Core55: Drug-induced adverse reaction: pseudomembranous colitis

🦠 High-yield / 要点：Pseudomembranous colitis is usually due to Clostridioides difficile after disruption of normal intestinal flora, especially by antibiotics.

Definition / 定義

• Pseudomembranous colitis = colitis with yellow-white pseudomembranes on colon endoscopy.
• Pseudomembranes are fibrinous exudates.
• Main etiology:
  • Clostridioides difficile infection.

Symptoms / 症状

• Watery, foul-smelling diarrhea.
• Fever.
• Cramping abdominal pain.
• Severe cases:
  • Fulminant colitis.
  • Toxic megacolon.

Medication risk factors / 薬剤リスク

Risk level	Drugs	Mechanism / note
High risk	Clindamycin, cephalosporins, fluoroquinolones	Strong disruption of normal intestinal flora
Moderate risk	Penicillins, macrolides	Can also predispose to C. difficile
Other	PPIs	Reduced stomach acidity → reduced antibacterial barrier

Treatment / 治療

• Stop the causative antibiotic if possible.
• Main options:
  • Oral vancomycin：acts locally in GI tract because it is poorly absorbed.
  • Oral fidaxomicin：macrocyclic antibiotic; useful especially for recurrent cases.
  • Metronidazole：oral or IV.
• Fulminant cases:
  • Oral vancomycin + IV metronidazole.
• Recurrent cases:
  • Fidaxomicin.
  • Fecal microbiota transplantation can be considered.

Important note / 注意

• IV vancomycin is used for systemic infections, but oral vancomycin is used for C. difficile because it stays in the gut.
• Vancomycin infusion reaction / “Red man syndrome” is related to IV use, not oral gut-local therapy.

Remember / 覚え方

• C. difficile = antibiotic-associated diarrhea
• Clindamycin, cephalosporins, fluoroquinolones = high risk
• Treat with oral vancomycin or fidaxomicin