The importance of correct estimation of renal function for drug treatment in hospitalized elderly patients, especially women: A prospective observational study

Aim : To compare renal function by several GFR formulas (particularly cystatin C eGFR-"CAPA") in relation to renal risk drugs (RRDs) in patients admitted to two geriatric wards in a university geriatric department.Materials and methods: This was a prospective quality improvement study including 108 patients, 2/3 women, age >= 75 years, admitted with multimorbidity. Renal function tests were performed with Cockcroft & Gault with uncalibrated (C&Guc) and calibrated creatinine (C&Gcc), and 3 - 4 points' iohexol clearance (mGFR) in mL/min, and eGFR with MDRD4, CKD-EPI, CAPA. and BIS2 clearance in mL/min/1.73m(2). Agreement was tested by Bland & Altman analysis. The number and type of RRDs were analyzed.Results: Measured GFR, C&Gcc, and C&Guc were mean 37, 39, and 32 mL/min. respectively. Estimated GFR by MDRD4. CKD-EPI, CAPA, and BIS2 were mean 56, 52. 45, and 40 mL/min/1.73m(2), respectively. Compared to mGFR, women had significantly higher clearance for all estimates except for C&Gcc and C&Guc. C&Gcc, C&Guc, and BIS2 showed the lowest bias. 38 RRDs were identified. 96 patients used a mean of 2.3 RRDs per patient, and 1.7 RRDs needed dose adjustments. Cardiovascular drugs and analgesics were the most frequent RRDs.Discussion: The C&Gcc. C&Guc, and BIS2 equations gave the best estimate of kidney function in relation to mGFR for drug dosing in the elderly. The eGFR methods showed significantly higher clearance than mGFR, C&Gcc, C&Guc, and BIS2. RRDs that needed dose adjustment were common in this geriatric population. If the eGFR formulas (MDRD4, CKD-EPI, and CAPA) are used instead of C&Gcc, C&Guc, and BIS2, higher and potentially more risky doses of RRDs may be administered to geriatric patients over 75 years, women in particular.