What is the recommended dose of atropine (anticholinergic medication) for treating bradycardia in cardiac arrest?

Atropine Dosing in Cardiac Arrest

For bradyasystolic cardiac arrest, administer atropine 1 mg IV, repeated every 3-5 minutes if asystole persists, up to a maximum total dose of 2.5 mg over 2.5 hours. 1, 2

Specific Dosing by Clinical Context

Cardiac Arrest (Asystole/Bradyasystolic Arrest)

• Initial dose: 1 mg IV 1, 2
• Repeat: Every 3-5 minutes if asystole persists 1, 2
• Maximum total dose: 2.5 mg over 2.5 hours 1
• Peak action occurs within 3 minutes of IV administration 1

Symptomatic Bradycardia (Non-Arrest)

• Initial dose: 0.5-1 mg IV 1, 3, 2
• Repeat: Every 3-5 minutes as needed 3
• Maximum total dose: 3 mg (complete vagal blockade) 1, 3
• For bradycardia without cardiac arrest, the recommended dose is 0.5 mg IV repeated every 5 minutes to a total of no more than 2 mg 1

Critical Dosing Considerations

Minimum Dose Warning

Never administer atropine doses less than 0.5 mg in adults, as this can cause paradoxical bradycardia. 1, 3 This paradoxical effect results from either central reflex stimulation of the vagus or peripheral parasympathomimetic effects on the heart 1

When Atropine May Be Ineffective or Harmful

• Type II second-degree or third-degree AV block with wide QRS complex: Atropine is likely ineffective because the block occurs in non-nodal (infranodal) tissue 3, 4
• Heart transplant patients: Atropine may cause paradoxical high-degree AV block or sinus arrest in 20% of cases due to lack of parasympathetic reinnervation 1, 3
• Infranodal heart blocks: Patients with blocks at the His-Purkinje level are at increased risk of adverse events, including ventricular standstill 4

Coronary Artery Disease Patients

• Limit total atropine dose to 0.03-0.04 mg/kg in patients with coronary artery disease 2
• The resulting sinus tachycardia may increase myocardial ischemia or infarct size 1, 3

Algorithm for Bradyasystolic Cardiac Arrest

1. Confirm asystole in at least two ECG leads (fine ventricular fibrillation may mimic asystole) 1
2. Administer atropine 1 mg IV immediately 1, 2
3. Continue CPR while awaiting response (peak effect within 3 minutes) 1
4. If asystole persists after 3-5 minutes, repeat 1 mg IV 1, 2
5. Do not exceed 2.5 mg total dose over 2.5 hours 1
6. If no response after maximum atropine, escalate to epinephrine and consider other reversible causes 3

Important Clinical Pitfalls

Adverse Effects to Monitor

• Sinus tachycardia (may worsen ischemia) 1
• Ventricular tachycardia or fibrillation (rare but reported) 1
• Central anticholinergic syndrome with excessive doses (>3 mg): confusion, hallucinations, fever 1, 3
• Paradoxical bradycardia with doses <0.5 mg 1

Route of Administration

• IV route is strongly preferred 1, 2
• Non-IV routes may result in paradoxical bradycardia 1
• Endotracheal administration is possible but requires higher doses 5

Evidence Quality Note

The recommendation for 1 mg dosing in cardiac arrest comes from established ACC/AHA guidelines 1 and FDA labeling 2, though research evidence shows limited efficacy of atropine in bradyasystolic arrest 6. One animal study even suggested atropine may accelerate cardiac arrest in hypoxic bradycardia 7. However, given minimal harm and guideline support, the 1 mg dose remains standard practice for asystole 1, 2.