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[Pharmacology](https://durgical.com/en/pharmacology/) · Class

# Cardiac glycosides

Plant-derived medicines (from foxglove) that make the heart contract a little stronger and slow conduction through the AV node.

Updated 2026-11-01

## What they are

Inhibitors of the sodium-potassium pump (Na⁺/K⁺-ATPase), originally from the foxglove plant (Digitalis). Today they are used for symptom control in heart failure and to slow the heart rate in atrial fibrillation.

## Mechanism of action

Blocking the sodium pump raises sodium inside the heart cell, so the sodium-calcium exchanger removes less calcium. More calcium is stored and released with each beat, which strengthens contraction. They also increase vagal tone, slowing the sinus node and AV conduction.

Target: Na⁺/K⁺-ATPase (sodium-potassium pump)

## Key points

- Narrow therapeutic range: toxicity is common, especially in older adults and in kidney failure.
- Hypokalaemia increases toxicity because potassium and digoxin compete for the same site on the pump.
- Toxicity: nausea, vomiting, confusion, yellow-green vision or halos, and almost any arrhythmia (classically atrial tachycardia with block or bidirectional ventricular tachycardia).
- Digoxin improves symptoms and hospital admissions in heart failure, but has not been shown to lower mortality.
- Severe toxicity has a specific antidote: digoxin-specific antibody fragments (Fab).

## Drugs in this class

- [**Digoxin** A medicine from the foxglove plant that strengthens the heartbeat and slows the heart rate. The line between effect… Na⁺/K⁺-ATPase (sodium-potassium pump)](https://durgical.com/en/pharmacology/digoxin/)

## Others in the class

- Digitoxin

## Test yourself

Think of the answer, then tap the question to see it.

## How does inhibiting the Na⁺/K⁺-ATPase increase myocardial contractility?

Intracellular sodium rises, the sodium-calcium exchanger removes less calcium, the sarcoplasmic reticulum stores more calcium and releases more with each beat.

## Why does hypokalaemia increase the risk of digoxin toxicity?

Potassium and digoxin compete for the same binding site on the pump; with less potassium, more digoxin binds and the effect is stronger.

## What is the specific treatment for severe digoxin toxicity?

Digoxin-specific antibody fragments (Fab), which bind the drug and remove it from its target.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Digoxin: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682301.html) (MedlinePlus (U.S. National Library of Medicine), 2017); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/) (World Health Organization, 2025); [DailyMed - DIGOXIN tablet](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f3d29508-e7cc-47ff-845d-b5375ee30407) (DailyMed (U.S. National Library of Medicine), 2026).

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