Estimating kidney function and use of oral antidiabetic drugs in elderly

The prevalence of diabetes mellitus (DM) and renal impairment rises with age making regular estimation of glomerular filtration rate (eGFR) in older diabetics necessary. This study investigated the differences among available estimating equations in assessing eGFR in older diabetics and examined the use of oral antidiabetic drugs (OADs) in relation to renal function. Patients with DM were participants of the Berlin Initiative Study (BIS), a population-based cohort study initiated in 2009 in Berlin, Germany, to evaluate kidney function in people 70years. GFR was estimated with the creatinine-based CKD-EPICREA (Chronic Kidney Disease Epidemiology Collaboration), the MDRD (Modification of Diet in Renal Diseases) and the BIS1 equation and was directly measured (mGFR) with iohexol clearance as a gold standard in a subgroup (n=137). Creatinine clearance was estimated with the Cockcroft-Gault equation (CrCl). DM prevalence was 26% (539 of 2070 overall participants). The antidiabetic drugs most commonly used among OAD patients were metformin (67%), glimepiride (27%) and glibenclamide (14%). Three of ten metformin patients had a CrCl <60mL/min. Compared to mGFR, the mean differences of filtration rates calculated by MDRD, CKD-EPICREA and BIS1 were +8.9, +6.7 and -1.8mL/min/1.73m(2), respectively. Summing up, many patients with a CrCl <60mL/min received metformin, although this represents a contraindication in Germany. Glibenclamide was commonly used despite its classification as potentially inappropriate medication in older adults. Finally, BIS1 performed better in estimating GFR in older diabetics than MDRD or CKD-EPICREA.