Evaluation of Renal Drug Dosing: Prescribing Information and Clinical Pharmacist Approaches

Abstract

Study Objective. To characterize renal function parameters reported in United States Food and Drug Administration-approved prescribing information (package inserts) to compare dosage recommendations for patients with impaired renal function between prescribing information and tertiary drug dosing references, and to evaluate renal function quantification methods most commonly used by clinical pharmacists to develop dosage regimens.

Design. Retrospective analysis and Web-based survey.

Data Sources. Prescribing information for all new molecular entities (NMEs) approved from 1998-2007 in which dosing recommendations were proposed for patients with impaired renal function, drug monographs from four tertiary drug dosing references (Micromedex, Lexi-Comp, Epocrates Rx, and American Hospital Formulary Service [AHFS] Drug lnformation) for all identified NMEs, and a Web-based survey of 204 nephrology and critical care pharmacy practitioner.

Measurements and Main Results. A total of 44 NMEs included renal dosing recommendations in their prescribing information, For all 44 NMEs, prescribing information was reviewed to determine methods to quantify renal function, units of measure reported, and use of chronic kidney disease terminology. The most common index of renal function was creatinine clearance; the Cockcroft-Gault equation was specified in the prescribing information of 11 NMEs. Standardization for body weight was inconsistent, with prescribing information for four NMEs reporting renal function in ml/minute/l.73m² The prescribing inlormation or tertiary sources did not mention use of estimated glOlnerular filtration rate (eGFR) or the Modification of Diet in Renal Disease Study (MDRD) equation. Epocrates Rx provided the most abbreviated renal dosing information, whereas AHFS Dmg Information was the most comprehensive, and Lexi-Cornp includes a renal function calculator. Nearly all (86%) clinical pharmacists indicated that automated eGFR is reponed at their institutions, although they do not use these predictions for dosing in patients with impaired renal function, and their approaches to renal function estimation varied widely.

Conclusion. Reporting of renal function methods and dosing recommendattons for patients with impaired renal function requires standardtzarion in order to ensure optimal dosing. Pharmacy clinicians do not substitute eGFR in place of creatinine clearance for renal dosing, which is consistent with current prescribing information, Studies are needed that will evaluate the validity of using eGFR to predict drug clearance and thereby generate dosage recommendations.