Metformin potentially underused among patients with mild kidney disease, study finds
More patients would be eligible for metformin use if estimated glomerular filtration rate were used to define kidney disease rather than serum creatinine, a recent study concluded.
More patients would be eligible for metformin use if estimated glomerular filtration rate (eGFR) were used to define kidney disease rather than serum creatinine (sCr), a recent study concluded.
Researchers used data from the 1999 to 2010 National Health and Nutrition Examination Survey (NHANES) to analyze 3,902 adult participants with diabetes (defined by self-report or an HbA1c ≥6.5%) who reported a routine site for health care. Results were published online on Aug. 25 by Diabetes Care.
Across all 12 years, 66.4% of adults with diabetes were treated with a diabetes medication, and this percentage increased over time, from 61.3% in 1999 to 2000 to 69.7% in 2009 to 2010. Metformin use among those with diabetes and a routine site for health care increased from 26.1% to 44.5%.
Among NHANES adults with diabetes and routine care access, 8.8% were ineligible for metformin because of the FDA's contraindication among individuals with sCr ≥1.4 mg/dL for women and ≥1.5 mg/dL for men. Compared with those who were eligible for the drug, those ineligible were older and more likely to be non-Hispanic black or to have a yearly family income less than $45,000.
Researchers also looked at the patients using (eGFR) categories: likely safe to take metformin, ≥45 mL/min/1.73 m2; contraindicated, <30 mL/min/1.73 m2; and indeterminate, 30 to 44 mL/min/1.73 m2. Evidence has shown eGFR to be a more accurate estimate of kidney function than sCr, the authors noted.
Among individuals ineligible for metformin using conventional sCr thresholds, 14.6% had an eGFR ≥45 mL/min/1.73 m2 and 50% had an eGFR between 30 and 44 mL/min/1.73 m2. Only 35.7% of study participants would be ineligible for metformin based on an eGFR <30 mL/min/1.73 m2.
Based on these results, just by adding those for whom metformin is safe according to eGFR criteria, the researchers estimated the number of individuals eligible for metformin in the U.S. can be expanded by between 86,900 and 834,800 people, depending on which method is used to estimate GFR. Most of the potentially eligible patients are male and non-Hispanic blacks. This figure does not take into account the population with eGFR of indeterminate safety (30 to 44 mL/min/1.73 m2), which could range from 784,700 to 1,636,000 people. A randomized controlled trial is needed to clarify whether metformin use in this subgroup would be safe and efficacious, the authors noted.
Limitations of the study are that NHANES is not a clinical database, although the researchers restricted the study population to those who self-reported a routine site for health care. They also noted that they could not determine the reasoning behind low levels of metformin use, which could include non-renal clinical conditions that contraindicate the use of metformin, such as liver disease.