Transcript Drugs Affecting The Autonomic Nervous System Adrenergic Agents and Adrenergic-Blocking Agents Copyright © 2002, 1998, Elsevier Science (USA).

Drugs Affecting The
Autonomic Nervous System
Adrenergic Agents and
Adrenergic-Blocking Agents
Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved.
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EIC Image #48:
The Sympathetic Nervous System
in Relationship to the Entire
Nervous System
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Adrenergic Agents
• Drugs that stimulate the sympathetic nervous
system (SNS)
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Adrenergic Agents
Also known as
• adrenergic agonists or sympathomimetics
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Adrenergic Agents
Mimic the effects of the SNS neurotransmitters:
• norepinephrine (NE) and epinephrine (EPI)
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Adrenergic Receptors
• Located throughout the body
• Are receptors for the sympathetic
neurotransmitters
Alpha-adrenergic receptors: respond to NE
Beta-adrenergic receptors: respond to EPI
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Alpha-Adrenergic Receptors
• Divided into alpha1 and alpha2 receptors
• Differentiated by their location on nerves
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Alpha1-Adrenergic Receptors
• Located on postsynaptic effector cells
(the cell, muscle, or organ that the nerve
stimulates)
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Alpha2-Adrenergic Receptors
• Located on presynaptic nerve terminals
(the nerve that stimulates the effector cells)
• Control the release of neurotransmitters
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The predominant alpha-adrenergic
agonist responses are:
• Vasoconstriction and CNS stimulation
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Beta-Adrenergic Receptors
All are located on postsynaptic effector cells
• Beta1-adrenergic receptors—located primarily
in the heart
• Beta2-adrenergic receptors—located in smooth
muscle of the bronchioles, arterioles, and visceral
organs
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The beta-adrenergic agonist
response results in:
• Bronchial, GI, and uterine smooth muscle
relaxation
• Glycogenolysis
• Cardiac stimulation
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Dopaminergic Receptors
• An additional adrenergic receptor
• Stimulated by dopamine
• Causes dilation of the following blood
vessels, resulting in INCREASED blood flow
– Renal
– Mesenteric
– Coronary
– Cerebral
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Adrenergic Receptor Responses
to Stimulation
LOCATION
RECEPTOR
RESPONSE
Blood vessels
alpha1 and beta2
Constriction /
dilation
Cardiac muscle
beta1
Increased
contractility
AV Node
beta1
Increased
heart rate
SA Node
beta1
Increased
heart rate
Cardiovascular
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Adrenergic Receptor Responses
to Stimulation
LOCATION
RECEPTOR
RESPONSE
Muscle
beta2
Decreased
motility
Sphincters
alpha1
Constriction
Gastrointestinal
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Adrenergic Receptor Responses
to Stimulation
LOCATION
RECEPTOR
RESPONSE
Bladder
sphincter
alpha1
Constriction
Penis
alpha1
Ejaculation
Uterus
alpha1 and beta2
Contraction/
relaxation
Genitourinary
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Adrenergic Receptor Responses
to Stimulation
LOCATION
RECEPTOR
RESPONSE
beta2
Dilation/relaxation
Respiratory
Bronchial
muscles
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Catecholamines
Substances that can produce a sympathomimetic
response
Endogenous:
• epinephrine, norepinephrine,dopamine
Synthetic:
• isoproterenol, dobutamine, phenylephrine
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Adrenergic Agents
Mechanism of Action
Direct-acting sympathomimetic:
• Binds directly to the receptor and causes a
physiologic response
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Direct-Acting Sympathomimetics
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Adrenergic Agents
Mechanism of Action
Indirect-acting sympathomimetic:
• Causes the release of catecholamine from the
storage sites (vesicles) in the nerve endings
• The catecholamine then binds to the receptors and
causes a physiologic response
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Indirect-Acting Sympathomimetics
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Adrenergic Agents
Mechanism of Action
Mixed-acting sympathomimetic:
• Directly stimulates the receptor by binding
to it
AND
• Indirectly stimulates the receptor by causing
the release of stored neurotransmitters from
the vesicles in the nerve endings
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Mixed-Acting Sympathomimetics
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Drug Effects of Adrenergic Agents
Stimulation of alpha-adrenergic receptors on
smooth muscles results in:
• Vasoconstriction of blood vessels
• Relaxation of GI smooth muscles
• Contraction of the uterus and bladder
• Male ejaculation
• Decreased insulin release
• Contraction of the ciliary muscles of the eye
(dilated pupils)
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Drug Effects of Adrenergic Agents
Stimulation of beta2-adrenergic receptors on
the airways results in:
• Bronchodilation (relaxation of the bronchi)
• Uterine relaxation
• Glycogenolysis in the liver
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Drug Effects of Adrenergic Agents
Stimulation of beta1-adrenergic receptors on
the myocardium, AV node, and SA node
results in CARDIAC STIMULATION:
• Increased force of contraction
(positive inotropic effect)
• Increased heart rate
(positive chronotropic effect)
• Increased conduction through the AV node
(positive dromotropic effect)
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Adrenergic Agents:
Therapeutic Uses
• Anorexiants: adjuncts to diet in the
short-term management of obesity
Examples:
benzphetamine
phentermine
dextroamphetamine
Dexedrine
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Adrenergic Agents:
Therapeutic Uses
Bronchodilators: treatment of asthma and
bronchitis
• Agents that stimulate beta2-adrenergic receptors
of bronchial smooth muscles causing relaxation
Examples:
albuterol
isoetharine
metaproterenol
ephedrine
isoproterenol
salmeterol
epinephrine
levalbuterol
terbutaline
• These agents may also affect uterine and vascular
smooth muscles.
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Adrenergic Agents:
Therapeutic Uses
• Reduction of intraocular pressure and
mydriasis (pupil dilation): treatment of
open-angle glaucoma
Examples:
epinephrine and dipivefrin
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Adrenergic Agents:
Therapeutic Uses
Nasal decongestant:
• Intranasal (topical) application causes constriction
of dilated arterioles and reduction of nasal blood
flow, thus decreasing congestion.
Examples:
epinephrine
ephedrine
phenylephrine
tetrahydrozoline
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naphazoline
Adrenergic Agents:
Therapeutic Uses
Ophthalmic
• Topical application to the eye surface affects
the vasculature of the eye, stimulating alpha
receptors on small arterioles, thus relieving
conjunctival congestion.
Examples:
epinephrine
phenylephrine
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naphazoline
tetrahydrozoline
Adrenergic Agents:
Therapeutic Uses
Vasoactive sympathomimetics (pressors,
inotropes), also called cardioselective
sympathomimetics
• Used to support the heart during cardiac failure
or shock.
Examples:
dobutamine
epinephrine
dopamine
fenoldopam
methoxamine
phenylephrine
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ephedrine
isoproterenol
norepinephrine
Adrenergic Agents: Side Effects
Alpha-Adrenergic Effects
• CNS:
– headache, restlessness, excitement, insomnia,
euphoria
• Cardiovascular:
– palpitations (dysrhythmias), tachycardia,
vasoconstriction, hypertension
• Other:
– anorexia, dry mouth, nausea, vomiting, taste
changes (rare)
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Adrenergic Agents: Side Effects
Beta-Adrenergic Effects
• CNS:
– mild tremors, headache, nervousness, dizziness
• Cardiovascular:
– increased heart rate, palpitations (dysrhythmias),
fluctuations in BP
• Other:
– sweating, nausea, vomiting, muscle cramps
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Adrenergic Agents: Interactions
• Anesthetic agents
• Tricyclic antidepressants
• MAOIs
• Antihistamines
• Thyroid preparations
• Antihypertensives
• Will directly antagonize another adrenergic
agent, resulting in reduced effects
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Adrenergic Agents:
Nursing Implications
• Assess for allergies and history of
hypertension, cardiac dysrhythmias, or other
cardiovascular disease.
• Assess renal, hepatic, and cardiac function
before treatment.
• Perform baseline assessment of vital signs,
peripheral pulses, skin color, temperature,
and capillary refill. Include postural blood
pressure and pulse.
• Follow administration guidelines carefully.
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Adrenergic Agents:
Nursing Implications
IV administration:
• Check IV site often for infiltration
• Use clear IV solutions
• Use an infusion device/IV pump
• Infuse agent slowly to avoid dangerous
cardiovascular effects
• Monitor cardiac rhythm
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Adrenergic Agents:
Nursing Implications
With chronic lung disease:
• Instruct patients to avoid factors that exacerbate
their condition.
• Encourage fluid intake
(up to 3000 mL per day) if permitted.
• Educate about proper dosing and
equipment care.
Salmeterol is indicated for PREVENTION
of bronchospasms, not management
of acute symptoms.
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Adrenergic Agents:
Nursing Implications
• Overuse of nasal decongestants may cause rebound
nasal congestion or ulcerations.
• Avoid OTC or other medications because of possible
interactions.
• Administering two adrenergic agents together may
precipitate severe cardiovascular effects such as
tachycardia or hypertension.
• Inform patients taking inhaled isoproterenol that
their sputum or saliva may turn pink.
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Adrenergic Agents:
Nursing Implications
Monitor for therapeutic effects
(cardiovascular uses):
• Decreased edema
• Increased urinary output
• Return to normal vital signs
• Improved skin color and temperature
• Increased LOC
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Adrenergic Agents:
Nursing Implications
Monitor for therapeutic effects (asthma):
• Return to normal respiratory rate
• Improved breath sounds, fewer rales
• Increased air exchange
• Decreased cough
• Less dyspnea
• Improved blood gases
• Increased activity tolerance
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Adrenergic-Blocking Agents
• Bind to adrenergic receptors, but inhibit or
block stimulation of the sympathetic nervous
system (SNS)
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Adrenergic Blocking Agents
• Have the opposite effect of adrenergic
agents
• Also known as
– adrenergic antagonists or sympatholytics
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Adrenergic Blocking Agents
• Sympatholytics inhibit—or LYSE—
sympathetic neurotransmitters
(norepinephrine and epinephrine)
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Adrenergic Blocking Agents
Classified by the type of adrenergic receptor
they block
• Alpha1 and alpha2 receptors
• Beta1 and beta2 receptors
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Alpha-Blocker Mechanisms
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Adrenergic-Blocking Agents:
Drug Effects and Therapeutic Uses
Ergot Alkaloids (Alpha-Blockers)
• Constrict dilated arteries going to the brain
(carotid arteries)
• Used to treat vascular headaches (migraines)
• Stimulate uterine contractions by inducing
vasoconstriction
• Used to control postpartum bleeding
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Adrenergic-Blocking Agents:
Drug Effects and Therapeutic Uses
Alpha-Blockers
• Cause both arterial and venous dilation, reducing
peripheral vascular resistance and BP
• Used to treat hypertension
• Effect on receptors on prostate gland and bladder
decreased resistance to urinary outflow, thus
reducing urinary obstruction and relieving effects
of BPH
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Adrenergic-Blocking Agents:
Drug Effects and Therapeutic Uses
Alpha-Blockers
• Phentolamine
– Quickly reverses the potent vasoconstrictive effects of
extravasated vasopressors such as norepinephrine or
epinephrine.
– Restores blood flow and prevents tissue necrosis.
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Adrenergic-Blocking Agents:
Side Effects
Alpha Blockers
Body System
Side/Adverse Effects
Cardiovascular
Palpitations, orthostatic
hypotension, tachycardia,
edema, dysrhythmias, chest pain
CNS
Dizziness, headache, drowsiness,
anxiety, depression, vertigo,
weakness, numbness, fatigue
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Adrenergic-Blocking Agents:
Side Effects
Alpha Blockers
Body System
Side/Adverse Effects
Gastrointestinal
Nausea, vomiting, diarrhea,
constipation, abdominal pain
Other
Incontinence, nose bleeding,
tinnitus, dry mouth, pharyngitis,
rhinitis
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Beta Blockers
• Block stimulation of beta receptors in
the SNS
• Compete with norepinephrine and
epinephrine
• Selective and nonselective beta blockers
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Beta Receptors
Beta1 Receptors
• Located primarily on the heart
• Beta blockers selective for these receptors
are called cardioselective beta blockers
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Beta Receptors
Beta2 Receptors
• Located primarily on smooth muscles
of bronchioles and blood vessels
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Nonspecific Beta Blockers
• Beta blockers that block both beta1 and
beta2 receptors
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Beta Blockers: Mechanism of Action
Cardioselective (Beta1)
• Decreases heart rate
• Prolongs SA node recovery
• Slows conduction rate through the AV node
• Decreases myocardial contractility, thus
decreasing myocardial oxygen demand
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Beta Blockers: Mechanism of Action
Nonspecific (Beta1 and Beta2)
• Effects on heart:
Same as cardioselective
• Bronchioles:
Constriction, resulting in
narrowing of airways and
shortness of breath
• Blood vessels:
Vasoconstriction
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Beta Blockers: Therapeutic Uses
• Anti-angina:
decreases demand for
myocardial oxygen
• Cardioprotective:
inhibits stimulation by
circulating catecholamines
• Class II antidysrhythmic
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Beta Blockers: Therapeutic Uses
• Antihypertensive
• Treatment of migraine headaches
• Glaucoma (topical use)
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Beta Blockers: Side Effects
Body System
Side/Adverse Effects
Blood
Agranulocytosis, thrombocytopenia
Cardiovascular
AV block, bradycardia, congestive
heart failure, peripheral vascular
insufficiency
CNS
Dizziness, mental depression,
lethargy, hallucinations
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Adrenergic-Blocking Agents:
Side Effects
Beta Blockers
Body System
Side/Adverse Effects
Gastrointestinal
Nausea, dry mouth, vomiting,
diarrhea, cramps, ischemic colitis
Other
Impotence, rash, alopecia,
bronchospasms
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Adrenergic Blocking Agents:
Nursing Implications
• Assess for allergies and history of COPD,
hypotension, cardiac dysrhythmias,
bradycardia, CHF, or other cardiovascular
problems
Any preexisting condition that might be
exacerbated by the use of these agents might
be a CONTRAINDICATION to their use.
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Adrenergic Blocking Agents:
Nursing Implications
• Remember that alpha blockers may
precipitate hypotension.
• Remember that beta blockers may
precipitate bradycardia, hypotension,
heart block, CHF, and bronchoconstriction.
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Adrenergic Blocking Agents:
Nursing Implications
• Avoid OTC medications because of possible
interactions.
• Possible drug interactions may occur with:
– Antacids (aluminum hydroxide type)
– Antimuscarinics/anticholinergics
– Diuretics and cardiovascular drugs
– Neuromuscular blocking agents
– Oral hypoglycemic agents
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Adrenergic Blocking Agents:
Nursing Implications
• Encourage patients to take medications
as prescribed.
• These medications should never be
stopped abruptly.
• Report constipation or the development of
any urinary hesitancy or bladder distention.
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Adrenergic Blocking Agents:
Nursing Implications
• Teach patients to change positions slowly to
prevent or minimize postural hypotension.
• Avoid caffeine (excessive irritability).
• Avoid alcohol ingestion and hazardous
activities until blood levels become stable.
• Patients should notify their physician if
palpitations, dyspnea, nausea, or vomiting
occur.
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Beta Blocking Agents:
Nursing Implications
• Rebound hypertension or chest pain may occur if
this medication is discontinued abruptly.
• Patients should notify their physician if they become
ill and unable to take medication.
• Inform patients that they may notice a decrease in
their tolerance for exercise; dizziness and fainting
may occur with increased activity. Notify the
physician if these problems occur.
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Beta Blocking Agents:
Nursing Implications
Patients should report the following to
their physician:
• Weight gain of more than 2 pounds (1 kg)
within a week
• Edema of the feet or ankles
• Shortness of breath
• Excessive fatigue or weakness
• Syncope or dizziness
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Adrenergic Blocking Agents:
Nursing Implications
Monitor for side effects, including:
Hypotension
Fatigue
Tachycardia (alpha blockers)
Lethargy
Bradycardia
Depression
Heart block
Insomnia
CHF
Vivid nightmares
Increased airway resistance
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Adrenergic Blocking Agents:
Nursing Implications
Monitor for therapeutic effects
• Decreased chest pain in patients with angina
• Return to normal BP and P
• Other specific effects, depending on the use
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