Determination of clonazepam ("Rivotril" or "Ro 5-4023") in plasma by gas chromatography using an internal standard

A method has been developed for gas-chromatographic determination of clonazepam ("Rivotril" or "Ro 5-4023") in plasma, using methyl-clonazepam ("Ro 4082") as an internal standard. Following extraction of the benzodiazepines and hydrolysis, the benzophenones are analyzed by gas-chromatography, using a glass column filled with 3% OV 225 on Gas Chrom Q and a 63Ni electron-capture detector. The technique has good selectivity. The limit of sensitivity is less than 1 ng/ml of plasma. Using this method the plasma kinetics of clonazepam may be studied in man and the correlations between plasma levels and therapeutic activity investigated. It is also available for toxicological analysis, as well as pharmacovigilance purpose. The same internal standard and a similar method can also be used for the determination of flunitrazpem ("Rohypnol" or "Ro 5-4200") and its major metabolite (N-desmethyl-flunitrazepam) in plasma.