Premedication- A2 Agonist And Phenothiazines Flashcards
What are the strongest available sedatives
A2 agonists
What is the MOA of a2 agonists and the location of their action?
Competitive a2 agonsit
Presynaptic membrane (CNS)
Post synaptic membrane (vascular smooth muscle)
Extra synaptic sites (pancreas / adipocytes)
When activated A2 receptors do what?
Inhibit norepi release from the presynaptic membrane
When norepi is released it binds to A2 as a negative feedback
What are the effects of a2?
Sedation (brain)
Analgesia (spinal cord and dorsal horn)
Reduction of stress
What is the most concerning side effect of a2 agonists?
Vasoconstriction
A2 in wall of arteries along with a1
A2 receptors can be found on adipocytes and pancreatic B cells, what effects will an agonist have concerning these sites?
Adipocytes - inhibition of lipolysis
Pancreas - inhibition of insulin release, hyperglycemia
What CNS effects do A2 agonists have?
Strong Sedative
Some analgesic effect
Muscle relaxation
What is the most important side effect of A2 agonists ??
Strong vasoconstriction
Reflex bradycardia -> low CO and tissue perfusion
What effects do A2 have on respiration
Mild depression
RR decrease but tidal volume increase
Upper airway resistance increases
-relaxation of larynx, pharynx and nares
V/Q mismatch
What a2 agonist is contradindicated in sheep and why?
Xylazine
- lung edema and hypoxia
What are the GI effects of a2 agonists
Decrease salivation
Lower esophageal sphincter tone decreases
GI motility
Vomiting - cats with xylazine
T/F: Xylazine can cause uterine contractions and abortion in cattle
True
When is the use of A2 agonists indicated?
Sedation of aggressive animals
Sedation in ICU
Sedation to manage post-op airway obstruction
What are contraindications to A2 agonist use?
Too young or too old
Hemodynamic instability
Severely debilitated patient
What is the most selective A2 agonsit used in small animals?
Dexmedetomidine
What is the a2 receptor specificity from most to least specific for A2 antagonists?
Atipamezole»_space; yohimbine»_space; tolazoline
T/F: atipamezole should be used to antagonize any a2 agonist
True
Yohimbine and tolazoline are ‘dirty drugs’ acting on other receptors and have many side effects
What is the number one choice for a2 agonists in large animals
Xylazine
T/F: the pre-medication dose for xylazine in horse and cattle is 0.5-1mg/kg
False
This is true for horses, but cattle are very sensitive and only require about 10% of this dose
T/F: the dose of medetomidine does not differ between horse and cattle
True
What is the duration of Xylazine ? How does this compare to detomidine
Xylazine 20-40min
Detomidine 90-120mins
What is the route of admin of detomidine?
IM, IV, and sublingual
What a2 agonist is used in horses and is thought to produce less ataxia than xylazine, thus is preferred for standing dental surgery
Romifidine
Given IM or IV
Duration : 45-90mins
What receptors does acepromazine work on?
Dopamine
Serotonin
A1
Histamine
-antagonist
