Estimated glomerular filtration rate leads to higher drug dose recommendations in the elderly compared with creatinine clearance.

PURPOSE: The elderly are at risk for adverse drug events because of inappropriate dosing of renally eliminated medications. The purpose of this study was to evaluate differences in estimates of kidney function and recommended doses of select medications in the elderly using the Modification of Diet in Renal Disease (MDRD) or the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations compared with the Cockcroft-Gault (CG) equation.
METHODS: Patients 65 years of age and older were included in this retrospective, observational analysis. Kidney function was estimated by CG, MDRD and CKD-EPI equations for all patients and by age category (65-69, 70-79, 80-89 and 90-100 years). Differences in estimates and dosing of allopurinol, enoxaparin, gabapentin, piperacillin/tazobactam and sulfamethoxazole/trimethoprim using the MDRD and CKD-EPI compared with the CG were assessed.
RESULTS: In the 4160 patients (98% male, mean age 74 ± 7 years), the MDRD and CKD-EPI estimates were significantly higher than CG estimates for all patients and by age category (p < 0.001). Dosing discordance was predominantly because of a higher dose recommended by MDRD and CKD-EPI estimates compared with CG. Discordance was highest with gabapentin (27%), the medication with the greatest number of dosing stratifications by estimated kidney function, and increased by 66% from the youngest to the oldest age category.
CONCLUSIONS: Until newer equations are used uniformly to develop dosing nomograms, it is prudent to adopt a process for drug dosing in the elderly that is more conservative than eGFR based dosing, but that considers the potential for underestimating kidney function with the CG equation.