What peri‑operative antibiotic regimen is recommended for an adult with acute appendicitis and no known drug allergies?

Antibiotic Prophylaxis for Acute Appendicitis in Adults

Preoperative Antibiotic Selection

For adults with acute uncomplicated appendicitis and no drug allergies undergoing appendectomy, administer a single dose of cefoxitin 2g IV or piperacillin-tazobactam 3.375g IV within 0-60 minutes before skin incision, with no postoperative antibiotics required. 1

First-Line Regimens (Uncomplicated Appendicitis)

• Cefoxitin 2g IV as a single preoperative dose 2, 1
• Cefoxitin plus metronidazole: Cefoxitin 2g IV with metronidazole 1g infusion as a single dose 2
• Piperacillin-tazobactam 3.375g IV as a single dose (broader-spectrum but narrower agents are equally effective) 1

Alternative Regimens

• Cefazolin 2g IV slow push as a single dose (if surgery duration exceeds 4 hours, re-inject 1g) 2
• Cefuroxime 1.5g IV slow push as a single dose (if surgery duration exceeds 2 hours, re-inject 0.75g) 2
• Cefamandole 1.5g IV slow push as a single dose (if surgery duration exceeds 2 hours, re-inject 0.75g) 2

β-Lactam Allergy Regimens

• Moxifloxacin 400mg IV combined with metronidazole as a single preoperative dose 1
• Ciprofloxacin plus metronidazole as a single preoperative dose 1
• Gentamicin 5mg/kg/day plus clindamycin 900mg IV slow push as a single dose (if surgery duration exceeds 4 hours, inject clindamycin 600mg) 2

Critical Timing

• Administer antibiotics 0-60 minutes before skin incision to ensure adequate tissue concentrations at the moment of bacterial exposure 1
• This timing window is supported by high-quality Cochrane meta-analyses of >9,000 patients showing significant reduction in wound infection and intra-abdominal abscess rates 1

Postoperative Antibiotic Management

Uncomplicated Appendicitis

Do not continue antibiotics postoperatively after uncomplicated appendectomy—this is a strong Grade 1A recommendation. 1, 3

• A single pre-incisional dose is as effective as prolonged postoperative courses for preventing surgical-site infection 1
• Postoperative antibiotics have no role in reducing surgical site infection rates in uncomplicated cases 3
• This applies to both adult and pediatric patients 3

Complicated Appendicitis (Perforation, Abscess, Gangrenous Disease)

For complicated appendicitis with adequate source control, discontinue antibiotics after 24 hours or limit to a maximum of 3-5 days postoperatively. 2, 1, 3

• Discontinuation after 24 hours is safe and associated with shorter hospital stays and lower costs 2, 3
• Fixed-duration therapy of 3-5 days produces outcomes similar to longer courses when adequate source control is achieved 2
• Courses beyond 5 days provide no additional benefit and increase antimicrobial resistance 1
• Postoperative broad-spectrum antibiotics are indicated only when complete source control has not been achieved 2, 3

Antibiotic Selection for Complicated Cases

• Piperacillin-tazobactam, ampicillin-sulbactam, ticarcillin-clavulanate, or carbapenems for broad-spectrum coverage against enteric gram-negative organisms and anaerobes (E. coli, Bacteroides spp.) 2, 3
• Extended-spectrum antibiotics offer no advantage over narrower-spectrum agents when adequate source control is achieved 2, 3
• Ceftriaxone plus metronidazole is an effective alternative that reduces broad-spectrum antibiotic utilization without increasing surgical site infections 4

Critical Pitfalls to Avoid

Resistance Considerations

• Avoid ampicillin-sulbactam because E. coli resistance exceeds 20% in acute appendicitis 1

Common Errors

• Do not confuse gangrenous with perforated appendicitis—only perforated cases with inadequate source control require extended antibiotics 3
• Do not extend antibiotics beyond 24 hours for uncomplicated cases, even in the presence of surgical drains 2
• Do not use extended-spectrum antibiotics (piperacillin-tazobactam, ceftazidime, cefepime, carbapenems) routinely when narrower agents are equally effective 2

Defining Adequate Source Control

• Source control is adequate when complete appendectomy was performed with no residual abscess or diffuse purulence remaining 3
• If source control is inadequate, postoperative broad-spectrum antibiotics are indicated beyond the standard 24-hour cutoff 2, 3

Pediatric Considerations

• Cefazolin 25-50 mg/kg as a single preoperative IV dose for children with non-perforated appendicitis 1
• Second- or third-generation cephalosporins (cefoxitin, cefotetan) are appropriate for uncomplicated pediatric cases 2, 3
• For complicated pediatric appendicitis, switch to oral antibiotics after 48 hours if clinically improving, with total duration <7 days 3
• Broader coverage for complicated pediatric cases includes piperacillin-tazobactam, ampicillin-sulbactam, or ticarcillin-clavulanate 3