Podcast Beta
Questions and Answers
What is the primary therapeutic use of beta antagonists in cardiovascular diseases?
Which beta blocker is specifically mentioned as being effective in controlling acute panic symptoms?
What is a common condition for which beta receptor antagonists have been shown to reduce mortality when administered early?
Which of the following beta blockers is recognized for its effectiveness in treating open-angle glaucoma?
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What characteristic most distinguishes beta blockers from each other?
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Which antiglaucoma drug is noted for being the most effective at reducing Na+/Ca2+ influx?
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What is the main role of Urapidil in the context of hypertension treatment?
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Which of the following conditions is contraindicated for the use of beta antagonists?
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What is the primary action of sympatholytics?
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Which drug is known for causing severe postural hypotension as an adverse reaction?
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What is the mechanism of action of α Methyldopa?
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Which of the following is NOT a use for Guanethidine?
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What adverse effect is associated with Reserpine?
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What is the initial recommended dose for Prazosin in treating hypertension?
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What is a common reason Clonidine is not frequently used now?
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Which drug acts mainly by preventing the release of norepinephrine at nerve endings?
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What is the adverse effect associated with Metyrosine?
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What is the pharmacological effect of bretylium?
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Which drug is indicated for the primary prevention of variceal bleeding in patients with portal hypertension?
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What is a significant risk associated with the abrupt discontinuation of β receptor antagonists after long-term treatment?
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Which β blocker is particularly useful in patients with diminished cardiac reserve or a propensity to bradycardia?
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Which β blocker is known for having significant first-pass metabolism?
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What is a common adverse effect of non-selective β adrenergic receptor antagonists on the central nervous system?
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Which drug combination can decrease the plasma concentrations of receptor antagonists like propranolol?
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Which β blocker is primarily indicated for controlling intraocular pressure in glaucoma patients?
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What adverse effect may worsen in patients with peripheral vascular disease when taking β receptor antagonists?
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Which of the following β blockers is noted for having a rapid onset and a short duration of action?
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Which β blocker is associated with better tolerance in patients compared to others in terms of CNS side effects?
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What is the half-life (t1/2) of doxazosin, and how does it compare to prazosin?
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Which medication is contraindicated for use with CYP3A4 inhibitors?
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What side effect is commonly associated with Silodosin?
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Which of the following drugs is NOT used for hypertension?
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What is the recommended initial dose of Terazosin for treating BPH?
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Which α1 selective antagonist has the highest bioavailability?
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Which medication is used to alleviate severe hypertension episodes associated with pheochromocytoma?
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What adverse effects are primarily associated with non-selective α adrenergic antagonists?
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What is the mechanism of action of Yohimbine?
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Which α1 receptor antagonist is considered less likely to cause orthostatic hypotension?
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What long-term effect do α receptor antagonists have on cardiac output?
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What is the primary use of phentolamine?
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What class of α adrenergic antagonists have irreversible and non-competitive blocking properties?
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Study Notes
Introduction
- The ANS (Autonomic Nervous System) is essential as it regulates various functions in the body without conscious control, like heart rate, blood vessel diameter, and glandular secretions.
- The ANS is also called the visceral, involuntary, or vegetative nervous system and is distributed widely throughout the body.
Sympatholytics
- Sympatholytics block or decrease the effects of sympathetic nerve stimulation, endogenous catecholamines, and adrenergic drugs.
Neuron Blocking Drugs - Indirect Acting Agents
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Guanethidine acts mainly by preventing the release of norepinephrine (NE) at nerve endings.
- It has various uses, including treatment of hypertension, glaucoma, neuropathic pain, and hypertensive crises.
- Prominent adverse reactions include postural hypotension, diarrhea, and renal impairment.
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Bretylium initially causes the release of NE but then blocks adrenergic transmission by preventing NE release from adrenergic nerve endings.
- Bretylium also acts as a class III antiarrhythmic by blocking potassium channels.
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Guanadrel acts as a false neurotransmitter, replacing NE with an inactive transmitter and creating a long-lasting blockade of the autonomic nervous system.
- It has a similar mechanism of action to guanethidine and shares similar adverse effects, such as hypotension, fatigue, lassitude, sexual dysfunction, and diarrhea.
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Reserpine inhibits the vesicular catecholamine transporter, leading to the depletion of NE from the storage vesicles.
- Can cause sedation, inability to concentrate, and occasionally psychotic depression with suicidal tendencies.
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Metyrosine inhibits tyrosine hydroxylase, an enzyme involved in the biosynthesis of catecholamines.
- Used as an adjunct to other adrenergic blockers in the treatment of pheochromocytoma.
- Can cause crystalluria as a side effect.
Central Sympatholytics
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α-Methyldopa is converted to α-methyl-NE, which acts on α2 receptors in the brain, inhibiting adrenergic discharge in the medulla, thereby reducing peripheral vascular resistance and blood pressure.
- Not frequently used due to various adverse effects, including cognitive impairment, postural hypotension, and a positive Coombs' test.
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Clonidine is an imidazoline derivative that acts as a partial agonist of central α2 receptors.
- It is not frequently used due to the development of tolerance and withdrawal hypertension.
Alpha Adrenergic Blocking Drugs
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Prazosin is a potent, selective α1-adrenergic receptor antagonist, well absorbed orally, and effective for hypertension, benign prostatic hyperplasia (BPH), and nightmares associated with post-traumatic stress disorder (PTSD).
- It has a known "first-dose response," where an exaggerated orthostatic hypotensive response can occur, potentially leading to syncope.
- Terazosin, similar to prazosin, but with longer duration of action and higher selectivity for α1 receptors, is a good option for BPH treatment.
- Doxazosin has similar pharmacokinetic and dynamic properties to prazosin, with a longer duration of action.
- Alfuzosin mainly used for BPH and has a shorter duration of action than other selective α1 antagonists.
- Tamsulosin is highly selective for α1a and α1d subtypes of α1 receptors and is used for BPH treatment.
- Silodosin blocks α1a and α1b receptors and is approved for BPH treatment.
Therapeutic Uses of Alpha Adrenergic Blocking Drugs
- Hypertension: Prazosin and its congeners are used effectively in the treatment of essential hypertension, improving lipid profiles and glucose-insulin metabolism in patients at risk for atherosclerotic disease.
- Congestive Heart Failure (CHF): α receptor antagonists are used in combination with other vasodilating drugs in the treatment of CHF.
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BPH: Prazosin can improve bladder emptying in some patients with BPH.
- Tamsulosin and silodosin are less likely to cause orthostatic hypotension compared to other α1 antagonists.
- Combination therapy with α1 antagonists and 5α-reductase inhibitors is often more beneficial than monotherapy.
- Other Disorders: Alpha-adrenergic receptor antagonists are used in the treatment of variant angina, vasospastic disorders, ventricular arrhythmias, and mitral or aortic valvular insufficiency.
α2 Receptor Antagonists
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Yohimbine is a competitive antagonist of α2 receptors and may benefit some patients with psychogenic erectile dysfunction.
- It is also used in the treatment of diabetic neuropathy and postural hypotension.
Non-Selective α Adrenergic Antagonists
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Phenoxybenzamine and Phentolamine are irreversible non-competitive antagonists of α receptors.
- They have a long duration of action and a prominent postural hypotensive effect.
- They are used primarily for the treatment of pheochromocytoma and hypertensive crises.
Therapeutic Uses of Non-Selective α Adrenergic Antagonists
- Pheochromocytoma: Phenoxybenzamine is used to prepare patients for surgery by controlling episodes of severe hypertension.
- Hypertensive Crises: Useful for hypertensive crises following clonidine withdrawal or tyramine-containing food intake during the use of non-selective MAO inhibitors.
Toxicity and Adverse Effects of Non-Selective α Adrenergic Antagonists
- Hypotension: The major adverse effect includes postural hypotension and syncope.
- Cardiovascular: Can lead to tachycardia, cardiac arrhythmias, and ischemic cardiac events.
- Urogenital: Reversible inhibition of ejaculation is a common side effect.
- Gastrointestinal: Should be used with caution in patients with a history of peptic ulcer disease.
Beta Adrenergic Receptor Antagonists
- β receptor antagonists are categorized by their relative affinity for β1 and β2 receptors, intrinsic sympathomimetic activity, lipid solubility, vasodilating capacity, and pharmacokinetic parameters.
Therapeutic Uses of Beta Adrenergic Receptor Antagonists
- Cardiovascular Diseases: Used in the management of hypertension, angina, acute coronary syndromes, congestive heart failure, and myocardial infarction.
- Glaucoma: β-blockers are effective in reducing intraocular pressure (IOP) by reducing the production of aqueous humor.
- Other Uses: β-blockers are used for migraine prophylaxis, panic disorder, essential tremor, alcohol withdrawal, and variceal bleeding prevention in patients with portal hypertension.
Adverse Effects of Beta Adrenergic Receptor Antagonists
- Cardiovascular System: Can worsen congestive heart failure, induce bradycardia, and exacerbate peripheral vascular disease.
- Pulmonary Function: Can increase airway resistance, particularly in patients with asthma.
- Central Nervous System (CNS): Can cause fatigue, sleep disturbances, and depression.
- Metabolism: Should be used with caution in patients with diabetes due to the risk of hypoglycemia.
- Miscellaneous: Can cause sexual dysfunction and are contraindicated in pregnancy.
Overdosage of β-blockers
- Hypotension, bradycardia, prolonged AV conduction times, and widened QRS complexes are common signs of overdosage.
- Glucagon: The first-line treatment for β-blocker overdose.
Non-Selective β Adrenergic Receptor Antagonists
- Propranolol is a potent, non-selective β-blocker that is used in the treatment of hypertension, angina, supraventricular arrhythmias, ventricular arrhythmias, MI, pheochromocytoma, essential tremor, and migraine prophylaxis.
- Nadolol is a long-acting, non-selective β-blocker with a long half-life.
- Timolol is a potent, non-selective β-blocker, and the ocular formulation for glaucoma treatment can be absorbed systemically, potentially leading to systemic adverse effects.
- Pindolol, a non-selective β-blocker with intrinsic sympathomimetic activity, is preferred for patients with diminished cardiac reserve or a propensity for bradycardia.
β1 Selective Adrenergic Receptor Antagonists
- Metoprolol is a β1-selective antagonist with no intrinsic sympathomimetic activity, used in the treatment of hypertension, angina, tachycardia, and CHF.
- Atenolol is a highly hydrophilic β1-selective antagonist, used in the treatment of hypertension and hyperthyroidism.
- Betaxolol is a β1-selective antagonist mainly used in the treatment of glaucoma.
- Esmolol is a rapidly acting, short-acting β1-selective antagonist, used during surgeries to treat tachycardia and supraventricular tachycardia (SVT).
- Acebutalol is a β1-selective antagonist with lipophilic properties, used in treatment of hypertension, arrhythmias, MI, and Smith-Magenis syndrome.
- Bisoprolol is a β1-selective antagonist with a high degree of β1 selectivity used in the treatment of hypertension and CHF.
Third Generation β-Blockers
- These agents offer additional features besides β-blockade, such as:
- Nitric oxide production: Celiprolol, Nebivolol, Carteolol, Bopindolol, Nipradilol
- Alpha2 receptor agonism: Celiprolol, Carteolol, Bopindolol
- Alpha 1 receptor antagonism: Carvedilol, Bucindolol, Bevantolol, Nipradilol, Labetalol
- Ca2+ entry blockade: Carvedilol, Betaxolol, Bevantolola
- K+ channel opening: Tilisolol
- Antioxidant activity: Carvedilol
Labetalol
- Labetalol is a selective α1 and non-selective β-blocker that reduces blood pressure by reducing systemic vascular resistance (SVR) via α1 blockade and partially inhibits reflex tachycardia via β-blockade.
- It is under consideration for use in managing vascular complications associated with Ehlers-Danlos syndrome.
Drug Interactions with β Blockers
- Aluminum salts, cholestyramine, and colestipol decrease β-blocker absorption
- Phenytoin, rifampin, and phenobarbital, smoking induce hepatic metabolic enzymes and decrease β-blocker plasma concentrations
- Cimetidine and hydralazine increase β-blocker bioavailability by affecting blood flow.
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Description
This quiz explores the pharmacological aspects of the Autonomic Nervous System (ANS), focusing on sympatholytics and neuron blocking drugs like Guanethidine and Bretylium. Assess your understanding of their mechanisms, uses, and adverse reactions. Dive into the intricacies of how these drugs impact the body’s involuntary functions.
