title: Radioimmunoassay for doxepin and desmethyldoxepin.
abstract: A simple and sensitive radioimmunoassay (RIA) for the determination of doxepin and desmethyldoxepin in plasma or serum has been developed using a previously reported antiserum to the tricyclic anti-depressants. Before assay, doxepin is separated from desmethyldoxepin with selective extraction at different pH values enabling each to be measured specifically. 3H-imipramine is used as tracer. By using the extraction procedure doxepin and desmethyldoxepin concentrations can be measured down to 9 nmol/1 from a 0.1 ml sample. If necessary, sensitivity can be doubled by taking a 0.2 ml sample to extraction. Recoveries of doxepin and desmethyldoxepin were quantitative when the drugs were added at different concentrations to normal, pooled human plasma and the inter- and intra-assay coefficients of variation did not exceed 9%. The concentrations obtained from patient samples by the present RIA correlated well with those by high-pressure liquid chromatography. The RIA was also shown to be useful in pharmacokinetic single dose studies with doxepin.
mesh_terms: D000918:Antibody Specificity; D002851:Chromatography, High Pressure Liquid; D004316:Doxepin / Q000031:analogs & derivatives* / Q000097:blood*; D006801:Humans; D001523:Mental Disorders / Q000097:blood; D011863:Radioimmunoassay / Q000379:methods; D013997:Time Factors
chemical_list: D004316:Doxepin; C028701:desmethyldoxepin