Digitalis

Digoxin is unique medication used in the treatment of heart failure and atrial fibrillation/flutter because of its unique properties.  Digoxin allows for increased contractility at low doses (raises intracellular calcium by inhibiting the sodium-potassium-adenosine triphosphatase enzyme exchanger) while slowing heart rate through increased vagal tone and inhibition of sympathetic activation of the heart.  These factors combine to allow for reduced hospitalizations and survivability in heart failure.  The effect of slowing heart rate while preserving blood pressure.  Digoxin is derived from the foxglove plant and has a narrow therapeutic index. Toxicity is treated by maintaining potassium levels and administration of digoxin antibodies.    

Class Drugs

• Digoxin

Class Mechanism of Action

Inhibition of Na/K-adenosine triphosphatase (ATPase) enzyme

• Reduces Na transport from the cell (Increased intracellular sodium)

• Increased intracellular sodium reduces the gradient that drives the Na-Ca exchanger, which decreases calcium efflux from the cell -- the resulting rise in intracellular calcium increases cardiac contractility during contraction cycles

• The resting membrane potential is increased due to this effect - leading to increased risk of arrhythmia

Increased vagal tone

• Lowers heart rate

• Decreases oxygen demand

Neurohormonal inhibition

• Inhibition of sympathetic activation by unknown mechanism (minimally reduced contractility)

Class Applications

Heart failure (reduced ejection fraction)

• Increased myocardial contractility

• Administered after initiation of ACE inhibitors, beta-blocker, and diuretic therapy

• Low serum concentrations have shown increased survival and fewer heart failure admissions

• Not used in diastolic heart failure or right-heart failure

Symptomatic Atrial Fibrillation and Atrial Flutter

• Increased vagal tone decreases ventricular rates in atrial fibrillation with rapid ventricular response and atrial flutter

Class Adverse Effects

• Narrow therapeutic index

• Anorexia, nausea, and vomiting are early signs of toxicity

• Yellow vision

• Blurred vision

• Cardiac arrhythmias

• Use digoxin carefully in conjunction with other AV nodal blockers as combinations with b-blockers and calcium channel blockers may lead to complete heart block

• Treatment of digoxin toxicity

Replenish low potassium levels

• Digoxin immune Fab binds to and inactivates digoxin in severe toxicity

Drug Table

Drug Name	Application	Comments	Image
Digoxin			"Digital Watch" "Oxen"