What is the recommended antibiotic regimen for acute appendicitis?

Antibiotic Coverage for Acute Appendicitis

For uncomplicated appendicitis undergoing surgery, administer a single preoperative dose of broad-spectrum antibiotics (0-60 minutes before incision) and discontinue antibiotics postoperatively—no postoperative antibiotics are needed if adequate source control is achieved. 1, 2

Surgical Management: Perioperative Antibiotics

Uncomplicated Appendicitis (Non-Perforated)

Preferred single-agent regimens:

• Piperacillin-tazobactam 3.375g IV every 6 hours is the preferred single-agent therapy due to its simplicity and broad coverage 2, 3
• Ertapenem 1g IV every 24 hours is an alternative single-agent option 2

Preferred combination regimens:

• Cefotaxime 2g IV every 8 hours PLUS metronidazole 500mg IV every 6 hours 2, 4
• Ceftriaxone 2g IV every 24 hours PLUS metronidazole 500mg IV every 6 hours 4
• Amoxicillin-clavulanate 1.2-2.2g IV every 6 hours 4

Duration: Single preoperative dose only—no postoperative antibiotics required 1, 2, 4

Complicated Appendicitis (Perforated/Abscess)

Broader-spectrum regimens for perforated appendicitis:

• Imipenem-cilastatin 1g IV every 8 hours for broader coverage 2
• Meropenem 1g IV every 8 hours as an alternative 2
• Piperacillin-tazobactam 4.5g IV every 6 hours 3

Duration: Discontinue antibiotics within 24 hours postoperatively if adequate source control is achieved 1, 2. If complete source control is not achieved, limit therapy to a maximum of 3-5 days postoperatively 1, 2. The evidence strongly supports that fixed-duration therapy of 3-5 days produces similar outcomes to longer courses when adequate source control is obtained 1.

Pediatric Patients

For non-perforated appendicitis:

• A single preoperative dose of second- or third-generation cephalosporin (cefoxitin or cefotetan) is sufficient 2
• No postoperative antibiotics are needed 1

For complicated appendicitis in children:

• Use the same regimens as adults with weight-based dosing 2, 4
• Early switch to oral antibiotics after 48 hours is safe and cost-effective, with total therapy duration shorter than 7 days 1, 2

Non-Operative Management (Antibiotics-First Strategy)

This approach is appropriate only for highly selected patients with CT-confirmed uncomplicated appendicitis without appendicolith. 1, 4, 5 Patients must be counseled about a 23-30% recurrence rate at one year and 39% at five years 2, 4.

Antibiotic regimen:

• Minimum 48 hours IV antibiotics followed by oral antibiotics for a total of 7-10 days 1, 2, 4
• IV options: piperacillin-tazobactam, cefotaxime/ceftriaxone plus metronidazole, or amoxicillin-clavulanate 2, 4, 6
• Oral switch: ciprofloxacin plus metronidazole 6

Critical patient selection criteria:

• CT-confirmed uncomplicated appendicitis 4, 5
• Absence of appendicolith (presence predicts 40-60% failure rate) 2, 5
• Appendiceal diameter <13mm on CT 5
• No mass effect on imaging 5

The evidence from population-based studies shows that 77% of unselected patients recover with antibiotics alone, though 23% require subsequent appendectomy 6. However, patients with high-risk CT findings (appendicolith, mass effect, or diameter >13mm) have approximately 40% treatment failure rates and should undergo surgery if medically fit 5.

Periappendiceal Abscess Management

For patients with periappendiceal abscess:

• Percutaneous drainage plus antibiotics is the preferred initial approach when interventional radiology is available 4
• Use broader-spectrum regimens: imipenem-cilastatin 1g IV every 8 hours or meropenem 1g IV every 8 hours 2
• Duration: 4-7 days total 2
• Interval appendectomy is NOT routinely recommended for patients <40 years old unless recurrent symptoms occur 4
• For patients ≥40 years old, perform colonoscopy and interval CT due to 3-17% risk of appendicular neoplasm 1, 4

Critical Antibiotic Selection Principles: What to AVOID

Do NOT use the following regimens due to resistance patterns:

• Ampicillin-sulbactam (E. coli resistance >20%) 2, 4
• Cefotetan or clindamycin (increasing Bacteroides fragilis resistance) 2, 4
• Aminoglycosides for routine use in adults (toxicity when equally effective alternatives exist) 2
• Narrow-spectrum cephalosporins alone without anaerobic coverage (appendicitis involves mixed aerobic-anaerobic flora) 2

Critically Ill or Healthcare-Associated Infections

For critically ill patients or healthcare-associated appendicitis:

• Meropenem 1g IV every 8 hours 2, 4
• Add vancomycin 25-30mg/kg loading dose if MRSA risk is present 2
• Consider echinocandin if high risk for invasive candidiasis 2

Common Pitfalls to Avoid

• Do NOT delay antibiotic administration while awaiting imaging—start empiric therapy as soon as appendicitis is clinically suspected 2
• Do NOT continue antibiotics beyond 24 hours postoperatively for uncomplicated appendicitis—longer courses provide no additional benefit and increase resistance risk 2
• Do NOT delay appendectomy beyond 24 hours from admission for patients requiring surgery, as delays are associated with increased adverse outcomes 1
• Do NOT offer non-operative management to patients with appendicolith on imaging—this predicts high failure rates 2, 5