(29) Emergence of Local Anesthetics in the Los Angeles Illicit Fentanyl Supply

Background & Introduction: The illicit drug market is constantly in flux, with recent examples including the introduction of illicitly manufactured fentanyl, and more recently, with opioid overdoses bolstered by polysubstance use with other drug classes, such as stimulants, sedatives, and benzodiazepines. In response, chemical analysis of the illicit drug supply has materialized as a crucial intervention. Community-based drug checking programs offer real-time drug supply monitoring using chemistry techniques. This study characterizes the emergence of local anesthetics in the Los Angeles fentanyl supply from one such program.

Local anesthetics, typically used for pain management, may be administered by local injection, regional injection, epidural injection, and topically with minimal side effects. While the presence of local anesthetics has been described as an adulterant in cocaine- with its use to mimic cocaine’s anesthetic properties- the inclusion of local anesthetics has not been detected at-scale in fentanyl. By describing the emergence of local anesthetics in the Los Angeles fentanyl supply, public health programs and policies can prepare for the potential concerning adverse health effects of the new inclusion of local anesthetics in the illicit fentanyl supply.

Methods: The data examined was routinely produced as part of the Drug Checking Los Angeles program. In this program, participants visit one of four community sites for immediate chemical analysis with a portable spectrometer and immunoassay test strips. Anonymous surveys capture field data, and participants are invited to share their expectation of drug contents, experiences using the substance, and thoughts on the results. Following this, residue swabs or vials of drug product are collected for confirmatory testing with direct analysis in real time mass spectroscopy (DART-MS) and liquid chromatography- mass spectroscopy (LC-MS) completed by the National Institute of Standards and Technology (NIST). Data for expected fentanyl samples were analyzed in Stata SE 18.5, where descriptive statistics as well as chi-squared tests and pooled t-tests were calculated to compare group differences for samples that did and did not contain lidocaine, cocaine, and procaine (i.e., local anesthetics). As a public health surveillance activity, the UCLA IRB deemed this project was not Human Subjects research and therefore exempt from review.

Results: Of the samples collected in Los Angeles from September 2023 through November 2024, n=377 samples expected to be fentanyl were qualitatively evaluated using DART-MS, with n=350 (92.8%) samples containing fentanyl.

Among samples with fentanyl confirmed by DART-MS, n=164 samples also contained any local anesthetic. Samples containing local anesthetics had statistically significant variation in the co-detection of BTMPS (p <.001), fluorofentanyl (p <.001), and xylazine (p <.001), as well as several common fentanyl precursors, metabolites, and bulking agents (e.g., 4-ANPP, mannitol, etc.).

A subset of expected fentanyl samples (n=240) was also quantitatively analyzed using LC-MS with a 12- substance panel. Pooled t-tests were utilized to compare differences in concentration of each substance by local anesthetic inclusion. When comparing expected fentanyl samples containing no local anesthetics to those with any local anesthetic, there were statistically significant lower concentrations of BTMPS (µ=24.2%-7.96%, p <.001), fentanyl (µ=14.5%-3.88%, p <.001), fluorofentanyl (µ=7.65%-1.12%, p <.001), methamphetamine (µ=52.7%-1.72%, p <.001), and xylazine (µ=2.92%-0.27%., p <.001).

Conclusion & Discussion: This project documents the increase of local anesthetics as a common adulterant in illicit fentanyl. We theorize that local anesthetics may be added to illicit fentanyl to mimic the effects of fentanyl itself. Although severe toxicity from local anesthetics is rare and dose dependent, mostly affecting the central nervous system and heart, there is an abundance of literature capturing the side effects of lidocaine, procaine, and cocaine, including nausea, vomiting, numbness, tinnitus, and drowsiness. Adverse reactions to local anesthetics may include transient blindness, cardiac toxicity, acute psychosis, visual, auditory, or gustatory hallucinations, tonic-clonic movements, and seizures. Results may include cross contamination from polysubstance use, e.g., co-use of cocaine and fentanyl.

Missing from the literature are the effects of smoking local anesthetics, the preferred route of administration for many fentanyl users. Future research should explore how frequency and the use of supratherapeutic doses may affect the health of people who are unwittingly exposed to local anesthetics in the short- and long-term. Although limited quantitative data was collected, expected fentanyl samples often contained cocaine, lidocaine, or both, that far exceeded the amount of fentanyl present. The emergence of significant local anesthetic adulteration poses a public health concern worth monitoring.

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