Phenobarbital in hair and drug monitoring

Phenobarbital analysis was performed in vertex hair of patients by gas chromatography mass spectrometry (GC/MS). After washing with dichloromethane, about 250 mg were ground to dust in a ball mill. A 50-mg sample was stirred mechanically for 10 min with 3 ml of NH₄Cl/HCl buffer (pH 2.0) containing phenobarbital D₅. A solid phase extraction was performed (extrelut Merck) and elution was achieved with chloroform/isopropanol/n-heptane (50:17:33; v/v). A full scan (40–240 uma) acquisition was realized by GC/MS with an ion trap (ITD 700 Finnigan) using a DB5-MS chromatographic column. Quantification was achieved by integrating dominants ions (phenobarbital, 204; phenobarbital D₅, 209). Compared to serum, hair concentrates phenobarbital during anti-epileptic therapy (average value 36.4 ng/mg, n = 40 vs. 18.7 mg/l, n = 23). A group correlation exists between phenobarbital in hair and phenobarbital in serum, and between phenobarbital in hair and clinic observation in some typical cases. Phenobarbital in hair yields good information over a long period, especially when blood collection has not been made, when clinical disorders are observed on long-term therapeutic observance.