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AIMFor drug dosing adaptation, the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines recommend using estimated glomerular filtration rate (eGFR) by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation, after 'de-indexation' by body surface area (BSA). In pharmacology, the Cockcroft-Gault (CG) equation is still recommended to adapt drug dosage. In the context of obesity, adjusted ideal body weight (AIBW) is sometimes preferred to actual body weight (ABW) for the CG equation. The aim of the present study was to compare the performance of the different GFR-estimating equations, non-indexed or de-indexed by BSA for the purpose of drugdosage adaptation in obese patients. METHODSWe analysed data from patients with a body mass index (BMI) higher than 30 kg m À2 who underwent a GFR measurement. eGFR was calculated using the CKD-EPI and Modification of Diet in Renal Disease (MDRD) equations, de-indexed by BSA, and the CG equation, using either ABW, AIBW or lean body weight (LBW) for the weight variable and compared with measured GFR, expressed in ml min À1 . RESULTSIn our population of obese patients, use of the AIBW instead of the ABW in the CG equation, markedly improved the overall accuracy of this equation [57% for CG ABW and 79% for CG AIBW (P < 0.05)]. For high BMI (over 40 kg m À2 ), the accuracy of the CG equations is no different when using LBW than when using AIBW. The MDRD and CKD-EPI equations de-indexed by the BSA also performed well, with an overall higher accuracy for the MDRD de-indexed equation [(80% and 76%, respectively (P < 0.05)]. WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT• For the purpose of chronic kidney disease follow-up, the CG equation is no longer recommended and GFR should be estimated using the creatinine-derived MDRD or CKD EPI equations and expressed in ml min À1 1.73 m -2 . We have recently shown that both equations perform similarly in a population of obese patients. For the specific issue of drug dose adaptation, thresholds of GFR are given in ml min À1 , and most authors recommend using the CG equation, although others recommend using the MDRD or CKD-EPI equation with de-indexation of the GFR result. Very few data are available, especially in obese patients, to recommend which is the best strategy.

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