Postmortem Drug Redistribution

Abstract

Postmortem drug concentrations in blood may not always reflect antemortem drug concentrations in blood due to the movement of the drugs after death. The phenomenon is referred to as Postmortem Redistribution (PMR). Mechanisms involved in postmortem redistribution are both complicated and poorly understood. However, postmortem drug concentrations in blood do follow some generally accepted trends that aid with interpretation; the characteristics of the drug itself can be used to indicate if a drug is subject to PMR. Large changes in blood drug concentrations are predicted for basic, lipophilic drugs with a high volume of distribution (>3L/kg). When PMR occurs, blood specimens drawn from the central body cavity and heart generally will have higher drug concentrations postmortem than specimens drawn from peripheral areas, most commonly the femoral vein. The diffusion of drugs from organ tissue into the blood may explain the observed phenomenon [1]. To compensate for PMR, postmortem blood specimens are recommended to be collected from at least two areas of the body at autopsy; a peripheral area and a central area (often the heart), so that a comparison can be made. While antemortem blood specimens are especially helpful in interpreting postmortem blood drug concentrations, relevant specimens are only very rarely available. In a set of case studies of six drugs, drug concentrations in postmortem femoral blood specimens always exceeded the antemortem concentrations in five cases, suggesting that even peripheral blood may still exhibit some redistribution [2]. The study did not, however, report the postmortem interval been death and autopsy. It appeared that a partial answer to the difficulties associated with interpretation of postmortem drug concentrations was provided by two papers published in the 1990s. The first provided detailed information about blood drug concentrations attained from different sites for over fifty drugs [3]. The second provided a tabular list of the drug concentrations from both cardiac and peripheral blood samples expressed as a ratio of cardiac to peripheral blood (C/P) for over one hundred drugs [4]. The C/P ratio became the accepted benchmark with the accepted guideline that “high ratios” were associated with “potential for redistribution” [4]. This guideline was repeated in a review published a few years later that republished the C/P ratios for many of the drugs included in the Dalpe-Scott and coworker’s paper