Comparison of equations for dosing of medications in renal impairment

Aim: To determine the concordance among the Cockcroft-Gault, the Modification of Diet in Renal Disease (MDRD) and the CKD-Epidemiology Collaboration (CKD-EPI) equations in hypothetical dosing of renally cleared medications.

Methods: A total of 2163 patients prescribed at least one of the 31 renally cleared drugs under review were included in the study. Kidney function was estimated using the three equations. We compared actual prescribed dosages of the same drug to recommended dosages based on the kidney function as calculated by each of the equations and applying dosing recommendations in the Australian Medicines Handbook.

Results: There was a significant difference in the kidney function values estimated from the three equations (P < 0.001). Despite the good overall agreement in renal drug dosing, we found selected but potentially important discrepancies among the doses rendered from the equations. The CKD-EPI equation non-normalised for body surface area had a greater rate of concordance with the Cockcroft-Gault equation than the MDRD equation for renal drug dosing.

Conclusions: There is need for a long-term multi-centre study in a diverse population to define the clinical effects of the discrepancies among the equations for drug dosing. Given the greater concordance of the non-normalised CKD-EPI equation with the Cockcroft-Gault equation for dosing, the recommendation by Kidney Health Australia and the United States National Kidney Disease Education Program that "dosing based on either eCrCl or an eGFR with body surface area normalisation removed are acceptable" seems suitable and practicable for the purpose of dosing of non-critical drugs in the primary care setting.