Synthesis and biological activity of some 3-amino compounds related to digoxigenin

3 alpha-Amino 1a and 3 beta-amino 1b analogues of digoxigenin 14 and their 12 beta-acetate derivatives 2a and 2b were prepared and tested for inotropic activity in the isolated guinea-pig atrial preparation. The 3 alpha-amino compounds were inactive whereas the 3 beta-amino compounds showed comparable activity to their 3 beta-hydroxy counterparts. The replacement of the 17 beta-butenolide ring by other ring systems was investigated. Compounds with a 3'-furyl ring, 9b and 16 were found to possess appreciable activity. A compound with a 4'-pyridazinyl ring 13b exhibited weak activity, whereas the isomeric butenolide compound 11b proved inactive. N-monomethylation of the amine 2b reduced activity and N-dimethylation abolished activity. Acetylation of the 12 beta-hydroxyl function gave less active compounds.

Asterixis associated with carbamazepine

Some antiepileptic drugs, when administered at toxic plasma levels or more rarely at levels within the therapeutic range, induce asterixis. We report the case of a patient with painful syndrome of central origin being treated with carbamazepine, in which asterixis appeared with toxic serum levels. A pharmacologic interference was also observed between carbamazepine and beta-methyldigoxin, which in our patient was being used to treat disease. The blood digoxin levels were inversely proportional to those of carbamazepine. The therapeutic effectiveness of digoxin being sharply reduced when carbamazepine reached toxic levels.

Spectral analysis of the configuration and solution conformation of dihydrodigoxigenin epimers

The C20 configuration and solution conformation of each epimer of dihydrodigoxigenin has been studied by circular dichroism (CD) and NMR spectroscopy. Results from the CD spectra indicate that the two epimers have opposite orientations of the beta-carbon in the lactone ring. This finding, together with X-ray crystallographic data from a separate study on the minor epimer, establishes the C20 configuration of the minor epimer as S and of the major epimer as R. NMR evidence indicates that the average lactone rotamer for the minor epimer has the C22 position located on the C12 side of the steroid nucleus, whereas the average lactone rotamer for the major epimer has the C21 position located on the C12 side of the steroid nucleus. Molecular models indicate that these are the least-hindered positions for the respective rotamers. Physical data characterizing the two epimers are provided.

Abolition of digitalis tachyarrhythmias by caffeine

Digitalis-induced ventricular tachyarrhythmias (VTAs) are believed to be due to oscillatory afterpotentials (OAPs) generated by an oscillatory release of calcium from the sarcoplasmic reticulum (SR). Caffeine blocks the calcium uptake into the SR and then may influence VTAs by depleting the SR stores of calcium. We studied the action of digitalis and caffeine, singly and in combination, in the isolated guinea pig heart perfused by means of a modified Langendorff apparatus. Digitalis (beta-methyldigoxin 1.27 X 10(-6) M) caused VTAs and ventricular fibrillation (VF) in all the hearts. Caffeine alone decreased heart rate but never caused VTAs. With the administration of digitalis and caffeine (1 mM), VTAs rarely developed and VF never occurs. With digitalis and higher concentration of caffeine (10 mM), neither VTAs nor VF were observed. In hearts with complete atrioventricular block, digitalis increased the ventricular rate from 143 +/- 10 to 270 +/- 13 beats/min (n = 8) in 12 +/- 1.9 min and provoked the appearance of multiple ventricular pacemakers. The addition of 10 mM caffeine to the digitalis-containing solution reduced the ventricular rate to 171 +/- 12 beats/min (P less than 0.001 vs. digitalis alone, not significant vs. control, n = 8) and abolished the digitalis-induced multiple pacemakers. Ventricular asystole was occasionally observed during the perfusion with digitalis + 10 mM caffeine. Caffeine alone did not modify the diastolic pressure, whereas caffeine and digitalis rapidly increase it. These results represent indirect evidence to support that SR plays an important role in the origin of the digitalis-induced VTAs.

On the pharmacokinetics of pengitoxin and its cardioactive derivative 16-acetyl-gitoxin

The pharmacokinetics of pengitoxin has been studied in 28 healthy subjects after intravenous and oral administration. The mean plasma concentration 24 h after 0.5 mg i.v. was 5.2 ng X ml-1. Following an open two-compartment model a mean elimination half-life of 60.5 h (24.9 to 103.5 h) and a mean volume of distribution (Vdarea) of 66.91 (31.8 to 109.61) were calculated. Absorption calculated by comparison of the AUC0-infinity-values amounted to 99%. Within 4 days, 16.7% (11.7 to 21.1%) or 27.8% (18.4 to 33.7%) (0.5 mg i.v. or 1.2 mg p.o.) was excreted in urine. After pengitoxin 0.5 mg i.v. total body clearance and renal clearance were 13.3 ml X min-1 (7.0 to 18.6 ml X min-1) and 3.0 ml X min-1 (1.9 to 3.9 ml X min-1) respectively. The elimination half-life of pengitoxin is longer than that of digoxin and distinctly shorter than that of digitoxin, whilst its distribution volume and clearance are closer to those of digitoxin than of digoxin.

Comparison of the pharmacokinetic parameters of digoxin and SC4453 a digoxin analogue, following a single bolus i.v. dose and following an infusion preceeded by an i.v. loading dose in the guinea-pig

The pharmacokinetics of SC4453 was studied in comparison with digoxin both after an intravenous injection and an intravenous infusion following an intravenous bolus injection of a loading dose in the guinea-pig. Doses of 7.8 micrograms/kg for digoxin and 30 micrograms/kg for SC4453 were administered as a bolus. The solutions were prepared from a stock solution (10(-3) M in ethanol-water 7:3) diluted with 0.9% saline. The half lives (t 1/2 beta) for digoxin and SC4453 were 8.4 h and 4.2 h respectively. The apparent volumes of distribution (V1) were respectively 11.4 l/kg and 3.7 l/kg. Using these parameters, an I.V. infusion was administered after an initial bolus injection of a properly calculated loading dose (D* = CpssV1). The perfusion constant K was calculated from the equation: K = CpssV1ke.

Relationship between myocardial uptake and actions in heart failure of methyldigoxin

1 Problems have been encountered in recent years in confirming useful benefit to patients with heart failure and sinus rhythm from acute exposure to digitalis glycosides, though effectiveness of these preparations upon cardiac contractile performance is indisputable. Undesired effects such as those upon systemic vascular resistance have been invoked to explain this. 2 Detailed haemodynamic responses have been studied by cardiac catheterisation in nine such patients for 30 min after intravenous methyldigoxin infusion. Myocardial glycoside uptake was simultaneously assessed. 3 Methyldigoxin uptake by the heart was rapid, passing its peak within 20 min, and was followed by substantial elution. 4 A small progressive and significant increase in cardiac output was observed, though left ventricular filling pressures were not significantly reduced after methyldigoxin. Cardiac contractile function as assessed by left ventricular maximum dP/dt, measured in six patients, showed consistent improvement.

[Digitalization without saturation dose using methyldigoxin. Experiences with 29 patients]

The indications and performance of oral digitalization without saturation dose are evaluated on the basis of clinical parameters and plasma digitalis levels. A group of patients with evident cardiac insufficiency received a daily maintenance dosage of digitalis (2 tablets of 0.1 mg methyldigoxin) from the outset. After 7, 15 and 30 days the plasma concentration of methyldigoxin was measured. Objective and subjective signs of cardiac insufficiency were noted. In 28 of 29 patients the therapeutic plasma level (0.8-2.0 ng/ml) was achieved with a mean plasma digitalis concentration of 1.47 +/- 0.4 ng/ml. A clinical improvement was observed in 18 patients. On the 15th and 30th day of treatment the mean plasma level of methyldigoxin showed no significant difference: X15 = 1.51 +/- 0.57 ng/ml and X30 = 1.40 +/- 0.46 ng/ml. The measured plasma values were not influenced by the patient's weight or age. In 6 patients with renal insufficiency a clear correlation between the plasma level of methyldigoxin and the creatinine level was observed. The evaluation of ECG signs showed only minimal alterations of conduction and repolarisation. On the basis of these results conclusions are drawn with regard to the clinical value and use of this therapy.

Hypermagnesemic periodic paralysis: treatment with digitalis and lithium carbonate

An 18-year-old man suffering from a hereditary hyperkalemic periodic paralysis showed, in addition, a hypermagnesemic periodic paralysis with a 2.5-fold increase in serum magnesium level. All other serum electrolyte levels were normal. The hypermagnesemic periodic paralysis seems to have been caused by a disturbance of the renal tubular system. Thus, magnesium-stimulated paralysis was prevented by treatment with lithium carbonate and digitalis, which blocked the active ion transport.

Influence of 16 beta formylation on Na, K-ATPase inhibition by cardiac glycosides

The inhibitory effect of formylated cardiac steroids (gitaloxin and its derivatives) on guinea-pig heart Na, K-ATPase was compared to that of other cardiac steroids with various hydroxy substituents. The decreasing order of potency of aglycones at equilibrium was as follows: gitaloxigenin greater than digitoxigenin greater than ouabagenin greater than digoxigenin greater than gitoxigenin greater than diginatigenin. This sequence was different to the sequence of drugs hydrophobic character. The compounds with hydroxy groups in the vicinity of the lactone ring (gitoxigenin, diginatigenin) were less potent than the hydrophilic compound ouabagenin. We propose that intramolecular bounding between 16 beta-OH and the lactone ring contributes to the relatively low potency of gitoxigenin and diginatigenin. The formylation of 16 beta-OH increased the potency of gitoxigenin by a factor of 41. The formylated compound (gitaloxigenin) was 5-fold more potent than digitoxigenin. The 3 beta-glycosylation of digoxigenin lead to pseudo-irreversible inhibitors of Na, K-ATPase. The half-time to achieve the equilibrium (for 5 mumol/l) was equal to 54 s, 90 s and 108 s respectively for digoxigenin monodigitoxoside, digoxin and desacetyllanatoside C. However, at equilibrium the three glycosides were equipotent, suggesting the existence of steric effects at the sugar site of the receptor. The sequence of potency observed for monodigitoxosides, monodigitalosides and tridigitoxosides after 60 min incubation was similar to that observed for the corresponding aglycones. These results suggest that the strongly negative inductive group 16 beta-OCHO is tightly bound to Na, K-ATPase, possibly to the same receptor site than that which is thought forming hydrogen and ionic bonds with the lactone ring. They show that the high toxicity of gitaloxin in guinea-pig heart is likely due to its high potency as Na, K-ATPase inhibitor.

[Effect of a fiber-rich diet on digoxin resorption]

In five female healthy volunteers the influence of dietary fiber (wheat bran or carob seed flour) on absorption of digoxin was investigated. Five minutes after ingestion of a formula diet alone or in combination with wheat bran or carob seed flour 0,8 mg beta-acetyldigoxin was given per os. The plasmaconcentration-time curve over eight hours, the area under curve and the cumulative urinary excretion were not changed significantly. It was concluded that there is no influence of dietary fiber on rate or degree of digoxin-absorption.

Metabolism of digoxin and absorption site

After oral intake of enteric-coated granules containing [3H]-digoxin extensive metabolism was observed. Maximum 66% of the 24 h urinary excretion was identified as [3H]-dihydrodigoxin, using high performance liquid chromatography for the analysis. It is suggested that metabolism of digoxin may depend on the absorption site.

Excretion of digoxin and its metabolites in urine after a single oral dose in healthy subjects

The 3-day urinary excretion of digoxin, its conjugated and unconjugated hydrolytic metabolites and dihydrodigoxin, was studied in 8 healthy men after oral administration of tritiated digoxin. Analysis was performed by high pressure liquid chromatography (HPLC). The total radioactivity corresponded to 45.4 +/- 2.0 per cent (mean +/- S.E.M.) of the dose. By HPLC 42.4 +/- 2.7 per cent was recovered before and 44.0 +/- 2.7 per cent after deconjugation of the samples. Digoxin and dihydrodigoxin constituted 40.3 +/- 2.9 per cent; of this 0.7 +/- 0.4 per cent was dihydrodigoxin. The sum of the hydrolytic metabolites was 2.1 +/- 0.3 per cent before and 3.4 +/- 0.5 per cent after deconjugation. No correlation was found between gastric pH and the production of hydrolytic metabolites. The relative amount of these metabolites was maximal (mean 13.4 per cent of the excretion) in the 4-8 h sampling period. During the first 8 h an average of 8.6 per cent of the radioactivity was not recovered by HPLC. The metabolism of digoxin as judged by urinary excretion was limited and showed great variation during the early hours after treatment. The excretion of unchanged digoxin in some individuals constituted as little as 60 per cent over the first 12 h after dosing.

Digoxigenin biotransformation

Two healthy subjects took 3H-digoxigenin-12 alpha and unlabeled digoxigenin. Metabolites were assayed by high-pressure liquid chromatography (HPLC) in serum and urine. Of the tritium activity in the serum at 30 min, less than 26% chromatographed with digoxigenin; the rest chromatographed as metabolites, most of which were polar. The main polar metabolites identified were glucuronides of 3-epidigoxigenin. An important route of biotransformation to polar metabolites appears to be from 3 beta-digoxigenin through 3-keto-digoxigenin to 3-epidigoxigenin. Several HPLC peaks remain unidentified. There was extensive cross reactivity between metabolites and antisera to digoxin. The digoxigenin route of digoxin biotransformation to polar metabolites may be important in some patients receiving digoxin and such metabolites could contribute an important fraction to the serum digoxin concentration measured by radioimmunoassay.

[Bioavailability of digoxin and beta-methyl-digoxin in patients with liver and gastro-intestinal diseases ]

The bioavailability of digoxin and beta-methyl-digoxin (BMD) was tested with a single dose on the grounds of peak serum concentration, tmax, area under the serum concentration-time curve and the cumulative 24 hour urinary excretion on one group of patients with liver disease (n = 20) and one with gastrointestinal disease (n = 10). Despite the smaller dose (0.5 mg BMD against 0.75 mg digoxin), peak serum concentration was significantly higher with BMD in both groups and was also reached earlier than with digoxin. The extent of absorption was also higher in both groups with BMD than with digoxin. A comparison of the results on hand with the results obtained in corresponding tests on healthy persons showed no significant differences with BMD. The excellent bioavailability of BMD was therefore also proved on patients with gastrointestinal diseases, whereas with digoxin the absorption in these patients was retarded, compared with healthy persons, but the extent of absorption was not reduced either. In gastrointestinal diseases with unknown conditions of absorption, the better bioavailability of BMD is probably of advantage, when compared with digoxin. According to medical literature, t/2 of BMD may be prolonged in liver diseases, so that in such cases the dose of BMD has to be adjusted or the use of digoxin is recommended.

The development and application of a radioimmunoassay for dihydrodigoxin, a digoxin metabolite

The cardioinactive digoxin metabolite, dihydrodigoxin, has been conjugated to bovine serum albumin and to bovine pancreatic ribonuclease by the periodate oxidation method. Rabbits immunized with the dihydrodigoxin-bovine serum albumin conjugate formed antibodies which bound a radioiodinated dihydrodigoxin-ribonuclease conjugate. This binding was inhibited by dihydrodigoxin. After affinity chromatography on a digoxin-ribonuclease-Sephacryl immunoadsorbent to remove antibodies which cross-reacted with digoxin, dihydrodigoxin was 300 times more effective than digoxin in inhibiting the binding of tracer by antibody. Digoxin-absorbed antidihydrodigoxin antibodies were coupled to Sephacryl and were used to develop a solid-phase radioimmunoassay capable of detecting 250 to 500 pg of dihydrodigoxin in 1 ml of human serum or urine. This radioimmunoassay has been used to define the pharmacokinetics of the metabolite in four normal human volunteers who ingested 125 to 500 micrograms of dihydrodigoxin by mouth. Dihydrodigoxin was quickly absorbed, with maximal serum concentrations achieved within 45 to 105 min, followed by a rapid fall in serum immunoreactivity over 2 to 4 hr and then by a slower, more gradual decline. The terminal half-life (beta) in serum varied from 4.24 to 11.9 hr (mean +/- S.E. = 8.1 +/- 1.3 hr). Most of the administered dose was excreted in the urine, with cumulative urinary recovery varying inversely with the dose. Urinary half-lives averaged 13.8 +/- 2.1 hr, and renal clearance rates were similar to those of creatinine. Dihydrodigoxin is rapidly absorbed and excreted in man and appears to be eliminated from the body at a faster rate than digoxin.