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Atropine (Atropen®, Isopto Atropine®)

Drug Overview
Class	Antimuscarinics
Subclass	Competitive Muscarinic Antagonist
Primary CV Use	Symptomatic Bradycardia
Route	IV / IM / SQ / Ophthalmic
Onset (IV)	1–2 minutes
Duration	30–60 minutes
Half-life	~2–4 hours
Metabolism	Hepatic
Elimination	Renal
Pregnancy	Category C
Renal Adjustment	No
Hepatic Adjustment	No
Black Box Warning	No
Controlled	No
FDA Approval	1939

Overview

Atropine is a competitive antagonist of muscarinic acetylcholine receptors.

In cardiovascular practice, it is used to treat symptomatic bradycardia by blocking parasympathetic (vagal) tone at the SA and AV nodes.

It increases heart rate by removing inhibitory cholinergic signaling.

Mechanism of Action

Primary Target:

M2 muscarinic receptors in the SA and AV nodes

Normal Physiology:

Vagal stimulation → M2 activation → ↓ cAMP → ↓ calcium influx → slowed heart rate

Atropine Effect:

Blocks M2 receptors
Prevents vagal inhibition
↑ cAMP
↑ SA node firing
↑ AV nodal conduction

Net Effect:

Increased heart rate
Improved AV conduction

Indications

Cardiovascular:

Symptomatic sinus bradycardia
AV nodal block (vagal-mediated)

Advanced Cardiac Life Support (ACLS):

First-line for unstable bradycardia

Other Uses:

Organophosphate poisoning
Pre-anesthetic to reduce secretions
Ophthalmic dilation

Dosing

Adult (ACLS bradycardia):

1 mg IV push
Repeat every 3–5 minutes
Max total dose: 3 mg

Important:

Doses < 0.5 mg may paradoxically worsen bradycardia

Pediatric dosing differs — weight-based.

Contraindications

Absolute:

None in emergent bradycardia

Relative:

Glaucoma
Severe tachyarrhythmias
Obstructive uropathy
Ileus

Adverse Effects

Common (Anticholinergic effects):

Tachycardia
Dry mouth
Urinary retention
Constipation
Blurred vision
Confusion (especially elderly)

Serious:

Arrhythmias
Hyperthermia (impaired sweating)

Drug Interactions

Additive anticholinergic effects with:

Other Antimuscarinics
Antihistamines
TCAs
Antipsychotics

Use caution with:

AV nodal blocking agents

Monitoring

Continuous ECG
Heart rate response
Blood pressure
Mental status (elderly)

Clinical Pearls

Removes vagal tone — does NOT stimulate the heart directly
Ineffective in Mobitz II or complete heart block distal to AV node
Avoid low doses (< 0.5 mg IV)
First-line ACLS drug for unstable bradycardia
Consider pacing if ineffective

Comparison Within Arrhythmia Management

Compared to:

Adenosine — slows AV node
Beta-Blockers — reduce sympathetic tone

Atropine:

Blocks parasympathetic tone
Increases heart rate
Short-acting
Used in bradycardia (not tachyarrhythmia)