Autonomic Nervous System Agents Flashcards

A patient on tyramine-rich foods while taking a MAO inhibitor experiences severe hypertension. Which mechanism explains this interaction?

Answer: Tyramine displaces NE from vesicles and MAO-A inhibition prevents its degradation, flooding synapses

Normally, gut and liver MAO degrades tyramine before it enters circulation; when inhibited, tyramine triggers massive norepinephrine release causing hypertensive crisis.

Phenylephrine is used in ophthalmic procedures to dilate the pupil. The mydriasis it causes is mediated by:

Answer: Stimulation of alpha-1 receptors on the iris dilator muscle

Phenylephrine activates alpha-1 adrenergic receptors on the radial dilator muscle of the iris, causing pupil dilation without cycloplegia.

A patient taking labetalol for hypertension is also using salbutamol for asthma. What interaction should the pharmacist warn about?

Answer: Labetalol's non-selective beta-blockade may blunt salbutamol's bronchodilatory effect

Labetalol blocks both alpha and beta receptors; its non-selective beta antagonism can competitively inhibit salbutamol (a beta-2 agonist) at bronchial receptors.

Succinylcholine causes prolonged paralysis in patients with pseudocholinesterase deficiency. This is because succinylcholine is normally:

Answer: Hydrolyzed rapidly by plasma pseudocholinesterase (butyrylcholinesterase)

Succinylcholine is normally rapidly hydrolyzed by plasma pseudocholinesterase; genetic deficiency prolongs neuromuscular blockade from minutes to hours.

Which adrenergic receptor subtype, when stimulated, mediates relaxation of bronchial smooth muscle and is the target of albuterol?

Answer: Beta-2

Beta-2 receptors in bronchial smooth muscle activate adenylyl cyclase, increasing cAMP and causing relaxation; albuterol is a selective beta-2 agonist.

A patient with Raynaud's disease would most benefit from which drug targeting the peripheral vasculature?

Answer: Prazosin (alpha-1 blocker) to reduce vasospasm

Raynaud's disease involves excessive alpha-1-mediated vasospasm; prazosin blocks these receptors, reducing digital vasospasm and improving blood flow.

Tropicamide is used as a short-acting mydriatic. Its mechanism involves blocking which receptor, resulting in both mydriasis and cycloplegia?

Answer: Muscarinic M3 receptors on iris sphincter and ciliary muscle

Tropicamide blocks M3 muscarinic receptors, preventing ACh from contracting the iris sphincter (causing mydriasis) and ciliary muscle (causing cycloplegia).