If you’ve ever participated in a patient code, you’re probably familiar with the drug atropine. Have you ever wondered how atropine works? Derived from the plant Atropa belladonna, atropine is an anticholinergic drug – a competitive, reversible antagonist of muscarinic receptors (McLendon & Preuss, 2021). For this blog, we’ll focus on atropine sulfate, the systemic formulation which has anti-salivation, anti-muscarinic effects, and is the first-line therapy to treat symptomatic bradycardia. Do not confuse it with Isopto atropine, which is an ophthalmic formulation used to dilate the pupils and temporarily paralyze the eye muscle. Here’s what you need to know about atropine sulfate.
How does it work?
Atropine sulfate blocks the action of acetylcholine at parasympathetic sites in smooth muscle, secretory glands, and the central nervous system causing an increase in cardiac output and reduced secretions (UpToDate, 2022). It also reverses the muscarinic effects of cholinergic poisoning by acting as a competitive antagonist of acetylcholine at muscarinic receptors. To understand how atropine affects the heart, first consider how the heart’s electrical conduction system functions.
Without Atropine
When the neurotransmitter acetylcholine is released, the vagus nerve stimulates the sinoatrial (SA) node (the heart’s pacemaker) and the atrioventricular (AV) node, which controls conduction between the atria and the ventricles of the heart. This inhibits electrical conduction and causes the heart rate to slow down.
With Atropine
Atropine competes with acetylcholine for cholinergic receptor sites on the SA and AV nodes. By blocking acetylcholine, atropine speeds up the heart rate. At specific doses, it prohibits vagal cardiac slowing or asystole. However, a large dose may occasionally cause atrioventricular (A-V) block.
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How is atropine delivered? (McLendon & Preuss, 2021)
Atropine may be administered subcutaneously, intramuscularly (IM), intravenously (IV) or by endotracheal tube (ET). Intravenous is the preferred method. For ET administration, dilute 1 mg to 2 mg in 10 mL of sterile water or normal saline.
Approved Indications
- Bradycardia during neuromuscular blockade reversal
- Sinus bradycardia, symptomatic
- Preoperative/preanesthetic medication to inhibit salivation and secretion
- Treatment of symptoms from muscarine-containing mushroom poisoning
- Antidote for anticholinesterase poisoning (carbamate insecticides, nerve agents, organophosphate insecticides)
For dosing, see our
Atropine Sulfate Nursing Pocket Card.
Side Effects
Common side effects of atropine include dry mouth, blurred vision, photophobia, tachycardia, flushed skin, constipation, difficulty with urination, inability to perspire appropriately, delirium or coma (McLendon & Preuss, 2021).
Contraindications
Atropine is contraindicated in patients with known hypersensitivity, suspected glaucoma, pyloric stenosis, or prostatic hypertrophy (Pfizer, 2021).
References
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