Adrenergic Agonists

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Name 4 catecholamines

Epinephrine, Norepinephrine, Dopamine, Dobutamine, Isoproterenol

Epinephrine's affinity for alpha & beta receptors

alpha1=alpha2
beta1=beta2

What blood pressure response will you see with stimulation of alpha receptors in the blood vessels?

Increased Diastolic BP

What blood pressure response will you see with stimulation of beta receptors in the CV system?

Increased Systolic BP

What response in the heart will you see from Epinephrine?

Positive inotropy, Positive chronotropy

What beta-2 activation response will you see in the skeletal muscle blood vessels with Epinephrine?

Skeletal muscle vessels dialate

Dosing of Epinephrine?

Asystole = 1mg IV q 3-5min
Hypotension = 1-10 mcg/min IV infusion
Bronchodilator = 0.1-0.5mg IM/SQ q 10-15 min

How is Epi metabolized?

Quick metabolism by COMT & MOA enzymes

Norepi's affinity for Alpha & Beta receptors?

Alpha-1=Alpha-2
Beta-1>>Beta-2

What effect on Blood Pressure will you see with Norepi?

Increase in Systolic & Diastolic BP

Why might you see a fall in HR or no increase in HR with Norepi?

The brain senses an increase in BP so it activates the PSNS to stimulate Muscarinic receptors located in the heart - compensatory

Dosing of Norepinephrine?

Continuous IV - 4mcg/min and titrate
Usual dose = 8-12mcg/min

What is the RULE OF 6?

6 x weight(kg) x desired dose/desired IV rate = amount of med (mg) to add to 100ml fluid

Isoproterenol's affinity for alpha & Beta receptors?

Potent Beta agonist; Beta-1>Beta-2>>>>>>>>alpha

Response seen in blood vessels with Isoproterenol?

Beta agonist=vasodilator

Response seen in the heart with Isoproterenol?

Increases inotropy & Chronotropy
Increased Cardiac Output
Fall in diastolic with slight increase or decrease in systolic

Why will you see a decreased Diastolic BP with Isoproterenol?

B/c Beta-2 effects

Dosing of Isoproterenol?

Arrhythmias = 5mcg/min IV infusion initially & titrate
Shock = 0.5-5mcg/min IV infusion & titrate

Dopamine's affinity for Alpha & Beta receptors?

D-1=D-2>>Beta>>alpha

Dosing for Dopamine?

LOW= 1-3mcg/kg/min (Dopa receptor activation)
INTERMEDIATE= 3-10mcg/kg/min (Dopa & Beta-1)
HIGH= >10mcg/kg/min (Dopa, Beta & Alpha)

Fenoldopam's affinity for Alpha & Beta receptors?

D-1>>D-2

What effects in some vascular beds will you see with Fenoldopam?

Peripheral Vasodilation

Primary use for Fenoldopam?

Severe Hypertension

Dobutamine's affinity for Alpha & Beta receptors?

Beta-1>Beta-2>>>>>>alpha

Cardiac effects seen with Dobutamine?

Increased Inotropy & Chronotropy by activating selective beta-1 receptors

Dosing for Dobutamine?

2.5-15mcg/kg/min
Max = 40mcg/kg/min

MOA for Phenylephrine?

Pure alpha agonist

Is phenylephrine inactivated by COMT

NO

3 Main uses for Phenylephrine?

1. Pupil dilation
2. Decongestant
3. Increased BP (minor)

MOA of Methoxamine?

Direct acting alpha-1 agonist
Powerful vasoconstrictor

Effects of Methoxamine?

Prolonged increase in BP - Rarely used clinically

Why do you see bradycardia with Methoxamine?

Because it is a potent vasoconstrictor, the brain senses the increase in BP and activates the PSNS to stimulate muscarininc receptors in the heart to dec. HR

MOA of Midodrine?

Selective alpha-1 agonist - direct acting

What cardiac effects do you see with Midodrine?

Increased DPB

Indication for Midodrine?

Postural Hypotension

Why is Midodrine not used clinically?

Used to treat postural HYPOtension, but will see HYPERtension when pt. is supine

Where does Ephedrine come from?

Ma-huang plant from China

MOA of Ephedrine?

Orally active Direct acting sympathomimetic
Releases stored catecholamines
Mimics epinephrine (but doesn't increase BP as much)

Why have we been able to modify ephedrine and come up with new meds?

It has 2 points of chirality allowing for isomers to be derived.

Why do you see mild CNS stimulant effects with Ephedrine?

It crosses BBB

Main use for for ephedrine?

Nasal Decongestant

MOA of Xylometazoline & Oxymetazoline

Direct acting Alpha Agonist

Uses for Xylometazoline & Oxymetazoline

Constriction of Nasal Mucosa (Afrin)
Topical Decongestant

Why do you not want to use Xylometazoline & Oxymetazoline long term?

Can cause rebound congestion b/c alpha receptors that are being stimulated get down regulated

Why may you see a Dec. in BP with increased used of Xylometazoline & Oxymetazoline?

You get good absorption systemically, it crosses BBB and can see effects of Alpha-2 stimulation in the brain leading to a dec. BP (like clonadine)

MOA of Amphetamines

Lipid soluble indirect sympathomimetic that Crosses BBB

Effects seen with Amphetamines

Marked stimulant effects on mood and alertness

Uses for Amphetamines

Appetite Depressant

MOA of Methamphetamine

Indirect acting Sympathomimetic that has a higher ratio of central to peripheral actions

Uses for Methamphetamine

Appetite Suppressant

Phenmetrazine MOA and use?

Indirect Sympathomimetic, used as appetite suppressant

MOA for Methylphenidate & Pemoline and use?

Indirect Sympathomimetic - stimulant used in children for ADHD

MOA for Modafinil and use?

Alpha-1b receptor agonist in the brain
Use=Narcolepsy

MOA of Cocaine?

Sympathomimetic that readily enters CNS and inhibits dopamine re-uptake into pre-synaptic neurons in the pleasure centers- Also alpha stimulation seen causing vasoconstriction

Tyramine MOA

NOT a drug but rather a metabolite of tyrosine
Indirect sympathomimetic (similar to norepi)
Releases stored catecholamines

How is Tyramine metabolized?

MAO

Effects seen in blood vessels with Alpha receptor stimulation

Vasoconstriction, Inc. SVR & Inc. DBP
Alpha 1

Effects seen in blood vessels with Beta receptor stimulation

Vasodialation, Dec. SVR
Beta 2

Effects seen in blood vessels with Dopamine receptor stimulation

D1 = Vasodilation in renal, coronary, visceral, & Cerebral vessels

Effects seen in the Heart with Beta Receptor Stimulation

Inc. Inotropy & Inc. Chronotropy
Beta 1 - is dominant

Effects seen in the Heart with Alpha receptor stimulation

Not many receptors present = no real effect

Effects seen in the eye with Alpha Stimulation

Pupil dilation via constriction of iris radial muscle & inc. in aqueous humor

Effects seen in the eye with Beta Stimulation

Pupil dilation via relaxing ciliary bodies & decreased in production of aqueous humor

Effects seen in the lungs with Alpha stimulation

Constriction of Bronchial blood vessels in upper airway = decongestants & dec mucus production

Effects seen in the lungs with Beta Stimulation

Bronchodilation via Beta -2

Effects seen in the GI tract with Alpha Receptor stimulation

Indirectly as heteroceptor - activates presynaptic alpha site on cholinergic nerve - leads to dec. ACh release and slowing of digestion
Also alpha 1 - contracts smooth muscle sphincters

Effects seen in GI tract with Beta Receptor stimulation

relaxes smooth muscle walls and slows down digestion - Beta -2

Effects seen in GU tract with Alpha Receptor stimulation

constriction of bladder base, urethral sphincter and prostate
Ejaculation
Uterine Contraction

Effects seen in GU tract with Beta Receptor stimulation

Relaxation of bladder walls - Beta 2
Uterine relaxation - Beta 2

Effects seen in sweat gland with alpha receptor stimulation

Apocrine - stimulation to release fatty oils
"Stinky puberty"
Eccrine - response to cool body off
via mACh

Beta 2 receptor effects on metabolic functions

Increases:
Glycogenolysis (breakdown glycogen for glucose)
Gluconeogenesis (protein breakdown for energy)

When do you want to use a direct acting alpha agonist?

Hypotensive emergencies:
- preserve cerebral blood flow
- Severe hemorrhage
- Spinal cord injury
- Anithypertensive OD
- CNS depressant OD

How do you initially want to treat shock?

Volume and treat underlying cause

What do you treat cardiogenic shock with?

CPR, possibly Beta agonists, but poor prognosis

What is an agent used in the OR to achieve Hemostasis?

Alpha agonists
Also reduces diffusion of local anesthetic away from desired site

Drug of Choice for Complete Heart Block & Cardiac Arrest

Epi & Isoproterenol

Drug used to treat Narcolepsy

Modafinil

2 alpha adrenoceptors used to treat ADHD

1. Methylphenidate
2. Clonidine

MOA for Clonidine in treating hypertension

UNIQUE alpha 2 agonist that can dec. BP by working on alpha receptors in the brain (presynaptic)

Other uses for Clonidine

Diarrhea, dec. appetite cravings, dec. hot flashes, treat hemodynamic instability in the OR

MOA for Desmedetomidine

Works on presynaptic inhibitory alpha 2 receptors in the brain to cause sedation

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