Phenytoin concentration in head hair sections: a method to evaluate the history of drug use

Phenytoin (PHT) levels were determined in sections of head hair taken from 60 patients (34 males and 26 females), aged 5 to 69 years, who were regularly receiving the drug. The hair sectional analysis included dissolution, liquid phase extraction procedures, and immunoassay (Abbott TDx) or high-pressure liquid chromatography (HPLC) analytical techniques. The values of PHT levels in the hair from the first section (close to the hair root) to the fifth section for female patients were 18.0, 15.2, 13.1, 11.6, and 10.7 microg/g, respectively, according to HPLC measurements. There were no significantly different results obtained using the immunoassay technique, according to which the mean values of PHT in the hair sections were 17.9, 15.2, 13.1, 11.9, and 10.9 microg/g, respectively, from the first to the fifth sections. The corresponding mean values for male patients by HPLC and immunoassay techniques, respectively, were 17.9, 15.0, 12.5, 12.1, and 12.3 microg/g and 17.8, 14.9, 12.2, 11.9, and 121 microg/g. Generally, a reduction of drug concentrations in hair from the first to the subsequent segments was observed. The hair PHT concentrations were found to be dependent on the dosage (by fluorescence polarization immunoassay: r = 0.987, p < or = 0.02; by HPLC: r = 0.988, p < or = 0.02). Mean dose and assay outcome values by hair color and correlation between hair PHT mean values, daily mean doses of the drug, and patients' age are presented. The differences among doses according to hair color were significant. PHT hair profiles from female and male patients compared with the mean +/- SD concentrations of the hair sections are discussed. The data indicate the possible use of hair section testing as a marker of the dosage history and the compliance of patients receiving long-term treatment with PHT.