Sympathomimetic Drugs

Sympathomimetic drugs, also known as adrenergic agonists, mimic the action of the stimulators (α, β, or dopamine receptors) of the sympathetic autonomic nervous system Autonomic nervous system The ANS is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ANS consists of the sympathetic and parasympathetic nervous systems. Autonomic Nervous System. Sympathomimetic drugs are classified based on the type of receptors the drugs act on (some agents act on several receptors but 1 is predominate). Clinical uses of sympathomimetics include the treatment of hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension, asthma Asthma Asthma is a chronic inflammatory respiratory condition characterized by bronchial hyperresponsiveness and airflow obstruction. The disease is believed to result from the complex interaction of host and environmental factors that increase disease predisposition, with inflammation causing symptoms and structural changes. Patients typically present with wheezing, cough, and dyspnea. Asthma, and anaphylaxis. The primary drugs used as IV vasopressors in the hospital are dopamine and norepinephrine. Dobutamine is given IV as an inotrope. Albuterol is used via nebulizer or metered-dose inhaler for asthma Asthma Asthma is a chronic inflammatory respiratory condition characterized by bronchial hyperresponsiveness and airflow obstruction. The disease is believed to result from the complex interaction of host and environmental factors that increase disease predisposition, with inflammation causing symptoms and structural changes. Patients typically present with wheezing, cough, and dyspnea. Asthma. Sympathomimetics may produce a wide range of adverse effects, which generally resemble excessive stimulation of the sympathetic nervous system Nervous system The nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system. General Structure of the Nervous System. The effects may include palpitations, tachycardia, and/or arrhythmias due to stimulation of cardiac β receptors.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Chemistry and Pharmacodynamics

Sympathomimetic drugs, also known as adrenergic agonists, mimic the action of the stimulators of the sympathetic autonomic nervous system Autonomic nervous system The ANS is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ANS consists of the sympathetic and parasympathetic nervous systems. Autonomic Nervous System, specifically α, β, or dopamine receptors:

Chemical structures

  • Phenylethylamine (parent compound)
  • 4 possible substitution sites:
    • Benzene ring: substitution by a hydroxyl group (-OH) at position 3 and 4 yields catecholamine (dopamine)
    • Terminal amino group (epinephrine)
    • Α or β carbons of the ethylamino chain (amphetamine and phenylephrine respectively)

Mechanism of action

  • At the end of a neuron, terminal buttons (structures at the end of an axon) carry signals to neighboring neurons (synapses), glands, or muscles.
  • The synapses provide room for the chemical signal to travel and exert the effect.
  • Sympathomimetics affect the adrenergic receptors of epinephrine, norepinephrine, or dopamine to produce effects on α, β, or dopamine receptors.

Classification

  • Classification is based on the type of receptors the drugs act on.
  • Direct agonists (selective) act on 1 or more adrenergic (α and β) receptors:
    • Α agonists:
      • Nonselective: norepinephrine
      • Α-1 selective: phenylephrine
      • Α-2 selective: clonidine
    • Β agonists:
      • Nonselective: epinephrine, isoproterenol
      • Β-1 selective: dobutamine
      • Β-2 selective: albuterol
  • Indirect agonists: 
    • Stimulants Stimulants Stimulants are used by the general public to increase alertness and energy, decrease fatigue, and promote mental focus. Stimulants have medical uses for individuals with ADHD and sleep disorders, and are also used in combination with analgesics in pain management. Stimulants: cause increased release of the endogenous neurotransmitter (e.g., amphetamines)
    • Tricyclic antidepressants Tricyclic antidepressants Tricyclic antidepressants (TCAs) are a class of medications used in the management of mood disorders, primarily depression. These agents, named after their 3-ring chemical structure, act via reuptake inhibition of neurotransmitters (particularly norepinephrine and serotonin) in the brain. Tricyclic Antidepressants: inhibit reuptake of neurotransmitters → “ anticholinergic Anticholinergic Anticholinergic drugs block the effect of the neurotransmitter acetylcholine at the muscarinic receptors in the central and peripheral nervous systems. Anticholinergic agents inhibit the parasympathetic nervous system, resulting in effects on the smooth muscle in the respiratory tract, vascular system, urinary tract, GI tract, and pupils of the eyes. Anticholinergic Drugs” side effects
  • Mixed: 
    • Employ mechanisms of both direct and indirect activation
    • Ephedrine: acts on α and β receptors to cause norepinephrine release (used for anesthesia Anesthesia Anesthesiology is the field of medicine that focuses on interventions that bring a state of anesthesia upon an individual. General anesthesia is characterized by a reversible loss of consciousness along with analgesia, amnesia, and muscle relaxation. Anesthesiology: History and Basic Concepts-related hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension)

Physiologic effects

  • Cardiovascular (e.g., epinephrine, norepinephrine):
    • Increases heart rate
    • Increases contractile force (positive inotropy)
    • Increases blood pressure by increasing total peripheral resistance
    • Isoproterenol (nonselective agent):
      • Increases cardiac output 
      • Decreases blood pressure (opposite of epinephrine)
  • Respiratory (e.g., albuterol):
    • Β-2 agonists relax smooth muscle → bronchodilation 
    • Albuterol is used for asthma Asthma Asthma is a chronic inflammatory respiratory condition characterized by bronchial hyperresponsiveness and airflow obstruction. The disease is believed to result from the complex interaction of host and environmental factors that increase disease predisposition, with inflammation causing symptoms and structural changes. Patients typically present with wheezing, cough, and dyspnea. Asthma.
    • Epinephrine is used for anaphylaxis.
  • Ocular:
    • Pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil dilation (mydriasis)
    • Accommodation is rarely affected.
    • Reduces intraocular pressure
  • Gastrointestinal:
    • Contracts smooth muscle in the splanchnic vessels
    • Low-dose dopamine causes vasoconstriction.
  • Renal:
    • Detrusor muscle relaxation
    • Trigone contraction
  • Genital tract (women):
    • Β-2 agonists cause uterine relaxation.
    • Terbutaline is used to suppress preterm labor Preterm labor Preterm labor refers to regular uterine contractions leading to cervical change prior to 37 weeks of gestation; preterm birth refers to birth prior to 37 weeks of gestation. Preterm birth may be spontaneous due to preterm labor, preterm prelabor rupture of membranes (PPROM), or cervical insufficiency. Preterm Labor and Birth.
  • Genital tract (men):
    • Α-1 agonists cause prostatic smooth muscle contraction Smooth muscle contraction Smooth muscle is primarily found in the walls of hollow structures and some visceral organs, including the walls of the vasculature, GI, respiratory, and genitourinary tracts. Smooth muscle contracts more slowly and is regulated differently than skeletal muscle. Smooth muscle can be stimulated by nerve impulses, hormones, metabolic factors (like pH, CO2 or O2 levels), its own intrinsic pacemaker ability, or even mechanical stretch. Smooth Muscle Contraction (α blockers are used for benign prostatic hypertrophy, which causes urinary outflow obstruction).
    • Ephedrine is sometimes used for urinary incontinence Urinary incontinence Urinary incontinence (UI) is involuntary loss of bladder control or unintentional voiding, which represents a hygienic or social problem to the patient. Urinary incontinence is a symptom, a sign, and a disorder. The 5 types of UI include stress, urge, mixed, overflow, and functional. Urinary Incontinence.

Pharmacokinetics and Indications

The primary drugs used as IV vasopressors in the hospital are dopamine and norepinephrine. Dobutamine is given IV as an inotrope. Albuterol is used via nebulizer or metered-dose inhaler for asthma Asthma Asthma is a chronic inflammatory respiratory condition characterized by bronchial hyperresponsiveness and airflow obstruction. The disease is believed to result from the complex interaction of host and environmental factors that increase disease predisposition, with inflammation causing symptoms and structural changes. Patients typically present with wheezing, cough, and dyspnea. Asthma. Typical uses of certain medications include:

Routes of administration

Many routes are available:

  • Oral:
    • Midodrine (used for orthostatic hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension)
    • Clonidine (a centrally acting antihypertensive agent)
    • Pseudoephedrine (nasal decongestant)
  • Rectal: phenylephrine (vasoconstrictor suppositories for hemorrhoids Hemorrhoids Hemorrhoids are normal vascular cushions in the anal canal composed of dilated vascular tissue, smooth muscle, and connective tissue. They do not cause issues unless they are enlarged, inflamed, thrombosed, or prolapsed. Patients often present with rectal bleeding of bright red blood, or they may have pain, perianal pruritus, or a palpable mass. Hemorrhoids)
  • Topical: eye drops for glaucoma Glaucoma Glaucoma is an optic neuropathy characterized by typical visual field defects and optic nerve atrophy seen as optic disc cupping on examination. The acute form of glaucoma is a medical emergency. Glaucoma is often, but not always, caused by increased intraocular pressure (IOP). Glaucoma (α agonists reduce intraocular pressure)
  • IV (pressors for hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension in hospitalized individuals):
    • Epinephrine
    • Dobutamine
    • Norepinephrine
  • Inhaled (for asthma Asthma Asthma is a chronic inflammatory respiratory condition characterized by bronchial hyperresponsiveness and airflow obstruction. The disease is believed to result from the complex interaction of host and environmental factors that increase disease predisposition, with inflammation causing symptoms and structural changes. Patients typically present with wheezing, cough, and dyspnea. Asthma):
    • Albuterol (short-acting β agonist)
    • Salmeterol (LABA)

Indications

Sympathomimetic drugs are used to augment endogenous catecholamines Catecholamines A general class of ortho-dihydroxyphenylalkylamines derived from tyrosine. Adrenal Hormones of the sympathetic nervous system Nervous system The nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system. General Structure of the Nervous System for therapeutic benefit.:

Α-1 selective agonist phenylephrine:

  • Used as an IV vasopressor to increase blood pressure by increasing total peripheral resistance
  • Does not directly act on the heart → induces reflex bradycardia (a counter-regulatory mechanism)
  • Contracts smooth muscle in the splanchnic vessels
  • Used topically as a vasoconstrictor for nasal congestion due to allergic rhinitis Rhinitis Rhinitis refers to inflammation of the nasal mucosa. The condition is classified into allergic, nonallergic, and infectious rhinitis. Allergic rhinitis is due to a type I hypersensitivity reaction. Non-allergic rhinitis is due to increased blood flow to the nasal mucosa. Infectious rhinitis is caused by an upper respiratory tract infection. Rhinitis

Α-2 selective agonist clonidine:

  • Decreases blood pressure by CNS accumulation → reduced sympathetic outflow
  • Not a 1st-line drug for hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension

Β-1 selective agonist dobutamine:

  • Mostly stimulates myocardial β-1 adrenergic receptors; increases cardiac output (contractility)
  • Increases blood pressure
  • Lesser effects of α-1 and β-2 receptor agonists, greater effects of β-1 receptor activation → vasodilation in addition to the inotropic and chronotropic actions
  • Route: IV
  • Onset of action: 1–10 minutes
  • Peak effect: 10–20 minutes
  • Metabolism: tissue and hepatic (to inactive metabolites)
  • Half-life elimination: 2 minutes
  • Excretion: urine (as metabolites)

Β-2 selective agonist albuterol:

  • Use: for bronchodilation with asthma Asthma Asthma is a chronic inflammatory respiratory condition characterized by bronchial hyperresponsiveness and airflow obstruction. The disease is believed to result from the complex interaction of host and environmental factors that increase disease predisposition, with inflammation causing symptoms and structural changes. Patients typically present with wheezing, cough, and dyspnea. Asthma or other causes of bronchoconstriction
  • Route: inhaled or oral (rarely used)
  • Onset and duration of action:
    • Nebulizer solution: ≤ 5 minutes, lasts 3–6 hours
    • Oral inhaler: 5–8 minutes, lasts 4–6 hours
  • Metabolism: hepatic
  • Excretion: 80% urine, 20% feces

Nonselective dopamine:

  • Works on different receptors at different doses:
    • Low dose: dopamine receptors
    • Intermediate dose: β receptors
    • High dose: α receptors
  • Route: IV
  • Onset of action:
    • Adults: within 5 minutes
    • Neonates and children: ≤ 1 hour
  • Duration in adults: < 10 minutes
  • Metabolism: 
    • Renal, hepatic, and plasma
    • 75% to inactive metabolites by MAO, 25% to norepinephrine (active)
  • Half-life elimination: approximately 2 minutes (excreted in the urine)

Mixed α-/β-agonist epinephrine:

  • Indications: 
    • Use SC for anaphylaxis and type 1 IgE-mediated reactions.
    • Use IV for hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension in septic shock Septic shock Organ dysfunction resulting from a dysregulated systemic host response to infection separates sepsis from uncomplicated infection. Patients commonly present with fever, tachycardia, tachypnea, hypotension, and/or altered mentation. Septic shock is diagnosed during treatment when vasopressors are necessary to control hypotension. Sepsis and Septic Shock.
  • Onset of action for bronchodilator (SC): approximately 5–10 minutes
  • Distribution: does not cross the blood-brain barrier
  • Metabolism: taken into the adrenergic neuron and metabolized by MAO and catechol O-methyltransferase (COMT) (the circulating drug undergoes hepatic metabolism)
  • Route: IV
  • Half-life elimination: < 5 minutes
  • Excretion: urine 
  • Used in advanced cardiac life support (ACLS) protocol for:
    • Sudden cardiac arrest Cardiac arrest Cardiac arrest is the sudden, complete cessation of cardiac output with hemodynamic collapse. Patients present as pulseless, unresponsive, and apneic. Rhythms associated with cardiac arrest are ventricular fibrillation/tachycardia, asystole, or pulseless electrical activity. Cardiac Arrest due to asystole
    • Pulseless electrical activity
    • Ventricular fibrillation Ventricular fibrillation Ventricular fibrillation (VF or V-fib) is a type of ventricular tachyarrhythmia (> 300/min) often preceded by ventricular tachycardia. In this arrhythmia, the ventricle beats rapidly and sporadically. The ventricular contraction is uncoordinated, leading to a decrease in cardiac output and immediate hemodynamic collapse. Ventricular Fibrillation
    • Pulseless ventricular tachycardia Ventricular tachycardia Ventricular tachycardia is any heart rhythm faster than 100 beats/min, with 3 or more irregular beats in a row, arising distal to the bundle of His. Ventricular tachycardia is the most common form of wide-complex tachycardia, and it is associated with a high mortality rate. Ventricular Tachycardia

Mixed α-/β-agonist norepinephrine:

  • Indications: severe hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension/ shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock
  • Α effects (vasoconstriction → blood pressure and coronary blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure) > β effects (inotropic and chronotropic effects)
  • Duration (vasopressor): 1–2 minutes
  • Protein binding: 25% mainly albumin
  • Mean half-life elimination: approximately 2.4 minutes
  • Time to peak steady state: 5 minutes
  • Excretion: urine
  • Metabolism: short duration of action due to:
    • Rapidly metabolized by COMT and MAO
    • Readily taken up into the nerve endings

Adverse Effects and Contraindications

Sympathomimetics may produce a wide range of adverse effects resembling excessive stimulation of the sympathetic nervous system Nervous system The nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system. General Structure of the Nervous System, including palpitations, tachycardia, and arrhythmias due to stimulation of cardiac β receptors.

Adverse effects

  • Due to excessive adrenergic receptor activity
  • IV extravasation of potent vasoconstrictors can cause local ischemia (central line is preferred).
  • Α-1 agonists (e.g., phenylephrine, norepinephrine):
    • Hypertension
    • Reflex bradycardia
    • Piloerection
    • Urinary retention
    • Vasoconstriction: may produce distal ischemia and necrosis
  • Α-2 agonists (e.g., clonidine):
    • Sedation
    • Respiratory depression
    • Bradycardia
    • Hypotension and shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock
    • Miosis
    • Rebound hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension
    • Xerostomia 
  • Β-1 agonists (e.g., dobutamine):
    • Tachycardia/arrhythmias
    • High-dose IV → can cause mesenteric ischemia Mesenteric Ischemia Mesenteric ischemia is a rare, life-threatening condition caused by inadequate blood flow through the mesenteric vessels, which results in ischemia and necrosis of the intestinal wall. Mesenteric ischemia can be either acute or chronic. Mesenteric Ischemia 
    • Acute coronary syndrome in individuals with underlying coronary artery disease
  • Β-2 agonists (e.g., albuterol, salmeterol):
    • Tremors
    • Agitation
    • Insomnia Insomnia Insomnia is a sleep disorder characterized by difficulty in the initiation, maintenance, and consolidation of sleep, leading to impairment of function. Patients may exhibit symptoms such as difficulty falling asleep, disrupted sleep, trouble going back to sleep, early awakenings, and feeling tired upon waking. Insomnia
    • Tachycardia
    • Hyperinsulinemia
    • Hyperglycemia
    • Hypokalemia Hypokalemia Hypokalemia is defined as plasma potassium (K+) concentration < 3.5 mEq/L. Homeostatic mechanisms maintain plasma concentration between 3.5-5.2 mEq/L despite marked variation in dietary intake. Hypokalemia can be due to renal losses, GI losses, transcellular shifts, or poor dietary intake. Hypokalemia

Drug-drug interactions

  • Βeta blockers: may antagonize the effects of β agonists → diminish the therapeutic effect
  • Cannabinoid products: may enhance the tachycardic effect of sympathomimetics
  • Stimulants Stimulants Stimulants are used by the general public to increase alertness and energy, decrease fatigue, and promote mental focus. Stimulants have medical uses for individuals with ADHD and sleep disorders, and are also used in combination with analgesics in pain management. Stimulants (e.g., caffeine, amphetamines): may enhance the adverse/toxic effect of sympathomimetics
  • Α-1 blockers (e.g., doxazosin, tamsulosin): 
    • May diminish the vasoconstrictive effect of dopamine
    • Dopamine may antagonize α-1 blocker vasodilation.
  • Serotonin-norepinephrine reuptake inhibitors (SNRIs): 
    • May enhance the tachycardic and vasopressor effects of α and β agonists
    • If coadministered → monitor for increased sympathomimetic effects (e.g., hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension, chest pain Chest Pain Chest pain is one of the most common and challenging complaints that may present in an inpatient and outpatient setting. The differential diagnosis of chest pain is large and includes cardiac, gastrointestinal, pulmonary, musculoskeletal, and psychiatric etiologies. Chest Pain, or headache)
  • Tricyclic antidepressants Tricyclic antidepressants Tricyclic antidepressants (TCAs) are a class of medications used in the management of mood disorders, primarily depression. These agents, named after their 3-ring chemical structure, act via reuptake inhibition of neurotransmitters (particularly norepinephrine and serotonin) in the brain. Tricyclic Antidepressants
    • May enhance the vasopressor effect of the α and β agonists (avoid combining if possible)
    • Monitor for evidence of increased pressor effects and consider reductions in initial dosages of the α and β agonists.

Contraindications for clinical use

  • Sympathomimetics should be used with caution in individuals with cardiovascular disorders; however, many are used in life-threatening situations.
  • Specific contraindications to certain agents:
    • Extreme bradycardia (phenylephrine)
    • Hypertrophic obstructive cardiomyopathy Cardiomyopathy Cardiomyopathy refers to a group of myocardial diseases associated with structural changes of the heart muscles (myocardium) and impaired systolic and/or diastolic function in the absence of other heart disorders (coronary artery disease, hypertension, valvular disease, and congenital heart disease). Overview of Cardiomyopathies (dobutamine)
    • Heart failure (isoproterenol)

Comparison of Medications

Table: Commonly used sympathomimetic drugs
Subclass Mechanism of action Effects Clinical applications Pharmacokinetics Pharmacokinetics Pharmacokinetics is the science that analyzes how the human body interacts with a drug. Pharmacokinetics examines how the drug is absorbed, distributed, metabolized, and excreted by the body. Pharmacokinetics and Pharmacodynamics, toxicities, interactions
Α-1 agonists (midodrine, phenylephrine) Activates phospholipase C → increased intracellular calcium and vasoconstriction Vascular smooth muscle contraction Smooth muscle contraction Smooth muscle is primarily found in the walls of hollow structures and some visceral organs, including the walls of the vasculature, GI, respiratory, and genitourinary tracts. Smooth muscle contracts more slowly and is regulated differently than skeletal muscle. Smooth muscle can be stimulated by nerve impulses, hormones, metabolic factors (like pH, CO2 or O2 levels), its own intrinsic pacemaker ability, or even mechanical stretch. Smooth Muscle Contraction → increases blood pressure Orthostatic hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension
  • Oral administration
  • Peak effect: 1 hour
  • Toxicity: hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension, piloerection (goosebumps), and urinary retention
Α-2 agonists (clonidine) Stimulates α-2 adrenoceptors in the brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain Stem → reduced sympathetic outflow Vasoconstriction is masked by the central sympatholytic effect → lowers blood pressure Hypertension
  • Oral, transdermal
  • Peak effect: 1–3 hours
  • Half-life of oral drug: approximately 12 hours
  • Produces xerostomia and sedation
Β-1 agonists (dobutamine) Activates adenylyl cyclase (increases myocardial contractility) Positive inotrope Cardiogenic shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock and acute heart failure
  • IV administration
  • Requires dose titration to the desired effect
Β-2 agonists (albuterol) Activates adenylyl cyclase Bronchial smooth muscle dilation Asthma
  • Administration via inhalation
  • Duration: 4–6 hours
  • Toxicity: tremor and tachycardia

References

  1. Horowitz, A. J., Smith, T., & Frey, D. (2021). Sympathomimetics. StatPearls. Retrieved September 24, 2021, from http://www.ncbi.nlm.nih.gov/books/NBK546597/
  2. Kanter, J., & DeBlieux, P. (2014). Pressors and Inotropes. Emergency medicine clinics of North America. 32(4), pp. 823–34. https://doi.org/10.1016/j.emc.2014.07.006
  3. Manaker, S. (2020). Use of vasopressors and inotropes. UpToDate. Retrieved September 24, 2021, from https://www.uptodate.com/contents/use-of-vasopressors-and-inotropes
  4. Lexicomp, Inc. (2021). Albuterol (salbutamol): Drug information. UpToDate. Retrieved September 29, 2021, from https://www.uptodate.com/contents/albuterol-salbutamol-drug-information
  5. Lexicomp, Inc. (2021). Norepinephrine: Drug information. UpToDate. Retrieved September 29, 2021, from https://www.uptodate.com/contents/norepinephrine-noradrenaline-drug-information
  6. Lexicomp, Inc. (2021). Dopamine: Drug information. UpToDate. Retrieved September 29, 2021, from https://www.uptodate.com/contents/dopamine-drug-information
  7. Lexicomp, Inc. (2021). Dobutamine: Drug information. UpToDate. Retrieved September 29, 2021, from https://www.uptodate.com/contents/dobutamine-drug-information

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