"There is no relationship between what you find in a living person and what you find in a dead person," Bruce Goldberger, vice-president of the American Academy of Forensic Sciences and editor of the Journal of Analytical Toxicology told New Scientist.
To spread the word about the error, Steven Karch, a pathologist at the San Francisco Medical Examiner's office set up an ad hoc committee of senior forensic toxicologists and pathologists, including Goldberger, at the American Academy of Forensic Sciences conference in Dallas, Texas, last month. They plan to publish scientific papers in general medical journals highlighting the issue.
In living patients, the dose someone has been given is calculated by multiplying their body weight, the concentration of the drug in their blood and a constant called the "apparent volume of distribution" (Vd). The Vd is a fudge factor that averages out the distribution of a particular drug between tissues in the body. The Vd of any particular drug depends on how it interacts with an individual's cells.
Studies have suggested that the Vd for some drugs can vary fivefold or more between different individuals, and the results also depend on when the drug was administered. So the technique is approximate, at best, even in the living. But Derrick Pounder at the University of Dundee, UK, another member of the committee, says the method fails completely in a dead body. "There is an assumption on the part of some people that a corpse is a frozen living person," he says. "But drug levels don't remain static after death."