From the Guidelines
Atropine is a competitive antagonist of muscarinic acetylcholine receptors that blocks the parasympathetic nervous system's effects, particularly on the heart, and is primarily used to treat symptomatic bradycardia with a standard dosing of 0.5 mg IV push, which can be repeated every 3-5 minutes up to a total dose of 3 mg, as recommended by the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1.
Mechanism of Action
Atropine works by preventing acetylcholine from binding to muscarinic acetylcholine receptors, which inhibits parasympathetic stimulation and allows sympathetic influence to predominate. This results in an increase in heart rate by blocking vagal influence on the sinoatrial node.
Clinical Uses
In clinical settings, atropine is used to treat:
- Symptomatic bradycardia (heart rate below 50 beats per minute with signs of hemodynamic compromise)
- As a premedication before surgery to reduce secretions
- As an antidote for organophosphate poisoning (requiring much higher doses)
- For certain types of eye examinations to dilate the pupil
- To treat some types of poisoning from cholinergic agents
Dosage and Administration
The standard dosing for bradycardia is 0.5 mg IV push, which can be repeated every 3-5 minutes up to a total dose of 3 mg, as recommended by the 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care 1.
Side Effects and Precautions
Side effects of atropine include dry mouth, blurred vision, urinary retention, tachycardia, and confusion, especially in elderly patients. Atropine should be used cautiously in patients with glaucoma, prostatic hypertrophy, or thyrotoxicosis, and its effectiveness may be limited in heart transplant patients or in complete heart block at the AV node level.
Key Considerations
Atropine appears to be safe in those patients with atrioventricular nodal block in the absence of infranodal conduction system disease, but its use in patients with infranodal conduction disease or block can be associated with exacerbation of block and is potentially harmful, as noted in the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1.
From the FDA Drug Label
Atropine is an antimuscarinic agent since it antagonizes the muscarine-like actions of acetylcholine and other choline esters. Atropine inhibits the muscarinic actions of acetylcholine on structures innervated by postganglionic cholinergic nerves, and on smooth muscles which respond to endogenous acetylcholine but are not so innervated Atropine-induced parasympathetic inhibition may be preceded by a transient phase of stimulation, especially on the heart where small doses first slow the rate before characteristic tachycardia develops due to paralysis of vagal control Adequate doses of atropine abolish various types of reflex vagal cardiac slowing or asystole The drug also prevents or abolishes bradycardia or asystole produced by injection of choline esters, anticholinesterase agents or other parasympathomimetic drugs, and cardiac arrest produced by stimulation of the vagus.
Atropine Mechanism and Uses: Atropine works by antagonizing the actions of acetylcholine, a neurotransmitter that stimulates muscarinic receptors in the body. This results in parasympathetic inhibition, which can lead to increased heart rate, bronchiolar dilatation, and other effects.
- Key Uses:
- Treating bradycardia (slow heart rate) by increasing heart rate and preventing vagal cardiac slowing or asystole
- Temporary blockade of severe or life-threatening muscarinic effects
- Antisialagogue (reducing saliva production)
- Antivagal agent
- Antidote for organophosphorus or muscarinic mushroom poisoning
- Treating bradyasystolic cardiac arrest 2, 2
From the Research
Atropine Mechanism
- Atropine is a muscarinic subtype non-specific antagonist that competitively inhibits acetylcholine (ACh) at postganglionic muscarinic sites 3.
- It is used to treat organophosphate (OP) poisoning and resulting seizures by inhibiting ACh at the muscarinic cholinergic receptors 3.
- Atropine produces several unwanted side-effects, including dilated pupils, blurred vision, light sensitivity, and dry mouth 3.
Clinical Uses
- Atropine is used to treat bradycardia, a condition characterized by a slow heart rate 4.
- It can also be used to prevent seizures and treat other conditions, such as organophosphate poisoning 3.
- In clinical settings, atropine can be administered in various doses, ranging from 0.0036 to 0.060 mg/kg 4.
Pharmacological Effects
- Atropine can inhibit ion currents mediated by neuronal nicotinic acetylcholine receptors 5.
- It can also potentiate or inhibit alpha4beta4 nicotinic receptor-mediated ion current, depending on the concentration of acetylcholine and atropine 5.
- Atropine can increase serotonin levels in discrete brain regions, such as the nucleus raphe dorsalis, but does not affect dopamine levels 6.