From the Guidelines
Atropine is a potent anticholinergic medication that blocks the action of acetylcholine at muscarinic receptors throughout the body, resulting in increased heart rate, decreased secretions, bronchodilation, pupillary dilation, and decreased gastrointestinal motility. The anticholinergic effects of atropine are well-documented, and it is commonly used in various clinical settings, including bradycardia, as a premedication for intubation, for organophosphate poisoning, and in ophthalmology as eye drops for pupillary dilation. According to the most recent and highest quality study 1, atropine remains the first-line drug for acute symptomatic bradycardia, with a recommended dose of 0.5 mg IV every 3 to 5 minutes to a maximum total dose of 3 mg.
Key Points
- Atropine works by preventing acetylcholine from binding to muscarinic receptors, resulting in increased heart rate and other anticholinergic effects.
- The typical dose of atropine for bradycardia is 0.5-1mg IV, repeated every 3-5 minutes as needed up to 3mg total.
- Atropine is also used as a premedication for intubation, for organophosphate poisoning, and in ophthalmology as eye drops for pupillary dilation.
- Side effects of atropine include dry mouth, blurred vision, urinary retention, tachycardia, confusion, and hyperthermia, particularly in elderly patients.
- Contraindications include narrow-angle glaucoma, myasthenia gravis, GI obstruction, and severe ulcerative colitis.
Clinical Considerations
- When administering atropine, monitor vital signs closely, especially heart rate and blood pressure, and be prepared to manage anticholinergic side effects if they occur.
- Use atropine cautiously in the presence of acute coronary ischemia or MI, as increased heart rate may worsen ischemia or increase infarction size, as noted in 2.
- Atropine administration should not delay implementation of external pacing for patients with poor perfusion, as recommended in 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 The receptors antagonized by atropine are the peripheral structures that are stimulated or inhibited by muscarine (i.e., exocrine glands and smooth and cardiac muscle).
The anticholinergic effects of Atropine include:
- Inhibition of muscarinic actions of acetylcholine on smooth muscles and exocrine glands
- Antagonism of peripheral structures stimulated or inhibited by muscarine, including:
- Exocrine glands
- Smooth muscle
- Cardiac muscle Atropine's anticholinergic effects can lead to various clinical effects, such as:
- Tachycardia due to paralysis of vagal control
- Bronchiolar dilatation
- Increased respiratory rate
- Decreased secretions from exocrine glands
- Potential for postural hypotension and changes in blood pressure 3
From the Research
Anticholinergic Effects of Atropine
The anticholinergic effects of atropine are well-documented in various studies 4, 5, 6, 7, 8. These effects can be categorized into two types: toxic and allergic reactions.
Toxic Reactions
Toxic reactions to atropine are the most common form and result from the anti-muscarinic effects of the drug 4. These reactions may appear at the usual therapeutic doses and are probably related to interpersonal variation in sensitivity to atropine. Common toxic effects of atropine include:
- Delirium
- Hallucinations
- Need for patient restraint
- Central toxicity, which may complicate the management of organophosphate poisoning 5
Allergic Reactions
Allergic reactions to atropine are less common and include local manifestations, usually after the administration of eyedrops, and systemic reactions in the form of anaphylaxis 4. However, severe allergic reactions to atropine are rare, as evidenced by the small number of case reports in the literature despite the drug's extensive use.
Management of Anticholinergic Effects
To minimize the anticholinergic effects of atropine, alternative anti-muscarinic drugs such as glycopyrrolate and scopolamine can be used 4, 5. A combination of atropine and glycopyrrolate has been shown to reduce mortality in organophosphate poisoning 5. Additionally, titrating atropine doses against response and toxicity can help reduce the risk of anticholinergic effects 6.
Factors Associated with Outcomes
Several factors can affect the outcomes of patients treated with atropine for organophosphate and carbamate poisoning, including: