Deliberate digitalis intoxication. A comparison of the toxic effects of four glycoside preparations

Digitalis cardiotoxicity

Clinical manifestations of digitalis toxicity were clearly described by Withering in 1785. One hundred years later, certain digitalis-induced arrhythmias were inscribed on the smoked drum, and shortly thereafter with the introduction of the electrocardiograph, manifestations of digitalis toxicity as recognized today were recorded in animals and human beings. With popularization of the direct-writing electrocardiograph in the late 1940s and the introduction of digitoxin in recommended doses (that in retrospect appear inappropriately high), the documented prevalence of digitalis toxicity increased rapidly. With increased understanding of the interaction of electrolytes and digitalis and perhaps, and more importantly, the widespread use of digoxin in doses derived largely from its inotropic action and, thus, inappropriately low for the management of many of the arrhythmias, the prevalence of digitalis toxicity began to decline again. In addition, the advent of serum level determinations and the widespread acceptance of the concept of "therapeutic" levels which, although frequently falling short of the desired clinical end point, served to preclude digitalis toxicity. With the decline in the incidence of digitalis toxicity consequent to these factors, some of the digitalis-related arrhythmias that were common are now rarely observed. This report focuses on arrhythmias that are highly specific for digitalis toxicity and on those that now are less commonly encountered. The discussion and classification of the arrhythmias are based on their most probable electrophysiologic mechanism.

Monosialoganglioside (GM1) treatment of ouabain-induced retinopathy in the rabbit

The mammalian retina is markedly influenced by cardiac glycosides. When nanomolar concentrations of ouabain are intravitreously injected into the rabbit, the visually evoked response completely disappears within 90 min, while scotopic ERG recordings show a remarkably decreased amplitude of the principal waves. When 33 nmol/kg monosialoganglioside are injected intravenously 30 min before topical intoxication, this functional impairment is significantly reduced. The electroretinographic response shows a limited amplitude reduction, while the cortical potential never disappears completely. Histological observations of intoxicated retinas show that a degenerative process begins in photoreceptor outer segment 24 h after the intravitreal ouabain injection. Presently, this process involves both the outer and inner nuclear layers and, finally, the ganglion cell layer. Comparing the intoxicated treated and untreated retinas, no difference is found in the degenerative pattern of the two groups. Autoradiographic studies are also reported to correlate the protective effect of monoganglioside (GM1) on this toxic retinopathy with its preferential accumulation in different retinal tissues.

Adverse psychiatric reactions to modern medication

From this survey it will be apparent that many psychiatric reactions to drugs are largely caused by their direct toxic actions or from combinations of drugs. As such, they are often dose related, although age and slow speed of detoxification will increase the risk of patients developing delirium, hallucinations, sleep disturbances, anxiety etc. Similar toxic reactions can also occur when drugs to which a patient has developed some measure of tolerance are abruptly withdrawn. In this context the effects of drugs upon patterns of sleep may be important determinants of adverse withdrawal symptoms. In contrast are the reactions which resemble one or other of the functional psychoses. In these patients it appears that a past history of an affective or schizophrenic psychosis is the best predictor of a similar illness being precipitated by a particular drug. Nonetheless, with substances like reserpine and cycloserine there is good reason for thinking that, given a sufficient quantity, practically any patient can develop an adverse psychiatric reaction.

Psychological effects caused by drugs in overdose

Drug overdose is a common occurrence which accounts for up to 25% of medical inpatient admissions. Intentional overdose or attempted suicide is the most common cause of overdose, but there are other types of overdose which are often unrecognised as are the effects caused by these overdoses. Iatrogenic overdose occurs frequently and is often unavoidable. Many patients will make mistakes with their treatment and unwittingly suffer from the toxic effects of the drugs they are taking. About 7% of intentional overdose patients who are admitted to hospital have taken the drug for some psychological effect they have been seeking and have taken too much. This group is described as those who take 'drugs for kicks'. As many of the drugs taken cross the blood-brain barrier and exert some toxic effect on the cerebral cortex, secondary psychological disturbances frequently occur in all of these groups of patients, and can sometimes be the only sign of dangerous toxicity. It is important to recognise the patient's gross disturbances of behaviour, thinking and perception as a manifestation of drug toxicity which can be life threatening and often requires intense medical treatment. The range of the psychological response is somewhat limited and there is not a specific psychological disturbance characteristic of the toxicity of each group of drugs. However, there are some reactions which, coupled with the physical symptoms shown by the patient, can help to identify the patient as suffering from the toxic effects of drugs and even give some indication as to the type of drugs taken. This article describes the various psychiatric syndromes caused by drugs in overdose and attempts to identify these with most of the commonly encountered groups of drugs.

Effects of aspirin and dimenhydrinate (Dramamine) on visual processes

1. The effect of three doses of either aspirin (1280 mg each) or dimenhydrinate (Dramamine) (100 mg each) in an 8 h period on visual processes was investigated double-blind on sixteen volunteer subjects. 2. Tests included night-vision, colour-discrimination, stereoacuity and stereopsis, reaction-time, pupil size, eye-movements, visual evoked cortical potentials, electroencephalographs, a dial-reading task, and a test of texture discrimination. 3. Both drugs affected colour discrimination, and dimenhydrinate degraded night-vision, reaction-time, and stereopsis. 4. The effect of aspirin was minor, but the impairments produced by dimenhydrinate appear to be of practical importance.

Effects of low levels of carbon monoxide on visions of smokers and nonsmokers

The scotopic sensitivity, reaction time, eye movements, and visually evoked cortical potentials of 12 nonsmokers and 6 smokers were measured during the course of 3 hr of exposure both to air and to 200 ppm CO in air. No significant degradation in performance was observed for any of these measures in either group during the course of the exposure.

Correlative studies of serum digitalis levels and the arrhythmias of digitalis intoxication

Correlative studies of serum digoxin levels, cardiac rhythm and related clinical laboratory data were carried out in 114 patients. Seventy-three patients who presented with 79 episodes of arrhythmias typical of digitalis intoxication could be separated into a normokalemic group of 55 patients whose serum digoxin level was 6.68 +/- 0.17 ng/ml (mean +/- standard error of the mean), and a hypokalemic group of 24 with a mean serum digoxin level of 1.13 +/- 0.04 ng/ml (P less than 0.001). Of 45 consectutive normokalemic patients with a high serum digoxin level (more than 2 mg/ml) who underwent serial studies, 17 had arrhythmias. Serial studies in 10 hypokalemic patients revealed an inconsistent relation between presence of arrhythmia and serum digoxin level. During repletion of serum potassium in seven of these patients with an arrhythmia, the arrhythmia disappeared without a significant change in serum digoxin level in four patients. A group of seven patients had 16 episodes of serum digoxin level greater than 2.2 ng/ml, but an arrhythmia occurred during only 3 of these episodes. A sharp border between toxic and therapeutic serum digoxin values was not found in these groups of study patients. The serum digoxin level at which arrhythmias occurred appeared to be variable for both groups and individual patients. However, correlative studies utilizing serum digoxin levels can define existing thresholds for therapeutic and toxic effects and may often be more useful than isolated observations.

Current considerations in digoxin usage

Basic considerations in biotransformation and pharmacodynamics are presented as a basis for understanding clinical usage. The role of polarity in determining a given glycoside's duration of action and extent of biotransformation is emphasized. The pharmacokinetics are summarized emphasizing the fact that digoxin is not completely absorbed by oral administration. The important relationship of serum digoxin levels to myocardial content and apparently to myocardial response is reviewed. This relationship and the development of precise methods for measurement of digoxin in serum provide the clinician with accurate means to assess myocardial tolerance for digoxin under diverse clinical circumstances. This review includes discussion of methods of digitalization, appropriate use of serum levels, apparent and real resistance to digoxin, and apparent and real sensitivity to digoxin. The limitations of serum levels as a precise guide to toxicity are analyzed. Finally, new developments in use of immunologic therapy for digoxin intoxication are presented.

Large-scale digitoxin intoxication

Because of an error in the manufacture of digoxin tablets a large number of patients took tablets that contained 0.20 mg. of digitoxin and 0.05 mg. of digoxin instead of the prescribed 0.25 mg. of digoxin. The symptoms are described of 179 patients who took these tablets and suffered from digitalis intoxication. Of these patients, 125 had taken the faultily composed tablets for more than three weeks. In 48 patients 105 separate disturbances in rhythm or in atrioventricular conduction were observed on the electrocardiogram. Extreme fatigue and serious eye conditions were observed in 95% of the patients. Twelve patients had a transient psychosis. Extensive ophthalmological observations indicated that the visual complaints were most probably caused by a transient retrobulbar neuritis.