Ultra high performance liquid chromatography-tandem mass spectrometry vs. commercial immunoassay for determination of vancomycin plasma concentration in children. Possible implications for everyday clinical practice

Background: Vancomycin therapeutic drug monitoring (TDM) is necessary for effective and safetherapy. The aim of the this paper was to develop a specific and robust ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method for vancomycin quantification starting from low plasma volumes to be applied for the routine TDM in children. Methods: Samples from children receiving intravenous vancomycin were analysed using a TSQ Quantum Access MAX Triple Quadrupole system coupled with an Accela 1250 UHPLC system after a rapid protein precipitation. Gradient separation chromatography was carried out using a Hypersil GOLD aQ C18 column (50 x 2.1 mm, particle size 1.9 mu m). Method performance was validated following international guidelines. Results: UHPLC-MS/MS allowed a rapid and specific quantification of vancomycin over the range 0.1-128 mu g/mL from 50 mu L of plasma with high reproducibility and accuracy in the absence of matrix effect. The comparison with the commercial immunoassay performed on 138 samples demonstrated the presence of a proportional bias. The concentrations of vancomycin measured with immunoassay were found to be 4.5% (95% CI: 1.3-7.7) higher than those determined with UHPLC-MS/MS. Importantly, a clinical discordance was found in about 10% of samples analysed. Conclusions: This new UHPLC-MS/MS method is accurate and specific for the measurement of vancomycin starting from small (50 mu L) plasma volumes. The use of UHPLC-MS/MS is recommended to prevent a misclassification of therapeutic or toxic vancomycin levels in paediatrics.