Protective effect of metformin against tuberculosis infections in diabetic patients: an observational study of south Indian tertiary healthcare facility

Background: World Health Organization estimated that people with diabetes (DM) are at 2-3 times higher risk for tuberculosis (TB). Studies have shown that DM not only increases the risk of active TB, but also puts co-affected persons at increased risk of poor outcomes. Objectives: To determine the protective effect of metformin against TB in DM patients and also, to investigate the relationship between poor glycemic control and TB. Methods: A case-control study was conducted over 8 months, where cases and controls were selected based on the inclusion and exclusion criteria of the study. The diabetics diagnosed with TB were selected as study group (SG = 152) and without TB were as control group (CG = 299). Exposure status of metformin in both groups were analyzed. Results: The mean (SD) age of both CG and SG were 55.54 +/- 11.82 and 52.80 +/- 11.75, respectively. Majority of the subjects in the study were males. The mean hospital stay of SG and CG were 7 days and 6 days, respectively. Poor glycemic control (HbA1c > 8) observed in SG (51.7%) vs CG (31.4%). HbA1c value <7 is associated protective factor for TB occurrence [OR = 0.52 (95% CI 0.29-0.93)]. The protective effect of metformin against TB was 3.9-fold in diabetics (OR = 0.256, 0.16-0.40). Conclusion: Poor glycemic control among diabetics is a risk factor for TB occurrence. The result shows metformin use is a protective agent against TB infection in diabetics. Hence, incorporation of metformin into standard clinical care would offer a therapeutic option for the prevention of TB. (C) 2017 Sociedade Brasileira de Infectologia. Published by Elsevier Editora Ltda.