What are the indications, dosing, and potential side effects of atropine (anticholinergic medication)?

Atropine: Indications, Dosing, and Side Effects

Primary Indications

Atropine is a life-saving anticholinergic medication indicated for symptomatic bradycardia with hemodynamic compromise, organophosphate/carbamate poisoning, and as an adjunct in cardiac arrest with asystole. 1, 2, 3

Cardiac Indications

• Symptomatic bradycardia: Use when heart rate <50 bpm is associated with hypotension, altered mental status, chest pain, acute heart failure, shock, or escape ventricular arrhythmias 2
• Type I second-degree AV block: Particularly effective when complicating inferior myocardial infarction with hemodynamic compromise 1
• Ventricular asystole: Recommended during cardiopulmonary resuscitation 1, 2
• Bradycardia following nitroglycerin administration 1
• Adjunct to morphine: For nausea/vomiting or to prevent morphine-induced bradycardia in acute MI 1

Toxicological Indications

• Organophosphate or carbamate poisoning: Immediate administration required for severe manifestations including bronchospasm, bronchorrhea, seizures, or significant bradycardia 1
• Muscarinic mushroom poisoning 3

Dosing Regimens

Standard Bradycardia Dosing

• Initial dose: 0.5 mg IV, repeated every 3-5 minutes as needed 1, 2, 3
• Maximum total dose: 3 mg (achieves complete vagal blockade) 1, 2
• Peak effect: Within 3 minutes of IV administration 1

Organophosphate/Carbamate Poisoning

• Initial dose: 2-3 mg IV for severe poisoning 1, 3
• Repeat every 20-30 minutes until full atropinization is achieved 1
• Atropinization endpoints: Clear chest on auscultation, heart rate >80/min, systolic blood pressure >80 mm Hg 1
• Maintenance: Continuous atropine infusion after achieving atropinization 1
• Dose doubling strategy: Double the initial dose every 5 minutes until atropinization is achieved in life-threatening cases 1

Cardiac Arrest (Asystole)

• Dose: 1 mg IV, repeated every 3-5 minutes if asystole persists 1
• Maximum cumulative dose: 2.5 mg over 2.5 hours 1

Special Population: Coronary Artery Disease

• Limit total dose to 0.03-0.04 mg/kg (approximately 2-3 mg maximum) to avoid excessive tachycardia and increased myocardial oxygen demand 3

Pediatric Dosing

• Higher weight-based doses required: 0.05-0.1 mg/kg may be necessary (significantly higher than the standard 0.02 mg/kg resuscitation dose) 1
• Titrate to complete resolution of cholinergic crisis 1
• Do not withhold for tachycardia: Unlike adults, repeated boluses do not cause cardiac arrhythmias in children 1

Critical Contraindications and Cautions

Absolute Contraindications to Atropine

• Type II second-degree AV block or third-degree AV block with new wide QRS complex: Block is at the infranodal (His-Purkinje) level where atropine is ineffective and may worsen the block 1, 2

Use With Extreme Caution

• Acute coronary ischemia or myocardial infarction: Atropine-induced tachycardia increases myocardial oxygen demand and may worsen ischemia or increase infarct size 1, 2, 3
• Post-cardiac transplant patients: May cause paradoxical slowing of heart rate due to denervated heart 1, 2
• Acute angle-closure glaucoma: Atropine may precipitate or worsen acute glaucoma 3
• Prostatic hypertrophy: May lead to complete urinary retention 3
• Pyloric stenosis: May convert partial obstruction into complete obstruction 3
• Chronic lung disease: May cause inspissation of bronchial secretions and formation of viscid plugs 3

Adverse Effects and Pitfalls

Paradoxical Bradycardia

Critical pitfall: Doses <0.5 mg or non-IV routes may cause paradoxical bradycardia and worsened AV conduction due to central vagal stimulation or peripheral parasympathomimetic effects 1, 2

Common Anticholinergic Effects

• Tachycardia (most common, may worsen ischemia) 1, 2, 3
• Dry mouth, blurred vision, photophobia with chronic administration 3
• Central nervous system effects: Hallucinations, fever, confusion with repeated administration 1, 2

Rare but Serious

• Ventricular tachycardia or fibrillation (rare after IV administration) 1, 2
• Anaphylaxis (extremely rare despite extensive use) 4

When Atropine Fails or Is Contraindicated

Alternative Pharmacologic Agents

• Glycopyrrolate: Peripheral antimuscarinic alternative for patients with proven atropine allergy 4
• Dopamine infusion: 5-20 mcg/kg/min for chronotropic effect in bradycardia 1
• Epinephrine infusion: 2-10 mcg/min titrated to hemodynamic response 1

Non-Pharmacologic Interventions

• Transcutaneous pacing: For unstable patients not responding to atropine 2
• Transvenous pacing: Definitive treatment for symptomatic bradycardia refractory to atropine 1

Route-Specific Considerations

• IV route is mandatory for reliable effect: Other routes (IM, oral, rectal) have variable absorption and may cause paradoxical effects 1
• Intramuscular administration: Acceptable in mass casualty organophosphate poisoning when IV access is limited; higher concentrations (2 mg/mL) facilitate IM dosing 5
• Ophthalmic route: Can cause systemic anticholinergic toxicity, particularly in children and adolescents 6