Kidney function decline in metformin versus sulfonylurea initiators: assessment of time-dependent contribution of weight, blood pressure, and glycemic control

Background and objective We recently reported that kidney function declined faster among initiators of sulfonylureas compared to metformin; however, sulfonylurea use compared to metformin use was also associated with increases in body mass index (BMI) and systolic blood pressure (SBP). We sought to determine if differences between sulfonylureas and metformin on kidney function decline were mediated by differential effects on BMI, SBP, or glucose control. Methods We identified 13238 veterans who initiated sulfonylurea or metformin treatment (2000-2007) with a baseline estimated glomerular filtration rate (eGFR) >60mL/minute, and followed them until a study event occurred, non-persistence on treatment, loss of follow-up, or end of the study. The composite outcome was a sustained decline from baseline eGFR of 25%, end-stage renal disease, or death. We estimated the association of cumulative measurements of potential mediators including BMI, SBP, and glycated hemoglobin on the study outcome. We determined if controlling for these time-varying covariates accounted for the differences in outcome between sulfonylurea and metformin initiators. Results Compared to sulfonylurea use, metformin use was associated with a lower risk for renal function decline or death [adjusted hazard ratio (aHR) 0.82, 95% confidence interval 0.70, 0.97]. This protective association remained significant [aHR 0.83 (0.70-0.98)] when accounting for the cumulative time-varying measurements of the three mediators of interest. Conclusion Metformin initiation was associated with a lower risk of kidney function decline or death compared to sulfonylureas, which appeared to be independent of changes in BMI, SBP, and glycated hemoglobin over time. Copyright (c) 2013 John Wiley & Sons, Ltd.