Digoxin

Question 1

1) What class of drug is Digoxin?
2) Give the 2 common clinical indications for the use of Digoxin.
3) When might Digoxin be used at an earlier stage in people with heart failure?

Answer 1

1) Cardiac glycoside

2) In AF/ atrial flutter to reduce ventricular rate (beta blockers of non-dihydropyridine are usually more effective).
In severe heart failure as a third line treatment. Used in patients with heart failure who are already taking an ACE inhibitors, beta blockers and aldosterone antagonist/ARB.

3) May be used at an earlier stage if the patient has co-existing AF.

Question 2

1) Describe the basic effect of digoxin.

2) How does Digoxin work in patients with AF or atrial flutter?

Answer 2

1) It is negatively chronotropic and positively inotropic.
2) Effect arises via an indirect pathway involving increased Vargas (parasympathetic) tone > reduced conduction at AVN > prevention of some impulses being transmitted to ventricles > reduction in ventricular rate.

Question 3

1) Describe how Digoxin works in heart failure.

Answer 3

1) Direct effect on myocytes. Inhibition of Na/K ATPase pumps > Na accumulation in myocytes > increase in intracellular Ca > increase in contractile force of the heart.

Question 4

1) Give 3 adverse effects of digoxin.

2) What can occur as a result of digoxin toxicity?

Answer 4

1) Bradycardia, GI disturbance, rash, dizziness, visual disturbance (blurred or yellow vision).
2) A wide range of arrhythmias, as digoxin is pro-arrhythmic.

Question 5

1) Give 3 types of patient that digoxin is contraindicated in.
2) In what condition should the dose of digoxin be reduced?
3) What can increase the risk of digoxin toxicity?

Answer 5

1) Can worsen conduction abnormalities so contraindicated in second degree heart block and intermittent complete heart block. Should not be used in patients with or at risk of ventricular arrhythmias.
2) Reduce dose in renal failure as digoxin eliminated by kidneys.
3) Those with certain electrolyte abnormalities (hypokalaemia, hypomagnesaemia, hypercalcaemia).

Question 6

1) Why are the effects of digoxin enhanced if a patient is hypokalaemic?

Answer 6

1) Because digoxin competes with Potassium to hind to the Na/K ATPase pump. When serum potassium levels are low, competition is reduced and so the effects of digoxin are enhanced.

Question 7

1) Name two classes of drug that can increase the risk of digoxin toxicity by causing hypokalaemia.
2) Give 4 types of drugs that can increase the risk of digoxin toxicity by increasing the plasma concentration of digoxin.

Answer 7

1) Loop and thiazide diuretics.

2) Amiodarone, calcium channel blockers, spironolactone and quinine.

Question 8

1) How is digoxin available for administration?
2) How is digoxin normally prescribed.
3) Why is a loading dose of digoxin required if a rapid response is needed?

Answer 8

1) Orally or through IV.
2) 500 micro gram loading dose followed by 250-500 micro grams 6 hours later, depending on response. Then a usual maintenance dose of 125-250 micro grams OD.
3) Because digoxin has a large volume of distribution.

Question 9

1) What ECG change can therapeutic doses of digoxin cause?
2) What is the best way to guide the effectiveness of Digoxin?
3) If a patient is taking digoxin, what should be checked periodically?

Answer 9

1) ST depression (reverse tick sign)
2) Patient symptoms and heart rate.
3) ECG, electrolytes and renal function periodically.

Question 10

Why is Digoxin rarely used on its own for AF control?

Answer 10

Because it relies on parasympathetic tone, and parasympathetic tone tends to be lost during stress and exercise.

It is sometimes used on its own for AF control on sedentary patients.