Rapid and sensitive high-resolution procedure for digitalis glycoside analysis by derivatization liquid chromatography

The separation and quantitative determination of digitalis glycosides by high performance liquid chromatography following derivatization with 4-nitrobenzoylchloride (4-NBC1) is described. The compounds of primary interest were the digitalis glycosides and aglycones of the pharmaceutically important A, B and C series, The derivatization step results in higher extinction values at a more favourable wavelength (260 nm), which permits the use of low-cost ultraviolet detectors. Detection limits are below 20 ng/ml for all of the glycosides tested. The chromatographic properties are also improved by reducing the polarity without a decrease in selectivity. The use of low-polarity and low-viscosity solvent systems on silica gel adsorbents permits rapid isocratic separations of complex mixtures as they usually occur in pharmaceutical products and extracts. The quantitative potential of this method was demonstrated by analyzing ampoule solutions containing desacetyl lanatoside C as the active compound. The active substance, by-products and degradation products were determined down to 0.1% of the total glycoside concentration in one ampoule.

Digitalis pharmacokinetics and metabolism

The pharmacokinetics of the cardiac glycofides have been elucidated as a result of the development of assays of sufficient sensitivity to measure the concentration of digitalis compounds in biological fluids. Digoxin can accumulate in the body without the administration of a loading dose, and a steady state blood concentration will be reached in 5 to 7 days. Digitoxin requires 35 days to accumulate to a plateau. If a loading dose of digoxin is used, it should be approximately three times the estimated daily maintenance dose. Factors that determine the selection of the appropriate maintenance dose of digoxin include renal function and lean body mass. Digitoxin is less dependent on renal function for its elimination than is digoxin. Knowledge of the pharmacokinetics of digitalis preparations is useful in determining how to change from one cardiac glycoside to another, each with different half-lives. One should wait 3 days before starting digoxin therapy when changing from maintenance digitoxin to digoxin (assuming normal renal function). The pharmacokinetics of changing from ouabain to digoxin without loss of digitalis effect are described. The metabolism of the commonly used digitalis preparations are summarized.

The reactivity of derivatives of digoxin and digitoxin as measured by the Na-K-atpase displacement assay and by radioimmunoassay

Derivatives of digoxin and digitoxin were measured by the Na-K-ATPase displacement assay and by radioimmunoassay and the data compared with biological potency of these compounds. There was a slightly higher affinity of digoxigenin-bis-digitoxoside as compared with digoxin using digoxin-specific antiserum and considerably less affinity of digoxigenin and dihydrodigoxin than the parent compound in the same system. A similar trend was observed for the derivatives of digitoxin using digoxin-specific antiserum. The recovery on extraction of some of the derivatives of digoxin and digitoxin differed from that of the parent compounds in the ATPase assay. The potency of the derivatives of these drugs in displacing 3H ouabain also differed from the parent compoundmboth the recovery on extraction and the potency for displacing ouabain must be considered in the estimation of the contribution of the derivatives of digoxin or digitoxin to the result of Na-K-ATPase assay. Quantitative information of the metabolites of digoxin and digitoxin in normal and pathological conditions is needed to properly interpret assay data obtained either by radioimmunoassay or by ATPase assay.

A solid phase radioimmunoassay for digoxin and its acylated derivatives

A solid phase radioimmunoassay (RIA) is presented for the determination of digoxin and its acylated derivatives. In the procedure the antiserum is covalently bound to bromacetylcellulose. Therefore the free and the immunologically bound digoxin fractions can easily be separated by centrifuging. The radioactivity in the supernatant representing the unbound digoxin is proportional to the digoxin concentration in the sample. This modification of the RIA for digoxin is far more time saving than the separation procedure using dextran-coated charcoal as an absorbent; nevertheless both methods are equally sensitive, specific and reliable. The use of the solid phase assay is demonstrated comparing the bioavailability of various digoxin derivatives.

The composition of phytosterols in first and second year Digitalis purpurea L

The phytosterols of Digitalis purpurea occur as lipids and as glucosides. Gas-liquid chromatography and mass-spectrometry indicated that both fractions contained sitosterol as the major component, and also varying proportions of stigmasterol, campesterol and cholesterol. Certain of the lipid fractions contained 24-methylenecholesterol. The phytosterol concentrations and relative proportions were determined at monthly intervals during the first year of growth, and also in various morphological units of second year plants. The composition of the phytosterol fractions depended upon the plant organ examined and also upon the phase of growth of the plant.