Metformin shields diabetics against tuberculosis

Among patients with diabetes mellitus (DM), the use of metformin may prove to be protective against tuberculosis (TB), a recent study has found.

Researchers retrospectively recruited 9,750 DM patients (mean age, 65.1±15.2 years; 55.7 percent male) who had baseline assessments of body mass index (BMI), fasting blood glucose (FBG), and glycated haemoglobin (HbA1c), among other factors. The main outcome was the diagnosis of TB infection, defined according to international standards and being on anti-TB medication for ≤2 months.

Less than a third (30.22 percent) of the patients were not taking metformin, while the remaining 69.78 percent were. The former group tended to be older and had a significantly greater male predominance (p<0.001 for both). HbA1c and FBG were significantly higher in the latter group (p<0.001 for both).

Forty-seven patients eventually developed TB, yielding an event rate of 0.48 percent. Multivariate Cox proportional hazard analysis revealed that metformin users were significantly shielded against TB, showing a nearly 50-percent reduction in risk vs no use (hazard ratio [HR], 0.54, 95 percent confidence interval [CI], 0.3–0.99; p=0.0475).

On the other hand, insulin use almost doubled the risk of TB (HR, 1.94, 95 percent CI, 1.04–3.61; p=0.0365).

Other significant risk factors included old age (>65 vs ≤65 years: HR, 6.36, 95 percent CI, 2.66–15.23; p<0.0001) and being male (HR, 3.35, 95 percent CI, 1.59–7.05; p=0.0015).

“Metformin remains the first choice of treatment for DM in cases without any contra-indication and could have a potential protective effect against TB infection,” the researchers said.