Autonomic Nervous System Agents Flashcards

Organophosphate poisoning produces a toxidrome best remembered by the mnemonic SLUDGE. Which drug is the antidote that reverses muscarinic effects?

Answer: Atropine

Atropine competitively blocks muscarinic receptors, reversing SLUDGE symptoms (salivation, lacrimation, urination, defecation, GI distress, emesis) from organophosphate poisoning.

Milrinone is used in acute heart failure. Its mechanism differs from catecholamines because it:

Answer: Inhibits phosphodiesterase-3, preventing cAMP degradation without acting on adrenergic receptors

Milrinone is a PDE-3 inhibitor that prevents cAMP breakdown, increasing contractility and causing vasodilation independently of adrenergic receptor stimulation.

A patient on guanethidine for severe hypertension is also prescribed a tricyclic antidepressant. The expected interaction is:

Answer: Reduced antihypertensive effect because TCAs block neuronal uptake of guanethidine

Guanethidine requires uptake via the norepinephrine transporter (NET) to enter adrenergic neurons; TCAs block NET, preventing guanethidine's entry and abolishing its effect.

Which ganglion blocker was historically used for hypertensive emergencies but fell out of use primarily due to blocking BOTH sympathetic and parasympathetic ganglia?

Answer: Hexamethonium

Hexamethonium and similar ganglion blockers non-selectively block nicotinic receptors at all autonomic ganglia, causing unpredictable parasympathetic and sympathetic effects.

A patient with benign prostatic hyperplasia (BPH) is prescribed tamsulosin. Its benefit over prazosin is due to tamsulosin's selectivity for:

Answer: Alpha-1A receptors predominant in prostatic smooth muscle over vascular alpha-1B receptors

Tamsulosin's alpha-1A selectivity targets prostatic smooth muscle more than vascular smooth muscle (alpha-1B), reducing urinary obstruction with less orthostatic hypotension.

A patient develops tolerance to nitroglycerin after continuous use. This pharmacodynamic tolerance is primarily due to:

Answer: Depletion of sulfhydryl groups required for bioactivation to nitric oxide

Nitroglycerin requires thiol (sulfhydryl) groups to be converted to NO; continuous use depletes these groups, reducing the drug's vasodilatory effect.

Reserpine lowers blood pressure by which unique mechanism compared to other antihypertensive sympatholytics?

Answer: Irreversibly blocks VMAT2, depleting norepinephrine from sympathetic nerve terminals

Reserpine irreversibly inhibits vesicular monoamine transporter 2 (VMAT2), preventing NE storage in vesicles so it is degraded by MAO, depleting sympathetic neurotransmitter.