A metabolite reported as a strong chromatographic peak has not necessarily been quantitatively measured. In a detailed MDMB-CHMICA autopsy investigation, relative metabolite signals helped identify useful analytical targets, but they did not establish metabolite concentrations, amounts in the body or a precise time of exposure.
What was studied in the laboratory and the autopsy
Gaunitz and colleagues combined one human postmortem case with duplicate pooled human liver microsome incubations and a negative incubation control. The microsomal experiment used a final MDMB-CHMICA concentration of 4 µg/mL. The autopsy was performed approximately 12 hours after the death of a 27-year-old man following a high fall.
Blood, urine, tissues and gastric content were available. Parent-drug MDMB-CHMICA was quantified separately, including 1.7 ng/mL in femoral blood. THC, amphetamine and MDMA were also present in femoral blood. The metabolite investigation was therefore conducted alongside, rather than in place of, a broader multidrug examination.
Product-ion scans supplied structural evidence
The investigators screened proposed metabolite pathways by liquid chromatography–electrospray tandem mass spectrometry using product-ion scans at two collision energies. Monohydroxylated metabolites were investigated at precursor m/z 401; ester hydrolysis at m/z 371; hydrolysis plus hydroxylation at m/z 387; and hydrolysis plus two hydroxylations at m/z 403. Fragment patterns helped assign which part of the molecule had changed.
The microsomal work detected seven monohydroxylated metabolites: six assigned to hydroxylation of the cyclohexylmethyl portion and one to hydroxylation of the indole portion. Additional signals were not accepted as further identified metabolites when suitable fragment evidence was lacking. Some apparent signals also occurred in negative controls and were attributed to matrix components.
This distinction matters: a peak at an expected precursor mass is a candidate signal, not automatically a confirmed metabolite. Reference evidence, fragmentation and controls determine how far identification can go.
The most abundant signal depended on the specimen
Monohydroxylated metabolites predominated in the microsomal extracts and were detected in postmortem blood, liver, psoas muscle and urine. One metabolite peak was strongest in liver and urine, while a different peak was strongest in the blood specimens and psoas. A metabolite prominent in the latter matrices was not detected in liver or urine.
The ester-hydrolysis product was detected in liver but not urine in this case. Hydrolyzed products with further hydroxylation were also restricted to liver among the postmortem specimens examined. No metabolites were found in brain, kidney, lung or gastric content under the study’s screening conditions, even though parent drug was detected in those specimens.
These are detection findings from one case. Absence under a particular extraction and scan method does not establish biological absence of all metabolites. Differences in extraction, instrument sensitivity, collection timing and matrix remain possible influences.
Why “100% intensity” did not mean 100% of the drug
The study expressed metabolite signals relative to the most abundant metabolite signal. A value of 100% identified the reference peak for that comparison. It did not mean that the metabolite represented all of the drug-derived material, or that its concentration was known in ng/mL or ng/g.
Different compounds can generate different signal responses. Without validated metabolite-specific calibration and suitable standards, peak-height or peak-intensity comparisons cannot be treated as molar ratios. The parent-drug quantitation procedures do not automatically validate quantitative measurement of every metabolite screened.
Target selection is different from dating exposure
The authors considered monohydroxylated metabolites useful targets for detecting MDMB-CHMICA intake. They also interpreted parent drug in urine and a limited urinary metabolite pattern as supporting use near death. The study did not test a controlled series with known exposure times, so it cannot turn that pattern into an individual exposure clock.
Microsomal incubation is also an in vitro metabolism experiment, not a model of decomposition in a cadaver. Similarity between a microsomal product and an autopsy signal does not establish whether a particular concentration changed after death. Detection of parent drug and metabolites remains separate from proof of impairment or cause of death.
For complementary analytical distinctions, see accurate mass and compound identification and specimen choice for postmortem screening.
Primary source
Gaunitz F, Lehmann S, Thomas A, Thevis M, Rothschild MA, Mercer-Chalmers-Bender K. Post-mortem distribution of the synthetic cannabinoid MDMB-CHMICA and its metabolites in a case of combined drug intoxication. International Journal of Legal Medicine. 2018;132:1645–1657. https://doi.org/10.1007/s00414-018-1911-8.
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