CHAPTER 7: ADRENERGIC ANTAGONISTS- Alpha Adrenergic Blockers Flashcards
Adrenergic antagonist mechanism
they bind to adrenoceptors but do not trigger usual receptor-mediated intracellular effects
do they work irreversibly or reversibly
work both ways by attaching to adrenoceptors, prevent activation by endogenous/exogenous agonists
sites of action: adrenergic antagonists
BLOCK THE SNS–> PSNS acts uncontrollably as result
- mydriasis
- inc GI secretion
- bronchoconstriction
- relaxed sphincters
-lowered BP
what are the 2 types and their subclasses?
alpha receptor
- non selective
- a1
- a2
beta receptor
- non selective first gen
- b1 selective second gen
- non selective third gen
- b1 selective third gen
alpha blockers do what?
non selective alpha blockers DEC peripheral resistance, INC cardiac output
- affect BP
- a2 selective have limited clinical utility
what are the alpha blocking agents?
phenoxybenzamine- nonselec noncompetitive blocker of a1 and a2
phentolamine- competitive blocker of a1 and a2
prazosin, terazosin, doxazosin- selective competitive blocker of a1
yohimbine- selective competitive a2
Phenoxybenzamine- cardiac effects
-block a1 vasoconstriction of peripheral blood vessels caused by endogenous catecholamines
-DEC peripheral resistance
-REFLEX tachycardia
-block presynaptic a2 on symp nerve terminals in heart
- INC NE release
-inc HR and cardiac output b\
-cardiac arrhythmias and anginal pain
what is angina?
chest pain as a result of reduced O2 to the heart
phenoxybenzamine- epinephrine reversal
vasoconstrictive action of epinephrine is interrupted
BUT vasodilation of other vascular beds caused by stimulation of B receptors is NOT blocked
(b2 vasodilation)
epinephrine reversal is done with?
ALL a-adrenergic blockers reverse the a-agonist actions of epinephrine
alpha adrenergic blockers have no effect on actions of….
ISOPROTERENOL, its a pure beta agonist
phenoxybenzamine- therapeutic uses/indications
treat sweating, hypertension associated with pheochromocytoma
sometimes treats Raynaud disease and frostbite
what is pheochromocytoma?
catecholamine secreting tumor of cells derived from the adrenal medulla
- cancer of adrenal medulla
phenoxybenzamine should be used with caution in patient with what diseases?
cardiovascular or cerebrovascular diseases (contraindication)
Phentolamine- actions
- a1 and a2 competitive blockers
- similar to phenoxybenzamine actions
Phentolamine- therapeutic uses/indications
-DIAGNOSIS and short term management of pheochromocytoma
-prevent dermal necrosis following extravasation of NE
-treat hypertensive crisis due to abrupt withdrawal of clonidine or ingestion of tyramine containing food in PTs taking monoamine oxidase inhibitors
what is extravasation?
leakage of IV administered solution into surrounding tissues
prazosin, terazosin, doxasozin (PTsD pneumonic)- what are they
- selective, competitive alpha 1 blockers
- metabolism leads to inactive products that are excreted in urine except for those of doxazosin (appear in feces)
pra,ter,doxazosin- actions
-DEC peripheral vasc resistance/LOWER BP
- relax arterial and venous smooth muscle
- MINIMAL cardiac output/renal blood flow/glomerular filtration rate changes
pra,ter,doxazosin -therapuetic uses/indications
-treate hypertension
-first dose may produce exaggerated orthostatic hypotensive response, result in syncope(fainting)
-NOT used as monotherapy for hypertension treatment
first dose effect
a drug induces an exaggerated orthostatic hypotensive result that may result in fainting
low BP=faint
pra, ter, doxazosin- adverse effects
a1 blockers may cause
-diziness (CNS)
-headache (CNS)
-lack of energy
-nasal congestion
-drowsiness
-orthostatic hypotension
additive hypertensive effect when a1 blocker given with vasodilators (nitrates, PDE 5 inhibitors like slidenafil)
Yohimbine- where is it found, how does it work
- found as part of bark of yohimbine tree, can be used as sexual stimulant
-treat erectile dysfunction
-works in CNS to inc SNS outflow to periphery
-contraindicated in CNS and cardiovasc bc its a CNS/cardiovasc stimulant
