Development of a method to evaluate the effects of external environments on drug stability in nails using micro‐segmental analysis

Abstract

Nails can be used as an alternative to hair for examining past drug use. However, daily hand‐and‐nail care can eliminate the internal drugs. Therefore, we developed an evaluation method to examine the effects of the external environment on drug stability in nails using micro‐segmental analysis. First, reference nails containing drugs were prepared by collecting fingernails from participants who had consumed hay‐fever medicines continuously for 4 months. Next, the entire free edge of a reference nail was cut into halves at the centerline; one side was stored as an untreated block, and the other was treated with various hand/nail care products. Both nail blocks were washed and segmented at 0.5‐mm intervals in the width direction. Each segment in the extraction solution was crushed with stainless‐steel beads, sonicated, and soaked in the solution for 24 h. The analytes in extracts were quantified by LC–MS/MS, and the drug concentrations between the treated and untreated blocks were compared. The drug concentrations decreased slightly in nails treated with manicure and gel‐nail products. The analytes in nails tended to be lower in water‐rich products such as hand soap and hand cream than in oil‐rich products such as nailcare oil and acetone‐free remover. The developed method using micro‐segmental analysis enabled the evaluation of the effects of various hand/nail care products on drug stability in a limited number of nails. This would also be useful for examining the effects of severe environments on drugs in nails collected from cases of unnatural death.