Comparison of Drug Dosing Recommendations Based on Measured GFR and Kidney Function Estimating Equations
Received 29 December 2008; accepted 18 March 2009. published online 18 May 2009.
Background
Kidney disease alters the pharmacokinetic disposition of many medications, requiring dosage adjustment to maintain therapeutic serum concentrations. The Cockcroft-Gault (CG) equation is used for pharmacokinetic studies and drug dosage adjustments, but the Modification of Diet in Renal Disease (MDRD) Study equation is more accurate and more often reported by clinical laboratories than the CG equation.
Study Design
Diagnostic test study.
Settings & Participants
Pooled data set for 5,504 participants from 6 research studies and 4 clinical populations with measured glomerular filtration rate (GFR).
Index Test
Estimated kidney function using the MDRD Study and CG equations incorporating actual (CG) or ideal body weight (CGIBW) and standardized serum creatinine concentrations.
Reference Test
Measured GFR assessed by using iodine-125–iothalamate urinary clearance.
Outcome
Concordance of assigned kidney function categories designated by the Food and Drug Administration (FDA) Guidance for Industry for pharmacokinetic studies and recommended dosages of 15 medications cleared by the kidneys.
Results
Concordance of kidney function estimates with measured GFR for FDA-assigned kidney function categories was 78% for the MDRD Study equation compared with 73% for the CG equation (P < 0.001) and 66% for the CGIBW equation (P < 0.001). Concordance between the MDRD Study equation and CG and CGIBW equations was 78% and 75%, respectively (P < 0.001). Concordance of kidney function estimates with measured GFR for recommended drug dosages was 88% for MDRD Study equation compared with 85% for the CG equation (P < 0.001) and 82% for the CGIBW equation (P < 0.001), with lower concordance when dosing recommendations for drugs included narrow GFR ranges. Concordance rates between the CG and CGIBW equations and MDRD Study equation were 89% and 88%, respectively (P < 0.05).
Limitations
Results based on simulation rather than pharmacokinetic studies. Outcome was drug dosage recommendations, rather than observed drug efficacy and safety.
Conclusions
The MDRD Study equation can also be used for pharmacokinetic studies and drug dosage adjustments. As more accurate GFR-estimating equations are developed, they should be used for these purposes.
A list of the CKD-EPI investigators and collaborators appears at the end of this article.
Because an author of this manuscript is an editor for AJKD, the peer-review and decision-making processes were handled entirely by an Associate Editor (Kamal Badr, MD, Lebanese American University) who served as Acting Editor-in-Chief. Details of the journal's procedures for potential editor conflicts are given in the Editorial Policies section of the AJKD website.
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