Bronchodilators: Beta 2-agonists and muscarinic antagonists

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Bronchodilators: Beta 2-agonists and muscarinic antagonists

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USMLE® Step 2 style questions USMLE

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A 50-year-old man is brought to the emergency department by his son after he was found confused on the floor of his apartment. The patient is lethargic but responsive and reports nausea, vomiting, and generalized weakness. Past medical history is significant for hypertension, diabetes mellitus type 2, and chronic kidney disease. Temperature is 36.7°C (98°F), pulse is 88/min, respirations are 19/min, and blood pressure is 140/75 mmHg. Laboratory results and ECG are shown below. The patient is immediately started on intravenous calcium gluconate. Administration of which of the following additional agents is indicated in this patient?  

Laboratory value  
Result
Serum chemistry  

Sodium
142 mEq/L
Potassium
7.5 mEq/L  
Chloride
95 mEq/L  
Creatinine
4.5 mg/dL  
BUN
49


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2024

2023

2022

2021

Albuterol p. 241

asthma p. 706

Asthma p. 692

albuterol for p. 241

Chronic obstructive pulmonary disease (COPD)

albuterol for p. 241

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In obstructive lung diseases like asthma, where individuals suffer from reversible narrowing of the airways, medications like bronchodilators are helpful in keeping the airways open.

Now, based on their mechanism of action, bronchodilators can be broadly divided into four main groups; β2-agonists, muscarinic antagonists, leukotrienes antagonist and methylxanthines.

In this video, we will focus on the bronchodilators like β2-agonist and muscarinic antagonist which mimics or inhibits the regulatory effects of the autonomic nervous system on bronchial smooth muscle.

So, if we take a look at the lungs, you’ve got the trachea, which branches off into right and left bronchi, and then continues to branch into thousands of bronchioles.

In the bronchioles you’ve got the lumen, the mucosa, which includes the inner lining of epithelial cells, as well as the lamina propria which contains many cells like the type 2 helper cells, B cells, and mast cells.

Surrounding the lamina propria, there is a layer of smooth muscles and submucosa. These muscles are innervated by the nerves of the autonomic nervous system, which means they can’t be controlled consciously.

The autonomic nervous system is made up the sympathetic system which is involved in the “fight or flight” response, like running from angry raccoons, and parasympathetic system which is involved in the “rest and digest” response, like taking a nap after a big dinner.

So let’s say that racoons are chasing you, the sympathetic nerves activates and release norepinephrine which bind to β2 adrenergic receptors on the smooth muscles in the respiratory tract, causing them to relax. The diameter of the airways increase and more oxygen gets to the lungs.

Sources

  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. "Regulation of airway inflammation and remodeling by muscarinic receptors: Perspectives on anticholinergic therapy in asthma and COPD" Life Sciences (2012)
  5. "Comparative efficacy of fixed-dose combinations of long-acting muscarinic antagonists and long-acting β2-agonists: a systematic review and network meta-analysis" Therapeutic Advances in Respiratory Disease (2016)
  6. "The Role of Bronchodilators in Preventing Exacerbations of Chronic Obstructive Pulmonary Disease" Tuberculosis and Respiratory Diseases (2016)
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