The relationship between gentamicin pharmacokinetics and measures of bioelectrical impedance (BI) in elderly patients was investigated with the aim of developing a potential noninvasive means of individualising gentamicin dosage. Linear regression analyses identified height/resistance2as a statistically significant predictor of gentamicin distribution volume, V, adjusted (adj)r2= 0.53, coefficient of variation (CV) = 15.2percnt;, and resistance/reactance and creatinine clearance (CLcr) as predictors of total systemic clearance, CL, adj r2= 0.52, CV = 20.1percnt;. Individualisation of gentamicin dosage regimens based on these relationships to achieve steady-state (SS), peak gentamicin concentrations, Css,max, and SS trough concentrations, Css,min, of 7.0 and 1.0 mu;g/ml, respectively, in an independent group of elderly patients resulted in serum gentamicin levels of 5.9 plusmn; 0.7 and 0.8 plusmn; 0.4 mu;g/ml. Mean absolute prediction errors averaged 0.7 plusmn; 0.5 mu;g/ml for Css,maxand 0.5 plusmn; 0.3 mu;g/ml for Css,min. Measures of BI provided the best predictions of Css,max, whereas models based on CLcralone were the best predictors of Css,min. This technique provides a means of complementing routine pharmacokinetic monitoring of gentamicin pharmacotherapy in the elderly hospitalised patient with reductions in patient discomfort and potential savings in time and cost.
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