Carbamazepine levels in head hair of patients under long-term treatment: A method to evaluate the history of drug use

Carbamazepine (CBZ) concentrations were determined in the sections of head hair from 40 patients (22 males and 18 females), ages 5 to 81, who were receiving this drug systemically. Hair treatment included dissolution, liquid phase extraction procedures, and immunoassay (Abbott TDx) or high-pressure liquid chromatography (HPLC) analytical techniques. The mean values of CBZ levels in the hair from the 1st section (close to hair root) to the 5th section for female patients were 26.82, 19.18, 17.28, 15.09, and 14.62 mu g/g according to HPLC measurements. Immunoassay gave generally slightly higher results. The mean values of CBZ in the hair sections according to the immunoassay technique were 30.53, 21.90, 19.83, 1745 and 26.99 mu g/g, respectively, from the 1st to the 5th sections. The corresponding mean values for male patients by HPLC and immunoassay techniques were 21.97 1730, 15.03, 13.02, and 12.21 mu g/g and 25.98, 20.52, 17.15, 14.87 and 12.31 mu g/g. Generally, a reduction of drug concentrations in hair from the first to the subsequent segments was observed. Higher amounts of CBZ were deposited in black, untreated hair (e.g, not dyed or permed). CBZ concentrations in hair sections were found to be dependent on the dosage (r = 0.979, p less than or equal to 0.002) but not on the gender. The data indicate the possible use of hair section testing as a marker of the dosage history and the compliance of patients under long-term treatment with CBZ. Journal of Clinical Pharmacology, 1999;39:55-67 (C) 1999 the American College of Clinical Pharmacology.