Mrs Chan, an 80 year old widow had recently been diagnosed to have atrial fibrillation. She was prescribed digoxin, metoprolol and warfarin by a cardiologist.

a) Regarding digoxin:

i) What was its purpose? (1 mark)

Anti-arrhythmic effect by reducing ventricular rate.

This is only effective when at rest, so patients require additional beta blocker or CCB for optimal rate control.

Mechanism of action is inhibition of the Na+/K+ pump on cells of the autonomic nervous system causing stimulation of the vagus nerve. The vagus nerve provides para-sympathomimetic control of the heart (reduces heart rate).

Via inhibition of Na/K pumps on the cardiac cells digoxin can also increases the force of contraction, which is useful in heart failure.

ii) Name ONE cardiovascular and ONE non-cardiovascular adverse effect. (2 marks)

Cardiovascular adverse effect: Arrhythmias

Non-cardiovascular adverse effect:

• Hypokalaemia (via inhibition of the Na+/K+ pump)
• Also GI side effects, CNS disturbance including visual disturbance

Digoxin inhibition of Na+/K+ pump affects all excitable tissue including smooth muscle and CNS. Outside the heart the GIT is the next most common site affected by toxicity.

Refs

BNF

EMC