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Questions and Answers
What effects can high doses of amphetamines produce?
What effects can high doses of amphetamines produce?
What is a primary use of Alpha-Methyldopa?
What is a primary use of Alpha-Methyldopa?
Which agents are classified as Selective Beta2 Agonists?
Which agents are classified as Selective Beta2 Agonists?
What is a significant feature of combined α and β-blockers?
What is a significant feature of combined α and β-blockers?
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Which classroom of drugs primarily blocks the vasoconstrictor action of adrenaline?
Which classroom of drugs primarily blocks the vasoconstrictor action of adrenaline?
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What type of drug is Prazosin?
What type of drug is Prazosin?
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What cardiovascular risks are associated with excessive use of amphetamines?
What cardiovascular risks are associated with excessive use of amphetamines?
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Which medication is commonly used for treating shock in various conditions?
Which medication is commonly used for treating shock in various conditions?
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What condition can selective alpha-1 blockers help alleviate?
What condition can selective alpha-1 blockers help alleviate?
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Chronic use of amphetamines is primarily limited due to:
Chronic use of amphetamines is primarily limited due to:
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Which adrenergic receptor subtype is primarily targeted by pseudoephedrine?
Which adrenergic receptor subtype is primarily targeted by pseudoephedrine?
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What is the primary use of norepinephrine in medical treatments?
What is the primary use of norepinephrine in medical treatments?
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Which statement correctly describes the action of adrenaline?
Which statement correctly describes the action of adrenaline?
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What class of drugs does amphetamine belong to?
What class of drugs does amphetamine belong to?
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Which of the following is NOT a route of administration for adrenaline?
Which of the following is NOT a route of administration for adrenaline?
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What effect do amphetamines have on mood and attention?
What effect do amphetamines have on mood and attention?
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Which adrenergic receptor is least affected by norepinephrine?
Which adrenergic receptor is least affected by norepinephrine?
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Which reaction is associated with non-selective adrenergic agonists like adrenaline?
Which reaction is associated with non-selective adrenergic agonists like adrenaline?
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Which mechanism represents the primary action of sympathomimetics?
Which mechanism represents the primary action of sympathomimetics?
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What is the effect of beta-blockers on the heart's chronotropic activity?
What is the effect of beta-blockers on the heart's chronotropic activity?
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Which of the following beta-blockers is considered non-selective?
Which of the following beta-blockers is considered non-selective?
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What is the main reason for the high protein binding of propranolol?
What is the main reason for the high protein binding of propranolol?
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How can the side effect of orthostatic hypotension be minimized when initiating beta-blocker therapy?
How can the side effect of orthostatic hypotension be minimized when initiating beta-blocker therapy?
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What is a potential effect of non-selective beta-blockers on the respiratory system?
What is a potential effect of non-selective beta-blockers on the respiratory system?
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Which condition is NOT effectively treated with beta-blockers?
Which condition is NOT effectively treated with beta-blockers?
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What is a notable adverse effect of sudden withdrawal from beta-blockers?
What is a notable adverse effect of sudden withdrawal from beta-blockers?
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What therapeutic use of beta-blockers helps reduce intraocular pressure in glaucoma patients?
What therapeutic use of beta-blockers helps reduce intraocular pressure in glaucoma patients?
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What effect do beta-blockers have on T4 levels in hyperthyroid patients?
What effect do beta-blockers have on T4 levels in hyperthyroid patients?
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Which condition requires careful monitoring and gradual withdrawal of beta-blockers?
Which condition requires careful monitoring and gradual withdrawal of beta-blockers?
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Study Notes
Pharmacology of the Sympathetic System
- The sympathetic system utilizes adrenergic receptors, also known as adrenoceptors, for its function.
- Adrenergic receptors are categorized into alpha (α₁ and α₂) and beta (β₁, β₂, and β₃) subtypes.
- Different receptors have varying responses to stimuli.
Adrenergic Stimulants (Sympathomimetics)
- Sympathomimetics mimic the effects of stimulating postganglionic sympathetic adrenergic nerves.
- Their uses include bronchodilation, cardiovascular stimulation, mydriasis, and nasal decongestion.
- Classification is based on receptor selectivity: selective or non-selective.
Non-selective (Mixed Alpha & Beta Agonists)
- These drugs stimulate multiple adrenergic receptor subtypes (α₁, α₂, β₁, and β₂).
- Examples include adrenaline (epinephrine), noradrenaline (norepinephrine), amphetamine, and pseudoephedrine.
Adrenaline (Epinephrine)
- Stimulates all four adrenergic receptor subtypes (α₁, α₂, β₁, and β₂).
- It has a rapid onset and short duration of action (t1/2 ≈ 2 minutes).
- Oral administration is ineffective; it is typically administered subcutaneously, intramuscularly, intravenously, by inhalation, or topically to the eye.
- Therapeutic uses include: anaphylactic shock, bronchial asthma, cardiac arrest, delaying absorption of local anesthetics, epistaxis management, glaucoma.
Norepinephrine (Noradrenaline)
- Binds to both alpha subtypes (α₁ and α₂), and to beta₁ receptors to a lesser extent.
- It has little to no affinity for beta₂ receptors
- Norepinephrine (IV infusion) is frequently the first-line vasopressor for shock, such as septic shock, and maintains cardiac output.
Pseudoephedrine (oral)
- Directly stimulates α₁, α₂, and β₁ receptors.
- Its vasoconstrictive action is utilized to treat nasal and sinus congestion, often combined with other agents, such as antihistamines, in cold remedies.
Amphetamines (e.g., methamphetamine)
- These drugs have marked central stimulating effects, including a mood-elevating effect (euphoria).
- This effect contributes to their widespread abuse, despite inducing insomnia and enhancing attention.
- Peripheral adrenergic actions include cardiac stimulation and increased blood pressure.
- Therapeutic uses include the treatment of attention deficit hyperactivity disorder (ADHD) in children and narcolepsy in adults.
Adverse Reactions of Non-selective Agonists
- CNS excitation (anxiety, fear, tremors)
- High doses can induce psychosis and convulsions.
- Long-term use can lead to tolerance, psychological dependence, and physical dependence.
- Cardiovascular stimulation (tachycardia, arrhythmias, cardiac arrest)
- Marked blood pressure elevation can cause cerebral hemorrhage.
Selective Adrenergic Agonists
- These drugs act on specific receptor subtypes.
Alpha₁ and Alpha₂ agonists
- Examples include naphazoline, and xylometazoline.
- These drugs cause rapid and prolonged vasoconstriction when applied intranasally, aiding in decongestion of nasal cavities and upper airways.
- Long-term usage can cause atrophy of mucous membranes.
Selective Alpha₂ Agonists
- Alpha-methyldopa is an oral medication that is often used as an antihypertensive agent in pregnancy.
Selective Beta₁ Agonists
- Dopamine is used as a shock treatment in hypovolemia and septic shock in varying doses, according to the cause of the shock.
Selective Beta₂ agonists
- Salbutamol and terbutaline are commonly administered in inhalation/IV form for addressing bronchospasm in conditions like asthma, bronchitis, and emphysema.
Adrenergic Antagonists (Sympatholytics)
- These agents block the effects of adrenergic stimulation.
Alpha-receptor blockers
- They inhibit vasoconstriction caused by adrenaline and noradrenaline.
Beta-receptor blockers
- They counteract the cardiac and vasodilating effects of adrenaline.
Combined alpha and beta blockers
- Examples include labetalol and carvedilol.
Selective Alpha₁-blockers
- These are competitive blockers of post-synaptic alpha₁ receptors, leading to peripheral vasodilation in arterial and venous smooth muscles.
- They cause less reflex tachycardia compared to non-selective blockers, and their use is common in pathologies such as benign prostatic hyperplasia (BPH) to improve urination/urine flow.
Drugs within this group include prazosin, doxazosin, and terazosin;
- Prazosin is a highly selective and reversible alpha₁ blocker, while doxazosin and terazosin have longer half-lives and allow for once-daily dosing.
Therapeutic uses
-
Severe hypertension (often in combination with other antihypertensive drugs).
-
Symptomatic treatment of urine obstruction (benign prostatic hyperplasia).
-
Side Effects
-
Orthostatic hypotension and syncope (low blood pressure when standing up; these effects are lessened by initially administering smaller doses or administration at bedtime).
Beta-Adrenergic Blocking Agents
- Drugs in this group block beta receptors.
Classification
- Non-selective beta-blockers (e.g., propranolol, timolol)
- Selective beta₁-blockers (e.g., atenolol, esmolol)
Propranolol
- Prototype beta-blocker.
- Possesses equal affinity for β₁ and β₂ receptors.
- High lipophilicity and local anesthetic properties.
- Pharmacokinetics of Propranolol*
- 70% of the drug is broken down in the liver in the first pass on its way from the gut to the general circulation.
- 30% reaches systemic circulation
- 90-95% binds to plasma proteins.
- Can cross the blood-brain barrier and is excreted through the urine.
- Pharmacological Actions of Propranolol*
- Heart (β₁)*
- Negative chronotropic (decreased heart rate)
- Negative inotropic (decreased contractility)
- Negative dromotropic (decreased conduction velocity)
- Reduced cardiac output
- Respiratory System (β₂)*
- Bronchoconstriction (a key adverse effect in susceptible patients)
- Eye*
- Topical beta-blockers used to reduce intraocular pressure (essential for treating open-angle glaucoma).
Therapeutic Uses
- Hypertension
- Angina pectoris
- Myocardial infarction
- Cardiac arrhythmias
- Hyperthyroidism
- Open-angle glaucoma
- Migraine
- Management of Familial tremors & anxiety
Adverse Effects
-
Beta₁ receptor blockade*
-
Negative inotropic or chronotropic effects
- Heart failure
- Bradycardia, Treated with atropine
- Heart block
-
Hypotension
-
Beta₂ receptor blockade*
-
Bronchospasm and asthma
-
Hypoglycemia (symptomless hypoglycemic coma)
-
Vasoconstriction
-
Sudden Withdrawal*
-
Exacerbation of angina
-
Tachycardia
-
Arrhythmias/Rebound hypertension
-
Gradual withdrawal is necessary.
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Description
Explore the intricacies of the sympathetic nervous system, including the functions of adrenergic receptors and the effects of sympathomimetics. This quiz covers various receptor subtypes and the application of adrenergic stimulants in medical scenarios. Test your knowledge on the pharmacology related to the sympathetic system.
