Adrenergic Agonists / Antagonists

Question 1

Adrenergic agonists are also referred as?

Answer 1

Sympathomimetics

Question 2

Adrenergic agonists bind to what receptors?

Answer 2

Adrenergic Receptors

Question 3

Drugs can activate adrenergic receptors by 4 basic mechanisms

Answer 3

Direct receptor binding
Promotion of Norepinephrine release
Inhibition of Norepinephrine reuptake
Inhibition of Norepinephrine inactivation

Question 4

Direct receptor binding - three natural transmitters.

Answer 4

drugs activate peripheral adrenergic receptors. Mimics the action of natural transmitters (Norepinephrine, epinephrine and dopamine).

Question 5

Promotion of Norepinephrine Release

Answer 5

Acting on terminals of sympathetic nerves to cause NE release, drugs can bring about indirect activation of adrenergic receptors.

Amphetamines and cocaine work this way –drugs cause NE release in the synapses but they don’t bind directly to receptors

Question 6

Inhibition of Norepinephrine reuptake

Answer 6

Blocking NE reuptake, drugs can cause NE to accumulate within the synaptic gap
This action increases receptor activity
Cocaine and tricyclic antidepressants have the ability to block NE reuptake

Question 7

Inhibition of Norepinephrine inactivation

Answer 7

Some of the NE in nerve terminals of adrenergic neurons undergoes inactivation by monoamine oxidase (MAO)

Drugs that inhibit MAO can increase the amount of NE available for release, and enhance receptor activation

MAO inhibitors are used to treat depression

Question 8

A1 Agonists - two main responses

Answer 8

Vasoconstriction in blood vessels of the skin, viscera, and mucous membranes

Mydriasis of the eye

Question 9

Indications for A1 Agonist use and examples

Answer 9

Alpha 1 agonists are given to stop bleeding, primarily in the skin and mucous membranes

Epinephrine, applied topically is the alpha 1 agonist used most often for this purpose

Nasal congestion results from dilation and engorgement of blood vessels in the nasal mucosa

A1 stimulating drugs can relieve congestion by causing alpha 1 mediated vasoconstriction

Phenylephrine and pseudoephedrine are examples

Question 10

Why is A1 Agonist combined with local anesthetics and what happens / where

Answer 10

To delay systemic absorption

Vasoconstriction reduces blood flow to the site of anesthetic administration

This is done to keep the drug at the local site of action to prolong anesthesia (LET –lidocaine, epinephrine, tetracaine)

Question 11

A1 Agonist on BP

Answer 11

Elevation of BP: A1 agonists can elevate blood pressure in hypotensive patients

They are typically used in patients where fluid replacement is contraindicated, or when fluid replacement has failed to restore adequate pressure (multiple fluid boluses)

Question 12

Adverse Effects of A1 Activation three effects

Answer 12

Hypertension: A1 receptor activation can easily cause HTN, especially with IV vasopressors

Necrosis: If IV lines used to infuse A1 agonists become extravasated (interstitial) A1 agonists can easily cause tissue death

Bradycardia: A1 agonists can cause a reflex which slows the heart (increase in BP→ baroreceptor reflex)

Question 13

A2 Agonists - Location, activation and when should it not be used?

Answer 13

A2 receptors are located presynaptically, and their activation inhibits NE release

Several adrenergic agonists (Epi & NE) are capable of causing A2 activation

There are no therapeutic applications of A2 activation in the peripheral nervous system

Question 14

What two effects are produced by A2

Answer 14

1. Reduction of sympathetic outflow to the heart and blood vessels
2. Relief of severe pain

Clonidine is an example of an alpha 2 agonist that causes receptor activation in the CNS. This drug reduces sympathetic tone to blood vessels and to the heart (HTN)

Question 15

B1 Agonists use in HF / Shock

Answer 15

B1 agonists are useful in the following conditions:

Heart failure: activation of b1 receptors in the heart has positive inotropic effects and activation can improve cardiac performance

Shock: B1 agonists are able to maintain blood flow to vital organs by increasing chronotropic & inotropic effects

Question 16

B1 effects on AV heart block and Cardiac Arrest

Answer 16

Atrioventricular heart block: activation of cardiac b 1 receptors can enhance impulse conduction through the AV node

Cardiac arrest: by activating cardiac b1 receptors drugs can initiate contraction of the heart

Question 17

B1 Agonist Adverse Effects

Answer 17

Overstimulation of cardiac b1 receptors can produce tachycardia and dysrhythmias

Angina pectoris: increasing the workload on the heart (making it pump harder and faster) can induce chest pain due to atherosclerosis. B1 agonists increase cardiac oxygen demand

Question 18

B2 Agonists - Location, Receptor activation, promotes and why selective b2 agonists are preferred plus an example.

Answer 18

B2 activation is limited to the lungs and uterus

B2 receptor activation is primarily used to treat asthma, and other forms of bronchospasm

B2 activation promotes bronchodilation

B2 selective agonists are preferred (Ventolin), because they will not increase cardiac workload (B1 effects)

Question 19

Isoproterenol

Answer 19

Isoproterenol is a drug which is not beta selective

It will activate B1 and B2 receptors, therefore it is not as desirable for patients with a cardiac history

Delay of preterm labour: by activating B2 receptors in the uterus, smooth uterine muscle relaxes and this has the ability to delay preterm labour

Question 20

Adrenergic Antagonists block what receptors?

Answer 20

Adrenergic antagonists cause direct blockade of adrenergic receptors

Nearly all cause reversible(competitive) blockade

Question 21

Alpha Receptor Antagonists - A1 and A2 blockers are not commonly used in EMS; give examples and why they are used.

Answer 21

A1 and A2 blockers are not commonly used in EMS services

An example of a non selective alpha blocker is Phentolamine. This drug can block A1 and A2 receptors

It’s uses include: prevention of tissue necrosis following extravasation of IV A1 blockers, and reversal of soft tissue anesthesia

Question 22

Beta Receptor Antagonists - Common Beta 1 blockers examples and three benefits

Answer 22

B1 blockers include metoprolol, labetalol, bisoprolol, atenolol, and esmolol

3 major benefits of B1 blockade are: reduced heart rate, reduced force of contraction, and reduced velocity of impulse conduction through the AV node

Question 23

Beta Receptor Antagonists - How are Beta 1 blockers commonly used to control high heart rates (atrial fibrillation/atrial flutter)?

Answer 23

Beta 1 blockers are commonly used to control high heart rates (atrial fibrillation/atrial flutter)

By blocking B1 receptors in the heart:

1. Rate of sinus nodal discharge is decreased
2. Conduction of atrial impulses through the AV node is slowed

Question 24

Beta Receptor Antagonists Other non EMS uses include:

Answer 24

Treatment of angina
Treatment of HTN
Treatment of MI
Treatment of heart failure
Treatment of Phenochromocytoma