4.7 Muscarinic Antagonists V2
Atropine is a competitive reversable muscarinic antagonist (anticholinergic) used for anti-vagal or bradycardic conditions. It is also used to treat asthma and gastrointestinal conditions.
Indications for Use
Due to its anticholinergic properties, there is a variety of uses for atropine. Therapeutic uses are dose dependent (Adams et al, 2018; Vallerand & Sanoski, 2025).
- Bradycardia: give 0.5-1.0 mg IV q 3-5 minutes. Do not exceed 3 mg.
- Respiratory – relaxes the bronchi, used for bronchospasm: inhalation – give 0.025- 0.05 mg/kg/dose q 4-6 hours as needed. Maximum 2.5 mg/dose.
- Decrease excess salivation: used pre-anesthesia or palliative clients. Can be given IM, IV.
- Ophthalmic: will dilate pupils for eye examinations. 1% solution
- GI: Decrease secretion of gastric acid in peptic ulcer disease and decrease GI motility with conditions causing severe diarrhea and cramping.
- Organophosphate Poisoning: to treat muscarinic symptoms of insecticide (organophosphorus or carbamate) poisoning or mushroom poisoning.
Mechanism of Action
Atropine is an anticholinergic drug that inhibits parasympathetic impulses, thereby inducing sympathetic stimulation (flight or flight response). It inhibits acetylcholine at the postganglionic sites located in smooth muscle, secretory glands and the CNS. It has a direct vagolytic action, allowing the preexisting sympathetic stimulation to predominate, resulting in increased heart rate, relaxation of the bronchi, drying of secretions and dilated pupils.
Vagolytic effect: For cardiac life support with bradycardic conditions usually related to sinus or AV nodal conduction issues, 0.4 mg/kg.
Nursing Considerations
Administration: Atropine can be administered by intravenous (IV), subcutaneous, intramuscular, or endotracheal (ET) methods; IV is preferred.
- IV administration: IV push or infusion. Assess vital signs and ECG frequently during IV administration. Report any paradoxical bradycardia, ventricular ectopy or hypotension.
- Endotracheal administration: Dilute 1 to 2 mg in 10 mL of sterile water or normal saline before administration.
- Once administered, it easily absorbed and widely distributed. Half life is 4-5 hours.
Heat stroke may occur in the presence of high temperatures.
Immediately report symptoms of overdose: urine retention, abnormal heart rhythm, dizziness, loss of consciousness, difficulty breathing, weakness, or tremors.
Antidote: Physostigmine has been used to reverse anticholinergic effects.
Pediatrics: Atropine can be given to pediatric clients, with doses adjusted according to the child weight.
Older adult: As with all anticholinergics, use with caution with the elderly, because elderly clients may react with agitation or drowsiness.
Drug interactions:
- Atropine will increase the effects of antihistamines, tricyclic antidepressants, procainamide.
- Atropine will decrease the effects of levodopa- carbidopa.
(Adams et al, 2018, Patel, McLendon, Preuss, 2025; Vallerand & Sanoski, 2024)
Adverse/side effects
Anticipate the following common side effects: Dry mouth, dry eyes, blurred vision, constipation, urinary retention and increased heart rate.
Contraindicated with glaucoma.
May cause urinary retention so caution with benign prostrate hypertrophy
Client Teaching
- Advise clients that use of these medications may cause dizziness and drowsiness, so clients should be aware of potential impact on their level of alertness.
- Inform client of side effects.
- For dry mouth, oral hygiene is important.
- Constipation: Increase fluids and fiber in the diet.
- Inform client to not take any herbal supplements without discussing first with the prescriber.
(Adams et al, 2018, Patel, McLendon, Preuss, 2025; Vallerand & Sanoski, 2024)
Example in Practice
A client with irritable bowel disease is experiencing considerable abdominal cramping and diarrhea. There is a concern with fluid and electrolyte losses and the considerable discomfort that the client is experiencing. The client is ordered Diphenoxylate with atropine po (trade name: Lomotil). Diphenoxylate (centrally acting opioid) with the anticholinergic effects of atropine will slow the gastrointestinal motility. The subtherapeutic amounts of atropine is included in the dosage form to discourage diphenoxylate abuse.
Critical Thinking Out Loud
A 48-year-old male goes to the emergency department with issues of dizziness and fatigue for the last two days. The client appears pale. Vital signs are HR 42 bpm BP 105/62 T 36.7 C RR 20 breaths/min with oxygen sats of 97%. No shortness of breath noted.
A 12 lead ECG is ordered and shows sinus bradycardia with HR 40 bpm, regular. No ectopy. Assess for other causes of bradycardia
Atropine is ordered as the heart rate is less than 60 bpm and the client is symptomatic. Order reads: atropine 0.5 mg IV q 3-5 minutes to a maximum of 3 mg.
Atropine is ordered as it will block the parasympathetic actions of acetylcholine, resulting in an increased heart rate.
Prior to first dose: HR, BP, RR, oxygen sats, and T. Assess client for poor perfusion such as pallor, fatigue, dizziness and altered mental status such as confusion.
Give atropine 0.5 mg IV over one minute.
After first dose and subsequent doses, monitor:
- Vital signs
- Anti-cholinergic effects can cause tachycardia, fluctuations in BP.
- Continuous telemetry monitored to observe for any changes.
- Assess for signs of adverse anti-cholinergic effects:
- Flushing, hot skin
- Neuro status: anxiety, delirium, hyperactivity
- Urinary retention
- Constipation
- Blurred vision, dry eyes, light sensitivity, pupil dilation
The goal is to increase the heart rate to over 60 bpm or whatever the HR the physician has ordered. Anticipate adverse effects and treat accordingly. Anticipate diagnostic tests to determine underlying cause of bradycardia.
Note: Answers to the Clinical Reasoning and Critical Thinking activities can be found in the “Answer Key” sections at the end of the book.
Atropine Medication Card
Now let’s take a closer look at the medication card on atropine in Table 4.8 (Vallerand & Sanoski, 2025; UptoDate, 2025). Because information about medication is constantly changing, nurses should always consult evidence-based resources to review current recommendations before administering specific medication.
Downloadable file (.docx): Atropine Medication Card
Interactive Activity
References:
Adams, M., Urban, C., El-Hussein, M., Osuji, J. & King, S. (2018). Pharmacology for Nurses. A pathophysiological approach (2nd Canadian ed.). Pearson Canada Inc: Ontario.
Patel, P., McLendon, K., & Preuss, C. (2025). Atropine. National Library of Medicine. https://www.ncbi.nlm.nih.gov/books/NBK470551/
UpToDate (2021). Atropine. https://www.uptodate.com/contents/search ↵
Vallerand, A. & Sanoski, C. (2024). Davis’s Canadian drug guide for nurses (19th ed.). F.A. Davis Company: Canada
