Treating some pneumonia patients with the antibiotic doxycycline instead of the more commonly prescribed azithromycin can reduce the risk of Clostridioides difficile infection by up to 45%, according to a study yesterday in the American Journal of Infection Control.
Using broad spectrum antibiotics to treat pneumonia is standard practice in US hospitals, but it raises the risk of patients acquiring C diff infections (CDI), which cause roughly 30,000 US deaths each year.
In the study, researchers looked at outcomes among 156,107 patients treated for pneumonia in Veterans Affairs Hospitals from January 2009 through August 2022. A pneumonia diagnosis was obtained within 48 hours of hospitalization to ensure that all cases were considered community-acquired pneumonia.
Current clinical guidelines recommend azithromycin, as it can treat all types of pneumonia, including Legionella pneumonia. Doxycycline is not effective against Legionella bacteria.
Overall, 87% of patients in the study were treated with azithromycin, and 13% received doxycycline. According to the authors, less than 1% of patients developed CDIs within 30 days of treatment, but among patients who had experienced a CDI in the year before their pneumonia diagnosis, 12% developed a new CDI.
Less gut microbiome disruption
The authors noted a 17% decreased risk of CDI with doxycycline compared to azithromycin when used with ceftriaxone. But in patients who had a diagnosis of CDI in the year prior to pneumonia, the risk dropped by 45%.
In cases where Legionella pneumonia can be ruled out prior to treatment, patients at increased risk of C. diff may benefit from the use of doxycycline as a first-line agent.
"Our analysis found that in patients with a prior history of C. diff, doxycycline was the only factor associated with a reduction in the incidence of new C. diff infections," said Kari A. Mergenhagen, PharmD, residency director for infectious diseases at the Veterans Affairs of Western New York Healthcare System and senior author of the study, in a press release from the journal's publisher. "These results suggest that, in cases where Legionella pneumonia can be ruled out prior to treatment, patients at increased risk of C. diff may benefit from the use of doxycycline as a first-line agent."
The authors of the study said the findings should prompt further investigation. They note that doxycycline has less of an impact on the gut microbiome, which may be why it was less likely to cause CDI.