Medical School · Year 2 · Pharmacology · includes a quiz and discussion video

Lecture 03: Autonomic Pharmacology

Unit 2.12: Pharmacology

Learning Objectives

By the end of this lecture, students will be able to:

1. Describe the organization and neurotransmitters of the autonomic nervous system
2. Explain cholinergic agonists and antagonists
3. Describe adrenergic agonists and their clinical uses
4. Explain adrenergic antagonists and their applications
5. Describe drugs affecting autonomic ganglia
6. Explain the clinical applications of autonomic drugs

Lecture Outline

I. Autonomic Nervous System Overview

The autonomic nervous system (ANS) regulates involuntary physiological functions throughout the body, maintaining homeostasis without conscious control. This system is divided into three primary divisions: the sympathetic nervous system, which mediates the "fight or flight" response during stress or danger; the parasympathetic nervous system, which promotes "rest and digest" functions during relaxation; and the enteric nervous system, which independently controls gastrointestinal function. Understanding the organization and function of the ANS is fundamental to autonomic pharmacology, as most autonomic drugs either mimic or block the effects of these divisions. The balance between sympathetic and parasympathetic activity determines the functional state of most organ systems at any given moment.

The anatomic organization of the sympathetic and parasympathetic divisions differs significantly, with important pharmacological implications. Sympathetic preganglionic neurons originate from the thoracolumbar spinal cord segments T1 through L2, with short preganglionic fibers synapsing in the paravertebral sympathetic chain ganglia and long postganglionic fibers extending to target organs. Parasympathetic preganglionic neurons arise from cranial nerves III, VII, IX, and X, and sacral segments S2 through S4, with long preganglionic fibers synapsing in ganglia located near or within target organs and short postganglionic fibers. This anatomic difference means parasympathetic effects tend to be more localized while sympathetic activation produces more diffuse, body-wide responses. The adrenal medulla represents a specialized sympathetic structure that releases catecholamines directly into the bloodstream, functioning as modified postganglionic neurons.

Neurotransmitter identity varies by location within the autonomic nervous system and determines receptor targets for pharmacological intervention. All autonomic preganglionic neurons, both sympathetic and parasympathetic, release acetylcholine (ACh) that acts on nicotinic receptors at the ganglia. Parasympathetic postganglionic neurons also release ACh, which acts on muscarinic receptors at target organs. Most sympathetic postganglionic neurons release norepinephrine (NE), which acts on adrenergic receptors, with the important exception of sympathetic neurons innervating sweat glands, which release ACh acting on muscarinic receptors. The adrenal medulla releases primarily epinephrine (80%) and norepinephrine (20%) directly into the circulation, providing hormonal supplementation to sympathetic neural activity.

Autonomic receptors fall into two major families: cholinergic receptors responding to acetylcholine and adrenergic receptors responding to norepinephrine and epinephrine. Cholinergic receptors include nicotinic receptors, which are ligand-gated ion channels found at autonomic ganglia (Nn) and the neuromuscular junction (Nm), and muscarinic receptors, which are G protein-coupled receptors with five subtypes (M1 through M5) found at parasympathetic effector organs and sympathetic sweat glands. Adrenergic receptors are G protein-coupled and include alpha receptors (alpha-1 and alpha-2) and beta receptors (beta-1, beta-2, and beta-3), each with distinct tissue distributions and effects. The specific receptor subtype activated determines the cellular response, making receptor selectivity a crucial consideration in autonomic drug development and clinical use.

<image>Panel A: Schematic diagram comparing sympathetic and parasympathetic pathways showing thoracolumbar origin with paravertebral ganglia for sympathetic versus craniosacral origin with terminal ganglia for parasympathetic, including relative fiber lengths and target organ connections. Panel B: Neurotransmitter diagram showing acetylcholine release at all preganglionic synapses (nicotinic receptors), acetylcholine at parasympathetic postganglionic synapses (muscarinic receptors), and norepinephrine at sympathetic postganglionic synapses (adrenergic receptors), with sweat glands as the cholinergic exception. Panel C: Adrenal medulla illustration showing modified postganglionic sympathetic neuron releasing epinephrine (80%) and norepinephrine (20%) directly into bloodstream for systemic distribution. Panel D: Receptor family tree showing cholinergic receptors (nicotinic Nn, Nm and muscarinic M1-M5) and adrenergic receptors (alpha-1, alpha-2, beta-1, beta-2, beta-3) with primary locations and coupled signaling pathways.</image>

II. Cholinergic Receptors

Nicotinic receptors are ligand-gated ion channels that mediate fast synaptic transmission at several critical sites within the nervous system. These pentameric receptors consist of five subunits surrounding a central ion pore that opens upon acetylcholine binding, allowing sodium influx and membrane depolarization. Nicotinic receptors at the neuromuscular junction (Nm) contain two alpha-1 and one each of beta, delta, and epsilon subunits, and their activation triggers skeletal muscle contraction. Neuronal nicotinic receptors (Nn) found at autonomic ganglia and in the central nervous system have different subunit compositions, typically containing alpha-3 and beta-4 subunits in ganglia. The rapid response time of nicotinic receptors, on the order of milliseconds, enables precise temporal control of neural transmission and muscle activation.

Muscarinic receptors are G protein-coupled receptors that mediate the effects of parasympathetic stimulation at effector organs and produce slower, modulatory responses compared to nicotinic receptors. Five muscarinic receptor subtypes (M1 through M5) have been identified, coupled to different G proteins and producing distinct cellular effects. M1 receptors couple through Gq to increase IP3, DAG, and intracellular calcium, located predominantly in the central nervous system where they modulate cognition and in gastric parietal cells where they stimulate acid secretion. M2 receptors couple through Gi to decrease cAMP and are the primary cardiac muscarinic subtype, mediating the vagal effects of decreased heart rate and slowed AV conduction. M3 receptors also couple through Gq and are found on smooth muscle and glands, producing smooth muscle contraction and increased glandular secretion. M4 and M5 receptors are found primarily in the CNS and have less well-defined physiological roles.

Parasympathetic activation through muscarinic receptors produces characteristic effects on multiple organ systems that oppose sympathetic activation. In the heart, M2 receptor activation decreases heart rate (negative chronotropy) and slows conduction through the AV node (negative dromotropy). In the eye, muscarinic activation causes pupillary constriction (miosis) through contraction of the circular pupillary sphincter muscle and accommodation for near vision through ciliary muscle contraction. Gastrointestinal effects include increased motility and secretions that promote digestion. Respiratory effects include bronchoconstriction and increased bronchial secretions. Bladder parasympathetic activation contracts the detrusor muscle while relaxing the internal sphincter, promoting urination. Exocrine glands including salivary, lacrimal, and sweat glands increase secretion in response to muscarinic stimulation.

Acetylcholine synthesis, storage, release, and degradation follow a regulated cycle that is targeted by various pharmacological agents. Acetylcholine is synthesized in the nerve terminal from choline and acetyl-CoA by the enzyme choline acetyltransferase (ChAT), with choline availability being the rate-limiting factor. Synthesized acetylcholine is transported into synaptic vesicles by the vesicular acetylcholine transporter (VAChT) for storage until release. Calcium-dependent exocytosis releases acetylcholine into the synaptic cleft upon nerve stimulation, where it diffuses to bind postsynaptic receptors. Signal termination occurs primarily through hydrolysis by acetylcholinesterase (AChE) in the synaptic cleft, cleaving acetylcholine into choline and acetate within milliseconds. The released choline is efficiently recycled via a high-affinity choline transporter back into the nerve terminal for resynthesis, making this transporter a potential pharmacological target.

<image>Panel A: Nicotinic receptor structure showing pentameric arrangement of subunits around central ion pore, acetylcholine binding sites at alpha-subunit interfaces, and sodium ion flow through open channel causing depolarization. Panel B: Muscarinic receptor signaling comparison showing M1/M3/M5 coupling through Gq to phospholipase C generating IP3 and DAG, versus M2/M4 coupling through Gi to inhibit adenylyl cyclase and decrease cAMP. Panel C: Organ system diagram showing parasympathetic effects mediated by muscarinic receptors: heart (M2, decreased rate), eye (M3, miosis), GI tract (M3, increased motility), airways (M3, bronchoconstriction), bladder (M3, contraction), and glands (M3, secretion). Panel D: Cholinergic nerve terminal showing acetylcholine synthesis from choline and acetyl-CoA by ChAT, vesicular storage, calcium-dependent release, receptor binding, AChE hydrolysis in synaptic cleft, and choline reuptake for recycling.</image>

III. Cholinergic Agonists

Direct-acting cholinergic agonists bind to and activate muscarinic or nicotinic receptors, producing effects similar to acetylcholine but often with improved selectivity or pharmacokinetic properties. Bethanechol is a selective muscarinic agonist resistant to acetylcholinesterase, used to stimulate bladder contraction in urinary retention and promote gastrointestinal motility in postoperative ileus. Carbachol activates both muscarinic and nicotinic receptors and is used topically in ophthalmology to produce miosis and reduce intraocular pressure in glaucoma. Pilocarpine is a naturally occurring muscarinic agonist used topically for glaucoma and orally to stimulate salivary secretion in patients with xerostomia from Sjogren syndrome or radiation therapy. Methacholine is used diagnostically in bronchial provocation testing to assess airway hyperreactivity, with asthmatic patients showing bronchoconstriction at lower doses than normal individuals.

Indirect-acting cholinergic agonists, also known as acetylcholinesterase inhibitors, enhance cholinergic transmission by preventing the breakdown of endogenous acetylcholine in the synaptic cleft. Edrophonium is an ultra-short-acting reversible inhibitor used historically in the Tensilon test for diagnosing myasthenia gravis, with improvement in muscle weakness after injection supporting the diagnosis. Neostigmine is a short-acting quaternary amine that does not cross the blood-brain barrier, used to reverse non-depolarizing neuromuscular blockade after surgery and as chronic therapy for myasthenia gravis. Pyridostigmine has intermediate duration and is the mainstay of symptomatic treatment for myasthenia gravis, improving muscle strength by prolonging acetylcholine action at the neuromuscular junction. Physostigmine is a tertiary amine that crosses the blood-brain barrier and is the specific antidote for central anticholinergic toxicity, reversing both peripheral and central effects.

Irreversible acetylcholinesterase inhibitors form covalent bonds with the enzyme, producing prolonged inhibition that persists until new enzyme is synthesized. Organophosphate compounds, including certain insecticides (malathion, parathion) and nerve agents (sarin, soman, VX), phosphorylate the serine residue at the active site of acetylcholinesterase, producing potentially lethal cholinergic crisis. Echothiophate is an organophosphate previously used topically for glaucoma but now largely obsolete due to the development of safer alternatives. The toxicity of irreversible inhibitors presents as cholinergic crisis with the mnemonic SLUDGE (Salivation, Lacrimation, Urination, Defecation, GI distress, Emesis) plus bradycardia, bronchospasm, and potential respiratory failure. Treatment of organophosphate poisoning includes the muscarinic antagonist atropine to block peripheral and central muscarinic effects, and pralidoxime to reactivate acetylcholinesterase if administered before the enzyme-inhibitor complex undergoes "aging."

The SLUDGE mnemonic captures the muscarinic manifestations of cholinergic excess, while additional nicotinic effects complete the clinical picture. Salivation reflects excessive muscarinic stimulation of salivary glands, producing profuse watery secretions that may threaten the airway. Lacrimation indicates increased tear production from lacrimal gland stimulation. Urination results from detrusor muscle contraction and sphincter relaxation, causing urinary incontinence. Defecation occurs from increased gastrointestinal motility and secretions combined with anal sphincter relaxation. GI distress includes abdominal cramping from smooth muscle spasm. Emesis results from combined central and peripheral cholinergic effects on the vomiting center and gastrointestinal tract. Beyond SLUDGE, nicotinic effects at the neuromuscular junction cause muscle fasciculations followed by paralysis, while nicotinic effects at autonomic ganglia can produce tachycardia and hypertension that may initially mask the muscarinic bradycardia.

<image>Panel A: Direct cholinergic agonist structures and receptor selectivity showing bethanechol (muscarinic selective, resistant to AChE), carbachol (muscarinic and nicotinic), and pilocarpine (muscarinic), with primary clinical applications for each. Panel B: Acetylcholinesterase inhibitor mechanism showing reversible inhibitors (edrophonium, neostigmine, physostigmine) blocking active site temporarily versus irreversible organophosphate forming covalent bond with serine residue. Panel C: Clinical applications of cholinesterase inhibitors showing myasthenia gravis treatment (pyridostigmine increasing ACh at NMJ), neuromuscular blockade reversal (neostigmine), and Alzheimer disease (donepezil in CNS). Panel D: SLUDGE and cholinergic crisis diagram showing salivation, lacrimation, urination, defecation, GI distress, emesis as muscarinic effects, plus nicotinic effects of muscle fasciculations/paralysis and autonomic instability, with treatment algorithm including atropine and pralidoxime.</image>

IV. Cholinergic Antagonists (Antimuscarinics)

Atropine is the prototypical muscarinic antagonist, derived from the deadly nightshade plant (Atropa belladonna), and produces competitive blockade of all muscarinic receptor subtypes. Cardiac effects of atropine result from M2 receptor blockade, removing vagal tone and producing tachycardia, which is clinically useful for treating symptomatic bradycardia. Ophthalmic effects include mydriasis (pupil dilation) from blockade of the pupillary sphincter muscle and cycloplegia (loss of accommodation) from ciliary muscle paralysis, useful for fundoscopic examination but causing photophobia and blurred near vision. Atropine markedly decreases secretions from salivary, bronchial, and sweat glands, useful as preoperative medication to reduce airway secretions. Gastrointestinal effects include decreased motility and reduced acid secretion, though more selective agents are now preferred for peptic ulcer disease. Atropine is the primary antidote for muscarinic manifestations of cholinergic toxicity from organophosphate or carbamate poisoning.

Other antimuscarinic agents have been developed with improved selectivity or pharmacokinetic properties for specific clinical applications. Scopolamine (hyoscine) has greater CNS penetration than atropine and is used transdermally for motion sickness prophylaxis, taking advantage of its vestibular suppressant effects. Ipratropium bromide is a quaternary ammonium compound that does not cross the blood-brain barrier and is delivered by inhalation, producing local bronchodilation without systemic anticholinergic effects for COPD and asthma treatment. Tiotropium is a long-acting inhaled antimuscarinic with sustained bronchodilatory effect, suitable for once-daily maintenance therapy in COPD. Oxybutynin and tolterodine are used for overactive bladder, blocking M3 receptors in the detrusor muscle to reduce urinary urgency and frequency. Benztropine and trihexyphenidyl are centrally acting antimuscarinics used in Parkinson disease to restore cholinergic-dopaminergic balance in the basal ganglia. Tropicamide is a short-acting mydriatic agent used for routine ophthalmologic examination.

Anticholinergic toxicity produces a characteristic syndrome that can be remembered with the mnemonic describing patients as "hot as a hare, dry as a bone, red as a beet, blind as a bat, and mad as a hatter." Hyperthermia develops because sweat glands are sympathetically innervated but cholinergically controlled, so muscarinic blockade prevents sweating and impairs thermoregulation; patients feel hot and may develop dangerous hyperpyrexia. Dryness affects all secretory surfaces, with xerostomia (dry mouth), decreased bronchial secretions, and anhidrosis (absent sweating) being prominent features. Cutaneous vasodilation produces flushed, red skin, particularly notable in the face and trunk. Visual disturbance results from both mydriasis causing photophobia and cycloplegia causing inability to accommodate for near vision. Central nervous system effects range from agitation and restlessness to confusion, hallucinations, and frank delirium, particularly in elderly patients who are more susceptible to anticholinergic cognitive effects.

Neuromuscular blocking agents act at nicotinic receptors at the neuromuscular junction to produce skeletal muscle paralysis, essential for surgical procedures and mechanical ventilation. Succinylcholine is a depolarizing neuromuscular blocker that initially activates the nicotinic receptor, causing transient fasciculations, followed by persistent depolarization and receptor desensitization that prevents further activation. Its ultra-short duration (5-10 minutes) due to rapid plasma cholinesterase metabolism makes it valuable for rapid sequence intubation, though it carries risks of hyperkalemia in susceptible patients and malignant hyperthermia in genetically predisposed individuals. Non-depolarizing neuromuscular blockers including rocuronium, vecuronium, and cisatracurium competitively block nicotinic receptors without activating them, producing paralysis without fasciculations. These agents are reversed by acetylcholinesterase inhibitors (neostigmine) that increase acetylcholine to overcome the competitive blockade, or by sugammadex, which directly encapsulates and inactivates rocuronium and vecuronium.

<image>Panel A: Atropine mechanism and effects showing competitive binding at muscarinic receptor, with organ-by-organ effects: heart (tachycardia via M2 block), eye (mydriasis and cycloplegia), secretory glands (decreased secretions), and GI tract (decreased motility). Panel B: Clinical antimuscarinic agents showing inhaled agents (ipratropium, tiotropium) for airways, bladder-selective agents (oxybutynin) for overactive bladder, and CNS-penetrating agents (benztropine) for Parkinson disease. Panel C: Anticholinergic toxicity mnemonic illustrated with patient showing hyperthermia (no sweating), dry skin and mucous membranes, flushed red skin, dilated pupils with photophobia, and agitated/delirious behavior. Panel D: Neuromuscular junction showing depolarizing blocker (succinylcholine) binding and causing initial depolarization then desensitization versus non-depolarizing blocker (rocuronium) competitively blocking without activation, with reversal agents neostigmine and sugammadex.</image>

V. Adrenergic Receptors

Adrenergic receptors mediate the effects of endogenous catecholamines norepinephrine and epinephrine, and are classified into alpha and beta subtypes based on pharmacological response profiles. Alpha-1 receptors couple through Gq to activate phospholipase C, increasing IP3, DAG, and intracellular calcium, producing smooth muscle contraction. Alpha-2 receptors couple through Gi to inhibit adenylyl cyclase and decrease cAMP, with important presynaptic autoreceptor function that provides negative feedback on norepinephrine release. Beta-1, beta-2, and beta-3 receptors all couple through Gs to activate adenylyl cyclase and increase cAMP, but differ in their tissue distribution and physiological effects. This receptor classification has profound clinical implications, as drugs with selectivity for specific subtypes can produce therapeutic effects while minimizing adverse effects mediated by other subtypes.

The tissue distribution of adrenergic receptor subtypes determines the physiological effects of sympathetic activation and the therapeutic applications of adrenergic drugs. Alpha-1 receptors on vascular smooth muscle mediate vasoconstriction, increasing peripheral resistance and blood pressure; they also mediate contraction of the radial muscle of the iris causing mydriasis and contraction of prostatic smooth muscle relevant to benign prostatic hyperplasia. Alpha-2 receptors on presynaptic nerve terminals reduce norepinephrine release when activated, serving as an inhibitory feedback mechanism; central alpha-2 receptors in the brainstem reduce sympathetic outflow when stimulated. Beta-1 receptors predominate in the heart, where they increase heart rate (positive chronotropy), increase contractility (positive inotropy), and enhance conduction velocity (positive dromotropy); they also stimulate renin release from juxtaglomerular cells. Beta-2 receptors on bronchial smooth muscle cause bronchodilation and on vascular smooth muscle cause vasodilation; they also relax uterine smooth muscle and stimulate skeletal muscle potassium uptake. Beta-3 receptors in adipose tissue stimulate lipolysis and in the bladder produce detrusor relaxation.

Sympathetic activation produces the integrated "fight or flight" response through coordinated effects on multiple organ systems mediated by these receptor subtypes. Cardiac effects include increased heart rate, increased contractility, and enhanced conduction, preparing the cardiovascular system to deliver oxygen to skeletal muscles. Blood vessel effects depend on the receptor population: alpha-1-predominant beds (skin, splanchnic circulation) vasoconstrict to redistribute blood, while beta-2-predominant beds (skeletal muscle) vasodilate to increase flow to exercising muscles. Bronchial smooth muscle relaxation (beta-2) increases airway diameter and facilitates ventilation. Pupillary dilation (alpha-1) increases light entry and peripheral vision. Gastrointestinal motility decreases as blood is shunted away from digestive functions. Hepatic glycogenolysis (beta-2) mobilizes glucose for energy. Sweat gland activation, though mediated by acetylcholine at muscarinic receptors rather than catecholamines, is sympathetically controlled and increases to facilitate heat dissipation.

Catecholamine synthesis proceeds through a series of enzymatic steps from the amino acid tyrosine to produce dopamine, norepinephrine, and epinephrine. Tyrosine is hydroxylated by tyrosine hydroxylase (TH) to form L-DOPA, which is the rate-limiting step in catecholamine synthesis and subject to feedback inhibition by catecholamine products. L-DOPA is decarboxylated by aromatic L-amino acid decarboxylase (DOPA decarboxylase) to form dopamine, which is the final product in dopaminergic neurons. Dopamine is hydroxylated within synaptic vesicles by dopamine beta-hydroxylase (DBH) to form norepinephrine, which is the primary neurotransmitter of postganglionic sympathetic neurons. In the adrenal medulla and certain CNS neurons, norepinephrine is N-methylated by phenylethanolamine N-methyltransferase (PNMT) to form epinephrine, with glucocorticoids from the adjacent adrenal cortex inducing PNMT expression. Understanding this pathway identifies targets for pharmacological intervention and explains drug effects and interactions.

<image>Panel A: Adrenergic receptor signaling pathways showing alpha-1 coupling through Gq to PLC generating IP3/DAG and calcium release, alpha-2 coupling through Gi to decrease cAMP, and beta receptors (1, 2, 3) coupling through Gs to increase cAMP via adenylyl cyclase. Panel B: Receptor distribution map showing alpha-1 on vascular smooth muscle, eye radial muscle, and prostate; alpha-2 on presynaptic terminals and brainstem; beta-1 on heart and kidney JG cells; beta-2 on bronchi, blood vessels, and uterus; beta-3 on adipose and bladder. Panel C: Integrated sympathetic "fight or flight" response diagram showing coordinated effects: increased cardiac output, redistributed blood flow, bronchodilation, pupil dilation, glucose mobilization, and sweating. Panel D: Catecholamine synthesis pathway from tyrosine through L-DOPA (tyrosine hydroxylase, rate-limiting), dopamine (DOPA decarboxylase), norepinephrine (dopamine beta-hydroxylase), to epinephrine (PNMT in adrenal medulla), with relevant pharmacological targets indicated.</image>

VI. Adrenergic Agonists

Direct-acting adrenergic agonists bind directly to adrenergic receptors and are classified by their receptor selectivity profiles, which determine their clinical applications and adverse effect profiles. Epinephrine activates all alpha and beta receptors and is the drug of choice for anaphylaxis, where it reverses bronchospasm (beta-2), improves blood pressure (alpha-1 vasoconstriction and beta-1 cardiac stimulation), and reduces mucosal edema (alpha-1 vasoconstriction); it is also used in cardiac arrest and combined with local anesthetics to prolong duration via local vasoconstriction. Norepinephrine has potent alpha-1 and alpha-2 activity plus beta-1 effects but minimal beta-2 activity, making it a powerful vasoconstrictor used for septic shock to restore blood pressure and organ perfusion. Phenylephrine is a selective alpha-1 agonist that produces vasoconstriction without cardiac stimulation, used as a nasal decongestant, mydriatic, and vasopressor in anesthesia-induced hypotension. Dobutamine is primarily a beta-1 agonist with some beta-2 and alpha-1 activity, used for inotropic support in acute decompensated heart failure and cardiogenic shock where it increases cardiac output with relatively less effect on vascular resistance.

Beta-2 selective agonists are critical in respiratory pharmacology for their bronchodilatory effects with minimal cardiac stimulation. Albuterol (salbutamol) is the most widely used short-acting beta-2 agonist (SABA) for acute relief of bronchospasm in asthma and COPD, typically administered by metered-dose inhaler or nebulizer to maximize local effect and minimize systemic absorption. Levalbuterol is the R-enantiomer of albuterol with potentially fewer side effects due to exclusion of the S-enantiomer. Terbutaline is a beta-2 agonist available in subcutaneous form for severe acute asthma and formerly used as a tocolytic to inhibit premature labor, though this use has declined due to cardiovascular risks. Salmeterol and formoterol are long-acting beta-2 agonists (LABAs) used for maintenance therapy in asthma and COPD, always in combination with inhaled corticosteroids for asthma due to safety concerns with LABA monotherapy.

Indirect-acting sympathomimetics do not bind directly to adrenergic receptors but instead increase norepinephrine availability in the synapse through various mechanisms. Amphetamine and methamphetamine are released into the presynaptic terminal by the norepinephrine transporter running in reverse, then displace norepinephrine from vesicles, producing massive catecholamine release; they are used therapeutically for ADHD and narcolepsy but have high abuse potential. Cocaine blocks the norepinephrine transporter (NET), serotonin transporter (SERT), and dopamine transporter (DAT), preventing reuptake and prolonging catecholamine action; its local anesthetic properties were historically exploited but systemic cardiovascular toxicity limits medical use. Tyramine, found in aged cheeses, fermented foods, and red wine, is normally metabolized by monoamine oxidase (MAO) in the gut and liver but can precipitate hypertensive crisis in patients taking MAO inhibitors by releasing stored norepinephrine. Mixed-acting sympathomimetics like ephedrine and pseudoephedrine combine direct receptor activation with norepinephrine release, used as decongestants but with cardiovascular stimulant effects that limit use in hypertensive patients.

The cardiovascular effects of adrenergic agonists differ based on their receptor selectivity profiles and demonstrate important physiological principles. Low-dose epinephrine predominantly activates beta-2 receptors in vascular beds, producing vasodilation and decreased peripheral resistance while beta-1 effects increase heart rate and contractility; the net effect is increased cardiac output with maintained or slightly decreased blood pressure. High-dose epinephrine recruits alpha-1 receptors, producing vasoconstriction that increases peripheral resistance and blood pressure while maintaining increased cardiac output. Norepinephrine produces potent alpha-1 vasoconstriction with marked increase in peripheral resistance and blood pressure; the baroreceptor reflex responds to this hypertension by increasing vagal tone, resulting in reflex bradycardia despite direct beta-1 stimulation of the heart. Pure beta agonists like isoproterenol (historical) decrease peripheral resistance (beta-2 vasodilation) while increasing heart rate and contractility (beta-1), potentially causing hypotension despite tachycardia. Phenylephrine produces isolated alpha-1 vasoconstriction and hypertension, triggering reflex bradycardia without direct cardiac effects.

<image>Panel A: Receptor selectivity profiles of direct adrenergic agonists showing epinephrine (all receptors), norepinephrine (alpha-1, alpha-2, beta-1), phenylephrine (alpha-1 selective), dobutamine (primarily beta-1), and albuterol (beta-2 selective), with primary clinical applications listed for each. Panel B: Indirect sympathomimetic mechanisms showing amphetamine reversing NET and displacing vesicular NE, cocaine blocking NET/SERT/DAT reuptake, and tyramine releasing stored NE, all increasing synaptic catecholamine concentration. Panel C: Beta-2 agonist comparison showing short-acting (albuterol, acute relief, 4-6 hours) versus long-acting (salmeterol, formoterol, maintenance therapy, 12 hours) bronchodilators with mechanism of airway smooth muscle relaxation via increased cAMP. Panel D: Cardiovascular effects diagram showing heart rate, contractility, and peripheral resistance changes for epinephrine (dose-dependent), norepinephrine (reflex bradycardia), isoproterenol (pure beta), and phenylephrine (reflex bradycardia), with blood pressure profiles for each.</image>

VII. Alpha Adrenergic Antagonists

Non-selective alpha-adrenergic antagonists block both alpha-1 and alpha-2 receptors, producing vasodilation but also removing presynaptic inhibition of norepinephrine release, which can cause pronounced reflex tachycardia. Phentolamine is a reversible, competitive alpha-blocker used diagnostically and therapeutically in pheochromocytoma, a catecholamine-secreting tumor; it is also used to reverse local vasoconstriction from extravasation of norepinephrine or dopamine. Phenoxybenzamine is an irreversible (covalent-binding) alpha-blocker used preoperatively in pheochromocytoma to control blood pressure before surgical resection; its long duration of action provides sustained alpha-blockade but makes dosing less predictable. The major adverse effects of non-selective alpha-blockade include orthostatic hypotension from loss of sympathetic vascular tone, reflex tachycardia from both hypotension-triggered baroreceptor activation and alpha-2 presynaptic disinhibition, and nasal congestion from mucosal vasodilation. In pheochromocytoma management, alpha-blockade must precede beta-blockade to prevent unopposed alpha-mediated vasoconstriction if beta-blockers are given first.

Alpha-1 selective antagonists provide therapeutic vasodilation while preserving presynaptic alpha-2 feedback inhibition, reducing the magnitude of reflex tachycardia. Prazosin was the first clinically useful alpha-1 selective blocker, used for hypertension and increasingly recognized for treating PTSD-associated nightmares by blocking alpha-1 receptors in the CNS. Terazosin and doxazosin are longer-acting alpha-1 blockers used for both hypertension and benign prostatic hyperplasia (BPH), where alpha-1 blockade relaxes prostatic and urethral smooth muscle to improve urinary flow. Tamsulosin has selectivity for alpha-1A and alpha-1D subtypes found predominantly in the prostate and bladder, minimizing cardiovascular effects like orthostatic hypotension; it is the most commonly prescribed alpha-blocker for BPH. Silodosin is even more alpha-1A selective, further reducing cardiovascular side effects but with increased incidence of retrograde ejaculation. All alpha-1 blockers can cause the "first-dose phenomenon," a pronounced hypotensive response to the initial dose that may cause syncope, managed by starting with low doses at bedtime.

Alpha-2 selective agonists, though pharmacologically opposite to alpha blockers, are included here because their clinical effect of reducing sympathetic outflow produces results similar to sympatholytic drugs. Clonidine stimulates alpha-2 receptors in the brainstem cardiovascular control centers, reducing sympathetic outflow and lowering blood pressure; it also activates peripheral presynaptic alpha-2 receptors to reduce norepinephrine release. Clinical uses of clonidine extend beyond hypertension to include opioid and alcohol withdrawal (reducing sympathetic hyperactivity), ADHD (improving attention), and various pain conditions. Methyldopa is a prodrug converted in the brain to alpha-methylnorepinephrine, which activates alpha-2 receptors; it is primarily used for hypertension in pregnancy due to its long safety record in this population. Dexmedetomidine is a highly selective alpha-2 agonist used intravenously for sedation in intensive care, producing "cooperative sedation" where patients can be aroused but return to sedation when unstimulated; it also provides analgesia and reduces opioid requirements. Abrupt discontinuation of chronic alpha-2 agonist therapy can cause rebound hypertension due to upregulated adrenergic receptors.

Side effects of alpha-blocking agents relate directly to their mechanism of blocking sympathetic vascular tone and vary with selectivity. Orthostatic hypotension is the most common adverse effect, resulting from inability to appropriately vasoconstrict upon standing; patients should be counseled to rise slowly from sitting or lying positions. The first-dose phenomenon represents exaggerated orthostatic hypotension with the initial dose before compensatory mechanisms develop; starting with low doses at bedtime minimizes this risk. Reflex tachycardia occurs more prominently with non-selective agents due to alpha-2 blockade but is reduced with alpha-1 selective agents that preserve presynaptic feedback. Nasal congestion results from mucosal vasodilation and loss of the decongestant effect of sympathetic tone. Sexual dysfunction including retrograde ejaculation (particularly with alpha-1A selective agents) and priapism (rare) can occur. In patients with coronary artery disease, the reflex tachycardia from non-selective alpha-blockade can precipitate angina, making alpha-1 selective agents or combined alpha-beta blockers preferable.

<image>Panel A: Non-selective alpha-blocker mechanism showing phenoxybenzamine and phentolamine blocking both alpha-1 (causing vasodilation and hypotension) and alpha-2 (removing presynaptic inhibition), resulting in combined vasodilation and reflex tachycardia. Panel B: Alpha-1 selective blockers for BPH showing tamsulosin blocking alpha-1A receptors on prostatic smooth muscle, causing relaxation, reduced urethral resistance, and improved urine flow, with minimal effect on vascular alpha-1B receptors. Panel C: Central alpha-2 agonist mechanism showing clonidine and methyldopa activating brainstem alpha-2 receptors (nucleus tractus solitarius) to reduce sympathetic outflow, resulting in decreased heart rate, decreased vascular resistance, and lower blood pressure. Panel D: Alpha-blocker adverse effects comparison showing non-selective agents with more pronounced orthostatic hypotension and reflex tachycardia versus alpha-1 selective agents with first-dose phenomenon, less tachycardia, and retrograde ejaculation risk with prostate-selective agents.</image>

VIII. Beta Adrenergic Antagonists

Non-selective beta-adrenergic antagonists block both beta-1 and beta-2 receptors, producing cardiac effects that are therapeutically useful but also respiratory and metabolic effects that may be problematic in certain patients. Propranolol was the first clinically useful beta-blocker and remains widely used for its cardiac effects (reducing heart rate, contractility, and renin release) and its high lipophilicity allowing CNS penetration useful for migraine prophylaxis, essential tremor, and performance anxiety. Nadolol is a non-selective beta-blocker with low lipophilicity and long half-life, eliminated primarily by the kidneys; its lack of CNS penetration may cause fewer central side effects. Timolol is used topically as ophthalmic drops to reduce intraocular pressure in glaucoma by decreasing aqueous humor production; even topical administration can produce systemic beta-blockade, requiring caution in patients with asthma or bradycardia. The major limitation of non-selective beta-blockers is beta-2 blockade causing bronchoconstriction, making these agents relatively contraindicated in patients with asthma or severe COPD.

Beta-1 selective antagonists preferentially block cardiac beta-1 receptors at therapeutic doses, reducing the risk of bronchospasm while maintaining antihypertensive and anti-ischemic effects. Metoprolol is the most widely prescribed beta-1 selective blocker, available in immediate-release and extended-release formulations for hypertension, angina, and heart failure; it also reduces mortality post-myocardial infarction. Atenolol is hydrophilic with low CNS penetration, originally popular for hypertension but now less favored due to evidence of inferior cardiovascular outcomes compared to other antihypertensives. Bisoprolol is highly beta-1 selective and evidence-based for chronic heart failure with reduced ejection fraction, producing mortality benefit when carefully titrated. Esmolol is an ultra-short-acting beta-1 blocker (half-life approximately 9 minutes) administered by continuous intravenous infusion, ideal for acute situations requiring titratable beta-blockade such as perioperative blood pressure control or supraventricular tachycardia. While beta-1 selective agents have reduced risk of bronchospasm compared to non-selective agents, selectivity is relative and may be lost at higher doses; caution is still warranted in patients with reactive airway disease.

Several beta-blockers possess additional pharmacological properties that influence their clinical utility and place in therapy. Carvedilol blocks beta-1, beta-2, and alpha-1 receptors, providing additional vasodilation through alpha-1 blockade; it is one of three beta-blockers proven to reduce mortality in heart failure and is preferred when additional blood pressure lowering is needed. Labetalol also provides combined alpha and beta blockade with approximately 3:1 beta:alpha blocking ratio when given orally and 7:1 when given intravenously; it is particularly useful for hypertensive emergencies and hypertension in pregnancy. Nebivolol is beta-1 selective and additionally stimulates endothelial nitric oxide release, producing vasodilation independent of alpha-blockade; this may offer advantages for endothelial function and erectile function. Some older beta-blockers possess intrinsic sympathomimetic activity (ISA or partial agonist activity), producing less bradycardia at rest; pindolol and acebutolol are examples, but this property has not proven clinically advantageous and these agents are less commonly used.

Clinical applications of beta-blockers span multiple cardiovascular conditions and extend to non-cardiac indications. In hypertension, beta-blockers are no longer first-line but remain useful especially when combined with other indications such as coronary disease or heart failure. In coronary artery disease, beta-blockers reduce myocardial oxygen demand by lowering heart rate and contractility, providing anti-anginal effect and mortality benefit post-MI. In heart failure with reduced ejection fraction, specific beta-blockers (carvedilol, metoprolol succinate, bisoprolol) paradoxically improve survival by blocking chronic neurohormonal activation; they must be initiated at low doses and titrated slowly in compensated patients. In arrhythmias, beta-blockers slow the sinus node and AV conduction, useful for rate control in atrial fibrillation and suppression of catecholamine-mediated arrhythmias. Non-cardiac uses include migraine prophylaxis (propranolol), essential tremor (propranolol), hyperthyroidism symptom control, and anxiety disorders.

<image>Panel A: Beta receptor selectivity spectrum showing non-selective agents (propranolol, nadolol, timolol) blocking both beta-1 and beta-2 versus beta-1 selective agents (metoprolol, atenolol, bisoprolol, esmolol) preferentially blocking cardiac beta-1, with clinical implications for each selectivity profile. Panel B: Beta-blockers with additional properties showing carvedilol (alpha-1 + beta blockade, vasodilation), labetalol (alpha-1 + beta blockade, emergency use), and nebivolol (beta-1 + NO release, vasodilation), with mechanisms of additional vasodilation illustrated. Panel C: Heart failure beta-blocker mechanism showing chronic sympathetic activation causing maladaptive remodeling, with beta-blockade reducing heart rate, decreasing myocardial oxygen demand, preventing remodeling, and improving survival, with careful titration protocol. Panel D: Clinical indications for beta-blockers showing hypertension, coronary artery disease (anti-anginal, post-MI), heart failure (mortality benefit), arrhythmias (rate control, SVT), and non-cardiac uses (migraine, tremor, thyrotoxicosis, anxiety).</image>

IX. Autonomic Drugs in Clinical Practice

Cardiovascular applications of autonomic drugs represent a major area of clinical pharmacology, with drug selection guided by the specific pathophysiology being targeted. Hypertension treatment may employ alpha-2 agonists (clonidine) to reduce sympathetic outflow, alpha-1 blockers (prazosin, doxazosin) to reduce peripheral resistance, or beta-blockers to reduce cardiac output and renin release; drug selection considers comorbidities and side effect profiles. Chronic heart failure management includes beta-blockers (carvedilol, metoprolol succinate, bisoprolol) that provide mortality benefit when carefully titrated, while acute decompensated heart failure may require inotropic support with dobutamine (beta-1 agonist) to augment cardiac output. Arrhythmia management utilizes beta-blockers to slow sinus rate and AV conduction in atrial fibrillation and supraventricular tachycardias, or atropine to increase heart rate in symptomatic bradycardia. Shock states require vasopressors: norepinephrine for septic shock (vasodilation-predominant), epinephrine for anaphylactic shock, and vasopressin or epinephrine for cardiac arrest.

Respiratory applications center on bronchodilation for obstructive airway diseases, utilizing both adrenergic and anticholinergic mechanisms. Beta-2 agonists are the mainstay of bronchodilator therapy: short-acting agents (albuterol) provide rapid relief of acute bronchospasm while long-acting agents (salmeterol, formoterol) provide sustained bronchodilation for maintenance therapy in asthma and COPD. Inhaled anticholinergics (ipratropium, tiotropium) produce bronchodilation by blocking muscarinic receptor-mediated bronchoconstriction; they are particularly effective in COPD where cholinergic tone contributes significantly to airway obstruction. In asthma, anticholinergics provide additive benefit when combined with beta-2 agonists in acute exacerbations. Tiotropium is a once-daily long-acting muscarinic antagonist (LAMA) that has become a cornerstone of COPD maintenance therapy. Anaphylaxis requires immediate epinephrine, which reverses bronchospasm (beta-2), restores blood pressure (alpha-1 and beta-1), and reduces mucosal edema (alpha-1 vasoconstriction); intramuscular injection into the lateral thigh provides rapid absorption.

Ophthalmologic applications of autonomic drugs address glaucoma (reducing intraocular pressure) and diagnostic procedures (pupil manipulation). Glaucoma treatment includes beta-blockers (timolol) that reduce aqueous humor production by the ciliary body, alpha-2 agonists (brimonidine) that both decrease production and increase outflow, and muscarinic agonists (pilocarpine) that increase outflow by contracting the ciliary muscle and opening the trabecular meshwork. Mydriasis for fundoscopic examination can be achieved with alpha-1 agonists (phenylephrine) that contract the radial dilator muscle or muscarinic antagonists (tropicamide) that relax the circular sphincter muscle; cycloplegia requires anticholinergics to paralyze the ciliary muscle. Miosis for glaucoma treatment employs muscarinic agonists (pilocarpine) that contract the sphincter muscle. Selection among agents considers onset and duration of action, systemic absorption risks, and specific clinical requirements.

Urologic applications address bladder dysfunction ranging from urinary retention to overactive bladder, utilizing opposing pharmacological strategies. Urinary retention may be treated with muscarinic agonists (bethanechol) that contract the detrusor muscle and relax the internal sphincter, promoting voiding; this is particularly useful for postoperative or postpartum urinary retention. Benign prostatic hyperplasia (BPH) causes bladder outlet obstruction addressed with alpha-1 blockers (tamsulosin, alfuzosin) that relax prostatic and urethral smooth muscle; these agents provide rapid symptomatic relief of lower urinary tract symptoms. Overactive bladder presents with urinary urgency, frequency, and urge incontinence, treated with antimuscarinic agents (oxybutynin, tolterodine, solifenacin) that block M3 receptors on the detrusor muscle, reducing involuntary contractions. Mirabegron, a beta-3 agonist, offers an alternative mechanism for overactive bladder by relaxing the detrusor through beta-3 receptor activation. The contrasting mechanisms for retention (enhance cholinergic, reduce adrenergic) versus overactive bladder (block cholinergic) illustrate the importance of understanding the underlying pathophysiology.

<image>Panel A: Cardiovascular drug selection flowchart showing hypertension (alpha-2 agonists, alpha-1 blockers, beta-blockers), chronic heart failure (beta-blockers for mortality), acute heart failure (dobutamine for inotropy), arrhythmias (beta-blockers for rate control, atropine for bradycardia), and shock (norepinephrine, epinephrine, dobutamine by type). Panel B: Respiratory pharmacology diagram showing airway smooth muscle with beta-2 receptors (relaxation via cAMP) and M3 receptors (contraction via calcium), targeted by beta-2 agonists and anticholinergics respectively for bronchodilation. Panel C: Glaucoma treatment mechanisms showing aqueous humor production in ciliary body (reduced by beta-blockers, alpha-2 agonists) and outflow through trabecular meshwork (increased by muscarinic agonists), with drug examples for each mechanism. Panel D: Urologic autonomic pharmacology showing bladder detrusor with M3 receptors (contraction) and beta-3 receptors (relaxation), prostate with alpha-1A receptors (contraction), with drug applications for retention (bethanechol), BPH (tamsulosin), and overactive bladder (oxybutynin, mirabegron).</image>

X. Autonomic Drug Toxicity

Cholinergic toxicity from excessive muscarinic activation produces the SLUDGE syndrome and requires prompt recognition and treatment to prevent respiratory failure. Clinical manifestations include profuse secretions (salivation, lacrimation, bronchorrhea), gastrointestinal hyperactivity (nausea, vomiting, diarrhea, abdominal cramping), urinary incontinence, miosis, bradycardia, and bronchospasm. The most life-threatening effects are bronchospasm combined with excessive bronchial secretions causing respiratory failure, and in severe cases, nicotinic effects causing neuromuscular weakness including respiratory muscle paralysis. Treatment centers on atropine, titrated to control secretions and bronchospasm (endpoints are dry lungs and adequate oxygenation rather than tachycardia, as very high doses may be needed). For organophosphate poisoning, pralidoxime (2-PAM) reactivates phosphorylated acetylcholinesterase if given before the enzyme-inhibitor complex "ages" (becomes permanent), typically within 24-48 hours. Supportive care includes airway management with mechanical ventilation if needed and benzodiazepines for seizures, which are common in organophosphate poisoning.

Anticholinergic toxicity produces the opposite clinical picture, characterized by peripheral antimuscarinic effects and central nervous system derangement. Peripheral effects include hyperthermia from inability to sweat, tachycardia from unopposed sympathetic activity, urinary retention from detrusor relaxation and sphincter contraction, decreased gastrointestinal motility potentially causing ileus, and mydriasis with cycloplegia causing blurred vision and photophobia. CNS effects range from agitation and confusion to visual hallucinations and frank delirium, particularly pronounced in elderly patients due to baseline cholinergic deficits. Treatment is primarily supportive: external cooling for hyperthermia, hydration, bladder catheterization if needed, and benzodiazepines for agitation and seizures. Physostigmine is the specific antidote, a centrally-penetrating cholinesterase inhibitor that can reverse both central and peripheral effects; however, it should be avoided in patients with cardiac conduction disturbances (prolonged QRS or QTc) due to risk of asystole. The decision to use physostigmine weighs the severity of toxicity against the risks of the antidote.

Sympathomimetic toxicity occurs from overdose of stimulant drugs (amphetamines, cocaine), decongestants, or MAO inhibitor interactions and produces a hyperadrenergic state. Clinical features include hypertension that may be severe (hypertensive emergency), tachycardia, hyperthermia from increased metabolic activity and impaired heat dissipation, mydriasis, diaphoresis (unlike anticholinergic toxicity where sweating is blocked), and CNS stimulation with agitation, psychosis, and seizures. Cardiovascular complications include myocardial ischemia (even in young patients without coronary disease), arrhythmias, and aortic dissection. Treatment focuses on benzodiazepines, which reduce sympathetic outflow, control agitation, lower blood pressure, and raise seizure threshold; they are first-line for most manifestations. Pure alpha-blockers (phentolamine) or vasodilators (nitroprusside) can be added for severe hypertension unresponsive to benzodiazepines. Beta-blockers must be avoided or used with extreme caution because blocking beta-2 vasodilation leaves alpha-1 vasoconstriction unopposed, potentially worsening hypertension ("unopposed alpha" phenomenon); if beta-blockade is needed, combined alpha-beta blockers (labetalol) are preferred.

Beta-blocker toxicity produces bradycardia, hypotension, heart failure, and bronchospasm, with severity depending on the dose ingested and the patient's underlying cardiac function. Cardiac effects include severe sinus bradycardia, AV block, and reduced contractility that may progress to cardiogenic shock; in massive overdose, even beta-1 selective agents lose selectivity. Bronchospasm is more prominent with non-selective agents but can occur with any beta-blocker. Hypoglycemia may develop, particularly in diabetic patients, and CNS depression occurs with lipophilic agents that cross the blood-brain barrier. Treatment begins with atropine for bradycardia, though response may be limited. Glucagon is the specific antidote, activating cardiac adenylyl cyclase independent of beta receptors to increase cAMP and thereby increase heart rate and contractility; it is given as IV bolus followed by infusion. High-dose insulin-euglycemia therapy (HIET) provides additional inotropic support by enhancing myocardial glucose utilization. Vasopressors (norepinephrine, epinephrine) may be needed for persistent hypotension. Intravenous lipid emulsion has shown benefit in severe cases with lipophilic beta-blockers. For beta-blocker-induced bronchospasm, inhaled beta-2 agonists (high doses may be needed) and ipratropium provide bronchodilation.

<image>Panel A: Cholinergic toxicity diagram showing SLUDGE manifestations (salivation, lacrimation, urination, defecation, GI distress, emesis) plus bronchospasm, bradycardia, and neuromuscular weakness, with treatment algorithm showing atropine titration, pralidoxime for organophosphates, and supportive care. Panel B: Anticholinergic versus cholinergic toxicity comparison showing opposite findings: dilated versus constricted pupils, dry versus wet skin, tachycardia versus bradycardia, hypoactive versus hyperactive bowel, urinary retention versus incontinence, with specific treatments for each. Panel C: Sympathomimetic toxicity showing hyperadrenergic state with hypertension, tachycardia, hyperthermia, mydriasis, and diaphoresis, with treatment algorithm emphasizing benzodiazepines first, avoiding unopposed beta-blockade, and using phentolamine or labetalol for severe hypertension. Panel D: Beta-blocker toxicity showing bradycardia, hypotension, bronchospasm, and hypoglycemia, with treatment ladder of atropine, glucagon (mechanism of receptor-independent adenylyl cyclase activation shown), high-dose insulin, vasopressors, and lipid emulsion.</image>

Summary

• The autonomic nervous system includes sympathetic ("fight or flight," norepinephrine) and parasympathetic ("rest and digest," acetylcholine) divisions with opposing effects on most organ systems
• Cholinergic receptors include nicotinic (ligand-gated ion channels at ganglia and NMJ) and muscarinic (GPCRs with M1/M3 coupling through Gq and M2 coupling through Gi)
• Muscarinic activation produces SLUDGE symptoms; muscarinic blockade produces the "hot, dry, red, blind, mad" syndrome
• Cholinesterase inhibitors (neostigmine, pyridostigmine, donepezil) enhance cholinergic transmission indirectly; physostigmine crosses the blood-brain barrier for central anticholinergic toxicity
• Antimuscarinics include atropine (broad use), ipratropium and tiotropium (respiratory), oxybutynin (bladder), and tropicamide (ophthalmology)
• Adrenergic receptors include alpha-1 (vasoconstriction, Gq), alpha-2 (presynaptic inhibition, Gi), beta-1 (cardiac, Gs), and beta-2 (bronchodilation, Gs)
• Epinephrine activates all adrenergic receptors; norepinephrine primarily alpha plus beta-1; dobutamine primarily beta-1; albuterol selectively beta-2
• Alpha-1 blockers (tamsulosin) treat BPH with orthostatic hypotension risk; alpha-2 agonists (clonidine) reduce central sympathetic outflow
• Beta-blockers include non-selective (propranolol) and beta-1 selective (metoprolol) agents, with additional properties in some (carvedilol with alpha-blockade)
• Toxicity management: atropine and pralidoxime for cholinergic crisis, physostigmine for anticholinergic toxicity, benzodiazepines for sympathomimetic toxicity, glucagon for beta-blocker overdose

Key Terms

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