Anticholinergic · Antidote
Atropine
Indications
- Symptomatic sinus bradycardia or AV-node-level block (first-line ACLS drug)
- Organophosphate, carbamate and nerve agent poisoning, with pralidoxime
- Vagal bradycardia from laryngoscopy, surgical reflexes or sheath removal
- With neostigmine or edrophonium in neuromuscular-blockade reversal, to block their muscarinic effects
- Antisialagogue before airway procedures
- Before emergency intubation in children, to prevent bradycardia (may be considered, AHA/AAP 2025)
Dosing
| Where | Dose |
|---|---|
| Rhythm control | Atropine: 1 mg IV every 3–5 min, max 3 mg |
On the quick cards
- Atropine (AtroPen)EMS Field Drugs: Cardiac arrest and ACLS: symptomatic bradycardia and cholinergic poisoning
- Atropine and pralidoxime (DuoDote, ATNAA)EMS Field Drugs: Toxicology: nerve agent and organophosphate auto-injector
- Rhythm controlPush and Emergency Meds: Bradycardia, SVT, AF and VT with a pulse
Mechanism of action
Atropine competitively and reversibly blocks all five muscarinic receptors (M1–M5), with little nicotinic effect at clinical doses. At the SA and AV nodes, blocking Gi-coupled M2 receptors removes vagal tone: acetylcholine can no longer open IKACh potassium channels or lower cAMP, so the rate rises and AV conduction speeds up. Blocking Gq-coupled M3 receptors dries secretions, relaxes bronchial, gut and bladder smooth muscle and dilates the pupil. The modernized Vaughan Williams scheme (Lei 2018) lists it in class II.
Pharmacology
- Cardiovascular: faster sinus rate and AV conduction, little BP change; small doses can first slow the rate (label), so doses under 0.5 mg were avoided
- Cardiovascular: little effect on block below the node (Mobitz II, third degree with a wide escape) and none on the denervated transplanted heart
- CNS: as a tertiary amine it crosses the BBB; sedation, then delirium, hallucinations and coma at high doses (central anticholinergic syndrome), worst in older adults
- Respiratory: bronchodilation and drier secretions, but thicker mucus and more dead space
- Other: mydriasis, slower gut, urinary retention, and no sweating (heat intolerance, fever in children) with flushing
Pharmacokinetics
| Onset | IV about 1 min |
|---|---|
| Peak | Heart-rate effect lags plasma levels, peaking about 7–8 min after IV; IM plasma peak about 30 min (label) |
| Duration | Roughly 1–2 h of vagal block, shorter than glycopyrrolate (2–3 h by its label) |
| Half-life | 2–4 h in adults (label); more than doubled under age 2 and over 65 |
| Distribution | Vd about 1–2 L/kg; crosses the BBB and placenta (label) |
| Protein binding | 14–44% (labels differ) |
| Metabolism | Liver hydrolysis to tropine and tropic acid, plus noratropine (label) |
| Elimination | Urine: 13–50% unchanged (label) |
| Routes | IV, IO, IM, endotracheal; autoinjectors for nerve agents |
Chemistry
- A tropane alkaloid from Atropa belladonna: an ester of tropine and tropic acid
- Racemic d- and l-hyoscyamine; nearly all activity is in the l-isomer (label)
- A tertiary amine, pKa about 9.4–9.8 (PubChem): over 99% ionized at pH 7.4, yet the un-ionized fraction crosses the BBB and placenta; quaternary glycopyrrolate cannot
- Given as the sulfate: 0.1 mg/mL syringes (1 mg/10 mL), 0.4 and 1 mg/mL vials, and DuoDote (2.1 mg with pralidoxime 600 mg)
Adverse effects and cautions
In the one-pagers
- Rhythm GallerySinus, atrial and junctional: Sinus bradycardia: under 60/min (here about 42). Symptomatic: atropine 1 mg IV every 3–5 min, max 3 mg.
- Temporary PacingTranscutaneous pacing (TCP): For unstable bradycardia (2025 AHA: usually under 50/min; older ACLS and many exams use 60) with hypotension, altered mentation, shock, ischemic chest pain or acute heart failure, after atropine fails; immediately for high-degree AV block without IV/IO access. Not for VF. Paramedics use TCP; transvenous and epicardial care is ICU and critical care transport.
- ACLS Algorithms in BriefBradycardia with a pulse: Atropine 1 mg IV, repeated every 3–5 min to a 3 mg total
- ACS and STEMI12-lead territories: Inferior MI block: nodal, transient, narrow escape; atropine may help. Anterior MI block: infranodal, wide unstable escape; prepare to pace. New BBB alone: pads on, watch.
- Toxidromes and AntidotesReversal antidotes: Organophosphates: Atropine 1–2 mg IV, doubled every 5 min; pralidoxime 1–2 g IV: Atropine endpoint: clear chest, not pupils
- Spinal Motion RestrictionCord injury: breathing and shock: Paramedic/ED: atropine for symptomatic bradycardia; suctioning can trigger it
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In the algorithms
- New Hypotension
- Bradycardia With a Pulse
- Arrest After Cardiac Surgery
- Pediatric Bradycardia With a Pulse
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Sources
- FDA label: Atropine sulfate injection, Hikma (2023)
- FDA label: AtroPen (2022)
- PubChem: atropine
- Lei 2018, 2025 update (classification)
For education and exam preparation only. Follow your institution’s protocols. Typical adult values for study. Follow your local protocols and medical direction.