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Is the volume of distribution of digoxin reduced in patients with renal dysfunction? Determining digoxin pharmacokinetics by fluorescence polarization immunoassay.

STUDY OBJECTIVE: To determine digoxin pharmacokinetics in subjects with different degrees of renal function using fluorescence polarization immunoassay (FPIA), which is associated with less interference from digoxin-like immunoreactive substances (DLIS) than radioimmunoassay. SETTING: University hospital clinical research center. PARTICIPANTS: Eighteen subjects (mean age 44 yrs) with different degrees of renal function: group 1, creatinine clearance (Clcr) below 10 ml/minute; group 2, Clcr 10-50 ml/minute; and group 3, Clcr greater than 50 ml/minute (6 patients in each group). INTERVENTION: Over 5-7 days, 15 serum samples were collected after a single intravenous dose of digoxin 7 or 10 micrograms/kg actual body weight (WT) for serum concentration measurements by FPIA. Two-compartment pharmacokinetic parameters (zero-time intercept of the concentration-time curve of the initial distribution phase [A], zero-time intercept of the concentration-time curve of the terminal elimination phase [B], initial distribution phase constant [alpha], terminal elimination rate constant [beta], volume of distribution in the central compartment [Vc] and at steady state [Vss], total body clearance [Cl], mean residence time [MRT], area under the concentration-time curve [AUC]) were determined using a nonlinear least squares regression program. MEASUREMENTS AND MAIN RESULTS: No significant differences were found among groups for A, B, alpha, beta, beta-half-life Vc/WT, MRT, AUC, and Cl/WT. Significant differences were observed in Vss/WT (4.8 +/- 1.0, 6.6 +/- 0.5, 6.4 +/- 0.7 L/kg) between group 1 versus group 2 and group 1 versus group 3 (p < 0.01). Measured Clcr was correlated with Cl (r2 = 0.40, p < 0.01), Cl/WT (r2 = 0.29, p < 0.05), Vss (r2 = 0.35, p = 0.01), and Vss/WT (r2 = 0.24, p < 0.05). CONCLUSION: This study confirmed that Vss is smaller in patients with chronic renal failure (Clcr < 10 ml/min) than those without chronic renal failure. Therefore, previous recommendations that lower digoxin loading doses should be administered in patients with renal failure are applicable to digoxin serum concentration monitoring using FPIA.

Adolescent↗

Correlation between electrocardiographic changes, serum digoxin, and total body digoxin content.

Serial electrocardiograms and serum digoxin levels were obtained in four healthy volunteers receiving daily doses of digoxin, 0.25 mg for the first two weeks and 0.5 mg for two more weeks. We found a linear relationship between serum digoxin levels and the "PTQ index" (a function of the PR-interval, corrected QT-time, and T-wave depression). In 3 of the 4 subjects the correlation was statistically significant. The degree of linear correlation was improved when PTQ was correlated with the computer-calculated total body burden of digoxin.

Adult↗

Relationship of serum and myocardial digoxin concentration to electrocardiographic estimation of digoxin intoxication.

Serum and myocardial digoxin levels were studied in 18 patients who came to autopsy. An independent analysis of electrocardiograms prior to death was made to ascertain the relationship between serum and tissue levels of digoxin and clinical estimation of drug toxicity. Patients with arrhythmias of digoxin toxicity had higher mean serum and tissue digoxin levels than patients without arrhythmia. There was overlap in the patient groups, however, and the differences were not statistically significant. The tissue to serum ratio was lower in the toxic patients. The latter phenomenon is unexplained but may be related to decreased tissue binding.

Aged↗

Interference from digoxin-like immunoreactive substance(s) in commercial digoxin kit assay methods.

We have examined the current state of interference by digoxin-like immunoreactive substance(s) (DLIS) in 10 commercially available digoxin assay methods, ie 5 radioimmunoassays (RIA) and 5 non-radioactive immunoassays. Fifty-five specimens of maternal venous blood (30 from third trimester pregnancy and 25 at delivery) and 32 cord samples from their offspring were tested (none of the subjects being medicated with digoxin). The results demonstrated a wide range of DLIS interference with values up to 1.1 micrograms.l-1 being obtained in the cord blood specimens. Of the methods tested the "Coat-a Count" RIA (Diagnostic Products Corporation) and the EMIT column method (Syva) run on the Cobas MIRA (Roche) consistently showed the least interference with respect to all 3 sources of specimens. The Delfia Method (LKB/Wallac) consistently showed the greatest crossreactivity with DLIS. The present study thus demonstrates that DLIS interference persists in several commercial digoxin methods and suggests that the use of data obtained from such methods may compromise patient management.

Blood Proteins↗

Comparative effects of the combination of digoxin and dl-sotalol therapy versus digoxin monotherapy for control of ventricular response in chronic atrial fibrillation. dl-Sotalol Atrial Fibrillation Study Group.

To establish the value of adjuvant dl-sotalol to digoxin for control of the ventricular response in chronic atrial fibrillation, 60 patients were evaluated in a multicenter, randomized, double-blind, parallel, placebo-controlled study. Patients were evaluated with serial ambulatory ECG monitoring and exercise testing during stable digoxin dosing and then with the addition of either a placebo or dl-sotalol, 80 mg/day, or dl-sotalol, 160 mg/day. The combination of digoxin and dl-sotalol, at either 80 or 160 mg/day, resulted in a statistically significant reduction in heart rate at rest and with exercise during both exercise testing and ambulatory monitoring. No significant difference was observed between the two doses of dl-sotalol. There was no significant difference with regard to symptoms or side effects among the three groups. In summary, dl-sotalol was noted to be a safe and effective adjuvant to digoxin for control of the ventricular response in chronic atrial fibrillation.

Atrial Fibrillation↗

Enalapril versus digoxin in patients with congestive heart failure: a multicenter study. Canadian Enalapril Versus Digoxin Study Group.

Patients with New York Heart Association functional class II or III heart failure stabilized on furosemide therapy were entered into a randomized controlled trial comparing enalapril (n = 72) and digoxin (n = 73). End points were clinical outcome, treadmill exercise capacity and echocardiographic left ventricular dimensions. Improvement in clinical outcome was defined as a reduction of at least one functional class or withdrawal because of an adverse clinical event. After 4 weeks, 13 patients receiving enalapril showed improvement, 55 had no change and 9 manifested deterioration compared with 7, 49 and 17, respectively, in the digoxin group (p less than 0.01). After 14 weeks, 13 patients receiving enalapril showed improvement, 50 had no change and 9 manifested deterioration, compared with 14, 37 and 22, respectively, in the digoxin group (p less than 0.025). More patients in the digoxin group were withdrawn because of an adverse clinical event (p less than 0.05). Exercise time and percent fractional shortening improved in both groups (p less than 0.001 and less than 0.05, respectively), with no significant difference between groups (p greater than 0.50). Both rate-pressure product and subjectively evaluated exertion during submaximal exercise were reduced only in the enalapril group. Although the majority of patients in both groups did well, those receiving enalapril experienced fewer adverse clinical events and had less fatigue during submaximal exercise.

Adult↗

Radioimmunoassay of digoxin in serum using monoclonal antibodies and assessment of interference by digoxin-like immunoreactive substances.

We used 7 monoclonal antibodies (MoAbs) and one polyclonal antibody to develop radioimmunoassays (RIAs) for digoxin in serum or plasma. These RIAs were tested for measuring apparent digoxin concentrations in serum from patients receiving the drug, from normal individuals, and in cord blood plasma. We found that two MoAbs cross-reacted significantly with substances in cord blood. The magnitude of cross-reactivity was dependent on the incubation time and temperature. Under equilibrium conditions, one antibody gave apparent digoxin values in cord blood plasma averaging 2.15 ng/ml. We suggest that this cross-reactivity is partially due to progesterone and 17-hydroxyprogesterone in cord blood plasma. The antibody that shows high cross-reactivity with digoxin-like immunoreactive substances may prove a useful tool for studies dealing with characterization of the cross-reacting compounds.

Adult↗

Interference of digoxin-like immunoreactive substances with TDx digoxin II assay in different patients.

The TDx digoxin II immunoassay was used in controls and in patients not taking digoxin or any other cardiac glycoside. We report the frequency of interference thought to be caused by digoxin-like factors (DLFs). We found a high incidence of false-positive results in 15 patients with severe hepatic disease (60% false-positive results). In newborn infants we found false-positive results both when their blood was drawn from a peripheral vein (89% false-positive results) and, more strikingly (100% false-positive results), when it was obtained from an umbilical cord vein (p less than 0.001). Compared to a control group, no statistically significant false-positive results were found in patients with mild to moderate chronic renal failure (n = 21) or in pregnant women (n = 15). In patients with chronic renal failure undergoing hemodialysis six of 25 had false-positive results. These results suggest that digoxin levels must be interpreted carefully in patients with chronic liver disease and chronic renal failure and in newborns until new methods that eliminate the interference caused by DLFs become readily available.

Adult↗

Treatment of human serum with sulfosalicylic acid structurally alters digoxin and endogenous digoxin-like immunoreactive factor.

Pretreatment of human serum with 5-sulfosalicylic acid (SSA) as used in the Abbott TDx digoxin assay produces deglycosylated congeners of digoxin (DIG) and of endogenous digoxin-like immunoreactive factor (DLIF). Using high-performance liquid chromatography analysis, we observed differences in the degree and pattern of DIG breakdown products among five patients. The aglycone digoxigenin was the major product in several samples. Smaller amounts of the bis- and mono-digitoxosides and unidentified products less polar than DIG were sometimes present. Treatment of DLIF-containing plasma with SSA produced similar patterns of DLIF-breakdown products. Incubation of normal plasma containing DIG with SSA for up to 30 min caused little change in measured DIG by TDx and radioimmunoassay (RIA) but decreased to 50% in the ACS DIG assay. These results are consistent with the near 100% cross-reactivities of deglycosylated DIG congeners in the TDx and RIA assays compared to their lower cross-reactivities in the ACS assay. We conclude that the breakdown of DIG and DLIF during treatment of serum with SSA may compromise the accuracy of TDx DIG assays and may explain discrepancies observed in other studies between digoxin immunoassays. This study underscores the importance of understanding the effects of pretreatment strategies used for analytes measured by immunoassay.

Benzenesulfonates↗

Digoxin-like immunoreactive substance in the elderly patient and its impact on the TDx digoxin assay.

This study was undertaken to examine the impact of endogenous digoxin-like immunoreactive substance (DLIS) on the therapeutic drug monitoring of digoxin in elderly patients. Serum digoxin concentrations were detected by TDx digoxin assay in 220 patients 65 years of age and older who were not administered cardiac glycosides, spironolactone, or canrenone. The influence of clinical factors and laboratory parameters on the presence of DLIS was also evaluated. The concentration of DLIS averaged .07 ng/ml (range, 0-0.74 ng/ml), and in 25 subjects DLIS was observed over the detection limit of the assay. None of the parameters demonstrated a significant contribution to the presence of DLIS except one: continuous intravenous drip infusion therapy with a sodium-containing solution (DIV). The frequency of DLIS was significantly higher in the elderly subjects than in 121 control subjects younger than 35 years of age (p = 0.01). However, the difference became insignificant when subjects administered DIV were excluded from the analysis (p = 0.15). It was suggested that DIV may be clinically important in indicating the presence of DLIS.

Adult↗

Falsely elevated serum digoxin levels secondary to endogenous digoxin-like immunoreactive substances.

Endogenous digoxin-like immunoreactive substances (DLIS) are produced by the human body and can be significantly elevated in specific clinical conditions. Commercially available digoxin assays do not have the specificity to fully distinguish DLIS from exogenous digoxin, though DLIS do not possess the same therapeutic properties as do the drug. The resultant artificial elevation of a reported digoxin level or a completely factitious level in a patient not taking the drug can have clinically significant consequences.

Animals↗

Use of amiodarone and digoxin specific Fab antibodies in digoxin overdosage.

A 61 year old man with mild aortic stenosis and chronic depression took 12.5 mg digoxin in a suicide attempt. Ventricular tachycardia and fibrillation were resistant to lignocaine and to phenytoin but responded to intravenous amiodarone, with restoration of pacing. Because of persistent hyperkalaemia he was also treated with Fab fragments of digoxin specific antibody, which bound most of the ingested digoxin. It is suggested that the treatment of choice in severe digoxin poisoning is amiodarone for ventricular arrhythmias followed by pacing if necessary and the use of Fab antibody fragments if hyperkalaemia persists.

Amiodarone↗

The serum digoxin test and digoxin toxicity: a Bayesian approach to decision making.

The clinician may often be uncertain about the presence of digoxin toxicity. This uncertainty is particularly important when the clinician must make initial therapeutic decisions about continuing or discontinuing digoxin. We describe a method that helps to clarify the role of the serum digoxin test in decreasing the uncertainty surrounding the diagnosis and treatment of toxicity. The relation between the test and toxicity was first determined in our patient population. An approach to the interpretation of the test based on the likelihood ratio was then developed by combining our data with selected data from the literature. The relation between the pretest risk of toxicity (the estimated risk of toxicity in the population under investigation before the test result is known) and the predictive value of the test was established. This relation was also used to analyze the importance of the degree of elevation of the test. The appropriate threshold probability for institution of treatment of toxicity was then determined by an interview technique. The test was able to make the patient's probability of toxicity cross the threshold probability for treatment of toxicity for an intermediate range of pretest risk. Our analysis suggests that the serum digoxin test may have a critical effect on therapeutic decisions and can be best considered as contributing to the spectrum of risk.

Arrhythmias, Cardiac↗

Therapeutic digoxin level in chylous drainage with no detectable plasma digoxin level.

A patient receiving digoxin for long-standing congestive heart failure developed a chylothorax following removal of an infected aortic graft. Drainage of the chylothorax resulted in plasma digoxin concentrations which were near zero while the digoxin levels in the chylous drainage fluid were therapeutic. The sequestration of even low lipid-soluble drugs, such as digoxin, in chyle should be recognized to prevent subtherapeutic plasma levels in patients undergoing chylothorax drainage.

Aged↗

Improved micro-radioimmunoassay of digoxin in serum, with use of 125I-labeled digoxin.

A micro-radioimmunoassay of 125I-labeled digoxin is described in which 10-mul rather than 50-mul aliquots of sera are required. The method is a modification of a simplified, rapid, and accurate procedure, which is commercially available as a kit. There is excellent correlation between results by these two methods, in which lyophilized digoxin standards and insoluble antibody polymer are used. The digoxin concentration in capillary sera was not significantly different from that in the corresponding venous blood. It is clinically useful to monitor digoxin therapy in capillary sera, particularly in patients in whom blood sampling by venipuncture is inconvenient or difficult.

Digoxin↗

Lack of specificity of current anti-digoxin antibodies, and preparation of a new, specific polyclonal antibody that recognizes the carbohydrate moiety of digoxin.

Current immunoassays for digoxin do not distinguish digoxin from its glycosidic metabolites. We have synthesized a novel digoxin/bovine serum albumin conjugate via reductive ozonolysis of the lactone ring such that the carbohydrate moiety of digoxin remains intact. Antibodies raised against this conjugate show minimal cross reactivity to digoxigenin, bisdigitoxide, monodigitoxide, digoxigenin, and digitoxin. With this antibody, digoxin can be measured in the presence of these metabolites.

Animals↗

[Affinity of polar digoxin and digitoxin metabolites for digoxin and digitoxin antibodies].

The affinities of some polar and non-polar digoxin and digitoxin metabolites to the related antibodies are largely dependent on the structure of their genin parts. Metabolites with unchanged genins show high cross reactivities towards their related antibodies when compared to the original immunogenic cardenolides. Towards the digoxin antibody the following cross reactivities were found: digoxin-16'-glucuronide 50%, digoxigenin 89.5%, and digoxigenin-3-glucuronide 85%. Values of the same order of magnitude were found with the corresponding digitoxin metabolites and the digitoxin antibody. In contrast, there is a marked decrease in cross reactivity caused by only minor changes in the genin part. With the digitoxin antibody the following cross reactivities are found: digoxin (i.e. 12-OH-digitoxin) 9.1%, 3-epi-digitoxigenin 5.6% and 3-epi-digitoxigenin-3-sulphate 1%. Bcause 12-hydroxylation has been reported to be one of several possible ways of digitoxin metabolisation in man, from a theoretical point of view erroneous results in the clinical digitoxin estimation by radioimmuno-assay are possible. In the case of all of the other metabolites the alterations in positive inotropic activity and cross reactivity run largely parallel.

Antibody Specificity↗

[Biological availability of digoxin and beta-methyl-digoxin administered in the fasting state or after meals].

Ten healthy volunteers were given 0.75 mg digoxin and 0.5 mg beta-methyl-digoxin (BMD) in tablet form in the fasting state or after breakfast. Serum concentrations and 24-hour urine excretion of glycoside were measured by radioimmunoassay. Neither the mean area under the serum concentration curve nor the mean cumulative urinary excretion was significantly changed by postprandial administration. Peak serum concentrations were higher when the subjects took the tablets while fasting than when they took them postprandially, but the difference was significant only for BMD. After BMD in the fed state the peak serum concentration was reached earlier and with less variation than after digoxin, but -- as after administration in the fasting state -- the differences were not significant. The peak serum concentration and the time when it is achieved are, as parameters for the rate of absorption, only of secondary importance for treatment with cardiac glycosides in medical practice. They suggest faster absorption of BMD compared with digoxin. Both the glycosides can be given equally well before, during or after food, a fact which facilitates prescription.

Adult↗