M.J. Santos

Determination of piperacillin in biological samples by HPLC

Abstract A rapid, specific and reliable technique has been developed for the determination of piperacillin in biological samples by High Performance Liquid Chromatography. To do so, reverse phase liquid chromatography was used, employing acetonitrile-phosphate buffer 0,1M and pH=6 as the mobile phase (20:80 v/v) and a detector wavelength of 254 nm. Concentrations ranged between 0,5 μg/mL and 200 μg/mL, divided into two calibrations: high concentrations, 15 μg/mL to 200 μg/mL, and low concentrations, 0,5 μg/mL to 15 μg/mL. The intraday and interday reproducibility of the analytical technique was studied by calculating the variation coefficient of 5 samples analyzed each day and on five consecutive days by ANOVA. The coefficients obtained were 4,02% and 7,11%, respectively, for concentrations ranging between 15–200 μg/mL and 5.71% and 7,54% for concentrations between 0,5 and 15 μg/mL.

Effect of Urea on the In Vitro Binding of Netilmicin to Renal Tissue in Rats

SummaryThe binding and release kinetics of netilmicin to the rat renal cortex and medulla were studied at therapeutic concentrations, together with the effect of urea on the binding kinetics of netilmicin to this type of tissue. The study was carried out using an equilibrium dialysis technique, determining free netilmicin concentrations via a reverse phase high-performance liquid chromatography technique with fluorescence detection and precolumn derivatisation. The binding of netilmicin to the renal cortex and medulla as a function of the free concentration proved to be linear, while the washout kinetics appropriately fitted a sigmoid function using the Weibull equation. Netilmicin binding to the renal cortex and medulla was characterised by a high partition coefficient in both tissues, with no statistically significant differences between the binding of the drug to either. Similarly, there were no statistically significant differences in the washout kinetics of netilmicin from the renal cortex and medulla.Previous incubation of renal tissue with urea significantly modified the washout kinetics of the compound from the renal cortex but not from the medulla, suggesting differences in the affinity of the drug for the renal cortex in situations of renal impairment.