Adrenergic Antagonists Flashcards
What is a synonym for adrenergic antagonists?
sympatholytics
What are the 2 broad classes of alpha-receptor antagonists?
Reversible
Irreversible
Who do alpha-receptor reversible antagonists compete with?
agonists
endogenous catecholamines
Describe the mechanism of alpha-receptor reversible antagonists
block receptor and dissociate if agonist is present in high enough concentration
What is a alpha-receptor reversible antagonist duration of action dependent on?
drug’s affinity for receptor
1/2 life of drug in the body
How do alpha-receptor irreversible antagonists bind?
form covalent bonds = permanent block
What is the alpha-receptor irreversible antagonist duration of action dependent on?
dependent on synthesis of new receptors (up to several days)
What do alpha-antagonists do in the cardiovascular system?
block alpha1-mediated vasoconstriction –> vasodilation –> decrease in peripheral vascular resistance and decrease in BP
What is a side effect of alpha-antagonists in the cardiovascular system?
orthostatic hypotension (body’s ability to adjust peripheral vascular resistance has been blocked
reflex tachycardia (response to maintain cardiac output; compensatory mechanism to drop in BP)
What are some other effects of alpha1 antagonists?
block mydriasis –> mitosis
block nasal vasoconstriction –> sinus congestion
block alpha-mediated urinary retention –> facilitates urination
What is phenoxybenzamine and what does it do?
alpha antagonist
irreversible blockade of alpha1 receptors (more so than alpha2 receptors)
What is the effect of phenoxybezamine?
blocks vasoconstriction –> vasodilation
also blocks presynaptic alpha2 receptors (blocks reuptake of norepinephrine (not as potent an effect))
What is phenoxybezamine used to treat?
conditions of excessive catecholamine release –> pheochromocytoma (adrenal gland tumor)
What are the symptoms of pheochromocytoma that are treated by phenoxybezamine?
over secretion of norepinephrine and epinephrine –> hypertension, headaches, palpitations, sweating
What is phentolamine?
reversible blockade of alpha1 receptors and presynaptic alpha2 receptors
What is the effect of phentolamine?
alpha1 blocking = decrease peripheral vascular resistance
alpha2 blocking due to increase in cardiac stimulation –> increase HR increase cardiac workload, potential for arrhythmias (due to increase norepinephrine activity b/c blocked norepinephrine reuptake)
What is phentolamine used for?
management of pheochromocytoma
What are some other examples of alpha1 antagonists?
Prazosin
Terazosin
Doxazosin
Tamsulosin
What is a side effect of prazosin?
orthostatic hypertension
What is tamsulosin used for?
enlarged prostate
HTN
BPH
What is the effect of tamsulosin?
relaxation of arterial/venous smooth muscle –> HTN
relax smooth muscle in prostate (most selective for this)
Some drugs have alpha1 antagonistic as a secondary mechanism of action, in these drugs what is the side effect that you’ll most likely see?
hypotension
What are some examples of drugs that have alpha1 antagonistic side effects and what are they usually used for?
Haloperidol = antipsychotic
Chlorpromazine = antipsychotic
Trazodone = sleep aid and antidepressant
Ergotamine and dihydroergotamine = migranes
How do beta-receptor antagonists bind to their receptors?
Reversibly
Are beta-receptor antagonists pure antagonists?
Most are, however some do have some beta-agonist activity (but usually only w/ low concentrations of endogenous catecholamines)
some have local anesthetic properties
Can beta-receptor antagonists be selective?
Yeah, differ in affinity and selectivity for blocking beta1 or beta2
However, selectivity will decrease w/ higher doses
Are there pharmacokinetic differences between beta-receptor antagonists?
Yeah, differences between distribution, 1/2 life, and elimination route
What are beta antagonists usually called in the cardiovascular system?
Beta blockers
What are beta antagonists used for in the cardiovascular system?
control high BP
angina
CHF
MI
What is the mechanism of action of beta-antagonists in the control of high BP?
complex and unclear mechanism
suppression of renin release
CNS actions
debatable first-line agent for high BP
What is the mechanism of action of beta antagonists in the control of angina, CHF, MI?
part of first-line therapy
reduce cardiac workload (negative inotropic, negative chronotropic effects)
slow AV node conduction –> decrease HR
suppress renin release
What is the net effect of beta-antagonists in the treatment of angina, CHF, or MI?
reduce peripheral vascular resistance, BP, overall workload of the heart
Why is it surprising that beta-antagonists (or blockers) decreases BP?
block peripheral Beta2 receptors –> expect inhibit vasodilation BUT w/ long term use BP decreases (unclear mechanism)
What can enhance vasodilation properties of beta antagonists?
drugs that also block alpha1 receptors
nonselective agents –> greater drop in BP b/c block vasoconstriction
What is an example of a nonselective adrenergic antagonist that is used to treat high BP?
labetolol –> blocks alpha and beta; blocks vasoconstriction
Why are beta antagonists used to treat angina?
help pts by improving balance between oxygen supply and demand