Liquid chromatography-mass spectrometry quantitation and prevalence of medetomidine and xylazine in New Haven, Connecticut.

The emergence of veterinary sedatives such as xylazine and medetomidine as adulterants in the illicit drug supply poses increasing challenges to clinical toxicology and public health. Medetomidine, a potent alpha-2 adrenergic receptor agonist not approved for human use, has recently been detected in overdose cases, particularly in fentanyl-positive individuals. To address this, we developed and validated a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay capable of detecting xylazine and medetomidine in urine with minimal sample preparation, a 60-min hydrolysis incubation, and a 7-min chromatographic run time. Analytical validation demonstrated acceptable precision, accuracy, linearity, and minimal matrix effects. We then analyzed 100 retrospective urine samples from a polydrug-using population. Xylazine was detected in 20 % and 3-hydroxymedetomidine (medetomidine's primary metabolite in urine) in 12 % of samples, with both compounds most frequently co-occurring with fentanyl. A subset of medetomidine-positive cases also tested positive for xylazine, indicating potential co-adulteration. This study highlights the value of expanded toxicological testing in identifying emerging adulterants that may otherwise go undetected by routine screening.