What is the recommended treatment for diverticulitis in a patient with a penicillin allergy?

Treatment of Diverticulitis in Patients with Penicillin Allergy

For patients with diverticulitis who have a penicillin allergy, the recommended first-line antibiotic regimen is ciprofloxacin plus metronidazole, or alternatively, aztreonam plus metronidazole for more severe cases requiring intravenous therapy. 1, 2

Antibiotic Selection Based on Disease Severity

Uncomplicated Diverticulitis

• Oral regimen (outpatient treatment):
  • Ciprofloxacin 500 mg PO twice daily + metronidazole 500 mg PO three times daily for 7-10 days 1, 3, 4
  • Alternative: Levofloxacin 500 mg PO once daily + metronidazole 500 mg PO three times daily for 7-10 days 5, 2

Complicated Diverticulitis

• Intravenous regimen (inpatient treatment):
  • Aztreonam 1-2 g IV every 8-12 hours + metronidazole 500 mg IV every 8 hours 1, 6
  • For severe infections: Aztreonam 2 g IV every 6-8 hours + metronidazole 6

Treatment Algorithm

1. Assess severity:

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

2. For uncomplicated diverticulitis:

   • Clear liquid diet until symptoms improve 1
   • Consider observation without antibiotics for mild cases 2
   • Use antibiotics if patient has:
     • Persistent fever or chills
     • Increasing leukocytosis
     • Age >80 years
     • Immunocompromised status
     • Chronic medical conditions (cirrhosis, CKD, heart failure, poorly controlled diabetes)
     • Pregnancy

3. For complicated diverticulitis:

   • NPO (nothing by mouth)
   • IV fluids
   • IV antibiotics (aztreonam + metronidazole)
   • Consider percutaneous drainage for abscesses 1
   • Surgical consultation for peritonitis, large abscesses, or obstruction

Dosage Adjustments

• Renal impairment:
  • For aztreonam: Halve the dose for CrCl 10-30 mL/min; for severe renal failure (CrCl <10 mL/min), give one-fourth of the usual dose 6
  • For ciprofloxacin: Reduce dose to 250-500 mg every 12 hours if CrCl <30 mL/min 3
  • For levofloxacin: Reduce dose to 250-500 mg every 24-48 hours based on CrCl 5

Duration of Therapy

• Uncomplicated diverticulitis: 7-10 days of antibiotics 1, 4
• Complicated diverticulitis: Continue antibiotics for at least 48 hours after patient becomes asymptomatic 6
• Persistent infections may require several weeks of treatment 6

Follow-up Care

• Colonoscopy 4-6 weeks after acute episode to rule out malignancy 1
• High-fiber diet after resolution of acute symptoms 1
• Consider fiber supplementation for prevention of recurrence 1, 7

Important Considerations

• Aztreonam is generally safe in patients with penicillin allergy as cross-reactivity is rare 6
• Fluoroquinolones (ciprofloxacin, levofloxacin) carry risk of tendinopathy, especially in elderly patients or those on corticosteroids 5, 3
• Monitor patients on fluoroquinolones for tendon pain and discontinue immediately if it occurs 3
• For elderly patients with penicillin allergy, carefully weigh the risks of fluoroquinolone-associated adverse events against benefits 3

Pitfalls to Avoid

• Don't use fluoroquinolones in patients with history of tendon disorders or aortic aneurysm
• Don't delay surgical consultation for patients with signs of peritonitis or sepsis
• Don't forget to adjust antibiotic doses in patients with renal impairment
• Don't start solid foods until clinical improvement is observed
• Don't forget to schedule follow-up colonoscopy to rule out malignancy