Oxycodone in Forensic Toxicology : Analytical Strategies and Interpretation

Abstract: Oxycodone is a common finding in forensic casework and widely used as an analgetic. Oxycodone’s pharmacokinetic and pharmacodynamic properties make the interpretation of post mortem oxycodone blood concentrations complicated. Coadministered substances and inter-individual differences in metabolic capacity can alter the oxycodone blood concentration and thereby cause an unexpected pharmacological effect and possibly lead to negative side-effects, respiratory depression, and death. As the level of tolerance often is unknown in post mortem cases the correlation between blood concentration and effect is weak. In this thesis, the overall aim was to increase the ability to determine cause and manner of death in suspected oxycodone intoxications, by studying concentrations of oxycodone and its metabolites, CYP2D6 phenotype, as well as endogenous substances in post mortem cases. Moreover, trends and patterns in prescription and post mortem findings of substances causing pharmacodynamic and pharmacokinetic interactions with oxycodone were studied.In paper I, concentrations of oxycodone, noroxycodone, oxymorphone and noroxymorphone were determined in femoral blood from 192 post mortem cases by LC-MS/MS. Concentrations and the metabolite-to-parent drug ratio were studied in groups separated by cause of death, A) intoxication by oxycodone, B) intoxication caused by oxycodone and additional substance/s, C) intoxication where oxycodone did not contribute, D) other causes of death than intoxication. It was found that concentrations above 0.2 μg/g indicate an oxycodone intoxication but that concentrations up to 0.3 μg/g can be seen in tolerant individuals. The results also demonstrated that a low noroxycodone/oxycodone ratio indicates an oxycodone intoxication. Paper II included LC-MS/MS analysis as in paper I, and in addition, genotyping for CYP2D6 enzyme activity in 174 cases. The metabolite-to-parent drug ratios were compared between poor, intermediate, extensive, and ultra-rapid metabolizers. It was concluded that with knowledge of CYP2D6 activity the oxymorphone/oxycodone ratio could distinguish between oxycodone-related deaths and other causes of deaths. Paper III was a pharmacoepidemiological study where post mortem findings were investigated in combination with prescription records in 1081 cases to evaluate the presence of interacting drugs in oxycodone-related intoxications. One of the main findings was that pharmacodynamically interacting drugs were twice as often prescribed, and five times more common as a co-finding in oxycodone-related intoxications compared to other causes of death. An oxycodone prescription was missing in 34% of all cases, with a trend that individuals, 35 years or below, more often lacked an oxycodone prescription. In paper IV, the post mortem metabolome was explored in 934 cases to reveal possible biomarkers correlated with oxycodone intoxications. The results showed that levels of acylcarnitines, a group of endogenous substances involved in mitochondrial metabolism, were significantly decreased in oxycodone-related intoxications compared to a control group, revealing post mortem metabolome analysis as a possible complemental approach of interpretation in post mortem toxicology.In conclusion, this thesis emphasizes the importance of including metabolites in the toxicological analytical strategy to improve the interpretation in post mortem case work. Also, the applicability of pharmacogenetic analysis is highly useful in certain cases. Furthermore, the use of post mortem metabolomics is a possible future promising strategy to the early identification of oxycodone-related deaths.