Which antibiotic is most commonly associated with pseudomembranous colitis?

• A. Clindamycin
• B. Amoxicillin
• C. Metronidazole
• D. Ciprofloxacin

Answer: (A)

Disruption of normal gut bacteria by an antibiotic allows Clostridioides difficile to overgrow and release toxins that inflame the colon. The toxins A and B damage the mucosa, leading to the characteristic pseudomembranes and diarrhea.

Among the options, clindamycin has the strongest historical association with this condition because it causes a substantial disruption of the gut anaerobic flora, creating a prime environment for C. difficile to flourish. While other broad-spectrum antibiotics can also predispose to C. difficile, clindamycin is the best known culprit, which is why it is the most likely answer. Metronidazole is now more commonly used to treat C. difficile infection, whereas amoxicillin and ciprofloxacin can also contribute but are less classic associations.