Analgesic and other pharmacological activities of a new narcotic antagonist analgesic (-)-1-(3-methyl-2-butenyl)-4-[2-(3-hydroxyphenyl)-1-phenylethyl]-piperazine and its enantiomorph in experimental animals

Novel Synthetic Opioids: The Pathologist's Point of View

Background: New Psychoactive Substances (NPS) constitute a broad range of hundreds of natural and synthetic drugs, including synthetic opioids, synthetic cannabinoids, synthetic cathinones, and other NPS classes, which were not controlled from 1961 to 1971 by the United Nations drug control conventions. Among these, synthetic opioids represent a major threat to public health. Methods: A literature search was carried out using public databases (such as PubMed, Google Scholar, and Scopus) to survey fentanyl-, fentanyl analogs-, and other synthetic opioid-related deaths. Keywords including “fentanyl”, “fentanyl analogs”, “death”, “overdose”, “intoxication”, “synthetic opioids”, “Novel Psychoactive Substances”, “MT-45”, “AH-7921”, and “U-47700” were used for the inquiry. Results: From our literature examination, we inferred the frequent implication of fentanyls and synthetic opioids in side effects, which primarily affected the central nervous system and the cardiovascular and pulmonary systems. The data showed a great variety of substances and lethal concentrations. Multidrug-related deaths appeared very common, in most reported cases. Conclusions: The investigation of the contribution of novel synthetic opioid intoxication to death should be based on a multidisciplinary approach aimed at framing each case and directing the investigation towards targeted toxicological analyses.

Identification of MT-45 Metabolites: In Silico Prediction, In Vitro Incubation with Rat Hepatocytes and In Vivo Confirmation

MT-45 is a synthetic opioid with a pharmacological activity comparable to morphine and it has been involved in intoxications and fatalities reported in Europe and in USA. It was recently subject to control measures, but to date the metabolic pathways of the substance are still unknown. Using rat hepatocytes and LC-HRMS, 14 novel Phase I and II MT-45 metabolites were identified, products of monohydroxylation, dihydroxylation and N-dealkylation; glucuronide conjugation of mono- and dihydroxylated metabolites also occurred. The detected metabolites were firstly predicted in silico, then incubation of the drug with rat hepatocytes was carried out and the obtained metabolites were identified by LC-HRMS, with retention times, mass shift between theoretical mass and observed mass (<5 ppm), peak abundance and fragmentation pattern. Hydroxylated MT-45 was found to be the major metabolite of MT-45 in vitro experiments. The presence of all metabolites was confirmed by in vivo experiments in urine samples of CD-1 male mice; in these samples hydroxy-MT-45-glucuronide and di-hydroxy-MT-45-glucuronide are the most abundant metabolites, while the parent drug is found at concentration <10 ng mL-1 after 300 min. The knowledge of Phase I and II MT-45 metabolite structure is then crucial to develop analytical methods to identify MT-45 consumption in clinical and forensic testing.

Central actions of AD-1211, an analgesic lacking common opiate features

The site of the analgesic action of AD-1211, the less active stereoisomer, and its pharmacological features were investigated. AD-1211, as well as pentazocine and morphine, blocked the reflex hypertension caused by injection of both bradykinin and bradykinin plus PGE1 into the splenic artery of dogs. In the rat or mouse writhing test, the analgesic activity of AD-1211 after intraperitoneal and intracisternal administration was equal to and more than 40 times, respectively, that after intravenous administration. The analgesic activity of AD-1211, unlike that of pentazocine and morphine, was incompletely reversed by naloxone and was not attenuated even by its repeated administration for 7 days in the mouse writhing and tail pressure test, respectively. AD-1211, unlike pentazocine and/or morphine, lacked some effects on central nervous, respiratory and cardiovascular function in conscious animals. These results demonstrate that AD-1211 produces its analgesic action through a central mechanism but lacks some of the common pharmacological actions shown by morphine-like analgesics.