Respiratory effects of insulin sensitisation with metformin: a prospective observational study

The mechanism for the association between diabetes mellitus and lung function impairment is unknown, as are any respiratory effects of antidiabetic agents. We aimed to assess whether treatment with metformin, an oral insulin-sensitising agent, improved lung function or symptoms in individuals with COPD and glucose intolerance. A prospective open-label observational study was conducted. Participants with moderate or severe COPD, BMI > 25 kg/m(2), and type 2 diabetes mellitus or impaired glucose tolerance took metformin twice daily for 6 months. Clinical outcomes included St George's Respiratory Questionnaire (SGRQ), transition dyspnoea index, and incremental shuttle walk test. Physiological outcomes including pulmonary function tests, exhaled nitric oxide, respiratory mouth pressures and handgrip strength. In total, 17 participants completed the study. SGRQ score improved by a median of 5 points, and TDI scores improved by 2 points. Inspiratory mouth pressures increased by 7.5 cmH2O. There were trends to improvements in hyperinflation, gas trapping and shuttle walk distance. Spirometry and exhaled nitric oxide were unchanged. In this proof-of-concept study, metformin was associated with improved dyspnoea and health status in COPD, possibly related to increased inspiratory muscle strength. These and other endpoints should be examined in a definitive study.