Fentanyl in postmortem forensic toxicology

CONTEXT: Fentanyl is a powerful opioid used for the induction of anesthesia as well as for the management of severe pain. In recent years, transdermal fentanyl "patches" have become popular for outpatient management of chronic pain. The high potency and outpatient availability of fentanyl has also made it a highly sought-after drug of abuse. Deaths in which fentanyl is detected challenge medical examiners who must decide whether a given case represents therapeutic administration or overdose. OBJECTIVES: The current review seeks to present data about fentanyl that are relevant to the interpretation of postmortem blood and tissue fentanyl concentrations as well as to highlight areas which can be helpful or misleading in the evaluation of deaths potentially related to fentanyl exposure. METHODS: Standard searching of the PubMed database for studies, case series, and case reports involving fentanyl kinetics, chemistry, and postmortem behavior was performed. Search terms typically included "postmortem" and "fentanyl," as well as "kinetics" and "analysis," where appropriate. Additional references were located as citations from reviewed papers or as conference abstracts. RESULTS AND CONCLUSIONS: The postmortem behavior of fentanyl is influenced heavily by pH changes and the antemortem kinetic behavior of the drug, especially, by its distribution. Postmortem blood fentanyl concentrations do not correlate directly with antemortem blood concentrations. Without adequate evaluation of kinetic data, investigative information and consideration of postmortem changes, misinterpretation of postmortem fentanyl results is likely.