Metformin is associated with a lower risk of active tuberculosis in patients with type 2 diabetes

ABSTRACT Background and objective Metformin is an oral anti‐diabetic therapy (ADT) to manage type 2 diabetes mellitus (T2DM), and has been reported to have potential anti‐tuberculosis (TB) effects. This study investigates the risk of active TB among persons with T2DM who were treated with various ADT and insulin therapies. Methods We conducted a nationwide population‐based cohort study using the Taiwan Longitudinal Health Insurance Database, including 49 028 T2DM patients who were metformin users ( n = 44 002) or non‐users ( n = 5026). A total of 5026 propensity score‐matched pairs of metformin users and non‐users with T2DM were evaluated from 1998 to 2010. The data were analysed using Cox proportional hazard models. Results Patients with T2DM had a significantly higher rate of incident TB than did the control subjects (adjusted hazard ratio: 2.01; 95% confidence interval (95% CI): 1.80–2.25). After adjusting for comorbidities, diabetes complications, ADT type and statin use, metformin use was an independent factor for predicting a reduced risk of active TB (adjusted relative risk (aRR): 0.24; 95% CI: 0.18–0.32). The association between metformin use and active TB risk was also consistent in most subgroup analyses, except for patients with metabolic disorders (aRR: 0.46; 95% CI: 0.11–1.87). This protective effect of metformin was dose‐dependent but diminished gradually in the elderly population. Conclusion Among all types of ADT and insulin therapies, metformin is the only agent with a decreased risk of active TB in the T2DM population. However, this effect was diminished in the elderly population and was not observed in patients with metabolic disorders.