High Risk Drugs

Question 1

What are the indications and mechanisms of action for digoxin?

Answer 1

Indications: atrial fibrillation and atrial flutter (BB or rate limiting CCB more effective)
In severe heart failure; third line treatment for those already taking an ACE I, BB and aldosterone agonist/ARB.

Digoxin reduces the heart rate and is positively ionotropic. Reduces conduction at the AV node.

Question 2

What are the adverse effects of digoxin?

Answer 2

Adverse effects; Brady cardia, Gi disturbance, rash, dizziness, and visual disturbances.
Low therapeutic index
Can cause arrthymias in toxicity which can be life threatening.

Question 3

What are the contraindications of digoxin?

Answer 3

May worsen conduction abnormalities - C/I in second degree heart block and complete heart block.
Risk of ventricular arrthymias
Really excreted therefore reduce dose in renal impairment.
Electrolyte abnormalities can increase the risk of toxicity - hypokalaemia, hypomagnesia, hypercalceamia.
Competes with K to bind to K/Na pump, low K increases digoxin effects.

Question 4

Digoxin;

What are the important interactions?

Answer 4

Loop and thiazides diuretics can increase the risk of toxicity by causing hypokalaemia.
Amiodarone, CCB, spironalactone and quinine can increase the plasma concentration. (Manufacturer advises to reduce the dose by half)

Question 5

When should levels be taken to determine plasma digoxin concentration?

Answer 5

Six hours post dose

Question 6

How should digoxin be given?

Answer 6

Can be oral or IV
IV digoxin effects seen within 30 mins, oral effects take 2 hours
Large volume of distribution
Dose may need to be reduced if digoxin has been given in the preceding two weeks.
When switching from IV to oral may need to increase dose by 20-30%.

Question 7

What monitoring is required?

Answer 7

Electrolytes 
K
Ca
Mg
Renal function 
Digoxin-plasma levels