What is the recommended antibiotic and dose for acute diverticulitis?

Antibiotic Selection and Dosing for Acute Diverticulitis

For uncomplicated acute diverticulitis in immunocompetent patients without systemic symptoms, antibiotics are not recommended as first-line therapy; however, when antibiotics are indicated, use oral ciprofloxacin 500 mg twice daily plus metronidazole 500 mg three times daily for 4-7 days, or alternatively amoxicillin-clavulanate. 1, 2, 3

When to Use Antibiotics vs. Observation Alone

Observation without antibiotics is appropriate for immunocompetent patients with uncomplicated diverticulitis who have: 1, 3

• No systemic inflammatory response
• No immunocompromised status
• Ability to tolerate oral intake
• Adequate home support

Antibiotics are indicated when any of the following risk factors are present: 1, 2, 4

• Immunocompromised status (chemotherapy, high-dose steroids, organ transplant)
• Systemic symptoms: persistent fever >101°F or chills
• Laboratory markers: WBC >15 × 10^9/L or CRP >140 mg/L
• Age >80 years
• Pregnancy
• Chronic medical conditions (cirrhosis, chronic kidney disease, heart failure, poorly controlled diabetes)
• CT findings: fluid collection or longer segment of inflammation
• Clinical factors: ASA score III or IV, symptoms >5 days, vomiting, or high pain score (≥8/10)

Outpatient Antibiotic Regimens

First-line oral regimens for uncomplicated diverticulitis: 1, 2, 3, 4

• Ciprofloxacin 500 mg PO twice daily PLUS Metronidazole 500 mg PO three times daily
  • Duration: 4-7 days for immunocompetent patients
  • Duration: 10-14 days for immunocompromised patients

Alternative oral regimen: 1, 2, 4

• Amoxicillin-clavulanate (dose not specified in guidelines, but standard dosing is 875/125 mg twice daily)
• Cefalexin PLUS Metronidazole (alternative option)

Inpatient IV Antibiotic Regimens

For patients requiring hospitalization (inability to tolerate oral intake, severe pain, systemic symptoms, significant comorbidities): 1, 2, 4

Standard IV regimens: 2, 4

• Ceftriaxone PLUS Metronidazole
• Cefuroxime PLUS Metronidazole
• Piperacillin-tazobactam (single agent)
• Ampicillin-sulbactam (single agent)

For immunocompromised or critically ill patients: 2

• Eravacycline
• Piperacillin-tazobactam

For septic shock: 2

• Meropenem
• Doripenem
• Imipenem-cilastatin
• Eravacycline

Transition strategy: Switch from IV to oral antibiotics as soon as the patient can tolerate oral intake to facilitate earlier discharge. 3, 5

Duration of Therapy

The evidence shows insufficient data to determine optimal duration, but current guidelines recommend: 6, 2, 3

• Immunocompetent patients with adequate source control: 4-7 days
• Immunocompromised or elderly patients: 7-14 days
• Complicated diverticulitis with abscess drainage: 4 days after adequate drainage
• Small abscesses treated with antibiotics alone: 7 days

Complicated Diverticulitis Management

For complicated diverticulitis (abscess, perforation, fistula, obstruction): 1, 2

• Abscesses ≥4-5 cm: Percutaneous drainage PLUS IV antibiotics for 4 days
• Abscesses <4 cm: IV antibiotics alone for 7 days
• Generalized peritonitis: Emergent surgical consultation with broad-spectrum IV antibiotics

Important Clinical Caveats

Avoid these common pitfalls: 1, 3

• Do not routinely prescribe antibiotics for all cases of uncomplicated diverticulitis in immunocompetent patients—this represents overtreatment and contributes to antibiotic resistance
• Do not stop antibiotics early even if symptoms improve; complete the full course
• Avoid alcohol until at least 48 hours after completing metronidazole to prevent disulfiram-like reactions
• Do not assume negative outcomes from the no-antibiotic approach—evidence shows no significant differences in complications, surgery rates, or quality of life between antibiotic and no-antibiotic groups at 1 month, 1 year, or even 11 years 6

Re-evaluation timing: 1, 3

• Schedule follow-up within 7 days of diagnosis
• Instruct patients to return immediately if fever persists, pain worsens, or they cannot tolerate oral intake
• Patients with inadequate response after 7 days warrant further diagnostic investigation

Monitoring parameters: 2

• White blood cell count
• C-reactive protein
• Procalcitonin (to assess response to therapy)

Evidence Quality Note

The 2022 American College of Physicians guidelines found insufficient evidence to determine superiority of any specific antibiotic regimen over another for acute diverticulitis. 6 The recommendations are based on antimicrobial spectrum coverage (gram-negative and anaerobic organisms) rather than head-to-head comparative trials. The most robust evidence supports the selective use of antibiotics rather than routine use in all cases of uncomplicated diverticulitis. 1, 3