Unit 7 - GI Drugs Flashcards
What are the clinical signs of gastrointestinal injury/dz?
V/D, constipiation, colid, bloat
all are physiological functions intended to protect animal from harmful substances that may have been ingested
definitions related to the area of injury or dz
What is GI movement controlled by?
nervous system - parasympathetic which stimulates receptors w/ acetylcholine (vagus nerve carries nerve impulse to and from abdominal organs)
Hormones
endocrine system
What happens to the GIT when given a parasympathetic?
stims receptors w/ acetylcholine
vagus nerve carries nerve impule to and from abdominal organs
drugs that mimic acetylcholine - inc digestive secretions, gut smooth muscle tone and mobility
improve blood flow
What happens to the GIT when given a sympathetic?
stimulates receptors w/ norepinephrine, stims adrenal glands to release epinephrine
dec blood flow to GIT, gastric and enteric motility, digestive secretions
Therefore - dec digestion and absorption of nutrients
What is the emetic center
Vomiting center
a group of special neurons loc in medullary portion of brain
sends and receives neurons to stimulate the vomiting reaction
Coordinates smooth muscle contractions and the act of vomiting itself - horses, rabbits, rats and guinea pigs cannot vomit
What are the major receptors associated w/ emetic or antiemetic drugs?
serotonin, acetylcholine, histamine, dopamine, norepinephrine/epinephrine
What are the 5 mechanisms to stimulating vomiting?
- binds to receptors w/ emetic center and stims neurons
- Binds to receptors on chemoreceptor trigger zone which send signal to emetic center
- local nerve signals from distended or irritated region such as pharynx, stomach, duodenum
- Signals from overactive inner ear balance mechanism
- Emotional center in brain - due to trauma or emotional upset
What is the chemoreceptor trigger zone?
monitors blood and CSF for chemicals that can stimulate vomiting
has all major receptors found in emetic center and also receptors for opioids
the number and types of receptors varies w/ species and individuals
What receptors are increased in cats? Why does this cause? Which species has less alpha receptors?
cats have inc population of A-rceptors on emetic center so epinephrine and norepinephrine stim or drugs that stimulate these receptors will inc likelihood of vomiting
Dogs have less A receptors
Between dogs and cats, which has more dopamine receptors?
dogs
What are the two method of actions for emetics?
- central acting emetics turn on the CRTZ and/or vomit center loc in the brain. Body senses presence of a “toxin” and triggers vomit to protect itself
- peripheral acting emetics irritate/activate nerves in the stomach
Where might emetics be indicated for?
toxin ingestion
must be given within 4 hours of ingestion
removes 40-60% of gastric contents w/ each vomit
works best if small amount of food given prior
Many toxins already cause vomit: do not need to give an additional emetic
ask owner for hx
what situations do we never give emetics?
NEVER induce vomit if caustic, acid or alkaline (can burn esophagus or lungs)
induce vomit if FB, if unconscious or siezuring
never induce in horses, ruminants, birds, rabbits bc they cant vomit
Never induce if bloat, gastric torsion or esophageal damage
ALWAYS check MSDS or poison control before inducing vomit
In what situations do we induce vomit?
toxins!!
rodenticides, anti-freeze, chocolate, plant toxicitities (lillies, foxglove)
most medication overdoses, including NSAIDs, anti-parasites, coccidiostats
Vomit within 4hrs of ingestion is most effective; otherwise
some toxins (chocolate) may cause vomit at a certain dose
ALL toxins have a species-specific toxic dose
How can mu-acting opiods induce vomit?
turns on CRTZ and vomit center of the brain
only works on first dose - need high enough first dose, otherwise sedation occurs and turns down vomit center
Some animals will not respond
can reverse with naloxone after vomited
most commonly used - apomorphine, hydromorphone
What is apomorphine used for?
1st choice in dogs
conjuctival tablet form
can dissolve in sterile saline and squirt into conjunctiva (rec flush as irritating) OR filtered via micro-filter (to sterilize) and then give IV
1st dose only
not in cats - lack receptors in the CRTZ
What is hydromorphone used for?
1st dose only in SA (best in dogs)
IM works best. SQ works. IV does NOT induce vomit bc sedation hits too fast - now aspiration risk
more sedation than apomorphine
What is xylazine used for?
A2 AGONIST
1st choice in cats
prods emesis in 90% of cats only 30% in dogs which have less a2 receptors in CRTZ
What is hydrogen peroxide (3%) used for?
direct irritant
damages mucosal lining of the stomach
there is a per kg dose AND a max dose of 3 tbsp (45mls) for ANY sized animal. Can exceed max dose
give 1 dose, wait 15min. can repeat once
will cause serious s/e if gets into lungs (corrosion, hemorrhage, necrosis)
can cause gastric perforation if give too much; risk still exists if given at recommended dose; increased risk if pre-existing erosion/ulcer and in certain patients
What is warm salt solution used for?
local emetic
must give water or IV fluids to reduce risk of salt toxicity or dehydration
What ways do antiemetics work?
can block CRTZ, vomit center
can control nausea
can dampen peripheral nerves in GI tract
Give 1st dose parenterally so will be absorbed
give when natural vomiting reflex in excessive and not considered helpful ex. pancreatitis
How do phenothiazine tranquilizers work? WHat is a common one?
acepromazine
works by blocking several types of receptors in CRTZ and vomiting center
s/e - Dec BP, small degree of sedation at antiemetic dose - often used for motion sickness
