digoxin

Question 1

Indication?

Answer 1

AF and atrial flutter; reduces ventricular rate.( BB or non-dihydropyridine CCB is more effective)

Severe heart failure (f treatment with an ACE inhibitor, β-blocker and either an aldosterone antagonist or angiotensin receptor blocker is insufficient, or at an earlier stage if there is co-existing AF)

Question 2

Mechanism of action?

Answer 2

It is negatively chronotropic ( reduces heart rate) and positively inotropic ( increases the force of contraction)

AF/flutter: increased vagal (parasympathetic) tone which reduces conduction of AV node, preventing impulses from being transmitted.

HF: Inhibition of Na+/K+ ATPase pumps causes cascade of events that leads to Ca2+ and to increased contractile force.

Question 3

What are important adverse events?

Answer 3

Bradycardia, GI upset, rash, dizziness, and visual disturbances.

It is proarrythmic

Question 4

What group of patients would you need to be cautious over?

Answer 4

Contraindicated in second-degree heart block , intermittent complete heart block ( as it can worsen conduction abnormalities)
Thyroid
Ventricular arrhythmias

hypertrophic cardiomyopathy
SVT
Dose should be reduced in:
renal failure - as it is eliminated by kidneys

electrolyte imbalances Increased risk of digoxin toxicity

Question 5

what electrolyte imbalances cause increased risk of digoxin toxicity?

Answer 5

hypokalaemia
hypomagnesaeia
hypercalcaemia

Especially potassium as digoxin competes with K+ to bind to Na+/K+ ATPase pump, so effects of digoxin are enhanced with low K+

Question 6

What are important interactions?

Answer 6

Loop and thiazide like diuretics as they can cause HYPOKALEAMIA.

Amiodarone, CCB,spironolactione, quinine can all increase the plasma conc and therefore increasing digoxin conc and therefore toxicity

Question 7

DIGOXIN
What are starting doses for different routes of administration?

Answer 7

Loading dose ONCE ONLY ADMIN:
0.75-1mg

maintenance dose-
125mcg to 250mcg daily

HF: 62.5-125mcg
(IV effective in 30mins)
(oral -2 hours)

Question 8

How must IV doses be given?

Answer 8

slowly

Question 9

what are monitoring requirements?

Answer 9

ECG -Digoxin can cause ST segment depression on ECG
Renal function
Digoxin level ( not needed routinely)
Checked after SIX hours

Question 10

Why is digoxin rarely used for AF?

Answer 10

As its effect on ventricular rate in AF relies on parasympathetic (rest and digest) tone tends to be lost during stress and exercise. Not usually given unless patient is sedentary