Medetomidine Quantitation and Enantiomer Differentiation in Biological Specimens Collected After Fatal and Non-Fatal Opioid Overdoses.

Medetomidine is an alpha-2 agonist and non-opioid sedative. Its presence in illicit fentanyl and heroin drug supplies poses significant risks to user health caused by cardiac effects and sedation. Medetomidine exists in two enantiomeric forms: dexmedetomidine and levomedetomidine. Dexmedetomidine is used in humans in medical settings, while dexmedetomidine alone and a racemic mixture of dexmedetomidine and levomedetomidine are used in animals in veterinary settings. Little information is known about circulating blood concentrations of medetomidine or its enantiomers in humans in situations involving synthetic opioids (e.g., fentanyl) and other sedatives (e.g., xylazine, benzodiazepines). A new toxicological workflow using liquid chromatography tandem quadrupole mass spectrometry (LC-QQQ-MS) was developed and validated for the quantitation of medetomidine and the qualitative enantiomeric separation of dexmedetomidine and levomedetomidine. The assays were applied to a case series of 100 authentic specimens from emergency department admissions and forensic postmortem investigations containing medetomidine, fentanyl, xylazine, and metabolites, among other substances. Medetomidine blood concentrations in non-fatal overdoses ranged 0.1-16 ng/mL (median: 1.5 ng/mL) and in fatal overdoses ranged 0.1-32 ng/mL (median: 0.31 ng/mL). Xylazine was co-detected in 76% of cases with higher median concentrations: 8.3 ng/mL (non-fatal) and 15 ng/mL (fatal). Fentanyl was co-detected in 93% of cases with median concentrations of 5.2 ng/mL (non-fatal) and 21 ng/mL (fatal). Dexmedetomidine and levomedetomidine were identified in 90% of cases; the remaining cases were confirmed or suspected medical-setting administration of dexmedetomidine. These findings demonstrate that medetomidine is arising from veterinary or clandestine sources, and we hypothesize the latter. Recreational medetomidine use causes adverse effects such as profound bradycardia and heightened sedation, especially when combined with fentanyl and xylazine. Forensic laboratories must remain aware of adulterants, like medetomidine, appearing in traditional opioid products (e.g., fentanyl, heroin), updating testing methods to capture these emerging adulterants in real-time.