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adrenergic agonists and antagonists

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phenylephrine
alpha 1 selective agonist
causes vasoconstriction and mydriasis
uses: nasal decongestant, eye surgery
oxymetazoline
non-selective alpha agonist
causes vasoconstriction and mydriasis
uses: nasal decongestant, eye surgery
clonidine
alpha 2 selective agonist
inhibits medullary CV center to lower BP
IV: 1st dose idiosyncratic (extrajunctional receptors), remaining doses decrease NE release (presynaptic receptors)
Oral: accumulates in brain, inhibits CV center
WITHDRAWAL: major concern, headache, etc. REBOUND HYPERTENSION
methyldopa
alpha 2 selective prodrug
converted > methyl-dopamine > methyl-NE
inhibits medullay CV center
dobutamine
beta 1 selective agonist, DA analog
causes increased contractility > increase CO
not much effect on HR
uses: cardiogenic shock, congestive heart failure
metaproterenol
non-specific beta agonist
uses: asthma, bronchospasm
albuterol, pirbuterol, terbutamine
beta 2 specific agonist
short duration
uses: asthma, bronchospasm, also given IV to stop labor
salmeterol, formoterol
beta 2 selective agonists
long duration of action
uses: asthma (in conjunction with steroids)
ephedrine
mimics epinephrine effect, less potent
uses: asthma and myasthenia gravis
pseudoephedrine
mimics epinephrine effect, less potent
uses: nasal decongestant
phentolamine
non-selective alpha antagonist
alpha 1 block: vasodilation of veins and arteries > orthostatic hypotension and decreased BP
alpha 2 block: prevents negative feedback to increase NE release
uses: short-term treatment of HTN in patients with pheochromocytoma
phenoxybenzamine
predominant alpha 1 blocker, some alpha 2 antagonism
IRREVERSIBLE
drop in arterial pressure > reflex increase in CO and HR
increased NE release
increased cutaneous and splanchnic flow
uses: Raynaud's, pheochromocytoma
prazosin (doxazosin, alfuzosin, tamsulosin)
selective alpha 1 blocker
inhibits contraction of smooth muscle > vasodilation
less intense response than non-selectives, no increased NE release
uses: essential hypertension, CHF, UTI associated with BPH
side effects: 1st dose postural hypotension and syncope
indoram
selective alpha 1 blocker
uses: hypertension, Raynaud's
yohimbine
selective alpha 2 blocker
causes vasodilation
uses: erectile dysfunction, Raynaud's
propandolol
non-selective beta antagonist
beta 1 block > decreased contractility and HR > decreased CO
decreased slope of pacemaker potential > prevent reentrant arrhythmias
uses: angina, arrhythmias, hypertension
side effects: bradycardia, bronchospasm, AV block, hypoglycemia
pindolol
beta 1 antagonist + beta 2 partial agonist
antihypertensive
less likely to cause bronchoconstriction and hypoglycemia, because of beta 2 partial agonism
metoprolol
selective beta 1 blocker
decreases CO, antihypertensive, antiarrhythmic
less bronchoconstriction
less hypoglycemia
crosses BBB > depression, fatigue, loss of libido
atenolol
selective beta 1 blocker
less bronchoconstrictoin
less hypoglycemia
does not enter CNS
esmolol
selective beta 1 blocker
very short half-life
rapid onset and cessation of beta blockade
used in URGENT setting when immediate onset is needed
labetalol
beta 1 antagonist + beta 2 partial agonist + alpha 1 antagonist
alpha 1 block > vasodilation
beta 1 block > decreased HR, decreased renin > decreased BP
beta 2 partial agonism > less bronchoconstriction and hypoglycemia
uses: chronic hypertension, hypertensive crisis (IV)
carvedilol
beta 1 antagonist + beta 2 partial agonist + alpha 1 antagonist + antioxidant and antiproliferative properties
uses: congestive heart failure, myocardial infarction, chronic heart failure
nebivolol
beta 1 antagonist + vasodilatory effects
lowers BP without decreasing left ventricular function
reduces peripheral resistance
vasodilation mediated by NO
metyrosine
inhibits tyrosine hydroxylase > no catecholamine production
uses: pheochromocytoma
quanethidine
rarely used antihypertensive
decreases activity of postganglionic sympathetic neurons
inhibits synaptic vesicle fusion