Unit 2 - ANS Pharm & Patho Flashcards
how is phenylephrine metabolized
MAO
synthetic catecholamines
isoproterenol, dobutamine
synthetic catecholamines
isoproterenol, dobutamine
2 neurotransmitters the ANS relies on
ACh & NE
NT of postganglionic PNS neurotransmission
cholinergic (ACh)
NT of postganglionic SNS neurotransmision
NE (adrenergic)
3 alpha selective drugs
- phenylephrine (α1)
- clonidine (α2)
- dexmedetomidine (α2)
infusion dose of phenylephrine
0.15-0.75 mcg/kg/min
HR effects of phenylephrine
significant reflex bradycardia may occur d/t baroreceptor activity
how does phenylephrine affect PAP
increases d/t direct vasoconstrictive action in lung vasculature & increased venous return
how can phenylephrine worsen ischemic event in a CAD patient?
CO decreased from strong baroreceptor reflex-induced bradycardia + abrupt increase in afterload
how to treat phenylephrine overdose
- alpha 2 blocker (phentolamine)
- time (duration is brief)
- do NOT use beta blocker
why are beta blockers contraindicated in phenylephrine overdose
induce pulmonary edema and catastrophic, irreversible CV collapse
3 locations of α2 receptors
- presynaptic (NE-releasing neurons in CNS & PNS)
- postsynaptic (smooth muscle, some organs)
- nonsynaptic (platelets)
location of α2 receptors in the nervous system
- medulla
- vagus nerve
- locus coeruleus
- dorsal horn of spinal cord
effect of α2 stimulation at medulla
decreased SNS tone
effect of α2 stimulation at vagus nerve
decreased PNS tone
effect of α2 stimulation at locus coeruleus
sedation, hypnosis
effect of α2 stimulation at dorsal horn of spinal cord
analgesia
effect of α2 stimulation in vasculature
vasoconstriction
effect of α2 stimulation in renal tubules
inhibits ADH (diuresis)
effect of α2 stimulation in pancreas
decreased insulin release
effect of α2 stimulation on platelets
increased platelet aggregation
effect of α2 stimulation in salivary glands
dry mouth (thick, viscous saliva)
effect of α2 stimulation in GI tract
decreased GI motility
protein binding of clonidine vs. dexmedetomidine
dex - 94%
clonidine - 50%
MOA of clonidine
- acts as α2 agonist at central presynaptic receptors (medulla and locus coeruleus)
- diminishes SNS outflow leading to sympatholysis (dec HR and BP)
how does clonidine affect vasculature
inhibits NE release, causing vasodilation
AEs of abrupt clonidine discontinuation
rebound HTN, tachycardia, arrhythmia
MOA of dexmedetomidine
stimulates presynaptic α2 receptors in the brain & spinal cord, leading to inhibition of neuronal firing
decreased sympathetic drive = hypotension, bradycardia, sedation, analgesia
AEs of dexmedetomidine
HTN, tachycardia, dysrhythmias
what role does dexmedetomidine play in pain signals
inhibition of NE release plays a role in modifying propagation of pain signals
effects of dexmedetomidine’s central sympatholytic effects
- anti-shivering
- reduction in neuroendocrine stress response to surgery
AEs of rapid dexmedetomidine admin
can stimulate postsynaptic α2 receptors in arterial and venous circulations and cause vasoconstriction/HTN
which adrenergic agonist is not arrhythmogenic
phenylephrine
metabolism of epinephrine
- reuptake
- MAO & COMT
receptor stimulation of epinephrine
β1 > β2, α1
receptors stimulated by norepinephrine
α1, β1 > β2
adrenergic agonists that decrease airway resistance
- epinephrine
- isoproterenol
metabolism of NE
- reuptake
- MAO & COMT
metabolism of dopamine
- reuptake
- MAO & COMT
metabolism of isoproterenol
COMT
metabolism of dobutamine
COMT
metabolism of ephedrine
liver
receptors stimulated by dopamine
β1 > β2, α1
receptors stimulated by isoproterenol
β1 > β2
receptors stimulated by dobutamine
β1 > β2 > α1
catecholamines that increase RBF
- dopamine
- dobutamine
net effect of epi in different tisuses/organs
- organs with higher incidence of β2 receptors (skeletal muscles) = vasodilation
- higher incidence of α receptors (mesentery, kidneys) = vasoconstriction
effects of low vs. higher doses of epi
- lower: favor β effects (increased HR, CO, inotropy, pulse pressure, decreased SVR)
- higher: favor α effects (increased SVR, decreas CO)ed
metabolic effects of epi
increased blood glucose
hypokalemia d/t transcellular K+ shift
what is “epinephrine reversal”
converting the pressor response (mediated by α receptors) to a depressor response (mediated by β2)
might see if giving epi to treat severe hypotension caused by alpha blockers
effects of low vs. high doses of NE
low: favor beta-1 effects (increased HR, CO, inotropy, dromotropy)
high: favor beta-1 and alpha effects (systemic vasoconstriction except coronaries, decreased HR)
NE effect on venous return
enhances by venous vasoconstriction
principal use of NE
increase total peripheral vascular resistance, increasing BP
HR changes with NE
may be clinically insignificant d/t vasoconstrictive stim. of baroreceptors to slow HR countered by beta-1 positive chronotropic effect
metabolic effects of NE
minimal- no BG increase
first line treatment of distributive shock states
NE
how does dopamine affect CO
increases by positive chronotropic, inotropic, and dromotropic activity via beta 1 receptors
dose, receptor & effects of low dose dopamine
- dose: < 3 mcg/kg/min
- receptor: D1
- effects: vasodilation, increased renal and splanchnic blood flow
dose, receptor & effects of moderate dose dopamine
- dose: 3-8 mcg/kg/min
- alpha 1 and beta 1 receptors in heart and periphery
- increased contractility and BP
dose, receptor & effects of high dose dopamine
- dose: > 10 mcg/kg/min
- pure alpha 1 agonist
- increased BP
effects of postsynaptic D1 receptors
vasodilation of renal, GI, coronary, and cerebral vessels
effects of presynaptic D2 receptors
inhibit NE release, cause vasodilation
where are D2 receptors found
- pituitary gland
- emetic center
- kidney
how does dopamine affect vascular beds
highly variable effects depending on dose and receptor type/density
why does dopamine have to be given as an infusion
rapidly metabolized
useful and unique clinical effect of DA
increase contractility and BP while increasing RBF and UOP
complications assoc. with low-dose dopamine
CV, pulmonary, GI, immune, and endocrine compllications
metabolite of epi and NE
vanillylmandelic acid (VMA)
end-product of dopamine metabolism
homovanillic acid (HMA)
infusion dose of isoproterenol
0.015-0.15 mcg/kg/min
MOA of isoproterenol
potent sympathomimetic with beta-1 and beta-2 activity
uses of isoproterenol
- manage RV dysfunction
- manage pulmonary congestion
infusion dose of dobutamine
2-20 mcg/kg/min
MOA of dobutamine
- selective beta-1 agonism with mild beta-2 effects
- increased contractility and HR
- reduces vascular tone
specific adverse events with dobutamine in CV surgery
extending a cardiac muscle infarction, increasing AV conduction
may trigger rapid ventricular rate in pts with A fib
use of dobutamine in pulm HTN
decreases PAP and PVR via beta-2 stim
MOA of ephedrine
- directly stim. alpha and beta receptors
- indirectly promotes NE release
what causes indirect actions of ephedrine
endocytosis of ephedrine into adrenergic presynaptic terminals, displacing NE from secretory vesicles
NE activates target alpha-1 and beta-1 receptors
why is tachyphylaxis seen with ephedrine
depletion of presynaptic NE causes ephedrine to be released from synaptic vesicles as a false NT
T/F ephedrine crosses the BBB
true
onset and duration of ephedrine
rapid onset
duration up to an hour (depending on dose)
why should ephedrine be given to CAD pts cautiously
positive inotropic and chronotropic effects can increase O2 demand
long-acting beta agonists
- salmeterol
- formoterol
AEs of chronic beta2 agonist therapy
- down-regulation of target receptors (tachyphylaxis)
- airway hyperresponsiveness
MOA of beta agonists
increase intracellular cAMP, decrease Ca2+
how do beta agoinsts affect uterine smooth muscle
relaxation; tocolytic effect
black box warning assoc. with beta agonists
long-acting beta agonists
risk of asthma-related death possibly d/t development of airway hyperresponsiveness
chemical precursor of epi
norepinephrine
which adrenoreceptor is metabolized by the liver
ephedrine
synthetic catecholamine derived from dopamine
isoproterenol
catecolamine used in treatment of vasoplegia
Norepi
precursor of norepi
dopamine
common side effect of prazosin
orthostatic hypotension
how do alpha antagonists lower BP
by preventing NE from acting on vascular smooth muscle alpha-1 receptors
why do alpha antagonists cause orthostatic hypotension
can greatly impair compensatory vasoconstriction assoc.with baroreceptor response to sudden position changes
MOA of phenoxybenzamine
- noncompetitive, irreversible alpha antagonist
- blocks α-mediated activity of NE and epi
- results in decreased peripheral vascular resistance and BP
how is clinical effect of phenoxybenzamine terminated
synthesis of new receptors
what is phenoxybenzamine used for
preoperative management of pheo to normalize BP and prevent episodic HTN
how to prevent significant acute-onset hypotension with phenoxybenzamine
low dose initiation increased over several days
how should phenoxybenzamine-induced hypotension be treated
vasopressin and fluids
(irreversible alpha block makes NE and phenylephrine ineffective)
MOA of phentolamine
competitive nonselective alpha receptor antagonist
use of phentolamine
- otherwise refractory HTN seen with abrupt clonidine discontinuation
- local infiltration after IV extravasation of a vasoconstrictor like epi or NE
why does phentolamine stimulate stomach acid secretion
affinity for 5HT3 receptors
also induces mast cell degranulation
why should phentolamine be used cautiously in pts with CAD
causes baroreceptor-mediated reflex tachycardia
MOA of prazosin
- highly selective alpha 1 antagonist
- α1:α2 1000:1
effects of prazosin
- decreased peripheral vascular resistance in arterioles and veins
- increased venous capacitance
- decreased preload and BP with little change in HR
main use of terazosin
BPH
why are terazosin, doxazosin, and tamulosin used in BPH treatment
large numbers of α1A receptors there
MOA & use of yohimbine
- selective α2 antagonist
- widely marketed for ED, athletic performance, weight loss, HTN, diabetic neuropathy
ANS effects of yohimbine
- increased PNS activity (cholinergic)
- decreased SNS activity (adrenergic)
how might yohimbe affect antihypertensives
might diminish effect
CV indications of beta blockers
- HTN
- SVT
- A fib
- CHF
- IHD
- reduces myocardial O2 consumption and improving perfusion
AEs of abrupt discontinuation of long-term beta blockers
rebound tachycardia and HTN
caution of beta blocker use in hypovolemia
may cause bradyarrhythmias and obtund CV response to hypovolemia, progressive heart block, heart failure
beta blockers with membrane stabilizing activity
propranolol
acebutolol
what is MSA?
- membrane stabilizing activity
- inhibition or abolition of AP propagation across the membrane
- beta blockers with MSA act as antiarrhythmics
beta-blockers with intrinsic sympathomimetic activity (ISA)
pindolol
labetolol
acebutolol
prototypical nonselective beta blocker
propranolol
MOA of propranolol
- competitive β1 & β2 antagonism
- prevents action of epi, NE, dopamine, dobutamine, and isoproterenol at these receptors
AEs of β2 antagonism
- bronchoconstriction
- hypoglycemia
- peripheral vascular constriction
- aggravates Raynaud’s/PVD
beta blocker with a very long half life
nadolol
nonselective beta blocker with weak beta agonist effects
pindolol
assoc. with less HR slowing, less impact on BP
CV effects of β receptor blockade
- decreased HR
- decreasd contractility
- decreased AV conduction
- moderates cardiac O2 cosumption
cardioselective β blockers
- metoprolol
- atenolol
- acebutolol
- esmolol
- bisoprolol
cardioselective β blocker with weak beta agonist effects
acebutolol
MOA of cardioselective β blockers
- competitive cardioselective β1 antagonist
- prevents action of epi and NE
why is metoprolol useful in IHD
exerts moderating effect on HR, limiting its increase during exercise and stress
use of metoprolol
- angina
- heart failure
- MI
- A fib
- HTN
dose of metoprolol
2.5-5 mg increments to max of 15mg
first-line drug for rapid periop control of HR and BP
esmolol
metabolism of esmolol
nonspecific esterases found in RBC
use of atenolol
- decrease cardiac work, reduce myocardial O2 demand
- HTN
- chronic angina
- MI survivors
- some cases of A fib
atenolol dosing
PO 25-200 mg once or twice a day
IV 5-10 mg
MOA of labetolol
alpha 1 and nonselective beta blockade
(ratio of beta to alpha block is 7:1)
primary indication of labetolol
acute HTN
effects of alpha 1 antagonism with labetolol
vasodilation
decreased vascular resistance
considerations for labetolol in pts with asthma or COPD
may produce bronchospasm
how does labetolol affect HR
due to mixed activity, produces vasodilation without triggering baroreceptor-increased HR
half-life and metabolism of labetolol
- about 6 hours
- metabolized in liver
- eliminated by kidneys
MOA & effects of carvedilol
- antagonist at alpha-1, beta-1, and beta-2 receptors
- impaired arterial vasodilation
- modest HR reduction
beta blocker with antioxidant and anti-inflammatory properties
carvedilol
use of carvedilol
success in managing pts with heart failure, LV dysfunction, HTN, acute MI
propranolol’s use as an antidysrhythmic is best related to its:
membrane stabilizing ability
which beta blocker has intrinsic sympathetic activity
labetolol
which beta blocker undergoes renal metabolism
atenolol
what receptors does nicotine activate
acts as ACh analog at postganglionic neurons (Nn subtype) in SNS and PNS
CV effects of nicotine
unopposed sympathomimetic activity = increased vascular tone
heart may receive conflicting signals from SNS & PNS, affecting rhythm
use of methacholine
provocative agent to identify RAD in patients without clinically apparent asthma
MOA of methcholine
activates M3 receptors to evoke bronchoconstriction, increase airway secretions, and impair peak expiratory flow rates
MAO and use of bethanechol
relatively M3 selective in GI and urinary tract; used for nonobstructive urinary retention in periop period
antimuscarinic with greatest affect on HR
atropine
antimuscarinic with greatest degree of sedation
scopolamine
antimuscarinic with greatest antisialagogue effects
scopolamine
structure of antimuscarinics
atropine, scopolamine - tertiary amines
glyco - quarternary amine
antimuscarinics that cross the BBB
atropine & scopolamine
why can low dose (< 0.1) mg atropine worsen bradycardia
by blocking presynaptic M1 receptors on preganglionic PNS fibers
s/s atropine toxicity assoc. with 0.5-1 mg
- increased HR
- dry mouth
- lack of sweating
- feeling thirsty
- mild pupil dilation
s/s atropine toxicity assoc. with 2-5 mg dose
- tachycardia
- palpitations
- mydriasis
- cycloplegia
- restlessness
- confusion
s/s atropine toxicity assoc. with > 5 mg dose
- tachycardia
- mydriasis
- cycloplegia
- hot flushed skin
- fever
- hallucinations
- coma
CNS s/s muscarinic toxicity
- excitation, restlessness
- sedation, confusion, stupor
- hallucinations, delirium
- seizures
- coma, death
treatment for muscarinic toxicity
- oxygenation
- ventilation
- physostigmine 1-2 mg IV
primary inhibitory neurotransmitter in CNS
GABA
agents that enhance GABA
- isoflurane
- sevoflurane
- desflurane
- propofol
- benzos
- barbiturates
- etomidate