Development and validation of a fast UPLC-MS/MS screening method for the detection of 68 psychoactive drugs and metabolites in whole blood and application to post-mortem cases.

We report a rapid and sensitive LC-MS/MS method that allows the simultaneous detection of 68 commonly prescribed antidepressants, benzodiazepines, neuroleptics, and metabolites in whole blood with a small sample volume after a rapid protein precipitation. The method was also tested on post-mortem blood from 85 forensic autopsies. Three sets of commercial serum calibrators containing a mix of prescription drugs of increasing concentration were spiked with red blood cells (RBC) to obtain 6 calibrators (3 "serum calibrators" and 3 "blood calibrators"). Curves obtained from serum calibrators and from blood calibrators were compared using a Spearman correlation test and by analyzing slopes and intercepts, to assess if the points from six calibrators could be plotted together in a single calibration model. The validation plan included interference studies, calibration model, carry-over, bias, within-run and between-run precision, limit of detection (LOD), limit of quantification (LOQ), matrix effect and dilution integrity. Four deuterated Internal Standards (Nordiazepam-D5, Citalopram-D6, Ketamine-D4 and Amphetamine-D5) and two different dilutions were assessed. Analyses were performed using an Acquity UPLC® System coupled with triple quadrupole detector Xevo TQD®. The degree of agreement with a previously validated method was calculated on whole blood samples of 85 post-mortem cases, by performing a Spearman correlation test with a Bland-Altman plot. Percentage error between the two methods was evaluated. Slopes and intercepts of curves obtained from serum calibrators and from blood calibrators showed a good correlation, and the calibration model was built plotting all points together. No interferences were found. The calibration curve appeared to provide a better fit of the data using an unweighted linear model. Negligible carry-over was observed, and very good linearity, precision, bias, matrix effect and dilution integrity were achieved. The LOD and the LOQ were at the lower limits of the therapeutic range for the tested drugs. In a series of 85 forensic cases, 11 antidepressants, 11 benzodiazepines and 8 neuroleptics were detected. For all analytes, a very good agreement between the new method and the validated method was demonstrated. The innovation of our method consists in the use of commercial calibrators, readily available to most forensic toxicology laboratories, for the validation of a fast, inexpensive, wide-panel LC-MS/MS method that can be used as a reliable and accurate screening for psychotropic drug in postmortem samples. As observed in the implementation on real cases, this method could be profitably applied in forensic cases.

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Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.