Development of a high-performance liquid chromatographic assay for digoxin using post-column fluorogenic derivatization

Digoxin – a therapeutic agent and mechanistic probe: review of liquid chromatographic mass spectrometric methods and recent nuances in the clinical pharmacology attributes of digoxin

Digoxin is an important therapeutic agent for the treatment of congestive cardiac failure. In spite of its narrow therapeutic index, digoxin has been used extensively by the medical community and, lately, the use of digoxin as a mechanistic probe for p-glycoprotein transporter activity has increased. This review describes recent trends in the bioanalysis of digoxin, where scores of liquid chromatographic–mass spectrometric assays have been successfully employed to measure digoxin in preclinical, clinical and mechanistic studies. It provides various considerations such as internal standard selection, extraction schemes, matrix effect, selectivity evaluation and optimization of mass spectral conditions, for example, to enable the development of sound bioanalytical methods for digoxin. Some recent updates with regard to clinical pharmacology, absorption and disposition aspects of digoxin have been included. Overall, liquid chromatographic–mass spectrometric assays represent an important tool for many future preclinical, clinical and mechanistic probe studies that would probe digoxin with or without other coadministered substrates.

Fluorescence detection of cardenolides in reversed-phase high-performance liquid chromatography after post-column derivatization

Methods for the fluorescence derivatization of cardiac glycosides with concentrated acids from TLC are adopted to HPLC for post-column derivatization. The column effluent is blended with concentrated acids in a knitted tube reactor, which enables derivatization with negligible increase in chromatographic peak width. The selectivity of the reaction is temperature-dependent and influenced by the respective acid. Reactivity increases from H3PO4-->CH3SO3H[symbol: see text]H2SO4. The conversion of digoxigenin, digitoxigenin and their digitoxosides is accelerated by Cu(II) acetate or Co(II) nitrate in H2SO4. Combined with a new two-mode, single-column solid-phase sample preparation, cardiac glycoside levels of less than 100 pg/glycoside in 1 ml plasma are detectable.

Chromatography of cardiac glycosides

Most of the recently reported methods for the quantitation of cardiac glycosides have been for digoxin and its metabolites. Recent procedures using high-performance liquid chromatography-radioimmunoassay (HPLC-RIA) and HPLC following derivatization show appreciable improvements in accuracy and specificity for quantitating digoxin in the low nanogram range. Gas chromatographic procedures have been explored to a very limited extent and further advances in the quantitation of cardiac glycosides are anticipated to arise from the use of laser desorption-Fourier transform mass spectrometry. However, currently, HPLC with derivatization and HPLC-RIA techniques remain the techniques of choice for quantitation of digoxin and/or its metabolites based on considerations of ease of use, sensitivity, specificity, accuracy and reproducibility.

Electrochemical detection of the 3,5-dinitrobenzoyl derivative of digoxin by high-performance liquid chromatography

Electrochemical detection of 3,5-dinitrobenzoyl derivatives of digoxin and its metabolites following high-performance liquid chromatography is reported. Partial resolution of derivatized digoxin and dihydrodigoxin was obtained using a Spherisorb ODS II analytical column. Both single- and dual-electrode detection were investigated and a maximum sensitivity equivalent to 0.39 ng of digoxin was found with the dual-electrode method. This system has the necessary sensitivity and selectivity for development into a therapeutic monitoring assay method.

Analysis of digoxin at therapeutic concentrations using high-performance liquid chromatography with post-column derivatization

A high-performance liquid chromatographic (HPLC) procedure has been developed for the analysis of digoxin in plasma at therapeutic concentrations. The assay method provides resolution of digoxin from its metabolites using a 15 cm X 4.6 mm HPLC column containing 3-micron octadecylsilane-bonded stationary phase. The effluent of the column is passed through a post-column reactor in which a fluorescent derivative is formed by the co-addition of hydrochloric acid and dehydroascorbic acid. Detection of the derivative is accomplished in a fluorometer with excitation at 336 nm and emission at 425 nm. The extraction efficiency for recovery of digoxin from plasma samples was 70% using chloroform-isopropanol (9:1) following a pre-wash with isooctane to remove endogenous substances. The calibration curve was linear (r = 0.9999) over the range 0.5-4 ng/ml digoxin in plasma using digitoxigenin as internal standard. The minimum detectable quantity of digoxin in plasma was 0.5 ng/ml at a signal-to-noise ratio of 4:1. Split-samples of digoxin control sera were assayed by the HPLC procedure and by the prescribed radioimmunoassay procedure. Excellent correlation was observed between the two methods (r = 0.999). No interference was noted when a selection of commonly co-prescribed drugs were evaluated for chromatographic co-elution or interference in detection with that of digoxin or the internal standard.