FENTANYL IN HAIR - CHEMICAL FACTORS INVOLVED IN ACCUMULATION AND RETENTION OF FENTANYL IN HAIR AFTER EXTERNAL EXPOSURE OR IN-VIVO DEPOSITION

The levels of fentanyl extractable from mouse hair after chronic syste mic administration and the suitability of externally loaded hair sampl es for establishing control and comparison samples were determined. Ad ditionally, the effects of chemical modification of specific polar fun ctionalities within the hair protein matrix on the deposition and reco very of fentanyl in hair subjected to external loading were determined . BALB/c mice entering a second phase of synchronized hair growth were treated ip with fentanyl (0.02, 0.05, or 0.10 mg/kg) on Monday, Wedne sday, and Friday for 3 weeks. At that time, fentanyl concentrations in hair, as determined by GC/MS, were 0.025-0.050 ng/mg of hair. Hair sa mples exposed to fentanyl in phosphate buffer (ionized drug) showed no significant accumulation of drug into the hair, as determined by loss of fentanyl from the loading solution or by extraction of the hair. H air samples exposed to nonionized fentanyl in methanolic solution (10, 50, and 100 ng/ml) showed significant accumulation of drug in the hai r and significant removal of drug from the incubation solution. Fentan yl removal from solution plateaued after 24 hr, suggesting equilibrati on between fentanyl in solution and fentanyl in the hair. A mass balan ce between drug lost from the incubation solution and drug recovered f rom hair samples suggests that 94% of accumulated fentanyl is tightly bound to the hair matrix or resides in water-inaccessible compartments within the hair; These results suggest that fentanyl accumulation aft er in vivo administration differs, in the nature of storage, from fent anyl accumulation from external solutions and that external spiking of hair may not provide suitable control samples. Chemical modification of hair protein functionalities (reaction with diazomethane to esterif y carboxylic acid groups or with acetic anhydride and pyridine to acet ylate amine and hydroxyl functionalities) led to reproducible protein structure modification, as demonstrated by Fourier transform-IR and by pH titration. Hair from BALB/c mice was used. The accumulation of fen tanyl was examined in hair samples exposed to fentanyl in methanol or methylene chloride solutions (10 ng/ml, 24 hr). Fentanyl was recovered from hair by 24-hr extraction in phosphate buffer, pH 6. Esterificati on of hair resulted in significantly less uptake of nonionized fentany l from a methanolic solution and significantly lower recovery of drug from hair, relative to untreated hair, suggesting that carboxylic acid functionalities are necessary for the incorporation of drug. Acetylat ion of hair resulted in increased removal of fentanyl from methylene c hloride solutions and increased recovery of fentanyl, This is consiste nt with the creation or expansion of a less polar compartment. Fentany l uptake from a methanolic solution was also greater in acetylated hai r. These results demonstrate that solution-accessible ionizable functi onalities of hair play a significant role in the accumulation and rete ntion of nonionized fentanyl from organic solutions.