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Toxicology – Digitalis (Digoxin) Toxicity
Source
Digoxin is a cardiac medication used to manage conditions like atrial fibrillation and heart failure. Similar cardiac glycosides are naturally found in plants such as foxglove, oleander, and milkweed, as well as in certain toads (e.g., Bufo species).
Typical Presentation
Patients—often elderly with underlying heart disease—may present with gastrointestinal complaints, abnormal heart rhythms, and visual disturbances. Toxicity can occur from acute overdose or chronic accumulation.
Clinical Features
Mechanism of Action
Digoxin works by inhibiting the sodium–potassium ATPase pump, which increases intracellular calcium and enhances cardiac contractility. It also increases vagal tone, slowing conduction through the heart. However, these same effects predispose to abnormal heart rhythms in overdose.
Management
Treatment focuses on stabilizing the patient and addressing arrhythmias:
Key Points
Source
Digoxin is a cardiac medication used to manage conditions like atrial fibrillation and heart failure. Similar cardiac glycosides are naturally found in plants such as foxglove, oleander, and milkweed, as well as in certain toads (e.g., Bufo species).
Typical Presentation
Patients—often elderly with underlying heart disease—may present with gastrointestinal complaints, abnormal heart rhythms, and visual disturbances. Toxicity can occur from acute overdose or chronic accumulation.
Clinical Features
- Acute toxicity: Symptoms usually appear several hours after ingestion and include nausea, vomiting, elevated potassium levels, and dangerous cardiac arrhythmias.
- Chronic toxicity: More subtle and varied, including fatigue, confusion, weakness, gastrointestinal upset, and visual changes (e.g., blurred vision, yellow-tinted vision or “xanthopsia”).
Mechanism of Action
Digoxin works by inhibiting the sodium–potassium ATPase pump, which increases intracellular calcium and enhances cardiac contractility. It also increases vagal tone, slowing conduction through the heart. However, these same effects predispose to abnormal heart rhythms in overdose.
Management
Treatment focuses on stabilizing the patient and addressing arrhythmias:
- Supportive care with cardiac monitoring
- Atropine for symptomatic bradycardia
- Correction of electrolyte imbalances (especially potassium and magnesium)
- Activated charcoal if ingestion is recent
- Digoxin-specific antibody fragments (Digoxin immune Fab) for severe toxicity (e.g., life-threatening arrhythmias, high potassium, or hemodynamic instability)
Key Points
- Toxicity can be acute or chronic, with different clinical patterns.
- Visual disturbances are a classic clue.
- Hyperkalemia in acute toxicity is a poor prognostic sign.
- Digoxin levels should be interpreted carefully, especially early after ingestion.
- Antibody therapy is the definitive treatment in severe cases.
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