Pharmacology Autonomic Nervous System Agents 2 — Questions and Answers
Question 1: A patient on prazosin for hypertension reports dizziness when standing up quickly. What is the mechanism behind this adverse effect?
- Blockade of alpha-1 adrenergic receptors causing venous pooling (Correct answer)
- Stimulation of beta-2 receptors causing vasodilation
- Inhibition of ACE reducing angiotensin II
- Blockade of muscarinic receptors reducing heart rate
Correct answer: Blockade of alpha-1 adrenergic receptors causing venous pooling
Prazosin blocks alpha-1 receptors in peripheral vasculature, reducing vascular tone and causing orthostatic hypotension from venous pooling.
Question 2: Which cholinomimetic agent is used to reverse non-depolarizing neuromuscular blockade and acts by inhibiting acetylcholinesterase?
- Neostigmine (Correct answer)
- Pilocarpine
- Bethanechol
- Carbachol
Correct answer: Neostigmine
Neostigmine is a reversible acetylcholinesterase inhibitor used to reverse neuromuscular blockade by increasing ACh at the neuromuscular junction.
Question 3: A patient with pheochromocytoma is scheduled for surgery. Which drug class should be started FIRST to prevent hypertensive crisis during tumor manipulation?
- Alpha-blockers before beta-blockers (Correct answer)
- Beta-blockers before alpha-blockers
- Calcium channel blockers alone
- ACE inhibitors alone
Correct answer: Alpha-blockers before beta-blockers
Alpha-blockers (e.g., phenoxybenzamine) must be given before beta-blockers to prevent unopposed alpha-mediated vasoconstriction, which would worsen hypertension.
Question 4: Dobutamine is preferred over dopamine in cardiogenic shock primarily because it:
- Selectively increases cardiac contractility with less peripheral vasoconstriction (Correct answer)
- Activates dopaminergic receptors to increase renal blood flow
- Blocks alpha-1 receptors to reduce afterload
- Stimulates beta-2 receptors to cause bronchodilation
Correct answer: Selectively increases cardiac contractility with less peripheral vasoconstriction
Dobutamine predominantly stimulates beta-1 receptors, increasing contractility and cardiac output without the significant vasoconstriction seen with dopamine.
Question 5: Which antimuscarinic drug is preferred for treating bradycardia during surgery due to its minimal CNS penetration?
- Glycopyrrolate (Correct answer)
- Atropine
- Scopolamine
- Benztropine
Correct answer: Glycopyrrolate
Glycopyrrolate is a quaternary ammonium compound that does not cross the blood-brain barrier, making it preferred over atropine when CNS effects are undesirable.
Question 6: A patient taking a non-selective beta-blocker develops severe bronchospasm. Which adrenergic drug would be MOST appropriate to treat this?
- Epinephrine (Correct answer)
- Metoprolol
- Phenylephrine
- Clonidine
Correct answer: Epinephrine
Epinephrine activates both alpha and beta receptors; high doses can overcome beta-blocker competition at beta-2 receptors to relieve bronchospasm.
Question 7: Physostigmine differs from neostigmine in clinical use primarily because physostigmine:
- Crosses the blood-brain barrier and can reverse central anticholinergic syndrome (Correct answer)
- Is a quaternary amine with better peripheral selectivity
- Has a longer duration of action
- Is used exclusively to treat glaucoma
Correct answer: Crosses the blood-brain barrier and can reverse central anticholinergic syndrome
Physostigmine is a tertiary amine that crosses the blood-brain barrier, allowing it to reverse central anticholinergic toxicity (e.g., from antihistamines or tricyclics).
Pharmacology Autonomic Nervous System Agents 2
A patient on prazosin for hypertension reports dizziness when standing up quickly.
What is the mechanism behind this adverse effect?