LAUSR

Background: Despite clinical practice guideline recommendations to use doxycycline as part of combination therapy for some patients hospitalized with pneumonia there is minimal research supporting this. Therefore, the purpose of our study was to examine the association between doxycycline use, as part of combination antibiotic therapy, and mortality for patients hospitalized with pneumonia. Methods: We identified patients > 65 years of age admitted to any US Department of Veterans Affairs hospital in fiscal years 2002-2012 with a discharge diagnosis of pneumonia. We excluded those patients who did not receive antibiotic therapy concordant with the 2019 ATS/IDSA clinical practice guidelines. Using a multilevel regression model, we examined the association of doxycycline on 30-day mortality, adjusting for demographics, comorbid conditions, severity of illness, prior outpatient medications, and admitting hospital. Results: Our cohort was comprised of 83,961 patients with a mean age of 77.8 (standard deviation 7.4) years, 98% were male, and 7.4% received doxycycline. Unadjusted mortality was 8.6% for those who received doxycycline vs. 11.7% in those who did not (p Conclusions: In this observational cohort study, we found that doxycycline use, as part of guideline-concordant antibiotic therapy, was associated with significantly lower mortality. While this supports the safety and efficacy of antibiotic regimes that include doxycycline, additional studies, especially randomized clinical trials, are needed to confirm this.