Evaluation of applicability of micro-segmental analysis to hair treated with heat and haircare products.

Purpose: Micro-segmental analysis (MSA), which enables the measurement of detailed drug distributions in hair by segmenting a single hair strand at 0.4 mm intervals, is indispensable for estimating the day of drug ingestion. However, haircare with dryers and various products can influence drug concentrations in hair. Therefore, the applicability of MSA to hair that was treated with heat or various haircare products was evaluated.

Methods: Reference hair strands containing drugs consistently along the hair shafts were collected from patients who ingested four hay-fever medicines (fexofenadine, epinastine, cetirizine, and loratadine) daily for 4 months. The hair strands were divided into eight 4 mm regions from the proximal end, and each region was placed on an electric hot plate at 100-200 °C or soaked in haircare products, such as shampoo and bleaching agent. The hair regions were subjected to MSA. Moreover, after a patient was administered midazolam at a single dose and the hair was bleached, the day of midazolam administration was estimated using MSA.

Results: Repetitive heating for 1 min and daily haircare products, such as shampoo, hardly affected the drugs in hair, whereas bleaching products containing H₂O₂ decreased the amounts of hay-fever medicines in the hair up to 58%. However, the amount of midazolam did not decrease in bleached hair and the day of midazolam administration was successfully estimated.

Conclusions: The analytes used in this study were minimally affected by ordinary haircare and could be detected even in bleached hair. Therefore, MSA can be applicable regardless of haircare history.