digoxin

digoxin

Indication

• For the treatment of congestive heart failure; also to slow the ventricular rate in dysrhythmias such as atrial fibrillation, atrial flutter and supraventricular tachycardia

Pharmacology

• Digoxin is a cardiac glycoside with positive inotropic and negative chronotropic actions
• The average oral absorption in neonates is approximately 70%
• Peak serum levels after oral administration occur by 1 to 3 hours
• Elimination half life in premature neonates is 61 to 170 hours and in full term neonates is 35 to 45 hours
• Digoxin has a very large volume of distribution; the drug attains concentrations in tissues (eg. myocardium, skeletal muscle, kidney, liver) up to 150 times serum concentrations
• About 4 to 6 hours are required after an oral or IV dose for distribution to be complete; therefore, serum levels should not be taken before 6 to 8 hours, and preferably at least 12 hours, after administration of a dose
• Serum digoxin is approximately 20% bound to plasma proteins in neonates
• An endogenous substance has been found in the serum of premature and term infants which cross-reacts with the radioimmunoassay (RIA)
• Digoxin is eliminated mainly by the kidneys; its clearance from the body parallels the maturation of kidney function
• Digoxin's positive ionotropic action is thought to be related to inhibition of the sarcolemmal Na⁺-K⁺ ATPase; the consequent elevation of intracellular Na⁺ activates the trans-sarcolemmal Na⁺-Ca exchange system; this creates an outflux of Na⁺, and an influx of Ca, resulting in a positive inotropic effect
• Digoxin indirectly increases vagal activity, thus slowing SA and AV nodal activity

Side Effects

• Toxic doses can produce cardiac arrhythmias, ventricular extrasystoles, AV block
• Toxic effects are potentiated by high serum Ca, low serum K, and increased/decreased serum Mg
• Vomiting, feeding intolerance, diarrhea
• Drowsiness, lethargy

Precautions

• Therapeutic digoxin serum levels 1.0 - 2.6 nmol/L; these are somewhat unreliable in the newborn but are useful to indicate toxicity
• Routine Monitoring - digoxin serum levels should be taken after digitalization and once weekly while on maintenance therapy; serum levels are taken preferably at least 12 hours after administration of a dose
• Monitor intake and output
• The response to digoxin is variable; a premature, asphyxiated or hypoxic baby is extremely sensitive
• Take the apical heart rate for one full minute prior to giving the medication; if the heart rate is less than 100 beats/minute, consult the physician; the drug may be held and an ECG done to measure the PR interval to see if there is sinus arrhythmia
• In renal impairment, reduce or hold the dose of digoxin

Dose

Supplied

• Pediatric Ampoule 50 mcg/mL (0.05 mg/mL), discontinued by manufacturer 2014
• Digoxin 0.25mcg/mL commercial product
• Pediatric Syringe 25 mcg/mL (0.025 mg/mL), prepared by Pharmacy
• Pediatric Elixir 50 mcg/mL (0.05 mg/mL)