What is atropine indicated for?

Indications for Atropine

Atropine is primarily indicated for temporary blockade of severe or life-threatening muscarinic effects, including treatment of symptomatic bradycardia, ventricular asystole, and as an antidote for organophosphorus or muscarinic mushroom poisoning. 1

Cardiovascular Indications

Bradycardia Management

• Symptomatic sinus bradycardia (generally heart rate <50 bpm associated with hypotension, ischemia, or escape ventricular arrhythmia) 2
• Ventricular asystole during cardiac arrest 2
• Symptomatic AV block occurring at the AV nodal level (second-degree type I or third-degree with narrow-complex escape rhythm) 2
• Bradycardia and hypotension after nitroglycerin administration 2

Specific Myocardial Infarction Scenarios

• Most effective for sinus bradycardia occurring within 6 hours of onset of acute MI symptoms 2
• Particularly useful in inferior MI with symptomatic type I second-degree AV block 2
• Can be effective for profound sinus bradycardia with hypotension associated with thrombolytic therapy (especially of the right coronary artery) 2

Non-Cardiovascular Indications

• Antisialagogue (reduction of salivation before surgery) 1
• Antidote for poisoning from:
  • Organophosphorus compounds
  • Muscarinic mushrooms
  • Nerve agents 1, 3
• Adjunct to morphine administration to reduce nausea and vomiting 2
• Ophthalmic use for cycloplegia, mydriasis, and amblyopia (topical administration) 4
• Treatment of chronic sialorrhea (sublingual administration) 4

Dosing Considerations

Cardiovascular Dosing

• For bradycardia: 0.5 mg IV, repeated every 5 minutes to a total dose of no more than 2 mg 2
• For ventricular asystole: 1 mg IV, repeated in 5 minutes if asystole persists (while CPR continues) 2
• Total cumulative dose should not exceed 2.5 mg over 2.5 hours 2
• In patients with coronary artery disease: Limit total dose to 0.03-0.04 mg/kg 1

Important Cautions

• Doses <0.5 mg may cause paradoxical bradycardia (parasympathomimetic effect) 2
• Use with caution in acute MI due to protective effect of parasympathetic tone against VF and myocardial infarct extension 2
• Not indicated for AV block occurring at infranodal level (usually with anterior MI with wide-complex escape rhythm) 2, 5
• Not indicated for asymptomatic sinus bradycardia 2

Efficacy Considerations

• Approximately 50% of patients with hemodynamically unstable bradycardia respond to atropine with either partial or complete response 6
• Patients with bradycardia tend to respond better than those with AV block 6
• AV nodal block is more likely to respond to atropine and is often transient 5
• Infranodal block is associated with extensive myocardial damage, higher mortality risk, and is less responsive to atropine 5

Adverse Effects

• Common anticholinergic effects: dry mouth, blurred vision, photophobia, tachycardia 1
• Repeated administration may cause CNS effects including hallucinations and fever 2
• Sinus tachycardia following administration may increase myocardial ischemia 2
• Rarely, ventricular tachycardia and fibrillation may occur 2
• Allergic reactions are rare but can include local manifestations and anaphylaxis 7

When Atropine Fails

If bradycardia is unresponsive to atropine:

• Transcutaneous pacing is indicated 2, 5
• Temporary transvenous pacing may be required for persistent symptomatic bradycardia 5
• Consider beta-adrenergic agonists (isoproterenol, dopamine, dobutamine) in cases without coronary ischemia 5

Atropine remains a cornerstone medication for managing acute bradyarrhythmias and cholinergic toxicity, but clinicians must be aware of its limitations in certain types of heart block and potential for adverse effects at both very low and high doses.