Anti-dysrrhythmics - Amiodarone

Question 1

what is amiodarone used for?

Answer 1

Tachyarrhythmias

• Afib
• atrial flutter
• supraventricular tachycardia (SVT)
• Ventricular tachycardia (VT)
• refractory ventricular fibrillation (VF)

(usually only used when other options dont work / inappropriate)

Question 2

how does amiodarone work?

Answer 2

Works on myocardial cells to :

• block Na+, Ca2+ and k+ channels
• block alpha and beta adrenergic receptors.

This causes:

• reduced spontaneous depolaristion
• increased resistance to depolarisation
• slow conduction
• interferes with AV node conduction —> slows rate in AF / atrial flutter.
• breaks the re-entry circuit in SVT to restore sinus rhythm

Question 3

What are the side effects of amiodarone?

Answer 3

-hypotension (with IV infusion)

Lungs:
-pneumonitis

Heart:

• bradycardia
• AV block

Liver:
hepatitis

Skin:

• photosensitivity
• grey discolouration

Thyroid abnormalities (hypo/hyper) due to iodine content and similar structure to thyroid hormone.

-long half life so takes months to be eliminated

Question 4

How does amiodarone restore sinus rhythm in supraventricular tachycardias?

Answer 4

in SVT there is a self perpetuating (re-entry) circuit that includes the AV node. Amiodarone interferes with AV node conduction to break the circuit and restore sinus rhythm.

Question 5

In what patients should amiodarone be avoided?

Answer 5

• sever hypotension
• heart block
• active thyroid disease

Question 6

What are the drug interactions of amiodarone?

Answer 6

Amiodarone reacts with many drugs.

Increases plasma concentrations of:

• digoxin
• dlitiazem
• verapamil

(this increases risk of bradycardia, AV block, heart failure. The doses of the drugs above should be halved when used with amiodarone)

Question 7

doses of which drugs should be halved when used with amiodarone?

Answer 7

• digoxin
• diltiazem
• verpamil

amiodarone increases the plasma conc of these drugs which can lead to bradycardia, AV block, heart failure. So half their doses.

Question 8

When is amiodarone given immediately in cardiac arrest?

Answer 8

Amiodarone is given immediately adter the 3rd shock in cardiac arrest for ;

• ventricular fibrillation
• pulseless ventricular tachycardia

The dose is 300mg IV as bolus injection with 20ml NaCl as a flush.

Question 9

How is the efficacy of amiodarone monitored?

Answer 9

• heart rate

- rhythm

Question 10

How is safety monitored in amiodarone therapy?

Answer 10

• continuous cardiac monitoring after IV bolus.

Long term:

• baseline renal, liver, thyroid
• chest xray