= Discovery stage. (16.60%, 2024)
= Translation stage. (37.02%, 2024)
= Clinically available. (46.38%, 2024)
MSACL 2024 : Halifax

MSACL 2024 Abstract

Self-Classified Topic Area(s): Small Molecule > Tox / TDM / Endocrine > Cases of Unmet Clinical Needs

Podium Presentation in Steinbeck 1 on Thursday at 13:50 (Chair: Christopher Chouinard / Difei Sun)

Monitoring the San Francisco Drug Supply: Results from a Bio-Surveillance Project of Opiate Treatment Patients Using High Resolution Mass Spectrometry

John Halifax (1,2), Lilly Lim (1,2), Kara Lynch (1)
(1) University of California, San Francisco, CA (2) University of California, Berkeley, CA

John Halifax, BS Chemistry, Magna Cum Laude (Presenter)

Presenter Bio: John Halifax graduated from Haverford College with a BS in Chemistry and Biochemistry, Magna cum Laude. He subsequently worked in the non profit sector in his hometown of San Francisco, CA, developing a drug checking service utilizing FTIR spectroscopy to monitor the drug supply in the context of the overdose crisis. He has continued this work in his current role as an academic researcher in the Lynch Clinical Chemistry Research Lab at UCSF. In the Lynch Clinical Chemistry Research Lab he worked extensively on small molecule detection and quantitation using LC-MS/MS and LC-QTOF-MS methods, as well as data science applications for improved analysis. John is currently a second year MS Epidemiology student at UC Berkeley School of Public Health, and will begin his PhD in Epidemiology at UC Berkeley's Department of Epidemiology and Biostatistics in Fall 2024.



The overdose crisis in the United States continues to accelerate. The most recently available national data shows the age adjusted risk of overdose rose by 14% from 2020 to 2021, a continued rise driven in part by a changing drug supply. The potent synthetic opioid fentanyl emerged a decade ago with devastating consequences for overdose mortality, and recent reports from eastern United States identify further troubling changes. Xylazine, a sedative associated with severe soft tissue damage, has been increasingly detected in overdose deaths involving illicitly manufactured fentanyl (IMF). Provisional national data from 2019-2022 indicate regional heterogeneity for xylazine prevalence; xylazine was detected in 49.9% of IMF-involved deaths in the Northeast U.S. Census Bureau Region, but only 1.1% of IMF-involved deaths in the West Region. Re-analysis of all accidental overdoses in San Francisco from 2022 found xylazine in 2.4% of cases. Additionally, nitazenes, a family of synthetic opioids structurally unrelated to fentanyl but of similar or greater potency, have been identified in eastern United States in limited cases. Nitazenes have not been identified on the West Coast, but in spring 2023 patients at opiate treatment programs reported drugs marketed as “Iso,” assumed to refer to the nitazene isotonitazene. The historical precedent of IMF’s westward spread after its emergence in the Northeast raises concerns that this lower prevalence of xylazine and nitazenes in Western US may be a preamble to a delayed but significant emergence in western states. Within this national context, local concerns about new changes in the drug supply prompted the initiation of a real-time surveillance of the drug supply utilizing urine from patients at a hospital-based opioid treatment program in San Francisco.

Initiated March1st, 2023, this bio-surveillance program utilized untargeted Liquid Chromatography-Quadrupole Time of Flight-Mass Spectrometry (LC-QTOF-MS) to provide toxicological analysis of de-identified urine aliquots from an at-risk patient population. Notable findings from the program include detecting a widespread but unsustained emergence of xylazine in San Francisco and refuting suggestions that drugs marketed locally as “Iso” consisted of isotonitazene. This real-time information on the state of the local substance supply informs clinicians, patients, and the San Francisco Department of Public Health. An interactive dashboard and a one-page document are updated weekly to communicate aggregated program results.


To demonstrate the effectiveness of utilizing a clinically validated LC-QTOF-MS comprehensive drug screen method to analyze de-identified urine samples from a population exposed to the local drug supply as a proxy for direct drug supply surveillance.


Each patient presenting for treatment at San Francisco General Hospital’s (SFGH) Opiate Treatment Outpatient Program (OTOP) provides urine for toxicology testing. Since March 1, 2023, a de-identified aliquot of each sample is analyzed on a clinically validated comprehensive drug test by untargeted high-resolution LC-QTOF-MS. Briefly, chromatographic separation is performed using a C-18 column with a 10-minute gradient from 2%-100% organic. Data is collected on a SCIEX TripleTOF®5600 operating in positive-ion mode using a TOF-MS survey scan with IDA-triggered collection of high-resolution product ion spectra (20 dependent scans). Parent ion masses of analytes of particular interest were added to an inclusion list for the TOF-MS scan to ensure collection of high-resolution product ion spectra even when the analyte’s abundance was below the IDA threshold. Data is analyzed using an in-house library containing >5000 small molecules including >150 fentanyl analogs and 12 nitazene-family compounds. Results are communicated weekly to OTOP clinicians in weekly aggregate in the form of an interactive dashboard. A one-page factsheet presenting weekly aggregated results for xylazine prevalence is updated weekly for use as a patient education material for SFGH clinics.


From March to November 2023, n = 383 urine samples were analyzed using the LC-QTOF-MS method. No samples were positive for any of the 12 nitazene compounds present in available libraries. In all samples, n =52 were positive for xylazine (13.58%), with xylazine prevalence varying temporally. The first xylazine positive sample was detected in late March 2023, but xylazine detections remained sporadic until late May, when the proportion of samples with xylazine began to steadily rise. From June 1st - July 31st, 31.9% of all samples (n=91) tested positive for xylazine compared to only 6.6% of all samples prior to June 1st (n=136). Since the end of July, xylazine prevalence has again fallen, with only 8.33% of samples (n=156) positive for xylazine. Detection of fentanyl analogs and their metabolites, predominantly fluorofentanyl (n=46) but also methoxy-furanyl fentanyl (n=33), methoxy-tetrahydrofuran-fentanyl (n=15, and norcarfentanil (n=1) provide nuanced insights into the local opioid supply, now dominated by fentanyl. All xylazine and fentanyl analog positive samples were also positive for fentanyl or its main metabolite, norfentanyl, suggesting that xylazine and fentanyl analogs are present in the drug supply as adulterants of fentanyl rather than stand alone drugs themselves.


Analysis of de-identified urine samples from a patient population at-risk of overdose by LC-QTOF-MS provides deeper comprehension of the illicit substance supply in a geographic region, aiding clinical practice and patient education. The LC-QTOF-MS untargeted method adapted to ensure spectra collection for analytes of interest facilitates a hybrid untargeted-targeted approach to flexibly assess the drug supply while reliably establishing target analyte prevalence in the sample population.

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