Gas Chromatographic Determination of Quazepam and Two Major Metabolites in Human Plasma

Abstract

Two rapid, sensitive, and specific gas chromatographic (GC) methods for the quantitative determination of quazepam (I), 7-chloro-5-(2-fluorophenyl-1, 3-dihydro-1-(2, 2, 2-trifluoroethyl)-2H-1, 4-benzodiaze-pine-2-thione), and its major active plasma metabolites, the 2-oxo compound (II) and the dealkylated oxo compound (III), have been developed; the first measures I and II and the second measures III. The compounds are extracted from plasma with toluene and quantitated by electron-capture detection using the internal standard method. The methods are capable of quantitating plasma levels of I and II as low as 0.75 ng/mL and plasma levels of III as low as 1.5 ng/mL. Correlation coefficients of standard curves were >0.9995 for all compounds. Precision of the methods was measured at two different concentrations for each compound; the CV values were 3–6% for all three compounds. The recovery of all compounds was >80%, and the ratio of recovery of each compound to that of its internal standard did not vary at different concentrations, indicating appropriate internal standards have been selected for the methods. Quazepam metabolites, other benzodiazepines, and drugs which are potential comedication do not interfere with either method. The methods were shown to be suitable for investigating the bioavailability and pharmacokinetics of quazepam at therapeutic doses.