Measurement uncertainty estimation of free drug concentrations in clinical laboratories using equilibrium dialysis.

OBJECTIVES: Developing procedures based on equilibrium dialysis (ED) that allow measuring the free drug concentration in plasma improves therapeutic drug monitoring (TDM) in those cases where its measurement is justified. However, this procedure requires specific sample preparation and presents different pitfalls, which are not error-free. As with any result provided by a clinical laboratory, this one should be as accurate as possible to allow a correct clinical interpretation. The measurement uncertainty (MU) is a parameter that enables the accuracy of results to be known, and that is mandated by ISO 15189. Herein, this study suggests how the MU for the results of the free drug concentrations in serum could be estimated when an ED is used. METHODS: A combination of the top-down and bottom-up approaches was used to estimate the MU based on the ISO/TS 20914:2019 and JCGM 100:2008 guidelines, including the concentration of free phenytoin in serum, as an example. Different scenarios were incorporated considering or not a significant bias related to the primary drawbacks of ED: the non-specific binding, the volume shift effect and the Gibbs-Donnan effect. RESULTS: The expanded uncertainties estimated ranged between 13.0 and 30.9 %. The highest MU corresponded to the free drug concentrations in serum results when significant biases related to the volume shift and Gibbs-Donnan effects exist. CONCLUSIONS: A detailed estimation of MU for free drug concentrations is presented using ED, considering different scenarios. This study could stimulate clinical laboratories to perform MU studies and its application in TDM.

A prospective study to analyse the concentration of octenidine in hand wounds after disinfection by LC-MS/MS.

Toxic reactions can appear after pressurised flushing of soft tissue with octenidine (OCT) containing disinfectants. Their use for surgical disinfection could complicate the diagnosis of possible contamination. In patients with open lacerations of their hand's subcutaneous tissue samples were taken before and after surgical disinfection with Octenisept® and analysed by ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). In 16 out of 20 tissue samples, OCT was detected after disinfection (lower limit of quantification (LLOQ)=10 pg/mL/mg). The concentration of OCT was below the LLOQ, estimation of mean of 0.6 pg/mL/mg (0.22-0.98 pg/mL/mg, 95%-CI) before disinfection and mean of 179.4 pg/mL/mg (13.35-432.0 pg/mL/mg, 95%-CI) after disinfection. This study shows that the disinfection of open wounds with Octenisept® leads to a quantifiable concentration of OCT in open wounds. In cases of suspected OCT-mediated toxic reaction, the use of antiseptics containing OCT should be avoided.

Sensitive quantification of free pazopanib using ultra-high performance liquid chromatography coupled to tandem mass spectrometry and assessment of clinical application.

Pazopanib is widely used to treat renal cell carcinomas and soft tissue tumors in Japan. Although several reports demonstrated the usefulness of therapeutic drug monitoring (TDM) of pazopanib, those studies measured only total pazopanib concentration. For drugs with high protein binding rates such as pazopanib, measuring free concentrations may be clinically more useful than measuring total concentrations. In this study, we aimed to develop a high-throughput method for quantification of free pazopanib in human plasma using ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). Free pazopanib was separated by ultrafiltration. After a simple solid-phase extraction step using a 96-well plate, pazopanib was analyzed by UHPLC-MS/MS in positive electrospray ionization mode. The novel method fulfilled the requirements of the US Food and Drug Administration guidelines for assay validation, and the lower limit of quantification was 0.05 ng/mL. The calibration curve was linear over the concentration range of 0.05-50 ng/mL. The average recovery rate was 66.9 ± 2.1% (mean ± SD). The precision was below 7.02%, and accuracy was within 10.60% across all quality control levels. Matrix effect varied between 44.4% and 60.4%. This assay was successfully applied to measure trough free pazopanib concentrations in three patients treated with pazopanib for soft tissue tumors. We succeeded to develop a novel high-throughput UHPLC-MS/MS method for quantification of free pazopanib in human plasma. This method can be applied to TDM for patients receiving pazopanib in the clinical setting.