Study Notes: Autonomic Nervous System Medications

1. Sympathetic Nervous System (SNS) – Adrenergic Drugs

 “Fight or Flight” (↑HR, ↑BP, bronchodilation, ↓GI/GU activity)

a. Adrenergic Agonists (Sympathomimetics)

• Direct-acting

  • Epinephrine – nonselective α1, β1, β2 agonist → ↑HR, bronchodilation, vasoconstriction

  • Norepinephrine – α1, β1 agonist → vasoconstriction, ↑BP, mild ↑HR

  • Phenylephrine – α1 agonist → vasoconstriction, mydriasis (pupil dilation)

  • Dobutamine – β1 agonist → ↑contractility, ↑HR

  • Albuterol, Salbutamol – β2 agonists → bronchodilation

• Indirect-acting

  • Amphetamines – ↑NE release

  • Cocaine – inhibits NE reuptake

• Mixed-acting

  • Ephedrine, Pseudoephedrine – both direct receptor stimulation + increase NE release

b. Adrenergic Antagonists (Sympatholytics)

• Alpha-blockers

  • Prazosin, Doxazosin – α1 blockers → vasodilation, ↓BP

  • Phentolamine – nonselective α blocker → ↓vasoconstriction

• Beta-blockers

  • Propranolol – nonselective β1, β2 blocker → ↓HR, bronchoconstriction

  • Metoprolol, Atenolol – β1 selective blockers → ↓HR, ↓contractility

  • Labetalol, Carvedilol – α1 + β blockers → ↓BP, ↓HR

2. Parasympathetic Nervous System (PSNS) – Cholinergic Drugs

“Rest and Digest” (↓HR, ↑GI/GU activity, bronchoconstriction, ↑secretions)

a. Cholinergic Agonists (Parasympathomimetics)

• Direct-acting (muscarinic agonists)

  • Bethanechol – stimulates muscarinic receptors → ↑urination, ↑GI motility

  • Pilocarpine – muscarinic agonist → ↑salivation, miosis (pupil constriction)

• Indirect-acting (acetylcholinesterase inhibitors)

  • Neostigmine, Pyridostigmine – inhibit AChE → ↑ACh at synapse, used in myasthenia gravis

  • Physostigmine – crosses BBB → used in atropine overdose

  • Donepezil, Rivastigmine – ↑ACh in CNS → Alzheimer’s treatment

b. Cholinergic Antagonists (Antimuscarinics / Parasympatholytics)

• Muscarinic blockers

  • Atropine – blocks muscarinic receptors → ↑HR, ↓secretions, mydriasis

  • Scopolamine – ↓motion sickness, sedation

  • Ipratropium, Tiotropium – bronchodilation in COPD/asthma

  • Oxybutynin, Tolterodine – ↓bladder spasms, urinary frequency

• Nicotinic blockers (neuromuscular blockers)

  • Succinylcholine – depolarizing NMJ blocker → muscle paralysis (short-acting)

  • Rocuronium, Vecuronium – non-depolarizing NMJ blockers → muscle relaxation in anesthesia

Quick Mnemonics

• SNS agonists = “-ine” (epi, norepi, dopamine, phenylephrine) / “-ol” for β2 agonists (albuterol, salbutamol)

• SNS antagonists = “-osin” (α-blockers), “-lol” (β-blockers)

• PSNS agonists = “choline” or AChE inhibitors (“-stigmine”, donepezil)

• PSNS antagonists = atropine-like (muscarinic blockers), “-ium” for NMJ blockers