Friedman Joseph, Molina Caitlin A, Koncsol Adam J, Romero Ruby, Godvin Morgan E, Jalayer Elham, Davila Spider, Arellano Oscar, Cowan Amanda, Hurley Brian, Shover Chelsea L
Department of Psychiatry, University of California, San Diego.
Department of General Internal Medicine and Health Services Research, University of California, Los Angeles.
medRxiv. 2025 May 14:2025.05.13.25327478. doi: 10.1101/2025.05.13.25327478.
The veterinary sedative xylazine has been mostly described on the East Coast-yet early reports indicate that it is now arriving to West Coast fentanyl markets. Emerging drug checking approaches can provide information about the concentration and prevalence of xylazine in illicit fentanyl.
Fentanyl samples from a community-based drug checking program in Los Angeles, California were assessed using direct analysis in real time mass spectrometry (DART-MS). A subset was analyzed with liquid chromatography gas spectrometry (LC-MS) to quantify the concentration of xylazine, fentanyl, and other compounds.
Among n=536 fentanyl-positive samples, xylazine positivity rose from 0% in 2023 Q1 to a peak of 29.5% in 2025 Q1. A significant time trend was observed (OR per quarter year= 1.35 [95%CI: 1.19-1.52]). Xylazine concentration in fentanyl samples was generally low, with a highly skewed distribution (mean=2.42%, sd=7.80%). 76.9% of xylazine-positive samples had <1.0% xylazine concentration. Compared to xylazine-negative samples, xylazine-positive samples were more likely to contain BTMPS (46.60% vs 17.30%), and lidocaine (65.0% vs 29.6%), and had lower average fentanyl concentration (6.12% vs 10.7%).
Among illicit fentanyl samples in LA, we note increasing xylazine positivity. The distribution of xylazine concentration is highly skewed, with a small number of very high concentration samples, and majority with <1%. Nevertheless, more research is needed to study the health impacts of even the low concentration xylazine that is most predominant here; given that the average participant in our sample consumes about 1.0g of illicit fentanyl daily, the corresponding dose of 24mg of xylazine per day may be physiologically significant.
兽医镇静剂赛拉嗪大多在东海岸被报道——但早期报告表明它现在正进入西海岸的芬太尼市场。新兴的药物检测方法可以提供有关赛拉嗪在非法芬太尼中的浓度和流行情况的信息。
使用实时直接分析质谱法（DART-MS）对来自加利福尼亚州洛杉矶一个基于社区的药物检测项目的芬太尼样本进行评估。一部分样本用液相色谱-气相色谱法（LC-MS）进行分析，以量化赛拉嗪、芬太尼和其他化合物的浓度。
在n = 536份芬太尼阳性样本中，赛拉嗪阳性率从2023年第一季度的0%上升到2025年第一季度的峰值29.5%。观察到显著的时间趋势（每季度的OR = 1.35 [95%CI：1.19 - 1.52]）。芬太尼样本中的赛拉嗪浓度普遍较低，分布高度偏态（均值 = 2.42%，标准差 = 7.80%）。76.9%的赛拉嗪阳性样本的赛拉嗪浓度<1.0%。与赛拉嗪阴性样本相比，赛拉嗪阳性样本更有可能含有丁硫妥英（46.60%对17.30%）和利多卡因（65.0%对29.6%），且平均芬太尼浓度较低（6.12%对10.7%）。
在洛杉矶的非法芬太尼样本中，我们注意到赛拉嗪阳性率在增加。赛拉嗪浓度的分布高度偏态，少数样本浓度非常高，而大多数样本<1%。然而，即使是这里最主要的低浓度赛拉嗪对健康的影响也需要更多研究；鉴于我们样本中的平均参与者每天消耗约1.0克非法芬太尼，每天相应剂量的24毫克赛拉嗪可能具有生理意义。
