Effect of analytical inaccuracy on dose adjustment for gentamicin using the Abbottbase Pharmacokinetic Systems

We studied the effect of analytical inaccuracy on the determination of gentamicin for estimation of the recommended dose regime (RDR) using the Abbottbase Pharmacokinetic System programme (PKS). The study was carried out in a group of 26 adult patients, determining their serum levels of gentamicin (Cmin and one hour after completing infusion, C1h) and these concentrations were processed using the PKS in order to establish the RDR (dose, posologic interval and infusion time) for each patient. Various simulations were made for each patient, adding and subtracting the clinically acceptable error (CAE) once, twice and three times to the experimentally determined Cmin and the estimated Cmax. The simulated dose regime (SDR) was calculated for each patient. The number of cases in which the SDR differed from the RDR were determined, and also the percentage of variation of the SDR with respect to the RDR. A highly significant correlation was found between C1h and the estimated Cmax (r = 0.941, p < 0.001). A statistically significant difference (p < 0.05) and a clinically significant difference were found between both populations of concentrations, and so the simulations were carried out using the estimated Cmax. A frequency of change of 29.87% was recorded in the RDR, and inaccuracies of +/- CAE in the Cmin and Cmax led to changes of the RDR in 21.2% of the cases studied. A higher frequency of change in the RDR was observed in additive-type simulations for Cmax, with this change mainly affecting the dose, and in subtractive-type simulations for Cmin, with this change affecting both the dose and the posologic interval. An inaccuracy of the order of +/- CAE in the serum concentrations of gentamicin (both for Cmin and Cmax) frequently led to changes in the RDR, thus requiring precise and accurate concentration results, particularly in the case of Cmin. For this reason, we would suggest the convenience of using a previous moment in the time concentration level in the monitoring of gentamicin instead of Cmin, which would be determined with greater imprecision and inaccuracy.