Addressing metformin

I read with interest the Lilly and Godwin article “Treating prediabetes with metformin. Systematic review and meta-analysis”1 and had several concerns. Lilly and Godwin base their conclusion on treatment of prediabetes (impaired glucose tolerance [IGT] or impaired fasting glucose [IFG]) with metformin on studies of patients with either IGT alone or IGT and IFG. I do not think the conclusions from their meta-analysis can be made for patients with isolated IFG. I was also concerned with their conclusion that treatment with metformin is beneficial for patients with IGT. In the case of prehypertension, for example, treating prehypertension with an antihypertensive medication would likely lower blood pressure with a very low number needed to treat; however, as there are no outcome studies that show treating prehypertension with a blood pressure–lowering agent will prevent complications, we treat prehypertension with lifestyle modification alone. The same is true for prediabetes. Although Lilly and Godwin raise the important issue of using glucose-lowering agents to treat prediabetes in the limitations discussion of their study, it is a serious enough limitation that it should have influenced the conclusion of their meta-analysis. Just because metformin lowers blood sugar (and therefore prevents diabetes) does not mean we should be treating all patients with prediabetes with metformin.

I do agree that prediabetes is a serious medical condition, warning patients that their risk of subsequent diabetes is very high. This is a golden opportunity to maintain close follow-ups with patients to ensure they are able to slowly make the lifelong lifestyle changes required to prevent diabetes. Just giving metformin to all prediabetes patients will not address this lifelong condition. Any amount of exercise and any amount of weight loss will do the same or more as metformin. Several studies have shown a 60% reduction of diabetes with lifestyle changes, twice as effective as metformin.2,3

There are patients with prediabetes who might require metformin, but these cases should be the exception not the rule.

• Copyright© the College of Family Physicians of Canada