Digoxin

General

• Type: Cardiac glycoside; CHF medications
• Mechanism of action- Inhibits Na+/K+ ATPase, leading to an increase in intracellular sodium that can increase cardiac contractility
• Dosage Forms: PO, IV, IM
• Common Trade Names: Digitek, Digox, Lanoxin

Adult Dosing

• Loading dose = 0.25mg IV q2hr until effect (max total = 1.5mg)
• in acute atrial fibrillation with RVR with heart failure = 0.5mg IV, then 0.25mg IV q4hr until effect or max 1.5mg

Special Populations

• Pregnancy Rating: C
• Lactation risk:
• Renal Dosing
  • Adult
  • Pediatric
• Hepatic Dosing
  • Adult
  • Pediatric

Indications

• RVR control in a-fib/flutter, PSVT

Contraindications

• Allergy to class/drug
• WPW
  • Increases conduction velocity in atrial tissue

Adverse Reactions

Digoxin toxicity

• GI: nausea and vomiting, diarrhea, abdominal pain
• CV: Bradycardia, SA/AV block, ventr arrhythmias
• Neuro: altered mental status, visual disturbances (yellow-tinted vision)

Pharmacology

• Onset of action
  • IV = 5-30 minutes
  • PO = 0.5-2 hours
• Half-life: 36-48 hours (may be increased with renal impairment)
• Absorption: 60-80% absorption after oral administration
• Metabolism: ~16% is converted to metabolites
• Excretion: Almost entirely by the kidneys

Mechanism of Action

• Inhibits Na+/K+ ATPase in the myocardium
  • Causes increase in intracellular sodium levels
  • Results in reversal of sodium-calcium exchanger
    • Normally imports three extracellular sodium ions into the cardiac myocyte in exchange for one intracellular calcium being exported
  • Sodium accumulates intracellularly and is exchanged for Calcium.
  • Causes an increase in the intracellular calcium concentration increasing contractility
    • Also a lengthening of phase 4 and phase 0 of the cardiac action potential which ultimately decreases heart rate
• Summary
  • Inhibits NaK pump
    • Positive inotropy
  • Negative chronotropy/dromotropy
    • Indirect vagal stimulator

See Also

• Digoxin Toxicity
• Antiarrhythmics