Patients with chronic obstructive pulmonary disease (COPD) should be more cautious when taking metformin, a common medication used to treat diabetes. In patients with both COPD and type 2 diabetes mellitus (T2DM), metformin carries a higher risk for pneumonia, hospitalization for COPD, and invasive mechanical ventilation.
This recommendation is based on a retrospective study of more than 20,000 patient records in Taiwan’s Longitudinal Cohort of Diabetes Patients (LHDB), part of the National Health Insurance Research Database (NHIRD).
The study, “Respiratory outcomes of metformin use in patients with type 2 diabetes and chronic obstructive pulmonary disease,” was published in the journal Nature Scientific Reports.
Nearly 10% of people with T2DM also have COPD. The presence of T2DM can worsen the progression and prognosis of COPD, as reduced respiratory function, chronic inflammation, and susceptibility to bacterial infection are all complications of hyperglycemia (high sugar levels).
Few studies, however, have investigated the effect of metformin on respiratory outcomes among patients with both COPD and T2DM and results have been largely inconclusive.
A team of scientists from multiple Taiwanese institutions searched the LHDB for records of patients diagnosed with both conditions from Jan. 1, 2000 to Dec. 31, 2012. From 402,153 patients with both diagnoses, the team identified 20,644 patients who used metformin, and a matched set of 20,644 non-users.
The records showed a slightly higher risk of being hospitalized for bacterial pneumonia among metformin users (3,133 patients hospitalized) than among the non-users (3,106 patients hospitalized). The hazard ratio, or the chance of something happening given a certain treatment versus no-treatment, was 1.17, meaning that on average metformin users experienced bacterial pneumonia infections 1.17 times more often than non-users.
A similar trend was found regarding COPD-related hospitalizations (hazard ratio of 1.34), the need for invasive ventilation (hazard ratio of 1.10), and the incidence of lung cancer (hazard ratio of 1.12), although this last association was not deemed significant because so few patients in either group were affected.
The results of this study contrasted with those of several prior studies suggesting that metformin use is associated with a decreased mortality and fewer COPD-specific emergency room visits. The team attributed this inconsistency to different sample sizes, patient ethnicities, and follow-up periods.
The use of NHIRD data imposed some limitations on the study, such as a lack of family history, body weight, smoking and drinking habits, and physical activity, which could influence the results. The database also does not contain the results of pulmonary function tests, making it impossible to measure the severity of a given patient’s COPD.
Nonetheless, based on the results, the team concluded that “metformin use in patients with T2DM and COPD was associated with higher risks of bacterial pneumonia, hospitalization for COPD and use of IMV [invasive mechanical ventilation],” and emphasized that “if patients with COPD use metformin, vigilance with regard to their pulmonary condition may be required.”
More studies are needed, the team noted. “Because of some unmeasured or inevitable bias still exist in this cohort study, stringent prospective studies or randomized control clinical trials are warranted to verify our results,” they wrote.