What is the recommended oral antibiotic regimen for a clinically stable patient with subacute appendicitis?

Oral Antibiotic Regimen for Subacute Appendicitis

For clinically stable patients with CT-confirmed uncomplicated subacute appendicitis, initiate oral moxifloxacin 400 mg once daily for 7 days total, or alternatively use oral amoxicillin-clavulanate 875 mg/125 mg twice daily for 7-10 days. 1, 2

Primary Oral Antibiotic Options

Moxifloxacin monotherapy is the preferred single-agent oral regimen for non-operative management:

• Moxifloxacin 400 mg orally once daily for 7 days 1
• This regimen is specifically recommended by the World Society of Emergency Surgery (WSES) for uncomplicated acute appendicitis treated non-operatively 1
• Avoid moxifloxacin if the patient has received quinolone therapy within the past 3 months due to high risk of quinolone-resistant Bacteroides fragilis 2

Amoxicillin-clavulanate is an alternative oral option:

• Amoxicillin-clavulanate 875 mg/125 mg orally every 12 hours for 7-10 days 3, 2
• This combination provides coverage against enteric gram-negative organisms and anaerobes 2
• The FDA-approved dosing for more severe infections is 875 mg/125 mg every 12 hours 3

Alternative Combination Oral Regimens

If beta-lactams and quinolones are contraindicated, consider:

• Ciprofloxacin 500 mg orally twice daily PLUS metronidazole 500 mg orally three times daily for 7-10 days 2, 4
• Levofloxacin 500 mg orally once daily PLUS metronidazole 500 mg orally three times daily for 7-10 days 5

Critical Prerequisites for Oral Antibiotic Therapy

CT confirmation is mandatory before initiating oral antibiotics alone:

• Must document uncomplicated appendicitis (appendiceal diameter <13 mm, no perforation, no abscess) 6, 1
• Absence of appendicolith is essential—presence increases failure rates to 47-60% 1, 6
• Patients with appendicolith, mass effect, or appendiceal diameter ≥13 mm should undergo appendectomy, not antibiotics alone 6

Patient must be clinically stable with:

• Ability to tolerate oral intake 2
• No signs of sepsis or peritonitis 2
• No significant comorbidities that would increase surgical risk 6

Treatment Monitoring and Expected Outcomes

Expect 70-78% initial success rate with oral antibiotics:

• Approximately 22-30% will require appendectomy during initial hospitalization due to treatment failure 6, 7
• Recurrence risk is 23-39% over 5 years, with most recurrences (11-14%) occurring within the first year 1, 7
• At 3-year follow-up, overall treatment success (no surgery, no recurrence) is approximately 63-65% 5

Clinical monitoring protocol:

• Reassess at 24-48 hours for symptom improvement 2
• If no improvement or worsening symptoms, proceed to appendectomy 2
• Patients should be counseled about alarm symptoms requiring immediate return 2

Special Considerations for Age >40 Years

Patients ≥40 years old require additional workup even with successful antibiotic treatment:

• Colonoscopy is mandatory due to 3-17% incidence of appendiceal neoplasms in this age group 1
• Interval contrast-enhanced CT scan should be performed 2, 1
• Consider lower threshold for surgical management in this population 2

Common Pitfalls to Avoid

Do not use oral antibiotics alone if:

• Appendicolith is present on imaging—this dramatically increases failure rates 1, 6
• CT shows complicated features (perforation, abscess, phlegmon) 2
• Patient cannot tolerate oral intake or has signs of sepsis 2
• Appendiceal diameter is ≥13 mm on CT 6

Do not confuse with postoperative management:

• The regimens above are for non-operative management only 1
• After appendectomy for uncomplicated appendicitis, no postoperative antibiotics are needed 2
• After appendectomy for complicated appendicitis, limit antibiotics to 3-5 days maximum with early switch to oral after 48 hours 8

Do not extend treatment beyond 7-10 days for uncomplicated cases—longer courses do not improve outcomes and increase antibiotic resistance 1, 2