Emerging Drugs and “Fatal Ranges”: How to Evaluate Concentration Testimony
A concentration reported in a fatal case is not automatically a concentration that caused the death. This distinction is especially important for emerging drugs, where published data may consist largely of selected case reports and series with multiple co-exposures.
The evidentiary question is not whether the substance can be dangerous. It is what the measured result, together with the rest of the record, supports about this event. General toxic potential and individual causation require related but different reasoning.
An instructive medetomidine comparison
In a 100-specimen case series, reported medetomidine blood concentrations overlapped between nonfatal overdoses, 0.1–16 ng/mL, and fatal overdoses, 0.1–32 ng/mL. The reported medians were 1.5 and 0.31 ng/mL, respectively. Fentanyl was co-detected in 93% of cases. These observations do not supply a fatal threshold or show that lower concentrations are more dangerous. Walton et al., peer-reviewed study, online May 8, 2025; abstract-only access, DOI: 10.1093/jat/bkaf040.
The full sampling, timing, and subgroup details must be examined before deeper comparison. The abstract is sufficient to identify overlap; it is not sufficient to construct a concentration-based mortality prediction model.
Ask what the comparison population represents
When an expert relies on a published range, establish how the cases entered the dataset. Were they deaths attributed to the substance, deaths with the substance detected, emergency presentations, or laboratory submissions selected for expanded testing? Ask whether the cited endpoint is death from any cause or a reasoned attribution to the drug.
The minimum and maximum of a case series are descriptive boundaries of observed values. They do not reveal how common each value was, establish a safe level below the minimum, or identify a lethal level above it. A survival at one concentration likewise does not prove that concentration safe for everyone.
Examine co-exposures and treatment rather than assuming that a single analyte explains the whole comparison. If those variables were incompletely measured, that uncertainty belongs in the opinion.
Match the specimen before matching the number
Record whether the case result came from antemortem blood, postmortem peripheral blood, central blood, serum, plasma, or another matrix. Request the exact collection site, time, preservation, and handling history. A numerical comparison should not conceal differences in what was measured.
Postmortem redistribution and specimen changes are questions to evaluate, not universal correction factors. Without applicable compound-specific evidence, an expert should not announce that a postmortem value can be converted into the concentration during life by a standard multiplier.
Units also deserve explicit checking. A table expressed in micrograms per liter is numerically equivalent to nanograms per milliliter, while milligrams per liter differs by a factor of 1,000. Arithmetic agreement does not resolve a matrix mismatch.
Make the causal reasoning visible
Organize the report around confirmed identity, analytical reliability, physiological plausibility, temporal fit, other substances, pathology, and alternative causes. Explain how each element strengthens or weakens the proposed contribution. Where the evidence supports contribution but not exclusivity, say so.
For examination, ask the witness to distinguish “reported in fatalities” from “validated to predict fatality.” Request the source for any claimed threshold and whether it has been tested outside the cases from which it was derived. This invites a scientific explanation rather than a contest over dramatic labels.
The proper limitation is not that concentrations are useless. Concentrations can be important evidence. Their value depends on a transparent connection between the measurement and the particular opinion being offered.
