Digoxin
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Introduction

Digoxin is a cardiac glycoside, which is most commonly used in atrial fibrillation and atrial flutter. However, beta blockers and the dipyridamole calcium channel blockers are generally more effective, and digoxin carriers a risk of toxicity which means that serum digoxin levels often have to monitored, meaning it is less convenient.
Classically it was used in older patients where it’s lower potency was not such an issue, although it is probably now used less and less often.
Cardiac glycosides have the following effects:
  • Positively ionotropic – Increase the force of contractions (through increased intracellular Ca2+‚Äč)
  • Negatively chronotropic – reduces the heart rate by reducing conduction through the AV node
In some cases, digoxin may also be used in heart failure as a third or fourth line agent.

Digoxin is derived from the foxglove plant – digitalis purpurea –¬†hence the name¬†digoxin.

Digital purpurea plant from which digoxin is derived
Digital purpurea plant from which digoxin is derived

Digoxin in Atrial fibrillation

  • Digoxin is not the first line treatment in any type of AF. Particularly in acute cases, it takes too long to act, and tachycardia may still persist even after the maximum dose. It is also less effective than many other agents, and unlike many of the other drug choices, it carries a risk of toxicity
  • It is most commonly used in milder cases of AF in older patients, in whom other drugs may be less well tolerated

Adverse effects

  • Gastrointestinal disturbance
  • Bradycardia
  • Arrhythmia
  • Rash
  • Dizziness
  • Digoxin toxicity (see below)

Warnings

Digoxin can worsen some arrhythmias and should be avoided in:

  • second degree heart block
  • Ventricular arrhythmias

Other electrolytes disturbances can increase the risk of digoxin toxicity:

Several other drugs can also increase the risk of digoxin toxicity:

Digoxin Toxicity

Digoxin has a narrow therapeutic window. This means that the concentration at which it is effective is very narrow Рtoo low and it doesn’t work, too high and it can be dangerous.

Digoxin toxicity results from increased digoxin levels in the blood

  • Can be particularly difficult to identify as it is often similar to patient deterioration due to underlying disease
  • Is more likely in elderly patients

May occur in renal failure ‚Äď as the drug is excreted by the kidneys

Symptoms

  • Xanthopsia ‚Äď a yellow ring / discolouration of the vision
  • Bradycardias
  • Ventricular ectopic beats
  • Heart block (various types)
  • VT/VF ‚Äď rare

Investigations

  • Always check potassium! Hypokalaemia predisposes to cardiac side effects of digoxin, even when the levels of digoxin are low / therapeutic

References

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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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