Quantification of U-47700 and its metabolites in plasma by LC-MS/MS

Novel Synthetic Opioids (NSO) have caused a recent epidemic both nationally and globally. NSO have gained popularity in the illicit drug market and have brought about an increase in fentanyl and its derivatives, as well as other chemically unrelated opioid agonists. U-47700, a non-fentanyl analog analgesic opioid, was first developed by The Upjohn Company and has a reported potency of 7.5 times that of morphine. Like many NSO, U-47700 is usually sold as a research chemical that can be purchased online but can also be found in "Gray Death" which is a mixture of fentanyl(s), heroin, and U-47700. With the emergence of these NSO, there is a need for laboratories to be able to detect these drugs in various matrices. In this study, a liquid chromatography tandem mass spectrometry (LC-MS/MS) method was optimized and validated to detect and quantify U-47700 and its metabolites, N-desmethyl-U-47700 and N,N-didesmethyl-U-47700, in 100 μL human plasma using an optimized solid phase extraction procedure. A small sample size (100 μL) was utilized for a future pharmacokinetic study in rats. The method was validated according to SWGTOX guidelines, including: precision and bias, linearity, carryover, interferences, matrix effects, limit of detection (LOD), limit of quantification (LOQ), dilution integrity, and stability. The LOD were 0.05 ng/mL for U-47700 and N-desmethyl-U-47700 and 0.1 ng/mL for N,N-didesmethyl-U-47700. Linear ranges for U-47700 and N-desmethyl-U-47700 were 0.1-100 ng/mL and 0.5-100 ng/mL for N,N-didesmethyl-U-47700. Matrix effects were analyzed following the post-extraction addition approach and were <5%, indicating little ion suppression or enhancement. Extraction recovery was >79%. Analytes were stable in all conditions and no endogenous or exogenous interferences were detected. This method was cross-validated in rat plasma with acceptable bias (2.1-6.2%) and precision (-14.7-15.7%) within acceptable limits. Matrix effects and extraction efficiency was comparable to human plasma validation. Postmortem whole blood samples (n = 15) were analyzed with the validated method. U-47700, N-desmethyl-U-47700 and N,N-didesmethyl-U-47700 concentration ranges were 1.1-1367 ng/mL, 4.0-1400 ng/mL and 0.7-658 ng/mL, respectively.