Use of digoxin in infants and children, with specific emphasis on dosage

Digoxin Associated With Greater Transplant-Free Survival in High- vs Low-Risk Interstage Patients

BACKGROUND

Digoxin has been associated with reduced interstage mortality for patients with functional single ventricles with aortic hypoplasia or ductal-dependent systemic circulation. The NEONATE (type of stage 1 palliation operation, postoperative extracorporeal membrane oxygenation, discharge with opiates, no digoxin at discharge, postoperative arch obstruction, moderate to severe tricuspid regurgitation without an oxygen requirement, and extra oxygen required at discharge in patients with moderate to severe tricuspid regurgitation) score can stratify patients by risk of death or transplantation (DTx) on the basis of clinical factors. The study investigators suspected a variable transplant-free survival benefit of digoxin in high-risk vs low-risk patients.

METHODS

National Pediatric Cardiology Quality Improvement Collaborative patients discharged after stage 1 palliation with complete data were categorized as high- or low-risk on the basis of a modified NEONATE score. The primary outcome of DTx was evaluated. A mixed-effect regression evaluated associations between digoxin prescription and risk factors.

RESULTS

A total of 1199 patients were included; 399 (33%) were high risk. Baseline demographics were similar between the cohorts. Blalock-Taussig shunt or a hybrid operation, postoperative extracorporeal membrane oxygenation, opiate prescription, and significant tricuspid regurgitation or arch obstruction were more common in high-risk patients. The odds of DTx were 65% lower in high-risk patients prescribed digoxin compared with patients who were not (P = .001). Digoxin prescription was associated with 60.8% lower DTx in the high-risk cohort (7.8% vs 19.9%; P = .001). There was no significant difference in the DTx rate according to digoxin prescription in the low-risk cohort (4.7% vs 5.7%; P = .46). Blalock-Taussig shunt, aortic arch obstruction, and significant tricuspid regurgitation were most strongly associated with deriving a benefit from digoxin.

CONCLUSIONS

Digoxin use is associated with significant improvement in transplant-free survival in high-risk but not in low-risk interstage patients. A tailored approach to the use of digoxin in interstage patients may be warranted.

Drug-induced cardiac abnormalities in premature infants and neonates

The Cardiac Safety Research Consortium (CSRC) is a transparent, public-private partnership that was established in 2005 as a Critical Path Program and formalized in 2006 under a Memorandum of Understanding between the United States Food and Drug Administration and Duke University. Our continuing goal is to advance paradigms for more efficient regulatory science related to the cardiovascular safety of new therapeutics, both in the United States and globally, particularly where such safety questions add burden to innovative research and development. This White Paper provides a summary of discussions by a cardiovascular committee cosponsored by the CSRC and the US Food and Drug Administration (FDA) that initially met in December 2014, and periodically convened at FDA's White Oak headquarters from March 2015 to September 2016. The committee focused on the lack of information concerning the cardiac effects of medications in the premature infant and neonate population compared with that of the older pediatric and adult populations. Key objectives of this paper are as follows: Provide an overview of human developmental cardiac electrophysiology, as well as the electrophysiology of premature infants and neonates; summarize all published juvenile animal models relevant to drug-induced cardiac toxicity; provide a consolidated source for all reported drug-induced cardiac toxicities by therapeutic area as a resource for neonatologists; present drugs that have a known cardiac effect in an adult population, but no reported toxicity in the premature infant and neonate populations; and summarize what is not currently known about drug-induced cardiac toxicity in premature infants and neonates, and what could be done to address this lack of knowledge. This paper presents the views of the authors and should not be construed to represent the views or policies of the FDA or Health Canada.

Management of Supraventricular Tachycardia in Infants

Supraventricular tachycardia is the most common tachyarrhythmia encountered in infants. In older children and adults, definitive treatment of the supraventricular tachycardia substrate with catheter ablation is a common approach to management. However, in infants, the risks of catheter ablation are significantly higher, and the patients often outgrow the potential to experience episodes. Therefore, antiarrhythmic medications are often utilized to minimize the likelihood of experiencing episodes. This article reviews the common arrhythmia mechanisms encountered in infants and the medications used to treat these patients.

Junctional Bradycardia as Early Sign of Digoxin Toxicity in a Premature Infant with Congestive Heart Failure due to a Left to Right Shunt

Introduction Congestive heart failure due to left to right cardiac shunt is usually managed medically with diuretics, angiotensin converting enzyme inhibitors, and, in some cases, with the addition of digoxin. Case We report a 31-week gestation premature male infant who did not respond to such treatment and developed hyperaldosteronism and severe hypokalemia secondary to activation of the renin angiotensin aldosterone system. The hypokalemia was not responsive to intravenous KCL supplementation and induced digoxin toxicity despite a relatively normal digoxin level. The earliest signs of digoxin toxicity in the patient were junctional rhythm and bradycardia. The discontinuation of digoxin and the administration of digoxin specific immunoglobulin fragments (Fab) reversed those changes. The addition of spironolactone (an aldosterone antagonist) had a dramatic effect, resulting in clinical improvement of the patient coupled with normalization of Q4 serum and urine electrolytes. Conclusion Serum Digoxin level alone may fail as an independent guide in the diagnosis of digoxin toxicity when hypokalemia is present. In premature infants with congestive heart failure and hypokalemia, addition of an aldosterone antagonist should be considered.

Therapeutic drug monitoring--the appropriate use of drug level measurement in the care of the neonate

Neonates and young infants are in a unique and dynamic pharmacokinetic state, in which they undergo relatively rapid maturational changes in drug absorption, distribution, metabolism, and excretion. In addition to these maturational changes, most drug pharmacokinetic studies in neonates show wide interindividual variability despite similar gestational and postnatal ages. Therapeutic drug monitoring is a necessary tool in the neonatal intensive care unit, despite the relative lack of outcome data. This article discusses therapeutic drug monitoring for several frequently used drugs in neonates.

Application of two-point assay of digoxin serum concentration in studying population pharmacokinetics in Egyptian pediatric patients with heart failure: does it make sense?

Digoxin pharmacokinetics (PK) was studied among a selected group of Egyptian pediatric patients (n = 40) with an age range of 0.33 to 15 years. All the patients had heart failure and were maintained on i.v. digoxin (10 microg/kg/d in 2 equal doses). For population PK analysis, 2 serum samples of digoxin were taken per patient. From 30 patients' trough (before the next dose) and 4 hours postdose samples were obtained, while in the other 10 patients, 0.5- and 6-hour postdose samples were taken. Serum concentrations were measured by fluorescence polarization immunoassay. PK modeling was performed using NONMEM software on log-transformed serum digoxin data. The best structural covariate-free model was a linear 2-compartment model with an exponential error model for intersubject variability and an additive model for intrasubject variability. Serum creatinine (SCR) was a significant covariate for clearance. The final population PK parameters were CL (L/h) = 0.388 - [0.78 x (SCR-0.6)], V1 (L/kg) = 1.38, Q (L/h/kg) = 0.48, V2 (L/kg) = 9.11, where CL is the total body clearance, V1 and V2 are the apparent volumes of distribution in the central and peripheral compartments, and Q is intercompartment clearance. A bootstrap resampling for internal validation achieved excellent agreement with the original data sets for PK parameters. In conclusion, 2 points of digoxin concentration allow good regression analysis for clearance-covariate relationship. The inclusion of SCR into the final model might allow better selection of initial maintenance dose of the drug. A prospective study on larger sample size of pediatric patients is recommended for clinical validation of the final model.

Population pharmacokinetics of digoxin in pediatric patients

Digoxin pharmacokinetics were studied in a pediatric population with an age range of 6 days to 1 year using the population pharmacokinetic approach. Digoxin data were analyzed by mixed-effects modeling according to a one-compartment steady-state pharmacokinetic model using NONMEM software. The final model selected for the population prediction of digoxin clearance in pediatric patients was as follows: [equation: see text] Individual empirical Bayesian estimates were generated on the basis of the population estimates and were used to correlate the optimum dose of digoxin and patient age according to the following equation: [equation: see text] This equation and its derived nomogram may be used for the initial dosing of digoxin in children aged between 0 and 1 year. The use of this nomogram in routine monitoring requires further pharmacokinetic and clinical validation.

Population pharmacokinetics of digoxin in Egyptian pediatric patients: impact of one data point utilization

A population pharmacokinetic (PK) study was designed to estimate the PK parameters of digoxin among a selected group of Egyptian pediatric patients (n = 30) with mean age +/- SD and body weight +/- SD of 8.88 +/- 3.01 years and 23.9 +/- 5.8 kg, respectively. All patients had heart failure and were maintained on digoxin given orally. Nonlinear mixed effect modeling software version 5 (NONMEM Project Group, San Francisco, CA) and one-compartment modeling were used for fitting the data. A one-trough steady-state plasma concentration level of digoxin was used in the analysis. The population mean estimates for clearance (CL/f) and volume of distribution (V/f), in which f represents oral bioavailability, were 8.61 L/h and 450 L, respectively. Because of the limited number of samples per patient, regression analysis could not detect a correlation between patient covariates and estimated PK parameters. The analysis did not converge to obtain good parameter estimates. At least two samples per patient should be used to improve the PK estimation and allow better analysis of the relation between the potential covariates and estimated PK parameters.

Pharmacology of inotropic agents in infants and children

Inotropic agents are drugs which increase the stroke work of the heart at a given pre-load and after-load. All of these agents work through a final common pathway involving the modulation of calcium interactions with various myocardial contractile proteins. The agents employed with pediatric patients include the cardial glycosides, catecholamine beta-agonists and the selective phosphodiesterase III inhibitors. Digoxin is the prototypic cardiac glycoside which has a long history of safe and effective use in infants and children. Its utility in improving right ventricular dysfunction in patients with cor pulmonale leading to biventricular dysfunction makes it ideally suited to the pediatric population. Monitoring digoxin pharmacokinetics in infants is confounded by the presence of an endogenous digoxin-like substance. Nevertheless, the drug is well suited for subacute and chronic myocardial support. In contrast, the catecholamines are the drugs of choice for acute intervention. Their pharmacokinetics permit rapid dosing titration. In infants and children the greatest experience has been accrued with dopamine, a mixed alpha- and beta-agonist but both epinephreine and norepinephrine are being used with increasing frequency as the need for drugs with increased potency and pressor activity becomes more common. The phosphodiesterase inhibitors amrinone and milrinone are the newest additions to our therapeutic armamentarium. In addition to their modest inotropic effects, amrinone and to a greater extent, milrinone offer significant pulmonary vasodilatation as part of their therapeutic package. These effects occur with little or any impact on myocardial oxygen consumpton while their lusitropic effects enhance relaxation in hypertrophied ventricular muscle. Of the two agents milrinone is probably preferred due to its greater therapeutic index and shorter elimination half-life. All of these agents remain important tools in the care of critically ill infants and children. The rational use of these drugs based upon their pharmacokinetic and pharmacodynamic properties is essential to achieve their optimal effects.

Magnesium deficiency and cardiogenic shock after cardiopulmonary bypass

Magnesium is an important cation that has a key role in cellular processes of energy transfer and utilization involving adenosine triphosphate, and influences cell membrane functions. Its antiarrhythmic properties are well-known and it is widely recognized as an adjunct for the treatment of arrhythmias after myocardial infarction and cardiopulmonary bypass. Magnesium may influence hemodynamic performance through its effects on vascular tone, modulation of intracellular calcium, regulation of catecholamine activity, and its essential role in adenosine triphosphate metabolism. The potential for magnesium deficiency to affect cardiovascular performance may be especially relevant in ischemic states. We report a case of cardiogenic shock developing after cardiopulmonary bypass that was initially unresponsive to therapeutic intervention, but that resolved promptly after magnesium administration. The potential role of magnesium in enhancing hemodynamic performance is discussed, with a review of its cellular metabolic properties and activities.

Pharmacokinetics of cardiovascular drugs in children. Inotropes and vasopressors

Infants and children with congenital or acquired heart disease and children with systemic disease often require pharmacological support of their failing circulation. Catecholamines may serve as inotropic (enhance myocardial contractility) or vasopressor (elevate systemic vascular resistance) agents. Noncatecholamine inotropic agents, such as the cardiac glycosides or the bipyridines, may be used in place of, or in addition to, catecholamines. Developmental changes in neonates, infants and children will affect the response to inotropic or pressor therapy. Maturation of the gastrointestinal tract, liver and kidneys alters absorption, metabolism and elimination of drugs, although there are few clear examples of this among the vasoactive drugs considered in this review. Changes in body composition affect the volume of distribution (Vd) and clearance (CL) of drugs. Developmentally based pharmacodynamic differences also affect the responses to both therapeutic and toxic effects of inotropes. These pharmacodynamic differences are based in part upon developmental changes in myocardial structure, cardiac innervation and adrenergic receptor function. For example, the immature myocardium has fewer contractile elements and therefore a decreased ability to increase contractility; it also responds poorly to standard techniques of manipulating preload. Available data suggest that dopamine and dobutamine pharmacokinetics are similar to those in adults. Wide interindividual variability has been noted. A consistent relationship between CL and age has not been demonstrated, although one investigator demonstrated an almost 2-fold increase in the CL of dopamine in children under the age of 2 years. The CL of dopamine appears to be reduced in children with renal and hepatic failure. Fewer data are available regarding the pharmacokinetics of epinephrine (adrenaline), norepinephrine (noradrenaline) and isoprenaline (isoproterenol). Digoxin pharmacokinetics have been extensively evaluated in infants and children. The Vd for digoxin is increased in infants and children. Children beyond the neonatal period display increased CL of digoxin, approaching adult values during puberty. Although it was previously thought that children both needed and tolerated higher serum concentrations of digoxin than adults, more recent studies indicate that adequate clinical response can be achieved with serum concentrations similar to those aimed for in adults, with decreased toxicity. Evaluation of studies of digoxin pharmacokinetics is complicated by the presence of an endogenous substance with digoxin-like activity on radioimmunoassay. Limited studies of amrinone pharmacokinetics in infants and children indicate a dramatically larger Vd, and a decreased elimination half-life in older infants and children, compared with values observed in adults.

Intrauterine treatment on non-immune hydrops fetalis

In 51 cases with non-immunologic hydrops fetalis (NIHF), perinatal management was performed based on our protocol. Twenty-two cases were treated by albumin and/or packed red cell (PRC) injection into the fetal abdominal cavity, and 9 cases by transplacental digitalization. Among the cases treated by albumin and/or PRC injection, 6 of 8 cases without pleural effusion recovered in utero, and all 6 cases are alive. However, of 14 cases with pleural effusion, none recovered in utero, and only one case is alive. Of 9 cases treated by transplacental digitalization, 2 cases recovered in utero, and only one case is alive. All fetuses with congenital heart anomaly died. This evidence indicates that albumin and/or PRC injection into the fetal abdominal cavity is an effective procedure for in utero treatment of NIHF without pleural effusion, but suggests that in NIHF resulting from either congenital heart anomaly and/or heart failure, the survival rate may not be increased by transplacental digitalization.

Physiologic sequelae of prematurity: the nurse practitioner's role. Part III. Congestive heart failure

The premature infant with resultant respiratory disease may also have signs and symptoms of impending congestive heart failure that have a variety of causes. The nurse practitioner can be instrumental in the early identification and treatment of congestive heart failure. This article, the third in a series, provides a discussion of the pathophysiology, signs and symptoms, data collection, treatment modalities, and parental education that can assist parents when coping and dealing with congestive heart failure in their premature infant.

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.