Switching to sulfonylureas increases the risk of serious adverse events compared with remaining on metformin in people with type 2 diabetes mellitus, according to research published in The BMJ (July 2018)
The study used UK general practice data on 77,138 patients who began metformin monotherapy between 1998 and 2013, of whom 25,699 went on to take sulfonylureas either alone or with metformin.
During a mean follow-up of 1.1 years, switching to sulfonylureas was found to be associated with a 26% increased risk of myocardial infarction and a 28% increased risk of all-cause mortality compared with continued metformin use. The risk of severe hypoglycaemia increased almost eight-fold.
In cases where sulfonylureas were added to metformin treatment, the risk of myocardial infarction and death was lower compared with patients who were switched to sulfonylurea alone.
The researchers said that previous research into the safety of sulfonylureas has considered their use as first-line drugs, which may not be applicable to second-line use.
“The associations with myocardial infarction and all-cause mortality were driven by the switching to sulfonylureas and not the addition of sulfonylureas,” they wrote. “Thus, in line with current recommendations on the treatment of type 2 diabetes, continuing metformin when introducing sulfonylureas is safer than switching.”
 Douros A, Dell-Aniello S, Yu OHY et al. Sulfonylureas as second-line drugs in type 2 diabetes and the risk of cardiovascular and hypoglycaemic events: population-based cohort study. The BMJ 2018;362:k2693. doi: 10.1136/bmj.k2693