Case Series: Magnitude and duration of fentanyl and xylazine detection in the urine of persons with opioid use disorder

Background/Objectives: The pharmacology of fentanyl and xylazine is not characterized in persons regularly exposed to illicit fentanyl. This case series presents individual-level urine pharmacokinetics of fentanyl, norfentanyl, and xylazine in persons with opioid use disorder (OUD). Methods: Participants (N = 11) provided urine samples (n = 95) for quantitative analysis. Terminal half-lives and predicted detection times were calculated. Results: Urinary half-life ranges were: fentanyl 1.5–28.7 h, norfentanyl 5.2–27.4 h, and xylazine 1.1–25.2 h. Predicted detection window ranges were: fentanyl 13.0–130.9 h (0.5–5.5 days), norfentanyl 64.8–255.9 h (2.7–10.7 days), and xylazine 13.8–123.4 h (0.6–5.1 days). Discussion/Conclusions: Persons are presenting with a high magnitude of drug exposure that lends to an extended duration of urinary detection. Significance: First characterization of urinary excretion in persons with OUD.