What antibiotics are used to treat appendicitis?

Antibiotic Treatment for Appendicitis

Preoperative Antibiotics (All Patients)

All patients with acute appendicitis undergoing appendectomy should receive preoperative broad-spectrum antibiotics covering gram-negative facultative/aerobic organisms and anaerobes. 1, 2

• Piperacillin-tazobactam is FDA-approved and highly effective as monotherapy for complicated appendicitis (with rupture or abscess) caused by beta-lactamase producing E. coli and Bacteroides fragilis group organisms 3

  • Standard dosing: 3.375 grams IV every 6 hours for uncomplicated cases 3
  • Higher dosing: 4.5 grams IV every 6 hours for complicated cases 3

• Alternative regimens include cephalosporins (ceftriaxone) plus metronidazole, or fluoroquinolones plus metronidazole 4, 5, 6

  • Ceftriaxone plus metronidazole is effective without requiring additional aminoglycosides for complicated appendicitis 6

• For beta-lactam allergies: Moxifloxacin 400 mg IV/PO once daily 7

Postoperative Antibiotics (Surgical Management)

For uncomplicated appendicitis treated surgically, no postoperative antibiotics are needed—a single preoperative dose is sufficient. 1, 7, 2

For complicated appendicitis (perforation, abscess, peritonitis) with adequate source control, continue postoperative antibiotics for 3-5 days maximum. 1, 2

• Duration should be guided by clinical resolution: absence of fever, declining C-reactive protein, and normalizing white blood cell count 1, 2
• Intravenous administration is recommended initially 1, 2
• The addition of empiric gentamicin to ceftriaxone/metronidazole does not reduce abscess rates compared to adjusting antibiotics based on clinical response 6

Non-Operative Management (Selected Patients)

For CT-confirmed uncomplicated appendicitis without appendicolith in patients who decline surgery, initiate IV antibiotics with transition to oral therapy for a total duration of 7-10 days. 1, 7, 4

Patient Selection Criteria:

• CT confirmation of uncomplicated appendicitis (appendiceal diameter <13 mm) 4
• Absence of appendicolith (critical—presence increases failure rates to 47-60%) 7, 4
• No mass effect or perforation on imaging 4
• Patient counseled on 23-39% recurrence risk over 5 years 7

Antibiotic Regimen:

• Minimum 48 hours IV antibiotics, then switch to oral based on clinical improvement 1, 7
• Total duration: 7-10 days 1, 7
• Piperacillin-tazobactam, cephalosporin/metronidazole combinations, or fluoroquinolone/metronidazole regimens are appropriate 4, 5
• For beta-lactam allergy: Moxifloxacin 400 mg once daily for 7 days total 7

Critical Caveats:

• Approximately 30% of antibiotic-treated patients require appendectomy within one year, though two-thirds successfully avoid surgery 8
• Success rates are only 58-82% with antibiotics versus near-universal success with surgery 4, 8
• High-risk CT findings (appendicolith, diameter >13 mm, mass effect) predict ~40% treatment failure—these patients should undergo surgery if fit 4
• Patients ≥40 years require colonoscopy and interval CT due to 3-17% incidence of appendiceal neoplasms 7

Special Populations

Elderly Patients:

• Preoperative broad-spectrum antibiotics are strongly recommended 1
• No postoperative antibiotics for uncomplicated cases 1
• For complicated cases: 3-5 days postoperatively, guided by fever and leukocytosis resolution 1
• Non-operative management should be avoided in elderly with diffuse peritonitis or free perforation 1

Pediatric Patients (≥2 months):

• Same antibiotic principles apply as adults 1, 3
• Piperacillin-tazobactam is FDA-approved for children ≥2 months 3
• Non-operative management is feasible in children with uncomplicated appendicitis without appendicolith, though recurrence risks apply 1

Key Pitfalls to Avoid

• Do not use postoperative antibiotics routinely for uncomplicated appendicitis—this increases unnecessary antibiotic exposure without benefit 1, 2
• Do not attempt non-operative management if appendicolith is present on imaging—surgical failure rates are unacceptably high 7, 4
• Do not extend postoperative antibiotics beyond 5 days for complicated cases unless clinical/laboratory parameters fail to improve 1, 2
• Do not skip colonoscopy in patients ≥40 years treated non-operatively, as malignancy incidence is 0.3-17% 7