title: Sensitive and specific LC-MS assay for quantification of digoxin in human plasma and urine.
abstract: Digoxin, a commonly prescribed cardiac glycoside with a narrow therapeutic window, is routinely used in pharmacokinetic studies to assess the in vivo activity of the drug efflux pump P-glycoprotein. To minimize adverse events, a sub-therapeutic dose of digoxin is usually administered, producing low plasma concentrations requiring a sensitive detection technique. Commonly available immunoassay techniques do not provide the required sensitivity to measure these low plasma concentrations and are potentially non-specific in certain subject populations. Previously published mass spectrometric techniques require either large plasma volumes or a tandem mass spectrometer. To overcome these challenges we have developed a sensitive and specific LC-MS method for the quantification of digoxin in small volumes of human plasma and urine. Plasma (1 mL) was extracted with methyl t-butyl ether under basic conditions followed by LC-MS detection of the sodium adducts of digoxin (803.4 m/z) and digitoxin (787.4 m/z, internal standard). Linearity and accuracy were demonstrated across a wide range of digoxin plasma concentration (0.05-1.5 ng/mL). This specific, sensitive, validated digoxin LC-MS assay can be used to quantify sub-therapeutic digoxin plasma concentrations in men and women (pregnant and non-pregnant).
authors.affiliation: Department of Pharmaceutics, University of Washington, Seattle, WA 98195, USA.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Kirby
authors.forename: Tom
authors.initials: T
authors.lastname: Kalhorn
authors.forename: Mary
authors.initials: M
authors.lastname: Hebert
authors.forename: Tom
authors.initials: T
authors.lastname: Easterling
authors.forename: Jashvant D
authors.initials: JD
authors.lastname: Unadkat
mesh_terms: D002853:Chromatography, Liquid / Q000379:methods*; D004074:Digitoxin / Q000097:blood / Q000737:chemistry / Q000652:urine; D004077:Digoxin / Q000097:blood* / Q000737:chemistry / Q000652:urine*; D005260:Female; D006801:Humans; D013058:Mass Spectrometry / Q000379:methods*; D011247:Pregnancy; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D004077:Digoxin; D004074:Digitoxin