How should I initially manage a 45‑year‑old man with three days of watery diarrhoea, one day of bloody stool, resolved hypovolaemic shock, mild renal impairment (creatinine 1.67 mg/dL), modest transaminitis (aspartate aminotransferase 60 U/L, alanine aminotransferase 78 U/L) and elevated C‑reactive protein?

Management of Complicated Diarrhea with Resolved Shock and Acute Kidney Injury

This 45-year-old man requires immediate hospitalization for intravenous fluid resuscitation, empiric broad-spectrum antibiotics covering enteric pathogens, comprehensive stool and blood work-up, and close monitoring for progression to sepsis or worsening renal function. 1

Immediate Priorities

Fluid Resuscitation and Renal Protection

• Continue aggressive IV fluid replacement with isotonic saline or balanced salt solution targeting urine output >0.5 mL/kg/h (approximately 35 mL/h for this patient) and normalization of creatinine 1
• The creatinine of 1.67 mg/dL with elevated urea (40 mg/dL) indicates acute kidney injury, likely hypovolemic in origin given the recent shock state 1
• Administer albumin 1 g/kg (up to 100 g) to optimize renal perfusion in the setting of recent hypovolemic shock and ongoing diarrhea 1
• Monitor daily weights, strict intake/output, and serial electrolytes every 12-24 hours to avoid both under-resuscitation and fluid overload 2

Empiric Antibiotic Therapy

Start empiric antibiotics immediately because this patient meets multiple criteria for complicated diarrhea: bloody stools, recent shock, elevated inflammatory markers (CRP 74→42), and mild transaminitis suggesting systemic involvement 1

• First-line regimen: Fluoroquinolone (ciprofloxacin 500 mg IV twice daily OR levofloxacin 500 mg IV daily) PLUS metronidazole 500 mg IV three times daily to cover enteric gram-negative organisms, gram-positive organisms, and anaerobes 1
• Alternative monotherapy: Piperacillin-tazobactam 4.5 g IV every 6-8 hours provides adequate broad-spectrum coverage 1
• The presence of blood in stool for one day suggests invasive bacterial pathogens (Shigella, Campylobacter, invasive E. coli, or Salmonella) 1

Critical Diagnostic Work-Up

Obtain immediately before starting antibiotics (do not delay treatment): 1

• Stool studies: Culture for Salmonella, Shigella, Campylobacter, Yersinia; Shiga-toxin testing (critical—if positive, STOP all antibiotics immediately due to hemolytic-uremic syndrome risk); Clostridium difficile toxin assay 1
• Blood cultures × 2 sets given recent shock and elevated inflammatory markers suggesting possible bacteremia 1
• Complete blood count with differential to assess for leukocytosis or neutropenia 1
• Comprehensive metabolic panel including sodium, potassium, bicarbonate, calcium to guide electrolyte replacement 1
• Repeat creatinine daily to monitor renal recovery 1

Symptomatic Management

Antimotility Agents—CONTRAINDICATED

Do NOT use loperamide or any opioid antidiarrheal agents because bloody stools indicate inflammatory/invasive diarrhea, and antimotility therapy risks toxic megacolon and clinical deterioration 1

Consider Octreotide for Refractory Cases

• If diarrhea remains severe (>10 stools/day) despite 24-48 hours of antibiotics and IV fluids, add octreotide 100-150 mcg subcutaneously three times daily OR 25-50 mcg/hour IV infusion, escalating up to 500 mcg subcutaneously three times daily 1
• Octreotide is particularly useful when severe secretory diarrhea persists and contributes to ongoing fluid losses 1

Monitoring and Red Flags

Daily Assessments Required

• Serial abdominal examinations to detect peritoneal signs, distension, or ileus that would indicate perforation or toxic megacolon 1
• Vital signs every 4-6 hours monitoring for recurrent hypotension, tachycardia, or fever >38.5°C 1
• Urine output hourly via Foley catheter if oliguric (<0.5 mL/kg/h) to guide fluid resuscitation 1
• Daily creatinine and electrolytes until renal function normalizes 1

Indications for Surgical Consultation

Obtain urgent surgical evaluation if any of the following develop: 1

• Persistent gastrointestinal bleeding despite correction of coagulopathy
• Evidence of free intraperitoneal perforation (peritoneal signs, free air on imaging)
• Clinical deterioration despite aggressive medical management
• Severe abdominal distension or signs of toxic megacolon

Hepatic Considerations

The modest transaminitis (AST 60, ALT 78) likely reflects hypoperfusion injury from recent shock rather than primary liver disease 1

• Avoid hepatotoxic agents and adjust medication doses for hepatic dysfunction if transaminases worsen 1
• Repeat liver function tests in 48-72 hours to confirm downtrending 1

Nutritional Support

• Keep patient NPO (nothing by mouth) initially if severe abdominal pain, distension, or concern for ileus 1
• Once diarrhea begins to improve and patient is hemodynamically stable, advance to clear liquids then light diet avoiding lactose, fatty foods, caffeine, and alcohol 1, 3
• Resume normal diet as tolerated once diarrhea resolves and appetite returns 1, 3

Antibiotic Stewardship

• De-escalate or discontinue antibiotics once stool culture results return if a specific pathogen is identified with known susceptibilities 1
• If Shiga-toxin testing is positive, STOP all antibiotics immediately and provide supportive care only, as antibiotics increase hemolytic-uremic syndrome risk 17-fold 1
• If Clostridium difficile is identified, switch to oral vancomycin 125 mg four times daily for 10 days 4

Common Pitfalls to Avoid

• Never use loperamide when blood is present in stool—this is the most critical error and can precipitate toxic megacolon 1
• Never delay antibiotics while awaiting stool studies in a patient with bloody diarrhea, recent shock, and elevated inflammatory markers 1
• Never start antibiotics before obtaining Shiga-toxin testing in bloody diarrhea, but do not delay empiric therapy while awaiting results 1
• Never under-resuscitate renal function—the creatinine of 1.67 indicates ongoing need for aggressive volume replacement 1
• Never overlook the possibility of ischemic colitis in a patient with recent shock and bloody diarrhea; colonoscopy may be needed if no infectious etiology is identified 5

Expected Clinical Course

• Diarrhea should begin improving within 24-48 hours of appropriate antibiotics if bacterial etiology 1, 6
• Creatinine should decrease by ≥0.3 mg/dL within 48 hours with adequate volume resuscitation 1
• If no improvement by 48-72 hours, reassess for antimicrobial resistance, non-infectious etiologies (inflammatory bowel disease, ischemic colitis), or complications 1, 5