Contacts

Rheumatic Fever Secondary Prophylaxis

PJP Prophylaxis (Pneumocystis jirovecii)

Post-Splenectomy / Asplenic Patients

Latent TB Treatment (Preventive Therapy)

Special Populations & Situations

Neonates — GBS Prophylaxis

Obesity (BMI ≥40)

Renal Impairment

β-Lactam Allergy Assessment

MRSA-Colonized Patients

Neutropenic Patients

ICU & Emergency Medicine Pearls

🚨 Post-Exposure Prophylaxis (PEP) — Time-Critical

🫁 VAP Prevention Bundle (not prophylaxis per se, but critical)

🦠 Surgical Prophylaxis Failures — Top Causes

💊 Antimicrobial Stewardship Quick Wins

📋 Open Fracture in the ED — Quick Protocol