Acute Appendicitis

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These materials are intended for general clinical education and guidance. They are not a substitute for a clinician’s knowledge, skill or judgment in treating patients.

Background

Appendicitis is an inflammation of the appendix and is primarily caused by appendiceal mechanical obstruction
Uncomplicated appendicitis: no perforation, abscess or gangrene
Complicated appendicitis: perforation, abscess or gangrenous appendix
Uncomplicated appendicitis may develop into complicated appendicitis, with secondary infectious complications including necrosis, perforation, peritonitis and abscess

Common pathogens

Enterobacterales (e.g., E. coli, K. pneumoniae, Proteus spp.)
Anaerobes (e.g., Bacteroides spp.)

Empiric therapy

Syndrome	1st line	Alternative for allergy to 1st line*	Duration of treatment (after surgery)
Uncomplicated appendicitis	Perioperative surgical antimicrobial prophylaxis only: Cefazolin 2 g IV (3 g if ≥ 120 kg) AND metronidazole 500 mg IV × 1 dose preoperatively Alternative for severe non-IgE drug allergy to beta-lactams: Vancomycin 15 mg/kg IV AND tobramycin 3 mg/kg AND metronidazole 500 mg IV × 1 preoperatively
Complicated appendicitis	Cefazolin 2 g IV q8h AND Metronidazole 500 mg IV q12h OR Amoxicillin/clavulanate 875 mg/125 mg PO BID	Ciprofloxacin 500 mg PO or 400 mg IV q12h AND Metronidazole 500 mg PO/IV q12h	Laparoscopic: 2 days Open: 4 days Conservative: 7 to 10 days dependent upon imaging and/or symptom resolution

Syndrome

1st line

Alternative for allergy to 1st line*

Duration of treatment (after surgery)

Uncomplicated appendicitis

Perioperative surgical antimicrobial prophylaxis only:

Cefazolin 2 g IV (3 g if ≥ 120 kg) AND metronidazole 500 mg IV × 1 dose preoperatively

Alternative for severe non-IgE drug allergy to beta-lactams:
Vancomycin 15 mg/kg IV AND tobramycin 3 mg/kg AND metronidazole 500 mg IV × 1 preoperatively

Complicated appendicitis

Cefazolin 2 g IV q8h AND
Metronidazole 500 mg IV q12h

OR

Amoxicillin/clavulanate 875 mg/125 mg PO BID

Ciprofloxacin 500 mg PO or 400 mg IV q12h AND
Metronidazole 500 mg PO/IV q12h

Laparoscopic: 2 days

Open: 4 days

Conservative: 7 to 10 days dependent upon imaging and/or symptom resolution

*Patients with a history of intolerance, non-specific rash to beta-lactams, or type I hypersensitivity to penicillin or amoxicillin can generally receive ceftriaxone safely. Patients with SJS/TEN, DRESS, AGEP or any other severe type II–IV hypersensitivity reaction should avoid ceftriaxone. See Beta-lactam Allergy Assessment and Management clinical summary.

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References

Kumar SS, Collings AT, Lamm R, et al. SAGES guideline for the diagnosis and treatment of appendicitis. Surg Endosc. 2024;38(6):2974–2994.
Jalava K, Sallinen V, Lampela H, et al. Role of preoperative antibiotic treatment while awaiting appendectomy: the PERFECT-Antibiotics randomized clinical trial. JAMA Surg. Published online July 2025.
de Wijkerslooth EM, Boerma EJ, van Rossem CC, et al. Two days versus five days of postoperative antibiotics for complex appendicitis: a pragmatic, open-label, multicentre, non-inferiority randomized trial. Lancet. 2023;401(10374):366–376.