Dosage of digoxin in premature infants

Maturity makes sense: managing supraventricular tachyarrhythmia in the late preterm and term fetus

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Fetal Arrhythmia Diagnosis and Pharmacologic Management

One of the most successful achievements of fetal intervention is the pharmacologic management of fetal arrhythmias. This management usually takes place during the second or third trimester. While most arrhythmias in the fetus are benign, both tachy- and bradyarrhythmias can lead to fetal hydrops or cardiac dysfunction and require treatment under certain conditions. This review will highlight precise diagnosis by fetal echocardiography and magnetocardiography, the 2 primary means of diagnosing fetuses with arrhythmia. Additionally, transient or hidden arrhythmias such as bundle branch block, QT prolongation, and torsades de pointes, which can lead to cardiomyopathy and sudden unexplained death in the fetus, may also need pharmacologic treatment. The review will address the types of drug therapies; current knowledge of drug usage, efficacy, and precautions; and the transition to neonatal treatments when indicated. Finally, we will highlight new assessments, including the role of the nurse in the care of fetal arrhythmias. The prognosis for the human fetus with arrhythmias continues to improve as we expand our ability to provide intensive care unit-like monitoring, to better understand drug treatments, to optimize subsequent pregnancy monitoring, to effectively predict timing for delivery, and to follow up these conditions into the neonatal period and into childhood. Coordinated initiatives that facilitate clinical fetal research are needed to address gaps in knowledge and to facilitate fetal drug and device development.

Cardiac glycoside toxicity in small laboratory animals

Cardiac glycosides are frequently administered to laboratory animals for research purposes. The effects achieved depend not only upon the particular glycoside and dose administered, but also upon an entire array of variables from the species of animal to the temperature of the animal housing facility. We review a number of these factors and their influence upon the effects achieved by the administration of cardiac glycosides to laboratory animals.

Age-related digoxin effects in an intact canine model

The inotropic and electrophysiologic effects of digoxin were studied in anesthetized neonatal and adult dogs to test the hypothesis that digoxin had comparable effects in these groups. Recordings of the ECG and central arterial pressure were made starting at 5.75 hours after an intravenous injection of 50 micrograms/kg of the drug. Parameters measured were heart rate (HR); PR interval; mean, systolic, and diastolic blood pressure; preejection period (PEP); and ejection time (ET). Two indices of systolic function were calculated, the systolic time interval (STI = PEP/ET) and total electromechanical systole (TMS = PEP + ET), which was indexed for HR. There was no significant difference from control animals in either the adult or neonatal groups in the PR interval or blood pressure. In the neonatal dogs, HR and STI were also not significantly different from control. However, in the neonatal dogs, there was a significant decrease in the indexed TMS, 288 +/- 7 vs 270 +/- 11 msec (p less than 0.01). In the adult animals, HR decreased from 116 +/- 35 to 66 +/- 25 bpm (p less than 0.01), STI decreased from 0.559 +/- 0.059 to 0.447 +/- 0.069 (p less than 0.01), and indexed TMS decreased from 333 +/- 10 to 291 +/- 13 msec (p less than 0.001). Two-way analysis of variance demonstrated that digoxin differed significantly in its effects on HR (p = 0.005), STI (p = 0.018), and TMS indexed for HR (p = 0.003) in neonatal compared to adult dogs. Pharmacokinetic studies showed a rapid distribution phase and equilibrium conditions at the time of physiologic measurements.(ABSTRACT TRUNCATED AT 250 WORDS)

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

The foregoing discussion leads to several general conclusions regarding the use of digoxin in the pediatric patient. First, pharmacokinetic studies indicate that somewhat higher doses are required in the infant to attain the same serum levels as in the adult. Important sources for this difference appear to be more rapid body clearance of digoxin and larger volume of distribution in the infant. Second, higher serum digoxin levels are not indicated on the basis of decreased myocardial uptake of digoxin in the infant. Tissue uptake of digoxin, as indicated by myocardium/serum digoxin ratios, is higher in infants and children than in adults. Third, according to results of animal studies, the inotropic sensitivity to digoxin in the young is probably greater--certainly not less--than in the adult. This is opposite to a commonly held view that the immature heart is less sensitive to cardiac glycosides and therefore requires higher serum levels for a therapeutic effect. Rather, the infant has decreased sensitivity of the conduction system to digitalis toxicity, and healthy myocardium less prone to arrhythmia than the adult. Therefore the infant may tolerate, but does not require, higher serum levels of digoxin. Fourth, high levels of serum digoxin (greater than 2 ng/ml) are not associated with greater inotropic effects in the pediatric patient. The higher dosages of digoxin are, instead, associated with greater frequency of toxic effects, especially in infants receiving concomitant diuretic therapy. Therefore, a digoxin dosage recommendation is presented, that will result in mean serum digoxin levels of 1.1 to 1.7 ng/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimation of digoxin dosage in VLBW infants using serum creatinine concentrations

Digoxin steady state plasma concentrations (Css) and the corresponding serum creatinine concentrations were studied in 17 VLBW infants. Birth weight was in the range of 760-1 500 g (mean 1 068 g), gestational age ranged from 26 to 32 weeks (mean 28.7 weeks). Digoxin steady state plasma concentrations were found in the range of 0.5-6.5 ng/ml (mean 1.88 ng/ml) during maintenance therapy with 1.6-8.4 micrograms/kg BW/24 h (mean 4.4 micrograms/kg BW/24 h) given in two divided doses intravenously. No digoxin-like immunoreactive substance could be detected in the plasma of 18 infants (10 patients with a birth weight less than or equal to 1 500 g, 8 patients with a birth weight of 2 100-4 730 g) that were not treated with digoxin. The calculated digoxin clearance ranged from 0.38-4.03 ml/min/kg BW. Serum creatinine concentrations were found in the range of 35-274 mumol/l (0.4-3.1 mg/100 ml). A hyperbolic correlation may be derived from the digoxin clearance and the corresponding serum creatinine concentration. A linear relationship was observed between the dose normalized digoxin concentrations (y = Css/dose in 24 h) and the respective creatinine concentrations x (y = 0.52x-0.05; n = 17; s = 0.24; r = 0.86; p less than 0.01). According to this equation we suggest a dosing schedule for digoxin in VLBW infants with impaired renal function. Digoxin maintenance dose is derived from the digoxin target and the creatinine serum concentration. This dose recommendation proved reliable on four VLBW infants (birth weight 770-1 260 g) with decreased renal function.

Twin transfusion syndrome: successful in utero treatment with digoxin

A pregnancy complicated by twin transfusion syndrome is presented. When signs of cardiac failure (edema, ascites and hydramnios) persisted in the recipient twin, maternal digoxin therapy was instituted at 27 weeks' gestation. The signs of failure resolved, and the twins were delivered electively by cesarean section at 34 weeks. At birth, the syndrome was confirmed by examination of the infants and placenta. Both infants survived. Digoxin therapy is recommended for fetal heart failure from circulatory overload in twin transfusion.

New concepts and drugs in the treatment of congestive heart failure

This article seeks to make clear the basic differences in the treatment of heart failure between therapeutic maneuvers that are aimed at improving the mechanical loading conditions of the heart and those that are aimed at augmenting the fundamental contractile or inotropic state of the myocardium. Emphasis is placed on recognizing that treatment expectations must be viewed within an age- or maturity-dependent framework, since a diminished margin of cardiocirculatory reserve exists in the smallest and youngest patients that limits the extent of benefit that may be derived from diverse treatment approaches.

Digitalis toxicity in infants and children

There is a narrow difference between the therapeutic and toxic ranges of cardiac glycosides. The availability in the past decade of radioimmunoassays for accurate measurement of these glycosides has resulted in an improved understanding of their pharmacokinetics and clinical use. Despite these advances, however, digitalis toxicity is still a common problem in infants and children.

Digoxin therapy and left ventricular performance in premature infants with patent ductus arteriosus

Left ventricular systolic time intervals were assessed in 16 preterm infants with symptomatic left-to-right ductal shunts, before, during and after digoxin therapy. An intravenous loading dose of digoxin, 20 micrograms/kg, resulted in a serum digoxin concentration of 1.94 +/- 0.44 nmol/l (mean +/- 1 SD) but in no significant change in heart rate or systolic time intervals. Digoxin maintenance, 2.5 micrograms/kg/12 h, led 3-7 days later to serum concentrations of 2.57 +/- 1.06 nmol/l with an associated shortening of left ventricular ejection time (p less than 0.05) which probably reflected a reduced ductal shunt. Digoxin therapy was withdrawn after ductal closure. The terminal serum half-life was 87 +/- 17 h. Decreasing digoxin concentrations were associated with prolongation of left ventricular ejection time (p less than 0.01). Digoxin therapy did not seem to influence left ventricular systolic time intervals while ductal patency persisted. This may be attributed to limitations of the method or the left ventricle already working at its maximum.

Comparative electrophysiologic effects of digoxin in the nonsedated chronically instrumented puppy

The electrophysiologic effects of acute but not chronic administration of cardiac glycosides have been studied. Nineteen chronically instrumented beagle puppies underwent 2-week courses of parenteral digoxin in three dosage regimens: six received digoxin, 0.04 mg/kg/day; seven received 0.03 mg/kg/day; and 11 received 0.02 mg/kg/day. Mean serum concentrations were 3.2 ng/ml, 1.3 ng/ml, and 1.0 ng/ml, respectively. Significant electrophysiologic effects on sinus node function were produced only by the highest dose. Atrioventricular node conduction was significantly delayed among animals receiving both high and middle dosages. All three regimens significantly effected atrioventricular specialized conduction system functional refractory periods. Atropine decreased digoxin-induced effects on all measured parameters but totally eliminated the digoxin effect on the corrected sinus node recovery time.

The pharmacokinetics of digoxin in newborn and adult sheep

The pharmacokinetics of digoxin were determined in 12 ewes and 13 newborn sheep after bolus drug administration and under steady state drug conditions. After death, tissue distribution of digoxin was determined and normalized to plasma drug concentrations at steady state. Volume of distribution and total drug clearance were lower at steady state than the comparable variables calculated from bolus drug administration. No significant difference between ewes and newborns was shown for drug distribution half-life (0.72 vs. 0.76 hr), drug elimination half-life (15.2 vs. 13.7), or renal drug clearance (0.86 vs. 0.89 liters/kg/hr). Total drug clearance as well as the area derived and steady state volumes of distribution were higher in newborns than in ewes. Digoxin secretion into the urine was limited in newborns, as evidenced by a lower renal digoxin clearance to creatinine clearance ratio in newborns than in ewes (371 vs. 600%). The plasma concentration of digoxin at steady state correlated well with myocardial drug concentrations. Drug distribution was similar in both age groups; however, the tissue to plasma digoxin ratio in kidney was higher in newborns than in ewes (mean 469 vs. 263, respectively). Although age-related differences in drug clearance and distribution volume existed, intersubject variation was substantial, and the demonstrated variations were not large enough to account for the high doses of digoxin used to treat congestive heart failure in immature subjects.

Neonatal emergency transport drug box

The neonatal drug transport box provides a readily available drug supply in appropriate dilutions for newborns. It also supplies a visible neonatal emergency drug dosage list. The use of this box has demonstrated a saving in nursing time, assured an appropriate supply of all necessary drugs, made drugs readily available for emergency use, and provided dosage check.

The physiologic effects of digoxin under steady-state drug conditions in newborn and adult sheep

The physiologic response to the chronic administration of digoxin was studied in 12 adult and 13 newborn sheep. Vascular pressures, cardiac output, isovolumic contraction phase indexes and systolic time intervals were measured before and after 2 weeks of digoxin therapy. Physiologic measurements were correlated with drug levels in plasma and myocardium. Resting myocardial function in newborns exceeded that in ewes. In ewes, the heart rate decreased from 98 to 74 beats/min, the preejection period (PEP) decreased from 76 to 57 msec, the ratio of PEP to left ventricular ejection time (LVET) decreased from 0.323 to 0.223 and dP/dt max increased from 2415 to 3460 mm Hg . sec-1 as plasma concentrations of digoxin increased to a mean of 1.8 ng/ml. Although the final steady-state plasma concentration of digoxin in newborn lambs averaged 1.7 ng/ml, cardiac output, PEP, PEP/LVET and dP/dt max did not change significantly from baseline values. These studies suggest that developmental differences in the physiologic response to digoxin are due either to a limited capacity for improvement in myocardial contractility shortly after birth or to an age-related difference in the effect of digoxin on myocardial tissue.