Adrenergic Antagonists Quiz
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Questions and Answers

What class of adrenergic antagonist interferes with the synthesis, storage, and/or release of adrenergic neurotransmitters?

  • α-Blockers
  • Adrenergic Neuron Blockers (correct)
  • Receptor Antagonists
  • β-Adrenergic Agonists

Which adrenergic antagonist is known for its irreversible action on receptors?

  • Prazosin
  • Phenoxybenzamine (correct)
  • Phentolamine
  • Dibenzyline

What is the primary use of Tamsulosin?

  • To treat hypertension
  • To decrease prostate size
  • To enhance libido
  • To treat benign prostatic hyperplasia (BPH) (correct)

How do receptor antagonists exert their effect at adrenergic receptors?

<p>They compete with norepinephrine for receptor binding (D)</p> Signup and view all the answers

Which α₁-blocker is specifically recommended for the urethra?

<p>Terazosin (B)</p> Signup and view all the answers

Which selective antagonist has greater selectivity for α₂- than for α₁- adrenoceptors?

<p>Yohimbine (D)</p> Signup and view all the answers

What is the therapeutic use of selective α₁-adrenergic blockers like Prazosin?

<p>To treat hypertension (D)</p> Signup and view all the answers

What receptor does the β1-adrenoceptor predominantly affect?

<p>Heart muscle (B)</p> Signup and view all the answers

Which of the following statements about non-selective irreversible α-antagonists is true?

<p>They form strong covalent bonds with α-receptors. (A)</p> Signup and view all the answers

What is a characteristic of Tamsulosin in relation to prostate size?

<p>It has no effect on prostate size. (C)</p> Signup and view all the answers

What effect do α₁-adrenergic blockers have on blood vessels?

<p>They induce vasodilation. (A)</p> Signup and view all the answers

Which type of adrenergic antagonist retains the highest affinity for the receptor but lacks intrinsic activity?

<p>Receptor antagonists (D)</p> Signup and view all the answers

What is the role of β2-adrenoceptors in the body?

<p>Causes smooth muscle relaxation (D)</p> Signup and view all the answers

Which drug is NOT used for treating benign prostatic hyperplasia (BPH)?

<p>Yohimbine (C)</p> Signup and view all the answers

What describes the action of phenoxybenzamine in relation to α-receptors?

<p>It alkylates α-receptors via electrophilic reactions. (C)</p> Signup and view all the answers

What effect do β-blockers have on the body?

<p>Decreased heart rate (B)</p> Signup and view all the answers

What is the primary clinical use of phenoxybenzamine?

<p>Treatment of hypertension caused by pheochromocytoma (B)</p> Signup and view all the answers

Which of the following drugs is a non-selective reversible blocker?

<p>Phentolamine (D)</p> Signup and view all the answers

How does the structure of terazosin differ from that of prazosin?

<p>It contains a tetrahydrofuran ring instead of a furan ring (A)</p> Signup and view all the answers

What effect does the reduction of the furan into THF have on pharmacokinetics?

<p>Increased hydrophilicity (A)</p> Signup and view all the answers

Which of the following properties is enhanced by the tetrahydrofuran structure in terazosin?

<p>Longer duration of action (B)</p> Signup and view all the answers

What is a common effect of selective α₁-antagonists like prazosin in the human body?

<p>Smooth muscle relaxation in the prostate (D)</p> Signup and view all the answers

What is one of the limitations of the clinical applications of tolazoline?

<p>Limited to antihypertensive use only (A)</p> Signup and view all the answers

Which receptor do the azosins primarily target to facilitate passage of kidney stones?

<p>α1-receptors (C)</p> Signup and view all the answers

What type of receptors do 1st generation (non-selective) β-adrenergic blockers inhibit?

<p>Both β₁ and β₂ receptors (D)</p> Signup and view all the answers

Which adverse effect is most associated with increasing lipophilicity of non-selective β-blockers?

<p>CNS side effects (D)</p> Signup and view all the answers

Which of the following is true about Propranolol HCl?

<p>It is contraindicated in patients with asthma. (A)</p> Signup and view all the answers

What is the primary use of Nadolol (Corgard®)?

<p>Hypertension and angina pectoris (C)</p> Signup and view all the answers

What structural feature is essential for the action of Propranolol HCl?

<p>A hydroxyl group (C)</p> Signup and view all the answers

What is a common consequence of significant first-pass metabolism in Propranolol?

<p>Decreased bioavailability (D)</p> Signup and view all the answers

Which of the following is an important consideration when using 1st generation β-adrenergic blockers?

<p>They require a secondary amine structure. (B)</p> Signup and view all the answers

Which metabolite is relevant to the action of Propranolol HCl?

<p>p-OH metabolite (D)</p> Signup and view all the answers

What characteristic feature of the structure of isoprenaline contributes to its β-selectivity?

<p>N-Isopropyl group (C)</p> Signup and view all the answers

Which statement about the structural features of β-blockers is correct?

<p>A secondary amine is essential for binding. (B)</p> Signup and view all the answers

What role does para-substitution play in the β-blockers' structure?

<p>It is necessary for β₁-selectivity. (A)</p> Signup and view all the answers

What is the significance of the carbinol carbon in the structure of aryloxypropanolamines?

<p>It is asymmetric with R being the most active. (A)</p> Signup and view all the answers

Which of the following is a feature shared by all members of the β-blocker class?

<p>Presence of an aromatic ring (A)</p> Signup and view all the answers

What impact does m-substitution have on the phenyl groups in β-blockers?

<p>It results in non-selective β-antagonism. (D)</p> Signup and view all the answers

Which structural element is required for enhanced activity in β-blockers due to H-bonding?

<p>An alcohol functional group (C)</p> Signup and view all the answers

Which of the following statements about β-blockers' selectivity is true?

<p>Substitution pattern directly affects β-antagonism selectivity. (D)</p> Signup and view all the answers

What is one primary therapeutic use of Timolol?

<p>Management of chronic open glaucoma (C)</p> Signup and view all the answers

Which characteristic does Pindolol have that makes it safer for patients with respiratory disease?

<p>Intrinsic sympathomimetic activity (ISA) (A)</p> Signup and view all the answers

What major side effect can occur with the use of non-selective β-blockers like Propranolol?

<p>Bronchospasm (C)</p> Signup and view all the answers

What is a unique feature of Esmolol regarding its pharmacokinetics?

<p>Rapid onset of action and short duration (A)</p> Signup and view all the answers

What is the reason that second-generation β-blockers are designed to be selective for β₁ receptors?

<p>To avoid β₂-antagonism and bronchospasm (B)</p> Signup and view all the answers

Which of the following drugs is NOT a selective β₁-blocker?

<p>Propranolol (C)</p> Signup and view all the answers

What type of bonding interaction is enhanced in second-generation β-blockers?

<p>Hydrogen bonding with β₁ receptors (D)</p> Signup and view all the answers

Which feature is NOT associated with Metoprolol?

<p>Non-selective β-antagonist activity (D)</p> Signup and view all the answers

Flashcards

Adrenergic Neuron Blockers

Drugs that interfere with the synthesis, storage, or release of adrenergic neurotransmitters.

Receptor Antagonists

Drugs that bind to receptors without activating them, preventing a cellular response.

α-Blockers

Drugs that block alpha-adrenergic receptors, often reducing blood pressure.

Irreversible α-Blockers

α-blockers that form permanent bonds with the receptors, creating a long-lasting effect.

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Phenoxybenzamine

An irreversible α-blocker used primarily to treat pheochromocytoma.

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α₁-adrenergic receptors

A type of adrenergic receptor that plays a role in blood vessel constriction and other functions.

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Vasodilation

Widening of blood vessels, leading to a decrease in blood pressure.

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Competitive blocker

A drug that binds reversibly to the receptor, competing with the normal molecule.

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Phenoxybenzamine's use

Limited to treating symptoms of pheochromocytoma (a benign adrenal gland tumor causing hypertension).

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Non-selective alpha-blockers

Imidazoline-related drugs that block both types of alpha receptors and have antihypertensive activity.

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Selective alpha1-antagonists

Drugs targeting specific alpha1 receptors, beneficial for treating Benign Prostatic Hyperplasia (BPH).

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Azosins: Structure

Quinazoline compounds with specific side chains impacting properties like bioavailability and action duration.

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Azosins & Urinary Flow

Relax smooth muscle in the bladder and other urinary structures, reducing resistance to urine flow.

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Tetrahydrofuran (THF)

Chemical alteration in azosins that improves hydrophilicity and bioavailability, lengthening duration of action.

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Alpha receptor blockers

Drugs that block the stimulation of alpha receptors, sometimes easing hypertension.

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Pheochromocytoma symptoms

Hypertension, generalized sympathetic stimulation, related to adrenal gland tumor.

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α₁-Antagonists for BPH

Drugs that block α₁ receptors in the prostate and urethra, used to treat symptoms of benign prostatic hyperplasia (BPH).

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Tamsulosin and Silodosin

Selective α₁-antagonists, particularly targeting α₁A receptors in the prostate. Used for BPH symptoms, not hypertension.

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Selective α₂-Antagonist

Drugs that block α₂ receptors more than α₁ receptors (e.g. Yohimbine).

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Yohimbine use

An α₂-antagonist used for erectile dysfunction (modest benefit), and postural hypotension.

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β₁-Adrenoceptor location

Primarily found in heart muscle, causing muscle contraction.

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β₂-Adrenoceptor location

Primarily located in bronchial smooth muscle, relaxing it.

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β₃-Adrenoceptor location

Primarily found in fat cells, involved in fat metabolism.

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β-blocker use

Drugs that block β-adrenergic receptors, potentially used for cardiovascular conditions.

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Aromatic ring (lipophilic)

Aromatic ring in beta-blockers crucial for interaction with receptor, enhancing lipophilicity.

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Spacer in beta-blockers

The spacer connects the aromatic ring to the amine group, affecting selectivity and activity.

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Amine group in beta-blockers

Secondary amine essential for beta-blocker activity as it forms ionic bonds with the receptor for efficient binding.

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β-directing group in beta-blockers

Branching N-alkyl groups enhance binding within specific pockets of the beta-adrenergic receptors. They improve selectivity for B-adrenergic receptors.

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Para-substitution for β₁-selectivity

Para-substitution is important to initiate additional H-bonding interaction with the receptor, ultimately leading to ẞ₁-selectivity.

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Substituted phenyl group

Substituents on the phenyl ring can modify the activity and selectivity of beta-blockers.

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Naphthyl group in beta-blockers

Naphthyl groups in beta-blockers contribute to non-selectivity.

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Propranolol's Active Metabolite

Propranolol is metabolized to an active metabolite, p-OH, which is released from tissue storage, contributing to its longer duration of action.

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Propranolol's Lipophilicity

Propranolol's lipophilicity contributes to both its significant first-pass metabolism and its potential for CNS side effects.

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Nadolol's Structure

Nadolol, a non-selective beta-blocker, retains the oxypropanolamine structure similar to Propranolol.

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Propranolol's Amine Group

Propranolol's secondary amine forms an ionic bond with the receptor binding site, essential for its activity.

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Propranolol's N-Isopropyl Group

The N-isopropyl group in Propranolol acts as a β-directing group, influencing its selectivity for β-receptors.

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Propranolol's Ether Group

The ether group in Propranolol acts as a hydrogen bond acceptor (HBA), contributing to its interaction with the receptor.

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Propranolol's Branched N-Alkyl Group

Propranolol's branched N-alkyl group fits into a hydrophobic pocket in the receptor, enhancing its binding affinity.

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Propranolol's Alcohol Group

The alcohol group in Propranolol is essential as a hydrogen bonding group, contributing to its interaction with the receptor.

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Substituted Naphthyl Ring

A structural modification in beta-blockers that increases water solubility, leading to a longer duration of action and reduced first-pass metabolism.

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Timolol (Timoptic®)

A non-selective beta-blocker used topically to manage chronic open glaucoma and ocular hypertension by reducing intraocular pressure. Also used orally for hypertension and angina.

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Pindolol (Visken)

A non-selective beta-blocker with intrinsic sympathomimetic activity (ISA). Safer for patients with respiratory disease and bradycardia due to its partial agonist effect.

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Indole Ring

A structural feature found in non-selective beta-blockers, particularly Pindolol.

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2nd generation selective β₁-blockers

Beta-blockers designed to selectively block β₁-adrenoceptors in the heart, minimizing effects on the lungs and bronchi.

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Metoprolol (Lopressor)

A selective β₁-blocker used for hypertension, angina pectoris, and myocardial infarction. It's available in oral and intravenous forms.

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Esmolol (Brevibloc®)

A selective β₁-blocker with a very short duration of action, primarily used for rapid control of heart rate in acute situations.

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p-substituted phenyl

The presence of a phenyl group at the para position in a molecule, which contributes to β₁ selectivity in beta-blockers.

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Study Notes

Adrenergic Antagonists

  • Adrenergic antagonists are classified into blockers and receptor antagonists.
  • Blockers interfere with the synthesis, storage, and/or release of the adrenergic neurotransmitter.
  • Receptor antagonists compete with norepinephrine (NE) for α or β receptors.
  • Receptor antagonists have higher affinity for the receptor than agonists but lack intrinsic activity.
  • The effect of receptor antagonists is reversible (competitive antagonists).
  • Some receptor blockers are irreversible; they act by forming stable complexes with the receptor.

Receptor Antagonists

  • Receptor antagonists bind to receptors but do not trigger the usual receptor-mediated intracellular effects.
  • They have affinity but no efficacy.

α-Blockers

  • α-adrenergic blocking agents comprise a variety of chemical classes, with little resemblance to agonists.
  • They block α₁-adrenergic receptors in arteries and smooth muscles, causing vasodilation and decreasing blood pressure.
  • They are used therapeutically as antihypertensive agents.
  • Examples include norepinephrine and various compounds.

Nonselective α-Antagonists

  • Nonselective irreversible blockers (β-haloalkylamines) such as phenoxybenzamine, spontaneously generate an electrophilic aziridinium cation.
  • This cation readily attacks α-receptors, alkylating them and forming strong covalent bonds.
  • This results in irreversible α-blockade.
  • Phenoxybenzamine primarily used for treating the symptoms of pheochromocytoma (tumors of the adrenal medulla).

Selective α₁-Antagonists

  • Azosins (quinazoline-containing compounds) such as prazosin are selective α₁-adrenergic, reversible (competitive) blockers.
  • Their structure differs from that of prazosin only in having a tetrahydrofuran instead of a furan ring.

β-Adrenergic Antagonists

  • There are three types of β-adrenoceptors: β₁, β₂, and β₃.
  • β₁-adrenoceptors are primarily found in the heart muscle and activation leads to muscle contraction.
  • β₂-adrenoceptors are primarily found in bronchial smooth muscle and lead to muscle relaxation.
  • β₃-adrenoceptors are primarily found in fat cells and activation results in fat metabolism.

Structural Features of β-blockers

  • The aromatic ring (lipophilic) and spacer are critical for β-blocker activity.
  • The amine group is ionized, forming an ionic bond with the binding site.
  • The substituent (R) on the amine is a crucial β-directing group (isopropyl, t-butyl, aralkyl).
  • Branched N-alkyl groups fit a hydrophobic pocket.
  • Extension of the N-alkyl group with an N-arylethyl group is beneficial.

First Generation Non-selective β-blockers

  • Commonly used for treatment of hypertension and other conditions.
  • Examples include propranolol, nadolol, and timolol.

Second Generation Selective β₁-blockers

  • Selective β₁-blockers like metoprolol, atenolol, and bisoprolol are used in managing hypertension.

Mixed α₁, β-adrenergic blockers

  • Mixed α₁, β-blockers like labetalol and carvedilol are used in managing hypertension and other related conditions.
  • Carvedilol possesses antioxidant activity.
  • Labetalol has both α₁ and β-blocking activity.

Adrenergic Neuron Blocking Agents

  • These drugs interfere with the synthesis, storage, and/or release of the adrenergic neurotransmitter.
  • Examples include guanethidine and reserpine.
  • These drugs are often transported into adrenergic neurons, binding to storage vesicles and preventing the release of norepinephrine (NE).

Bretylium Tosylate

  • Bretylium tosylate is a class III antiarrhythmic agent.
  • It blocks the release of norepinephrine from nerve terminals.
  • Used primarily for ventricular arrhythmias resistant to other treatments.

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This quiz explores the classification and mechanisms of adrenergic antagonists, focusing on blockers and receptor antagonists. You will learn about α-blockers, their effects, and how they interact with receptors. Test your understanding of these crucial pharmacological agents in this informative quiz.

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