Antimuscarinic (Anticholinergic) Agent
Atropine Sulfate
Brand names: Minims Atropine (eye drops), atropine injection — generic
Adult dose
Dose: Bradycardia (cardiac): 300–600 mcg IV bolus; repeat every 3–5 min; max 3 mg. Cycloplegia/mydriasis (eye drops): 1% 1 drop once. Organophosphate poisoning: 2 mg IV, repeated every 5–10 min until secretions dry. Premedication: 300–600 mcg IM
Route: Intravenous (cardiac/poisoning); intramuscular (premedication); topical (eye drops)
Frequency: As needed (acute); see ophthalmic schedule
Clinical pearls
- First-line pharmacological treatment for symptomatic bradycardia (ALS/ACLS algorithm) — before pacing
- Paradoxical bradycardia at subtherapeutic IV doses (<0.5 mg) — always give at least 300 mcg IV for cardiac use
- For organophosphate/carbamate poisoning: large doses may be needed until secretions (SLUDGE/DUMBELS) are controlled — titrate to dry secretions, not heart rate
- Ophthalmic atropine: longer-acting than shorter mydriatics; used for cycloplegic refraction, uveitis, amblyopia management
- Myopia control: low-dose atropine eye drops (0.01%) used in paediatric myopia progression (specialist use)
- Resuscitation: atropine 3 mg IV now only indicated for asystole in ALS guidelines (UK Resuscitation Council 2021)
Contraindications
- Acute angle-closure glaucoma (mydriasis risk — eye drops, systemic)
- Paralytic ileus
- Pyloric stenosis
- Myasthenia gravis (antimuscarinic worsens)
- Bladder outflow obstruction
Side effects
- Dry mouth (very common)
- Urinary retention (especially in BPH)
- Tachycardia
- Blurred vision and photophobia (mydriasis)
- Constipation
- Confusion, agitation (especially in elderly — anticholinergic syndrome)
- Paradoxical bradycardia at very low doses (0.5 mg)
Interactions
- Other antimuscarinics — additive anticholinergic effects
- Antihistamines (H1 blockers), tricyclic antidepressants, antipsychotics — additive antimuscarinic burden
- Anticholinesterases (neostigmine) — atropine used to prevent muscarinic effects of neostigmine
Monitoring
- Heart rate and rhythm (ECG) when used for cardiac indications
- Urinary output (retention risk in elderly men)
- Anticholinergic burden score in elderly patients on multiple medications
Reference: BNF; UK Resuscitation Council Advanced Life Support Guidelines (2021); TOXBASE/National Poisons Information Service (organophosphate poisoning); RCOphth ophthalmic formulary; https://bnf.nice.org.uk/drugs/atropine-sulfate/. Verify against your local formulary and the latest BNF before prescribing.
Related
Curated clinical cross-links plus same-class fallbacks.