Development and validation of a dried plasma spot LC-MS/MS method for the therapeutic monitoring of vancomycin and comparison with enzyme-multiplied immunoassay.

Vancomycin is used as an antimicrobial agent for the treatment of severe gram-positive infections. The importance of therapeutic monitoring of antimicrobials has led to the development of more specific sample preparation techniques capable of identifying with accuracy the concentration of this substance in the organism. An aliquot of 10 μL of plasma was transferred to the Whatman 903® paper and dried at room temperature. The extraction was performed by cutting and transferring the paper to a microtube and adding sodium phosphate buffer, and internal standard. The mixture was shaken, centrifuge, and a 5 μL aliquot was injected into the analytical system. The optimization of the main parameters that can influence the extraction efficiency was performed through multivariate approaches to obtain the best conditions. The method developed was validated, providing coefficients of determination higher than 0.994 and lower limit of quantification of 1 mg/L. Within and between-run precision ranged from 11.4% to 17.30% and 6.65% to 13.51%, respectively. This method was successfully applied to 75 samples of patients undergoing vancomycin therapy. The method was rapid, simple and environmentally-friendly with satisfactory analytical performance and consisted of advantages over laborious and time-consuming methodologies used in TDM routine analyses.