MRCP-0504

A 76-year-old woman is admitted with a productive cough and pyrexia. Chest x-ray shows a pneumonia and she is commenced on intravenous ceftriaxone. Following admission a stool sample is sent because of diarrhoea. This confirms the suspected diagnosis of Clostridium difficile diarrhoea and a 10-day course of oral metronidazole is started. After 10 days her diarrhoea is ongoing but she remains clinically stable. What is the most appropriate treatment?