Sympatholytics- Alpha Drugs Flashcards
Name three drugs that are competitive alpha adrenergic antagonists
phentolamine, prazosin, & yohimbine
what is different about the receptor binding of phenoxbenzamine
binds covalently to produce an IRREVERSIBLE and insurmountable type of alpha blockade
how does the binding of phenoxybenzamine get reversed
effects cannot be reversed by sympathomimetics- effects are terminated by METABOLISM
what does phenoxybenzamine treat
high BP
heavy sweating due to tumor of the adrenal glands (pheochromocytoma)
which two drugs are nonselective alpha antagonist
phentolamine & phenoxybenzamine
phentolamine BP effects
peripheral vasodilation, decrease BP
phentolamine manifest its effects___ and last ____
2 min
10-15 min
what are the heart rate effects of phentolamine
cardiac dysrhythmias
angina
why are there associated cardiac effects with phentolamine
alpha receptor blockade permits enhanced neural release of NE increase HR and CO
where does phentolamine have direct action
vascular smooth muscle
PNS is predominant after phentolamine what does this cause (3)
hyperperistalsis
abdominal pain
diarrhea
where is phentolamine metabolized
what percent is unchanged by the kideny
liver
10% unchanged by the kidney
what two condition does phentolamine treat
HTN emergencies from pheochromocytoma
autonomic nervous system hyperreflexia
phentolamine push dose
30-70mcg/kg (1-5mg)
phentolamine continuous infusion
0.1-2mg/min
phentolamine as a local infiltration dose of extravasation of a sympathomimetic medication
5-15mg in 10cc ns
phenoxybenzamine what is the GI absorption
incomplete
phenoxybenzamine onset of blockade
slow up to 60 min to peak after IV administration. This accounts for the modification of the drug molecule to become pharmacologically active
phenoxybenzamine elimination half time
24 hour
can phenoxybenzamine accumulate
yes with repeated doses
phenoxbenzamine receptor binding
alpha 1 more than 2
phenoxybenzamine what are the systemic bp changes in a normovolemic patient
little changes
for phenoxybenzamine what is prominent in the presence of preexisting hypertension or hypovolemia
orthostatic hypotension
what are the changes to cerebral and coronary vascular resistance with phenoxybenzamine
no changes
what is the result of phenoxybenzamine for maternal patients
If given during maternal treatment can cause neonatal hypotension and respiratory distress in first 72 hours of life
phenoxybenzamine
BP effect
CO effect
renal blood flow effect
decreasing BP
increased CO
renal blood flow is not greatly altered unless preexisting renal vasoconstriction is present
phenoxybenzamine blood loss or vasodilation effects?
exaggerated BP decreases in response to blood loss of vasodilating drugs such as volatile anesthetics.
phenoxybenzamine chronic therapy effects
sedation
phenoxybenzamine sinus effect
Nasal stuffiness is d/t unopposed vasodilation in mucous membranes in the presence of alpha adrenergic block
phenoxybenzamine alpha receptor stimulation prevents epi from doing what
prevents the inhibitory action of epi on the secretion of insulin
phenoxybenzamine po dose
0.5-1mg/kg PO
when do we give phenoxybenzamine
preop to control BP in patients with pheochromocytoma
phenoxbenzamine HCT effects
expansion of intravascular fluid volume by relieving intense peripheral vasoconstriction thus will see a fall in HCT
does phenoxbenzamine help with PVD
no because PVD is skeletal muscle blood flow and not cutaneous blood flow
other than administration for pheochromocytoma what else can we give phenoxybenzamine for?
raynauds disease- due to the cutaneous vasoconstriction
once volume has been restored on a patient and we still see tissue ischemia from vasoconstriction what medication relieves the vasconstriciton
phenoxybenzamine
yohimibine receptor
alpha 2 receptor antagonist
yohimibine
past uses
current uses
past impotence
current orthostatic hypotension
doxazosin receptor
alpha 1 antagonist
doxazosin uses
HTN
benign prostatic hypertrophy
prazosin receptor
alpha 1 antagonist
prazosin uses
pheochromocytoma
terazosin receptor
alpha 1 antagonist
terazosin uses
BPH
tamsulosin receptor
alpha 1 antagonist
tamsulosin uses
BPH
tamsulosin which medication decreases the clearance of it
cimetidine
tolazoline receptor
non selective alpha antagonists
tolazoline uses
pul HTN in new borns replaced by nitric oxide
alpha 2 agonist pharmacology effects (3)
sedation, hypotension, bradycardia
alpha 2 receptors are found where
CNS- Brainstem and locus ceruleus
where are alpha 2 receptors pre or post synpatic
presynaptic
which mechanism do alpha 2 receptors use
negative feed back mechanism
as a result of alpha 2 negative feed back what is not being released from the presynaptic nerve terminal
NE
inhibition of alpha 2 receptors has what effect on glucose and insulin
inhibition of insulin release and induction of glucagon from pancreas
is binding of alpha 2 agonist reversible
yes
withdrawal from alpha 2 agonist can result in what
increase HR and HTN
clonidine cardiac effects?
dose dependent decreases in HR and BP
clonidine what two things does it treat
resistant HTN and tremors from central stimulant medication
what forms do we give clonidine
IV, PO, transdermal
clonidine terminal half life
12-16 hours
clonidine partial agonists on which receptors
400:1 alpha 2 over alpha 1
clonidine metabolized where and excreted where
liver and excreted in the bile and feces
Dexmedetomidine: receptor
Selective alpha 2 agonist with 1,600:1 preference of alpha 2
dex IV dose
0.1-1.5mcg/kg/min
dex terminal elimination half life
2 hours
when is dex used most often
icu or OR as a sedative and analgesic d/t its central sympatholytic effects
dex is under goes what in the liver and excreted mostly in the
biotransformation in liver and excreted in the urine
dex withdrawal
tachycardia HTN Anxiety
Dexmedetomidine
Large IV boluses (0.25 to 1 mcg/kg over 3-5 min) result in a paradoxical hypertension with a decrease in HR and resembles phenylephrine and is the resultant effect of crossover alpha 1 stimulation.
