Antiemetics Flashcards
(52 cards)
What is emesis?
the action or process of vomiting as a reflex to eject contents of the stomach through the mouth
What are 6 common causes of emesis?
- ingestion of toxins - plants, spoiled food, human medication, string/yarn, certain human food
- medications - chemotherapy, radiation
- intense pain
- emotional stress - fear, anxiety
- reaction to certain smells or odors
- early stages of pregnancy (not really in animals)
In what 2 ways do most emetics work?
- locally acting on GI system
- centrally acting on the chemoreceptor trigger zone (CTZ) and vomiting center in the CNS
What are the 3 major parts of the brain responsible for emesis? What stimuli do they respond to?
- CTZ - uremic toxins, hepatotoxins, endotoxins
- vestibular aparatus - motion
- cerebral cortex - anxiety, stress
What stimuli does the GI tract respond to when inducing emesis?
- toxins
- cell necrosis
- inflammation
- distension
- chemotherapy
- radiation
Emesis triggers and centers:
What 4 stimuli tend to stimulate the vomiting center in the brain, causing nausea and vomiting?
- CTZ stimulation
- disturbance of vestibular system
- higher cortical centers stimulation
- periphery (pharynx, GI) via sensory nerves
4 parts of the brain responsible for emesis and their receptors:
What are the 7 main neurotransmitters in the emetic center?
- histamine (H1)
- serotonin (5-HT3)
- substance P (NK1)
- GABA (a + b)
- endorphins (µ, κ, CB1)
- dopamine (D2)
- acetylcholine (M1)
When is therapeutic emesis induced?
in prevention of clinical signs in dogs and cats who have had oral exposure to toxins, medications, plant hazards, and people food
What 2 emetics are commonly used in dogs?
- apomorphine
- hydrogen peroxide
What 3 emetics are commonly used in cats?
- xylazine
- medetomidine/dexmedetomidine
- midazolam/hydromorphone combo
Why do dogs and cats respond differently to emetics?
dogs and cats have different receptors in their CTZ
DOGS: increased D2 and H1 receptors
CATS: decreased D2 receptors and increased sensitivity to α2 receptors
(dopamine and histamine = dog)
(α-2 stimulants = cats)
What is the mechanism of action of Apomorphine (Apokyn)? How does it work as an emetic in dogs and cats?
non-selective dopamine agonist (D1 and D2)
DOGS: works really well due to high numbers of D2 receptors
CATS: have less D2 receptors - less likely to vomit
Why are drugs readily able to act on the CTZ?
no BBB
Where in the brain does Apomorphine act?
CTZ
Contrary to its name, Apomorphine does not bind opioid receptors. Why does it have this name?
has some opioid-like repressive effects on the CNS
- sedation
- cardiac and respiratory depression
- suppression of emetic vomiting center (causes and represses???)
Why is Apomorphine able to stimulate and repress emesis?
depends on which center in the brain is reached faster
- CTZ first = emesis (IV injection)
- emesis center first = prevents emesis (once it crosses BBB, the animal is able to stop vomiting)
What is the best way to administer Apomorphine to stimulate emesis?
IV or transmucosal
What version of Apomorphine is used transmucosally?
Clevor, a highly dissolvable tablet applied to conjunctiva and eyeball, making it easily absorbable
- can irritate sclera
- tablet must be fished out
In what 2 situations is Apomorphine reversed? How is this done?
too much sedation
- opioid antagonist = Naloxone, which reverses CNS effects, NOT EMESIS
too much emesis
- dopaminergic antagonist = Acetopromazine (ACE)
What classification of drugs works best for emesis in cats? Where in the brain does it affect?
α2-agonists, like Xylazine and Medetomidine/Dexmedetomidine
CTZ and emetic center - highly lipophilic, directly stimulates receptors in brain and GI —> vomiting in minutes
What 2 drugs are used to reverse emesis in cats?
(α2 antagonists)
1. Yohimbine (when using Xylazine)
2. Atipamezole (when using Medetomidine)
- not reliable in dogs
- can be used in lower doses for sedation
What is the purpose of antiemetics? Why should they be used carefully?
stop or decrease nausea and vomiting
vomiting is a protective mechanism —> only use when vomiting is deterrent to patient’s health and recovery
- can mask signs of disease/improvement and allow toxins to remain in GI
