The study, presented here during a poster session on October 14^th, found that the use of the Modification of Diet in Renal Disease (MDRD) equation and Simplified MDRD (SMDRD) were both imprecise tools for deciding on appropriate dosage of medication in hospitalized patients who received antibiotic therapy.

"We wanted to find the optimal method for dosing of vancomyin," said principal investigator Henry Fraimow, MD, associate professor of medicine, University of Medicine and Dentistry of New Jersey, Camden, New Jersey. "The MDRD has been used as a means of monitoring renal disease progression, but has not been validated as a method of adjusting the dose of patients or of determining the optimal delivery of medication."

The glomerular filtration rate, as calculated using the SMDRD, is often reported with serum creatinine. Physicians have also used the MDRD or simplified MDRD to determine medication dosing.

Dr. Fraimow and colleagues conducted their study to compare vancomycin regimens derived from 4 methods of estimating renal function including MDRD, abbreviated MDRD (AMDRD), Cr clearance from Cockcroft-Gault formula (CG CrCl), and adjusted CG CrCl to optimized regimens determined from steady state vancomycin levels in patients over age 65.

Patients were excluded from the study if they had a greater than 30% increase in serum creatinine during monitoring; if they were on hemodialysis or other renal replacement therapies, and if they had baseline serum creatinine greater than 2.7 mg/dL or calculated creatinine clearance less than 20 mL/min.

Of the 4 methods used to determine dosing, the adjusted CG CrCl is the only one that includes body weight and height in calculating medication dose and most closely approximated optimized level-based vancomycin dose.

Specifically, using adjusted CG CrCl, 65% of patients would have received the correct dose, compared with 34% with CG CrCl, 32% with MDRD, and 18% with SMDRD, yielding a statistically significant P value of less than .01.

"Most patients would have been overdosed using the other methods," Dr. Fraimow said. "[adjusted CG CrCI] is more reliable because you need to know a patient's body mass to determine the correct medication dosage."

The study was independently conducted.


[Presentation title: MDRD is Inferior to Adjusted Creatinine Clearance for Vancomycin Dosing in Elderly Patients. Poster 9]

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