Atropine and Amiodarone

[versatile_kat]

Hey all ... I read the earlier thread about atropine and dose dependant bradycardia. I was hoping to get some clinical reason as to why atropine's effects won't work when the patient is receiving amiodarone. I've asked a pharmacist and didn't get a very concrete answer, just that "it does". Any insight?

[unknown99, BSN, RN]

My understanding is that amiodarone inhibits adrenergic stimulation, which in turn supresses arrythmias. You would not use it for bradycardia, because it causes a decrease in heart rate. Atropine, on the other hand does just the opposite. It inhibits the action af acetylcholine, which in turn increases heart rate. It is used to treat bradycardia.

I hope that helps.:)

[Brenna's Dad]

Just a guess here, but Amiodarone is primarily a potassium channel blocker (prolongs phase 3 of the cardiac action potential). However, it also blocks Ca++, Beta, Muscarinic, Na+ and alpha channels and receptors.

Atropine works by binding to Muscarinic 2 receptors on the heart to decrease cholinergic stimulation.

My only thought, if this is indeed true (ie. Atropine ineffective in increasing heart rate in the Amiodarone pt) , is that the beta, Ca++, Na+, and K+ channel/receptor blockade prevents the normal increase in heart rate associated with the anticholinergic effects of atropine.

However, like all things, this may be dose related. Perhaps the dose of atropine needs to be increased to see a clinical effect.

[Tenesma]

amiodarone is a great beta-blocker... you can cause increased heart rate with atropine, but you just need a far larger dose than usual... amiodarone dosing in my experience hasn't prevented me from using successfully glycopyrrolate or atropine