Comparison of dosing recommendations for antimicrobial drugs based on two methods for assessing kidney function: cockcroft-gault and modification of diet in renal disease

To quantify the difference between glomerular filtration rates (GFRs) estimated by using the Cockcroft-Gault and Modification of Diet in Renal Disease (MDRD) equations, and to determine whether dosing recommendations for four commonly prescribed antimicrobial agents are discordant when determined by using these equations.

Prospective, observational study.

Tertiary-care medical center.

Two hundred seven consecutive adults without normal renal function but not receiving dialysis who were admitted to a non-intensive-care ward and had two consecutive serum creatinine concentration (S(cr)) values measured 20-24 hours apart.

The patients' mean +/- SD S(cr) was 1.41 +/- 0.95 mg/dl. Kidney function was estimated by using two versions of the four-variable MDRD equation and four versions of the Cockcroft-Gault equation. Mean estimated GFRs ranged from 52.3-73.1 ml/minute. Dosing for cefepime, levofloxacin, meropenem, and piperacillin-tazobactam was determined using the two equations that had the highest level of correlation; these were the MDRD equation unadjusted for body surface area and the Cockcroft-Gault equation adjusted for ideal body weight and S(cr). When the total daily doses based on these two equations for the four antimicrobials were compared, the discordance rate was 22.8-36.3%, and statistically significant differences were observed for most of the discordant doses. When discordance was present, the MDRD equation resulted in a higher dose of the drug.

Discordance rates for drug dosing ranged from 22.8-36.3% between the MDRD and Cockcroft-Gault methods for estimating GFR. Although use of the MDRD equation is a well-accepted and accurate method of estimating GFR to stage chronic kidney disease, our results demonstrated a significant difference in drug dosing regimens between the MDRD method and the Cockcroft-Gault method.