Cardiac Glycosides - Digoxin Flashcards
What is digoxin used for?
Digoxin is used for:
1) Atrial fibrillation
2) Atrial flutter
3) Severe heart failure (3rd line treatment if ACEi, BB, ARB already used)
How does digoxin work?
Digoxin is a negatively chronotopic - REDUCED HEART RATE, it does this by reducing the rate of conduction of the AV node.
Digoxin is positively inotropic - INCREASES FORCE OF CONTRACTION, it does this by inhibiting the Na+/K+ ATPase pumps in the myocytes. This causes Na+ to accumulate in the cell. Ca2+ also increases in cell —–> increased contractile force.
What are the side effects of digoxin?
1) bradycardia
2) GI disturbance
3) Rash
4) dizziness
5) Visual disturbance ( blurred / yellow vision)
6) digoxin toxicity —-> arrhythmias (digoxin has a low therapuetic index, so the safety margin is narrow.
In what patients should digoxin be avoided in?
1) second degree heart block
2) intermittent complete heart block
3) ventricular arrhythmia
What precautions should we take with renal failure and digoxin?
Digoxin is excreted by kidneys.
in kidney failure reduce dose of digoxin.
What electrolyte abnormalities increase the risk of digoxin toxicit?
- hypokalaemia ( digoxin competes with K+ to bind to Na+/K+ ATPase pump sites, When K+ is low, less competition, so more digoxin binds, so effects enhanced.)
- hypomagnesaemia
- hypercalaemia
what are the drug interactions of digoxin?
1) Loop diuretics and thiazide diuretics cause hypokalaemia so increase risk of digoxin toxicity.
2) Amiodorone, calcium channel blockers, spironolactone and quinine increase calcium conc so increase risk of digoxin toxicity.
What is the route of digoxin?
Oral and IV
What is the dose of digoxin for a new patient?
loading dose = 500 micrograms followed by 250-500micrograms 6 hours later.
Then 125-250 micrograms daily.
How is the effectiveness of digoxin measured?
1) symptoms and heart rate
2) ECG (ST depression - normal)
3) electrolytes
4) renal function
