Rifaximin therapy for metronidazole-unresponsive Clostridium difficile infection: a prospective pilot trial

BACKGROUND: Clostridium difficile infection (CDI) is a recent epidemic in the United States, particularly in the hospital setting. Oral metronidazole is standard therapy for C. difficile infection, but resistance to metronidazole is becoming a clinical challenge. METHODS: We evaluated the efficacy of the nonsystemic oral antibiotic rifaximin for the treatment of metronidazole-resistant C. difficile infection. Twenty-five patients with C. difficile infection were enrolled in the study. All had mild-to-moderate C. difficile infection (5-10 bowel movements a day without sepsis) unresponsive to metronidazole (i.e. stools positive for toxins A and B after oral metronidazole 500 mg three times daily [t.i.d.] for 5 days). After discontinuation of metronidazole, rifaximin 400 mg t.i.d. for 14 days was prescribed. Patients were followed for 56 days and stool was tested for C. difficile using polymerase chain reaction (PCR) to assess the effect of treatment. A negative PCR test result was interpreted as a favorable response to rifaximin. RESULTS: Sixteen of 22 patients (73%) were eligible for study inclusion and completed rifaximin therapy experienced eradication of infection (stool negative for C. difficile) immediately after rifaximin therapy and 56 days post-treatment. Three patients (12%) discontinued therapy because of abdominal distention. Rifaximin was generally well tolerated. CONCLUSIONS: In conclusion, rifaximin may be considered for treatment of mild-to-moderate C. difficile infection that is resistant to metronidazole. Larger randomized trials are needed to confirm these positive findings.