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Drugs and other toxins , Blood and/or plasma distribution

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  213

2026-10-14

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Drugs and other toxins

Blood and/or plasma distribution

One issue that is often overlooked in comparing postmortem data with that from living patients, is that most postmortem laboratories analyse whole blood, whereas clinical laboratories invariably analyse serum or plasma. Many drugs are not evenly distributed between plasma and erythrocytes, and therefore concentrations may be misrepresented by a factor of up to two or more. For example, digitoxin is primarily distributed into plasma, with virtually none in the red cells, with a blood: plasma ratio of 0.5, whereas digoxin has a blood: plasma ratio of close to 1.0 (Lukas and Peterson 1966; Abshagen et al. 1971). Similarly, D9-tetrahydrocannabinol (D9-THC) has a blood: plasma ratio approaching 0.5, which indicates that most of the drug is distributed in the plasma, with little in the erythrocytes (Mason and McBay 1985). The significance of this is that most postmortem measurements are conducted on whole blood, whereas many of the pharmacokinetic data are based on plasma measurement. Although the blood : plasma distribution is not likely to have as big an influence on interpretation as post mortem redistribution for some drugs, it is a factor that should not be overlooked, particularly if the analytical results are being compared with those obtained from plasma and/or serum specimens.