Mg Of Digitoxin Research Articles

Digitoxin for Airway Inflammation in Cystic Fibrosis: Preliminary Assessment of Safety, Pharmacokinetics, and Dose Finding

Cystic fibrosis (CF) lung disease progresses by a combination of airway inflammation, bacterial colonization, and infection. Airway inflammation is predominantly neutrophilic and complicates airway clearance therapies through cellular debris; excessive DNA; excessive and viscous mucus; and high concentrations of neutrophils, IL-8, and related cytokines liberated along the nuclear factor-κB signaling pathway. We conducted a preliminary, single-site, randomized, double-blind, placebo-controlled study to evaluate the effects over 28 days of two dose levels (0.05 mg and 0.1 mg daily) of an older cardiac glycoside, digitoxin, as compared with placebo, on safety, pharmacokinetics, and inflammatory markers in induced sputum obtained from 24 subjects with mild to moderate CF lung disease. Patients with CF 18-45 years old with any genotype combination were eligible. The primary objective was to measure the effects of digitoxin on IL-8 and neutrophil counts in induced sputum. Secondary objectives were to measure (1) the pharmacokinetics of digitoxin in sera of patients with stable CF; (2) safety indices, including ECG changes and sputum microbiology; (3) the effect of digitoxin on gene expression in nasal epithelial cells of patients with stable CF; and (4) quality-of-life scores using the Cystic Fibrosis Questionnaire-Revised. It took several weeks to achieve a therapeutic serum level of digitoxin in subjects with CF. No safety concerns emerged during the study. Digitoxin treatment showed a trend toward reduction in sputum free neutrophil elastase and neutrophil counts, but not a reduction in sputum IL-8. Digitoxin treatment did not reach statistical significance for the primary or secondary outcome measures over the 28-day study period. However, the nasal mRNA from the group receiving 0.1 mg of digitoxin daily had a distinct distribution of global gene expression levels as compared with either the 0.05-mg dose or placebo treatment. The mRNAs encoding chemokine/cytokine or cell surface receptors in immune cells were decreased in nasal epithelial cells at the higher dose, leading to pathway-mediated reductions in IL-8, IL-6, lung epithelial inflammation, neutrophil recruitment, and mucus hypersecretion. At a dose of 0.1 mg daily for 28 days, digitoxin was safe for adults with CF lung disease, but it did not achieve a significant decrease in sputum inflammatory markers. Clinical trial registered with www.clinicaltrials.gov (NCT00782288).

Reversal of advanced digitoxin toxicity and modification of pharmacokinetics by specific antibodies and Fab fragments.

The effects of Fab fragments of high-affinity specific antibodies have been studied in a canine experimental model of lethal digitoxin toxicity. Selected antiserum from sheep immunized and boosted with a digoxin-serum albumin conjugate contained antibodies that cross-reacted with digitoxin with an average intrinsic association constant of 1.4 x 10(10) M(-1) as determined by equilibrium dialysis. Rapid second-order association kinetics (k(f) = 3.7 x 10(6) M(-1) per s) and slow dissociation kinetics (k(r) = 1.9 x 10(-4) per s) were documented for the antibody-digitoxin complex. Eight dogs given 0.5 mg/kg digitoxin intravenously developed ventricular tachycardia after 23+/-4 (SEM) min. Control nonspecific Fab fragments were then given. All animals died an average of 101+/-36 min after digitoxin administration. Another eight dogs given the same digitoxin dose similarly developed ventricular tachycardia after 28+/-3 min. This group then received a molar equivalent dose of specific Fab fragments intravenously over 3 min, followed by a 30-min infusion of one-third of the initial dose. All dogs survived. Conducted sinus beats reappeared 18+/-4 min after initial Fab infusion, and stable normal sinus rhythm was present at 54+/-16 min. Plasma total digitoxin concentrations increased threefold during the hour after initial Fab infusion, while plasma free digitoxin concentration decreased to less than 0.1 ng/ml. Effects on digitoxin pharmacokinetics of these Fab fragments and the antibody population from which they were derived were further investigated in a primate species. Unlike common laboratory animals previously studied, the rhesus monkey was found to have a prolonged elimination half-life, estimated at 135 and 118 h by radioimmunoassay and [(3)H]digitoxin measurements, respectively, similar to man and thus providing a clinically relevant experimental model. Intravenous administration of 2 mol of specific Fab fragments per mole of digitoxin 6 h after 0.2 mg of digitoxin produced a rapid 4.3-fold increase in plasma total digitoxin concentration followed by a rapid fall (t((1/2)) 4 h) accompanied by a 14-fold enhancement of urinary digitoxin excretion over control values during the 6-h period after Fab was given. Analytical studies were consistent with increased excretion of native digitoxin rather than metabolites, and the glycoside was found in equilibrium dialysis studies to be excreted in the urine in Fab-bound form. Administration of 2 mol of specific antibody binding sites per mole of digitoxin as intact IgG caused a greater and more prolonged increase in plasma total digitoxin concentration, peaking 13-fold above control levels. In contrast to the effects of Fab, however, specific IgG reduced the rate of urinary digitoxin excretion substantially below control values. We conclude that Fab fragments of antibodies with high affinity for digitoxin are capable of rapid reversal of advanced, otherwise lethal digitoxin toxicity, and are capable of reducing the plasma half-life and accelerating urinary excretion of digitoxin.

Bleaching of Chlorophyll by Digitoxin

Summary Digitoxin has been found to bleach chlorophylls a and b when administered in an alcoholic solution to the dry powder of freshly frozen leaves of Digitalis purpurea. The cardenolide causes the formation of a phase separation with distinct color renditions within the final chloroform-ethanol and chloroform-ethyl ether extracts. A detailed analysis of light absorption bands from the green to the red shows almost complete disappearance of the 526 and 661 nm peaks, the latter indicating a probable aggregation of a colloidal chlorophyll-adigitoxin complex by coordination of the Mg atom of chlorophyll with the C23-carbonyl group of digitoxin with absorption in the 670 to 680 nm range and with a free energy of reaction of - 9.4 kcal. Chlorophyll-b reacted with digitoxin by an apparent increase of concentration at a low dose of 10 mg of digitoxin per 25 g of powder and by its destruction at a higher dose of 30 mg with a free energy release of -9.6 kcal as shown by the behavior of its 644 nm absorption peak. The reactions are composed of three concentration dependent phases with distinct halfdose values. Some thoughts are stated about the ability of the plant to control its production of autotoxic secondary plant products, specifically in regard to chlorophyll. Its implications on the status of plant communities are pointed out.

Determination of digitoxin in pharmaceutical oral dosages by automatic discrete-sample analysis

An automatic procedure for determination of digitoxin in pharmaceutical oral dosages is described. The procedure is based on the fluorimetric determination of digitoxin in hydrochloric acid media in the presence of hydrogen peroxide. Operational conditions and analytical setup are detailed. Results for repeatability, linearity, and tablet analysis are given. The procedure can be used for analysis of sets of up to 30 tablets at the rate of 17 readings per hour. Contents as low as 0.1 mg of digitoxin can be determined.

Digoxin-Estradiol-17β Interaction: A Study of Uteiotropic Effects in Rats

The uterotropic effects of digoxin and concurrent digoxin and estradiol-17P treatments were studied in rats. Digoxin in a low-dose range (10-200 M.g/kg) was found to have weak uterotropic effects at both 6 and 30 hr after injection. The uterotropic activity of digoxin was at best 3% that of estradiol. At a high-dose range (1,000-4,000 l-ig/kg), digoxin had almost no uterotropic effects. The 6-hr uterotropic effects of moderate doses of estradiol were inhibited at both of these 2 vastly different dosages of digoxin. The inhibition observed with digoxin at the low-dose range is thought to represent the end result of hormone receptor competition whereas the inhibition with digoxin at the high-dose range is probably related to the effects of digitalis toxicity on uterine metabolism. It is concluded that digoxin has weak uterotropic activity, that digoxin may compete with estradiol for hormone receptor sites, and that toxic doses of digoxin can inhibit the uterotropic activity of estradiol. {Endocrinology 90: 843, 1972) HPHREE clinical findings in patients taking •*• digitalis—gynecomastia in elderly men ( 1 6), marked cornification of the vaginal squamous epithelium (4), and decreased urinary gonadotropins (5) in postmenopausal women—have suggested that digitalis exerts estrogen-like effects. However, these clinical studies have often been marred by the presence of various diseases and by administration of drugs. Little attention has been given to these observations in the laboratory. Scott and Read (6) reported that digoxin, 2 mg/kg, had uterotropic effects in oophorectomized rats; however, only five rats were given this treatment and no quantitative data were presented. Britsch and Azar (7) reported cornification of vaginal squamous epithelium in mice (18 g median weight) given 0.18 mg of digitoxin in 6 injections over an 18day period. However, only 13 mice, distributed among four different treatment groups, survived this experiment. In both studies, large doses were used. The mechanism of digitalis estrogenicity is unexplored. Chemically, both digoxin and estradiol have a steroid nucleus but digoxin lacks an aromatic A ring (8) (Fig. 1). If digoxin acts as a weak estrogen, it might antagonize the uterotropic effects of a stronger estrogen by competing for binding sites on uterine estrogen receptor proteins (9-11). Since estrogen priming has been Received September 21, 1971. This investigation was supported in part by Research Grant AM-S628 from the National Institutes of Health, Public Health Service. shown to protect dogs and rabbits against digitalis-induced arrhythmias (12,13), such inhibition would be of additional interest in that a similar competition for binding sites could occur in the myocardium The purpose of this study was to verify the estrogenicity of digoxin and to investigate the possible competitive effects between digoxin and estradiol. Materials and Methods Sprague-Dawley female rats, 21-23-days-old (3449 g), were used for these studies. All injections were given sc. Sesame oil was used for estradiol-173 (henceforth referred to as estradiol) injections; isotonic saline was used for digoxin (parenteral Lanoxin, Burroughs Wellcome & Co., Inc.). The digoxin doses ranged from 0.04-160 ng/dose or approximately 10-4,000 ng/kg. Either one injection of digoxin or saline was given or both digoxin and estradiol injections were given within 1 min of each other. The animals were killed at 6 or 30 hr after injection. The 6-hr uterine weight

Interruption of the enterohepatic circulation of digitoxin by cholestyramine. II. Effect on metabolic disposition of tritium-labeled digitoxin and cardiac systolic intervals in man.

Previous studies of digitalis glycoside metabolism and excretion have indicated that these compounds undergo a significant enterohepatic cycle in some species. It has been suggested that the existence of such a cycle in man contributes to the prolonged action of certain cardiac glycosides. Previous studies have demonstrated that cholestyramine binds digitoxin and digoxin in vitro and accelerates the metabolic disposition of digitoxin in rats and guinea pigs, presumably by interrupting the enterohepatic circulation. In order to assess the role of the enterohepatic circulation in the metabolism of digitalis glycosides in humans, maintenance doses of cholestyramine were administered to 7 of 15 normal human subjects beginning 8 hr after digitalization with 1.2 mg of digitoxin-(3)H. All subjects had frequent measurements of serum radioactivity, left ventricular ejection time (LVET), and electromechanical systole (QS(2)), the latter recorded as the interval from onset of Q wave to first major component of second heart sound. Measurement of the LVET and QS(2) intervals affords a sensitive index of the cardiac response to digitalis. In addition, chloroform extraction of serum was performed to separate unchanged digitoxin and active metabolites from cardioinactive metabolites of digitoxin. Cholestyramine treatment resulted in reduction in half-life to total serum radioactivity from 11.5 to 6.6 days, and in chloroform-extractable radioactivity from 6.0 to 4.5 days, as compared to controls. In addition, cholestyramine treatment was accompanied by more rapid return to base line values of digitoxin-induced changes in the LVET and QS(2) intervals. A significant positive correlation was found between QS(2) values and chloroform-extractable radioactivity, the latter reflecting unchanged digitoxin-H(3) (r=0.64; P=<0.01). The results indicate that administration of cholestyramine to digitalized human subjects accelerates the metabolic disposition of digitoxin and abbreviates the physiologic response to the glycoside. This effect is presumably mediated by interruption of the enterohepatic circulation of digitoxin by cholestyramine.

Relationship of plasma digitoxin and digoxin to cardiac response following intravenous digitalization in man.

The value of plasma digitalis determinations will depend upon the accuracy with which they mirror the myocardial effects of digitalis. Ten volunteers received 0.8 mg of digitoxin intravenously, and after 2 hours the mean plasma digitoxin level was 45.6 ± 6 mµg/ml but declined over 4 to 6 hours during plasma-tissue equilibration. The cardiac response, as indicated by decreases in the left ventricular ejection time index (LVETI) and Q-S 2 intervals ( P &lt; 0.01), was present at 2 hours and reached maximum at 4 to 6 hours. Subsequently, plasma level, LVETI, and Q-S 2 changed in the same direction during slow excretion. Six subjects received 1.0 mg of digoxin intravenously. Mean plasma digoxin at 30 min was 6.8 ± 0.3 mµg/ml; it fell after 3 to 4 hours to levels usually seen during maintenance digoxin administration (&lt;3 mµg/ml) and then declined more slowly. Correlation of individual digoxin levels with ΔLVETI values during the first 4 hours was significant ( P &lt; 0.01). The half-life (T ½ ) for the dominant slope of the plasma curve was 30.5 hours by plasma determinations and 29 hours by LVETI determination. Plasma levels of digitoxin and digoxin were related to their cardiac effects under the conditions studied. Prior to plasma-tissue equilibration, plasma determinations of digoxin and digitoxin will be higher than levels seen during maintenance administration of these drugs.

Effects of digitoxin on the ultrastructural myocardial changes in the rat subjected to chronic exercise

Female Sprague-Dawley rats were divided into 4 groups: Group A (control rats); Group B (rats receiving 0.15 mg of digitoxin per 100 g of body weight daily for 6 days of each week); Group C (swimming control rats); and Group D (swimming rats receiving digitoxin in the manner of Group B). The exercised animals swam 6 hours daily, 6 days a week until 400 to 1,500 hours of total swimming time had been reached. Electron microscopic data indicated that although the number of mitochondria increased in hearts from rats subjected to swimming, degeneration occurred in a significant proportion of the mitochondria. The swimming rats given digitoxin, unlike the untreated swimming rats, had insignificant mitochondrial damage. Therefore, mitochondrial integrity, in relation to the morphologic appearance, is apparently better preserved in the swimming rat receiving digitoxin than in the untreated swimming rat.

Effects of digitoxin on the development of cardiac hypertrophy in the rat subjected to chronic exercise

Sixty female Sprague-Dawley rats were divided into four groups of 15 animals each: Group A, control animals; Group B, rats receiving 0.15 mg of digitoxin per 100 g of body weight daily for 6 days of each week; Group C, swimming control animals; and Group D, rats that received digitoxin and also swam. The exercised animals swam 6 hours a day, 6 days a week until 400 to 1,500 hours of total swimming time had been reached. The parameters measured were body weight, heart weight, right and left ventricular thickness, myocardial isometric systolic tension and ventricular pressure before and during acute aortic occlusion. The presence or absence of digitoxin was not a significant source of variation in any of these parameters in either the control or the swimming rats, but the swimming factor was a significant source of variation. There was no detectable interaction between swimming and digitoxin. Therefore, it can be stated that, unlike the pathologic hypertrophy of disease, the physiologic hypertrophy produced by intermittent exercise and the increment in myocardial function concomitant to the hypertrophy are not altered by treatment with digitoxin.

Effects of digitoxin on exchangeable and tissue potassium contents.

Summary1. The daily intravenous administration of 0.1 mg of digitoxin per kg of body weight to normal rabbits resulted, within 7 days, in an increase in body weight and a reduction in the serum potassium concentration and the exchangeable potassium content. These changes in potassium metabolism were corrected within one week by discontinuing the glycoside. 2. The intravenous administration of a single large dose of digitoxin (0.2 mg per kg) to normal rabbits resulted within 24 hours in a decrease in the mean potassium content of all the tissues and organs. Statistically significant decreases in potassium content were noted in the abdominal and diaphragmatic muscles and in the subcutaneous connective tissue. The results suggest that one of the effects of the administration of digitoxin in these dosages is to deplete the body store of potassium.

Effect of intravenous digitoxin on fluid distribution in hospitalized males without cardiovascular disease

SummaryThe intravenous administration of 1.2 mg of digitoxin to 5 male subjects with no cardiovascular disorder was found to cause a significant decrease in the serum protein concentration and an increase in the total circulating protein content within 8 hours. The results were interpreted as indicating an increase in the water and protein content of the vascular compartment.

Effect of Intravenous Digitoxin on Fluid Distribution in Hospitalized Males without Cardiovascular Disease.

SummaryThe intravenous administration of 1.2 mg of digitoxin to 5 male subjects with no cardiovascular disorder was found to cause a significant decrease in the serum protein concentration and an increase in the total circulating protein content within 8 hours. The results were interpreted as indicating an increase in the water and protein content of the vascular compartment.