Evolution of Equations for Estimating Renal Function and Their Application to the Dosing of New Antimicrobials

Objective: To address the background and rationale for the recent introduction of the Modification of Diet in Renal Disease (MDRD) equation for renal dose adjustment of antimicrobials and to provide recommendations for pharmacists dosing new antimicrobial agents. Data Sources: Comprehensive MEDLINE and EMBASE literature searches (from August 2018 to October 2019) were performed. Search terms included creatinine clearance, Cockcroft-Gault, MDRD, and glomerular filtration rate and a subsequent search included the preceding terms AND antimicrobials OR antibiotics. Study Selection and Data Extraction: Available English-language studies on the derivation and/or use of the Cockcroft-Gault (CG) and MDRD study equation were evaluated as well as those that specifically discussed their use for dosing antimicrobial agents. Data Synthesis: The US Food and Drug Administration (FDA) approval of delafloxacin and meropenem-vaborbactam in 2017 ushered in a new era in renal dosing of antibiotics, in that both agents are recommended to be dosed by the MDRD equation. Studies demonstrate that the CG and MDRD equations can result in discrepant dosing recommendations. Relevance to Patient Care and Clinical Practice: The renal estimation equation recommended in a new antibiotic label should dictate the dosing of that medication. It is noteworthy that these equations are not interchangeable. Conclusion: Recently approved antimicrobials utilizing the MDRD equation for renal dose adjustment will be interspersed with old and new antimicrobials utilizing the CG equation because of lack of singular guidance by the FDA. This requires pharmacists to be vigilant in evaluating drug labels to determine which equation is recommended and to understand the differences, strengths, and limitations of each equation.