Implications of using the MDRD or CKD-EPI equation instead of the Cockcroft-Gault equation for estimating renal function and drug dosage adjustment in elderly patients.

The objectives of this study were to compare the estimations of renal function obtained with six equations, including the Cockcroft-Gault (CG), Modification of Diet in Renal Disease (MDRD), and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations and to evaluate the implication of using other equations for drug dosing in elderly patients in place of CG. An observational prospective study was conducted over 6 months in two geriatric hospitals with inclusions of all hospitalized inpatients. A list of 36 drugs for which recommendations of dosage adjustment for renal function were mentioned in the manufacturer dosing guidelines was used to compare the implications of using the various equations for drug dosing. A total of 249 patients with a mean age of 83.6 years were included. Mean estimates of renal function from the CG, MDRD, and CKD-EPI equations were 51.3 ± 23.5 mL/min, 72.2 ± 35.2, and 64.3 ± 22.5 mL/min/1.73 m2 , respectively (P < 0.001). Twenty percent of patients had at least one drug for which the dose was not appropriately adjusted to renal function. The use of the MDRD and CKD-EPI equations in place of the CG equation was associated with dosage discrepancy in 20-25% of patients and 15% of drug orders, resulting in potential overdosage in 95% of cases. Use of MDRD or CKD-EPI equations results in higher estimates of renal function and may have important implications for drug dosing decision and drug safety in elderly patients. The best way is to directly measure the drug effect or its concentration when it is possible to do so.