Metformin use and the risk of bacterial pneumonia in patients with type 2 diabetes

Persons with type 2 diabetes (T2D) have neutrophil dysfunction with a higher risk of infection than those without diabetes. We conducted this study aiming to compare the risk of pneumonia between metformin use and nonuse in persons with T2D. We identified 49,012 propensity score-matched metformin users and nonusers from Taiwan's National Health Insurance Research Database between January 1, 2000, and December 31, 2017. We used the Cox proportional hazards model to compare the risks of pneumonia and respiratory death. The mean (SD) age of the participants was 57.46 (12.88) years, and the mean follow-up time for metformin users and nonusers was 5.47 (3.71) years and 5.15 (3.87) years, respectively. Compared with the nonuse of metformin, the adjusted hazard ratios (95% CI) for metformin use in bacterial pneumonia, invasive mechanical ventilation, and respiratory cause of death were 0.89 (0.84-0.94), 0.77 (0.73-0.82), and 0.64 (0.56-0.74), respectively. A longer cumulative duration of metformin use had further lower adjusted hazard ratios in these risks compared with nonuse. In patients with T2D, metformin use was associated with significantly lower risks of bacterial pneumonia, invasive mechanical ventilation, and respiratory cause of death; moreover, longer metformin use duration was associated with lower hazard ratios of these risks.