Halazepam as a precursor of desmethyldiazepam: quantitation by electron-capture gas-liquid chromatography

Halazepam and its major metabolite desmethyldiazepam (DMDZ) can be reliably quantitated in human plasma following single doses of halazepam. After addition of appropriate internal standards, halazepam and DMDZ are extracted directly into an organic solvent at physiological pH. The organic extract is separated, evaporated to dryness, reconstituted, and directly chromatographed using a 50:50 methyl:phenyl silicone column (SP-2250) and an electron-capture detector. After a single 40 mg oral dose of halazepam, the parent compound appears in plasma only transiently and at low levels. DMDZ appears in higher concentrations and is slowly eliminated. During multiple-dose therapy with halazepam, DMDZ will be the major active substance in blood.