Digoxin Flashcards
Mechanism of action of Digoxin
“Cardiac glycoside”
Induces an increase in intracellular sodium that drives an influx of calcium into the heart increasing contractility.
It also increases vagal activity which reduces AV conduction which also reduces rate.
Digoxin indications
- Mild to moderate heart failure
- In atrial fibrillation to maintain ventricular rate
- Tachycardia
Therapeutic index
1.0-2.0 ng/mL (mcg/L)
Monitoring with digoxin
Renal function - excretion largely depends on kidneys
U+E’s - especially K+ (hyperkalaemia may occur from digoxin)
BP
Pulse
Toxic adverse effects
Nausea and vomiting
Abdominal pain
Visual disturbances
Fatigue
Delirium
Bradycardia
Digoxin and amiodarone
Amiodarone doubles serum concentration of digoxin (if being given together, half the concentration of digoxin)
Digoxin and Calcium channel blockers
Verapamil increases serum digoxin conc. by 40% with a daily dose of 160mg and by about 70% with a daily dose of 240mg.
Digoxin dose should be reduced and monitored
Digoxin and Spironolactone
Spironolactone can increase serum digoxin conc. by 25%
Digoxin and diuretics
Potassium-depleting diuretics are thought to be implicated in increasing digoxin toxicity i.e. thiazide-like so it is preferred to use potassium-sparring diuretics
Digoxin and St. John’s wort
Plasma conc. of digoxin reduced by St. John’s wort
Digoxin and Erythromycin
Macrolide antibiotics can produce a two to four fold increase in digoxin conc. e.g. Erythromycin, clarithromycin, azithromycin
Overview of interactions of digoxin
- Amiodarone - doubles digoxin
- Calcium channel blockers - verapamil increases digoxin
- Spironolactone - increases digoxin
- Diuretics - potassium-depleting diuretics cause toxic effects
- St. John’s wort - reduces digoxin
- Macrolide antibiotics - increases digoxin
