A patient develops Clostridioides difficile-associated diarrhoea (CDAD) after broad-spectrum antibiotic therapy. The preferred antibiotic for a first severe episode is:

• A Metronidazole 500 mg orally three times daily for 10 days
• B Fidaxomicin 200 mg orally twice daily for 10 days ✓
• C Vancomycin 125 mg orally four times daily for 10 days
• D Rifaximin 550 mg orally three times daily for 10 days

Explanation

Current IDSA 2021 guidelines recommend fidaxomicin as preferred therapy for initial and recurrent non-severe and severe CDAD episodes, as it achieves superior sustained clinical cure rates and significantly lower recurrence rates compared to vancomycin (due to minimal systemic absorption and minimal disruption of intestinal microbiome flora — preserving colonisation resistance). Vancomycin is an acceptable alternative. Oral metronidazole is now considered inferior for severe CDAD. Rifaximin has no primary role.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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