SIMULTANEOUS DETERMINATION OF PHENYTOIN AND CARBAMAZEPINE IN HUMAN HAIR BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

Drug detection in human hair has been regarded as a potentially useful technique for therapeutic drug monitoring and for the assessment of t herapeutic compliance. An isocratic high-performance liquid chromatogr aphy (HPLC) assay for the simultaneous measurement of phenytoin and ca rbamazepine in human hair was used to assess therapeutic compliance in a population of patients with epilepsy. After alkaline digestion, phe nytoin and carbamazepine were separated on a reverse-phase column by u sing a mobile phase of acetonitrile/methanol/water (9:37:54) and monit ored at a wavelength of 214 nm with methylphenyl-5-phenylhydantoin as internal standard. The assay was linear in the range from 0 to 66.66 n g/mg hair, and recoveries of both drugs at concentrations of 8.33, 33. 3, and 66.66 ng/mg hair from the hair matrix ranged from 91.2 to 104.0 %. inter-and intraassay coefficients of variation for both drugs (asse ssed at three concentrations in the calibration range) were < 10%. The limits of detection for phenytoin and carbamazepine were 2.0 and 1.33 ng/mg hair, respectively.