Retrospective Evaluation of Novel Synthetic Opioids and Xylazine Chronic Intake by Post‐Mortem Hair Testing

ABSTRACT Fentanyl and its derivatives (nonpharmaceutical fentanyl, NPFs) represent the largest group among synthetic opioids. Fentanyl‐related deaths and fatalities from tampering with pharmaceutical products have been reported. Furthermore, in the United States, adulterants such as xylazine and other substances, including the nitazenes class of opioids, have been found in an increasing number of unintentional overdose deaths, drug seizures, and reports of use by recreational drug users. Monitoring the diffusion of fentanyl, NPFs, nitazenes, and adulterants among the population is a fundamental pursuit in forensic toxicology. The use of hair analysis is perfect for this purpose, providing essential information regarding previous intake or exposure to xenobiotics. The present study focused on the development and validation of a UPLC‐MS/MS method for the detection and quantification of fentanyl, NPFs, and xylazine, as well as the semiquantitative detection of nitazenes in hair samples from post‐mortem cases collected under the jurisdiction of the Jefferson County Coroner/Medical Examiner's Office (Birmingham, AL, USA). The method was validated according to international guidelines and applied to the analysis of n = 250 post‐mortem hair samples. In 52% of the analyzed hair samples, fentanyl, its main metabolites, and related analogs were detected, showing significant exposure to these substances in the population. Moreover, xylazine was detected in n = 48 hair samples (19.2%). The developed UPLC‐MS/MS method proved suitable for rapid chromatographic separation and sensitive detection of the studied compounds. In addition, this is the first time that xylazine and protonitazene have been measured in hair samples of subjects exposed to synthetic opioids.