Adrenergic Antagonists- T2 Flashcards
alpha adrenergic receptor antagonists may be classified as
reversible competitive antagonists and irreversible competitive alpha-adrenergic antagonists
phentolamine is a
non-selective (both alpha 1 and 2) reversible competitive alpha-adrenergic receptor antagonists.
prazosin, doxazosin, and terazosin are
alpha1 selective reversible competitive alpha-adrenergic receptor antagonists
tamsulosin and silodosin (rapaflo) are
alpha1A/D selective reversible competitive alpha-adrenergic receptor antagonists
phenoxybenzamine is
a irreversible competitive non selective alpha adrenergic antagonist
4 piperazinyl quinazolines
prazosin, terazosin, doxazosin, alfuzosin
3 indoles
yohimbine, indoramin, silodosin
alpha1 and 2 adrenoceptors are responsible for the
maintenance of TPR and maintain pressure.
in many patients with essential HTN, TPR may be abnormally elevated due to
increased alpha-adrenergic receptor stimulation.
the 6 alpha-adrenergic receptor subtypes
1a, 1b, 1d, 2a, 2b, 2c
agents that antagonize both alpha1 and 2 tend to be
less efficacious in lowering BP than alpha1 selective
blockade of alpha2 adrenoceptors will cause
enhanced release of NE at the sympathetic neurons leading to excess adrenoceptor stimulation.
alpha2 blockage causes veno___ which leads to__
venodilation leading to a reduction in preload and then reduces SV.
why would we want to give a selective alpha antagonist opposed to non selective
giving a selective reduces the peripheral resistance, if it doesn’t have selectivity, we won’t have effects that come from antagonizing a specific alpha receptor.
prazosin and htn tx
a alpha1 selective antagonist that is prone to hepatic metabolism, has the shortest half life and primarily eliminated in the bile. if the patient has renal impairment you would want to use this.
doxazosin and terazosin in htn tx.
alpha1 selective antagonists have more renal eliminated of the parent compound and longer half life of elimination, would want to use these if the pt had liver failure.
antagonism of alpha1 adrenoceptors result in
dilation of arteries, arterioles, and veins.
arteriolar dilation results in
decreased after load (decreased TPR)
afterload is
the pressure that the heart has to work against.
venous dilation causes
decreased preload
decreased preload decreases
myocardial stretch and thus the CO.
efferent arteriolar dilation causes
decrease GFR which causes decrease Na in DCT and causes increased renin release.
what agents have equivalent BP lowering capacity to alpha1 selective antagonists
Ca channel blockers and thiazides
adverse effects of alpha1 selective adrenergic receptor antagonists
hypotension (first dose or orthostatic), dizziness, HA, congestion, impaired ejaculation and miosis
the lest well tolerated alpha1 selective antagonist
prazosin
alpha1 selective antagonists contraindicated in pts with
right heart failure or cardiac valvular stenosis.
how do alpha blockers make right heart failure worse
right HF is the right ventricle not ejecting the right amount of blood, too little filling, not enough stretch. alpha blockers decrease the preload, which makes RHF worse.
alternative use for alpha1 selective antagonists other than HTN
benign prostatic hyperplasia
tamsulosin is selective for what receptor
alpha1a
___ receptors predominate in the vasculature
alpha1b
why would you give terazosin for HTN and BPH?
because it isn’t subtype selective like flomax is.
what is phenoxybenamines MOA and what is its therapeutic use
alkylates alpha 1 &2 adrenoceptors to cause decrease in receptors available for activation by catecholamines. used for pheochromocytoma where excess catecholamine production results in dangerously high BP
yohimbine is a selective
alpha2 receptor blocker that produces increase BP via CNS effects.
4 non selective b-receptor antagonists
propranolol, nadolol, timolol, pindolol
4 b1 receptor selective antagonists
metoprolol, atenolol, esmolol, acebutolol
2 beta and alpha1 selective antagonists
labetalol and carvedilol
what drug is a beta blocker with additional effects
bystolic, dilates blood vessels by NO release.
5 general things that distinguish members of the beta adrenergic receptor antagonist class
b1 vs non selectivity, partial agonism, alpha adrenoceptor blocking, lipid solubility, and inverse agonists.
b1 vs non-selectivity
propranolol has equivalent affinities for the 2 receptors while metoprolol, esmolol and atenolol show greater b1 receptor affinity
partial agonism with beta adrenergic antagonists
propranolol is an antagonist with no ability to active b-receptors; while pindolol and acebutolol behave more as a partial agonist
alpha-adrenoceptor blocking activity in regards to beta-adrenergic antagonist
most agents in this class are relatively b-selective however labetalol and carvedilol have significant alpha1 blocking activity.
lipid solubility
more lipophilic agents have greater CNS effects. this is why propranolol can be used for stage fright.
generally b-blockade causes
greater decreases in HR and contractility during sympathetic NS activity.
major effect of b-blockade
decrease cardiac rate and contractility to decrease Co and thereby MBP
initially ___ may rise due to beta2-blockade and/or reflex baroreceptor mechanism to maintain BP
TPR
partial agonists or alpha blocking activity may produce less increase in
TPR
b-antagonists also ___ renin release..
decrease. causing less circulating angiotensin II.
how do mixed antagonists decrease BP
by slpha1 blockage in the vasculature as well as beta-blockade in the heart.
partial b-receptor agonists produce smaller decreases in __ and may be preferred in pts with
CO. preferred in pts with bradycardia or decreased cardiac reserve.
pharmacological adverse effects of b-adrenergic antagonists
HF, bradycardia, angina after withdrawal, bronchoconstriction in asthmatics, fatigue, insomnia, depression.
