Cardiac Glycosides

Question 1

Give an example of a cardiac glycoside

Answer 1

Digoxin

Question 2

What are the indications for use

Answer 2

• AF + atrial flutter - reduces ventricular rate (BB or CaCB usually more effective)
• Severe HF - 3rd line Tx (already ACEi, BB, ARB/ aldosterone antagonist)

Question 3

What is the mechanism of action

Answer 3

• Negatively chronotropic (reduced heart rate)
• Positively inotropic (increases force of contraction)
• In AF –> via indirect pathway involving increased vagal (parasymp) tone –> reduce conduction at AV node
• HF –> inhibits Na+/K+ ATPase pumps = ^ contractile force

Question 4

What are the side effects

Answer 4

• bradycardia
• GI disturbances
• Dizziness
• Rash
• Visual disturbances
• Digoxin toxicity (low therapeutic index)

Question 5

What are the contra-indications

Answer 5

• 2nd degree heart block
• Intermittent heart block
  (may worsen conduction)
• Ventricular arrhythmias
• Dose reduced in renal failure

Increase risk digoxin toxicity

• Hypokalaemia
• Hypomangnesaemia
• Hypercalcaemia

Question 6

What are some important interactions

Answer 6

• Loop + Thiazide diuretics (increase risk toxicity) –> hypokalaemia
• Amiodorone, CaCB, spironolactone, quinine –> increase plasma conc digoxin