Digoxin Flashcards
When is digoxin indicated for use?
- AF
- Atrial flutter
- Severe heart failure
How is digoxin used in AF/atrial flutter?
To reduce ventricular rate via indirect pathway involving increased vagal tone, which reduces AV node conduction, preventing impulses being transmitted to ventricles
How is digoxin used in Severe heart failure?
Third-line treatment in patients who are already taking ACEi, B-blocker and either ARBs or aldosterone antagonists
How does digoxin generally work?
Negative chronotropic (reduces heart rate) and positiviely intotropic (increases force of contraction)
What is the mechanism of digoxin in heart failure?
Direct effect on myocytes through inhibition of Na+/K+-ATPase pumps, causing Na+ to accumulate in the cell. As cellular extrusion of Ca2+ requires low intracellular Na+ concentrations, elevation of intracellular Na+ causes Ca2+ to accumulate in the cell, increasing contractile force
What are the main adverse effects of digoxin?
- Bradycardia
- GI disturbance
- Rash
- Dizziness
- Visual disturbance
- Arrythmias
What visual disturbances can occur with digoxin use?
Blurred or yellow vision
When is digoxin contra-indicated for use?
- Second-degree heart block
- Intermittent compltete heart block
- Risk of ventricular arrythmias
What electrolyte abnormalities can increase the risk of digoxin toxicity?
- Hypokalaemia
- Hypomagnasaemia
- Hypercalcaemia
Why can hypokalaemia cause digoxin toxicity?
Digoxin competes with potassium to bind the Na+/K+-ATPase pump. When serum potassium levels are low, competition is reduced and the effects of digoxin are enhanced
What are important interactions to be aware of when using digoxin?
- Loop/thiazide diuretics - can cause hypokalaemia
- Amiodarone
- CCBs
- Spironolactone
- Quinine
How can digosxin be administered?
- Oral
- IV
How long after IV administration of digoxin would you see an effect?
30 mintues
How long after administration of oral digoxin would you see an effect?
2 hours
Why is a loading dose required for digoxin if rapid effect is needed?
Due to its large volume of distribution
What dose of digoxin would you give as a loading dose if you wanted to obtain rapid effect of the drug?
500 micrograms, followed by 500 micrograms 4 hours later. Maintenance of 62.5-250 micrograms daily following this
What does the maintenance dose of digoxin depend on?
- Heart rate
- Renal function
How would you note a loading dose of digoxin in a drug kardex?
In the once only section. Maintenance is written in regular meds section
What parameters would you use to monitor digoxin therapy?
- Symptoms
- Heart rate
- Renal function
- ECG
- Electrolytes
What ECG changes can the therapeutic dose of digoxin cause?
ST-segment depression - reverse tick sign
What might the “reverse tick sign” on ECG indicate in someone taking digoxin?
Expected effect - does not signify toxicity
Why can digoxins effect on AF be lost during stress and exercise?
It relies on increasing parasympathetic tone - in these states sympathetic is to overpowering. This is why it is a better option for sedentary patients
Can digoxin toxicity occur when digoxin levels are within therapeutic range?
Yes
