Atropine: Indications, Dosing, Contraindications, and Monitoring
Indications
Atropine is indicated for temporary blockade of severe or life-threatening muscarinic effects, including symptomatic bradycardia, organophosphate/nerve agent poisoning, and as an antisialagogue. 1
Cardiac Indications – Symptomatic Bradycardia
- Sinus bradycardia with low cardiac output, peripheral hypoperfusion, or frequent premature ventricular contractions warrants immediate atropine administration. 2
- Acute inferior myocardial infarction with symptomatic type I second-degree AV block is a Class I indication. 2
- Bradycardia with hypotension following nitroglycerin administration requires atropine. 2
- Ventricular asystole is treated with atropine during cardiopulmonary resuscitation. 2
- Atropine is contraindicated in heart-transplant recipients without autonomic re-innervation because the denervated heart cannot respond to vagolytic agents. 3
Toxicologic Indications – Organophosphate/Nerve Agent Poisoning
- Severe organophosphate or nerve agent poisoning with bronchospasm, bronchorrhea, seizures, or significant bradycardia requires immediate high-dose atropine. 3, 4
- Atropine is the drug of choice for organophosphate intoxication and has been used for this indication for decades. 5
Dosing Regimens
Adult Dosing – Symptomatic Bradycardia
Administer 0.5 mg IV bolus, repeated every 3–5 minutes as needed, up to a maximum total dose of 3 mg (complete vagal blockade). 3, 4
- Peak hemodynamic effect occurs within 3 minutes of each IV dose. 2, 4
- In patients with coronary artery disease, limit the total dose to 0.03–0.04 mg/kg to avoid increasing myocardial oxygen demand and worsening ischemia. 3, 1
- If no response after 3 mg total, proceed immediately to transcutaneous pacing—do not continue atropine. 4
Adult Dosing – Organophosphate/Nerve Agent Poisoning
Initiate with 2–3 mg IV bolus, then double the dose every 5 minutes until all atropinization endpoints are met. 3, 4, 1
Dose-Escalation Protocol (Dose-Doubling Every 5 Minutes)
- 2 mg → 4 mg at 5 min → 8 mg at 10 min → 16 mg at 15 min, continuing until endpoints are achieved. 4
- Typical cumulative doses: 10–20 mg within the first 2–3 hours; severe cases may require up to 50 mg in the first 24 hours. 3, 4, 6
- Tachycardia is NOT a contraindication to continued escalation—the therapeutic goal is control of muscarinic symptoms, not normalization of heart rate. 4, 7
Atropinization Endpoints (All Five Must Be Present)
- Clear chest on auscultation (resolution of bronchorrhea) 4
- Heart rate > 80 beats/min 4
- Systolic blood pressure > 80 mm Hg 4
- Dry skin and mucous membranes 4
- Mydriasis (pupil dilation) 4
Maintenance Infusion
After achieving atropinization, transition to continuous infusion at 10–20% of the total loading dose per hour, not exceeding 2 mg/h in adults. 4
- Example: 20 mg loading dose → 2–4 mg/h infusion. 4
- Continuous infusion is superior to intermittent boluses for maintaining atropinization. 4
Pediatric Dosing – Bradycardia
Administer 0.02 mg/kg IV/IO (range 0.01–0.03 mg/kg), with a minimum single dose of 0.1 mg and a maximum single dose of 0.5 mg. 3
- Endotracheal administration: 0.04–0.06 mg/kg (double to triple the IV dose) when IV access is unavailable, followed by 5 mL normal saline flush and 5 positive-pressure ventilations. 3
Pediatric Dosing – Organophosphate Poisoning
Initial dose: 0.02 mg/kg IV/IO (minimum 0.1 mg, maximum 0.5 mg per dose), then double the dose every 5 minutes until atropinization is achieved. 3, 7
- Children require relatively higher doses compared to standard pediatric resuscitation doses. 7, 8
- For a 13 kg child: 0.26 mg initially → 0.52 mg at 5 min → 1.04 mg at 10 min, continuing escalation. 7
- Expected total requirements: 10–20 mg in the first 2–3 hours for severe poisoning. 7
- Tachycardia is even less of a concern in children than in adults—do not stop escalation due to elevated heart rate. 7
Concurrent Therapy for Organophosphate Poisoning
Pralidoxime (2-PAM) – Essential Co-Therapy
Always administer pralidoxime concurrently with atropine—atropine alone is insufficient. 4, 7
- Adult regimen: 1–2 g IV loading dose over 15–30 minutes, then 400–600 mg/h continuous infusion. 4, 7
- Pediatric regimen: 25–50 mg/kg loading dose, then 10–20 mg/kg/h infusion. 4, 7
- Pralidoxime reverses nicotinic effects (muscle weakness, paralysis) that atropine cannot address. 4, 7
- Must be given early before "aging" of the organophosphate-enzyme bond—for soman, aging occurs within minutes; for agricultural organophosphates, a therapeutic window of up to 24 hours exists, but efficacy drops by 50% after 6 hours. 7
Benzodiazepines – Seizure Control
Administer diazepam 0.2 mg/kg IV or midazolam 0.05–0.1 mg/kg IV for seizures and agitation. 4, 7
Airway Management
Perform early endotracheal intubation for life-threatening poisoning. 4, 7
- Avoid succinylcholine and mivacurium—they are metabolized by cholinesterase and are contraindicated. 4, 7
Decontamination
Healthcare workers must wear full personal protective equipment (PPE) when handling contaminated patients or gastric contents. 4, 7
- Remove contaminated clothing and irrigate skin with soap and water immediately. 4, 7
- Secondary exposure has caused severe poisoning in healthcare workers, requiring atropine, pralidoxime, and intubation. 4, 7
Contraindications
There are no absolute contraindications to atropine. 1
- However, atropine is ineffective and potentially harmful in heart-transplant recipients without autonomic re-innervation. 3
- Atropine is rarely effective for type II second-degree AV block or third-degree AV block at the His-Purkinje level and may worsen the block by increasing sinus rate. 2, 4
Adverse Effects
Dose-Related Toxicity
Doses < 0.5 mg IV or non-IV routes may cause paradoxical bradycardia and worsened AV conduction via central vagal stimulation or peripheral parasympathomimetic effects. 2, 3, 4
Central Nervous System Effects
Repeated administration may cause hallucinations, fever, and toxic psychosis. 2, 7
- Fever is an expected adverse effect with high-dose atropine therapy in organophosphate poisoning and does not indicate treatment failure or warrant cessation. 7
Cardiovascular Effects
Atropine-induced sinus tachycardia may increase myocardial ischemia in patients with coronary artery disease. 2, 3
- Rarely, ventricular tachycardia and fibrillation occur after IV atropine. 2
Ophthalmic Effects
Systemic absorption of ophthalmic atropine can cause a typical anticholinergic toxidrome, including stroke-like symptoms, even at normal topical doses. 9
Allergic Reactions
Severe allergic reactions to atropine are rare but include anaphylaxis. 5
- Alternative anti-muscarinic drugs for patients with proven atropine allergy include glycopyrrolate (peripheral effects only) combined with benzodiazepines or scopolamine (central and peripheral effects). 5
Monitoring Recommendations
Cardiac Monitoring
Continuous ECG monitoring is mandatory during atropine administration to assess for resolution of bradycardia, detect dysrhythmias, and confirm adequate dosing. 3, 4
Organophosphate Poisoning – Specific Monitoring
Serial respiratory assessments every 5–10 minutes during dose escalation to auscultate for bronchorrhea resolution. 4, 7
- Monitor for all five atropinization endpoints—do not stop escalation when only heart rate is adequate. 4
- Check creatine kinase and potassium for rhabdomyolysis detection. 7
- Observe for 48–72 hours for delayed complications, including intermediate syndrome (delayed muscle weakness 24–96 hours post-exposure). 4, 7
Critical Pitfalls to Avoid
Bradycardia Management
- Never administer < 0.5 mg IV atropine—this causes paradoxical worsening. 2, 3, 4
- Do not use atropine for asymptomatic bradycardia > 40 beats/min without signs of hypoperfusion. 2
- Do not delay pacing while waiting for atropine to work in unstable patients with poor perfusion. 3, 4
Organophosphate Poisoning Management
- Do not stop at 2 mg total dose—the higher dosing protocol (up to 50 mg in 24 hours) is required. 3, 4, 7
- Do not withhold atropine because of tachycardia—this is a dangerous error that leads to respiratory failure and death. 4, 7
- Do not use fixed-dose repetition—the protocol mandates dose-doubling every 5 minutes. 4
- Do not delay pralidoxime—it must be given concurrently with atropine. 4, 7
- Do not confuse standard cardiac dosing with toxicological dosing—organophosphate poisoning requires aggressive, high-dose atropine without arbitrary limits. 3, 4
- Underdosing is more dangerous than overdosing—titrate aggressively to dry secretions and reverse bronchospasm. 3
Ophthalmic Use
Atropine ophthalmic drops are used for cycloplegia, mydriasis, and amblyopia treatment. 9