Digoxin

Question 1

Mechanism of action?

Answer 1

Digoxin is negatively chronotrope, positively ionotrope.
It has an indirect effect in AF/atrial flutter, working by increasing the vagal tone (parasympathomimetic) which reduces conduction at the AV node preventing some impulses from being transmitted to the ventricles. Thereby, reducing the heart rate (chronotropy).
A direct effect on myocytes in heart failure through inhibiting Na/K pumps, high intracellular Na prevents Ca from leaving the cell (extrusion of Ca requires low intracellular Na) which stimulates contractile force (ionotrope).

Question 2

Indication?

Answer 2

• AF/atrial flutter (although b blockers or non-DHP Ca channel blockers are more effective)
• severe heart failure as a thrid-line treatment in patients who are already on ACE inhibitor, b blocker &aldosterone antagonist/angiotensin antagonist.

Question 3

Important AE?

Answer 3

bradycardia, gatrointestinal upset, dizziness, rash, headache &visual disturbance (blurred or yellow vision). &Hypokalemia.

Question 4

Important interactions?

Answer 4

Digoxin has a low therapeutic index. +loop/thiazide diuretics, risk of severe hypokalemia &arrhythmias occurrence.
+amiodarone/Ca channel blockers/spironolactone : increased C of digoxin.

Question 5

Important cautions?

Answer 5

As digoxin is excreted by kidney, certain electrolyte abnormalities increase the risk of digoxin toxicity : hypokalemia, hypoMg &hyperCa, with hypokalemia being the most probable of the three as digoxin competes with K to bind to the Na/K ATPase pump. When K levels are low, digoxin effects are enhanced.

Question 6

How is Digoxin taken?

Answer 6

either orally or IVously, delay of action when taken IV is 30mns, compared to 2h following an oral administration. For that reason, IV is usually unnecessary. If rapid effect is desired, a loading dose is given 500mg followed by maintenance doses of 250-500mg the next day &on.

Question 7

Communication?

Answer 7

Digoxin slows down the abnormally fast heart rhythm &makes the heart beat more strongly. Beware of side effects as they may be suggest increased doses that need to be lowered.

Question 8

A clinical tip about Digoxin

Answer 8

Since Digoxin’s effect on AF is dependent on the parasympathetic (rest &digest) tone, it tends to be lost during exercice/stress. Digoxin is therefore now rarely used on its own of AF, although it may be an option in sedentary patients.