Disagreement in Estimates of Kidney Function for Drug Dosing in Obese Inpatients

The Cockcroft-Gault (CG), Modification of Diet in Renal Disease (MDRD), and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations are used to estimate kidney function. However, utility has been questioned in the obese population.

To evaluate differences in estimates of kidney function in obese patients and implications for drug dosing.

This was a retrospective study of adult inpatients with a body mass index ≥30 kg/m² and stable kidney function. Patients were categorized based on creatinine clearance (CrCl): group 1-CrCl ≥ 60 mL/min and group 2-CrCl 15 to 59 mL/min. Mean estimates of kidney function and recommended doses of 8 renally eliminated medications were compared.

For the 166 patients included, mean estimates using CG, MDRD, and CKD-EPI for group 1 were 87 (23) mL/min, 91 (21) mL/min, and 96 (23) mL/min, respectively. Group 2 estimates were 42 (13) mL/min, 51 (15) mL/min, and 51 (16) mL/min, respectively. MDRD and CKD-EPI estimates were significantly higher than CG in 125 (75%) and 140 (84%) patients, respectively. Dose discrepancies were most often due to higher dose recommendations using MDRD or CKD-EPI compared to CG.

Careful consideration of the method used to estimate kidney function, the method used for developing dosing recommendations, and the risk-benefit profile is warranted when designing drug regimens in obese individuals.