How should I manage acute peritonitis in an adult, including empiric antibiotics for secondary peritonitis (no cirrhosis) and spontaneous bacterial peritonitis (cirrhosis with ascites), and what are beta‑lactam allergy alternatives?

Management of Acute Peritonitis in Adults

Immediate Diagnostic Differentiation: Secondary vs. Spontaneous Bacterial Peritonitis

The critical first step is distinguishing secondary bacterial peritonitis (requiring surgical intervention) from spontaneous bacterial peritonitis (SBP), as this fundamentally changes management—perform diagnostic paracentesis immediately and obtain CT imaging if any surgical drains are present, recent abdominal procedures occurred, or clinical features suggest a surgically correctable source. 1, 2

Key Diagnostic Features to Differentiate:

Secondary Peritonitis (Non-Cirrhotic or Cirrhotic):

• Ascitic fluid protein >1 g/dL (often >3 g/dL) 1, 3
• Ascitic fluid glucose <50 mg/dL 1, 3
• Ascitic fluid LDH greater than serum LDH (>240 U/L in all cases) 1, 3
• Polymicrobial flora on culture 3, 4
• PMN count often >1,000/mm³ 2
• Presence of surgical drains, recent procedures, or umbilical hernia complications 1, 4

Spontaneous Bacterial Peritonitis (Cirrhosis with Ascites):

• Ascitic fluid PMN ≥250 cells/mm³ 5, 2, 6
• Monomicrobial infection (typically E. coli, Klebsiella, Streptococcus) 5, 7
• Low ascitic protein (<1 g/dL) 3
• No surgically correctable intra-abdominal source 4

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Empiric Antibiotic Management for Secondary Peritonitis (No Cirrhosis)

For secondary peritonitis, initiate broad-spectrum antibiotics covering polymicrobial aerobic and anaerobic flora immediately, with piperacillin-tazobactam or a carbapenem (meropenem 1g IV every 8 hours) plus metronidazole as first-line agents. 1

Mandatory Surgical Consultation:

• Surgical evaluation is non-negotiable for source control 1
• Persistence of symptoms despite antibiotic therapy indicates need for surgical intervention 4

Beta-Lactam Allergy Alternatives for Secondary Peritonitis:

• For severe penicillin hypersensitivity: Vancomycin plus aztreonam plus metronidazole provides comparable coverage 5
• Alternative: Fluoroquinolone (ciprofloxacin or levofloxacin) plus metronidazole for community-acquired cases without recent antibiotic exposure 5

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Empiric Antibiotic Management for Spontaneous Bacterial Peritonitis (Cirrhosis with Ascites)

For community-acquired SBP, immediately start cefotaxime 2g IV every 6-8 hours or ceftriaxone 1-2g IV every 12-24 hours for 5-7 days—do not wait for culture results, as each hour of delay increases mortality by 10% in septic shock. 5, 2, 8

Community-Acquired SBP (First-Line):

• Cefotaxime 2g IV every 6-8 hours (resolution rates 77-98%) 2, 8
• Ceftriaxone 1-2g IV every 12-24 hours (resolution rates 73-100%) 2, 8
• Duration: 5 days is sufficient for uncomplicated cases 5, 8

Hospital-Acquired/Nosocomial SBP:

For nosocomial SBP, use meropenem 1g IV every 8 hours plus daptomycin 6 mg/kg/day due to high prevalence of ESBL-producing organisms and multidrug-resistant bacteria (86.7% efficacy vs. 25% with ceftazidime). 1, 9

Beta-Lactam Allergy Alternatives for SBP:

For patients with severe beta-lactam allergy:

• Ciprofloxacin 200 mg IV every 12 hours for 2 days, then 500 mg PO every 12 hours for 5 days (76-80% resolution rate) 8
• Critical exclusions for ciprofloxacin use: Do NOT use if patient is on quinolone prophylaxis, has septic shock, renal failure, hepatic encephalopathy, GI bleeding, or ileus 5, 8
• Aztreonam plus vancomycin is an alternative for true beta-lactam allergy with severe presentation 5

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Mandatory Albumin Administration for SBP

Albumin is NOT optional—administer 1.5 g/kg IV within 6 hours of diagnosis, followed by 1.0 g/kg on day 3, as this reduces mortality from 29% to 10% and prevents hepatorenal syndrome (from 30% to 10%). 5, 2

Patients Who Benefit Most:

• Serum creatinine ≥1 mg/dL 5, 2
• Blood urea nitrogen ≥30 mg/dL 5, 2
• Total bilirubin ≥4 mg/dL 5, 2

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Monitoring Treatment Response

Perform repeat paracentesis at 48 hours to assess treatment efficacy—treatment failure is defined as PMN count decrease <25% from baseline, which should prompt broadening of antibiotic coverage and investigation for secondary peritonitis. 5, 2, 8

When to Suspect Treatment Failure:

• Persistent fever or worsening clinical signs 5
• PMN count fails to decrease appropriately 5, 2
• Multiple organisms on culture 2, 3
• Consider CT imaging to rule out secondary peritonitis 1, 2

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Critical Pitfalls to Avoid

• Never assume SBP in the presence of surgical drains or recent abdominal procedures—always rule out secondary peritonitis first 1, 2
• Never delay antibiotics waiting for culture results—empirical therapy must start immediately 1, 2
• Never use aminoglycosides due to nephrotoxicity in cirrhotic patients 1
• Never forget albumin administration—it provides mortality benefit independent of antibiotics 1, 2
• Never use quinolones as first-line if patient is on quinolone prophylaxis due to high resistance rates 5, 8

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Post-Treatment: Secondary Prophylaxis for SBP

All patients surviving SBP require indefinite secondary prophylaxis with norfloxacin 400mg PO daily (or ciprofloxacin 500mg daily as alternative) until ascites resolves or liver transplantation occurs, as 1-year recurrence rate is 70% without prophylaxis. 5, 1, 2, 8