How does digoxin work in the body?
Digoxin is a cardiac glycoside that mainly affects the heart through inhibition of the Na+/K+-ATPase pump in cardiac cells. Blocking this pump increases intracellular sodium, which then reduces the activity of the sodium-calcium exchanger (NCX). The result is higher intracellular calcium during each cardiac cycle, which strengthens heart muscle contraction (positive inotropy).
Digoxin also slows conduction through the atrioventricular (AV) node and increases vagal tone, which is why it helps control the ventricular rate in some atrial arrhythmias.
Why does digoxin strengthen heart contractions?
By inhibiting Na+/K+-ATPase, digoxin shifts ion balance in cardiomyocytes so calcium builds up inside the cell. More intracellular calcium leads to a stronger force of contraction when the heart cells depolarize. Clinically, this is the basis for digoxin’s use in certain patients with heart failure (especially when symptoms persist despite other therapies) and for some rhythm control situations.
How does digoxin slow the heart rate?
Digoxin raises parasympathetic (vagal) influence on the AV node. This slows AV nodal conduction, which means fewer impulses pass from the atria to the ventricles. That is why digoxin can reduce the ventricular response rate in atrial fibrillation or atrial flutter (it does not “cure” the atrial rhythm, but it can limit how fast the ventricles beat).
What digoxin effects should clinicians watch for?
Because digoxin is narrow therapeutic index (the dose that helps is close to the dose that can harm), its same mechanism that increases contractility and alters AV nodal conduction can also contribute to toxicity—especially when drug levels rise or potassium is low.
Common factors that increase digoxin risk include hypokalemia, renal impairment (reduced clearance), drug interactions, and dehydration. Symptoms of toxicity can include gastrointestinal upset (like nausea) and neurologic effects, along with rhythm disturbances.
What conditions does digoxin target based on its mechanism?
The ion- and AV-node effects explain why clinicians use digoxin for:
- Increasing contractile strength in selected heart failure patients.
- Controlling ventricular rate in atrial fibrillation/flutter by slowing AV nodal conduction.
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