Digitalis drugs are a class of cardiac glycosides derived from the foxglove plant (Digitalis purpurea). They have been used for centuries to treat various heart conditions, but their primary modern use is in managing heart failure and certain heart rhythm disorders. The most common digitalis drug used today is digoxin.
How digitalis works
Digitalis drugs exert their effects through two main mechanisms:
- Positive inotropic effect: Digoxin increases the force of heart muscle contraction by inhibiting the sodium-potassium ATPase pump in heart muscle cells. This causes an increase in intracellular calcium, which strengthens each heartbeat and improves cardiac output.
- Heart rate control: Digitalis also affects the electrical conduction system of the heart by slowing electrical signals in the atrioventricular (AV) node. This helps to slow down an overactive heart rate.
Uses
Though largely replaced by newer therapies like beta-blockers and ACE inhibitors, digoxin is still used in specific cases:
- Heart failure: For patients with reduced ejection fraction, digoxin helps manage symptoms by improving the heart's pumping ability.
- Atrial fibrillation and flutter: Digoxin is used to control the heart rate in patients with chronic atrial fibrillation when other medications are ineffective.
Side effects and toxicity
Digitalis has a narrow therapeutic window, meaning there is a small margin between an effective dose and a toxic one. Digitalis toxicity can be life-threatening and may be worsened by certain electrolyte imbalances, particularly low potassium.
Common side effects include:
- Gastrointestinal problems (nausea, vomiting, diarrhea, loss of appetite)
- Weakness, fatigue, and dizziness
- Headache
Symptoms of digitalis toxicity include:
- Cardiac arrhythmias: Irregular, fast, or slow heartbeat.
- Visual disturbances: Seeing halos or having blurry, yellow, or green vision.
- Neurological issues: Confusion, anxiety, and delirium.
- Gastrointestinal distress: Severe nausea, vomiting, or loss of appetite