Opioid overdoses involving xylazine in emergency department patients: a multicenter study

From Patient Registry to Multi-Center Research Consortium: the Toxicology Investigators Consortium (ToxIC) Turns Fifteen

The Toxicology Investigators Consortium (ToxIC) was launched as a prospective multi-center registry of cases who receive medical toxicology consultations. Now, with over 100,000 cases, the Core Registry continues to address many medical toxicology research questions and has served as the foundation for multiple sub-registries, including the North American Snakebite Registry and the Medications for Opioid Use Disorder sub-registry. ToxIC also has evolved a portfolio of non-registry-based projects utilizing medical toxicology physician site principal investigators who enroll patients through emergency departments, irrespective of whether they received a medical toxicology consultation. These studies include the FDA-ACMT COVID-19 ToxIC Pharmacovigilance Project, which identifies adverse drug reactions related to the treatment of COVID-19, the Fentalog Study a toxico-surveillance study of suspected opioid overdose cases, the Drug Overdose Toxico-Surveillance Reporting Program which enrolls either suspected stimulant or opioid overdose cases, and the just being launched Real-World Examination of Naloxone for Drug Overdose Reversal project. Given ToxIC's experience in multi-center studies and its well-developed infrastructure, it is well-positioned to provide a nimble response on the part of the medical toxicology community to addressing evolving toxicological threats, drug and chemical toxicosurveillance, and other important medical toxicology priorities.

EDucated: The emergency medicine pharmacotherapy literature of 2023

The purpose of this article is to summarize pharmacotherapy related emergency medicine (EM) literature indexed in 2023. Articles were selected utilizing a modified Delphi approach. The table of contents from pre-determined journals were reviewed and independently evaluated via the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system by paired authors. Pharmacotherapy-related publications deemed to be GRADE 1A and 1B were reviewed by the collective group for inclusion in the review. In all, this article summarizes and provides commentary on the potential clinical impact of 13 articles, 6 guidelines, and 5 meta-analyses covering topics including guideline releases and updates on rapid sequence intubation in the critically ill, managing cardiac arrest or life-threatening toxicity due to poisoning, and management of major bleeding following trauma. Also discussed are ongoing controversies surrounding fluid resuscitation, time and treatment modalities for ischemic stroke, steroid use in community-acquired pneumonia, targeted blood product administration, and much more.

"Tranq-dope": The first fatal intoxication due to xylazine-adulterated heroin in Italy

BACKGROUND AND AIMS

The number of xylazine-involved overdose deaths tremendously increased from 2019 onwards in the US. This is due to the "tranq-dope" trend consisting in mixing opioids with the sedative to reduce drug manufacturing costs and enhance their effects. In this study, we report the first fatality involving xylazine-adulterated heroin in the EU.

MATERIALS AND METHODS

The subject was a 33-year-old Caucasian male with a documented history of drug abuse who was found dead in a public area with puncture marks at the elbow. Peripheral blood and urine were collected at the autopsy and analyzed by liquid chromatography-high-resolution tandem mass spectrometry (LC-HRMS/MS) after protein precipitation.

RESULTS

6-Monoacetylmorphine, total/free morphine, and codeine blood concentrations of 20.3, 236/105, and 38.3 ng/mL, respectively, indicated recent heroin consumption. Methadone blood concentration was below 10 ng/mL. Alprazolam, nordiazepam, and flurazepam blood concentrations were 23.9, 61.4, and 55.0 ng/mL, respectively. Benzoylecgonine blood concentration was below 5 ng/mL. Xylazine blood and urine concentrations were 105 and 72.6 ng/mL, respectively.

CONCLUSION

The combination of central nervous system depressants, i.e., opioids, benzodiazepines, and xylazine, was the principal cause of death by cardiorespiratory failure. The case was promptly reported to the UE Early Warning System on drugs.

Public health surveillance of new psychoactive substances: recent developments

PURPOSE OF REVIEW

New psychoactive substances (NPS) continue to emerge globally and present a threat to public health. This article summarizes the most recent literature on approaches for monitoring NPS use and adverse events related to use.

RECENT FINDINGS

A variety of approaches have recently been employed for surveillance of NPS use and associated harms, including the use of toxicology testing of patients in emergency departments, surveys of sentinel populations, drug checking and syringe services programs, wastewater-based epidemiology, and retrospective analyses of clinical samples and toxicology reports. These studies cover a range of time periods and NPS examined across numerous countries.

SUMMARY

Areas of particular interest for future research include the use of data from drug checking services to inform surveillance efforts of the illicit drug supply and the development of methods for wastewater-based monitoring of NPS. Studies that combine self-report data with toxicology testing in particular are important for capturing unintentional or unknown exposure to NPS including fentanyls and drugs like xylazine. Given the limitations associated with individual indicators of drug use and associated harms, the harmonization of multiple data sources can help present a more complete picture of both trends involving NPS to better inform public health responses.

National Institute on Drug Abuse Clinical Trials Network Meeting Report: Managing Patients Exposed to Xylazine-Adulterated Opioids in Emergency, Hospital and Addiction Care Settings

Used as a veterinary sedative and not approved for human use, xylazine has been increasingly linked with opioid overdose deaths in the United States. A growing number of people have been exposed to xylazine in the illicit opioid supply (especially fentanyl) or in other drugs, particularly in some areas of the Northeast. Xylazine is an α-2 adrenergic agonist that decreases sympathetic nervous system activity. When combined with fentanyl or heroin, it is purported to extend the duration of the opioid's sedative effect and to cause dependence and an associated withdrawal syndrome; however, data to support these concerns are limited. Despite the escalating frequency of detection of xylazine in people with nonfatal and fatal opioid overdose, direct links to these outcomes have not been identified. Because the strongest causal link is to fentanyl coexposure, ventilatory support and naloxone remain the cornerstones of overdose management. Xylazine is also associated with severe tissue injury, including skin ulcers and tissue loss, but little is known about the underlying mechanisms. Nonetheless, strategies for prevention and treatment are emerging. The significance and clinical effects of xylazine as an adulterant is focused on 4 domains that merit further evaluation: fentanyl-xylazine overdose, xylazine dependence and withdrawal, xylazine-associated dermal manifestations, and xylazine surveillance and detection in clinical and nonclinical settings. This report reflects the Proceedings of the National Institute on Drug Abuse Center for the Clinical Trials Network convening of clinical and scientific experts, federal staff, and other stakeholders to describe emerging best practices for treating people exposed to xylazine-adulterated opioids. Participants identified scientific gaps and opportunities for research to inform clinical practice in emergency departments, hospitals, and addiction medicine settings.

Empirical assessment of wounds among people who use substances

BACKGROUND

Wounds are a significant source of morbidity among people who use substances (PWUS). This project sought to identify the incidence and severity of wounds among PWUS in the South Bronx, a region of New York City with one of the highest morbidities of substance use disorder.

METHODS

This study recruited PWUS within the past 30 days. Research staff were trained to document the presence and severity of wounds. The primary outcome measure was the incidence of wounds. Acceptability of on-the-street wound care was assessed by the number of participants encountered. The association between participant characteristics and wounds was also evaluated.

RESULTS

In total, 586 PWUS were assessed (19.4 % female: 69 % Hispanic; 23 % Black; 5 % White). Heroin (65.7 %) and psychostimulants (58.3 %) were the most commonly used drugs. Approximately 23 % of outreach recipients disclosed a wound. Among those with a wound, 60.9 % reported one wound, 27.8 % had two wounds, and 11.3 % had three or more wounds. Small wounds (approximately the size of a cherry) were the most common (78.6 %). Recent use of stimulants or heroin, along with intravenous use of any substance were significantly associated with having a wound.

CONCLUSIONS

This study found that drug-related wounds were common among PWUS. Toxicology data from other sources indicate that xylazine was present in the NYC market at the time, though its prevalence among the current sample is difficult to determine. The occurrence and severity of substance-related wounds in NYC should continue to be monitored as a function of changes in the xylazine adulteration.

Classics in Chemical Neuroscience: Xylazine

Xylazine (also known as "tranq") is a potent nonopioid veterinary sedative that has recently experienced a surge in use as a drug adulterant, most often combined with illicitly manufactured fentanyl. This combination may heighten the risk of fatal overdose. Xylazine has no known antidote approved for use in humans, and age-adjusted overdose deaths involving xylazine were 35 times higher in 2021 than 2018. In April 2023, the Biden Administration declared xylazine-laced fentanyl an emerging drug threat in the United States. In 2022, the Drug Enforcement Agency (DEA) reported nearly a quarter of seized fentanyl powder contained xylazine. This dramatic increase in prevalence has solidified the status of xylazine as an emerging drug of abuse and an evolving threat to public health. The following narrative review outlines the synthesis, pharmacokinetics, pharmacodynamics, and adverse effects of xylazine, as well as the role it may play in the ongoing opioid epidemic.

Xylazine: A Drug Adulterant of Clinical Concern

PURPOSE OF REVIEW

The opioid epidemic has been responsible for significant morbidity and mortality in the USA and worldwide. As a result, it is essential to recognize the threat these potent drugs can cause when illicitly used. Specifically, introducing fentanyl as a drug adulterant has been shown to impact overdose rates drastically. In this regard, the Drug Enforcement Agency recently released a public safety alert announcing the new threat of a new adulterant called xylazine. Xylazine is a powerful animal sedative with a different mechanism of action when compared to illicit opioids such as heroin and fentanyl. Xylazine is typically injected intravenously via a syringe, often in combination with multiple other drugs. One of the most common drugs, xylazine, is taken in combination with fentanyl, with users of this drug combination describing xylazine as prolonging the euphoric sensation produced by fentanyl.

RECENT FINDINGS

Xylazine may cause adverse effects such as bradycardia, brief hypertension followed by hypotension, premature ventricular contractions, ataxia, slurred speech, sedation, and respiratory depression. Much of the recent literature on xylazine use in humans comes from case reports and review articles. Related to widespread use in veterinary medicine and increasing circulation in illicit drug markets, there is a critical need for public awareness and additional clinical-based studies to further increase understanding of mediated or modulated pharmacological effects of xylazine in humans. Further research is urgently needed to more clearly understand the implications of unregulated xylazine in the illicit drug market, to formulate public health interventions, and to implement harm reduction strategies.

Xylazine co-occurrence with illicit fentanyl is a growing threat in the Deep South: a retrospective study of decedent data

BACKGROUND

Xylazine is a dangerous veterinary sedative found mainly in illicit fentanyl in the Northeast and Midwest. Its role in the Deep South overdose crisis is not well-characterized.

METHODS

We conducted a retrospective review of autopsy data in Jefferson County, Alabama to identify trends in xylazine prevalence among people who fatally overdosed from June 2019 through June 2023.

RESULTS

165 decedents met inclusion criteria. While the first identified xylazine-associated overdose was in June 2019, xylazine has become consistently prevalent since January 2021. All cases of xylazine-associated fatal overdoses were accompanied by fentanyl, and most (75.4%) involved poly-drug stimulant use. The average age was 42.2, and most decedents were white (58.8%) and male (68.5%). Overall, 18.2% of people were unhoused at the time of death.

DISCUSSION

Xylazine is prevalent in the Deep South. Efforts to promote harm reduction, publicly viewable drug supply trends, and legalization of drug checking and syringe service programs should be prioritized.

Emergence of xylazine as a public health threat: what does the anesthesiologist need to know for perioperative care?

This paper explores the rapid emergence of xylazine exposure in the USA and its implications for anesthesiologists. Xylazine, a non-opioid sedative and analgesic often used in veterinary medicine, has increasingly been found as an adulterant in the illicit substance supply, leading to serious health implications. The pharmacological properties of xylazine, its clinical effects, and the challenges it poses for clinicans will be discussed. Perioperative strategies for anesthesiologists to manage these potential cases are provided. Furthermore, this paper necessitates an epidemiological understanding for detection and multidisciplinary collaboration in addressing this emerging public health threat. The manuscript concludes by emphasizing the role anesthesiologists will have to play in managing the clinical implications of xylazine and contributing to public health strategies aimed at curbing its misuse.

Reported xylazine exposure highly associated with overdose outcomes in a rapid community assessment among people who inject drugs in Baltimore

BACKGROUND

Addressing xylazine harms are now a critical harm reduction priority, but relatively little epidemiological information exists to determine prevalence, magnitude, and correlates of xylazine use or related outcomes.

METHODS

We conducted a rapid behavioral survey among people who inject drugs (n = 96) in Baltimore November-December 2022. Using a novel indicator of self-reported presumed xylazine effects, we examined prevalence and sociodemographic correlates of past year presumed xylazine effects and association with overdose and wound-related outcomes. Chi-square and descriptive statistics were used to examine bivariate associations overall and separately for those who reported xylazine by name and by reported fentanyl use frequency.

RESULTS

Almost two-thirds (61.5%) reported experiencing xylazine effects. There were no differences by socio-demographics, but xylazine effects were more commonly reported among those who reported injecting alone (66% vs 38%%, p < 0.007) and daily fentanyl use (47% vs 24% p < 0.003). Those reporting xylazine exposure was three times as likely to report overdose (32% vs 11%, p < 0.03) and twice as likely to have used naloxone (78% vs 46%, p < 0.003). They also more commonly reported knowing someone who died of an overdose (92% vs 76%, p < 0.09) and to report an abscess requiring medical attention (36% vs 19%, p < 0.80). These associations were higher among respondents who specifically named xylazine and those who used fentanyl more frequently, but fentanyl frequency did not fully explain the heightened associations with xylazine effects.

CONCLUSIONS

This study provides insight into the scope of xylazine exposure and associated health concerns among community-based PWID and suggests measures that may be instrumental for urgently needed research.

Xylazine in Overdose Deaths and Forensic Drug Reports in US States, 2019-2022

Importance

Xylazine is increasingly reported in street drugs and fatal overdoses in the US, yet state-level data are limited, hampering local public health responses.

Objective

To gather available state-level data on xylazine involvement in overdose deaths and in forensic drug reports.

Design, Setting, and Participants

This cross-sectional study was a secondary analysis of 2019 to 2022 data from the National Forensic Laboratory Information System (NFLIS), National Center for Health Statistics, and individual states' medical examiner or public health agency reports. Data were analyzed from August to October 2023.

Exposure

State.

Main Outcomes and Measures

Yearly xylazine-related overdose deaths per 100 000 residents; xylazine NFLIS drug reports, both per 100 000 residents and as a percentage of all NFLIS drug reports (from samples of drugs seized by law enforcement and analyzed by NFLIS-participating laboratories).

Results

A total of 63 state-years were included in analyses of mortality rates, while 204 state-years were included in analyses of NFLIS reports. According to the publicly available data compiled in this study, at least 43 states reported at least 1 xylazine-related overdose death from 2019 to 2022, yet yearly totals of xylazine-related deaths were available for only 21 states. Of states with data available, xylazine-involved overdose death rates were highest in Vermont (10.5 per 100 000 residents) and Connecticut (9.8 per 100 000 residents) in 2022. In 2019, 16 states had zero xylazine reports included in NFLIS reports; in 2022, only 2 states had zero xylazine reports and all but 3 states had recorded an increase in xylazine's representation in NFLIS reports. In 2022, xylazine represented 16.17% of all NFLIS reports in Delaware and between 5.95% and 7.00% of NFLIS reports in Connecticut, Maryland, District of Columbia, New Jersey, and Rhode Island, yet less than 1.0% of NFLIS reports in 35 different states.

Conclusions and Relevance

In this cross-sectional study of publicly available data on fatal overdoses and drugs analyzed by forensic laboratories, xylazine's reported presence in overdose deaths and forensic reports was concentrated in the eastern US yet extended across the country to encompass nearly all states. In spite of xylazine's geographic reach, yearly state-level numbers of xylazine-related overdose deaths were publicly available for less than half of all states.

N-desethyl isotonitazene detected in polydrug users admitted to hospital in Birmingham, United Kingdom

INTRODUCTION

Nitazenes are potent synthetic opioids and N-desethyl isotonitazene, a metabolite of isotonitazene, has emerged as a drug in its own right.

METHODS

This is an observational case series of patients with suspected or declared substance use who were admitted to hospitals in the Sandwell and West Birmingham National Health Service Trust between July and October 2023. All patients were found on toxicological screening to have been exposed to N-desethyl isotonitazene.

RESULTS

Twenty presentations involving 19 patients who tested positive for N-desethyl isotonitazene were included in the study. In 19 presentations, multiple substances were detected on toxicological screening. The number of patients testing positive for other substances were: 19 for cocaine and its main metabolite benzoylecgonine, 13 for morphine, 11 for the heroin-specific metabolite 6-monoacetylmorphine, ten for xylazine, eight for gabapentinoids (pregabalin and/or gabapentin), seven for methadone and/or the metabolite, 2-ethylidene-1, 5-dimethyl-3, 3-diphenylpyrrolidine, six for benzodiazepines and five for the synthetic cannabinoid MDMB-4en-PINACA. Only one patient had no other substances detected apart from N-desethyl isotonitazene. This patient presented with coma, miosis, bradypnoea and hypercapnia and responded to naloxone. In this cohort, the median concentration of N-desethyl isotonitazene was 1.53 µg/L (n = 14; range 0.59-5.48) in whole blood and 27.75 µg/L (n = 16; range 0.51-91.53) in urine.

DISCUSSION

The majority of the patients in this cohort presented with features typical of an opioid overdose, which is unsurprising as they were all experienced users of diamorphine. Although these features are also consistent with the known effects of N-desethyl isotonitazene, in only one case is it possible to attribute the patient's features to N-desethyl isotonitazene toxicity alone.

CONCLUSIONS

This case series highlights the need for toxicovigilance in the illicit drug market as patterns of substance misuse evolve and novel psychoactive substances continue to emerge.

Research Priorities to Improve Treatment of Patients Exposed to Xylazine-fentanyl: Rapid Communication from a National Institute on Drug Abuse Center for the Clinical Trials Network Meeting

ABSTRACT

In response to the rapid escalation in the detection of xylazine in the unregulated drug supply, in April 2023, the White House designated fentanyl contaminated with xylazine an "emerging threat." The National Institute on Drug Abuse Center for Clinical Trials Network convened a multidisciplinary meeting of stakeholders, federal staff members, researchers, and clinicians caring for patients with fentanyl and xylazine exposures. This convening focused on the most critical areas of concern with the goal of describing current practices and a xylazine-fentanyl research agenda. Discussions focused on the domains of epidemiology and laboratory detection, xylazine withdrawal and overdose, and dermal manifestations. The authors were involved in planning and moderating the program and providing a summary of the proceedings.

Evaluation of the relationship of xylazine and fentanyl blood concentrations among fentanyl-associated fatalities

INTRODUCTION

Illicit fentanyl and fentanyl-analogs have produced a devastating increase in opioid fatalities in the United States. Increasingly, xylazine has been found in the illicit fentanyl supply. The role of xylazine in fentanyl intoxication remains unclear. We reviewed coroner records to evaluate trends and effects associated with xylazine in fentanyl-related fatalities.

METHODS

This is a retrospective cohort study of all deaths reported to the Franklin County Coroner's Office in Ohio from 1 January 2019 to 16 March 2023, in which fentanyl was determined causative or contributory to death. Cases identified as fentanyl-associated fatalities were separated into two groups based on whether or not xylazine was also detected.

RESULTS

There were 3,052 fentanyl-related fatalities during the study period. 4.8 percent of these decedents also tested positive for xylazine. There was no meaningful demographic difference between fentanyl-related fatalities in which xylazine was detected versus those without xylazine detected. There was a mean of 726 fentanyl-associated fatalities per year, with a peak of 846 deaths in 2020 and a decline thereafter. The percentage of fentanyl-related fatalities with xylazine detected increased in linear fashion from 2.7 percent in 2019 to 6.6 percent in 2022. The median fentanyl concentration was 17.0 µg/L (inter-quartile range: 7.9, 27.0) in cases with xylazine detected and 10.0 µg/L (inter-quartile range: 5.6, 18.0) without xylazine. The odds of a fentanyl concentration greater than 40 µg/L in cases with xylazine detected was more than twice as great (odds ratio: 2.41; 95 percent confidence interval: 1.58-3.64) than that in cases without xylazine detected.

CONCLUSIONS

Postmortem fentanyl concentrations were greater in cases with xylazine detected than those without xylazine detected. Though it is unclear why patients who were exposed to xylazine tolerated higher opioid doses prior to succumbing to death, we postulate that xylazine may act to competitively antagonize some degree of mu-opioid receptor binding by opioids.

Qualitative and quantitative characteristics of xylazine-associated deaths detected using a post-mortem toxicology testing program

INTRODUCTION

The United States drug overdose crisis continues to evolve. Xylazine has been increasingly identified as an adulterant in illicit opioid supplies. The incorporation of novel adulterants, like xylazine, into the illicit drug supply adds complexity to post-mortem toxicology testing, public health messaging, substance use mitigation, and the treatment of people who use drugs.

METHODS

We assessed trends, decedent characteristics, drug co-detection, and blood concentrations of xylazine-positive post-mortem cases in Michigan. We utilized a toxicology testing program capable of detecting several opioids and non-opioids in post-mortem blood samples within 72 hours.

RESULTS

A total of 279 deaths were xylazine-positive between October 2019 and June 2023, with 100 percent positive for fentanyl. Only 30 percent of xylazine-involved samples were positive for naloxone, while 21.2 percent of xylazine-negative and opioid-positive samples were positive for naloxone. The percentage of xylazine-positive deaths increased from 3.2 percent in 2021 to 4.7 percent in January-June 2023. A median of five total drug groups were present among xylazine-positive deaths. Post-mortem xylazine concentrations for 55 decedent blood samples ranged from 5.2 to 200 µg/L.

DISCUSSION

Our study demonstrated increases in xylazine detection among post-mortem cases. Our findings are consistent with national trends of increasing xylazine presence among drug-involved deaths. Our range of detected post-mortem xylazine blood concentrations was consistent with what has been reported in previous literature. Fentanyl was detected in 100 percent of xylazine-positive overdose deaths. Naloxone detection was relatively low, highlighting the continued importance of increasing naloxone access and distribution. Deaths associated with xylazine often involved multiple other drugs. Limited human clinical xylazine research precludes accurate interpretation and attribution of causality from these data.

CONCLUSIONS

Overdose-related deaths with xylazine detection are increasing in Michigan and across the United States. Further clinical and toxicological research can help contextualize the clinical significance of xylazine in opioid overdose, clarify epidemiologic and clinical research, and inform appropriate public health messaging.

Self-reported Xylazine Experiences: A Mixed-methods Study of Reddit Subscribers

OBJECTIVES

Xylazine is an α 2 -agonist increasingly prevalent in the illicit drug supply. Our objectives were to curate information about xylazine through social media from people who use drugs (PWUDs). Specifically, we sought to answer the following: (1) What are the demographics of Reddit subscribers reporting exposure to xylazine? (2) Is xylazine a desired additive? And (3) what adverse effects of xylazine are PWUDs experiencing?

METHODS

Natural language processing (NLP) was used to identify mentions of "xylazine" from posts by Reddit subscribers who also posted on drug-related subreddits. Posts were qualitatively evaluated for xylazine-related themes. A survey was developed to gather additional information about the Reddit subscribers. This survey was posted on subreddits that were identified by NLP to contain xylazine-related discussions from March 2022 to October 2022.

RESULTS

Seventy-six posts were extracted via NLP from 765,616 posts by 16,131 Reddit subscribers (January 2018 to August 2021). People on Reddit described xylazine as an unwanted adulterant in their opioid supply. Sixty-one participants completed the survey. Of those who disclosed their location, 25 of 50 participants (50%) reported locations in the Northeastern United States. The most common route of xylazine use was intranasal use (57%). Thirty-one of 59 (53%) reported experiencing xylazine withdrawal. Frequent adverse events reported were prolonged sedation (81%) and increased skin wounds (43%).

CONCLUSIONS

Among respondents on these Reddit forums, xylazine seems to be an unwanted adulterant. People who use drugs may be experiencing adverse effects such as prolonged sedation and xylazine withdrawal. This seemed to be more common in the Northeast.

"Tranq-dope" overdose and mortality: lethality induced by fentanyl and xylazine

Introduction: The recreational use of fentanyl in combination with xylazine (i.e., "tranq-dope") represents a rapidly emerging public health threat characterized by significant toxicity and mortality. This study quantified the interactions between these drugs on lethality and examined the effectiveness of potential rescue medications to prevent a lethal overdose. Methods: Male and female mice were administered acute doses of fentanyl, xylazine, or their combination via intraperitoneal injection, and lethality was determined 0.5, 1.0, 1.5, 2.0, and 24 h after administration. Both fentanyl and xylazine produced dose-dependent increases in lethality when administered alone. Results: A nonlethal dose of fentanyl (56 mg/kg) produced an approximately 5-fold decrease in the estimated LD50 for xylazine (i.e., the dose estimated to produce lethality in 50% of the population). Notably, a nonlethal dose of xylazine (100 mg/kg) produced an approximately 100-fold decrease in the estimated LD50 for fentanyl. Both drug combinations produced a synergistic interaction as determined via isobolographic analysis. The opioid receptor antagonist, naloxone (3 mg/kg), but not the alpha-2 adrenergic receptor antagonist, yohimbine (3 mg/kg), significantly decreased the lethality of a fentanyl-xylazine combination. Lethality was rapid, with death occurring within 10 min after a high dose combination and generally within 30 min at lower dose combinations. Males were more sensitive to the lethal effects of fentanyl-xylazine combinations under some conditions suggesting biologically relevant sex differences in sensitivity to fentanyl-xylazine lethality. Discussion: These data provide the first quantification of the lethal effects of "tranq-dope" and suggest that rapid administration of naloxone may be effective at preventing death following overdose.

Xylazine Adulteration of the Heroin-Fentanyl Drug Supply : A Narrative Review

Xylazine is an animal sedative, approved by the U.S. Food and Drug Administration, that is commonly used in veterinary medicine and is not approved for human use. Since 2016, xylazine has consistently appeared in the illicitly manufactured fentanyl supply and has significantly increased in prevalence, likely due to its low cost, easy availability, and presumed synergistic psychoactive effect. Clinical experience along with the available pertinent research were used to review xylazine adulteration of the drug supply and provide guidance on the care of patients exposed to xylazine. This review discusses xylazine pharmacology, animal and human clinical effects, and what is known to date about care of patients experiencing acute overdose, xylazine-fentanyl withdrawal, and xylazine-associated wounds.

Xylazine in Drug Seizure Reports and Overdose Deaths in the US, 2018-2022

Xylazine is increasingly reported in street drugs and fatal overdoses in the United States (US), often in combination with synthetic opioids, yet state-level xylazine data are limited, hampering local public health responses. The present study analyzed 2018-2022 state-level data from the National Forensic Laboratory Information System (xylazine-positive reports of seized drugs analyzed by forensic laboratories), the Centers for Disease Control and Prevention (population estimates, synthetic opioid overdose mortality rates), and individual states' medical examiner/public health agency reports (numbers of xylazine-involved overdose deaths). An ordinary least squares regression model predicted state-level synthetic opioid overdose mortality rates by xylazine seizure report rates, adjusting for US Census Region. In 2018, relatively low rates of xylazine seizure reports were observed, with 21 states reporting zero xylazine seizures. In 2022, only three states reported zero xylazine seizures, and the highest xylazine seizure report rates (per 100,000 residents) were observed in New Jersey (30.4), Rhode Island (22.7), Maryland (18.9), Virginia (15.5), New Hampshire (13.0), and Ohio (10.9). Data on 2019-2022 xylazine-involved overdose deaths were available for 21 states/DC (60 state-years), with the highest 2022 xylazine-involved overdose death rates (per 100,000 residents) in Vermont (10.5) and Connecticut (9.8). Finally, in 2021, at the state level, each additional reported xylazine seizure per 100,000 residents was associated with a 2% higher synthetic opioid overdose mortality rate (b=0.02, robust standard error=0.01; p=0.049). Overall, study results emphasize xylazine's increasing involvement in US law enforcement drug seizure reports and overdose deaths, primarily in the East, yet also extending across the country.