Alpha 2 agonists and antagonists Flashcards
Name the alpha 2 agonists
- Dexmedetomidine (Dexdom)
- Xylazine
Name the alpha 2 antagonists
- Atipamezole
- Yohimbine
____________ is a mixed A2 agonist/antagonist
Medetomidine / Vatinoxan (Zenalpha)
Which parts of the pain pathway do A2 agonists act on?
- Transmission
- Modulation
- Perception
Xylazine is approved for use in __________
Horse, deer, elk
Dexmedetomidine is approved for us in __________
Dogs, cats, exotics
Which species is most sensitive to xylazine?
Cows
Why is xylazine not frequently used in small animals?
More potent than dexdom, increased morbidity
What is the overall clinical effect of A2 agonists?
Sedation and analgesia
Which A2 agonist is more selective to A2?
Dexmedetomidine
less A1 effects
How are A2 agonists commonly given?
IV or IM
Why are A2 agonists not given SQ?
Poor absorption due to local vasoconstriction (some a1 effects)
Which A2 agonist has a longer duration of action?
Dexmedetomidine > xylazine
What is the clinical indications for use of xylazine in cats?
Emetic of choice for cats to induce vomiting
stimulation of A2 receptors in the emetic center and CRTZ
What occurs in phase I when using A2 agonists?
Phase I - Peripheral phase
- Peripheral vasoconstriction mediated by a1 receptors
- Causes reflex bradycardia and INC. systemic BP
dont give anticholinergics (Atropine, Glycopyrrolate) during Phase I
What occurs in phase II when using A2 agonists?
Phase II - Central phase
- Decreased sympathetic tone (Dec NE)
- HR stays low
- Peripheral vasodilation leading to hypotension and bradycardia
CO can decrease 30-50% with A2 agonists
What is the most common arrhythmia seen with A2 agonists?
2 degree AV block
What does a biphasic effect mean in regards to A2 agonists?
Initial vasoconstriction and hypertension followed by vasodilation and hypotension due to CNS depression
What might happen to BP if you give atropine for reflex bradycardia?
Hypertension and increased afterload (not good)
___________ is a specific competitive antagonist for dexmedetomidine
Atipamezole (Antisedan)
___________ is a specific competitive antagonist for yohimbine
Xylazine
You want to reverse the effects of an A2 agonist, what route of admin would you give the reversal?
IM
More side effects when given IV like CV collapse
Effect of A2 agonists on GI motility?
Decreases GI motility
Emetic of choice in cats
Effects of A2 agonists on the uterus?
Stimulates myometrial contractions, risk for abortions
Effects of A2 agonists on the kidneys?
Mild diuresis (PU) by reducing ADH release
What can be high on a biochem panel when using A2 agonists?
Glucose (hyperglycemia)
Due to decrease release of insulin
more pronounced in horses and ruminants
be careful using A2 agonists on diabetic patients
Which metabolic condition would be a precaution when selecting an A2 agonist?
Diabetes
A2 decreases insulin resulting in hyperglycemia
A2 agonists can cause _________ (hypothermia/hyperthermia)
Hypothermia (low temp) due to vasoconstriction
What precaution must be taken when using A2 agonists on deer?
Delayed hypersensitivity rxn
A2 agonists should not be used concurrently with ____________
Epinephrine and atropine
__________ is the most selective A2 antagonist
Atipamezole (Antisedan)
What GI side effects can be seen after administration of Atipamezole?
Mild salivation and diarrhea
(A2 antagonist - Reversal agent)
What side effects can be seen if an A2 antagonist is given without an A2 agonist?
CNS excitement, tachycardia and hypotension due to vasodilation
Why might Medetomidine/Vatinoxan (ZenAlpha) be used over other A2 agonists?
Faster onset, shorter duration
- can still be reversed with Atipamezole
- less CV depression (less hypotension)
good for outpatient procedures
Medetomidine/Vatinoxan (ZenAlpha) precautions?
Beware of hypotension in cats and horses
Other therapeutic uses for A2 agonists?
Mitoban toxicity, Amitraz tick collar toxicity
A2 agonists can be used in horses for?
Chemical ejaculation
