Fentanyl in Hair: Chemical Factors Involved in Accumulation and Retention After External Exposure or In Vivo Deposition

The study investigated the accumulation and retention of fentanyl in mouse hair following both systemic administration and external exposure. It was found that fentanyl concentrations in hair after systemic administration were 0.025-0.050 ng/mg. Hair exposed to nonionized fentanyl in methanolic solutions showed significant drug accumulation, unlike hair exposed to ionized fentanyl in phosphate buffer. Chemical modifications of hair proteins, such as esterification and acetylation, affected fentanyl uptake and recovery, indicating that specific hair functionalities are crucial for drug incorporation. The study concluded that fentanyl accumulation from in vivo administration differs from external exposure, and external spiking may not be suitable for control samples.