Pharmacodynamics and pharmacokinetics of the novel synthetic opioid, U-47700, in male rats

Neuropharmacology. 2020 Oct 15;177:108195. doi: 10.1016/j.neuropharm.2020.108195. Epub 2020 Jun 10.


Novel synthetic opioids are appearing in recreational drug markets worldwide as adulterants in heroin or ingredients in counterfeit analgesic medications. Trans-3,4-dichloro-N-[2-(dimethylamino)cyclohexyl]-N-methyl-benzamide (U-47700) is an example of a non-fentanyl synthetic opioid linked to overdose deaths. Here, we examined the pharmacodynamics and pharmacokinetics of U-47700 in rats. Male Sprague-Dawley rats were fitted with intravenous (i.v.) catheters and subcutaneous (s.c.) temperature transponders under ketamine/xylazine anesthesia. One week later, rats received s.c. injections of U-47700 HCl (0.3, 1.0 or 3.0 mg/kg) or saline, and blood samples (0.3 mL) were withdrawn via i.v. catheters at 15, 30, 60, 120, 240, 480 min post-injection. Pharmacodynamic effects were assessed at each blood withdrawal, and plasma was assayed for U-47700 and its metabolites by liquid chromatography tandem mass spectrometry. U-47700 induced dose-related increases in hot plate latency (ED50 = 0.5 mg/kg) and catalepsy (ED50 = 1.7 mg/kg), while the 3.0 mg/kg dose also caused hypothermia. Plasma levels of U-47700 rose linearly as dose increased, with maximal concentration (Cmax) achieved by 15-38 min. Cmax values for N-desmethyl-U-47700 and N,N-didesmethyl-U-47700 were delayed but reached levels in the same range as the parent compound. Pharmacodynamic effects were correlated with plasma U-47700 and its N-desmethyl metabolite. Using radioligand binding assays, U-47700 displayed high affinity for μ-opioid receptors (Ki = 11.1 nM) whereas metabolites were more than 18-fold weaker. Our data reveal that U-47700 induces typical μ-opioid effects which are related to plasma concentrations of the parent compound. Given its high potency, U-47700 poses substantial risk to humans who are inadvertently exposed to the drug.

Keywords: Analgesia; Catalepsy; Metabolites; Opioid; U-47700.

Publication types

  • Research Support, N.I.H., Intramural

MeSH terms

  • Analgesics, Opioid / administration & dosage*
  • Analgesics, Opioid / blood*
  • Animals
  • Benzamides / administration & dosage*
  • Benzamides / blood*
  • Dose-Response Relationship, Drug
  • Injections, Subcutaneous
  • Male
  • Pain Measurement / drug effects
  • Pain Measurement / methods
  • Rats
  • Rats, Sprague-Dawley
  • Synthetic Drugs / administration & dosage*
  • Synthetic Drugs / metabolism*


  • Analgesics, Opioid
  • Benzamides
  • Synthetic Drugs
  • U-47700