Is atropine an antiparasympathetic (anticholinergic) agent?

From the Guidelines

Atropine is indeed an antiparasympathetic (anticholinergic) agent, as it blocks the effects of the parasympathetic nervous system by competitively inhibiting acetylcholine at muscarinic receptors. This is evident from its use in clinical settings, such as increasing heart rate during bradycardia, as described in the 2019 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1. The guideline notes that atropine, at dosages of 0.5 to 2 mg, usually enhances automaticity in patients with sinus bradycardia, although it can have variable effects depending on the dose.

Some key points about atropine's anticholinergic properties include:

• It prevents the parasympathetic nervous system from exerting its effects by blocking acetylcholine at muscarinic receptors
• It is used to increase heart rate during bradycardia, with a typical dose range of 0.4-1mg intravenously, as supported by studies such as the one mentioned in the guideline 1
• Its effects last for 4-6 hours, and side effects reflect its anticholinergic properties, including dry mouth, blurred vision, urinary retention, and tachycardia
• Understanding atropine's mechanism as a parasympathetic blocker is essential for appropriate clinical use, as it produces effects opposite to parasympathetic stimulation, which is crucial for managing conditions like bradycardia, as discussed in the guideline 1.

In terms of its clinical application, atropine's anticholinergic properties make it a valuable agent in various medical scenarios, including reducing secretions before surgery, dilating pupils for eye examinations, and as an antidote for certain poisonings like organophosphate exposure. However, its use must be carefully considered, given its potential side effects and the importance of dosing, as highlighted in the guideline 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

Atropine is an antiparasympathetic (anticholinergic) agent because it antagonizes the actions of acetylcholine, a key neurotransmitter in the parasympathetic nervous system. The drug's mechanism of action involves competitive antagonism of muscarinic receptors, which are stimulated by acetylcholine. This leads to parasympathetic inhibition, characterized by effects such as tachycardia and decreased secretions. 2

From the Research

Atropine as an Antiparasympathetic Agent

• Atropine is classified as an anticholinergic agent, which means it acts by blocking the action of the neurotransmitter acetylcholine at muscarinic receptors in the central and peripheral nervous system 3, 4, 5, 6, 7.
• The anticholinergic properties of atropine result in various clinical effects, including increased heart rate, reduced salivation and bronchial secretions, and dilation of the pupils 3, 4, 5.
• Atropine's ability to inhibit the parasympathetic nervous system makes it useful for treating conditions such as bradycardia, organophosphate poisoning, and nerve agent exposure 3, 6.
• The drug's anticholinergic effects can also lead to side effects like dry mouth, constipation, and blurred vision, particularly at high doses or with prolonged use 3, 4, 6.

Mechanism of Action

• Atropine's primary mechanism of action involves competitive inhibition of acetylcholine at muscarinic receptors, which are widely distributed in the body 4, 5, 6.
• The drug has been shown to inhibit cAMP-specific phosphodiesterase type 4, leading to increased cardiac contractility and heart rate 5.
• Atropine's interaction with muscarinic receptors can also result in paradoxical effects, such as accentuating the parasympathetic actions of acetylcholine at low concentrations 7.

Clinical Applications

• Atropine is used in various clinical settings, including ophthalmology, cardiology, and emergency medicine, due to its anticholinergic and antiarrhythmic properties 3, 4, 5.
• The drug is often administered topically or systemically to treat conditions like cycloplegia, mydriasis, and bradycardia, as well as to reduce salivation and bronchial secretions prior to surgery 3, 4.