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Estimating renal function is important for patients taking renally eliminated medications in order to maximize effectiveness while limiting toxicity. The glomerular filtration rate (GFR) is an effective indicator of renal function and normal values are approximately 130 mL/min/1.73 m2 for men and 120 mL/min/1.73 m2 for women (Table 33-1). The gold standard for approximating GFR is the inulin clearance method. Inulin is filtered by the glomerulus and is not secreted or reabsorbed, making it an ideal agent for approximating GFR. The inulin clearance method is rarely done because it is costly, invasive, and requires technical expertise. Additional markers used to estimate GFR include iothalamate, iohexol, and ethylenediaminetetraacetic acid. Like inulin, these markers are expensive and have limited availability, making them impractical in the clinical setting. Numerous methods have been developed to estimate GFR and examples include the Cockcroft-Gault and the Modification of Diet in Renal Disease (MDRD) equations (Table 33-2).

TABLE 33-1Classification of Renal Function Based on eGFR or Estimated CrCl
TABLE 33-2Equations for the Estimation of Creatinine Clearance and Glomerular Filtration Rate in Adults with Stable Renal Function

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