Atropine: Indications, Dosing, Contraindications, and Adverse Effects
Symptomatic Bradycardia
For acute symptomatic bradycardia, administer atropine 0.5 mg IV bolus every 3–5 minutes up to a maximum total dose of 3 mg. 1, 2
Adult Dosing
- Initial dose: 0.5–1 mg IV bolus 1, 3
- Repeat every 3–5 minutes as needed 1, 2
- Maximum cumulative dose: 3 mg 1, 2
- Peak effect occurs within 3 minutes of IV administration 4
Pediatric Dosing
- Initial dose: 0.02 mg/kg IV (range 0.01–0.03 mg/kg) 1
- Minimum single dose: 0.1 mg 1
- Maximum single dose: 0.5 mg for children, 1.0 mg for adolescents 1
- Maximum total dose: 1 mg for children, 2 mg for adolescents 1
- Endotracheal route when IV unavailable: 0.04–0.06 mg/kg (double to triple the IV dose), followed by 5 mL normal saline flush and 5 positive-pressure ventilations 1
Specific Indications
- Sinus bradycardia with heart rate <50 bpm associated with hypotension, ischemia, or escape ventricular arrhythmia 2
- Symptomatic AV block at the AV nodal level 2
- Acute inferior MI with symptomatic type I second-degree AV block 1
- Bradycardia with hemodynamic compromise (hypotension, altered mental status, chest pain, acute heart failure, or shock) 2
- Ventricular asystole: 1 mg IV, repeated every 3–5 minutes up to maximum 2.5 mg over 2.5 hours 1, 2
Critical Dosing Warnings
- Doses below 0.5 mg can paradoxically worsen bradycardia through central vagal stimulation 1, 2, 5
- In patients with coronary artery disease, limit total dose to 0.03–0.04 mg/kg to avoid increasing myocardial oxygen demand and worsening ischemia 1, 3
- Administer as direct IV bolus without dilution for rapid effect 1
When Atropine Fails
- Consider transcutaneous pacing for unstable patients not responding to atropine 2
- Alternative therapies: epinephrine infusion (2–10 mcg/min IV) or dopamine infusion (5–20 mcg/kg/min IV) 1, 2
Organophosphate/Nerve Agent Poisoning
For organophosphate poisoning, initiate atropine at 2–5 mg IV and repeat every 20–30 minutes until muscarinic symptoms resolve, with no arbitrary maximum dose. 1, 3
Adult Dosing
- Initial dose: 2–5 mg IV 1, 3
- Repeat every 20–30 minutes until full atropinization 1
- Cumulative doses may reach 10–20 mg in the first 2–3 hours 1
- Total 24-hour doses may reach up to 50 mg before full muscarinic antagonism appears 1
Pediatric Dosing
- Initial dose: 0.05 mg/kg IV (up to adult dose of 2–5 mg) 1
- Double the dose as needed without defined maximum, titrated to clinical effect 1
Endpoints of Full Atropinization
- Clear chest on auscultation 1
- Heart rate >80/min 1
- Systolic blood pressure >80 mm Hg 1
- Drying of secretions 1
Critical Management Points
- Underdosing is more dangerous than overdosing in organophosphate poisoning 1
- Do not confuse standard cardiac dosing (3 mg maximum) with toxicological dosing (no arbitrary limit) 1
- Maintenance atropinization can be achieved with continuous IV infusion after initial boluses 1
- Administer benzodiazepines (diazepam or midazolam) for seizure control and agitation 1
- Consider early endotracheal intubation for life-threatening poisoning 1
Pre-operative Antisialagogue Use
For antisialagogue or antivagal effects perioperatively, administer atropine 0.5–1 mg IV as an initial single dose. 3
Dosing
- Initial single dose: 0.5–1 mg IV 3
- Can be repeated every 5 minutes as needed 4
- Maximum cumulative dose in OR setting: 2 mg 4
Administration Timing
- Following intramuscular administration, give approximately 1 hour before induction 6
- Following oral administration, give approximately 2 hours before induction 6
Ophthalmic Mydriasis
Ophthalmic atropine is used for cycloplegia, mydriasis, and amblyopia treatment, but systemic absorption can cause anticholinergic toxicity. 7
Important Safety Consideration
- Normal ophthalmic doses can result in systemic absorption causing stroke-like symptoms and anticholinergic toxidrome 7
- If systemic toxicity occurs, physostigmine IV can completely reverse symptoms 7
Contraindications
Atropine has no absolute contraindications per FDA labeling, but several clinical scenarios warrant extreme caution or avoidance. 3
Relative Contraindications
- Heart transplant recipients without autonomic re-innervation: atropine can cause paradoxical heart block or sinus arrest in 20% of these patients 1, 2
- Type II second-degree or third-degree AV block with new wide-QRS complex: block is likely infranodal and atropine will not help 2, 4
- Acute coronary ischemia or myocardial infarction: increased heart rate may worsen ischemia or increase infarct size 2
Cautions
Common Adverse Effects
The most common adverse effects are directly related to atropine's antimuscarinic action and include dry mouth, blurred vision, photophobia, and tachycardia. 3
Dose-Related Adverse Effects
- Sinus tachycardia that may increase myocardial ischemia 1, 8
- Ventricular tachycardia or fibrillation (rare but serious) 2, 8
- CNS effects: hallucinations, fever, toxic psychosis with repeated administration 1, 2, 8
- Paradoxical bradycardia with doses <0.5 mg or non-IV routes 1, 2
Adverse Effect Risk Factors
- Higher initial doses (≥1.0 mg vs. usual 0.5–0.6 mg) correlate with increased adverse effects 8
- Total cumulative doses exceeding 2.5 mg over 2.5 hours significantly increase risk of ventricular arrhythmias, sustained sinus tachycardia, and toxic psychosis 8
Allergic Reactions
- Rare but can include local manifestations (especially after ophthalmic administration) or systemic anaphylaxis 9
- Alternative antimuscarinic agents for proven atropine allergy: glycopyrrolate (peripheral effects) or scopolamine (peripheral and central effects) 9
Monitoring Parameters
- Continuous ECG monitoring during administration to assess symptom resolution and detect adverse effects 1
- Monitor for signs of excessive dosing: tachycardia, anticholinergic toxicity, resolution of miosis 1
- In organophosphate poisoning, monitor for resolution of bronchospasm, secretions, and bradycardia 1