Comparison of aminoglycoside clearance and calculated serum creatinine clearances

Calculated creatinine clearance (CrCL) estimates are frequently used as estimates of aminoglycoside clearance (AGCL), despite being inadequately studied. Thirty surgical intensive care unit (SICU) patients with stable serum creatinines (0.6-6.3 mg/dl) and steady-state aminoglycoside levels were studied. A one-compartment pharmacokinetic infusion model was used to calculate k and Vd; AGCL = (k) (Vd). CrCLs using the equations of Cockroft-Gault (CGCL), Jelliffe (JCL), and Jelliffe uncorrected for body surface area (JCLu) were calculated, then compared to the AGCL. The JCLu was a better fit to the data (y = 0.98x + 0.44, r = 0.91) with a superior regression correlation (p less than 0.02) than CGCL (y = 0.91x + 6.07, R = 0.89) and JCL (y = 1.11x + 2.11, R = 0.89) correlations. CGCL overpredicted the AGCL whereas JCL and JCLu underpredicted the AGCL. All three methods showed a precision of approximately 20 ml/min. Relative bias and precision show JCLu better than JCL, CGCL better than JCL only for bias, and CGCL and JCLu not different. The absolute percentage error of the CrCL estimates tended to be lower at higher AGCL and did not differ for CGCL, JCL, and JCLu. In the SICU setting, we suggest the use of the JCLu for estimating the AGCL.