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Case Highlights: Drug overdose vs mixed drug intoxications

By The Forensic Experts Group

The deceased’s sister took the insurance firm to Court to seek pay-outs on two personal accident policies. Our expert was requested to review toxicology reports to provide independent opinions on potential adverse drug interactions, and on the allegedly “elevated” concentrations of four prescribed drugs identified in postmortem blood. Our TFEG expert reported that two drugs (bromazepam and mirtazapine) were actually below toxic levels in living persons, and could not be rightly described as “elevated”. Additionally, based on the findings from a recent Finnish study where duloxetine, mirtazapine and olanzapine were encountered in respectively, 109, 2179 and 1127 of postmortem cases, the concentrations of these three drugs in the deceased’s blood were below the postmortem blood concentrations of fatal poisoning cases. Thus, the levels of the four drugs in the deceased were not excessive, and did not provide evidence of overdose.

“Insurance suit: Man’s death ‘not accident”, The Straits Times (2 Apr 2016).

The Science behind it

Postmortem toxicology has been described as a “toxicological nightmare”, owing to postmortem drug redistribution (“PMR”).8 PMR refers to the processes by which drugs, toxicants and metabolites move between tissues, organs and body fluids after death. This well-known phenomenon, which can significantly change drug concentrations after death, was first reported in the mid-1970s. Large errors and wrong conclusions can arise when postmortem measurements are used to estimate antemortem drug concentrations and the ingested dose.

  1. Postmortem drug levels can be greatly affected by drug properties, cadaver handling and storage conditions, cardiopulmonary resuscitation attempts, the chosen site (eg heart, femoral vein, liver, etc), time interval after death, and the technique for postmortem blood sampling.
  2. There is often no reliable or obvious relation between concentrations measured before and after death. Thus, comparison of postmortem levels with compilations of therapeutic and toxic drug levels in living persons in order to determine overdose can be misleading, and can lead to miscarriages of justice.
  3. The case history and circumstances of any fatality suspected to be caused by overdose must be carefully evaluated. Leading forensic practitioners repeatedly warn that postmortem drug concentrations have been over-interpreted in the past.
  4. The awaited solution to this conundrum has been the development in recent years of large databases of post-mortem drug levels in drug-induced deaths (fatal poisonings), and deaths not caused by drugs present. Earlier postmortem studies suffered from small sample sizes, limited drug types, varied sampling procedures and disparate analytical techniques. In 2009, Swedish toxicologists Jones and Holmgren reported concentration distributions  of 25 common drug in femoral blood from 24,876 autopsies. In 2014, Finnish analytical chemists Launiainen and Ojanpera followed up with the largest and most comprehensive study ever undertaken on drug levels in postmortem blood; this landmark study involved 129 drugs and 57,903 autopsy cases over an 11-year period. The sheer size of this database makes it a reliable and valuable source of objective reference data for the forensic practitioner when interpreting postmortem toxicology results, instead of comparing with therapeutic drug levels in living persons, a method questioned by members in the scientific and medical community, or relying solely on the experience of the practitioner. Read more about “Forensic Toxicology”.