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
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
- Myasthenic Crisis and Guillain-Barré SyndromeNIV or intubation: Intubate electively, with a vasopressor and atropine ready
- 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
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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 the order, the label and your institution's protocols.