Cardiac Glycosides are a class of drugs that strengthen the force of the heart’s contraction and slow its rhythm. The most well-known example is Digoxin, derived from the foxglove plant (Digitalis purpurea).
These medications have been used for centuries to manage heart failure and atrial fibrillation. In this article, we’ll explore their mechanism of action, clinical uses, side effects, and essential nursing considerations — all explained in a simple, student-friendly way.
Introduction to Cardiac Glycosides
Class:
- Pharmacologic (P): Cardiac Glycosides
- Therapeutic (T): Inotropes
Example:
- Digoxin (Lanoxin)
- Routes: PO, IM, IV
Cardiac Glycosides are positive inotropic agents, meaning they increase the force of heart contraction without increasing oxygen demand significantly. This makes them valuable in heart failure, where the heart struggles to pump effectively.
Mechanism of Action (MOA)
Cardiac Glycosides like Digoxin exert a positive inotropic effect — they strengthen the heart muscle’s contractions.
They work by inhibiting the sodium-potassium ATPase pump in cardiac cells, leading to increased intracellular calcium. More calcium inside heart cells means stronger contractions.
Main Effects:
↑ Myocardial Contractility (Positive Inotropy): Improves cardiac output.Mnemonic:
“Time to DIG for a deeper contraction.”
“DIG” reminds you of Digoxin, which helps the heart dig deeper to pump blood more effectively.
Therapeutic Uses of Cardiac Glycosides
| Condition | Mechanism of Benefit |
|---|---|
| Heart Failure (CHF) | Increases contractility and cardiac output, reducing symptoms like fatigue and edema. |
| Atrial Fibrillation (AF) | Slows conduction through the AV node, controlling heart rate. |
| Atrial Flutter | Helps regulate abnormal rhythm in the atria. |
Note: Digoxin is not a first-line therapy in modern practice but remains useful when other medications are insufficient or contraindicated.
Pharmacological Effects on the Heart
1. Increased Force of Contraction:Improves systolic performance and cardiac output.
Allows longer ventricular filling time.
Especially at the AV node — beneficial in atrial fibrillation.
Enhances perfusion to vital organs.
Adverse Effects (Mnemonic: DIG)
To remember Digoxin’s adverse effects, think “DIG” — because it helps the heart dig for deeper contraction but may dig into toxicity if overdosed.
| Letter | Meaning | Explanation |
|---|---|---|
| D | Dysrhythmias | Irregular heartbeat due to toxicity. |
| I | Impaired Vision (Yellow Halos) | Classic sign of digoxin toxicity — blurred or yellow-tinted vision. |
| G | GI Effects | Nausea, vomiting, diarrhea are early warning signs. |
Other symptoms include weakness, confusion, dizziness, and fatigue, particularly in elderly patients.
Toxicity and Therapeutic Range
Therapeutic Serum Level: 0.5 – 2.0 ng/mLToxicity Symptoms:
- Visual disturbances (“yellow halos”)
- Nausea and vomiting
- Bradycardia or irregular pulse
Antidote: Digoxin Immune Fab (Digibind) — used in life-threatening toxicity cases.
Drug Interactions
1. Diuretics (Loop or Thiazide):
Cause hypokalemia and hypomagnesemia, increasing digoxin toxicity risk.
2. ACE Inhibitors & ARBs:
- Can increase potassium levels, which may alter digoxin’s effect.
- Also increase the risk of toxicity when renal function is impaired.
May enhance bradycardia or conduction delays when combined.
Contraindications
Avoid or use with caution in the following conditions:
- Ventricular Fibrillation
- Ventricular Tachycardia
- Wolff-Parkinson-White Syndrome (WPW)
- Severe Renal Impairment
- Hypokalemia or Hypercalcemia (Predispose to toxicity)
Note: Always correct electrolyte imbalances before starting digoxin therapy.
Nursing Considerations
1. Monitor Apical Pulse:
- Check for 1 full minute before administering.
- Hold dose if HR < 60 bpm (adult) or as per hospital protocol.
2. Assess for Toxicity Signs:
Nausea, vomiting, vision changes, or irregular pulse.
3. Monitor Serum Levels:
Maintain within therapeutic range (0.5–2.0 ng/mL).
4. Electrolyte Monitoring:
Watch potassium, magnesium, and calcium levels.
5. Educate Patients:
- Take medication at the same time each day.
- Do not double doses if one is missed.
- Report any visual disturbances or irregular heartbeat.
At higher risk of toxicity due to decreased renal clearance.
Clinical Pearls
- Hypokalemia enhances toxicity, while hyperkalemia decreases digoxin’s effect.
- Renal function is crucial — dose adjustments may be necessary.
- Bradycardia + Yellow vision = Suspect toxicity.
- Always check pulse and potassium before each dose.
Summary Table
| Parameter | Details |
|---|---|
| Drug Class | Cardiac Glycosides |
| Example | Digoxin |
| Mechanism | Inhibits Na⁺/K⁺ ATPase → ↑ intracellular Ca²⁺ → stronger contraction |
| Uses | Heart Failure, Atrial Fibrillation |
| Adverse Effects (DIG) | Dysrhythmias, Impaired Vision, GI Upset |
| Therapeutic Range | 0.5–2.0 ng/mL |
| Antidote | Digoxin Immune Fab (Digibind) |
| Interactions | Diuretics, ACE Inhibitors, ARBs |
| Contraindications | Ventricular Fibrillation, WPW Syndrome |
| Route | PO, IM, IV |
FAQs About Cardiac Glycosides
Q1. What is the primary action of Digoxin?
It increases the force of myocardial contraction (positive inotropy) and slows heart rate.
Q2. Why is Digoxin dangerous in low potassium levels?
Hypokalemia increases digoxin’s binding to cardiac tissue, leading to toxicity.
Q3. What visual change indicates Digoxin toxicity?
Patients may see yellow or green halos around lights.
Q4. What should a nurse do before giving Digoxin?
Check the apical pulse for one full minute and hold if HR < 60 bpm.
Q5. What is the antidote for Digoxin toxicity?
Digoxin Immune Fab (Digibind).
Q6. Can Digoxin be given with diuretics?
Yes, but with caution — monitor electrolytes and cardiac rhythm closely.
Mnemonic Recap
DIG for a deeper contraction:
D — DysrhythmiasCardiac Glycosides, especially Digoxin, remain essential drugs for managing heart failure and atrial fibrillation, though modern medicine uses them more selectively. Understanding their mechanism, side effects, and toxicity prevention is vital for safe administration.
With proper monitoring and patient education, Digoxin can significantly improve cardiac performance and quality of life.
