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Spontaneous resumption of sinus rhythm in an elderly patient after 13 years of permanent atrial fibrillation.

One female patient--with slight pure mitral stenosis, mild hypertension and ischemic cardiomyopathy and disabling pulmonary emphysema--developed at 54 years of age permanent atrial fibrillation, had a gratuitous mitral commissurotomy four months later, sustained chronic fibrillation for 13 years, then spontaneously resumed sinus node command at age 67 without any discernible reason. Sinus rhythm was being maintained at follow-up nine months later. Her cardiac status of fair compensation under modest digitoxin and diuretic therapy has neither improved nor worsened with the return of atrial systole. The duration, in this observation, of permanent auricular fibrillation before spontaneous return of sinus rhythm, is one of the longest ever published, exceeded, to the best of my knowledge, only by one case of Lewis and by another one of Reeve and associates. Such an exceptional event points out a fascinating enigma: how can major longstanding atrial dysrhythmias (fibrillation, flutter), whose causes and pathogenesis seem at least partly elucidated, spontaneously disappeer in atria so badly diseased? I think we must humbly confess that no satisfactory explanation is at present available for this disconcerting phenomenon.

Adult↗

Fast atom bombardment and tandem mass spectrometry for structure determination of steroid and flavonoid glycosides.

The combination of fast atom bombardment (FAB) and tandem mass spectrometry (MS-MS) was tested for its applicability to generate useful structural information for steroid and flavonoid glycosides. The following compounds were investigated: quercetin, myricitrin, apigetrin, fraxin, rutin, neohesperidin, hesperidin, naringin, apiin, cymarin, digoxin, digitoxin, xanthorhamnin, and frangulin. Upon FAB, the sample molecules are desorbed as (M + H)+, (M - H)-, or as (M + Na)+ or (M + K)+. Collisional activation of (M + H)+ or (M - H)- ions in the MS-MS experiment leads to sequential losses of glycoside moieties in a manner which permits the sequence of glycosides to be established. Some glycosides occur as mixtures of homologs. Proper interpretation of the MS-MS or collisional activation decomposition spectra often allows the homology to be located. In addition to the simple and highly selective fragmentations observed in this combined experiment, FAB and MS-MS also remove interference caused by the ubiquitous matrix ions which are desorbed by FAB.

Chemical Phenomena↗

Interaction of cardiac glycosides and Na,K-ATPase is regulated by effector-controlled equilibrium between two limit enzyme conformers.

The paper describes the dissociation parameters of the complexes between [3H]-digitoxin and Na,K-ATPase (Na+ + K+-activated, Mg2+-dependent ATP phosphohydrolase, E.C. 3.6.1.3) from pig cardiac muscle and brain cortex formed and dissociated in the presence of different combinations and concentrations of the enzyme effectors ATP, Mg2+, Na+ and K+. Systematic variation of effector-ligation of Na,K-ATPase allowed production of glycoside complexes with two enzyme conformers only, which showed either rapid or slow dissociation kinetics. Appropriate changes of enzyme ligation allowed the interconversion of the two conformer types. Biphasic, rapid and slow glycoside release was not bound with the presence of two Na,K-ATPase isozymes, but caused by the enzyme ligation-determined coexistence of the two conformers of Na,K-ATPase. The rate constants for the rapid and slow glycoside release were within the complexes of each dissociation type much alike indicating uniform isomerization kinetics of the two conformers even when differently liganded. Taken together, the observations indicated the effector-controlled isomerizations of two conformers of Na,K-ATPase possessing different geometries of the glycoside binding domain. Present findings and relevant literature data were integrated in a circular, consecutive and simultaneous model for induced conformation changes that accounted for the regulation of the interaction of cardiac glycosides and Na,K-ATPase through an effector-controlled equilibrium between two limit enzyme conformers.

Adenosine Triphosphate↗

A comparative study of the homogeneous enzyme immunoassay (EMIT) and two radioimmunoassays (RIA's) for digoxin.

Our experience with the determination of digoxin in plasma or serum using a homogeneous enzyme immunoassay technique (EMIT) is reported. The day-to-day precision of the EMIT digoxin assay was investigated with different series of calibrators. Coefficients of variation varied from 10 to 25 percent in the range of 0.65--7.0 ng digoxin/ml. The accuracy was established by determining the mean recovery (96 percen) of spiked serum samples (0.0--6.0 ng digoxin/ml). The cross reactivity of structure related compounds: digitoxin, spironolactone (Aldactone) and prednisone were investigated. Amniotic fluid, umbilical cord serum and serum of pregnant patients were examined for false positive reaction. Serum samples of 111 patients from two hospitals, who were treated with digoxin, were analysed by EMIT and 3H-radioimmunoassay (RIA); 38 of these samples were also determined by 125I-RIA. A good correlation was found between EMIT assay and these techniques (r =0.90 and 0.91, respectively).

Animals↗

High affinity and low affinity ouabain binding sites in the rat heart.

Ventricular muscle of rat heart has two classes of receptors which are responsible for the positive inotropic effect of ouabain. Low affinity receptors are apparently related to Na+, K+-ATPase. To determine if high affinity receptors are also sarcolemmal Na+, K+-ATPase of muscle cells, their characteristics were examined. Binding of [3H]ouabain to the high affinity binding site required ATP in the presence of Mg2+ and Na+, was stimulated by Na+ in the presence of Mg2+ and ATP, and was inhibited by K+. Digoxin, digitoxin and cassaine all inhibited [3H]ouabain binding to the high affinity site. Cassaine was about an order of magnitude less potent than the glycosides. These results indicate similarities in high affinity ouabain binding sites in ventricular muscle of rat heart and Na+, K+-ATPase obtained from other sources. Destruction of sympathetic nerve terminals with 6-hydroxydopamine failed to affect the high affinity ouabain binding sites indicating that high affinity sites do not represent the Na+, K+-ATPase in sympathetic nerve terminals. Labeling of Na+, K+-ATPase from [gamma-32P]ATP indicates that high affinity ouabain binding sites account for 25% of the total enzyme molecules present in ventricular muscle of rat heart.

Animals↗

Sugar moiety of cardiac glycosides is essential for the inhibitory action on the palytoxin-induced K+ release from red blood cells.

Palytoxin (PTX), a highly toxic and sugar-containing substance isolated from Palythoa tuberculosa, caused K+ release from rabbit red blood cells. Cardiac glycosides, such as ouabain, convallatoxin, cymarin, digoxin and digitoxin, inhibited the PTX-induced K+ release. Their corresponding aglycones did not inhibit the K+ release, but antagonized the inhibitory effect of the glycosides. All these cardiotonic steroids equally inhibited the activity of (Na+ + K+)-ATPase prepared from hog cerebral cortex. These results suggest that the sugar moiety of the cardiac glycosides is important for the inhibitory effect on the K+ release induced by PTX and that the inhibition is not related to their inhibitory potency on the (Na+ + K+)-ATPase activity.

Acrylamides↗

Suncus murinus: a new experimental model in emesis research.

Effects of various emetic and antiemetic drugs were studied using Suncus murinus for its potential use as an experimental model in emetic research. Subcutaneous injection of nicotine bitartrate (10-15 mg/kg), veratrine sulfate (0.5-1.0 mg/kg), emetine dihydrochloride (40-80 mg/kg) and oral administration of copper sulfate (20-100 mg/kg) caused dose-dependent emesis in suncus. The ED50 of nicotine, veratrine, emetine and copper sulfate were 7.9, 0.4, 47.6 and 21.4 mg/kg, respectively. However, subcutaneously injected apomorphine hydrochloride (0.1-100 mg/kg), digitoxin (0.5-1.0 mg/kg) and orally administered emetine dihydrochloride (10-80 mg/kg) did not induce the vomiting. Chlorpromazine and promethazine decreased the emetic effect of nicotine, veratrine and copper sulfate, but scopolamine hydrobromide was not effective. These results indicate that the Suncus murinus is sensitive to various emetic and antiemetic drugs and can be used as a new experimental animal model for the emesis. Emetic behavior of suncus was discussed in comparison with other animals.

Animals↗

Influence of age-related changes in rodent liver morphology and physiology on drug metabolism--a review.

Age-related changes in weight, morphology and physiology of the rodent liver influencing hepatic drug metabolism are reviewed. Next to the changes in liver weight/body weight ratio with age, the spontaneous occurrence of neoplastic and non-neoplastic lesions may be of particular importance. In addition, the decrease in liver blood blow with age diminishes the biotransformation capacity of the total liver. However, the albumin concentration in plasma and drug uptake do not play important roles, since they are unchanged or only slightly lower in old rats or mice. Drugs are generally metabolized by the liver in two phases: the so-called phase I and phase II metabolism. For most drugs, the phase I reaction is an oxidation. This reaction is catalyzed by cytochrome P-450, cytochrome b5 and NADPH-cytochrome c reductase. In microsomes, a decrease with age is generally observed in the cytochrome P-450 concentration and the NADPH-cytochrome c reductase activity, while there is no change in cytochrome b5. In addition, most microsomal drug-metabolizing enzymes decrease with age in male rats but not in females. The changes in enzyme activities in the male and female mouse are more complex. In fact, increases, decreases and no changes were found. Important phase II reactions are glutathione conjugation and glucuronidation; changes in both reactions with age seem to be of minor importance. Studies with hepatocytes isolated from male rats of different ages reveal that the monooxygenase system mediated metabolism of digitoxin and aflatoxin B1 decreases with age. It can be concluded that the observed decrease in the functional capacity of the monooxygenase system greatly determines the decrease in drug metabolism with age. However, it should always be kept in mind that, among others, the age-related changes in drug metabolism in rats are strongly sex dependent, which is not the case in man. Therefore, caution should be exercised in transferring these data to the human situation.

Aging↗

Sex difference in the biliary excretion of digoxin and its metabolites in aging Wistar rats.

The biliary excretion of digoxin (Dg3) and its metabolites was studied in both young (3-month-old) and old (25- and 30-month-old) Wistar rats of both sexes. The 2 h biliary recovery (% of the dose) of intravenously injected [3H]Dg3 (0.01 mg/100 g) radioactivity was similar between young male and female rats, while the first 10 min excretion was significantly higher in females. In old (25-month-old) male rats, the 2 h biliary recovery of radioactivity was significantly lower than the corresponding young value. This was primarily due to the drastic decrease with age in excretion of bis-digitoxoside. On the other hand, in old female rats (25- and 30-month-old) the 2 h recovery value was not significantly different from the corresponding young (3-month-old) value. This was due to the much higher percentage (more than 80% of the total) of Dg3 in the female bile radioactivity which did not significantly decrease with age. The results suggest that the rate of stepwise cleavages of the sugar chain of Dg3 decreases with age more rapidly in male than in female rats as has been previously shown by the authors for digitoxin. Large sex differences observed in the age-dependent alteration in Dg3 metabolism and its biliary excretion raise a caution against a generalization of the data obtained from a single sex in this animal species with regard to the effect of aging.

Aging↗

Monitoring of ajmaline in plasma with high-performance liquid chromatography.

A rapid, reliable and sensitive assay for routine determination of ajmaline in plasma by high-performance liquid chromatography with fluorimetric detection is presented. A low limit of detection in plasma (less than 1 ng/ml ajmaline) could be achieved by the extraction of plasma samples and the use of fluorimetric detection. Deproteinization of the plasma sample instead of extraction, or the use of an ultraviolet detector, yielded a higher limit of detection (less than 50 ng/ml). Two different eluents were studied. Eluent 1 allowed clear separation of ajmaline from isoajmaline and sandwicine, but did not separate isoajamaline from sandwicine. With eluent 2, separation of isoajmaline and sandwicine was achieved, but separation of ajmaline from sandwicine was less optimal than with eluent 1. Therefore, eluent 1 was used for further clinical studies. No interference was observed from therapeutic doses of other commonly co-administered drugs, such as acetylsalicylic acid, digoxin, digitoxin, ranitidine, dopamine, dobutamine, furosemide, captopril or glycerol trinitrate. In addition, the chemical stability of ajmaline and a possible rearrangement of ajmaline to its stereoisomers isoajmaline and sandwicine was studied in vivo and in vitro. Ajmaline proved to be unusually stable under both in vivo and in vitro conditions.

Ajmaline↗

Specific and sensitive determination of digoxin and metabolites in human serum by high performance liquid chromatography with cyclodextrin solid-phase extraction and precolumn fluorescence derivatization.

A precolumn fluorescence derivatization high performance liquid chromatographic method has been developed for the simultaneous determination of digoxin and its metabolites digoxigenin bisdigitoxoside, digoxigenin monodigitoxoside digoxigenin, and dihydrodigoxin (20-R and 20-S epimers) in human serum. Digoxin and its metabolites were extracted from serum samples (containing digitoxin as internal standard) with a cyclodextrin solid-phase extraction (SPE) column. Fluorescent derivatives were formed by reaction of the analytes with 1-naphthoyl chloride in the presence of 4-dimethylaminopyridine under a nitrogen atmosphere in a glove box with controlled relative humidity (26% r.h. or less). The derivatives were isolated using cyclodextrin and C1 SPE columns sequentially, and determined by HPLC using silica column separation and fluorescence detection. Calibration curves were linear over the concentration range from 0.25 to 4.0 ng ml-1. Recoveries of digoxin and its metabolites from serum ranged from 62 to 86%, and coefficients of variation from repetitive analyses ranged from 6.9 to 20.9% and from 5.8 to 12.2% at 0.5 ng ml-1 and 2.0 ng ml-1, respectively. This method has been shown capable of specifically determining digoxin and its major metabolites in serum, and has been successfully used in the determination of digoxin and its metabolites in serum samples collected from patients undergoing digoxin therapy. This method thus permits the investigation of digoxin metabolism and pharmacokinetics after the administration of commercial dosage forms.

Calibration↗

Bretylium in severe ventricular arrhythmias associated with digitalis intoxication.

Bretylium has been well-recognized as an effective antiarrhythmic agent for acute ventricular arrhythmias, but its use is believed to be contraindicated in digitalis intoxication. We report of two patients in whom digitalis-induced malignant ventricular arrhythmias were refractory to lidocaine. One patient had had repeated episodes of ventricular fibrillation associated with digitoxin and quinidine intoxication, and one patient had had malignant premature ventricular beats associated with digoxin intoxication. Cardiac electrical activity was paced in both instances. In the two patients, ventricular arrhythmias rapidly resolved, and no side effect was encountered. These observations support the administration of bretylium for severe digitalis-induced ventricular arrhythmias.

Aged↗

Review of clinical experience with digoxin immune Fab (ovine).

Following the development of methods for eliciting and purifying digoxin-specific Fab fragments with high affinity and specificity for cardiac glycosides, clinical studies were undertaken as a multicenter, open-label trial to test safety and efficacy in patients with advanced and potentially life-threatening digitalis toxicity that failed to respond to conventional therapeutic measures. One-hundred fifty such patients were treated with digoxin-specific antibody fragments purified from immunoglobulin G (IgG) produced in sheep. Doses of Fab were equivalent to the amount of digoxin or digitoxin in the patient's body, as estimated from the medical history or serum concentration measurements. Of 150 patients included in this trial, detailed information is available on 148. One-hundred nineteen (80%) had resolution of all signs and symptoms of digitalis toxicity following specific Fab fragment infusions, 14 (10%) improved, and 15 (10%) showed no response. Among 14 patients with adverse events possibly or probably caused by Fab, the most common events were development of hypokalemia and exacerbation of congestive heart failure. Analysis of the available clinical data indicates that a treatment response was observed in at least 90% of patients with convincing evidence of advanced and potentially life-threatening digitalis toxicity. The data from this multicenter trial have been augmented by findings from an observational surveillance study conducted to monitor the safety and effectiveness of treatment with digoxin immune Fab (ovine) following commercial availability. In this experience, 74% of patients were judged to have a complete or partial response to treatment, and 12% no response. The response for the remaining 14% was not reported or reported as uncertain. In this clinical experience, digoxin-specific Fab was generally well tolerated and clinically effective in patients with potentially life-threatening digitalis toxicity.

Adolescent↗

Experience with digoxin immune Fab (ovine) in patients with renal impairment.

Digibind is a purified antigen binding fragment (Fab) of immunoglobulin G antibodies raised to bind digoxin. Studies in animals suggest renal excretion accounts for a substantial portion of Fab's elimination. Thus it is expected that elimination of antidigoxin Fab fragments would be prolonged in patients with renal impairment; it remains unclear whether digoxin might be released with possible recurrence of toxicity. To shed light on this potential for recrudescent digitalis toxicity following release of bound digoxin, the author scrutinized the records of patients with impaired renal function who were treated with Digibind. Data are available from three sources: the original multicenter investigation of Digibind in 150 patients with life-threatening digoxin or digitoxin toxicity, a postmarketing surveillance study of 745 patients treated with Digibind, and all other reports in the literature or to Burroughs Wellcome Co of physician experience with any antidigoxin Fab. Sixty percent of patients in the multicenter trial and 80% of patients in the postmarketing surveillance trial had some degree of renal impairment. Patients with poor renal function had no evidence of decreased effectiveness or safety either in terms of percent of patients responding, onset of effect or evidence of recrudescence. From all sources the authors identified 28 patients treated with Fab who were functionally anephric. Twenty-seven of these patients had no evidence of recrudescent toxicity. One patient was reported to have complete resolution of digoxin-induced third-degree atrioventricular (AV) block, but AV block recurred 10 days after Fab treatment and persisted for 10 days thereafter. Although this case offers the only clinical evidence suggesting recrudescence can occur, there were no likely alternative explanations for the clinical findings.(ABSTRACT TRUNCATED AT 250 WORDS)

Creatinine↗

Recognition and management of digitalis intoxication: implications for emergency medicine.

Digitalis intoxication is among the most common serious adverse drug reactions in clinical medicine. While the recent development of a radioimmunoassay to accurately measure serum concentrations of digoxin has been of assistance, digitalis intoxication remains a difficult diagnosis to make with certainty. The difficulty in diagnosing digitalis intoxication arises from the nonspecificity of its associated signs and symptoms. The most common symptoms include fatigue, weakness, nausea, and anorexia. These symptoms can occur with many illnesses other than digitalis intoxication. Similarly, the electrocardiographic disturbances caused by cardiac glycosides may be nondiagnostic. The arrhythmias commonly associated with digitalis toxicity are often nonspecific and can be a reflection of the patient's underlying heart disease. The measurement of serum digoxin levels is useful, but studies have demonstrated overlap of the levels between groups with and without toxicity. Due to the modulation of the cardiac effects of digitalis glycosides by such clinical variables as underlying myocardial or renal disease, electrolyte and acid-base imbalances, and other factors, the correlation of toxicity with particular serum digoxin concentrations may vary. Because of the inherent difficulties in confirming the diagnosis of digitalis intoxication in some cases, digoxin-specific Fab antibodies may play a role as a diagnostic tool. Certainly, digoxin-specific Fab antibodies play a significant part in the treatment of digitalis intoxication. Fab antibodies have been successfully used to reverse the effects of digoxin, digitoxin, and oleander poisoning. These antibodies are useful in the treatment of acute and chronic digitalis intoxication in all age groups, including geriatric and pediatric populations.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical Protocols↗

The new black magic: activated charcoal and new therapeutic uses.

Activated charcoal has been used for centuries as antidotal therapy for poisonings. New variations of charcoal therapy have developed over the last two decades. These modifications include multiple-dose activated charcoal (MDAC) therapy, charcoal hemoperfusion, and a new "superactive" charcoal (SAC). Recent literature suggests using initial charcoal therapy instead of ipecac as a first-line antidotal agent for many acute poisonings. The palatability of charcoal slurries has been enhanced by the addition of carboxymethylcellulose, sucrose, saccharin, chocolate syrup, or sorbitol. The new SAC has shown to adsorb 1.7 to 4 times the amount of substance tested compared with other activated charcoal preparations. Multiple-dose activated charcoal therapy has been shown effective in treating phenobarbital, digoxin, digitoxin, theophylline, and dapsone intoxications, among others. The problems associated with charcoal hemoperfusion therapy have been partially alleviated, and it is now alternative therapy for the seriously intoxicated patient.

Charcoal↗

Heme impairs allosterically drug binding to human serum albumin Sudlow's site I.

Human serum albumin (HSA), the most prominent protein in plasma, is best known for its exceptional ligand (e.g., heme and drugs) binding capacity. Here, the binding of chlorpropamide, digitoxin, furosemide, indomethacin, phenylbutazone, sulfisoxazole, and tolbutamide to HSA and ferric heme-HSA is reported. Moreover, ferric heme binding to HSA in the absence and presence of drugs has been investigated. Values of the association equilibrium constant for drug binding to Sudlow's site I of ferric heme-HSA (ranging between 1.7 x 10(3) and 1.6 x 10(5)M(-1)) are lower by one order of magnitude than those for drug binding to ferric heme-free HSA (ranging between 1.9 x 10(4) and 1.8 x 10(6)M(-1)). According to linked functions, the value of the association equilibrium constant for heme binding to HSA decreases from 7.8 x 10(7)M(-1), in the absence of drugs to 7.0 x 10(6)M(-1), in the presence of drugs. These findings represent a clear-cut evidence for the allosteric inhibition of drug binding to HSA Sudlow's site I by the heme. According to linked functions, drugs impair allosterically heme binding to HSA. These results appear to be relevant in the drug therapy and management.

Allosteric Site↗

Chromatographic analysis of carbamazepine binding to human serum albumin.

In this study, high-performance affinity chromatography was used to characterize the binding of carbamazepine to an immobilized human serum albumin (HSA) column. Frontal analysis was first used to determine the association equilibrium constant and binding capacity for carbamazepine on this column at various temperatures. The non-specific binding of carbamazepine within the column was also considered. The results indicated that carbamazepine had a single binding site on HSA with an association equilibrium constant of 5.3 x 10(3)M(-1) at pH 7.4 and 37 degrees C. This was confirmed through zonal elution self-competition studies. The value of DeltaG for this reaction was -5.35 kcal/mol at 37 degrees C, with an associated change in enthalpy (DeltaH) of -6.45 kcal/mol and a change in entropy (DeltaS) of -3.56 cal/molK. The location of this binding region was examined by competitive zonal elution experiments using probe compounds with known sites on HSA. It was found that carbamazepine had direct competition with l-tryptophan, a probe for the indole-benzodiazepine site of HSA, but allosteric interactions with probes for the warfarin, tamoxifen and digitoxin sites. Changes in the pH, ionic strength, and organic modifier content of the mobile phase were used to identify the predominant forces in the carbamazepine-HSA interaction.

Allosteric Site↗