Cardioprotective effect proposed for metformin

By Eleanor McDermid

A large retrospective analysis suggests that metformin could be cardioprotective in insulin-dependent patients with Type 2 diabetes.

The findings, based on data from the UK Clinical Practice Research Datalink, found a reduced risk of major adverse cardiac events (MACE) and all-cause mortality among patients taking the drug.

To minimise the effects of confounding by indication, Craig Currie (Cardiff University, UK) and co-workers analysed only patients who had been started on insulin, with metformin started simultaneously or added later.

None of the 12,020 patients analysed had prior MACE or cancer at baseline. During an average 3.5 years of follow-up, the MACE rate among the 5536 patients taking insulin plus metformin was 15.9 per 1000 person-years, compared 26.3 with per 1000 person-years among the 6484 patients taking insulin monotherapy. The all-cause mortality rate was also lower, at 21.2 versus 61.3 deaths per 1000 person-years.

After accounting for multiple confounders, including cumulative insulin exposure, patients given metformin had a significant 25% reduced risk of MACE and a 40% reduced risk of mortality, the team reports in PLoS ONE.

Among patients matched for the propensity to be prescribed metformin, outcome rates were 14.9 versus 22.2 per 1000 person-years for MACE and 23.1 versus 44.4 per 1000 person-years for mortality. The mortality difference persisted after accounting for confounders, at a 30% reduction, although the difference in MACE became nonsignificant.

The team found no association between cancer risk and metformin treatment, despite previous suggestions that it may have a protective effect.

Currie et al note that the various contraindications and cautions for metformin treatment, such as tissue hypoxia and renal impairment, mean that "the population of people receiving insulin in combination with metformin may be healthier than the monotherapy group."

Given this, and other drawbacks of a retrospective study, they conclude that more research is needed "to determine the risks and benefits of insulin in type 2 diabetes and the possible benefits associated with the administration of concomitant metformin."

Source: PLoS ONE 2016; 11: e0153594

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