Equine Field Anesthesia: The Drugs Flashcards
what are the categories of drugs
- tranquilizers: phenothiazines, butyrophenones
- alpha 2 agonists
- benzodiazepines
what class of drug is acepromazine
phenothiazine
what is the effect of acepromazine
- calming
- indifference
- decreased locomotor activity
what is the mechanism of action of acepromazine
- dopamine D1 and D2
- a2
- muscarinic
- serotnergic
- histamine
how is acepromazine administered
injectable and PO
what is the time to peak effect after acepromazine administration
IV: 20 min
IM: 45-60 min
what drugs does acepromazine act synergistically with
a2 agonists and opioids for analgesia and CNS depression
what is the effect of acepromazine and opioid combo
acepromazine may counteract opioid excitability
how does acepromazine reduce mortaility in GA (4)
- antiarrhythmic
- vasodilation –> perfusion increases
- anesthetic requirements decreased
- smoother recovery
what are the disadvantages of acepromazine (5)
- no reliable sedation
- no analgesia
- long duration of action (4-6 hours)
- no antagonist
- not licensed or in table 1 for farm animals
what are the adverse effects of acepromazine (4)
- vasodilation –> hypotension
- seizure threshold decreases
- priapism
- may increase risk of of regurgitation
what are the contraindication of acepromazine (3)
- pre-exisiting hypotension
- history of seizures
- breeding stallions
what are alpha 2 agonists
sedative
do alpha 2 agonists have analgesia
yes
do alpha 2 agonists offer reliable sedation in horses
yes
what are the effects of alpha 2 agonists
- resp: upper airway obstruction
- CV: bradycardia, initial hypertension, arrhythmogenicity
- others: decreased GI motility, diuresis, sweating, muscle relaxation
what are the alpha 2 agonists and their concentration, volume required, duration of action, standing chemical restraint (yes/no), routes of administration, species

what is the benzodiazepine mechanism of action
GABAA receptor agonist
what are benzodiazepine used for
sedatives and adjunct anesthetic drugs
what are examples of benzodiazepine
midazolam and diazepam
can benzodiazepine be used in foals
yes < 4 weeks
what are the effects and side effects of benzodiazepine (6)
- CNS: sedation, anesthetic sparing effect, anticonvulsive action
- resp: depression
- minimal effects at clinically relevent doses
- muscle relaxation
- counteracts muscle rigidity caused by ketamine
- ataxia after prolonged infusion in horses
what opioid is allowed in food producing animals
butorphanol
what are the opioids and the licensing, receptor action, administration, duration of action, sedative action, species

what are the opioids side effects in horses (4)
- CNS: locomotion, dysphoria
- resp: minimal effects at clinically relevant doses, increase resp rate (alone), potentiation of resp depression (with alpha 2 agonists)
- CV: minimal effects, opioids alone heart rate and BP increased, when combined with a2 agonists tend to predominate
- histamine release: morphine + pethidine
what are the actions of NSAIDs
- anti-inflammatory
- anti-pyretic
- analgesia
what are the anesthetic induction drugs (5)
- ketamine
- thiopentone
- propofol
- alfaxalone
- guaifenesin
what effect does ketamine have
- dissociative anesthetic
- analgesic (skin and musculoskeletal pain, poor for visceral pain)
what mechanism of action does ketamine use
NMDA antagonist
what is ketamine used for (4)
- sedation in pigs and cattle
- induction
- anesthetic maintenance
- post operative analgesia
what is ketamine combined with for induction
benzodiazepines or guaifenesin
+/- thiopentone in food producing animals
how is ketamine used for anesthetic maintanence
+/- muscle relaxant and/or alpha 2 agonist
emergency top up drug in horses
what are the effects and side effects of ketamine

what is thiopentone
short acting barbiturate
GABAA receptor agonist
what is the onset and duration of thiopentone
fast onset (30s) and short duration (<10 min)
does thiopentone provide analgesia
no
is thiopentone licensed
no
what are the uses of thiopentinone
emergency top up in horses
what are the side effects of thiopentone

what is guaifenesin
centrally acting muscle relaxant
does guaifenesin provide analgesia
no
how is guaifenesin administered
infused IV to effect or as part of triple drip
what are the effects and side effects of guaifenesin

how does propofol act
GABAA agonist
what is propofol used
- anesthetic induction
- anesthetic maintenance
what is alfaxalone
GABAA agonist
what is alfaxalone used for
- induction
- sedation in pigs (IM) in combo with opioid and midazolam
what are the effects on recovery in horses of alfaxalone
poor recoveries