Evaluation of aminoglycoside clearance using the modification of diet in renal disease equation versus the Cockcroft-Gault equation as a marker of glomerular filtration rate.

BACKGROUND

Accurate estimation of kidney function is essential for safe administration of renally cleared drugs. Current practice recommends adjusting renally eliminated drugs according to the Cockcroft-Gault (CG) equation as an estimation of glomerular filtration rate. Few data exist regarding the utility of the Modification of Diet in Renal Disease (MDRD) equation in drug dosing.

OBJECTIVE

To evaluate glomerular filtration rate based on creatinine clearance (CrCl) derived from the MDRD or the CG equation compared with patient-specific CrCl calculated from aminoglycoside peak and trough concentrations.

METHODS

Medical records of patients who received aminoglycoside antibiotics were reviewed over 1 year. Patients who received aminoglycosides via conventional dosing with peak and trough concentrations at steady state were included. Calculations based on standard pharmacokinetic equations were used to estimate CrCl from aminoglycoside serum concentrations. Patient-specific CrCl estimated from aminoglycoside concentrations was compared with estimated CrCl from the CG or MDRD equation.

RESULTS

Fifty-five patients were included in the final analysis. The primary outcome showed concordance between estimated and actual aminoglycoside clearance was 0.53 (95% CI 0.18 to 0.88) for the CG equation and 0.41 (95% CI 0.04 to 0.78) for the MDRD equation. Subgroup analysis also favored CG as a better predictor of CrCl. This signified a stronger correlation between the CG equation and aminoglycoside clearance.

CONCLUSIONS

Compared with the MDRD equation, the CG equation provided better correlation of estimated glomerular filtration rate for aminoglycoside antibiotics. Institutions should continue to use the CG equation as the standard of practice to safely adjust aminoglycoside doses in patients with renal dysfunction.