Adrenergic Antagonists Flashcards
reseerpine inhibitor
NE
SYMPATHOMIMETIC DRUGS
Drugs that mimic the actions of Epinephrine or Norepinephrine
Alpha-1 Receptor Agonist
1. Phenylephrine - nasal decongestant which causes vasoconstriction. 2. Methoxamine 3. Midodrine (withdrawn) – can block ANS 4. Metaraminol
Alpha-2 Receptor Agonist
- Clonidine - present pre-synaptically; used for HTN, by the decrease of cAMP which reduces the release of Norepinephrine thereby reducing the BP (also considered sympatholytic)
- Methyldopa
- Guanabenz r
- Guanfacine
- Rilmerudine
- Dexmetomidine –combine with Opiates = prevent Resp.
depression - Brimonidine
- Moxonidine
Beta-1 Receptor Agonist
- Dobutamine
2. Dopamine CHF treatment, Inc. CO not HR
Beta-2 Receptor Agonist
- Fenoterol
- Formoterol
- Albuterol
- Terbutaline
- Salbutamol
- Pirbuterol
- Levalbuterol
- Metaproterenol
- Bitollerol
NON SELECTIVE DIRECT ACTING
- Epinephrine
- Norepinephrine
- Oxymetazoline (binds to α1 and α2)
Xylometazoline – both are former a1, but has higher affinity to a2 receptor - Isoproterenol- has higher affinity to β receptor
INDIRECT AGONISTS
they do not bind to the receptor instead they increase
the level and effect of Norepinephrine in the synaptic
cleft
Steps in IA
- By acting as a releasing agent/displacing agent, e.g.
Amphetamine and Tyramine, they would stimulate release
of NE from the vesicle - by acting inhibitor they would inhibit the reuptake of NE
like Cocaine and Tricyclic Anti-depressants - By inhibiting the enzyme that will degrade your NE
prevent enzymatic metabolism of NE (MAO and
COMT).
Ex: Entacapone (COMT inhibitor- used for Parkinson’s
disease).
Selegiline (MAO inhibitor- anti-depressant)
they only prolong the effect of the NE that is released.
actions are dependent on their ability to enhance the
actions of endogenous catecholamine
Mixed Acting
they directly bind or indirectly stimulate the release
\1. Ephedrine
2. Pseudoephedrine
3. Phenylpropanolamine (PPA)
How do u differentiate the 3?
DIRECT ACTING AGONIST WITH PRIOR
TREATMENT TO RESERPINE: the response is not
reduced because even in the absence of NE stores since they directly bind to the
receptor their response is NOT AFFECTED
INDIRECT ACTING AGONIST WITH PRIOR TREATMENT
TO RESERPINE:
affected with NE stores; since Reserpine
blocks the storage of NE, so if you give Amphetamine that
displaces NE and there is decreased levels of NE the
response will be ABOLISHED/ DIMINISHED
WITH MIXED ACTING
since this directly stimulates the
adrenoceptor and may displace the NE the response will
still be there. However, it is REDUCED comparing it with
indirect acting
Reserpine will diminish effect of direct-acting adrenergic
agonist.
False.
Reserpine will diminish effect of mixed-acting adrenergic
agonist.
True
Reserpine will abolish the effect of indirect-acting
adrenergic agonist
True
DESENSITIZATION
● Decrease in response of the agonist receptor as you
increase the time of administration
● In a long term use of a drug the response of these drugs
to its agonist receptor binding will be diminished
● After a cell or tissue has been exposed to an agonist (in
this case, catecholamines and other sympathomimetic
drugs) for a period of time, it often becomes less
responsive to further stimulation by that agent
Tolerance
progressively reduced therapeutic
effectiveness due to enhancement of their
own metabolism
Refractoriness
lack of responsiveness to a drug
Clinical significance: May limit the therapeutic response to
sympathomimetic agents
Homologous desensitization-
refers to loss of
responsiveness EXCLUSIVELY OF THE RECEPTORS
that have been exposed to repeated or sustained
activation by a agonist
- E.g. is Arestine binding to G-protein
coupled receptorsleading to inhibition of the same
receptor
Heterologous desensitization
desensitization of 1
RECEPTOR BY ITS AGONIST ALSO RESULTS IN
DESENSITIZATION OF ANOTHER RECEPTOR that
has been directly activated by the agonist
Longer the side chain
e longer action of duration
PHENYLETHYLAMINE
not a catecholamine. It is
only a parent structure of your other catecholamines. it
consists of a benzene ring, with an ethylamine side
chain
Catecholamines are combination of
of CATHECOL and
phenylethylAMINE. The OH groups at 3 and 4 position
found in catechol is joined with the parent structure
phenylethylamine leading to the derivation of the structures
of your catecholamines: DOPAMINE, EPINEPHRINE,
NOREPINEPHRINE AND ISOPROTERENOL (NE and Epi
- most potent)