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Drugs and other toxins Blood and/or tissue distribution

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  P213-214

2026-10-14

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Drugs and other toxins

Blood and/or tissue distribution

Liver and brain have been used extensively for the postmortem measurement of drugs. Initially, tissues were used because many drugs are present at concentrations of up to 10–50 times that in blood, and because tissues provided a large volume of material for extraction and analysis. This was essential in the days when physical isolation of the poison, crystallisation and pharmacological testing was a goal. As analytical methods improved, analyses for most drugs could be performed on blood, leading to a trend in the analysis of blood alone. However, with the recognition that redistribution and related phenomena could seriously decrease confidence in postmortem blood drug concentrations, analysis of tissues is regaining importance. While concentrations of some drugs can increase by as much as 2- to 10-fold after death in postmortem blood, concentrations in tissues such as liver remain relatively stable. The problem lies with the interpretation of tissue drug concentrations. Unlike in blood, reference ranges for drugs in tissues are not obtainable from clinical studies, and animal data are not directly transferable to humans. Forensic toxicologists have to rely on empirical data from other cases in their own laboratories, or on published material. To be useful, such postmortem data must include cases in which drugs are likely to have been taken in therapeutic doses, not just overdose cases. The question can be posed, ‘How do you convert a tissue concentration into a blood concentration?’ You do not. Organs are anatomically distinct entities with different kinetics from blood. Although it is generally true that very high blood concentrations tend to be associated with high tissue concentrations and that a useful relationship can be demonstrated, there is too much variation to attempt mathematical conversion for any single case. Although virtually no studies have examined dose time–concentration relationship in tissues, and certainly none in humans, some studies have demonstrated marked variation in drug concentrations within an organ, such as the liver and the brain. This further demonstrates why caution must be exercised in attempting to convert tissue concentrations into an equivalent blood concentration. A tissue concentration provides an additional piece of the puzzle. Multiple tissue concentrations provide additional pieces, and help to build a picture of the body burden of the drug in a qualitative sense. This information, together with blood concentrations, information from the autopsy and the circumstances of death, can help formulate informed conclusions about the role of the drugs (if any) in a death.