Pharmacology · Year 2 · from Pharmacology
Case 3: Clostridioides difficile Infection Post-Antibiotic
Clinical Scenario
A 68-year-old female develops profuse watery diarrhea 10 days after completing a course of clindamycin for a dental infection.
Patient Demographics
- Age: 68 years
- Sex: Female
- Weight: 65 kg
Chief Complaint
Watery diarrhea (10-15 episodes daily) with abdominal cramping for 3 days
History of Present Illness
The patient completed a 7-day course of clindamycin for a dental abscess 10 days ago. Three days ago, she developed profuse, watery, foul-smelling diarrhea occurring 10-15 times per day. She has diffuse abdominal cramping, low-grade fever, and has noticed blood streaks in her stool today.
Medications
- Lisinopril 10 mg daily
- Metformin 1000 mg twice daily
- Completed clindamycin 300 mg QID (7 days, ended 10 days ago)
Physical Examination
- Vital Signs: BP 105/68 mmHg, HR 98 bpm, RR 18, T 38.3C
- General: Appears dehydrated, uncomfortable
- Abdominal: Diffuse tenderness, hyperactive bowel sounds, no rebound or guarding
- Rectal: Guaiac positive stool
Workup and Results
| Test | Result | Reference Range |
|---|---|---|
| WBC | 22,400/mcL | 4,500-11,000/mcL |
| Creatinine | 1.6 mg/dL | 0.6-1.2 mg/dL |
| Albumin | 2.8 g/dL | 3.5-5.0 g/dL |
| Lactate | 1.8 mmol/L | 0.5-2.0 mmol/L |
| C. difficile toxin PCR | Positive | Negative |
| C. difficile toxin EIA | Positive | Negative |
CT Abdomen: Diffuse colonic wall thickening consistent with colitis
Diagnosis
Clostridioides difficile infection (CDI) - moderate-severe (WBC >15,000, creatinine rise, hypoalbuminemia)
Antimicrobial Pharmacology Principles Illustrated
- Disruption of normal flora: Clindamycin has excellent anaerobic coverage that disrupts protective gut microbiome.
- C. difficile pathogenesis: Spore-forming organism produces toxins A and B causing colonic inflammation.
- High-risk antibiotics: Clindamycin, fluoroquinolones, cephalosporins, and carbapenems have highest CDI risk.
- Vancomycin oral formulation: Achieves high colonic concentrations with minimal systemic absorption - treatment of choice.
- Fidaxomicin: Narrow-spectrum macrolide that preserves gut flora; lower recurrence rates.
- Metronidazole role: Now reserved only for non-severe CDI when oral vancomycin unavailable.
Treatment
- Oral vancomycin 125 mg QID for 10-14 days (first-line for moderate-severe CDI)
- IV fluids for dehydration and acute kidney injury
- Avoid antidiarrheals (loperamide) - can worsen toxin retention
- Contact isolation precautions
- Monitor for complications:
- Fulminant colitis (ileus, toxic megacolon)
- Perforation
- If refractory: surgical consultation
- Consider fidaxomicin for patients at high risk of recurrence
- Bezlotoxumab (anti-toxin B antibody) for recurrent CDI prevention
Severity Classification and Treatment
| Severity | Criteria | Treatment |
|---|---|---|
| Non-severe | WBC <15,000, Cr <1.5x baseline | PO vancomycin 125 mg QID or fidaxomicin |
| Severe | WBC >15,000 OR Cr >1.5x baseline | PO vancomycin 125 mg QID |
| Fulminant | Hypotension, shock, ileus, megacolon | PO vancomycin 500 mg QID + IV metronidazole + surgical consult |
Key Learning Points
- C. difficile is the most common healthcare-associated infection
- Oral vancomycin (not IV) is the treatment - it is not absorbed systemically
- Antimicrobial stewardship reduces CDI incidence
- Recurrence occurs in 20-25% of cases; fecal microbiota transplant effective for multiply recurrent CDI