What antibiotics are used to treat diverticulitis?

Antibiotic Selection for Diverticulitis

For immunocompetent patients with uncomplicated diverticulitis, antibiotics are not routinely recommended—observation with supportive care is first-line therapy. 1 When antibiotics are indicated (immunocompromised status, systemic symptoms, WBC >15 × 10⁹/L, CRP >140 mg/L, or CT findings of fluid collection/longer inflammation segment), use oral ciprofloxacin 500 mg twice daily plus metronidazole 500 mg three times daily for 4-7 days, or alternatively amoxicillin-clavulanate 875/125 mg twice daily. 1, 2, 3

When to Use Antibiotics vs. Observation

Observation WITHOUT Antibiotics (First-Line for Most Patients)

• Immunocompetent patients with uncomplicated diverticulitis require no antibiotics, as multiple high-quality trials demonstrate antibiotics neither accelerate recovery, prevent complications, nor reduce recurrence rates. 1, 4, 5
• Uncomplicated diverticulitis is defined as localized inflammation without abscess, perforation, fistula, or obstruction on CT imaging. 1
• Hospital stays are actually shorter with observation alone (2 days) versus antibiotic treatment (3 days). 1

Mandatory Antibiotic Indications

• Immunocompromised status (chemotherapy, organ transplant, high-dose steroids >20 mg prednisone daily). 1, 3
• Systemic inflammatory response: persistent fever >101°F, chills, or sepsis. 1, 3
• Laboratory markers: WBC >15 × 10⁹ cells/L or CRP >140 mg/L. 1
• CT findings: fluid collection, abscess, or longer segment of colonic inflammation. 1
• Clinical factors: age >80 years, pregnancy, refractory symptoms, vomiting, inability to maintain hydration, or ASA score III-IV. 1, 3

Outpatient Oral Antibiotic Regimens (4-7 Days)

First-Line Options

• Ciprofloxacin 500 mg PO twice daily PLUS metronidazole 500 mg PO three times daily for 4-7 days. 1, 2
• Amoxicillin-clavulanate 875/125 mg PO twice daily for 4-7 days (single-agent alternative). 1, 2, 3

Alternative Options

• Cefalexin plus metronidazole (if penicillin allergy concerns but cephalosporins tolerated). 3

Duration Specifics

• 4-7 days for immunocompetent patients with adequate clinical response. 1, 2
• 10-14 days for immunocompromised patients (corticosteroids, chemotherapy, transplant recipients). 1

Inpatient IV Antibiotic Regimens

Standard IV Regimens (for hospitalized patients)

• Ceftriaxone 1-2 g IV daily PLUS metronidazole 500 mg IV every 8 hours. 1, 3
• Piperacillin-tazobactam 3.375-4.5 g IV every 6-8 hours (single-agent broad-spectrum). 1, 2, 3
• Cefuroxime 1.5 g IV every 8 hours PLUS metronidazole 500 mg IV every 8 hours. 2, 3
• Ampicillin-sulbactam 3 g IV every 6 hours (alternative). 2, 3

Critically Ill or Septic Shock Regimens

• Meropenem 1 g IV every 8 hours. 2
• Doripenem or imipenem-cilastatin (carbapenem alternatives). 2
• Eravacycline (for immunocompromised or critically ill patients). 2

Transition Strategy

• Switch from IV to oral antibiotics as soon as the patient tolerates oral intake (typically within 48 hours) to facilitate earlier discharge. 1, 2
• Transition criteria: temperature <100.4°F, pain score <4/10, tolerating oral diet. 1

Complicated Diverticulitis Management

Abscess Management

• Abscesses <4 cm: Antibiotics alone for 7 days. 4
• Abscesses ≥4-5 cm: Percutaneous drainage PLUS antibiotics for 4 days. 1, 4
• Post-drainage antibiotic duration is 4 days with adequate source control in immunocompetent patients. 1, 2

Generalized Peritonitis

• Emergent laparotomy with colonic resection plus IV antibiotics (piperacillin-tazobactam, meropenem, or ceftriaxone plus metronidazole). 4, 3
• Postoperative mortality: 0.5% for elective resection vs. 10.6% for emergent resection. 3

Outpatient vs. Inpatient Decision Algorithm

Outpatient Treatment Appropriate When:

• Can tolerate oral fluids and medications. 1, 4
• No significant comorbidities or frailty. 1
• Temperature <100.4°F and pain score <4/10 controlled with acetaminophen. 1
• Adequate home support and reliable follow-up within 7 days. 1

Hospitalization Required For:

• Complicated diverticulitis (abscess, perforation, obstruction). 4
• Inability to tolerate oral intake or severe vomiting. 1
• Systemic inflammatory response or sepsis. 1
• Immunocompromised status or significant comorbidities (cirrhosis, chronic kidney disease, heart failure). 1, 3
• Age >80 years with high-risk features. 1

Critical Pitfalls to Avoid

• Do not routinely prescribe antibiotics for all uncomplicated diverticulitis—this contributes to antibiotic resistance without clinical benefit. 1, 5
• Do not apply the "no antibiotics" approach to complicated diverticulitis, immunocompromised patients, or those with high-risk features—these populations were excluded from trials showing safety of observation. 1
• Do not extend antibiotics beyond 4-7 days in immunocompetent patients unless immunocompromised (10-14 days) or critically ill. 1, 2
• Do not delay surgical consultation for frequent recurrences (≥3 episodes) significantly impacting quality of life—elective sigmoidectomy improves outcomes. 1
• Do not assume all patients require hospitalization—outpatient management is safe for most uncomplicated cases and reduces costs by 35-83% per episode. 1

Follow-Up and Monitoring

• Re-evaluate within 7 days of diagnosis; earlier if clinical deterioration occurs. 1, 2
• Warning signs requiring immediate return: fever >101°F, severe uncontrolled pain, persistent vomiting, inability to eat/drink, signs of dehydration. 1
• Complete full antibiotic course even if symptoms improve to prevent incomplete treatment and recurrence. 1