A patient, Dr. Young, has both asthma and high blood pressure. Her physician prescribed the drug propranolol to treat her hypertension; this drug blocks all types of β-adrenergic receptors. She also takes the drug albuterol for asthma, which activates β₂ receptors on bronchial smooth muscle. Will the pairing of these two drugs cause problems for Dr. Young? Explain.

Verified step by step guidance

1. Step 1: Understand the role of β-adrenergic receptors in the body. β1 receptors are primarily found in the heart and are involved in increasing heart rate and contractility, while β2 receptors are found in bronchial smooth muscle and are responsible for bronchodilation (relaxation of airway muscles).
2. Step 2: Analyze the mechanism of propranolol. Propranolol is a non-selective β-blocker, meaning it blocks both β1 and β2 adrenergic receptors. Blocking β1 receptors helps lower blood pressure by reducing heart rate and cardiac output, but blocking β2 receptors can interfere with bronchodilation, potentially causing bronchoconstriction.
3. Step 3: Examine the mechanism of albuterol. Albuterol is a β2 receptor agonist, meaning it activates β2 receptors on bronchial smooth muscle to promote bronchodilation, which is beneficial for asthma patients as it helps open up the airways.
4. Step 4: Consider the interaction between propranolol and albuterol. Since propranolol blocks β2 receptors, it can counteract the effects of albuterol, reducing its ability to promote bronchodilation. This could exacerbate asthma symptoms and lead to breathing difficulties for Dr. Young.
5. Step 5: Conclude that the pairing of these two drugs may cause problems for Dr. Young. The physician should consider prescribing a cardioselective β-blocker (e.g., atenolol or metoprolol) that primarily blocks β1 receptors and has minimal effect on β2 receptors, to avoid interfering with albuterol's action on bronchial smooth muscle.

Key Concepts

β-adrenergic receptors

β-adrenergic receptors are a class of G protein-coupled receptors that are activated by catecholamines like adrenaline. They are divided into three subtypes: β1, β2, and β3, each with different physiological roles. β1 receptors primarily affect the heart, increasing heart rate and contractility, while β2 receptors are mainly found in the lungs and cause bronchodilation. Understanding these receptors is crucial for evaluating the effects of drugs like propranolol and albuterol.

Propranolol

Propranolol is a non-selective β-adrenergic antagonist (beta-blocker) used primarily to manage hypertension and other cardiovascular conditions. By blocking β1 and β2 receptors, it reduces heart rate and myocardial contractility, but it can also lead to bronchoconstriction due to the inhibition of β2 receptors in the lungs. This dual action is significant in patients with respiratory conditions like asthma, as it may exacerbate their symptoms.

Albuterol

Albuterol is a selective β2-adrenergic agonist commonly used as a bronchodilator in the treatment of asthma. It works by stimulating β2 receptors in the bronchial smooth muscle, leading to relaxation and dilation of the airways, which helps alleviate asthma symptoms. The interaction between albuterol and propranolol is critical to consider, as propranolol's non-selective blockade can counteract the bronchodilatory effects of albuterol, potentially leading to respiratory complications.