Characterizing metabolites and potential metabolic pathways for the novel psychoactive substance methoxetamine.

The classic approach of controlled volunteer studies to study drug metabolism is difficult or impossible to undertake for novel psychoactive substances (NPS), as there is generally very limited information available to allow appropriate dose finding and safety. A viable and powerful alternative is the identification and characterization of phase I and II metabolites of such drugs by examining the concordance of data gathered from analysis of microsomal incubates with that from analysis of specimens collected from individuals with analytically confirmed use of NPS. Liquid chromatography-high resolution mass spectrometry provides the ability to reliably identify such metabolites. We used this technique here to study the metabolism of the ketamine analogue methoxetamine. A large number of metabolites were identified in the in vitro studies including normethoxetamine, O-desmethylmethoxetamine, dihydromethoxetamine, dehydromethoxetamine and several structural isomers of hydroxymethoxetamine and hydroxynormethoxetamine. pH dependent liquid-liquid extraction was used to discriminate phenolic from alcoholic metabolites. Phase II glucuronide conjugates included those of O-desmethylmethoxetamine, O-desmethylnormethoxetamine and O-desmethylhydroxymethoxetamine. The majority of these phase I and II metabolites were confirmed to be present in urine collected from three individuals presenting with acute methoxetamine toxicity.

The poppy seed defense: a novel solution.

A major toxicological challenge is distinguishing whether morphine in urine, in the absence of 6-monoacetylmorphine (6-MAM), originates from 'street' heroin use or poppy seed ingestion. Manufacturing byproducts from the synthesis of illicit heroin include those that originate from the reaction of acetic anhydride with the alkaloid impurity, thebaine, which undergoes skeletal rearrangement, resulting in compounds with a 2-(N-methylacetamido)ethyl side-chain. The hypothesis that the tertiary amide in this side-chain is resistant to endogenous hydrolysis was supported from in-vitro experiments; a glucuronide metabolite (designated 'ATM4G') was identified that may be used as a marker of 'street' heroin administration. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis for this metabolite was then performed on selected urine specimens from 22 known heroin users, these being negative on routine testing for 6-MAM by gas chromatography-mass spectrometry (GC-MS), using the generally applied reporting threshold of 10 ng/mL, but positive for the presence of morphine. Peaks corresponding to the retention time for the metabolite marker were clearly observed for 16 of the 22 samples, with variations of the ratios of its three dependent ions being within ± 30% of that produced in vitro. Conversely, 6-MAM was detected in only 3 samples, but at concentrations <1 ng/mL. Such a high frequency for the presence of the metabolite marker in urine, in the absence of 6-MAM, is noteworthy and suggests that detection of this metabolite may offer an important advance in forensic toxicology, allowing the development of a new and more definitive test for heroin abuse and thus a potential solution to the so-called 'poppy seed defense'.