A validated LC-MS/MS assay for the simultaneous determination of periplocin and its two metabolites, periplocymarin and periplogenin in rat plasma: Application to a pharmacokinetic study.

A sensitive and reliable LC-MS/MS method was developed and validated for the simultaneous determination of periplocin and its two metabolites (periplocymarin and periplogenin) in rat plasma using psoralen as the internal standard (IS). After liquid-liquid extraction with ethyl acetate, chromatographic separation was performed on a C18 column with a 13 min gradient elution using 0.1% formic acid and acetonitrile as mobile phase at a flow rate of 0.3 mL/min. The detection was accomplished on a tandem mass spectrometer via an electrospray ionization (ESI) source by multiple reaction monitoring (MRM) in the positive ionization mode. The lower limits of quantitation (LLOQs) for periplocin, periplocymarin and periplogenin were 0.5, 1 and 0.1 ng/mL, respectively. The mean recoveries of the analytes and IS were higher than 67.7%. The proposed method was successfully applied to evaluating the pharmacokinetic studies of periplocin and its metabolites (periplocymarin and periplogenin) in rats after a single oral administration of periplocin at 50 mg/kg.

A validated LC-MS/MS method for determination of periplogenin in rat plasma and its application in pharmacokinetic study.

A method coupling high performance liquid chromatography with tandem mass spectrometry has been developed and validated for quantifying periplogenin in rat plasma using psoralen as an internal standard (IS). Plasma samples were pretreated using a simple liquid-liquid extraction with ethyl acetate and the chromatographic separation of periplogenin and psoralen was achieved on a Waters XBridge™ BEH C18 column with 0.1% formic acid and acetonitrile as mobile phase at a flow rate of 0.4mL/min. The detection was performed on a positive ion mode with electrospray ionization (ESI) source. The optimized ion transition pairs for quantitation were m/z 391.3→m/z 337.2 for periplogenin and m/z 187.0→m/z 131.0 for IS. The total run time was 9.0min. The calibration curve was linear over the range of 0.2-250ng/mL (r>0.99) with the lower limit of quantitation (LLOQ) at 0.2ng/mL. The intra- and inter-day precision were below 9.85% and the mean accuracy were from -10.03% to 10.26%. The average recoveries of periplogenin in plasma ranged from 85.1% to 95.6%. The proposed method was successfully applied in evaluating the pharmacokinetics of periplogenin after an oral dose of 30mg/kg Cortex Periplocae extract in rats.

Measurement of serum digitoxin in patients by radioimmunoassay using specific antiserum.

INTRODUCTION: Digitoxin is used to treat patients with heart failure. METHODS: A radioimmunoassay procedure for the specific determination for digitoxin in serum was developed using the antiserum (antiserum (A)) raised against digitoxin 3'-hemisuccinate-BSA conjugate. RESULTS: The intra- and interassay variability were <10% in the range of 5-100 ng/ml. The specificities of antiserum (A) and the commercial anti-digitoxin antiserum (antiserum (B)) were assessed by cross-reactivity studies with various related compounds. Antiserum (A) was highly specific for digitoxin. Mean digitoxin concentrations in serum samples (n=34) from digitalized patients by RIA using these antisera were 10.0 and 12.4 ng/ml, respectively. CONCLUSION: This RIA using antiserum (A) measure unmetabolized digitoxin and may be applicable for pharmacokinetic studies.

Photoaffinity labeling of erythrocyte membrane (Na+ + K+)-ATPase with high specific activity [125I]iodoazidogalactosyl digitoxigenin.

Photoaffinity labeling of (Na+ + K+)-ATPase in erythrocyte membranes with cardiotonic steroid derivatives, followed by gel electrophoresis, requires a radiolabel of very high specific activity, since the enzyme represents less than 0.05% of the total membrane protein. We report the synthesis of a radioiodinated, photosensitive derivative of the cardiac glycoside, 3-beta-O-(4-amino-4,6-dideoxy-beta-D-galactosyl)digitoxigenin, with very high specific activity. The product, [125I]iodoazidogalactosyl digitoxigenin ([125I]IAGD), is carrier-free with a specific activity of 2200 Ci/mmol. Incubation of [125I]IAGD (1.8 nM) with human erythrocyte membranes (300 micrograms protein), followed by photolysis and analysis by SDS-PAGE, showed specific radiolabeling of a polypeptide that had the same molecular weight as catalytic alpha subunit (100,000 Mr) of (Na+ + K+)-ATPase in eel electroplax microsomes. Photoaffinity labeling of erythrocyte and electroplax membranes by [125I]IAGD was specific for the cardiac glycoside binding site of (Na+ + K+)-ATPase since radiolabeling of the alpha subunit was inhibited when ouabain was included in the pre-photolysis incubation. [125I]IAGD can, therefore, be used as a probe in structural studies of human erythrocyte membrane (Na+ + K+)-ATPase.

Bioavailability of the bis- and monodigitoxosides of digitoxigenin.

The pharmacokinetic behavior of digitoxigenin is affected by the number of glycosides present. This study was conducted to compare the bioavailabilities of the bis- and monodigitoxosides of digitoxigenin in man. Intravenous and oral doses of the two drugs were administered to six normal volunteers. Blood samples were collected up to 28 days after each dose, and assayed for the specific drug administered and for total radioassayable drug. Both drugs were virtually completely absorbed, based on serum concentrations of administered drug plus metabolites. However, the mean bioavailability of unchanged bisdigitoxoside was only 56.3% indicating that substantial metabolism occurred prior to entry into the systemic circulation. Monodigitoxoside was virtually completely metabolized prior to entry into the systemic circulation.

Kinetics of digitoxin and the bis- and monodigitoxosides of digitoxigenin in normal subjects.

The kinetics of digitoxin and two of its metabolites, the bis- and monodigitoxosides of digitoxigenin, were determined in six normal subjects. Mean t 1/2s and total body clearances were 134.4, 15.4, and 0.59 hr and 2.66, 27.3, and 1071 ml/min. Mean renal clearance of the monodigitoxoside was more rapid (7.24 ml/min) than those of digitoxin (0.81 ml/min) or the bisdigitoxoside (0.94 ml/min). The volumes of distribution were of the same order, 0.45 l/kg for digitoxin, 0.57 l/kg for the bisdigitoxoside, and 0.83 l/kg for the monodigitoxoside. The short t 1/2 of monodigitoxoside would make it unsuitable for clinical use, but the bisdigitoxoside of digitoxigenin has a t 1/2 of an intermediate length and may have significant therapeutic advantages.

Kinetics of digitoxin and the bis- and monodigitoxosides of digitoxigenin in renal insufficiency.

The kinetics of digitoxin and two of its major metabolites, the bis- and monodigitoxosides of digitoxigenin, were determined in six subjects with renal insufficiency and compared to those in six age- and sex-matched normal control subjects. No significant differences between the two groups were found in elimination t 1/2, total body clearance, or volume of distribution. Average renal clearances of all three drugs were reduced in subjects with renal failure, but the differences were significant only in the case of digitoxin. The bis-digitoxoside of digitoxigenin has kinetic properties that offer clinical advantages.

Quantitation of digitoxin and the bis- and monodigitoxosides of digitoxigenin in serum.

A specific assay is described for measuring the concentration of digitoxin and the bis- and monoglycosides of digitoxigenin in serum. The procedure includes: (1) addition of a tracer amount of tritium labeled parent compound to the serum in order to measure percentage recovery; (2) solvent extraction to separate polar and non-polar metabolites; (3) reversed-phase thin-layer chromatography of the non-polar fraction to separate digoxigenins from digitoxigenins; (4) thin-layer chromatography to isolate digitoxin, and the bis- and monoglycosides of digitoxigenin; and (5) use of an 125I-radioimmunoassay to determine the concentration of the glycosides. Each of these three glycosides was administered intravenously to a normal subject, and the concentration of parent compound was measured in the serum at various times.

Studies on digitalis. IV. A method for thin-layer chromatographic separation and determination of digitoxin and cardioactive metabolites in human blood and urine.

A thin-layer chromatographic method for the separation of digitoxin and its cardioactive metabolites in one system is described. Pre-coated silica gel plates impregnated with 15% formamide solution in acetone were developed twice in the same direction (running distance 18cm) with ethyl methyl ketone-xylene (50:50) as solvent. The system showed no border-zone effects, and the reproducibility was good. Samples (5 ml) of serum or urine were extracted with dichloromethane, the extracts were evaporated, the residues were dissolved in 70% ethanol, the ethanol solutions were washed twice with light petroleum and then evaporated, and the residues were dissolved in chloroform-methanol for application to the thin-layer plates. After development, the metabolites were scraped from the plates and analyzed by means of a modified rubidium-86 method. The recovery for the whole procedure was 59%, and the sensitivity of the method permitted the determination of down to 0.5 ng per spot. The method will facilitate the study of digitoxin metabolism in patients undergoing treatment with the drug.