Lecture 3 - Adrenergics & Cholinergics - NICOLE Flashcards
alpha 2 agonists are sedatives and analgesics that
DECREASE CARDIAC OUTPUT
alpha 2 agonists characteristics (good for what vs bad for what)
-good premeds for anesthesia
-good for standing procedures
- bad in patients with compromised CV function
reducing dose of alpha 2 agonists does NOT reduce
the magnitude of the adverse effects on cardiac output, but does reduce the duration of these effects
how do alpha 2 agonists provide sedation and analgesia?
-sedation due to inhibition of NE release in brainstem
- analgesia due to reduced neurotransmitter release and signal transmission in afferent pathways
how do alpha 2 agonists reduce cardiac output? (long one sorry)
- Initial effect on blood vessels is vasoconstriction which increases blood pressure (also increases after load which decreases cardiac output).
- The increase in bl. pres. is sensed by baroreceptors, which triggers a decrease in sympathetic tone and an increase of parasympathetic tone.
- Increased parasympathetic tone to the heart will slow the heart rate to reduce cardiac output (BRADYCARDIA that results from alpha 2 agonism)
xylazine is a(n)
alpha 2 agonist
xylazine is commonly used in
horses and ruminants
do horses or cows get more xylazine
ruminants take approx 1/10th the horse dose to achieve the same effect
do you use xylazine on sick animals
generally reserved for healthy animals
side effects of xylazine an alpha 2 agonist
AV block, reduced GI motility, sweating, increased myometrial tone
how do you reverse xylazine
yohimbine or atipamezole
clinical tips for xylazine
combine with butorphanol (opioid) for better sedation and pain control
use caution with xylazine in late pregnant animals, increased risk of premature delivery
the alpha 2 agonists commonly used in large animals are
xylazine, detomidine, and romifidine
(listed in order of intensity of cardiovascular effects)
alpha 2 agonists tend to have a
diuretic effect
sedation with xylazine compared to detomidine in horses
serum half life of xylazine is longer (50 mins) and detomidine is 25 mins but sedation is deeper and more reliable than sedation with xylazine
CV effects (bradycardia and bradyarrythmias) are more pronounced after detomidine than xylazine
sedation with romifidine in horses
serum half life of 135 minutes in horse
tends to cause less ataxia in horses than other alpha 2 agonists, so may be preferred for procedures such as standing mri where the horse standing still and not swaying is important
however its more expensive
alpha 2 agonists sedative vs analgesic effects time
analgesic effects do not last as long as sedative effects - alpha 2 agonists are selective, not specific for alpha 2 receptors so they also have some binding to alpha 1 receptors
detomidine potency vs xylazine
50-100 times more potent than xylazine
what do you primarily use xylazine in
horses but can be used in cattle
does xylazine or detomidine have better sedation and pain control for surgery
detomidine
is detomidine or xylazine LESS likely to cause premature delivery in pregnant animals?
detomidine
how do you reverse detomidine?
an alpha 2 antagonist such as atipamezole
dexmedetomidine is a
alpha 2 agonist
dexmedetomidine is similar to
medetomidine
what is dexmedetomidine used commonly for
small animals getting procedures that require sedation
dosage of dexmedetomidine is based on
body surface area
when used as a premed dexmedetomidine reduces
maintenance anesthetic needs
how to reverse dexmedetomidine
alpha 2 antagonist - atipamezole
clinical tip dexmedetomidine
makes over 50% of cats vomit
dexmedetomidine is the most selective of
alpha 2 agonists. it has an alpha 2: alpha 1 selectivity of 1620:1 (10x better than xylazine)
most common alpha 2 agonists used for sedation in small animal practice
dexmedetomidine and medetomidine (dexdomitor and domitor, respectively)
dexmedetomidine and meditomidine are enantiomers
compounds that are mirror images and rotate polarized in opposite directions.
dexmedetomidine vs metomidine pharmacodynamics and dose
similar pharmacodynamic effects but dose of metedomidine required to exert a clinical effect approximately twice the dose of dexmetedomidine required to exert the same effect (bc half the molecules of med are in inactive form)
they have similar efficacy but dexmed is more potent
most concerning alpha 2 agonist side effects
cardiovascular effects
alpha 2 agonists will decrease
cardiac output
alpha 2 agonists - initial vasoconstriction leads to bradycardia then presynaptic effects can then lead to
vasodilation so we get hypertension, followed by vasodilation. however, the bradycardia is generally persistent
best to use alpha 2 agonists in
HEALTHY animals.
DO NOT use alpha 2 agonists in
animals with CV disease or in shock
alpha 2 agonists - good analgesia but shorter than
the sedative effect
alpha 2 agonists have better sedation and analgesia when paired with an
opoid
can paradoxical excitement occur with alpha 2 agonists
yes - common to get xylazine rage
what is dobutamine
beta 1 agonist
dobutamine is a positive
inotrope that does NOT increase heart rate (at normal doses) but does increase stroke volume
half life of dobutamine
2 minutes
is dobutamine pricey
yes
adverse effects of dobutamine
- correct hypovolemia before administration
- incompatible with bicarbonate
-at high doses can cause tachycardia
-seizures in cats! use low doses only, if at all
dobutamine is sometimes used to
raise blood pressure in anesthetized patients.
dobutamine activates what receptors
dopamine, alpha 1, and beta 1 receptors (causing vasoconstriction and increasing intropy)
clenbuterol is a
beta 2 agonist
can you give clenbuterol to food animals
NO YOU CANNOT !!! DONT DO IT
clenbuterol has what effects
-bronchodilator (rarely used now to treat equine asthma)
-inhibits uterine tone/contractions (aids in dystocia)
clenbuterol is banned in food animals because
used to be used as a growth promotant but residues in meat have caused tachycardia, muscle tremors, and headaches in consumers
epinephrine is a
non selective adrenergic agonist
epinephrine is used for
emergency treatment of anaphylaxis or for cardiopulmonary resuscitation
epinephrine is sometimes added to local anasthetics to
cause vasoconstriction
epinephrine increases cardiac output but also
myocardial oxygen consumption
you can give epinephrine
IV, IM, SC, IT
in anaphylaxis, epinephrine is given for its
vasoconstrictive (alpha 1) and bronchodilator (beta 2) effects and is very useful
in CPR situations, epinephrine is indicated when
the animal has a non-shockable rhythm and that only low-dose epinephrine is now recommended
prazosin is an
alpha 1 antagonist
prazosin has what effects
reduces blood pressure - arterial and venous vasodilatory
- sometimes used as adjunctive treatment for heart failure but there are better choices
prazosin is no longer recommended for
blocked cats !!!!!!!!
why is prazosin no longer used for blocked cats
it was often given after unblocking for several weeks to decrease urethral spasms but recent evidence shows this may INCREASE the risk of reblocking :(
is prazosin protein bound?
yes - 97% protein bound
atipamezole is an
alpha 2 antagonist
atipamezole is a competitive inhibitor of
alpha 2 receptors
atipamezole clinical effects
reverses sedation, cardiovascular effects, and analgesia associated with alpha 2 agonist administration
atipamezole is normally administered
IM in small amounts
in horses atipamezole is normally given
1/2 IM and 1/2 IV and IV is injected SLOWLY
cats are often castrated under an injectible anesthetic combo of dexmed, butorphanol, and ketamine. If reversing this after the procedure, make sure that
you wait long enough that the ketamine has worn off before administering atipamezole. Also, whenever you reverse an alpha 2, consider pain control as you’re also reversing the alpha 2 analgesic effect
esmolol is a
beta 1 antagonist
esmolol is an ultra short acting IV
beta blocker
esmolol is used to treat
supraventricular tachycardias or to test if beta blockers will be effective in controlling arrthymias (esp in cats with HCM)
- anesthesia
-CPR
esmolol is a negative
inotrope and chronotrope
esmolol may
decrease myocardial oxygen demand
reduces systolic and diastolic blood pressure
esmolol adverse effects
hypotension and bradycardia
drugs that act similarly to acetylcholine are called
parasympathomimetics / cholinergics / cholinoreceptor stimulants
neostigmine is a what
cholinergic
neostigmine is a reversible
inhibitor of acetylcholinesterase
neostigmine results in
decreased breakdown of Ach at the synaptic cleft and enhanced activity
neostigmine is used to increase
gut motility/for its smooth muscle effects and is also used in treatment of myasthenia gravis
in myasthenia gravis, autoantibodies attach nicotinic Ach receptors in skeletal muscles. This results in
muscle weakness.
by inhibiting acetylcholinesterase, neostigmine causes
more Ach to be available, increasing its interaction with the receptors that are still present and helping to counteract the weakness that results from this disease
is neostigmine or pyridostigmine preferred for myasthenia gravis treatment
pyridostigmine because it has a longer duration of action and fewer GI effects
atropine and glycopyrrolate are what
anticholinergics
atropine and glycopyrrolate are competitive muscarinic antagonists used to
reduce response to parasympathetic nerve impulses
effects of atropine and glycopyrrolate are
dose dependent
atropine and glycopyrrolate increase
HR and conduction veolcity , inhibit GI smooth muscle contraction, mydriatic, decrease secretions, and bronchodilator
glycopyrrolate and atropine are used for
emergency treatment of bradyarrythmias, to facilitate opthalmic exams, such as adjunctive treatment for equine recurrent uveitis
adverse effects of atropine and glycopyrrolate
primarily tachycardias
at high doses atropine may cause mania
can cause ileus, especially in horses
glycopyrrolate or atropine - which one crosses BBB more
atropine - so glycopyrrolate has fewer CNS effects
the combination of anticholinergics and alpha 2 agonists creates the potential for
myocardial hypoxemia to develop as a result of increased myocardial work
N-butylscopolammonium bromide/ hyoscine buytlbromide: is an
anticholinergic
N-butylscopolammonium bromide/ hyoscine buytlbromide is only used in
horses but is labelled for cattle in some countries
N-butylscopolammonium bromide/ hyoscine buytlbromide has effects similar to
atropine
N-butylscopolammonium bromide/ hyoscine buytlbromide is especially useful in horses with
gas/spasmodic colic (relaxes intestine)
- but heart rate increases after administration and can’t be used to monitor pain for about 30 min
N-butylscopolammonium bromide/ hyoscine buytlbromide can be useful for
performing rectal exams in horses and for acute asthma treatment
N-butylscopolammonium bromide/ hyoscine buytlbromide common name
buscopan - used to treat spasmodic colic, relax rectum for rectal exams. ad relax esophageal smooth muscle in choked horses
