Comparative study of post-mortem concentrations of benzodiazepines and z-hypnotics in several different matrices.

Benzodiazepines and z-hypnotics are detected in the majority of fatal overdose cases in Norway, often in combination with other drugs of abuse, and their concentrations in peripheral blood might be important to elucidate the cause of death. In some forensic autopsies, peripheral blood is however not available. The aim of the present study was to compare concentrations of benzodiazepines and z-hypnotics in five alternative matrices to assess whether these concentrations are comparable to concentrations in peripheral blood. A total of 109 forensic autopsy cases were included. Peripheral blood, cardiac blood, pericardial fluid, psoas muscle, lateral vastus muscle and vitreous humour from each case were analysed using UHPLC-MS/MS. We were able to detect clonazepam, 7-aminoclonazepam, flunitrazepam, 7-aminoflunitrazepam, nitrazepam, 7-aminonitrazepam, diazepam, nordiazepam, oxazepam, alprazolam, midazolam, zopiclone and zolpidem in all the analysed matrices. Concentrations measured in vitreous humour were generally much lower than those of peripheral blood for all compounds except zopiclone. 7-amino metabolite concentrations were high compared to the parent compounds, although less so for the muscle samples. In muscles, concentrations of the parent nitrobenzodiazepines were higher than in peripheral blood, but for the other compounds, concentrations in muscle showed good correspondence with peripheral blood. Both cardiac blood and pericardial fluid were viable alternative matrices for peripheral blood, although a larger variation and a tendency for higher concentrations in pericardial fluid was observed. This study shows that cardiac blood, psoas and lateral vastus muscle samples and pericardial fluid can give comparable concentrations to peripheral blood for benzodiazepines and z-hypnotics, while vitreous humour was less suitable. The concentrations in alternative matrices must, however, be interpreted carefully.