What is the recommended treatment for a patient with diverticulitis who has an allergy to penicillin (PCN)?

Treatment of Diverticulitis in Patients with Penicillin Allergy

For patients with diverticulitis who have a penicillin allergy, the recommended first-line antibiotic regimen is ceftriaxone plus metronidazole for inpatient treatment or ciprofloxacin plus metronidazole for outpatient management. 1

Antibiotic Selection Based on Setting and Severity

Outpatient Treatment (Uncomplicated Diverticulitis)

• First choice: Ciprofloxacin plus metronidazole
• Alternative: Trimethoprim-sulfamethoxazole plus metronidazole
• Duration: 7-10 days (can be individualized based on clinical response)

Inpatient Treatment (Complicated Diverticulitis)

• First choice: IV ceftriaxone plus metronidazole
• Alternative options:
  • Aztreonam plus metronidazole (for severe penicillin allergy)
  • IV ciprofloxacin plus metronidazole

Severity Assessment

Complicated diverticulitis includes:

• Presence of abscess
• Phlegmon
• Fistula
• Obstruction
• Bleeding
• Perforation

Special Considerations for Penicillin Allergy

1. Allergy Testing: The American College of Gastroenterology recommends referral for penicillin allergy testing after failure of first-line therapy, as most patients who believe they have a penicillin allergy are found not to have a true allergy 2

2. Aztreonam Use: For patients with severe penicillin allergy requiring IV therapy, aztreonam is a safe alternative. The recommended dosage is:

   • For moderately severe systemic infections: 1-2g every 8-12 hours
   • For severe systemic infections: 2g every 6-8 hours 3
   • Dose adjustment required for renal impairment

3. Monitoring: Patients treated as outpatients should be monitored for:

   • Worsening abdominal pain
   • Persistent or high fever
   • Changes in bowel movements
   • Nausea or vomiting
   • Increasing abdominal distension 1

Treatment Algorithm

1. Assess severity:

   • Uncomplicated: No abscess, perforation, fistula, or obstruction
   • Complicated: Presence of abscess, perforation, fistula, or obstruction

2. Determine treatment setting:

   • Outpatient: Uncomplicated diverticulitis with ability to tolerate oral intake, no significant comorbidities, adequate family support
   • Inpatient: Complicated diverticulitis, inability to tolerate oral intake, significant comorbidities, or inadequate support

3. Select appropriate antibiotics based on penicillin allergy:

   • For outpatient: Ciprofloxacin plus metronidazole
   • For inpatient: Ceftriaxone plus metronidazole (if no cross-reactivity) or aztreonam plus metronidazole

4. Treatment duration: 7-10 days, with reassessment at 4-7 days to confirm symptom improvement 4

5. Consider surgical consultation for complicated cases with peritonitis or hemodynamic instability

Important Caveats

• Fluoroquinolones (e.g., ciprofloxacin) should be used with caution due to FDA warnings about serious side effects, but they remain a valuable option for penicillin-allergic patients 5
• For patients with small abscesses (<4-5 cm), antibiotic therapy alone may be sufficient, while larger abscesses require percutaneous drainage plus antibiotics 1
• CT scan with oral and IV contrast is the gold standard for diagnosis with 95-99% sensitivity/specificity and should be obtained before initiating treatment 1
• Recent evidence suggests amoxicillin-clavulanate may reduce the risk of Clostridioides difficile infection compared to metronidazole-fluoroquinolone combinations in non-allergic patients, highlighting the importance of penicillin allergy testing when appropriate 5