Alpha blockers Flashcards
antagonists shift the dose response curve
to the right
all alpha blocking agents are ______ except _______
competitive antagonists
phenoxybenzamine
phenoxybenzamine is a
non-competitive irreversible antagonist
nonocompetitive irreversible antagonists
diminish maximum response
shift curve to the right
competitive antagonists
the maximum effect is the same
shift curve to the right
alpha blockade decreases
vasoconstriction, blood pressure, PVR
reflex tachycardia occurs with alpha blockade due to
- decreased BP decreases vagal tone by baroreceptor reflex
2. a2 blockage increases NE–> B1
postural hypotension occurs due to
blockage of a1 receptors in venous smooth muscle
blocking alpha receptors means that giving epi will have effects
similar to those of isoproterenol
alpha blockers are widely used to treat
BPH (decreased resistance to urine flow)
phentolamine blocks
a1 and a2
phentolamine CV effects
- block a1 –> decrease PVR
2. block a2 –> increased NE release
phentolamine short term tx
htn crises in pheochromocytoma or MAO + tyramine
if NE/vasoconstrictor is accidentally injected into tissues, treat necrosis with
phentolamine
phenoxybenzamine effects lasts
days, until new receptors are produced
phenyoxybenzamine effects are most pronounced when
standing up
phenoxybenzamine is used to treat
pheochromocytoma (too much sympathetic tone)
phenyoxybenzamine causes severe hypotension if
hypovolemic
using vasodilators
using ETOH
pheochromocytoma is indicated by
sudden onset severe htn, tachycardia, arrhythmia
tumor which releases Epi/NE
your patient is an old man with hypertension and BPH, what’s your DOC
prazosin
prazosin is less likely to increase HR bc
its highly selective for a1
give prazosin
2x daily, duration of action 7-10 hrs
decrease dose of prazosin
CHF
first dose phenomenon is associated with
prazosin, terazosin, doxazosin
first dose phenomenon is
postural hypotension/syncope 30-90 minutes after first dose of drug.
To avoid, start prazosin at night
alpha blockers + ED drugs (sildenafil) =
SEVER HYPOTENSION
sildenafil
viagra
2 a1 specific blockers that are similar to prazosin, but are dosed once daily
terazosin, doxazosin
tamsulosin is selective for
a1a
a1a is found in
prostate
a1b is found in
blood vessels
tamsulosin BP effects
FEW bc it’s more selective
your patient has BPH and postural hypotension when he takes a1 receptors. what are your DOC
tamsulosin, alfuzosin
alfuzosin is
tamsulosin + dizziness
anti-clonidine
yohimbine
yohimbine is dangerous in
htn
yohimbine is
a2 selective antagonist
a2 antagonism
increases NE release —> increased sympathetic tone
