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Papers of the Week

Papers: 13 Jun 2020 - 19 Jun 2020

Animal Studies, Pharmacology/Drug Development

2020 Jun 10


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


Truver MT, Smith CR, Garibay N, Kopajtic TA, Swortwood MJ, Baumann MH
Neuropharmacology. 2020 Jun 10:108195.
PMID: 32533977.


Novel synthetic opioids are appearing in recreational drug markets worldwide as adulterants in heroin or ingredients in counterfeit analgesic medications. 3,4-Dichloro-N-[(1R,2R)-2-(dimethylamino)cyclohexyl]-N-methylbenzamide (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later, rats received s.c. injections of U-47700 HCl (0.3, 1.0 or 3.0 mg/kg) or saline, and blood samples (0.3 mL) were withdrawn via i.v. catheters at 15, 30, 60, 120, 240, 480 min post-injection.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 (ED = 0.5 mg/kg) and catalepsy (ED = 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 (C) achieved by 15-38 min. C 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.