====== Atropine (Atropen®, Isopto Atropine®) ======

<WRAP right 300px>
<WRAP infobox>
^ Drug Overview | {{ :cardio:arrhythmias:atropine.svg |}}|
| Drug Class | [[cardio:autonomics:antimuscarinics:start|Antimuscarinics]] |
| Subclass | Competitive Muscarinic Antagonist |
| Primary CV Use | [[cardio:arrhythmias:bradycardia|Symptomatic Bradycardia]] |
| Route | IV / IM / SQ / [[ophthalmology:mydriatics:start|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 |
</WRAP>
</WRAP>

===== Overview =====

Atropine is a competitive antagonist of muscarinic acetylcholine receptors.

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

It increases heart rate by removing inhibitory cholinergic signaling.

<WRAP clear></WRAP>

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===== Mechanism of Action =====

Primary Target:
  * M2 muscarinic receptors in the SA and AV nodes (see [[cardio:autonomics:muscarinic_receptors|Muscarinic Receptors]])

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:
  * ↑ Heart rate
  * Improved AV conduction

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===== Indications =====

Cardiovascular:
  * [[cardio:arrhythmias:bradycardia|Symptomatic sinus bradycardia]]
  * [[cardio:arrhythmias:av_block|Vagal-mediated AV nodal block]]

ACLS:
  * First-line medication for unstable [[cardio:arrhythmias:bradycardia|bradycardia (ACLS)]]

Other Uses:
  * [[toxicology:organophosphates:start|Organophosphate poisoning]]
  * Pre-anesthetic reduction of secretions
  * [[ophthalmology:mydriatics:start|Ophthalmic mydriasis/cycloplegia]]

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===== 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

If ineffective:
  * Proceed to [[cardio:arrhythmias:bradycardia|pacing / pressor support]] (see [[cardio:arrhythmias:bradycardia|Bradycardia Algorithm]])

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===== Contraindications =====

Absolute:
  * None in emergent unstable bradycardia situations

Relative / Cautions:
  * [[ophthalmology:glaucoma:start|Narrow-angle glaucoma]]
  * Severe tachyarrhythmias (see [[cardio:arrhythmias:start|Dysrhythmias]])
  * Obstructive uropathy
  * Ileus

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===== Adverse Effects =====

Common (anticholinergic effects):
  * Tachycardia
  * Dry mouth
  * Urinary retention
  * Constipation
  * Blurred vision
  * Confusion (especially elderly)

Serious:
  * Arrhythmias
  * Hyperthermia (impaired sweating)

Mechanism-based:
  * “Hot as a hare, dry as a bone, blind as a bat, mad as a hatter”

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===== Drug Interactions =====

Additive anticholinergic effects with:
  * [[cardio:autonomics:antimuscarinics:start|Other antimuscarinics]]
  * [[psych:tcAs:start|Tricyclic antidepressants (TCAs)]]
  * [[psych:antipsychotics:start|Antipsychotics]]
  * [[allergy:antihistamines:start|First-generation antihistamines]]

Bradycardia context / AV node:
  * Use caution if combined with AV nodal blockers:
    * [[cardio:beta_blockers:start|Beta-Blockers]]
    * [[cardio:ccb:non_dhp|Non-DHP Calcium Channel Blockers]]
    * [[cardio:arrhythmias:digoxin|Digoxin]]

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===== Monitoring =====

  * Continuous ECG
  * Heart rate response
  * Blood pressure
  * Mental status (elderly)
  * Signs of anticholinergic toxicity

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===== Clinical Pearls =====

  * Atropine removes vagal tone — it does NOT increase contractility directly.
  * Ineffective in infranodal block (e.g., [[cardio:arrhythmias:av_block|Mobitz II / complete heart block distal to AV node]]).
  * Avoid low doses (< 0.5 mg IV) due to paradoxical bradycardia.
  * If no response, escalate quickly to [[cardio:arrhythmias:bradycardia|pacing and/or pressors]].

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===== Comparison Within Arrhythmia Management =====

Opposite AV nodal effects compared to:
  * [[cardio:arrhythmias:adenosine|Adenosine]] (transient AV nodal block)
  * [[cardio:beta_blockers:start|Beta-Blockers]] (↓ sympathetic tone)
  * [[cardio:ccb:non_dhp|Non-DHP CCBs]] (↓ AV nodal conduction)

Atropine:
  * ↑ SA node rate
  * ↑ AV conduction
  * Used for bradycardia, not tachyarrhythmias

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===== Related =====

  * [[cardio:arrhythmias:start|Dysrhythmias Module]]
  * [[cardio:arrhythmias:bradycardia|Bradycardia]]
  * [[cardio:arrhythmias:adenosine|Adenosine]]
  * [[cardio:beta_blockers:start|Beta-Blockers]]
  * [[cardio:ccb:start|Calcium Channel Blockers]]
  * [[cardio:intro:start|Cardiovascular Pharmacology]]