Metformin, a first-line diabetes drug, delays the onset of type 2 diabetes in the prediabetic population; however, in prediabetic patients, differences in glycaemic response to metformin among racial groups are unknown. We aimed to compare glucose-lowering effects of metformin between Whites and African Americans (AAs).

We performed a secondary analysis using data from the diabetes prevention program, a multi-center randomized clinical trial, in which all participants were prediabetic. The metformin group (582 Whites and 210 AAs) received 850mg of metformin twice daily, and was followed for 3years.

We found that after 6months on metformin, Whites had a drop of 3.89±0.39 (mg/dL, mean±SEM) in the fasting plasma glucose level, significantly less than that in African Americans (6.04±0.72, P=0.006); at years 1 and 2, the differences were also significant. Consistently, the linear mixed model showed that, within 1year of metformin treatment, the rate in reduction of glucose levels was more pronounced in AAs than in Whites (P=0.025 following adjustment for age and sex).

Therefore, AAs have a better glycaemic response to metformin treatment than Whites in the prediabetic population.