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adrenoceptor agonists
A mind map about adrenoceptor agonists. Its basic chemical structure is beta-phenylethylamine. There are alpha-receptor agonists, alpha-beta receptor agonists, and beta-receptor agonists.
Edited at 2023-10-25 15:49:47
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adrenoceptor agonists
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- Outline
adrenoceptor agonists
QSAR
The basic chemical structure is β-phenylethylamine
Different chemical groups (OH) on the benzene ring
Affects the intensity and duration of drug action
Affects the ability of drugs to enter the central nervous system
The number of hydroxyl groups is ↓, the central effect is strengthened, the peripheral effect is weakened, the action time is prolonged, and poF is increased.
The hydrogen on the α carbon atom of the alkylamine side chain is substituted
Substitution with methyl group improves stability and prolongs action time
Affects the stability of drugs on MAO
Amino hydrogen atoms are substituted
Drug selectivity for α and β receptors will change
Classification
alpha receptor agonists
Norepinephrine NA
Metahydroxylamine
phenylephrine
Methoxamine
Alpha and beta receptor agonists
Adrenaline
dopamine DA
Ephedrine
beta agonists
isoproterenol
dobutamine
alpha receptor agonists
Norepinephrine NE/NA
Sympathetic postganglionic fibers release endogenous neurotransmitters
internal processes
po
Due to local effects, gastric mucosal vasoconstriction affects its absorption.
Easily destroyed by alkaline intestinal fluid in the intestines
subcutaneous injection
Vigorous contraction of blood vessels results in little absorption, and local tissue necrosis is prone to occur → iv.
Exogenous NA cannot easily penetrate the BBB and rarely reaches brain tissue.
Pharmacological effects
Blood vessel
Stimulates vascular α1 receptors and constricts blood vessels
Mainly: venules, arterioles
resistance vessels
Even cerebral blood vessels and skeletal muscle blood vessels (rarely)
Arterial constriction → blood flow decreases, venous constriction → total peripheral resistance increases
Coronary vasodilation (β2)
←Heart excitement, myocardial metabolites increase
Skin and mucosal blood vessels>renal blood vessels>mesenteric and hepatic blood vessels
Heart (weak)
Stimulates cardiac β1 receptors, strengthens myocardial contractility, accelerates heart rate, accelerates conduction, and increases cardiac output.
Overall, heart rate slows down
Increased blood pressure and slowed reflexes
Strongly constricts blood vessels, increases peripheral resistance, increases cardiac ejection resistance, and causes cardiac output to remain unchanged or decrease.
blood pressure
Small dosesiv.
Vasoconstriction effect is not obvious
Cardiac excitement increases systolic blood pressure SP, but the diastolic blood pressure DP does not increase significantly.
Increased pulse pressure
large dose
Vasoconstriction significantly increases peripheral resistance → SP increases and DP also increases significantly
Decreased pulse pressure
Clinical application
early neurogenic shock
Early blood pressure drops
Metahydroxylamine
The pressor effect is weaker than NA, slow and lasting, and less likely to cause renal failure.
Hypotension after pheochromocytoma resection or drug intoxication
CNS depressant overdose
Hypotension caused by chlorpromazine overdose
local hemostasis
PO constricts the blood vessels of the esophageal and gastric mucosa
upper gastrointestinal bleeding
Adverse reactions
local tissue ischemia and necrosis
Intravenous infusion time is too long, concentration is too high, leakage → ischemic necrosis
Stop injection or change injection site
local hot compress
The α-receptor blocking drug phentolamine causes local infiltration → dilates blood vessels
deal with
acute renal failure
Cause: Infusion time is too long or dose is too large
Severe contraction of renal blood vessels, resulting in oliguria, anuria and renal parenchymal damage
Contraindications
hypertension
arteriosclerosis
organic heart disease
Oliguria, anuria
Severe microcirculation disorder
pregnant woman
Metahydroxylamine
NA substitutes, which have both direct and indirect effects on alpha receptors
Features
direct effect
It acts directly on α-R and can be administered directly through intramuscular injection. Its vasoconstrictive effect is only 10/1 of NA, but it can also reduce renal blood flow.
Weak effect on β1-R and difficult to cause arrhythmia
indirect effect
It can be taken up by adrenergic nerve endings into vesicles and promote the release of NA in the vesicles through displacement.
Not easily destroyed by MAO
The effect is long-lasting, and short-term continuous use can produce rapid tolerance.
Alpha and beta receptor agonists
Adrenaline AD
internal processes
After oral administration, it is easily destroyed and oxidized in alkaline intestinal juice, intestinal mucosa and liver.
Quickly absorbed by intramuscular injection
Distribution: Sympathetic effectors
Metabolism: COMT, MAO
Pharmacological effects
heart
Stimulates β1 receptors, increases cardiac excitability, strengthens myocardial contractility, accelerates conduction, and accelerates heart rate
Blood vessel
Stimulates α1 receptors, constricts blood vessels in skin, mucous membranes, mesentery, and kidneys
Isoproterenol None
Stimulates β2 receptors, dilates skeletal muscle and liver blood vessels
Coronary vasodilation: action of adenosine
blood pressure
small dose
Increased systolic blood pressure → cardiac excitement, increased cardiac output
Diastolic blood pressure remains unchanged or decreases, and pulse pressure difference increases← skeletal muscle vasodilation offsets or exceeds skin and mucosal vasoconstriction
large dose
SP and DP increase, pulse pressure difference becomes smaller←Mucocutaneous vasoconstriction exceeds skeletal muscle vasodilation
β2 receptors are highly sensitive to low concentrations of AD
bronchial smooth muscle
dilated bronchi
Relieve bronchial asthma
Inhibit mast cells from releasing allergenic substances
Shrink bronchial mucosal blood vessels and eliminate bronchial mucosal edema
metabolism
Promote glycogen and fat decomposition and increase blood sugar
CNS
Difficult to pass through BBB
Excitement in large doses
Clinical application
cardiac arrest
Caused by drowning, anesthesia, accidents during surgery, drug poisoning, infectious diseases and heart block, etc.
Allergic reaction rescue, anaphylactic shock
Bronchospasm, vasodilation, and Bp↓ can be seen.
First choice for anaphylactic shock
acute bronchial asthma attack
Compatible with local anesthetics
Constrict blood vessels, reduce absorption of local anesthetics, and prolong the action time of local anesthetics
local hemostasis
glaucoma
Adverse reactions
Palpitations, irritability, headache, blood pressure ↑
When α-receptors are over-excited, blood pressure may rise sharply, which may lead to the risk of cerebral hemorrhage → Use with caution in the elderly
When beta receptors are overexcited, myocardial oxygen consumption increases, causing myocardial ischemia, arrhythmia, and even ventricular fibrillation → Strictly control the dose
Contraindications
cerebral arteriosclerosis
hypertension
Hyperthyroidism
organic heart disease
diabetes
dopamine DA
NA precursor
internal processes
After po, it is easily destroyed in the intestines and liver and becomes ineffective.
Generally intravenous infusion, it is quickly metabolized and inactivated by MAO and COMT in the body → the action time is short
Difficult to penetrate BB, exogenous DA has no central effect
Pharmacological effects
Small doses of D1 receptor agonists
Splanchnic vasoconstriction, renal vasodilation, renal blood flow increase, and coronary vasodilation
Direct natriuresis and diuresis
Moderate dose agonist of β1 receptors
The heart is excited, cardiac output increases, and cardiac contractility increases
High-dose α1 receptor agonist
Causes vasoconstriction (direct action)
Promote NA release (indirect effect)
Clinical application
Various shocks
Suitable for patients with weakened myocardial contractility and decreased urine output
intravenous drip
acute renal failure diuretics
acute cardiac insufficiency
Anti-shock mechanism of action
Boost blood pressure so that blood supply is properly distributed. Appropriate doses of DA enable proper blood distribution
Enhance myocardial contractility and increase cardiac output (cardiotonic effect) β1
Protect the kidneys and increase urine output. Kidneys and mesenteric blood vessels dilate, blood supply to important organs increases, and damage is reduced. D1
Skeletal muscle and skin blood vessels constrict, increasing microcirculatory perfusion pressure. α
Ephedrine
Mechanism
Causes of tolerance: transmitter depletion, receptor saturation, decreased affinity
Indirect effect (main mechanism)
Promote the release of NA from adrenergic nerve terminals, mimicking adrenergic effects
Direct action (secondary mechanism)
Stimulates alpha and beta receptors
Pharmacological effects
cardiovascular
alpha increases blood pressure
beta excited heart
Reflexively reduces sympathetic resonance and slows down the heart rate, offsetting the effect of directly increasing the heart rate, resulting in little change in the heart rate.
bronchial smooth muscle
Has a weak relaxing effect, fast onset and long maintenance time
CNS
Has a significant stimulating effect on the central nervous system
Larger doses can excite the cerebral cortex, causing mental excitement, restlessness, and insomnia.
tachyphylaxis
After repeated short-term treatment, the effect of this product gradually weakens.
Clinical application
Prevent and treat bronchial asthma
Prevention of attacks and treatment of mild cases, poor efficacy in severe acute attacks
It has a central stimulant effect and should be taken in conjunction with a small dose of sedative-hypnotic drugs at night.
Treat nasal congestion caused by congestion of nasal mucosa
0.5% ~ 1.0% ephedrine hydrochloride nasal drops can eliminate mucosal swelling
Acute rhinitis, paranasal sinusitis, chronic hypertrophic rhinitis
Treat various hypotensive states
Prevent and treat hypotension caused by spinal anesthesia, epidural anesthesia, and subarachnoid anesthesia
Relieve skin and mucosal symptoms of urticaria and angioedema
Pharmacological characteristics
Chemically stable, effective orally available
Adrenomimetic effects are weak but long-lasting
The central effect is more obvious
tachyphylaxis
beta agonists
isoproterenol
internal processes
Inhalation, intravenous administration
COMT metabolism
Pharmacological effects
Mainly agonizes β-receptors, with very low selectivity for β1 and β2 receptors
heart
Has a strong agonistic effect on cardiac β1 receptors
positive inotropy
positive frequency
Compared with AD
Accelerates heart rate and has strong accelerating conduction effect
Myocardial oxygen consumption increased significantly
blood vessels and blood pressure
Stimulating β2 receptors causes skeletal muscle vasodilation and increases pulse pressure
Cardiac excitement and peripheral vasodilation increase systolic blood pressure and slightly decrease diastolic blood pressure.
bronchial smooth muscle
Stimulates β2 receptors and relaxes bronchial smooth muscle
Clinical application
cardiac arrest
Ventricular slow rhythm
atropine
high grade atrioventricular block
sinus node failure
concurrent cardiac arrest
Atrioventricular block (II, III degree)
Powerful acceleration of conduction
atropine
Bronchial Asthma (β2)
Control acute exacerbations of bronchial asthma. Sublingual or spray administration has fast and powerful effects.
shock
Septic shock with high central venous pressure and low cardiac output
Adverse reactions
Palpitations, dizziness ← Vasodilator reaction
Arrhythmia
tachyphylaxis
dobutamine
Pharmacological effects
β1 receptor agonist
Selective beta-1 agonists: preterol, zamoterol
Less likely to affect heart rate, less likely to increase myocardial oxygen consumption, less likely to cause tachycardia
Clinical application
Myocardial infarction complicated by heart failure
Selectively agonizes β2 receptors
albuterol
Terbutaline
Clenbuterol
Relaxes bronchial smooth muscle (β2), but has no cardiac stimulant effect
Treat bronchial asthma
Similarities and differences between AD, NA, and isoproterenol on the cardiovascular system
Same point
Both are adrenergic receptor agonists
All have a constrictive effect on blood vessels
Increase systolic blood pressure
dilation of coronary arteries
All have exciting effects on the heart
Increased myocardial contractility
difference
AD
excitatory alpha receptors
skin visceral vasoconstriction
Excitatory β1 receptors
increased heart rate
Increased myocardial contractility
Coronary artery dilation improves blood supply to the myocardium
Excitatory beta2 receptors
skeletal muscle coronary vasodilation
Alpha, beta adrenoceptor agonist
NA
excitatory alpha receptors
Skin, visceral vasoconstriction
Excitatory β1 receptors
increased cardiac output
Increased myocardial oxygen consumption
Coronary artery dilation improves blood supply to the myocardium
Alpha adrenoceptor agonist
isoproterenol
Excitatory β1 receptors
increased heart pressure
Excitatory beta2 receptors
skeletal muscle coronary vasodilation
β-adrenoceptor agonist
Anti-shock properties
AD
Bronchodilation, vasodilation, and decrease in blood pressure can be seen
Intramuscular or subcutaneous administration, intravenous injection should be slow
NA
Improve microcirculation and replenish blood volume
NA→Maintain stable systolic blood pressure and ensure blood supply to the heart and brain
Long-term/high dose → aggravate microcirculation disorder (causing renal failure)
DA
Constrict blood vessels in skeletal muscles and skin, increase microcirculatory perfusion pressure, and distribute blood reasonably.
Kidneys and mesenteric blood vessels dilate, blood supply to important organs increases, and damage is reduced
It is more effective in patients with shock who are accompanied by decreased cardiac contractility and decreased urine output but whose blood volume has been replenished.
Reasons why AD is the first choice drug for treating anaphylactic shock
Characteristics of anaphylactic shock
Small blood vessels dilate, capillary permeability increases, blood volume and peripheral resistance decrease, and blood pressure decreases
Bronchial smooth muscle spasm, mucosal edema, dyspnea
Cardiac depression
Treatment mechanism
Treat the symptoms
Stimulate alpha receptors, contract blood vessels, increase blood pressure, constrict bronchial smooth muscle blood vessels, eliminate edema, and improve ventilation
Stimulates β1 receptors, excites the heart, enhances myocardial contractility, dilates coronary arteries, and improves cardiac function.
Stimulates β2 receptors, dilates bronchial smooth muscle, and relieves bronchial smooth muscle spasm
Treat the root cause
Stimulating β2 receptors can inhibit the release of histamine and other allergic substances from mast cells and reduce the release of allergic mediators.