Cardiac Glycosides - Digoxin

Question 1

Which of the following drugs is our core drug that is classed as cardiac glycoside?

1 - Digoxin
2 - Glyceryl trinitrate
3 - Isosorbide mononitrate
4 - Terlipressin

Answer 1

1 - Digoxin

Question 2

Digoxin is the core drug that is classed as a cardiac glycoside. What is the mechanism of action of this drug?

1 - prodrug for lypressin (also known as lysine vasopressin) that is a vasoconstrictor and antidiuretic agent.
2 - inhibits Na+/K+ ATPase pump
3 - once metabolised released nitric oxide
4 - converted in mitochondria by aldehyde dehydrogenase in smooth muscle cells to nitric oxide

Answer 2

2 - inhibits Na+/K+ ATPase pump

• Na+ and Ca+2 build up in the cell
• causes more powerful cardiac contractions and cardiac output
• slows AV node conduction
• also increases renal blood-flow, urine output and reduced peripheral oedema

Question 3

If b-blockers and Ca2+ channel blockers fail, digoxin is indicated in the treatment of atrial fibrilliation and atrial flutter. Why is digoxin a good medication to treat atrial arrhythmias?

1 - increased vagus nerve stimulation
2 - decreased vagus nerve stimulation
3 - inhibits AV node firing rate
4 - Increased AV node firing rate

Answer 3

1 - increased vagus nerve stimulation

• increased vagus nerve = increased parasympathetic activity, which predominantly works on the atria
• reduced conduction of AV node and subsequent impulses
• this reduces heart rate and arrhythmias

Question 4

The digoxin effect on AF arrhythmias is reliant on parasympathetic tone. Does exercise of stress have any affect on the effects of digoxin?

Answer 4

• yes
• reduces the effectiveness of digoxin, also the reason why it is not prescribed alone

Question 5

Digoxin is indicated in severe heart failure, but is not the 1st line treatment. It is generally added an ACE inhibitor, B-blocker, aldosterone antagonist or angiotensin receptor blocker. Why is digoxin good for severe heart failure?

1 - increased Ca2+ and Na+ in cardiomyocytes, causing more efficient cardiac contraction
2 - increased sinus node activation to increase heart rate
3 - reduces O2 demand on the heart
4 - Increased AV node firing rate

Answer 5

1 - increased Ca2+ and Na+ in cardiomyocytes, causing more efficient cardiac contraction

• this also increased renal flow and urine output
• reduces peripheral oedema

Question 6

Does digoxin have a negative or positive inotropic (relates to contraction force) effect?

Answer 6

• positive
• makes the heart pump more effectively

Question 7

Does digoxin have a negative or positive chronotropic (relates to heart rate) effect?

Answer 7

• negative
• reduces heart rate

Question 8

All of the following are adverse events of digoxin, EXCEPT:

1 - tachycardia
2 - GI upset
3 - rash
4 - dizziness
5 - visual disturbances

Answer 8

1 - tachycardia
- digoxin improves contractile efficiency so heart doesn’t need to beat as fast

Question 9

Digoxin has a narrow therapeutic index, meaning there is a risk of toxicity. This toxicity could affect a number of organs and tissues, but what is the most dangerous?

1 - liver failure
2 - CKD
3 - GI ischaemia
4 - cardiac arrhythmias
5 - pulmonary fibrosis

Answer 9

4 - cardiac arrhythmias

• can be life threatening
• can cause bradycardia

Question 10

When prescribing digoxin which of the following should be performed at baseline, prior to administering the medication?

1 - ECG
2 -

Question 11

Which 3 of the following conditions is digoxin contraindicated in?

1 - seond degree heart block
2 - intermitent complete heart block
3 - renal failure
4 - ventricular arrythmias

Answer 11

1 - seond degree heart block
2 - intermitent complete heart block
4 - ventricular arrythmias

• it can be used in renal failure, but the dose must be lowered as digoxin is removed via the kidneys

Question 12

Specific electrolyte disturbances can increase the risk of digoxin toxicity. How can hypokalaemia increase the risk of arrhythmia?

1 - K+ binds with digoxin and increases digoxin effects
2 - if K+ is low then digoxin cannot bind to Na+/K+ ATPase
3 - digoxin competes with K+ to bind Na+/K+ ATPase, low K+ means effects of digoxin are enhances

Answer 12

3 - digoxin competes with K+ to bind Na+/K+ ATPase, low K+ means effects of digoxin are enhances

Question 13

In addition to hypokalaemia, which 2 other electrolyte disturbances can increase the risk of digoxin toxicity?

1 - hypercalcaemia
2 - hypermagnesaemia
3 - hypocalcaemia
4 - hypomagnesaemia

Answer 13

1 - hypercalcaemia
4 - hypomagnesaemia

Question 14

Loop diuretics and thiazide diuretics can increase the risk of digoxin toxicity, how?

1 - competes with digoxin binding
2 - causes hypercalcaemia
3 - causes hypokalaemia
4 - causes decreased sensitivity of clearance in the kidneys

Answer 14

3 - causes hypokalaemia

• loop and thiazide diuretics increase Na+ excretion and K+ follows in collecting ducts

Question 15

Caution should be used when prescribing digoxin alongside all of the following drugs, EXCEPT:

1 - amiodarone
2 - Ca2+ channel blockers
3 - sprionolactone
4 - quinine
5 - B-blockers

Answer 15

5 - B-blockers

• all other drugs increase plasma concentration of digoxin and increase risk of toxicity

Question 16

Digoxin can be given orally or IV, taking 2 hours and 30 minutes respectively to have an affect. Digoxin requires a loading dose to have a rapid effect. What is the standard loading dose?

1 - 50 micrograms
2 - 250 micrograms
3 - 500 micrograms
4 - 1mg

Answer 16

3 - 500 micrograms

• followed by 250-500 micrograms 6 hours later
• then maintenance does is 125-250 micrograms
• should be monitored every 6 hours

Question 17

When prescribing digoxin all of the following should be routinely checked before and during administration, EXCEPT:

1 - renal function
2 - ECG
3 - echocardiogram
4 - U&Es

Answer 17

3 - echocardiogram

Question 18

The therapuetic effect of digoxin can affect an ECG in what way?

1 - flattened P wave
2 - inverted T wave
3 - ST segment depression
4 - QRS extension

Answer 18

3 - ST segment depression

• often referred to as the reverse tick