CARDIO: DIGOXIN

Question 1

DIGOXIN: INDICATIONS

Answer 1

• AFib and A Flutter -> reduce ventricular rate (Beta blocker or a non-dihydropine calcium channel blocker
• Severe Heart Failure - Digoxin used as a 3rd line treatment in patients who are already taking an ACE inhibitor, beta blocker and either an aldosterone antagonist or angiotension receptor blocker

Question 2

DIGOXIN: MOA

Answer 2

• Negatively chronotropic (reduces heart rate) and positively inotropic (increases the force of contraction)
• In AFib and AFlutter, indirect pathway involving increased vagal (parasympathetic tone)
• Reduces conduction at the AV node preventing some impulses from being transmitted to the ventricles, thereby reducing the ventricular rate
• Heart Failure, direct effect on myocytes via the 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 the contractile force]

Question 3

DIGOXIN: ADVERSE EFFECTS

Answer 3

• Bradycardia, GI disturbance, rash, dizziness and visual disturbances (blurred or yellow vision)
• Digoxin is proarrhythmic and has a low theraputic index => that is there is a narrow safety margin between theraputic and toxic doses
• Wide range of arrhythmias can cause DIGOXIN TOXICITY

Question 4

DIGOXIN: WARNINGS

Answer 4

• Can worsen conduction abnormalities so is contra indicated in second-degree heart block and intermittent complete heart block
• Should not be used in patients at risk of ventricular arrhythmias
• Reduce dose in renal failure patients => as eliminated by the kidneys
• Hypokalaemia, hypomagnesaemia and hypercalcemia increase the risk of DIGOXIN TOXICITY
• POTASSIUM DISTURBANCE is the most important, digoxin competes with the Na+/K+/ATPase pump
• When serum potassium levels are low, competition is reduced and the effects of digoxin are enhanced

Question 5

DIGOXIN: INTERACTIONS

Answer 5

• Loop and Thiazide diuretics -> increase risk of digoxin toxicity and cause hypokalaemia
• Amiodarone, CCBs, Spironolactone and Quinine can all increase the plasma concentration of digoxin therefore causing increased risk of toxicity