What is the best course of treatment for a 79-year-old female patient with a history of Parkinson's disease, presenting with a 2-month history of a draining ulcer on her right lower extremity (RLE), chronic pain (5-7/10), swelling, decreased oral intake, and diarrhea (8-10 bowel movements per day) after recent antibiotic (metronidazole) use, and with a history of antibiotic-associated diarrhea?

Management of Antibiotic-Associated Diarrhea with Non-Healing Leg Ulcer in Elderly Patient with Parkinson's Disease

Immediate Priority: Test for Clostridioides difficile Infection and Discontinue Metronidazole

This patient requires immediate testing for C. difficile infection (CDI) given the severe diarrhea (8-10 bowel movements/day) following metronidazole exposure, and if positive, should be treated with oral vancomycin 125 mg four times daily for 10 days, NOT metronidazole. 1, 2, 3

Critical Clinical Context

This presentation is highly concerning for CDI given:

• Severe diarrhea onset after metronidazole use (started 2 days ago, now 8-10 BMs/day) 1
• Recent multiple antibiotic exposures (Augmentin, then metronidazole) - major risk factor for CDI 1
• Age 79 years - elderly patients have higher CDI risk and worse outcomes 1
• Signs suggesting possible severe disease: dizziness on standing (orthostatic hypotension from volume depletion), decreased oral intake 1

Diagnostic Workup Required Immediately

Test for CDI now - the Infectious Diseases Society of America recommends testing when metronidazole is being used for suspected CDI, as severe CDI can present with abdominal pain and leukocytosis. 2

Assess for severe/fulminant CDI by checking for: 1, 2

• Hypotension or shock (she has orthostatic dizziness)
• Leukocytosis >15,000/μL (obtain CBC urgently)
• Serum creatinine elevation >50% above baseline
• Serum lactate elevation
• Ileus or megacolon (obtain abdominal imaging if clinical concern)

Treatment Algorithm for CDI (If Positive)

For non-severe CDI (no signs below): 1, 2

• Oral vancomycin 125 mg four times daily for 10 days (preferred over metronidazole) 2, 3
• Alternative: Fidaxomicin 200 mg twice daily for 10 days 1, 2
• Do NOT use metronidazole - guidelines have shifted away from metronidazole as first-line 2

For severe CDI (WBC >15,000, creatinine rise >50%, hypotension, or signs of peritonitis): 1

• Oral vancomycin 125 mg four times daily for 10 days 1
• If oral route impossible: vancomycin 500 mg every 6 hours via nasogastric tube PLUS IV metronidazole 500 mg every 8 hours PLUS vancomycin retention enema 500 mg in 100 mL saline every 4-12 hours 1

For fulminant CDI (hypotension, ileus, megacolon): 2

• Escalate to oral vancomycin 500 mg every 6 hours PLUS IV metronidazole 500 mg every 8 hours 2
• Obtain surgical consultation early - do not delay if lactate >5.0 mmol/L or clinical deterioration 1

Management of the Leg Ulcer/Abscess

Stop immodium immediately - antiperistaltic agents must be avoided in suspected CDI as they increase risk of toxic megacolon. 1

For the draining RLE ulcer/abscess: 1

• If abscess >3 cm or worsening despite antibiotics, consider percutaneous drainage (CT or ultrasound-guided) 1
• Antibiotics should cover Gram-negative bacteria and anaerobes: fluoroquinolone or third-generation cephalosporin PLUS metronidazole (but only IV metronidazole if CDI confirmed, not oral) 1
• If abscess <3 cm without fistula and patient not on steroids, may respond to antibiotics alone 1
• Clinical improvement should occur within 3-5 days; if not, repeat imaging and consider drainage repositioning or surgical intervention 1

Critical Pitfalls to Avoid

Do NOT continue oral metronidazole - this patient is already on metronidazole which may have caused or worsened CDI, and metronidazole is no longer first-line for CDI treatment. 2

Do NOT use antidiarrheal agents (stop immodium) - these are contraindicated in CDI and can precipitate toxic megacolon. 1

Do NOT delay CDI testing - waiting increases risk of progression to fulminant disease with high mortality. 1, 2

Monitor for deterioration closely - elderly patients with Parkinson's disease are at higher risk for delirium, functional decline, and sepsis from infections. 4, 5

Supportive Care Measures

• Aggressive IV fluid resuscitation for orthostatic hypotension and volume depletion 1
• Correct electrolyte abnormalities 1
• Thromboprophylaxis with low molecular weight heparin 1
• Nutritional support given decreased oral intake 1

Special Considerations for Parkinson's Disease

Parkinson's patients have increased infection susceptibility due to autonomic dysfunction, frailty, and cognitive impairment. 4, 5

UTI and other infections commonly precipitate acute deterioration in PD patients, causing delirium and functional decline. 4

Antibiotic exposure itself may be associated with PD progression - use narrowest spectrum and shortest duration necessary once infection controlled. 6, 7

If CDI Testing is Negative

If CDI is ruled out, the diarrhea is likely antibiotic-associated (non-CDI):

• Discontinue metronidazole if possible 1
• Consider probiotics (though safety data limited in frail elderly) 1
• Supportive care with hydration and electrolyte repletion 1
• Continue appropriate antibiotics for leg ulcer based on culture results 1