atropine

antimuscarinic· Brands: Atropine Sulfate, Atropine, AtroPen, Isopto AtropineIMIVNEBPOSCTOP

Mechanism of action

Atropine competitively blocks muscarinic acetylcholine receptors, preventing the actions of acetylcholine at parasympathetic postganglionic effectors. This results in increased heart rate, reduced secretions, bronchodilation, and decreased gastrointestinal motility. It also acts centrally at higher doses.

Pharmacokinetics

Atropine is rapidly absorbed from the gastrointestinal tract and is well distributed. It undergoes hepatic metabolism via hydrolysis and oxidation. Excretion is primarily renal, with a small amount in the faeces. The half-life is approximately 2 to 3 hours, and effects last about 4 to 6 hours. It crosses the placenta and blood-brain barrier.

Indications & dosing

Symptomatic bradycardia (e.g., acute myocardial infarction, perioperative)

Repeat until adequate heart rate; total max 3 mg.

adult · IV: 0.5–1 mg every 3-5 min PRN · Repeat until adequate heart rate; total max 3 mg.

Organophosphate or carbamate insecticide poisoning

Titrate to atropinization; doses may exceed standard.

adult · IV: 2 mg every 5-10 min · Titrate to atropinization; doses may exceed standard.

Preoperative reduction of secretions (e.g., salivation, bronchial secretions)

Given 30-60 min preoperatively.

adult · IM: 0.3–0.6 mg single dose · Given 30-60 min preoperatively.

Symptomatic bradycardia in children

Minimum single dose 0.1 mg; maximum single dose 0.5 mg (1 mg in adolescents).

pediatric · IV: 0.02 mg/kg every 5 min · Minimum single dose 0.1 mg; maximum single dose 0.5 mg (1 mg in adolescents).

Uveitis and cycloplegic refraction (ophthalmic)

Use atropine sulfate 1% eye drops.

adult · TOP: 1–2 drops twice daily · Use atropine sulfate 1% eye drops.

Contraindications & precautions

Angle-closure glaucoma · Atropine can precipitate acute glaucoma by increasing intraocular pressure.
Paralytic ileus · Atropine reduces gastrointestinal motility and may worsen obstruction.
Prostatic hyperplasia with urinary retention · May cause or worsen urinary retention due to increased bladder sphincter tone.
Tachyarrhythmias · Atropine may increase heart rate and worsen existing arrhythmias.
Use with caution in the elderly due to increased risk of confusion, constipation, and urinary retention.
Use with caution in patients with cardiovascular disease, especially coronary artery disease, as tachycardia may increase myocardial oxygen demand.
Avoid in hot environments or during strenuous exercise because reduced sweating can precipitate heat stroke.
Use with caution in children, who are more susceptible to atropine toxicity including excitement and hallucinations.
Use with caution in pregnancy and during lactation; atropine crosses the placenta and appears in breast milk.
Use with caution in severe hepatic impairment as atropine is metabolised in the liver.

Adverse effects

Dry mouth
Blurred vision
Tachycardiaserious
Constipation
Urinary retentionserious
Confusion and agitation in the elderlyserious

Renal & hepatic adjustment

eGFR 0–30: Use with caution; consider dose reduction due to reduced clearance.
Hepatic impairment (severe): Use with caution; consider dose reduction due to reduced metabolism.

Monitoring, pregnancy & toxicity

Heart rate · After administration
Blood pressure · After administration
ECG · Baseline and during therapy
Signs of anticholinergic toxicity (dry mouth, blurred vision, urinary retention, confusion) · Regularly during therapy
Pregnancy: Atropine should be used during pregnancy only if clearly needed, as it crosses the placenta and may cause fetal tachycardia and anticholinergic effects. Consider alternative antimuscarinics if available.
Toxicity: Anticholinergic syndrome: dry mouth, dilated pupils, blurred vision, tachycardia, urinary retention, confusion, hallucinations, seizures, hyperthermia. · Supportive care: airway management, cooling, cardiovascular support. In severe cases, physostigmine may be used cautiously under specialist supervision.
Toxicity: CNS excitation: agitation, delirium, seizures. · Benzodiazepines for agitation or seizures. Avoid phenothiazines.
Toxicity: Hyperthermia from impaired sweating. · Active cooling; avoid anticholinergic drugs.

Clinical notes

Atropine is used for symptomatic bradycardia, cardiac arrest, organophosphate and nerve agent poisoning, and to reduce secretions before surgery. It may be given before anticholinesterases to prevent bradycardia. Adverse effects include dry mouth, blurred vision, urinary retention, and confusion, especially in the elderly. Dose titration is important; in children, the dose for bradycardia is higher per kg than in adults. Local protocols and guidelines may vary; always refer to up-to-date formularies.

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BNF; local formulary