What is the recommended antibiotic regimen for acute appendicitis?

Antibiotic Selection for Acute Appendicitis

For uncomplicated acute appendicitis, use cefotaxime 2g every 8 hours plus metronidazole 500mg every 6 hours, or alternatively piperacillin-tazobactam 3.375g every 6 hours as monotherapy. 1, 2

Uncomplicated Appendicitis (Non-Perforated)

First-Line Regimens for Adults

Single-agent therapy:

• Piperacillin-tazobactam 3.375g IV every 6 hours (preferred for simplicity and broad coverage) 2, 3
• Ertapenem 1g IV every 24 hours 2
• Moxifloxacin 400mg IV every 24 hours 2
• Cefoxitin 2g IV every 6 hours 2

Combination therapy:

• Cefotaxime 2g IV every 8 hours PLUS metronidazole 500mg IV every 6 hours (explicitly recommended by WSES 2020) 1, 2
• Ceftriaxone 2g IV every 24 hours PLUS metronidazole 500mg IV every 6 hours 1, 2
• Ciprofloxacin 400mg IV every 8 hours PLUS metronidazole 500mg IV every 6 hours (for beta-lactam allergy) 1, 2

Pediatric Patients (Non-Perforated)

• Single dose of second- or third-generation cephalosporin (cefoxitin or cefotetan) is sufficient 2
• Extended-spectrum antibiotics offer no advantage over narrower-spectrum agents in children 2

Complicated Appendicitis (Perforated/Abscess)

Adult Regimens

Broader coverage is mandatory for perforated appendicitis:

• Piperacillin-tazobactam 4.5g IV every 6 hours 3, 2
• Imipenem-cilastatin 1g IV every 8 hours 2
• Meropenem 1g IV every 8 hours 2
• Ticarcillin-clavulanate PLUS gentamicin 2

Pediatric Regimens (Perforated)

Most common combination:

• Ampicillin PLUS clindamycin (or metronidazole) PLUS gentamicin 2

Alternatives:

• Piperacillin-tazobactam 2
• Ampicillin-sulbactam 2
• Ceftriaxone PLUS metronidazole 2

Critical Antibiotic Selection Principles

What to Avoid

• Do NOT use ampicillin-sulbactam due to high E. coli resistance rates (>20%) 2
• Do NOT use cefotetan or clindamycin due to increasing Bacteroides fragilis resistance 2
• Avoid aminoglycosides for routine use in adults due to toxicity when equally effective alternatives exist 2
• Do NOT use quinolones unless local E. coli susceptibility is ≥90% 2
• Avoid moxifloxacin if patient received quinolones within 3 months (high resistance risk) 2

Coverage Requirements

Antibiotics MUST cover:

• Enteric gram-negative aerobes (E. coli, Klebsiella) 2
• Enteric gram-positive streptococci 2
• Obligate anaerobes (Bacteroides fragilis group) 2

Empiric enterococcal coverage is NOT necessary for community-acquired appendicitis 2

Empiric antifungal coverage is NOT recommended 2

Duration of Therapy

Uncomplicated Appendicitis (Surgical)

• Single preoperative dose is sufficient for non-perforated appendicitis 2
• No postoperative antibiotics needed if adequate source control achieved 2

Complicated Appendicitis (Surgical)

• 24 hours postoperatively is adequate if complete source control achieved 2
• Maximum 3-5 days postoperatively even without complete source control 2
• Prolonging beyond 5 days offers no benefit and increases resistance 2

Non-Operative Management

• Minimum 48 hours IV followed by oral antibiotics for total 7-10 days 1
• Early switch to oral antibiotics (after 48 hours) is safe and cost-effective in children 2

Special Considerations for Non-Operative Management

Patient selection is critical:

• CT-confirmed uncomplicated appendicitis WITHOUT appendicolith 1, 4
• Appendicolith presence predicts 40-60% failure rate of antibiotic therapy 1, 4
• Appendiceal diameter >13mm associated with higher failure rates 4

Expected outcomes:

• 70-78% initial success rate 4, 5
• 39% recurrence rate at 5 years (patients must be counseled) 1
• Lower immediate complication rate (18%) versus surgery (25%) 5
• Higher readmission rate (relative risk 6.98) 1

Critically Ill Patients

For healthcare-associated or high-severity infections:

• Meropenem 1g IV every 8 hours 2
• Add vancomycin 25-30mg/kg loading dose if MRSA risk 2
• Consider echinocandin if high risk for invasive candidiasis 2