Determination of phenytoin in sections of head hair: a preliminary study to evaluate the history of drug use.

Phenytoin (PH) levels were determined in the head hair of twenty five patients (fourteen males and eleven females, aged from five to seventy seven years old) who were receiving this drug chronically. The assay method involved sectional hair analysis by dissolution and liquid phase extraction procedures, using both high pressure liquid chromatography (HPLC) and immunoassay (Abbott TDx) techniques. Five sections were studied, the first being the one closet to the root. The phenytoin levels of the hair sections ranged: a) 1st: 0.68 to 39.56 micrograms/g (mean 16.12 micrograms/g), b) 2nd: 0.85 to 34.15 micrograms/g (mean 9.45 micrograms/g), c) 3rd: 1.33 to 27.90 micrograms/g (mean 3.72 micrograms/g), d) 4th: 1.10 to 10.96 micrograms/g (mean 3.04 micrograms/g) and e) 5th: 1.05 to 7.00 micrograms/g (mean 2.84 micrograms/g) according to the HPLC analysis. The immunoassay technique gave similar results. The mean values of phenytoin in the hair sections according to the immunoassay technique were: 16.28; 9.47; 3.77; 3.22; 2.97 micrograms/g, respectively from the 1st to the 5th section. A reduction of drug concentrations in hair from the first to the consecutive segments was observed. Higher amounts of phenytoin were deposited in black, untreated hair in comparison to blond brown or grey hair. Phenytoin concentrations in hair sections correlated with the oral daily dosage of the drug. Our data indicate to the use of hair testing as a marker of the dosage history and evaluation of the compliance of patients under long treatment with phenytoin.