What is the best course of treatment for an elderly patient with Parkinson's disease, presenting with persistent diarrhea and a draining wound on the RLE, who recently developed severe diarrhea after being treated with metronidazole for a wound infection, and has lab results indicating anemia, neutrophilia, hypernatremia, elevated BUN, and impaired renal function?

Management of Metronidazole-Associated Diarrhea with Wound Infection

This patient requires immediate discontinuation of metronidazole, testing for Clostridioides difficile infection, empiric treatment with oral vancomycin 125 mg four times daily, aggressive IV fluid resuscitation, and broad-spectrum antibiotics covering the polymicrobial wound infection (Staph aureus and Bacteroides fragilis).

Immediate Actions Required

Discontinue Metronidazole and Test for C. difficile

• Stop metronidazole immediately given the severe diarrhea (8-10 bowel movements today) that developed after starting this antibiotic 1
• The clinical presentation—profuse watery diarrhea for 2.5 weeks following antibiotic initiation, failure of loperamide, dehydration (elevated BUN 30, creatinine 1.10, eGFR 51), and neutrophilia (79.1%)—is highly suspicious for C. difficile infection (CDI) 1
• Order stool testing for C. difficile toxin immediately using either toxin enzyme immunoassay or PCR 1, 2
• The dark-brown to blackish watery stools warrant evaluation for occult blood, fecal leukocytes, and complete stool workup including culture for Salmonella, E. coli, and Campylobacter 1

Empiric Treatment for Suspected Severe CDI

• Start oral vancomycin 125 mg four times daily immediately without waiting for test results given the severity of presentation 1, 3
• This patient meets criteria for severe CDI: profuse diarrhea, neutrophilia >15,000 equivalent (79.1% of normal range), elevated creatinine (>50% above likely baseline given age), and signs of dehydration 1
• Metronidazole should not be used for treatment given it was the inciting antibiotic and is inferior to vancomycin for severe CDI 1
• Continue vancomycin for 10 days if CDI is confirmed 1, 3

Aggressive Supportive Care

Fluid Resuscitation and Monitoring

• Hospitalize for IV fluid resuscitation given severe dehydration evidenced by elevated BUN:creatinine ratio (30:1.10 = 27:1), decreased oral intake, and orthostatic dizziness 1
• The 1L NS bolus in the ER was insufficient; continue aggressive IV hydration with normal saline and monitor electrolytes closely 1
• Measure serum lactate as a marker of severity; levels >5.0 mmol/L indicate need for surgical consultation 1
• Monitor for signs of toxic megacolon, ileus (absent bowel sounds, vomiting), or peritonitis given the severity of colitis 1

Avoid Antimotility Agents

• Do not use loperamide or other antimotility agents in this patient with suspected infectious/inflammatory diarrhea and neutrophilia 1
• Antimotility agents in severe CDI or neutropenic enterocolitis can precipitate toxic megacolon and increase risk of bacteremia 1

Management of Polymicrobial Wound Infection

Antibiotic Coverage for Wound

• The wound culture grew Staph aureus and Bacteroides fragilis, requiring coverage for both organisms 1
• Start IV piperacillin-tazobactam 3.375-4.5g every 6-8 hours (adjusted for renal function with eGFR 51) to cover both the Staph aureus and anaerobic Bacteroides 1
• Alternative: IV cefepime or ceftazidime plus metronidazole IV if piperacillin-tazobactam unavailable, though metronidazole IV is less ideal given the oral metronidazole-associated diarrhea 1
• If MRSA is suspected based on local epidemiology or patient risk factors, add IV vancomycin (separate from oral vancomycin for CDI) with dosing adjusted for renal function 1
• Obtain repeat wound culture to assess for superinfection given the chronic drainage 1

Wound Care

• Continue local wound care with dressing changes 1
• Surgical consultation may be needed if there is evidence of abscess, necrotizing infection, or failure to respond to antibiotics 1

Special Considerations for Parkinson's Disease

Medication Interactions and Complications

• Parkinson's disease patients have impaired gastrointestinal motility at baseline, increasing risk for severe complications from CDI including ileus and toxic megacolon 1
• Monitor closely for signs of ileus (absent bowel sounds, abdominal distension, vomiting) which may develop rapidly 1
• Avoid anticholinergic medications which can worsen ileus 1
• The patient's Parkinson's medications should be continued but monitored for absorption issues given severe diarrhea 4

Monitoring and Follow-up

Clinical Response Assessment

• Expect clinical improvement within 3 days of starting vancomycin: decreased stool frequency and improved consistency 1
• If no improvement after 72 hours, consider treatment failure and escalate to octreotide 100-150 mcg subcutaneously three times daily plus continued IV antibiotics 1
• Monitor daily: stool frequency, vital signs, mental status, urine output, and laboratory values (CBC, CMP, lactate) 1

Recurrence Risk

• After successful treatment, recurrence of CDI occurs in 18-25% of patients within 4 weeks 3
• If recurrence occurs, treat with vancomycin 125 mg four times daily for 14 days, potentially using a tapered/pulsed regimen 1
• Consider fidaxomicin 200 mg twice daily for 10 days for first recurrence as it has lower recurrence rates than vancomycin, though more expensive 1

Nutritional Support

• Once diarrhea begins to improve, advance diet gradually starting with bland, low-fiber foods (bananas, rice, applesauce, toast) 1
• Avoid lactose-containing products initially as chemotherapy and severe diarrhea can cause secondary lactose intolerance 1, 5
• Consider nutritional consultation given decreased appetite, poor oral intake, and elderly age with Parkinson's disease 4

Key Pitfalls to Avoid

• Do not continue metronidazole for the wound infection; it is the likely trigger for CDI and there are better alternatives for Bacteroides coverage 1
• Do not delay vancomycin while waiting for stool test results given severity of presentation 1
• Do not use probiotics in this immunocompromised state (neutrophilia, severe infection) as safety data are lacking 1
• Do not discharge until diarrhea is improving, patient is tolerating oral intake, and renal function is stabilizing 1