Overestimation Of Postmortem Drug Concentrations In A Fatal Pentobarbital Intoxication

Introduction Interpretation of drug concentrations in post-mortem toxicology is complicated by post-mortem redistribution (PMR) and potential peri and postmortem absorption-like processes may also occur. Discrepancies between antemortem and postmortem values may lead to significant overestimation of drug exposure at the time of death. We report a fatal pentobarbital intoxication case, showing marked postmortem concentration increases and a misleading segmental hair profile. Objectives Compare perimortem and postmortem drug concentrations across matrices; evaluate contribution of peri and postmortem absorption-like processes and PMR; assess the interpretative value of segmental hair analysis. Methods A 41-year-old male was found in cardiocirculatory arrest supine position on his bed. At the scene, two empty glass bottles (labeled as (1) pentobarbital for veterinary use and (2) a skin cosmetic product), and empty zolpidem blister packs were present. Peri-mortem blood sampling, including whole blood, serum and plasma, was performed in a hospital setting during cardiocirculatory arrest, approximately 30 minutes pre-death declaration. A forensic autopsy was performed after 7 days. Postmortem specimens included femoral and cardiac blood, vitreous humor, urine, brain, liver, kidney, lung, gastric content, and esophageal content. A 1-cm segmental hair analysis (20 segments from proximal S1 to distal S20) was performed. All results were achieved using fully validated LC–MS/MS methods. Results Perimortem concentrations were consistent across matrices, with pentobarbital ranging from 32 to 37 µg/mL and zolpidem from 6 to 12 ng/mL. Postmortem concentrations were markedly increased: femoral blood showed 162 µg/mL (pentobarbital) and 1400 ng/mL (zolpidem), while cardiac blood reached 206 µg/mL and 2500 ng/mL, respectively. Central-to-peripheral ratios were moderate (≈1.3–1.8). Vitreous humor concentrations were lower (22 µg/mL (pentobarbital) and 9 ng/mL (zolpidem). Extremely high concentrations were detected in gastric and esophageal contents, indicating a large unabsorbed drug reservoir. Tissue concentrations were elevated, particularly in liver and lung. Segmental hair analysis revealed detectable concentrations of both compounds across all segments. A similar distribution was observed in both washing and hair samples, with relatively low concentrations in proximal segments (S1–S10). Discussion Peri-mortem sampling suggests that active gastrointestinal absorption appeared to be negligible at that time. The marked increase in postmortem concentrations, including in femoral blood (≈5x for pentobarbital and ≈150x for zolpidem) is unlikely to be fully explained by PMR alone, according to literature. This finding may support a combined effect of (i) a rising concentration phase prior to arrest, (ii) passive diffusion from a large gastro-esophageal reservoir after death, and (iii) redistribution from highly perfused tissues, particularly for pentobarbital. Vitreous humor concentrations likely better reflect late perimortem blood levels, highlighting the risk of overestimation when relying solely on postmortem blood. The segmental hair pattern is more consistent with peri and postmortem external contamination (washing/hair ratio >0.5) resulting in a spatial distribution that may be misinterpretable as temporal exposure. Conclusions This case demonstrates that postmortem blood (even peripheral) concentrations may substantially exceed perimortem levels due to combined peri and postmortem absorption-like processes and PMR. Segmental hair analysis should be cautiously interpreted in such contexts. Integrated interpretation of perimortem blood, unconventional matrices (i.e. vitreous humor) is essential for accurate forensic conclusions.