High-performance liquid chromatography-ionspray mass spectrometry for the specific determination of digoxin and some related cardiac glycosides in human plasma.

An original method based upon high-performance liquid chromatography coupled to ionspray mass spectrometry (HPLC-ISP-MS) has been developed for the identification and quantification in plasma of several cardiac glycosides, namely digoxin, digitoxin, lanatoside C and acetyldigitoxin. After single-step liquid-liquid extraction by chloroform-2-propanol (95:5, v/v) at pH 9.5 using oleandrin as an internal standard, solutes are separated on a 4 microm NovaPak C18 (Waters) column (150x2.0 mm, I.D.), using a gradient of acetonitrile-2 mM NH4COOH, pH 3 buffer (flow-rate 200 microl/min, post-column split 1:3). Detection is done by a Perkin-Elmer Sciex API-100 mass analyzer equipped with an ISP interface. In most instances the major ion observed is not [M+H]+ as expected, but [M+NH4]+. The mean retention times (min) are: lanatoside C, 5.74; digoxin, 6.00; digitoxin, 8.08, oleandrin, 8.30, acetyldigitoxin, 8.66 and 9.01 (isomers alpha and beta, respectively). The lower limits of detection in single ion monitoring mode range from 0.15 ng/ml (alpha- and beta-acetyldigitoxin) to 0.60 ng/ml (lanatoside C), making the method less sensitive than radioimmunoassay, whereas it is much more specific.

[Guidelines for prescription of the assay of digitalis glycosides by immunologic methods]. / Règles de prescription du dosage des digitaliques par méthodes immunologiques.

Digoxin, digitoxin and acetyldigitoxin are the most widely prescribed of cardiotonic glycosides. Analytical exploration can be performed by a single assay when only one compound is prescribed or by multiple assays in cases of imprecise prescription or when several glycosides are given concomitantly. In addition, the metabolic transformation of digitoxin into digoxin and the presence of endogenous "digitalis-like compounds" mean that a number of precautions must be taken during prescription. These examples underline the ambiguity of the so-called "digitalinaemia" prescriptions and the need for biologists to be supplied with maximum information by clinicians.

Measurement of plasma glycoside level following pengitoxin administration.

16-Acetyl-gitoxin, the cardioactive metabolite of pengitoxin, was estimated by the 86Rb uptake technique. In 70 consecutive patients taking an oral maintenance dose of pengitoxin 0.4 mg (Pentagit), the mean plasma concentration was 20.8 +/- 6.7 ng/ml. Toxic signs were not observed up to plasma levels of 40 ng per ml.