5 - Adrenergic Agonists Flashcards
Direct acting adrenergic receptor agonists
DA
NE
Epi
Dopamine to NE
DOPA B hydroxylase
Structural differene between Epi and NE
Terminal NH2 on epi contains a methyl group
NE vs Epi selectivity
Epi = non-selective
______ drugs have not yet been marketed
receptor-subtype-specific
Direct acting α1 recepor agonists
Phenylephrine
Methoxamine
Oxymetazoline
Oxymetazoline
(visine)
Direct α1 agonist
Direct α1 agonists act via what MOA
Gq –> PLC –> PIP2
>> Ca++ increase / PK-C activation
α1 agonists promote _____
mydriasis
β1 receptors are important in what two functions
Cardio (ino/chrono)
Renin
Direct acting α2 receptor agonists
Clonidine
Methyldopa
Guanabenz
Guanfacine
Tizanidine
α2 agonists act via what MOA
Gi -> ↓ Adenylate cyclase -> ↓cAMP
↓ cAMP-dependent kinase activity
Clonidine does not _____
Uses?
decrease renal blood flow
Hypertensive urgency, ADHD, tourette
Direct acting non-selective B recepor agonists
Isoproterenol
B1 selective agonists
Dobutamine
Dopamine
B2 selective agonists
Terbutaline
Metaproterenol
Albuterol
Salmeterol
Ritodrine
Direct acting B receptor agonists MOA
Gs –> ↑Adenylate Cyclase –> ↑cAMP –>
↑ cAMP-dependent protein kinase
Explain EC50
The concentration needed in order to give 50% response response
Receptor activation comparison for a1 receptors
PENI
Receptor activation comparison for B1 and B2 receptor (agonists)
I, E, N, P
NE displays less activation of which of the B receptors
B2
(activation/concentraiton curve shifted to RIGHT)
Cardiovascular effects of sympathomimetics (Pulse rate)
NE = decrease
Epi and Iso = increase
(Isoproterenol > Epi)
Cardiovascular (BP) effects of sympathomimetics
NE = Increase
Epi = Basically no change
Iso = reduce
Cardiovascular (peripheral resistance) effects of sympathomimetics
NE = Large increase
Epi = Slight decrease
Iso = Large decrease
Isoproterenol has effects on both ____
B1 and B2
= Direct stimulation of the heart
Phenylephrine cardiovascular effects
Increased BP (vasoconstriction)
Reduced HR (↑ vagal tone -> ↑ baroreceptor)
Phenylephrine CV effects are similar to…
NE
Increase BP by vasoconstriction
decrease heart rate via baroreceptor stimulation of vagal tone
Epinephrine CV effects
a1 vasoconstriction & B2 vasodilation cancel each other out
= NO change in BP
B1 = ↑HR
Isoproterenol CV effects
Reduced BP – Vasodilation (B2)
Increased HR – B1 (also baroreceptor)
L norepinephrine:
- receptor
- Metabolism
- Use?
Potent α and β1 receptor agonist
Substrate for MAO and COMT
Used as pressor
Epi:
- Metabolism
- Use
Substrate for COMT and MAO
Anaphylaxis and Glaucoma
_________ is used in preparations to prevent oxidation of _____ and _________
Sodium bisulfite
L-Norepi and Epi
Phenylephrine receptor
a1
Phenylephrine metabolism
Substrate for MAO
(not for COMT because missing the OH group)
2 aralkylimidazolines compounds
Naphazoline
Tetrahydrozoline
Oxymetazoline
2-aralkylimidazolines receptor
a1 - PARTIAL agonists
2-aralkylimidazolines use
local/topical vasoconstriction (nasal/ophth. decongestants)
2-aralkylimidazolines chemistry
basic imidazoline ring causes them to exist in ionized form at physiologic pH
a2 receptor locations
CV control center (solitary tract in medulla)
Clonidine receptor
Selective a2 agonist
Function of dichlorophenyl group in clonidine
decreases the basicity of the guanidine group
Clincal use for clonidine
HTN
Opiate withdrawal
*especially for refractory patients
a2 agonist general MOA
general effects?
reduce Sy output from brain –> reduce BP
REDUCE: HR, inotropy, Renin, vasoconstriction
“Open ring” imidazolidines (compounds)
receptor?
Guanabenz
Guanafacine
a2 receptor agonists
Guanabenz/Guanfacine : Function of two-atom bridge to guanine group
dereases pKa
(drug is mostly non-ionized at physiological pH)
Shortest half life imidazolidine
Guanabenz (6h)
Use for Guanabenz / Guanfacine
HTN and ADHD
Guanfacine may affect…
a2 receptors outside the CV control center in medulla
Methyldopa receptor
a2 agonist
Methyldopa is a…
prodrug
metabolized to active agonist =
(1R, 2S) -a-MethylNorepinephrine
Methyldopa acts at…
central a2 receptors to decrease sympathetic outflow
Parenteral solution of methyldopa
Methyldopate (water soluble ester)
Methyldopa clinical use
HTN
Enzymes involved in Methyldopa metabolism to 1R,2S MethylNE
- L-aromatic amino acid-Decarboxylase
- Dopamine B-hydroxylase
Other uses for a2 agonists
Apraclonidine = glaucoma
Tizanidine = muscle spasticity
Adverse effects of a2 agonists
Sedation
Na/Water retention
Dry mouth
Withdrawal Symptoms
Co-treatment for a2 agonists
diuretics, to reduce water retention
a2 receptors are also present in…
the spinal cord (reflexes)
Dampening the a2R will reduce muscle spasiticty
Nonselective B agonists
Isoproterenol
Isoproterenol effects
Bronchodilation
Increased CO
(nonsel. activation of B receptors)
Isoproterenol metabolism
metabolized by conjugation reactions (Phase 2)
and by COMT
(not sensitive to MAO)
What causes B selectivity for isoproterenol?
Putting a larger group on the terminal amine
Isoproterenol use
Asthma + COPD
Cardiostimulant
Selective B2 agonists
Metaproterenol, Terbutaline
Albuteral/Levalbuterol, Salmeterol
Salmeterol, Formoterol
Metaproterenol and Terbutaline are derivatives of
Resorcinol
Albuterol and Salmeterol are derivatives of
Meta hydroxymethyl
____ are only obsserved at higher doses of Resorcinol and meta hydroxymethyl derivatives
Cardiac effects
Metaproterenol and Terbutaline metabolism
not metabolized by MAO or COMT
= longer duration of action than isoproterenol
Metaproterenol and Terbutaline use
Asthma/COPD
Terbutaline = tocolytic (prevent premature labor)
Albuterol and salmeterol metabolism and use
neither MAO nor COMT
Asthma / COPD
Racemic mixtures
Albuterol + Salmeterol
Dobutamine
More potent isomer for second gen B2 receptor agonists
Levalbuterol
R group = C(CH3)3
3rd gen B2 agonists are all _______
Very long acting
(No metabolism by COMT/MAO….12-24 hour duration)
What is the main issue with 3rd gen B2 agonists
Long onset of action
Salmeterol = 10-20 Minutes
Formoterol = Less than 5 minutes
3rd gen B2 agents
Salmeterol and Formoterol
Salmeterol and Formoterol use
Long term Asthma
COPD
*NOT acute/rescue inhaler
Direct acting beta agonist with mixed properties
Dobutamine
Dobutamine is a derivative of
DA
Dobutamine racemic mixture and receptor
(+) = potent B1 agonist, a1 antagonist
(-) = a1 agonist, B1 potency reduced 10x
Net effect of dobutamine enantiomers
Positive inotropy
Little/no chronotropic
Dobutamine metbolism
COMT and conjugation
Not sensitive to MAO
Dobutamine PK
Short half life!
(2 minutes)
Dobutamine use
Acute HF
Shock
Indirect acting sympathomimetics
- Amphetamine
- Pseudoephedrine
- Ephedrine
- Phenylpropanolamine
- Tyramine
Amphetamine mechanism of action
- Competitive blocking of NET-mediated uptake (also includes DAT for dopamine) ** reverse action of plasma membran transporter**
- Release of NT via VMAT
*both increase the amount of NE in synapse
Clincal use for amphetamines
ADHD, narcolepsy, anorexiant
Other uses for amphetamines
nasal decongestants
Derivatives of ephedra
D-(-)-ephedrine
L-(-)-pseudoephedrine
D-(-)-ephedrine has desired…
R-configuration at the beta OH
S-configuration ata the alpha carbon
= DIrect agonist activity of adrenergics!
L-(-)-pseudoephedrine configuration
S,S distereoisomer
the S configuration of B-OH reduces its agonist activity
Major mechanism of L-(-)-pseudoephedrine
Reversal of the transporter
Structural difference between the ephedrine and pseudoephedrine
The configuration of the OH group on the beta carbon
L-(-)-pseudoephedrine doesn’t have…
CNS penetration
d/t OH group S configuration
Synthesis of methamphetamine
ephedrine — (lithium + NH4+) –>methamphetamine
ephedrine and pseudo cause ____ via the ___ receptor
vascular constriction
a1 receptor