Questions and Answers
Which of the following are antimuscarinic drugs?
Atropine has no effect on nicotinic receptors.
True
What is the mechanism of action of atropine?
Competitive antagonist at muscarinic receptors
Hyoscine has an excitatory effect on the CNS at low doses.
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What are the two categories of synthetic antimuscarinic drugs for asthma?
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Atropine is a natural alkaloid from __________.
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What is a pharmacological action of atropine?
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What condition is treated with atropine during pre-operative care?
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Which adrenergic receptor is primarily affected by norepinephrine?
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What is the effect of epinephrine on blood pressure?
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Nicotine addiction is treated using nicotine replacement therapy and __________.
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Which drug acts as a synthetic beta-agonist?
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Amphetamine decreases the release of norepinephrine.
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What is the major pharmacokinetic concern of catecholamine drugs?
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What are the indications for the treatment of amphetamine derivatives?
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Which of the following foods contain tyramine?
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Tyramine increases sympathetic activity by decreasing norepinephrine release.
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What serious interaction can occur when tyramine is taken with MAOIs?
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What is one of the indications for ephedrine?
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Ephedrine is banned in sports because it is a _______ stimulant.
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Which of the following are adverse effects of ephedrine?
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What is the mechanism of action for phenoxybenzamine?
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Phentolamine is a selective competitive alpha-receptor blocker.
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What are the indications for phentolamine?
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Which of the following describe the pharmacokinetics of selective alpha-1 blockers?
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Match the following beta blockers with their classification:
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Beta-blockers can mask hypoglycemia warning signs.
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The absorption of beta-blockers is affected by ______ metabolism.
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Study Notes
Cholinergic Antagonists
- Classified into three categories based on cholinergic receptors involved.
Antimuscarinic Drugs
- Block muscarinic (M) receptors in periphery and glands, no effect on nicotinic receptors.
Natural Agents
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Atropine (Hyoscyamine)
- Natural alkaloid from Atropa belladonna.
- Pharmacokinetics: Tertiary amine, lipophilic, good CNS actions, and oral absorption.
- Mechanism: Competitive antagonist at muscarinic receptors.
- Actions:
- CNS stimulant.
- Causes constipation and urinary retention.
- Inhibits secretions leading to dryness in mouth and eyes.
- Causes passive mydriasis and cycloplegia affecting IOP.
- Cardiovascular effects: Low doses decrease heart rate, high doses induce tachycardia.
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Indications:
- Limited clinical use due to non-selectivity.
- Eye examinations (not preferred) and pre-anesthetic medications.
- Treatment for organophosphorus poisoning and bradycardia.
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Adverse Effects:
- Dry mouth, blurred vision, tachycardia, urinary retention, constipation.
- Contraindications: Benign Prostatic Hyperplasia (BPH), glaucoma.
Scopolamine
- CNS effects: Sedation at low doses, excitatory at high doses.
- Mainly used for motion sickness.
Synthetic Antimuscarinic Drugs
- Quaternary ammonium compounds, poor CNS distribution.
- Used for respiratory conditions (e.g., COPD, asthma).
- Drugs include long-acting (tiotropium, glycopyrrolate) and short-acting (ipratropium, aclidinium).
Antimuscarinics for Urinary Incontinence
- Selective for M3 receptors.
- Drugs: Oxybutynin, tolterodine, solifenacin, trospium.
Antiparkinsonism Antimuscarinics
- Benztropine and trihexyphenidyl block muscarinic receptors to alleviate parkinsonism symptoms.
Ganglionic Blockers
- Experimental drugs that block autonomic outflow, not clinically used.
Nicotine
- Binds nicotinic receptors leading to sympathetic and parasympathetic stimulation.
- Complex effects; block at high doses may lead to respiratory failure.
- Treatment for addiction includes nicotine replacement therapy.
Adrenergic Receptors Agonists (Sympathomimetics)
- Norepinephrine synthesis occurs predominantly in postganglionic sympathetic neurons.
- Inhibition of norepinephrine storage via vesicular monoamine transporter (VMAT) by reserpine.
- Inhibition of norepinephrine transport by NET, inhibited by cocaine and tricyclic antidepressants.
Function of Adrenergic Receptors
- Alpha and beta receptors have various subdivisions affecting selectivity in drug actions.
- Selectivity examples include tamsulosin targeting α1A in the prostate.
Sympathomimetic Drug Categories
- Catecholamines: rapid metabolism, short duration (e.g., epinephrine, norepinephrine).
- Non-catecholamines: longer duration, systemic actions (e.g., ephedrine, amphetamines).
Pharmacological Actions
- Norepinephrine: Mainly α1 effects leading to vasoconstriction and potential reflex bradycardia.
- Epinephrine: Stronger β receptor affinity; cardiac and vascular effects.
- Isoproterenol: Non-selective β stimulation; similar effects to epinephrine.
Dopamine
- Functions in the cardiovascular and renal systems, increasing cardiac output and renal vasodilation.
Non-Catecholamine Sympathomimetics
- Phenylephrine: Selective α1 agonist used as a nasal decongestant.
- Clonidine: Also acts on α2 – used for ADHD, opioid withdrawal, and hypertension.
Beta Agonists
- Short-acting β2 agonists used for acute asthma attacks (e.g., salbutamol).
- Long-acting β2 agonists used for asthma prevention (e.g., salmeterol).
Indirect-Acting Sympathomimetics
- Influence the release or metabolism of epinephrine and norepinephrine (e.g., cocaine, amphetamines).
Mixed Action Sympathomimetics
- Ephedrine and pseudoephedrine: Act on both α and β receptors and increase norepinephrine levels.
Sympatholytics
- Alpha and beta blockers inhibit adrenergic receptor activity or prevent norepinephrine release/storage.
- Non-selective alpha-blockers include Phenoxybenzamine.
Key Takeaways
- Cholinergic antagonists and sympathomimetics play crucial roles in medication targeting the autonomic nervous system.
- Each drug class has unique pharmacokinetic properties, mechanisms of action, and clinical applications.### Pharmacology of Alpha and Beta Blockers
Phenoxybenzamine
- Long-action due to covalent binding with receptors.
- Non-selective irreversible α blocker (blocks α and β) causing blood vessel relaxation and decreased blood pressure.
Pharmacological Actions of Phenoxybenzamine
- Cardiovascular System: α1 blockade causes vasodilation and reduced blood pressure, leading to reflex tachycardia and increased norepinephrine (NE) due to α2 blockage.
- Urinary System: α1 blockade in trigone and sphincter increases urine flow.
- Miosis occurs from α1 blocking in radial muscles.
- Acts as an antagonist at histamine, acetylcholine, and serotonin receptors.
Indications for Phenoxybenzamine
- Effective in treating pheochromocytoma, alleviating hypertension and sweating.
- Adverse effects include reflex tachycardia, postural hypotension, nasal stuffiness, and first-dose syncope.
Phentolamine
- Non-selective competitive alpha-receptor blocker with a short half-life.
- Acts as an agonist on histamine and acetylcholine receptors; blocks serotonin receptors.
Indications for Phentolamine
- Used for hypertension, hypertensive emergencies, pheochromocytoma, Raynaud's disease vasospasm, and impotence (intracavernosal injection increases blood flow for erections).
- Can reverse local anesthesia by counteracting epinephrine.
Selective α1 Blockers
- Includes prazosin, terazosin, doxazosin, noted for poor bioavailability due to extensive first-pass metabolism.
- Doxazosin has the longest half-life; all selectively and reversibly block α1 receptors.
Indications for Selective α1 Blockers
- Prescribed for hypertension, peripheral vascular disease, and benign prostatic hyperplasia (BPH).
- Fewer cardiac side effects compared to non-selective agents, particularly regarding tachycardia.
Selective α1A Blockers
- Examples: tamsulosin and silodosin, primarily used for BPH.
- Higher selectivity for α1A (in prostate) over α1B (in blood vessels) leads to fewer adverse effects, particularly postural hypotension.
- Serious risk of intraoperative floppy iris syndrome; patients should cease tamsulosin 4 weeks before cataract surgery.
Other α1 Blockers
- Alfuzosin known for QT prolongation.
- Indoramine and urapidil are selective α1 blockers.
- Labetalol and carvedilol are mixed antagonists blocking both α1 and β receptors.
- Chlorpromazine, haloperidol, trazodone, and ergotamine also exhibit α blocking activity.
α2 Blockers
- Yohimbine, a natural alkaloid, acts as an α2 blocker, increasing NE release and blood pressure.
- Uses include reversing sedating effects of xylazine in veterinary medicine and previously as an aphrodisiac.
Beta Blockers
Pharmacokinetics of Beta Blockers
- Generally well-absorbed but undergo significant first-pass metabolism, especially propranolol.
- Propranolol and penbutolol are highly lipophilic, crossing the blood-brain barrier effectively.
- Propranolol and metoprolol are extensively metabolized in the liver; use caution in patients with liver conditions.
Pharmacodynamics of Beta Blockers
- Cardiovascular Actions: β1 blockade results in negative inotropic and chronotropic effects, while β2 blockade leads to unopposed vasoconstriction, contraindicated in peripheral vascular disease.
- Renal Effects: Reduction of renin release.
- Respiratory Impact: Blockage of β2 induces bronchoconstriction; contraindicated in asthma.
- Ocular Effects: Decreased aqueous humor production lowers intraocular pressure, effective for glaucoma treatment.
- Metabolic Effects: Decreased glycogenolysis and hypoglycemia risk, especially harmful for diabetics.
Clinical Considerations for Beta Blockers
- Avoid beta-blockers in type 1 diabetics to prevent masked hypoglycemia warning signs.
- Abrupt withdrawal can lead to life-threatening arrhythmias, especially with short-acting agents.
Indications for Beta Blockers
- Commonly used in hypertension, arrhythmias, heart failure, glaucoma, and thyrotoxicosis.
- Adverse effects include bradycardia, fatigue, sedation, bronchoconstriction, and hypoglycemia.
Types of Beta Blockers
- First Generation (Non-selective): Propranolol, with notable contraindications for asthma and diabetes.
- Second Generation (Selective β1 blockers): Atenolol, bisoprolol, metoprolol, preferred for patients with COPD and safer for diabetics.
- Third Generation: Nebivolol has vasodilatory properties and enhances NO levels, improving hypertension treatment.
- Ophthalmic Beta Blockers: Timolol and betaxolol for glaucoma treatment via lowered intraocular pressure.
- Partial Agonists: Pindolol and acebutolol have lower bradycardia risks and are effective in hypertension management.
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Description
Explore the intricacies of cholinergic antagonists in this quiz designed for pharmacology students. This quiz covers the classification of these drugs, their types, and specific examples such as atropine. Test your knowledge on how these drugs interact with muscarinic receptors and their pharmacokinetic properties.
