Comparison of vancomycin pharmacokinetics in hospitalized elderly and young patients using a Bayesian forecaster

Limited data have been published that compare the pharmacokinetic parameters of vancomycin in elderly versus young patients. This study was designed to assess vancomycin pharmacokinetics in 148 elderly (> or = 60 years of age) and 140 young (18-59 years of age) hospitalized infected patients. Serum vancomycin concentrations were determined using fluorescence polarization immunoassay. Serum concentration-versus-time data were fitted to a two-compartment Bayesian forecasting program. Elderly versus young vancomycin pharmacokinetic parameters derived were as follows (patients with serum creatinine < or = 1.5 mg/dL); mean +/- standard deviation terminal disposition half-life (t1/2) of 17.8 +/- 11.8 versus 7.5 +/- 6.7 hours, respectively, P < .05; volume of distribution (Vz) of 74.2 +/- 32.3 versus 67.0 +/- 30.7 L, respectively, P = .16; and total body clearance (CL) of 0.71 +/- 0.41 versus 1.22 +/- 0.50 mL/min/kg, respectively, P < .05. Comparing subjects with normal serum creatinine values (< or = 1.5 mg/dL), the elderly required smaller daily doses as compared with the young group to maintain target peak and trough vancomycin serum concentrations (18.2 +/- 5.8 verus 25.2 +/- 7.8 mg/kg/day, P < .05). Stepwise multiple regression models for the pharmacokinetic parameters were developed to assess the predictive power of age, controlling for the effects of gender, total body weight, serum creatinine, and creatinine clearance. Age was consistently an independent and significant predictor of t1/2, Vz, and CL. These data demonstrate that elderly patients exhibit significant differences in vancomycin pharmacokinetic parameters compared with young patients and constitute a patient population in need of individualized vancomycin dosing due to substantial heterogeneity in physiologic and pharmacokinetic parameters.
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