Muscarinic antagonists

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Muscarinic antagonists


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USMLE® Step 2 questions

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Muscarinic antagonists

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USMLE® Step 2 style questions USMLE

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A 65-year-old man comes to the emergency department during the winter due to shortness of breath and a productive cough. The symptoms have progressively worsened over the past two years, and the patient has had to limit his daily activities to avoid becoming short of breath. Each morning, he coughs up large quantities of viscous sputum. Past medical history is significant for hypertension and type II diabetes mellitus. Current medications include lisinopril and metformin. Temperature is 36.4°C (97.6°F), pulse is 120/min, respirations are 24/min, and blood pressure is 147/98 mmHg. Oxygen saturation is 93% on room air. Physical examination reveals a markedly increased anteroposterior chest diameter. Cardiopulmonary examination reveals tachycardia and poor air movement bilaterally with scattered expiratory wheezes. A chest radiograph is obtained and shown below. Which of the following medications is most appropriate for managing this patient’s symptoms?  

Image reproduced from Radiopedia

External References

First Aid








Adverse effects/events

atropine p. 242

Atropine p. 242

antimuscarinic reaction p. 252

for β -blocker overdose p. 329

cholinesterase inhibitor poisoning p. 241

toxicity treatment p. 249


atropine for p. 242


atropine p. 242

Geriatric patients

atropine in p. 242

Glaucoma p. 555

atropine p. 242


atropine as cause p. 242

Urinary retention

atropine p. 242


Muscarinic antagonists, or antimuscarinic medications, are a class of medications that prevent muscarinic receptors of the parasympathetic nervous system from getting stimulated by acetylcholine.

Okay, first things first, the nervous system is divided into the central nervous system, so the brain and spinal cord; and the peripheral nervous system.

The peripheral nervous system can be divided into the somatic nervous system, which controls voluntary movement of our skeletal muscles; and the autonomic nervous system, which is further divided into the sympathetic and parasympathetic nervous systems, and controls the involuntary movement of the smooth muscles, and the glands of our organs.

Now, the autonomic nervous system is made up of a relay that includes two neurons.

We’ll focus on just the parasympathetic nervous system.

Signals for the parasympathetic nervous system start in the hypothalamus.

These hypothalamic neurons synapse with nuclei in the brainstem or spinal cord, which send out signals to preganglionic neurons that travel to the rest of the body.

Their targets are the parasympathetic ganglion, which consist of many postganglionic neuron cell bodies and are located nearby or directly in the target organs.

The postganglionic neurons extend the rest of the way to the target cell, where they release the neurotransmitter acetylcholine, which is why they are also called cholinergic neurons.


Muscarinic antagonists, also known as antimuscarinic medications, are a class of drugs that block the activation of muscarinic receptors of the parasympathetic nervous system. Examples of muscarinic antagonists include atropine, scopolamine, and ipratropium. These drugs are used to treat a variety of conditions, such as asthma, glaucoma, and urinary incontinence. They can also be used to treat the symptoms of poisoning from organophosphate insecticides.


  1. "Katzung & Trevor's Pharmacology Examination and Board Review,12th Edition" McGraw-Hill Education / Medical (2018)
  2. "Rang and Dale's Pharmacology" Elsevier (2019)
  3. "Goodman and Gilman's The Pharmacological Basis of Therapeutics, 13th Edition" McGraw-Hill Education / Medical (2017)
  4. "Muscarinic receptor subtypes in airways" Life Sci (1993)
  5. "Pharmacologic therapy of obstructive airway disease" Clin Chest Med (1990)
  6. "[Atropine. Principles and rules of utilization]" Rev Prat (2001)
  7. "Antimuscarinic drugs" Prof Nurse (2004)

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