Biochemical Identification and Clinical Description of Medetomidine Exposure in People Who Use Fentanyl in Philadelphia, PA

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Abstract
Medetomidine, a veterinary α2-adrenergic agonist, has recently emerged as an adulterant in the non-medical opioid supply, yet human exposure has remained poorly characterized. We conducted a pragmatic retrospective cohort analysis utilizing chart review and liquid chromatography–tandem mass spectrometry (LC-MS/MS) toxicology testing on available urine samples from patients presenting to two hospitals in Philadelphia, PA, who fit two clinical phenotypes, intoxication or withdrawal. Samples also underwent glucuronidase pre-treatment to assess impact on the yield of medetomidine and xylazine metabolite detection. Testing identified universal exposure to medetomidine (58/58 samples) via the 3-hydroxy-medetomidine (3-OH-M) metabolite, post glucuronidase treatment and variable xylazine exposure (40/58 samples). Importantly, 32% of medetomidine exposures would have been missed without enzymatic pre-treatment. Patients exhibited two distinct clinical phenotypes: intoxication, characterized primarily by sedation; bradycardia; and often hypotension, and withdrawal, presenting with life-threatening tachycardia; hypertension and often encephalopathy. Notably, clinical phenotype correlated with urinary concentrations of 3-OH-M but not xylazine. These findings underscore the critical need for heightened clinical awareness and need for contemporaneous toxicologic screening mechanisms for medetomidine exposure, emphasizing its distinct clinical presentations and the potential public health implications posed by its widespread adulteration in illicit opioids.

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