Investigation of the μ and κ‐opioid receptor activation by eight new synthetic opioids using the [ 35 S]‐GTPγS assay: U‐47700, isopropyl U‐47700, U‐49900, U‐47931E, N ‐methyl U‐47931E, U‐51754, U‐48520 and U‐48800

Non-fentanyl new synthetic opioids - An update

BACKGROUND

New synthetic opioids (NSO) constitute one of the fastest-growing group of New Psychoactive Substances, which emerged on the illicit drug marker in the second half of 2000's. The most popular and the largest NSO subgroup are high potency fentanyl and its analogs. Subsequent to core-structure scheduling of fentanyl-related substances many opioids with different chemical structures are now emerging on the illicit drug market, rendering the landscape highly complex and dynamic.

METHODS

PubMed, Scopus and Google Scholar were searched for appropriate articles up to December 2022. Moreover, a search for reports was conducted on Institutional websites to identify documentation published by World Health Organization, United Nations Office on Drugs and Crime, United States Drug Enforcement Administration, and European Monitoring Centre for Drugs and Drug Addiction. Only articles or reports written in English were selected.

RESULTS

Non-fentanyl derived synthetic opioids, i.e., 2-benzylbenzimidazoles (nitazenes), brorphine, U-compounds, AH-7921, MT-45 and related compounds are characterized, describing them in terms of available forms, pharmacology, metabolism as well as their toxic effects. Sample procedures and analytical techniques available for detection and quantification of these compounds in biological matrices are also presented. Finally, as overdoses involving highly potent NSO may be difficult to reverse, the effectiveness of naloxone as a rescue agent in NSO overdose is discussed.

CONCLUSIONS

Current review presents key information on non-fentanyl derived NSO. Access to upto-date data on substances of abuse is of great importance for clinicians, public health authorities and professionals performing analyses of biological samples.

Comparative neuropharmacology of structurally distinct non-fentanyl opioids that are appearing on recreational drug markets worldwide

BACKGROUND

The emergence of novel synthetic opioids (NSOs) is contributing to the opioid overdose crisis. While fentanyl analogs have historically dominated the NSO market, a shift towards non-fentanyl compounds is now occurring.

METHODS

Here, we examined the neuropharmacology of structurally distinct non-fentanyl NSOs, including U-47700, isotonitazene, brorphine, and N-desethyl isotonitazene, as compared to morphine and fentanyl. Compounds were tested in vitro using opioid receptor binding assays in rat brain tissue and by monitoring forskolin-stimulated cAMP accumulation in cells expressing the human mu-opioid receptor (MOR). Compounds were administered subcutaneously to male Sprague-Dawley rats, and hot plate antinociception, catalepsy score, and body temperature changes were measured.

RESULTS

Receptor binding results revealed high MOR selectivity for all compounds, with MOR affinities comparable to those of morphine and fentanyl (i.e., nM). All drugs acted as full-efficacy MOR agonists in the cyclic AMP assay, but nitazene analogs had greater functional potencies (i.e., pM) compared to the other drugs (i.e., nM). When administered to rats, all compounds induced opioid-like antinociception, catalepsy, and body temperature changes, but nitazenes were the most potent. Similar to fentanyl, the nitazenes had faster onset and decline of in vivo effects when compared to morphine. In vivo potencies to induce antinociception and catalepsy (i.e., ED₅₀s) correlated with in vitro functional potencies (i.e., EC₅₀s) but not binding affinities (i.e., K_is) at MOR.

CONCLUSIONS

Collectively, our findings indicate that non-fentanyl NSOs pose grave danger to those individuals who use opioids. Continued vigilance is needed to identify and characterize synthetic opioids as they emerge in clandestine drug markets.