Despite the limitations of their study, the authors conclude “The main finding of our study that doxycycline is associated with lower risk of CDI in hospitalized patients receiving ceftriaxone is robust, biologically plausible, and largely consistent with data from other studies.”
Dr. Sarah Doernberg and colleagues at San Francisco General Hospital, California point out that antibiotic therapy is a major risk factor for C. difficile infection, but the risk is lower with doxycycline than other antibiotics. There is also evidence that doxycycline may even be protective.
To investigate, the team examined the incidence of C. difficile infection among 2305 patients treated at their hospital with ceftriaxone, a high-risk antibiotic for CDI. The patients were hospitalized for community-acquired pneumonia (CAP), bone and joint infections, meningitis, endocarditis and UTI. Doxycycline was also given in 39% of the cases.
CDI occurred within 30 days of receiving ceftriaxone in 43 patients. The incidence rate of CDI was 1.67 cases per 10,000 patient-days among those given doxycycline compared with 8.11 cases per 10,000 patient-days in those who did not, the researchers report.
“The most straightforward explanation for why doxycycline may be associated with lower risk of CDI is its in vitro activity against anaerobic bacteria, including C. difficile,” the authors comment. It may also inhibit C. difficile toxin production and, because it is mainly absorbed in the upper GI tract, it may have minimal effects on gut flora.
Dr. Doernberg and colleagues note that guidelines recommend the combination of ceftriaxone and doxycycline as a second-line regimen for some patients with CAP. They conclude, based on their findings, “Further clinical studies would help define whether doxycycline-containing regimens should be a preferred therapy for CAP.”