title: Quantitative determination of dexamethasone in human plasma by stable isotope dilution mass spectrometry.
abstract: An analytical method for the quantitation of nanogram to subnanogram amounts of dexamethasone is described. Dexamethasone was isolated from human plasma using a C18-bonded reverse-phase cartridge, purified by subsequent normal-phase HPLC, and the corresponding trimethylsilyl derivative analyzed by gas chromatography-mass spectrometry (GC-MS). The quantitation by isotope-dilution MS was carried out by selected-ion monitoring on the (M + 1)+ ion of the trimethylsilyl derivative of dexamethasone and its stable isotopically labeled diluent, [ 13C6 ,2H3]dexamethasone (681 and 690 m/z, respectively). Methane was used as the GC carrier gas and as the chemical-ionization reagent gas. The sensitivity of the method, judged from the lower limit of detection of the mass spectrometer, was at approximately 100 pg. The inter- and intraassay coefficients of variation (CV) determined at two different concentrations were 3.83 and 3.78% for 2 ng/mL and 2.64 and 1.29% for 5 ng/mL, respectively. Plasma concentration profiles for dexamethasone following a single 1-mg iv and a 2-mg oral dose of dexamethasone administered 24 h apart to two healthy volunteers are presented. The mass fragmentographic method described here is useful for bioavailability and pharmacokinetic studies of the synthetic glucocorticoid.
mesh_terms: D000284:Administration, Oral; D000328:Adult; D001682:Biological Availability; D055598:Chemical Phenomena; D002621:Chemistry; D003907:Dexamethasone / Q000097:blood*; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods; D006801:Humans; D007275:Injections, Intravenous; D007700:Kinetics; D008297:Male; D013058:Mass Spectrometry / Q000379:methods; D008875:Middle Aged; D013607:Tablets
chemical_list: D013607:Tablets; D003907:Dexamethasone