A 43-year-old man is brought to the emergency department 45 minutes after his wife found him on the floor sweating profusely. On arrival, he is lethargic and unable to provide a history. He vomited multiple times on the way to the hospital. His temperature is 37.3°C (99.1°F), pulse is 55/min, respirations are 22/min, and blood pressure is 98/65 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 80%. Examination shows profuse diaphoresis and excessive salivation. He withdraws his extremities sluggishly to pain. The pupils are constricted and reactive. Scattered expiratory wheezing and rhonchi are heard throughout both lung fields. Cardiac examination shows no abnormalities. There are fine fasciculations in the lower extremities bilaterally. Muscle strength is reduced and deep tendon reflexes are 1+ bilaterally. His clothes are soaked with urine and feces. Which of the following is the mechanism of action of the most appropriate initial pharmacotherapy?

Competitive antagonism of mACh receptors

Non-selective α-adrenergic antagonism

An investigator is studying a local anesthetic that causes increased sympathetic activity. When given intravenously, it causes euphoria and pupillary dilation. Which of the following is the most likely effect of this drug at the synaptic cleft?

Decreased reuptake of norepinephrine

Increased release of norepinephrine

Decreased release of acetylcholine

Decreased breakdown of norepinephrine

You have been asked to deliver a lecture to medical students about the effects of various body hormones and neurotransmitters on the metabolism of glucose. Which of the following statements best describes the effects of sympathetic stimulation on glucose metabolism?

Epinephrine increases liver glycogenolysis.

Norepinephrine causes increased glucose absorption within the intestines.

Without epinephrine, insulin cannot act on the liver.

Peripheral tissues require epinephrine to take up glucose.

Sympathetic stimulation to alpha receptors of the pancreas increases insulin release.

A 19-year-old woman is brought to the emergency room by her mother. She found her daughter pale, cold to the touch, and collapsed next to her bed earlier this morning. The patient has no previous medical or psychiatric history, but the mother does report that her daughter has not had her periods for the last 3 months. In the emergency department, the patient is alert and oriented. Her vitals include: blood pressure 80/60 mm Hg supine, heart rate 55/min. On physical examination, the patient appears pale and emaciated. A urine pregnancy test is negative. She is suspected of having an eating disorder. Which of the following treatment options would be contraindicated in this patient?

Selective serotonin reuptake inhibitors

A 57-year-old man is brought to the emergency department by his son for odd behavior. The patient and his son had planned to go on a hike today. On the drive up to the mountain, the patient began acting strangely which prompted the patient's son to bring him in. The patient has a past medical history of constipation, seasonal allergies, alcohol abuse, and IV drug abuse. His current medications include diphenhydramine, metoprolol, and disulfiram. The patient's son states he has been with the patient all morning and has only seen him take his over the counter medications and eat breakfast. His temperature is 102.0°F (38.9°C), blood pressure is 147/102 mmHg, pulse is 110/min, and oxygen saturation is 98% on room air. The patient appears uncomfortable. Physical exam is notable for tachycardia. The patient's skin appears dry, red, and flushed, and he is confused and not responding to questions appropriately. Which of the following is the best treatment for this patient's condition?

IV fluids, thiamine, and dextrose

Clinical applications in autonomic disorders for USMLE Step 3: High-Yield Pharmacology Lessons

ANS Overview - The Body's Wiring

Sympathetic (SNS): Thoracolumbar (T1-L2) origin. Short preganglionic, long postganglionic fibers. "Fight or flight."
Parasympathetic (PNS): Craniosacral (CN III, VII, IX, X; S2-S4) origin. Long preganglionic, short postganglionic fibers. "Rest and digest."

⭐ The adrenal medulla is a modified sympathetic ganglion; preganglionic fibers release ACh, stimulating chromaffin cells to secrete epinephrine (80%) and norepinephrine (20%) into blood.

Sympathetic Nervous System: Anatomy & Neurotransmitters

Cholinergic Agonists - Rest & Digest Boosters

Mechanism: Mimic acetylcholine (ACh) to activate parasympathetic responses.

Type	Drugs & Uses	Mechanism
Direct	Bethanechol: Post-op urinary retention Pilocarpine: Glaucoma, xerostomia	Bind muscarinic receptors
Indirect	Neostigmine/Pyridostigmine: Myasthenia gravis Physostigmine: Anticholinergic toxicity Donepezil: Alzheimer's disease	Inhibit acetylcholinesterase (↑ACh)

⭐ Physostigmine reverses CNS and peripheral effects of anticholinergic toxicity (e.g., atropine overdose) as it crosses the blood-brain barrier.

Cholinergic Antagonists - Blocking Parasympathetic

Mechanism: Competitively block muscarinic receptors (anticholinergics).
Key Drugs & Uses:
- Atropine: Treats bradycardia, antidote for cholinesterase inhibitor poisoning.
- Ipratropium/Tiotropium: Inhaled for COPD & asthma; ↓ bronchoconstriction & secretions.
- Scopolamine: Prophylaxis for motion sickness.
- Benztropine, Trihexyphenidyl: Treat Parkinson's disease & drug-induced extrapyramidal symptoms.
Toxicity: Presents as anticholinergic syndrome.
- 📌 Mnemonic: "Blind as a bat (mydriasis), Mad as a hatter (delirium), Red as a beet (flushing), Hot as a hare (hyperthermia), Dry as a bone (anhidrosis)."

⭐ Antidote: Physostigmine, a cholinesterase inhibitor that can cross the blood-brain barrier, is used to reverse central and peripheral toxicity.

Adrenergic Agonists - Fight-or-Flight Fuel

Direct-Acting: Bind directly to receptors.
- Epinephrine: Anaphylaxis, cardiac arrest (broad α & β effects).
- Norepinephrine: Septic shock (α1 > β1).
- Dobutamine: Cardiogenic shock, acute HF (β1).
- Phenylephrine: Decongestant, hypotension (α1).
- Albuterol, Terbutaline: Asthma (β2).
Indirect/Mixed: ↑ NE release (Amphetamine) or ↓ reuptake (Cocaine); Ephedrine (mixed).

⭐ Dopamine's effects are dose-dependent: low dose targets D1 receptors for renal perfusion; medium dose hits β1 for heart contractility; high dose activates α1 causing vasoconstriction.

Adrenergic Antagonists - Pumping the Brakes

α-Blockers: Relax smooth muscle. Used for BPH (Tamsulosin) & pheochromocytoma (Phenoxybenzamine). Risk: orthostatic hypotension.
β-Blockers: Decrease cardiac output & renin. Used for hypertension, angina, post-MI, & heart failure. 📌 Mnemonic: A-M names (Atenolol, Metoprolol) are β1-selective; N-Z (Nadolol, Propranolol) are non-selective.

⭐ In cocaine toxicity, avoid pure β-blockers (e.g., propranolol) due to risk of unopposed α-adrenergic receptor stimulation, causing extreme hypertension.

High-Yield Points - ⚡ Biggest Takeaways

Bethanechol is for non-obstructive urinary retention and postoperative ileus.

Pilocarpine treats glaucoma and Sjögren's syndrome by increasing secretions.

Pyridostigmine is the mainstay for Myasthenia Gravis long-term treatment.

Atropine is critical for treating bradycardia and organophosphate poisoning.

Dobutamine is a key inotropic agent for acute heart failure and cardiogenic shock.

Phenylephrine is a pure α-agonist used for septic shock and as a decongestant.

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