Historically, metronidazole has been prescribed more frequently as the first-line agent in CDAD. Proponents of the drug tout its low cost and the importance of minimizing the development of vancomycin-resistant enteric pathogens. There are two small, prospective, randomized studies comparing the efficacy of the agents against one another in the treatment of C. difficile infection, with similar efficacy demonstrated in both studies. In the early 1980s, Teasley and colleagues randomized 94 patients with C. difficile infection to either metronidazole or vancomycin.5 All the patients receiving vancomycin resolved their disease; 95% of patients receiving metronidazole were cured. The differences were not statistically significant.
In the mid-1990s, Wenisch and colleagues randomized patients with C. difficile infection to receive vancomycin, metronidazole, fusidic acid, or teicoplanin therapy.6 Ninety-four percent of patients in both the vancomycin and metronidazole groups were cured.
However, since 2000, investigators have reported higher failure rates with metronidazole therapy in C. difficile infections. For example, in 2005, Pepin and colleagues reviewed cases of C. difficile infections at a hospital in Quebec.7 They determined the number of patients with C. difficile infection initially treated with metronidazole who required additional therapy had markedly increased. Between 1991 and 2002, 9.6% of patients who initially were treated with metronidazole required a switch to vancomycin (or the addition of vancomycin) because of a disappointing response. This figure doubled to 25.7% in 2003-2004. The 60-day probability of recurrence also increased in the 2003-2004 test group (47.2%), compared with the 1991-2002 group (20.8%). Both results were statistically significant. Such data contributed to the debate regarding whether metronidazole or vancomycin is the superior agent in the treatment of C. difficile infections.
In 2007, Zar and colleagues studied the efficacy of metronidazole and vancomycin in the treatment of CDAD patients, but the study stratified patients according to disease severity.8 This allowed the authors to investigate whether one agent was superior in treating mild or severe CDAD. They determined disease severity by assigning points to individual patient characteristics. Patients with two or more points were deemed to have “severe” CDAD.
The investigators assigned one point for each of the following patient characteristics: temperature >38.3 degrees Celsius, age >60 years, albumin level <2.5 mg/dL, and white blood cell count >15,000 cells/mm3 within 48 hours of enrolling in the study. Any patient with endoscopic evidence of pseudomembrane formation or admission to the intensive-care unit (ICU) for CDAD treatment was considered to have severe disease.
Medical-on-Line/Alamy
A scanning electron micrograph of C. difficile.
This was a prospective, randomized controlled trial of 150 patients. Patients were randomly prescribed 500 mg metronidazole by mouth three times daily or 125 mg of vancomycin by mouth four times daily. Patients with mild CDAD had similar cure rates: 90% metronidazole versus 98% vancomycin (P=0.36). However, patients with severe CDAD fared statistically better when treated with oral vancomycin. Ninety-seven percent of severe CDAD patients treated with oral vancomycin had a clinical cure, while only 76% of those treated with metronidazole were cured (P=0.02). Recurrence of the disease was similar in each treatment group.
Based on this study, metronidazole and vancomycin appear equally effective in the treatment of mild CDAD, but vancomycin is the superior agent in the treatment of patients with severe CDAD.
Back to the Case
Our patient had several risk factors predisposing her to developing CDAD. She was of advanced age and took a fluoroquinolone antibiotic during a recent hospitalization. She also presented with signs consistent with a severe case of CDAD. She had a fever, a white blood cell count >15,000 cells/mm3, and was older than 60. Thus, she should be treated with supportive care, placed on contact precautions, and administered oral vancomycin 125 mg by mouth every six hours for 10 days as empiric therapy for CDAD. Stool cultures should be sent to confirm the presence of the C. difficile toxin.