Race May Attenuate Metformin Benefit

Black patients may have a better response to metformin than white patients, researchers found.

In an analysis of data from one healthcare system, African Americans had greater improvements in HbA1c when taking the drug than did white patients, L. Keoki Williams, MD, MPH, of Henry Ford Health System in Detroit, Mich., reported online in the Journal of Clinical Endocrinology and Metabolism.

"Given the disproportionate burden of diabetes complications faced by African-American individuals, it is heartening to know that metformin appears to be efficacious in this group," they wrote.

Trials of metformin tested the drug mostly in white patients, so to better understand its efficacy in black patients, Williams and colleagues looked at medical and pharmacy records from 19,672 patients taking metformin in the Henry Ford Health System between 1997 and 2013.

Overall, 7,429 patients were black and 8,783 were white, and baseline HbA1c values were higher in black patients – 7.81% compared with 7.38%.

The researchers found that the maximum dose of metformin was associated with a greater reduction in HbA1c in black patients than in white patients, with a mean drop of 0.9% compared with a decline of just 0.42%.

These differences persisted after controlling for age, sex, body mass index (BMI), use of other diabetes drugs, baseline HbA1c levels, time on treatment, and metformin dose/patient adherence, the researchers said.

"When one considers that the goal HbA1c level for individuals being treated for diabetes is less than 7% and that the average starting HbA1c level in our patients was around 7.5%, these differences in treatment response are clinically important," Williams said in a statement. "Moreover, since African Americans are more likely to suffer from diabetic complications when compared with white individuals, it is heartening to observe that metformin is likely more effective at controlling blood glucose in the former group."

They noted that the Diabetes Prevention Program showed black patients given metformin were less likely to develop diabetes compared with white patients. The reduction in disease incidence was 44% compared with 24%, although it wasn't a significant difference, they said.

More studies are needed to confirm the findings, Williams and colleagues wrote, and to test whether the differences in glycemic response mirror changes in the risk of hard clinical endpoints such as vascular disease and death.

Also, pharmacogenomic studies looking at the effects of genetic ancestry -- rather than self-reported race or ethnicity -- may help clarify whether there is a heritable component to the differences in response to metformin, they wrote.

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