GENTAMICIN DOSING IN ELDERLY PATIENTS BASED ON BIOELECTRICAL-IMPEDANCE ANALYSIS

The relationship between gentamicin pharmacokinetics and measures of b ioelectrical 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/resis tance2 as a statistically significant predictor of gentamicin distribu tion volume, V, [adjusted (adj)r2 = 0.53, coefficient of variation (CV ) = 15.2%], and resistance/reactance and creatinine clearance (CL(cr)) as predictors of total systemic clearance, CL, adj r2 = 0.52, CV = 20 .1%. Individualisation of gentamicin dosage regimens based on these re lationships to achieve steady-state (SS), peak gentamicin concentratio ns, C(ss,max), and SS trough concentrations, C(ss,min), of 7.0 and 1.0 mug/ml, respectively, in an independent group of elderly patients res ulted in serum gentamicin levels of 5.9 +/- 0.7 and 0.8 +/- 0.4 mug/ml . Mean absolute prediction errors averaged 0.7 +/- 0.5 mug/ml for C(ss ,max) and 0.5 +/- 0.3 mug/ml for C(ss,min) Measures of BI provided the best predictions of C(ss,max), whereas models based on CL(cr) alone w ere the best predictors of C(ss,min). This technique provides a means of complementing routine pharmacokinetic monitoring of gentamicin phar macotherapy in the elderly hospitalised patient with reductions in pat ient discomfort and potential savings in time and cost. invasive.