Pharmacology of Digoxin

Pharmacology
Indication	For the treatment and management of congestive cardiac insufficiency, arrhythmias and heart failure.
Pharmacodynamics	Digoxin, a cardiac glycoside similar to digitoxin, is used to treat congestive heart failure and supraventricular arrhythmias due to reentry mechanisms, and to control ventricular rate in the treatment of chronic atrial fibrillation.
Mechanism of action	Digoxin inhibits the Na-K-ATPase membrane pump, resulting in an increase in intracellular sodium. The sodium calcium exchanger (NCX)in turn tries to extrude the sodium and in so doing, pumps in more calcium. Increased intracellular concentrations of calcium may promote activation of contractile proteins (e.g., actin, myosin). Digoxin also acts on the electrical activity of the heart, increasing the slope of phase 4 depolarization, shortening the action potential duration, and decreasing the maximal diastolic potential.
Absorption	Absorption of digoxin from the elixir pediatric formulation has been demonstrated to be 70% to 85% complete (90% to 100% from the capsules, and 60% to 80% for tablets).
Volume of distribution	Not Available
Protein binding	25%
Metabolism	Hepatic (but not dependent upon the cytochrome P-450 system). The end metabolites, which include 3 b-digoxigenin, 3-keto-digoxigenin, and their glucuronide and sulfate conjugates, are polar in nature and are postulated to be formed via hydrolysis, oxidation, and conjugation.
Route of elimination	Following intravenous administration to healthy volunteers, 50% to 70% of a digoxin dose is excreted unchanged in the urine.
Half life	3.5 to 5 days
Clearance	Not Available
Toxicity	Toxicity includes ventricular tachycardia or ventricular fibrillation, or progressive bradyarrhythmias, or heart block. LD50 = 7.8 mg/kg (orally in mice).