Plasma digoxin concentrations and digoxin toxicity in hospital patients

Expert Consensus on the Diagnosis and Management of Digoxin Toxicity

While there has been a decline in the use of digoxin in patients with heart failure and atrial fibrillation, acute and chronic digoxin toxicity remains a significant clinical problem. Digoxin's narrow therapeutic window and nonspecific signs and symptoms of toxicity create clinical challenges and uncertainty around the diagnostic criteria of toxicity and responsive treatment choices for the bedside clinician. A systematic review of published literature on digoxin toxicity (34,587 publications over 6 decades, with 114 meeting inclusion criteria) was performed to develop 33 consensus statements on diagnostic and therapeutic approaches which were then evaluated through a modified Delphi process involving a panel of experts in cardiology, nursing, emergency medicine, and medical toxicology. The results demonstrate agreement about the need to consider time of ingestion and nature of the exposure (ie, acute, acute-on-chronic, chronic) and the use of digoxin immune Fab for life-threatening exposure to decrease risk of death. While several areas of continued uncertainty were identified, this work offers formalized guidance that may help providers better manage this persistent clinical challenge.

Digoxin and Symptomatic Bradyarrhythmia: the 'demon' or a 'red herring'

Digoxin toxicity has been implicated in all forms of cardiac arrhythmias with the notable exception of Mobitz II atrioventricular block, which is very rare. The manifestation is quite variable, ranging from being asymptomatic to gastrointestinal, cardiac, and neurologic symptoms. The manifestations can be protean in the elderly, the most vulnerable group, where degenerative cardiac conduction system diseases add another layer of intrigue by providing an intrinsic substrate for cardiac dysrhythmia. This is in addition to age-related alteration of digoxin pharmacokinetics, use of multiple medications, chronic conditions, and electrolyte derangement, all of which increase the propensity for digoxin toxicity. We present a case of various atrioventricular conduction blocks in a septuagenarian following the use of digoxin.

Quality, origins and limitations of common therapeutic drug reference intervals

Therapeutic drug monitoring (TDM) is used to manage drugs with a narrow window between effective and toxic concentrations. TDM involves measuring blood concentrations of drugs to ensure effective therapy, avoid toxicity and monitor compliance. Common drugs for which TDM is used include aminoglycosides for infections, anticonvulsants to treat seizures, immunosuppressants for transplant patients and cardiac glycosides to regulate cardiac output and heart rate. An essential element of TDM is the provision of accurate and clinically relevant reference intervals. Unlike most laboratory reference intervals, which are derived from a healthy population, TDM reference intervals need to relate to clinical outcomes in the form of efficacy and toxicity. This makes TDM inherently more difficult to develop as healthy individuals are not on therapy, so there is no "normal value". In addition, many of the aforementioned drugs are old and much of the information regarding reference intervals is based on small trials using methods that have changed. Furthermore, individuals have different pharmacokinetics and drug responses, particularly in the context of combined therapies, which exacerbates the challenge of universal TDM targets. This focused review examines the origins and limitations of existing TDM reference intervals for common drugs, providing targets where possible based on available guidelines.

Digoxin intoxication: An old enemy in modern era

Objectives

Although development of new treatment modalities limited digoxin usage, digoxin intoxication is still an important issue which could be easily overlooked. In this report, we analyzed a case series definitively diagnosed as digoxin intoxication in the modern era.

Methods

We analyzed 71 patients hospitalized with digoxin intoxication confirmed by history, complaints, clinical and electrocardiograph (ECG) findings, and serum digoxin levels > 2.0 ng/mL, during a five year period. The demographic and clinical data, indications for digoxin use, digoxin dosage, concurrent medications, laboratory data, hospital monitoring, and ECG findings were obtained from all patients.

Results

Thirty-eight of 71 patients (53.5%) had symptoms of heart failure during admission or later. Sixty-four percent of patients were older than 75 years. The percentage of females was 67%. Atrial fibrillation, hypertension and gastrointestinal complaints were more frequent in the females (64% in females, 30% in males, P = 0.007; 81% in female, 52% in males, P = 0.01; 50% in female, 17.3% in males, P = 0.008, respectively). The mortality rate during the hospital course was 7%.

Conclusions

This report demonstrated the reduced mortality rates in patients with digoxin intoxication over the study period. Gastrointestinal complaints are the most common symptoms in this population.

Digitalis therapy in a 70-year-old population

In the population study "70-year-old people in Gothenburg" 14% of the probands were found to be undergoing treatment with digitalis, 6% with digoxin, 6% with digitoxin and 2% with other glycosides. A comparison between results of the interview method and those of S-digoxin analyses indicates that the interview method was acceptable. As far as can be judged from S-digoxin analyses, only about 60% of the treated patients were on a dosage considered to be effective and free from obvious risks of side-effects. Out of the 130 70-year-olds who were on digitalis treatment, 37% had obvious symptoms of heart disease requiring such treatment, 34% lacked symptoms of arrhythmia and/or congestive failure but had heart volumes larger than those used as reference values in younger age groups, and 29% had no symptoms indicating digitalis treatment. At least 13% of the population had indications for digitalis therapy and about 75% of those apparently needing digitalis were on such treatment. Thus both over- and underdiagnosis of heart disease requiring digitalis therapy were common in this age group.

Extreme digitalis intoxication

A case of massive digoxin intoxication is described. The concentration of digoxin in plasma, 15.5 ng/ml, is one of the highest observed in an individual not having heart diease who survived the intoxication. During the first two days there was complete heart block but only moderate hyperkalaemia. The advantage of temporary pacemaker treatment under these conditions is emphasized.

Therapeutic drug monitoring of antiarrhythmic drugs

Most antiarrhythmic drugs fulfil the formal requirements for rational use of therapeutic drug monitoring, as they show highly variable plasma concentration profiles at a given dose and a direct concentration-effect relationship. Therapeutic ranges for antiarrhythmic drugs are, however, often very poorly defined. Effective drug concentrations are based on small studies or studies not designed to establish a therapeutic range, with varying dosage regimens and unstandardised sampling procedures. There are large numbers of nonresponders and considerable overlap between therapeutic and toxic concentrations. Furthermore, no study has ever shown that therapeutic drug monitoring makes a significant difference in clinical outcome. Therapeutic concentration ranges for antiarrhythmic drugs as they exist today can give an overall impression about the drug concentrations required in the majority of patients. They may also be helpful for dosage adjustment in patients with renal or hepatic failure or in patients with possible toxicological or compliance problems. Their use in optimising individual antiarrhythmic therapy, however, is very limited.

Digoxin level and clinical manifestations as determinants in the diagnosis of digoxin toxicity

The aim of this study was to determine the relative importance of different risk factors in the diagnosis of digitalis toxicity. The authors recruited inpatients for whom serum digoxin level was requested and prospectively followed them for a week to ascertain if they showed digitalis toxicity. The predictive value of different factors for the assessment of digoxin toxicity was analyzed by multiple logistic regression. Forty-one toxic and 58 nontoxic patients were included. In the univariant analysis, intoxicated patients were older, most were women, and they had worse renal function and higher digoxin level; but there were no differences in serum electrolytes or other risk factors. In the multivariant analysis, digoxin level was the only independent factor related to digitalis toxicity. A different risk of toxicity for each clinical manifestation was found for a certain digoxin level. Patients with signs of automaticity in the electrocardiogram had a higher likelihood of being intoxicated than patients with gastrointestinal symptoms, atrioventricular block, or bradycardia. Therefore, in the population evaluated in this study, digoxin level is the key independent factor in digoxin intoxication, although the probability of being intoxicated is also a function of the type of clinical manifestations. A graphic approximation of this probability based on these two factors is presented.

Effect of aging on the incidence of digoxin toxicity

OBJECTIVE

To evaluate the relationship of the therapeutic serum digoxin concentration (SDC) range (0.5-2 ng/mL, as recommended in previous clinical studies) with the incidence of digoxin toxicity during digoxin maintenance therapy.

METHODS

Subjects included all inpatients (n = 462) and outpatients (n = 437) receiving digoxin oral maintenance therapy for heart failure and/or atrial fibrillation with tachycardia at Kosei Hospital, Anjo, Japan. SDC and blood chemistry analysis were determined, and a 24-hour Holter electrocardiographic recording was performed when the SDC was at the presumed steady-state concentration.

RESULTS

Analysis of clinical data showed that there was an overlapping (toxic and nontoxic) range of SDCs in which the incidence of digoxin toxicity was patient-dependent (1.4-2.9 ng/mL). No patient exhibited signs or symptoms of digoxin toxicity when the SDC was <1.4 ng/mL; all patients had evidence of toxicity when the SDC was >3 ng/mL. Additionally, it was shown that the concentration range of this overlapping range tended to broaden and shift to lower concentrations with increasing age. Patients with signs of toxicity when their SDCs were in the overlapping range had normal serum creatinine, blood urea nitrogen, digoxin clearance, creatinine clearance, and potassium concentrations, except for a significantly higher mean age than patients without toxicity. The incidence of digoxin toxicity was dependent on increasing age in patients whose SDCs were within the recommended therapeutic range. Moreover, clinical evidence of digoxin toxicity in patients >71 years old was 26.5%, despite their SDCs falling between 1.4 and 2 ng/mL.

CONCLUSIONS

Increased age is most likely associated with enhanced susceptibility to digoxin toxicity, possibly due to unknown pharmacodynamic changes. This raises the possibility that patients >71 years show clinical evidence of digoxin toxicity despite having SDCs within the recommended therapeutic range.

A case series of hospitalized patients with elevated digoxin levels

PURPOSE

Although there is renewed enthusiasm for the use of digoxin in patients with heart failure, current dosing guidelines are based on a nomogram published in 1974. We studied the incidence of and risk factors for elevated digoxin levels in patients admitted to a community hospital, and compared their dosage regimens to published guidelines.

SUBJECTS AND METHODS

We reviewed the charts of all patients who had serum digoxin levels greater than 2.4 ng/mL during a 6-month period. We collected demographic and clinical data, indications for digoxin use, digoxin dosage, concurrent medications, laboratory data, and clinical and electrocardiographic features of digoxin toxicity.

RESULTS

Of the 1,433 patients with digoxin assays, 115 (8%) patients had elevated levels. Of the 82 patients with complete records and correctly timed digoxin levels, 59 (72%) had electrocardiographic or clinical features of digoxin toxicity. Patients with serum digoxin levels >2.4 ng/mL were slightly older (78 +/- 8 versus 73 +/- 9 years of age; P = 0.12) and had greater serum creatinine levels (3.1 +/- 7.3 versus 1.4 +/- 0.3 mg/dL; P = 0.01) than those with levels < or =2.4 ng/mL. Forty-seven patients had elevated digoxin levels on admission, including 21 patients admitted for digoxin toxicity. Impaired or worsening renal function contributed to high levels in 37 patients, and a drug interaction was a contributory factor in 10 cases. Twenty (43%) of these patients were taking the recommended maintenance dose based on the scheme employed in the Digitalis Investigation Group study. Thirty-five patients developed high digoxin levels while in hospital. In 26 patients, this followed a loading dose of digoxin for the control of rapid atrial fibrillation. Impaired renal function was implicated in all of these patients. Despite the elevated digoxin level, rate control was achieved in only 11 patients of these patients.

CONCLUSIONS

Elevated digoxin levels and clinical toxicity remains a common adverse drug reaction. Elderly patients, particularly those with impaired renal function and low body weights, are at the greatest risk. As published digoxin nomograms often result in toxicity, clinical variables need to be monitored. In patients with congestive heart failure and normal sinus rhythm the potential benefit of digoxin is small; thus, patients should receive a dose that minimizes the risk of toxicity. For patients with new onset atrial fibrillation, other agents may be preferable for rate control.

Digitalis in the treatment of heart failure in the elderly. The GIFA study results

Digitalis glycosides have played an important role in the treatment of patients with heart failure (HF) for more than two centuries. Despite the introduction of new therapeutic strategies in the treatment of HF, and controversies regarding the role of digitalis in HF in sinus rhythm and its effect on mortality, digoxin is one of the most commonly prescribed drugs in the community and in hospital settings, particularly in the elderly. The Italian Group of Pharmacosurveillance in the Elderly (GIFA) monitored 20,047 hospitalized patients in 1988, 1991 and 1993, and found that digoxin was the most frequently prescribed drug in the management of HF. Inappropriate prescriptions of digitalis, defined with standardized criteria, were uncommon, and the mean daily dosage was low. Compared to earlier studies the incidence rate of adverse drug reactions (ADRs) to digoxin, was also low. The reduction in ADRs incidence was probably due to a better understanding of digoxin pharmacokinetics and to a lower daily dosage in the elderly. Nevertheless, digoxin toxicity was significantly more frequent in patients aged >or= 80 years than in those aged < 65 and and 65-79 years. In a multidrug approach to the treatment of chronic HF, digoxin exerts clinical benefits also in patients with sinus rhythm, it is not costly, it is easy to administer, and toxic effects are not common.

The impact of age on risk of adverse drug reactions to digoxin. For The Gruppo Italiano di Farmacovigilanza nell' Anziano

To assess the association of age and other potential risk factors with digoxin toxicity, adverse drug reactions to digoxin (ADRDIG) were studied in all patients (n = 1338) on digoxin therapy consecutively admitted to 41 clinical wards throughout Italy during 4 months in 1988. At the time of admission, 28 patients (2.1%) had evidence of ADRDIG. In multivariate logistic regression analysis, significant associations with ADRDIG were found for age > or = 80 years compared to age 65-79 years (OR = 2.75, 95% CI = 1.17-6.45), daily digoxin dosage of > or = 0.25 mg (OR = 2.51, 95% CI = 1.16-5.47), serum creatinine > or = 120 mumol/L (OR = 3.75, 95% CI = 1.69-8.32), and for treatment with amiodarone, propafenone, quinidine or verapamil (OR = 2.60, 95% CI = 1.07-6.30). Those aged < 65 years had a similar risk of digoxin toxicity as those aged 65-79 years (OR = 1.07, 95% CI = 0.28-4.12). Adverse drug reactions to digoxin were found in 1 in 50 patients hospitalized on digoxin therapy. Patients aged 65-79 years were not at increased risk for digoxin toxicity compared to younger patients, while advanced age (> or = 80 years) was an independent risk factor for this outcome.

The use of antibodies in clinical cardiology

Monoclonal antibody technology has resulted in an entirely new class of agents, which have been applied to a variety of problems in cardiology and which hold great promise for future diagnostic, as well as therapeutic, applications. The four antibodies, which have been most widely used in clinical cardiology, are Digibind, OKT3, Myoscint, and 7E3. Each demonstrates the unique potential for the use of antibodies in clinical cardiology.

Digoxin toxicity in the aged. Characterising and avoiding the problem

Digoxin is one of the most frequently prescribed drugs, particularly in the elderly population where there is an increased prevalence of atrial fibrillation and cardiac failure. The drug has a narrow therapeutic range and has gained a reputation for producing adverse effects in older patients. The more frail elderly patients with coexistent disease, often taking other treatments, are more at risk from digoxin toxicity due to inappropriate dosing, noncompliance, or increased sensitivity to digoxin resulting from pharmacokinetic or pharmacodynamic interactions. Application of basic pharmacological principles may be helpful in anticipating these problems. Elderly patients more commonly receive digoxin than younger patients, which in part accounts for the higher rates of toxicity in this group. Numerous components contribute to the development of toxicity, and diagnosis of toxicity is difficult in this age group. The measurement of serum concentrations can contribute to the clinical diagnosis. A major problem is the accurate diagnosis of digoxin toxicity which may have numerous nonspecific clinical manifestations, many of which are related to coexisting disease in elderly patients. This diagnostic imprecision is well recognised but has been helped by the introduction of serum digoxin measurement. However, reliance on serum concentrations should not replace clinical judgement, since these do not always correlate with toxicity. The apparently decreasing incidence of toxicity over recent years probably reflects several factors: the improvement in digoxin formulations, awareness of digoxin pharmacology, utilisation of serum concentrations, and the realisation that digoxin withdrawal is a viable proposition in elderly patients. Greater knowledge about the causes and prevention of digoxin toxicity should further reduce the morbidity and mortality arising from digoxin overdose, especially in the elderly population.

The drug treatment of atrial fibrillation

1. Atrial fibrillation is an inefficient cardiac rhythm associated with impaired exercise tolerance, exertional dyspnoea, palpitation and a substantial risk of thromboembolism. 2. The first decision in management is to consider cardioversion which can be achieved in suitable cases electrically, or pharmacologically with a class Ic antiarrhythmic drug like flecainide or propafenone. 3. Prophylaxis in paroxysmal atrial fibrillation is best achieved with a class Ic drug or a class III drug such as sotalol or amiodarone. 4. Control of ventricular rate in chronic atrial fibrillation can be achieved by pharmacological manipulation of the atrioventricular node by digoxin alone, or in combination with the calcium channel blockers verapamil or diltiazem, or beta-adrenoceptor blockers with intrinsic sympathomimetic activity like pindolol or xamoterol. 5. In view of the considerable risk of thromboembolism in patients with chronic atrial fibrillation anticoagulation or at least treatment with aspirin should be considered.

Risk factors and manifestations of digoxin toxicity in the elderly

The incidence of digoxin toxicity increases with age, largely because the two most common conditions that benefit from use of digoxin, congestive heart failure and atrial fibrillation, are markedly more prevalent in old age. Whether the elderly are more sensitive to the effects of digoxin because of age per se is unclear. However, several other factors render the elderly more susceptible to digoxin toxicity. These include an age-related decline in renal function and a decrease in volume of digoxin distribution. There is also an increase in the number of comorbid conditions, including cardiovascular and chronic obstructive pulmonary disease, which heighten susceptibility to digoxin toxicity. Moreover, treatment of these diseases with such interactive medications as quinidine and calcium channel blockers may increase the serum level of digoxin. Similarly, such electrolyte imbalances as hypokalemia and hypomagnesemia occur more frequently in the elderly as a result of diuretic therapy. However, recent data suggest that manifestations of digoxin toxicity among younger and older patients do not differ. Similar incidences of cardiac toxicity, gastrointestinal toxicity, and altered mental status are found in both patient populations. Treatment of digitalis toxicity in the elderly is the same as for younger patients. Response rates to Digibind are not diminished in the elderly.

The evolving pattern of digoxin intoxication: observations at a large urban hospital from 1980 to 1988

Digoxin intoxication has been reported to be a common adverse drug reaction with an in-hospital incidence of 6% to 23% and an associated mortality rate as high as 41%. A retrospective review was conducted to assess the accuracy of diagnosis, the morbidity and mortality of digoxin intoxication, and its incidence in hospitalized patients with heart failure. We reviewed the medical records of 219 patients discharged with the diagnosis of digoxin intoxication between 1980 and 1988. Patients were classified as follows: (1) Definite intoxication--patients with symptoms and/or arrhythmias suggestive of digoxin intoxication that resolved after discontinuation of digoxin; (2) possible intoxication--patients with symptoms and/or arrhythmias suggestive of digoxin intoxication in the absence of documented resolution after discontinuation of digoxin, or the presence of other clinical illnesses that could possibly account for those findings; (3) no intoxication--patients whose symptoms or ECG abnormalities were clearly explained by other associated clinical illnesses and persisted after withdrawal of digoxin. We identified only 43 patients (20%) with definite intoxication. The majority of patients discharged with the diagnosis of digoxin intoxication (133 or 60%) were classified as possibly digoxin intoxicated, and 43 patients (20%) had no clinical evidence to support this diagnosis. To estimate the incidence of digoxin intoxication, we also reviewed the medical records of 994 patients admitted in 1987 with heart failure. Of these, 563 were receiving digoxin and in 27 the diagnosis of digoxin intoxication was made by their clinicians. Our review showed that only four were definitely intoxicated (0.8%), and the diagnosis could not be excluded in another 16 (4%).(ABSTRACT TRUNCATED AT 250 WORDS)

A comparative trial of digoxin and digitoxin in the treatment of congestive heart failure

A randomized, crossover, single-blind study compared the efficacy and dosing accuracy of digoxin and digitoxin in 15 ambulatory patients wth congestive heart failure. Loading doses and maintenance doses were calculated according to published equations that adjust for sex, height, and lean body weight (for digitoxin), plus estimated creatinine clearance (for digoxin). At each 2-week visit, serum drug concentrations were measured and compliance with the prescribed regimen was assessed by tablet count. At the end of each study period, a congestive heart failure (CHF) score was determined in a blinded fashion by the same physician. Patient compliance was unusually high (greater than or equal to 80%) at every visit. Therapeutic concentrations were achieved with digoxin and digitoxin in 5 and 14 patients, respectively (p less than 0.05). During digitoxin therapy, CHF scores were lower than pretreatment values (p less than 0.05). The difference between CHF scores during the digoxin and digitoxin periods did not achieve significance (0.05 less than p less than 0.06). Therapeutic serum concentrations can be achieved more easily and frequently with digitoxin than digoxin without compromising the patient's CHF status.

Digoxin toxicity in patients with high serum digoxin concentrations

A retrospective study of the clinical course and outcome of patients with serum digoxin concentrations (SDCs) greater than 3 ng/mL was conducted to determine the probability of a patient without initial signs or symptoms of digoxin toxicity subsequently developing signs or symptoms. Of 123 patients with SDCs greater than 3 ng/mL, 54 had no apparent signs or symptoms of toxicity at the time the index SDC was determined (group 1). Of these 54, two patients developed definite digoxin toxicity, although neither suffered significant morbidity. Digoxin administration was reduced or discontinued in all patients but one in group 1. There were no significant differences between the patients who had no signs or symptoms of digoxin toxicity (group 1) and those who did have signs or symptoms (group 2) in the mean SDC (3.9 +/- 0.1 vs 4.2 +/- 0.2 ng/mL, respectively), the serum creatinine (2.9 +/- 0.2 vs 3.4 +/- 0.4 mg/dL), or the incidence of atrial fibrillation (29/54 vs. 35/69) and coronary artery disease (21/54 vs. 18/69). The authors conclude that clinically stable patients receiving digoxin who have elevated SDCs but are without signs or symptoms of digoxin toxicity are at low risk of developing serious digoxin toxicity and do not generally require treatment beyond the discontinuation of digoxin therapy.

Serum digoxin levels and mortality in 5,100 patients

A retrospective study of 5,100 patients on digoxin, with a four-week follow up after digoxin levels were measured, was done to determine the mortality rate. A significant increase in mortality was correlated with an increasing serum digoxin level, up to 50% at a level of 6.0 ng/mL and more. Clinical toxicity was suspected in only 0.25% of all patients on digoxin, although almost 10% had levels above the therapeutic range. Deliberate digoxin overdoses were fatal in 50% of cases. This study shows a correlation between increasing digoxin levels and increasing mortality rates. We recommend the use of serum digoxin measurements to identify those asymptomatic patients with elevated levels. The physician should seriously consider the indications for initiating or continuing digoxin treatment in any patient because of an increased mortality in patients with levels of more than 1.0 ng/mL.

Antibodies and digitalis: the modern revolution in the use of an ancient drug

Although digitalis glycosides have been widely used in clinical medicine since the classic description by William Withering in 1785, it was not until the advent of a specific immunoassay that their clinical pharmacology could be examined intensively under a wide variety of circumstances. The insights gained into the relations among dosage, plasma concentration, bioavailability, distribution, metabolism, excretion and interactions with other drugs and the manifestations of toxicity certainly have reduced the frequency of adverse reactions to this highly toxic but useful group of drugs. More recently, antibodies have also been utilized as specific antidotes for digitalis toxicity, with dramatic life-saving effect.

A collection of therapeutic, toxic and fatal blood drug concentrations in man

In order to assess the significance of drug concentrations measured in clinical and toxicological investigations, it is essential that good collections of data are readily available. As a guide to interpreting findings, the present work provides a compilation of therapeutic, toxic and fatal blood concentration ranges of 298 drugs of interest to clinical pharmacologists, clinical toxicologists, and forensic toxicologists. Wherever possible, ranges are expressed concisely in terms of the maximum blood concentrations which account for 10, 50 and 90% of the data collected. They provide easy access to the most reliable information which relates the blood drug concentration to the biological response it produces. Where appropriate, the different toxic effects of a drug and/or the different degrees of severity of toxic symptoms associated with different drug levels are clearly defined. The original sources of all data used are provided to allow the analyst to obtain further analytical, pharmacokinetic and toxicological information should this be necessary. Those factors (e.g. age, capacity for drug metabolism, drug interactions, etc) which can modify the relationship between a drug concentration and the response it produces are briefly discussed.

Correlation between manifestations of digoxin toxicity and serum digoxin, calcium, potassium, and magnesium concentrations and arterial pH

In 18 patients with gastrointestinal manifestations of digoxin toxicity the mean serum digoxin concentration (+/- SEM) was 3.16 micrograms/l (+/- 0.25), the calcium to potassium ratio 0.31 (+/- 0.01), and the mean arterial pH 7.406 (+/- 0.017). In contrast 19 patients with digoxin induced automaticity had a mean serum digoxin concentration of 1.24 micrograms/l (+/- 0.15; p less than 0.001), a calcium to potassium ratio of 0.38 (+/- 0.01; p less than 0.01), and an arterial pH of 7.498 (+/- 0.008; p less than 0.001). Eight out of 13 patients with digoxin induced cardiotoxicity had serum concentrations of the drug within the therapeutic range (0.8-2.0 micrograms/l). The calcium to potassium ratio, however, was lower than in the patients with automaticity (0.31 +/- 0.02; p less than 0.01) and the arterial pH was 7.370 (+/- 0.033; p less than 0.05). Serum magnesium concentrations were similar in all groups. In this study patients with digoxin induced gastrointestinal symptoms had high serum concentrations of the drug, whereas those with drug induced automaticity had therapeutic concentrations. This second group, however, was identified by their higher calcium to potassium ratios and higher pH values.

Suicidal digoxin poisoning: conventional treatment and antibody therapy

A 66-year-old mand suffering from severe coronary heart disease took digoxin with suicidal intent an was treated for the ensuing complete atrioventricular block with digoxin-specific antibody fragments. Two and a half hours after intravenous infusion of the antibody fragments, the signs of intoxication passed off, and atrial fibrillation with a normal ventricular rate was reinstated. Antibody therapy is capable of permanently abolishing the signs of symptoms of digitalis poisoning after a matter of hours. Such a rapid or complete response cannot be achieved by any conventional form of treatment. This advantage must be weighed against the risks (immunologic reactions, loss of the therapeutic effect of the cardiac glycoside if an overdose of antibody is given). Moreover, antibody therapy does not take effect immediately, as is understandable in view of the mechanism of action. It should therefore be instituted in good time in potentially life-threatening cases of intoxication.

Re-examination of digoxin dosage regimen: comparison of the proposed nomograms or formulae in elderly patients

1 Comparison of measured trough serum digoxin concentrations (SDC) with those predicted at steady-state by forty sets of previously described pharmacokinetic equations in conjunction with either measured or estimated creatinine clearance (Clcr) was made in an elderly group of patients with varying Clcr (25-89 ml/min) who received maintenance digoxin therapy. 2 Mean values of day-to-day variation (% coefficient of variation) for serum creatine and measured Clcr examined three times within a week in 7 of 40 elderly patients were 6.42 and 8.36% respectively, while this value for SDC was 12.46%. 3 There was a statistically significant correlation (r = 0.72 to 0.79, P less than 0.001, n = 40) between measured Clcr and that estimated from three different methods. Siersbaek-Nielsen's nomogram approach gave the best correlation. 4 The calculated correlation coefficient values between measured and predicted SDC lay within a relatively narrow range but were weak (r = 0.443-0.628). Prediction error analysis, however, allowed us to determine the best set of pharmacokinetic equations for a first approximation to appropriate digoxin maintenance dosage requirements, namely Gault-estimated elimination rate constant, measured Clcr, and Jusko-estimated volume of distribution.

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.

The role of Holter monitoring in detecting digitalis-provoked arrhythmias

Certain arrhythmias detected on the electrocardiogram are considered to be reliable indicators of digitalis intoxication. We have evaluated the incidence of these arrhythmias on 24-hour electrocardiographic monitoring (Holter monitoring) in 69 consecutive patients who had serum levels of digoxin determined within 24 hours of the onset of continuous electrocardiographic monitoring. According to teh serum level of digoxin, the patients were divided into the following three groups: (1) group 1 had 0 to 1.0 ng/ml (31 patients); (2) group 2 had 1.1 to 2.0 ng/ml (27 patients); and group 3 had greater than or equal to 2.1 ng/ml (11 patients). The following arrhythmias were considered to reflect digitalis-provoked arrhythmias: (1) persistent sinus bradycardia or sinus pauses (or both); (2) atrioventricular block; (3) paroxysmal atrial tachycardia with block; (4) accelerated junction rhythm; (5) complex ventricular arrhythmias (multifocal ventricular premature beats, bigeminy and trigeminy, and pairs); and (6) ventricular tachycardia. There was no significant difference in the incidence of these six categories of arrhythmias among the three groups. In addition, there was no significant difference in the mean serum level of digoxin for patients with and without the arrhythmias within each category. Ten of the 69 patients had combinations of three of the so-called digitalis-provoked arrhythmias, with incidences among the three groups showing no significant differences. In conclusion, rhythms considered to be potentially due to digitalis intoxication are frequently observed in hospitalized patients undergoing 24-hour electrocardiographic monitoring, are frequently unrelated to the serum level of digoxin, and appear unlikely to reflect true digitalis intoxication in many of these patients.

A standard approach to compiling clinical pharmacokinetic data

A standard format for a Clinical Pharmacokinetic Summary is proposed. It consists of a heading, tables, notes, and references for each drug reviewed. The table presents a unified and logical set of clinically useful population pharmacokinetic parameters. They concern four major areas: absorption, distribution, elimination, and the relationship of concentration to effect. Within each major group, parameters dealing with extents and rates of processes are given. Each such parameter is really two: a population mea value (for example, average volume of distribution) and the standard deviation of individual values about this mean. The first value allows individual predictions of dosage or drug level to be made; the second allows computation of the likely proximity of subsequently observed quantities to those predictions. The table presents single consensus values for each population parameter, rather than a list of values. A procedure for computing these consensus values, and for revising them in the light of new data, or reinterpreted old data, is given. Examples of Summaries are given. The method appears applicable to a variety of drugs. We suggest our approach as a standard one for preparing Clinical Pharmacokinetic Summaries, and urge our colleagues to consider it for that purpose.

Comparison of two different loading doses of digoxin in severe renal impairment

The correct loading dose of digoxin in patients with advanced renal failure is still a matter of discussion. The effects has been studied of loading doses of digoxin 0.625 mg or 1.25 mg given over 48 h according to randomized crossover design to healthy volunteers and to two different groups of patients with renal impairment and the same mean endogenous creatinine clearance of about 15 ml/min. The subsequent maintenance dose for 4 days was digoxin 0.25 mg in the volunteers and 0.125 mg in both groups of patients. The minimum plasma digoxin concentrations before each dose was measured by radioimmunoassay and the plasma levels in the different groups have been compared. In the healthy volunteers no significant difference was found during the study, despite wide variation in the plasma digoxin concentration. In contrast, in patients with renal failure, the group with the higher loading dose showed significantly higher plasma concentrations 24, 36 and 48 h after drug administration, reaching the highest mean value of 2.2 ng/ml at 48 h. However, after 120 h of maintenance therapy a mean digoxin concentration of 1.3 ng/ml was found in both groups. Thus, despite different loading doses identical plasma concentrations were reached during administration of the same maintenance therapy. The higher plasma digoxin concentration obtained during administration of a higher loading dose might be the cause of arrythmias in individual patients.

Digoxin dosage in renal insufficiency: impracticality of basing it on the creatinine clearance, body weight and volume of distribution

Previous dosing schedules for digoxin in renal failure have considered the decrease in the elimination rate constant but not the decrease in the volume of distribution. A dosing schedule based on the creatinine clearance, body weight and volume of distribution has been developed from pharmacokinetic data taken from the literature. Its validity was tested in a clinical study of 35 patients with chronic renal insufficiency not requiring dialysis. The dosing schedule resulted in correct digitalization expressed as a steady state plasma digoxin concentration in the therapeutic range (0.5-2.0 ng/ml) in 25 out of 27 patients (93%). However, of 82 possible candidates for the study, it could not be performed in 47 (57%). The high drop-out rate was mainly due to the complicated dosing schedule and to the difficulty of repeatedly measuring creatinine clearance on a routine basis. Therefore, safe dosing of digoxin in renal insufficiency does not seem to be feasible in practice. Digitoxin may be a better alternative.

Treatment of a case of lanatoside C intoxication with digoxin-specific F(ab')2 antibody fragments

In animal experiments arrhythmias induced by cardiac glycosides which prove fatal if untreated can be terminated by administration of glycoside-specific antibodies. Immunotherapy with digoxin-specific antibody fragments had hitherto only been employed on one occasion, namely in a person who had taken a massive overdose of digoxin with suicidal intent and who had failed to respond to symptomatic treatment. The present paper describes the use of F(ab')2 fragments of digoxin-specific antibodies in a female patient with lanatoside C intoxication to treat the associated life-threatening cardiac arrhythmia. The arrhythmia was rapidly terminated and normal sinus rhythm was restored. Treatment with the heterologous antibodies did not cause any side-effects.

Digitalis delirium in elderly patients

Case histories of four elderly patients with central nervous system signs of digitalis toxicity were reviewed. Evidence of toxicity included lethargy, depression which was not present previously, confusion, restlessness, emotional instability, hyperventilation, and vertigo. Vomiting developed four days after the onset of the mental changes. No cardiac arrhythmias were observed. Digoxin serum levels ranged between 4.2 and 7.0 ng/ml. Serum potassium values were within normal limits. Three of the four patients recovered with a return of their mental status to the pretoxic state. The fourth case was fatal. At autopsy long-standing myocardial ischemia was the only significant finding.

One hundred digitalis blood levels. A utilization review

One hundred consecutive digitalis serum level determination requests and results were analyzed to evaluate the rational of ordering the test and utilizing the results at his hospital. Sixty-six percent of the reasons given for ordering the test were categorized as "acceptable". As many as 25% of physicians requesting the test considered digitalis levels as "routine" diagnostic tests in a patient taking these drugs. There were 12 levels within the potentially toxic range, 19 below the usual therapeutic range. The physicians modified their therapeutic management in 38 patients as a result of their knowledge of the digitalis level in blood. It is concluded that digitalis level determinations at this hospital are reasonably well utilized and that knowledge of the digitalis levels improve the accuracy of digitalis utilization in at least one third of the patients in whom this test is done.

The prevention and reversal of digoxin intoxication with specific antibodies

The formation of digoxin-specific antibodies was induced in sheep by immunization with a digoxin-albumin conjugate. The efficacy of the antibodies was investigated in anesthetized cats. When the digoxin-specific antibodies were administered prophylactically as a gammaglobulin, IgG or F (ab')2 preparation, the dose of digoxin needed to induce ventricular dysrhythmia was significantly greater (p less than 0.001) for the pretreated animals than for the controls. To investigate therapeutic efficacy, the animals were digitalized with digoxin over a period of three days and were given digoxin injections on the fourth day to provoke ventricular tachycardia. Of the control animals, three died before two hours had elapsed and the arrhythmia persisted in the two remaining animals. By contrast, a stable sinus rhythm was restored in all animals which were treated with F (ab')2 fragment of the digoxin-specific antibodies after onset of ventricular tachycardia. The doses of digoxin required to trigger renewed ventricular dysrhythmia in these animals were greater than those required at the start of the experiment. The potential clinical use of digoxin-specific antibodies is discussed in the light of these results and reports in the literature.

Dose-independent pharmacokinetics of digoxin in humans

Nine healthy male volunteers received single 0.5, 1.0, and 1.5 mg. doses of intravenous digoxin in a randomized three-way crossover study. Multiple venous blood samples were drawn during 35 hours after each dose, and all urine was collected for 6 consecutive days. Concentrations of digoxin in serum and urine were determined by radioimmunoassay. Over-all mean values for kinetic variables were: distribution half-life, 0.35 hours; elimination half-life, 27.9 hours; volume of distribution, 5.46 liters/Kg; total clearance, 2.51 ml./min./Kg. The mean projected cumulative urinary excretion of digoxin was 70.1% of the dose; mean renal clearance of digoxin was 1.71 ml./min./Kg., not significantly different from creatinine clearance (1.50 ml./min./Kg.). None of the identifiable pharmacokinetic variables was significantly influenced by dose, suggesting that digoxin disposition is dose-independent in healthy individuals.