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

Digoxin, magnesium, and potassium levels in a forensic autopsy material of sudden death from ischemic heart disease

In 91 cases where the cause of death was heart disease, digoxin, Mg and K concentrations in serum and ventricular myocardium were measured post mortem. Forty per cent were positive for digoxin in both serum and myocardium. The mean serum level was 5.1 +/- 2.4 nmol/l and the mean myocardial level was 42.6 +/- 27.5 ng/g. Correlation could be established between serum and myocardial concentrations of digoxin. There were statistically significant differences in serum as well as in myocardial digoxin levels in persons on 0.13 mg and 0.25 mg per day, respectively. Myocardial levels of Mg and K were low as generally found in persons with ischemic heart disease. There was no correlation between these levels and myocardial digoxin concentrations. Caution must be exercised in the assessment of digoxin results from cadaver samples because of the postmortem rise of digoxin serum concentrations. Considering this fact, the results still indicate that the prevalence of toxic digoxin concentrations might be more common than previously thought.

Serum levels of digoxin in sudden cardiac deaths

Digoxin was determined in postmortem serum samples from 100 patients who died suddenly of cardiac disease. Twenty patients had digoxin levels below the therapeutic range. Twenty-one patients had normal values within the therapeutic range (1.2-2.5 nmol/l). In ten cases there was probably an overdosage. Another 15 patients had markedly elevated levels. No digoxin concentration was found (below 0.5 nmol/l) in 34 patients. The importance of determination of digoxin levels both by the clinician and the pathologist is stressed as well as the necessity of using a correct sampling technique at autopsy.

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.

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.