Atropine
- Class: Anticholinergic
- Used for: a dangerously slow heartbeat
- Say it: AT-roh-peen
- Forms: injection, eye drops
ATROPINE is named for ATROPOS, the Fate with the shears. It cuts the vagus nerve's brake off the heart, and the rate climbs back.
The etymology is real — it comes from deadly nightshade, Atropa belladonna. It adds no stimulation; it only removes an inhibition, which is why it fails when the block sits below the AV node.
Acetylcholine acting on cardiac muscarinic receptors is what holds the heart rate down. Atropine blocks those receptors, so the vagal brake is released and the intrinsic rate takes over.
Side effects
Common: dry mouth, fast heartbeat, blurred vision
Serious: confusion, urinary retention
Typical dose
0.5–1 mg intravenously, repeated every 3–5 minutes, maximum 3 mg
Doses below 0.5 mg can paradoxically slow the heart further — do not under-dose it.
Check yourself
How does atropine raise the heart rate?
- It blocks muscarinic receptors, removing the vagal slowing of the heart
- It stimulates beta-1 receptors directly
- It blocks calcium channels in the AV node
- It increases circulating adrenaline
Show answer
A. It blocks muscarinic receptors, removing the vagal slowing of the heart
Atropine adds no stimulation of its own — it removes an inhibition. That distinction matters: where the slow rate is caused by disease below the AV node rather than by vagal tone, blocking muscarinic receptors achieves nothing.
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