Xylazine: evaluation of antemortem and postmortem specimen storage conditions

Xylazine, a popular compound found independently and in polydrug mixtures throughout the United States, is intended for use in veterinary medicine and not for human consumption. When xylazine is ingested by humans, life-threatening central nervous system depression responses could potentially occur. With its increase in prevalence, several methods of detection were developed within forensic toxicology. Since xylazine is not approved for human clinical use, little is known about its behavior, such as its stability in stored biological matrices. Knowledge of drug stability in biological matrices can provide critical insight into the limitations surrounding specimen storage conditions, which is of great importance in forensic toxicology. This study assessed the stability of xylazine in preserved antemortem and postmortem blood under three storage conditions (23, 2-8, and -20°C) at two concentrations (3 and 160 ng/mL). Once prepared, samples were extracted using a validated protein precipitation procedure and analyzed by liquid chromatography-tandem mass spectrometry. Xylazine was considered stable if the deviation in calculated concentration was within ±20% of the Day 0 concentration. When the results of each individual pool prepared were averaged for reporting, the following results were obtained. When stored at 23 °C in both matrices, xylazine was unstable by Day 7 at 3 ng/mL and unstable by Day 10 at 160 ng/mL. When stored between 2 and 8°C in antemortem blood, xylazine was unstable by Day 10 at 3 ng/mL and unstable by Day 24 at 160 ng/mL. When stored between 2 and 8°C in postmortem blood, xylazine was unstable by Day 29 at both 3 and 160 ng/mL. When stored at -20°C in antemortem blood, xylazine was unstable by Day 3 at both 3 and 160 ng/mL. When stored at -20°C in postmortem blood, xylazine was unstable by Day 21 at 3 ng/mL and unstable by Day 10 at 160 ng/mL.