B-269 Snapshot: Prevalence of xylazine and/or medetomidine in fentanyl screen-positive urine drug screen samples in a Philadelphia Center City hospital, Summer 2024

Background Xylazine (X), an alpha-2 adrenoreceptor agonist, has for years been an additive to the illicit fentanyl drug supply in Philadelphia. Recently, medetomidine (M), another alpha-2 adrenoreceptor agonist, has also been identified. Our objective in this study was to assess the prevalence of xylazine and/or medetomidine among fentanyl screen-positive urine drug screen samples in our hospital, an academic medical center hospital in Center City, Philadelphia. Methods Fentanyl screen-positive urine specimens (Roche immunoassay) were obtained from among drug-screen samples submitted to the clinical laboratory during a two-week interval in July 2024. Measurement of X and M was performed by LC-MS/MS. A 50 µL aliquot of urine sample was added to 200 µL of MeOH containing internal standards (D5-norofentanyl for X: 13C,D4-medetomidine for M). Samples were vortexed and spun at 30,000 g for 10 minutes. 100 µL of supernatant was used for injection of 10 µL into the LC system. LC used mobile phases of H2O (A), and MEOH (B) with 0.1% formic acid. Chromatography was carried out using a Phenomenex Kinetix C18 column (100 Å, 5 µm × 4.6 mm), at 40 °C. A ramp of %B from 50% to100% caused elution of X (1.3 min), M (2.0 min), with a total run-time of 6 minutes. For MS/MS, positive ion pairs (Q1/Q3) were 221.0/164.0 (X) and 201.1/95.1 (M). The assay was linear (r>0.99) across the range of standards for X and M (0-500 ng/mL). Interassay precisions were deemed acceptable for research-use-only screening purposes (mean (ng/mL), coefficient of variation): for X (298, 5.2%; 31.3, 6.5%); for M (238, 4.2%; 22.2, 15.2%). Lower limits of quantitation (LLOQ) were 5 ng/mL (X), 10 ng/mL (M). Results above LLOQs were deemed as positive. Use of specimens in this study, as well as review of medical records for fentanyl prescription (Rx), was approved by our Institutional Review Board (IRB). Results Among 80 fentanyl screen-positive specimens isolated for the study, 9 (11.3%) were excluded because of in-house administration of fentanyl for medical treatment (Rx). Among 71 non-Rx specimens, 60 (84.5%) were X-positive, M-negative. X concentrations ranged from 5 ng/mL to 20 µg/mL. 1 specimen (1.4%) was X-negative, M-positive (16 ng/mL). 10 specimens (14.1%) were X-negative, M- negative. Prevalence of [X or M] was 61/71 (85.9%). Conclusions Prevalence of [X or M] among non-Rx fentanyl screen-positive urine samples was high (86%) in our small study population (n = 71). Prevalence of M was low (< 2%). X prevalence was marginally increased from that in a previous snapshot study (78%) conducted in our hospital in 2021. Institution-specific knowledge of prevalence of X and M is useful to emergency care providers in the absence of availability of rapid testing for either X or M. However, it is possible that measurement of metabolites of M, rather than measurement of M, may be the more appropriate assay for detection of exposure to M.