Metformin Use Prior to Admission for Pneumonia Decreases Mortality Risk

Metformin use was associated with decreased mortality rates among older patients with diabetes hospitalized with community-acquired pneumonia (CAP). These study results were published in Clinical Infectious Diseases.

Between October 2001 and September 2012, researchers conducted a retrospective study to assess the association between metformin use prior to hospitalization for community-acquired pneumonia among older patients (≤65 years old) with diabetes. The primary outcomes were all-cause mortality within 30 and 90 days after admission. Eligible patients were those who were diagnosed with diabetes and reported at least 3 outpatient clinic visits within the past year. All patients received least 1 dose of antimicrobial therapy within 48 hours of admission. Outcomes were compared between patients who did vs did not report receipt of at least 1 prescription for metformin within 90 days of admission. Propensity score and nearest-number matching were used to balance measured confounders between the cohorts, with scores derived via logistic regression.

After propensity-score matching, the metformin and control cohorts each comprised 6899 patients. The mean (SD) patient age was 75.1 (6.6) years, 98.7% were men, and approximately 83% were Black.

In the matched analysis, the rate of all-cause 30-day mortality was significantly lower among patients in the metformin vs control cohorts (9.6% vs 13.9%; relative risk [RR], 0.86; 95% CI, 0.78-0.95; P <.003). Similar results were noted for the rate of all-cause 90-day mortality between the cohorts (15.8% vs 23.0%; RR, 0.85; 95% CI, 0.79-0.92; P <.001).

Further analysis was performed using Cox proportional hazards models. Results showed a significant association between prior metformin use and decreased 90-day all-cause mortality risk (hazard ratio [HR], 0.85; 95% CI, 0.80-0.91). This association also was observed among patients with diabetes-related complications (HR, 0.76; 95% CI, 0.66-0.87), those with a history of chronic obstructive pulmonary disease (HR, 0.85; 95% CI, 0.77-0.93), and those who used insulin (HR, 0.76; 95% CI, 0.66-0.87).  

Limitations include the lack of microbiologic and vaccination data, as well as the predominance of men in the study population.

“Prospective, well-designed studies are needed to further examine the association of metformin, and other potentially protective medications, in populations that are at high risk of respiratory infections,” the researchers concluded.

Disclosure: One author declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.