Pharmacology Lecture 6: Adrenergic Agonists

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Questions and Answers

What is the primary off-label use of terbutaline?

To treat chronic obstructive pulmonary disease

For hypertension control

To manage acute asthma attacks

As a uterine relaxant to suppress premature labor (correct)

Which side effect is commonly associated with β agonist agents such as terbutaline?

Hypotension

Respiratory depression

Nausea

Tremor (correct)

What is a significant risk when using monoamine oxidase inhibitors (MAOIs) with β agonists?

Adverse cardiovascular effects (correct)

Increased insulin resistance

Severe muscle pain

Respiratory failure

How long does a single dose of salmeterol or formoterol provide bronchodilation?

12 hours Signup and view all the answers

Why should mirabegron be used cautiously in certain patients?

It may increase blood pressure Signup and view all the answers

Which characteristic is NOT associated with catecholamines?

Long half-lives due to resistance to COMT Signup and view all the answers

What characterizes the pharmacokinetics of non-catecholamines like phenylephrine and ephedrine?

They have increased lipid solubility. Signup and view all the answers

What structural feature greatly affects the potency of adrenergic drugs?

The number and location of OH substitutions on the benzene ring Signup and view all the answers

Which of the following agents is classified as a direct-acting agonist?

Ephedrine Signup and view all the answers

Why do catecholamines have a brief period of action when administered parenterally?

They are rapidly metabolized by COMT and MAO Signup and view all the answers

Which mechanism characterizes indirect-acting adrenergic agonists?

They block norepinephrine reuptake. Signup and view all the answers

Which of the following is a characteristic of non-catecholamines?

They have longer half-lives due to resistance to COMT Signup and view all the answers

What common side effects are attributable to catecholamine action on the CNS?

Anxiety, tremor, and headaches Signup and view all the answers

Which of the following is a characteristic of mixed-action agonists?

They stimulate receptors and release norepinephrine. Signup and view all the answers

How does the structure of adrenergic drugs impact their ability to differentiate between α and β receptors?

By the nature of substituents on the amino nitrogen Signup and view all the answers

Which of the following statements is true about the metabolic pathway of adrenergic agonists?

Some non-catecholamines have prolonged action due to poor MAO substrate characteristics. Signup and view all the answers

Which agent is specifically mentioned as causing the release of norepinephrine?

Amphetamine Signup and view all the answers

Which of the following statements about catecholamines is true?

They are primarily used in emergency medical situations Signup and view all the answers

Which option includes both types of adrenergic agonists?

Ephedrine and amphetamine Signup and view all the answers

Which combination of features contributes to the effectiveness of adrenergic agonists?

High potency and rapid inactivation Signup and view all the answers

Which is a common feature of adrenergic agonists with greater lipid solubility?

They have increased access to the central nervous system. Signup and view all the answers

What effect does norepinephrine have on blood vessels compared to epinephrine?

Norepinephrine causes greater vasoconstriction than epinephrine. Signup and view all the answers

Which therapeutic use is primarily associated with norepinephrine?

Increasing vascular resistance in shock Signup and view all the answers

What physiological response is triggered by increased vagal activity due to norepinephrine?

Bradycardia Signup and view all the answers

How does atropine influence the effects of norepinephrine on the heart?

It allows for stimulation of the heart by norepinephrine, resulting in tachycardia. Signup and view all the answers

Isoproterenol is known for its action on which receptors?

Both β1 and β2 receptors Signup and view all the answers

Which of the following best describes the action of isoproterenol?

It significantly stimulates heart rate, contractility, and cardiac output. Signup and view all the answers

What drawback is associated with isoproterenol's non-selectivity?

Increased risk of serious side effects. Signup and view all the answers

What physiological change occurs when norepinephrine increases blood pressure?

Stimulation of baroreceptors. Signup and view all the answers

What can happen if a patient taking MAOIs consumes substances that are ordinarily oxidized by MAO?

It can precipitate serious vasopressor episodes. Signup and view all the answers

How does cocaine affect norepinephrine levels in the synaptic space?

It blocks the uptake of norepinephrine, causing accumulation. Signup and view all the answers

Which of the following is NOT a characteristic of ephedrine and pseudoephedrine?

They have a short duration of action. Signup and view all the answers

What effect does ephedrine have on blood pressure?

It raises systolic and diastolic blood pressures. Signup and view all the answers

What distinguishes cocaine from other local anesthetics?

It blocks the norepinephrine transporter. Signup and view all the answers

In comparison to epinephrine, how does the potency of ephedrine in producing bronchodilation measure up?

It is less potent and slower acting than epinephrine. Signup and view all the answers

Which characteristic applies to both ephedrine and pseudoephedrine?

They have excellent oral absorption. Signup and view all the answers

What is the typical primary action of mixed-action adrenergic agents like ephedrine?

Release stored norepinephrine and stimulate both α and β receptors. Signup and view all the answers

Study Notes

Characteristics of Adrenergic Agonists

Adrenergic drugs primarily derive from β-phenylethylamine, varying based on side chain and benzene ring modifications.
Key features affecting receptor interaction: number/position of OH substitutions on the benzene ring and nature of amino nitrogen substituents.

Catecholamines

Include epinephrine, norepinephrine, isoproterenol, and dopamine.
High potency due to presence of -OH groups at positions 3 and 4 on the benzene ring.
Metabolized quickly by Catechol-O-methyltransferase (COMT) and Monoamine oxidase (MAO), resulting in brief action when given parenterally and ineffectiveness when administered orally.
Polar nature results in poor central nervous system (CNS) penetration but can cause CNS-related side effects (e.g., anxiety, tremors).

Non-Catecholamines

Lack catechol hydroxyl groups, leading to longer half-lives due to less susceptibility to COMT inactivation.
Examples include phenylephrine, ephedrine, and amphetamine.
Increased lipid solubility enhances CNS access and prolongs duration of action.

Mechanism of Action

Direct-acting agonists: Stimulate α or β receptors directly; examples include epinephrine and norepinephrine.
Indirect-acting agonists: Block norepinephrine reuptake or promote its release; examples include cocaine (reuptake inhibitor) and amphetamines (release promoters).
Mixed-action agonists: Stimulate receptors and release norepinephrine; examples are ephedrine and pseudoephedrine.

Norepinephrine

Causes significant vasoconstriction without compensatory vasodilation, making it less suitable for asthma treatment.
Increases blood pressure and stimulates baroreceptors, leading to bradycardia through vagal activity, which can be counteracted by atropine.
Therapeutically used for shock treatment by increasing vascular resistance and blood pressure.

Isoproterenol

A synthetic catecholamine stimulating both β1 and β2 receptors, rarely used due to non-selectivity.
Increases heart rate, contractility, and cardiac output comparably to epinephrine.
Side effects include tremor and may lead to tachycardia or arrhythmia, particularly in patients with existing heart conditions.

Salmeterol and Formoterol

Long-acting β agonists (LABAs) selective for β2 receptors.
Provide prolonged bronchodilation (up to 12 hours) compared to albuterol.
Recommended in combination with corticosteroids, not monotherapy.

Mirabegron

A β3 agonist that relaxes detrusor smooth muscle, increasing bladder capacity, and used for overactive bladder treatment.
May raise blood pressure, contraindicated in patients with uncontrolled hypertension.

Cocaine

Unique as a local anesthetic that blocks norepinephrine transporter, enhancing sympathetic activity.
Accumulated norepinephrine leads to magnified effects of catecholamines and prolonged action duration.

Mixed-Action Adrenergic Agonists

Ephedrine and pseudoephedrine stimulate α and β receptors while releasing stored norepinephrine.
Both exhibit long durations of action and good oral absorption, but are less potent than epinephrine.
Used to treat hypotension through vasoconstriction and cardiac stimulation, while inducing slower-acting bronchodilation compared to other catecholamines.

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Description

In this quiz, you will explore the characteristics and structural features of adrenergic agonists as discussed in Pharmacology Lecture 6 by Dr. Salem Abukres. Understand the role of these compounds in affecting alpha and beta receptors. Test your knowledge on the derivatives of β-phenylethylamine and their impact on the central nervous system.