Digitalis toxicity in infants and children

Prevalence of arrhythmias among children below 15 years of age with congenital heart diseases attending Mulago National Referral Hospital, Uganda

BACKGROUND

In Uganda, few children with congenital heart diseases (CHD) benefit from early corrective cardiac surgery. These children are at high risk of developing heart failure and electrolyte imbalances; factors which increase their risk of developing arrhythmias. This study aimed to determine the prevalence and factors associated with arrhythmias among children with congenital heart diseases receiving care at Mulago Hospital.

METHODS

This was a cross-sectional study carried out from August 2013 to March 2014 at Mulago Hospital. Children were consecutively enrolled into the study. Standard 12-lead electrocardiograms (ECGs) were performed on 194 children with CHD (age range 10 days-15 years). Data was analysed using SPSS 16.0.

RESULTS

Out of 194 children studied, 53/194 (27.3 %, 95 % CI 21.0 - 33.6) children had arrhythmias. Of the CHD children, 44/194 (22.7 %, 95 % CI 16.8 - 28.6) had first degree AV block while 9/194 (4.6 %, 95 % CI 1.7 - 7.6) children had either ectopic atrial rhythm, premature atrial contractions, junctional rhythm, complete atrioventricular (AV) dissociation or premature ventricular contractions. Children using digoxin were more likely to have first degree AV block (OR 3.75, 95 % CI 1.60-8.86) while those aged 5 years and below were less likely to have first degree AV block (OR 0.16, 95 % CI 0.07-0.37).

CONCLUSION

Arrhythmias are common among children with CHD receiving care from Mulago Hospital. These are associated with digoxin use, child's age and electrolyte imbalances; factors which can easily be assessed, managed and where possible modified in these children during their care.

Serum digoxin concentrations and clinical signs and symptoms of digoxin toxicity in the paediatric population

BACKGROUND

Serum digoxin levels have limited utility for determining digoxin toxicity in adults. Paediatric data assessing the utility of monitoring serum digoxin concentration are scarce. We sought to determine whether serum digoxin concentrations are associated with signs and symptoms of digoxin toxicity in children.

METHODS

We carried out a retrospective review of patients 2 ng/ml).

RESULTS

There were 87 patients who met study criteria (male 46%, mean age 8.4 years). CHD was present in 67.8% and electrocardiograms were performed in 72.4% of the patients. The most common indication for digoxin toxicity was heart failure symptoms (61.5%). Toxic serum digoxin concentrations were present in 6.9% of patients (mean 2.6 ng/ml). Symptoms associated with digoxin toxicity occurred in 48.4%, with nausea/vomiting as the most common symptom (36.4%), followed by tachycardia (29.5%). Compared with those without toxic serum digoxin concentrations, significantly more patients with toxic serum digoxin concentrations were female (p=0.02). The presence of electrocardiogram abnormalities and/or signs and symptoms of digoxin toxicity was not significantly different between patients with and without serum digoxin concentrations (p>0.05).

CONCLUSION

Serum digoxin concentrations in children are not strongly associated with signs and symptoms of digoxin toxicity.

Efficacy of digoxin specific Fab fragments (Digibind) in the treatment of toad venom poisoning

Chan Su, a traditional Chinese medication, and Love Stone, a topical aphrodisiac, are both made from dried venom of the toad bufo bufo gargarizans and contain bufalin, cinobufotalin, cinobufagin, and other cardioactive steroids of the bufadienolide class. Deaths have occurred following ingestion of these products and the clinical course resembles digoxin toxicity. The purpose of this study was to determine the efficacy of digoxin specific Fab fragments in treating Chan Su poisoning. An ethanolic extract was prepared from Chan Su. Digoxin specific Fab fragments were reconstituted in normal saline to a concentration of 80 mg/ml. An approximate LD90 dose was determined in preliminary experiments. Mice were then randomly divided into a treatment group of 15 mice and a control group of 30 mice. The treatment group was pretreated with 20 ml/kg of digoxin specific Fab fragment solution by intraperitoneal injection at t = 0, followed by 10 ml/kg of digoxin specific Fab fragments intraperitoneal at t = 30 min. The control group was pretreated with equal volumes of intraperitoneal normal saline at the same times. Immediately following the 30 min injection, both groups were given the estimated LD90 dose of Chan Su extract by subcutaneous injection. An endpoint of survival at 6 h was chosen after preliminary results showed that all deaths occurred in the first 4 h. All 30 of the control mice had seizures followed by death compared to 11 seizures and 7deaths in the 15 treatment mice. These results were statistically significant by Fisher's exact test (p = 0.00003 for mortality and p = 0.009 for seizures). Digoxin specific Fab fragments are effective in the treatment of Chan Su poisoning in mice and may be effective for poisoning by other cardioactive steroids of the bufadienolide class.

Treatment of toad venom poisoning with digoxin-specific Fab fragments

Toxicity from toad venom poisoning is similar to digoxin toxicity and carries a high mortality rate. We report on six previously healthy men who developed vomiting and bradycardia after ingesting a purported topical aphrodisiac. Each patient had positive apparent digoxin levels and the first four patients died of cardiac dysrhythmias. The last two patients recovered following treatment with digoxin Fab fragments. We analyzed samples of the purported aphrodisiac and found that it was identical to Chan Su, a Chinese medication made from toad venom. To our knowledge, this is the first reported use of digoxin Fab fragments to treat toad venom poisoning.

The use of digoxin-specific Fab fragments for severe digitalis intoxication in children

BACKGROUND

Because life-threatening digitalis intoxication is unusual in children, treatment with digoxin-specific-antibody Fab fragments (Fab) has rarely been reported. We describe the efficacy of Fab in the treatment of children with severe digitalis intoxication.

METHODS

Twenty-nine children with intoxication due to digoxin (28) or digitoxin (1) received Fab at 21 participating hospitals between 1974 and 1986. Data were gathered about the patients' medical illnesses, doses and serum concentrations of digitalis, responses to Fab therapy, and outcomes.

RESULTS

In the infants and young children with acute digoxin intoxication, the digoxin doses ranged from 0.30 to 0.96 mg per kilogram of body weight; two adolescents had severe intoxication after doses of only 0.20 and 0.26 mg per kilogram. The serum digoxin concentrations ranged from 3.0 to greater than 100 ng per milliliter (mean, 13.8). Atrioventricular block (present in 22 patients [76 percent]) was the most common sign of toxicity. All the patients in this series had severe disturbances of cardiac rhythm, hyperkalemia (mean serum potassium concentration, 5.4 mmol per liter), or both. In 27 patients (93 percent), digitalis toxicity resolved after the administration of Fab. Of the 19 patients for whom data were available on the timing of the response to Fab, 15 responded within 180 minutes. Three patients required retreatment with Fab. Seven died of complications unrelated to the administration of Fab.

CONCLUSIONS

We recommend that Fab be used in the treatment of digitalis poisoning in infants and young children who have ingested greater than or equal to 0.3 mg of digoxin per kilogram, who have underlying heart disease, or who have a serum digoxin concentration of greater than or equal to 6.4 nmol per liter (greater than or equal to 5.0 ng per milliliter) in the elimination phase; and who also have a life-threatening arrhythmia, hemodynamic instability, hyperkalemia, or rapidly progressive toxicity. Adolescents, who are more sensitive to the toxic effects of digoxin than younger children, may require treatment with Fab after ingesting lower doses.

Age-related differences in digoxin toxicity and its treatment

Digoxin toxicity remains a common medical problem for both adults and children. In addition to a vastly improved understanding of the mechanisms for digoxin action on the heart, there are now data which clearly demonstrate that there are potentially important developmental differences in both the pharmacodynamics and pharmacokinetics of digoxin which have a direct impact on its efficacy and toxicity profile. The developmental pharmacokinetics of the drug have been extensively studied such that profiles for age-dependent differences in the apparent volume of distribution, plasma and renal clearance and elimination half-life now exist. It is these data which have also produced the current age-specific dosing guidelines for the therapeutic administration of digoxin in various paediatric subpopulations. Despite this new knowledge, both accidental and iatrogenic digoxin toxicity still occurs in paediatric patients, with potentially life-threatening arrhythmias being produced when steady-state serum digoxin concentrations exceed 5.1 nmol/L. Consequently, the clinician may be faced with the decision to use antidotal therapy with digoxin-specific Fab fragments (d-Fab). This article reviews the developmental basis for digoxin disposition and its pharmacological and toxic effects. Additionally, the treatment of acute digoxin toxicity in children is reviewed, especially as pertains to the therapeutic use of d-Fab.

Results of multicenter studies of digoxin-specific antibody fragments in managing digitalis intoxication in the pediatric population

Digitalis toxicity continues to be a problem for pediatric patients undergoing therapy with cardiac glycosides for heart failure or arrhythmias, as well as in accidental ingestions. In this article the previous use of digoxin-specific antibody Fab fragments to treat digitalis overdose or intoxication in children is reviewed. The case reports cited in the medical literature and the 57 pediatric cases gathered as a result of the multicenter clinical trial and postmarketing surveillance study reported here indicate that digoxin-specific antibody Fab fragments are effective in ameliorating signs of digitalis poisoning in children. Not only can Fab fragments rapidly eradicate potentially life-threatening arrhythmias and conduction defects, but they are also effective in treating hyperkalemia and other noncardiac manifestations of digitalis toxicity. In the small samples of patients studied to date, complications have been minimal and no allergic reactions to digoxin-specific Fab fragments have been observed. Recommendations for the management of digitalis intoxication in children are outlined.

Pharmacokinetics and efficacy of digoxin specific Fab fragments in a child following massive digoxin overdose

The use of digoxin-specific Fab fragments (d-Fab) to treat life-threatening digitalis intoxication has been widely substantiated in adults. This reports a case of a 2-year-old girl who ingested 90-92, 0.25 mg tablets of digoxin and within four hours, developed vomiting, lethargy, tachycardia and AV block (Mobitz type I and II). These symptoms were associated with total and free serum digoxin concentrations of 17.1 and 12.4 ng/ml, respectively. Following GI decontamination, a total dFab dose of 1280 mg (32 vials) was given with resolution of electrocardiographic abnormalities within 40 minutes and a concomitant reduction in the free serum digoxin concentration to 0.11 ng/ml. Repeated blood sampling over 19 days revealed an apparent elimination half-life (t1/2) of 134.9 and 129.9 hr for total and free digoxin, respectively. The long t1/2 for digoxin corresponded to a low apparent renal clearance of total digoxin which ranged from 0.56 to 0.82 ml/minute over four separate collection intervals. The free serum digoxin concentration never exceeded 3% of the total concentration and the patient did not develop a recurrence of toxic symptoms or any adverse effects (e.g. fever) attributable to dFab. Administration of an equimolar dFab dose to children following acute, massive digoxin intoxication represents safe, effective treatment which produces a prompt, sustained reversal of toxic effects. Digoxin specific Fab fragments should be promptly administered to any infant or child with significant, life-threatening symptoms following acute digoxin intoxication.

Does digoxin have a place in the treatment of the child with congenital heart disease?

The place of digoxin in the pediatric cardiologist's armamentarium remains uncertain. As an antiarrhythmic, its use in the Wolff-Parkinson-White syndrome is obsolete, but it remains useful in the treatment of the chronic atrial fibrillation seen in some patients postoperatively and in children with dilated cardiomyopathy. The efficacy of digoxin in heart failure is unproven. There is some evidence of improvement in non invasive left ventricular contractile indices in neonates and infants, but it is unclear whether this is associated with sustained clinical improvement. There is even less evidence of its effectiveness in the older child. Whilst the measurement of any effect will undoubtedly be difficult, the time has come for double-blind, placebo-controlled trials in selected groups of patients. These should be designed not only to test the notion that digoxin does not improve ventricular function, but also to embrace the possibility that its administration may result in clinical improvement over and above that following diuretics alone. An absence of proof of efficacy must be distinguished from no efficacy--more data are needed.