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 after both systemic administration and external exposure. BALB/c mice were treated with fentanyl, and the drug's concentration in hair was measured. It was found that fentanyl binds tightly to the hair matrix, with 94% residing in water-inaccessible compartments. The study also explored how chemical modifications to hair proteins affect fentanyl uptake. Esterification reduced fentanyl uptake, indicating the importance of carboxylic acid groups, while acetylation increased uptake and recovery, suggesting the creation of a less polar compartment. These findings highlighted the significant role of hair's ionizable functionalities in drug accumulation from organic solutions.