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Introduction to Pharmacology > Antiemetics > Flashcards

Antiemetics Flashcards

1
Q

What is emesis?

A

the action or process of vomiting as a reflex to eject contents of the stomach through the mouth

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2
Q

What are 6 common causes of emesis?

A
  1. ingestion of toxins - plants, spoiled food, human medication, string/yarn, certain human food
  2. medications - chemotherapy, radiation
  3. intense pain
  4. emotional stress - fear, anxiety
  5. reaction to certain smells or odors
  6. early stages of pregnancy (not really in animals)
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3
Q

In what 2 ways do most emetics work?

A
  1. locally acting on GI system
  2. centrally acting on the chemoreceptor trigger zone (CTZ) and vomiting center in the CNS
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4
Q

What are the 3 major parts of the brain responsible for emesis? What stimuli do they respond to?

A
  1. CTZ - uremic toxins, hepatotoxins, endotoxins
  2. vestibular aparatus - motion
  3. cerebral cortex - anxiety, stress
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5
Q

What stimuli does the GI tract respond to when inducing emesis?

A
  • toxins
  • cell necrosis
  • inflammation
  • distension
  • chemotherapy
  • radiation
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6
Q

Emesis triggers and centers:

A
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7
Q

What 4 stimuli tend to stimulate the vomiting center in the brain, causing nausea and vomiting?

A
  1. CTZ stimulation
  2. disturbance of vestibular system
  3. higher cortical centers stimulation
  4. periphery (pharynx, GI) via sensory nerves
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8
Q

4 parts of the brain responsible for emesis and their receptors:

A
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9
Q

What are the 7 main neurotransmitters in the emetic center?

A
  1. histamine (H1)
  2. serotonin (5-HT3)
  3. substance P (NK1)
  4. GABA (a + b)
  5. endorphins (µ, κ, CB1)
  6. dopamine (D2)
  7. acetylcholine (M1)
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10
Q

When is therapeutic emesis induced?

A

in prevention of clinical signs in dogs and cats who have had oral exposure to toxins, medications, plant hazards, and people food

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11
Q

What 2 emetics are commonly used in dogs?

A
  1. apomorphine
  2. hydrogen peroxide
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12
Q

What 3 emetics are commonly used in cats?

A
  1. xylazine
  2. medetomidine/dexmedetomidine
  3. midazolam/hydromorphone combo
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13
Q

Why do dogs and cats respond differently to emetics?

A

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)

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14
Q

What is the mechanism of action of Apomorphine (Apokyn)? How does it work as an emetic in dogs and cats?

A

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

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15
Q

Why are drugs readily able to act on the CTZ?

A

no BBB

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16
Q

Where in the brain does Apomorphine act?

A

CTZ

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17
Q

Contrary to its name, Apomorphine does not bind opioid receptors. Why does it have this name?

A

has some opioid-like repressive effects on the CNS
- sedation
- cardiac and respiratory depression
- suppression of emetic vomiting center (causes and represses???)

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18
Q

Why is Apomorphine able to stimulate and repress emesis?

A

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)
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19
Q

What is the best way to administer Apomorphine to stimulate emesis?

A

IV or transmucosal

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20
Q

What version of Apomorphine is used transmucosally?

A

Clevor, a highly dissolvable tablet applied to conjunctiva and eyeball, making it easily absorbable
- can irritate sclera
- tablet must be fished out

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21
Q

In what 2 situations is Apomorphine reversed? How is this done?

A

too much sedation
- opioid antagonist = Naloxone, which reverses CNS effects, NOT EMESIS

too much emesis
- dopaminergic antagonist = Acetopromazine (ACE)

22
Q

What classification of drugs works best for emesis in cats? Where in the brain does it affect?

A

α2-agonists, like Xylazine and Medetomidine/Dexmedetomidine

CTZ and emetic center - highly lipophilic, directly stimulates receptors in brain and GI —> vomiting in minutes

23
Q

What 2 drugs are used to reverse emesis in cats?

A

(α2 antagonists)
1. Yohimbine (when using Xylazine)
2. Atipamezole (when using Medetomidine)

  • not reliable in dogs
  • can be used in lower doses for sedation
24
Q

What is the purpose of antiemetics? Why should they be used carefully?

A

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

25
Q

What are the 7 most common antiemetic drug classes?

A
  1. serotonin (5-HT3) receptor antagonists
  2. dopamine (D2) receptor antagonists
  3. substance P (NK1) receptor antagonists
  4. histamine (H1) receptor antagonists
  5. acetylcholine (muscarinic) receptor antagonists
  6. cannabinoids
  7. glucocorticoids
26
Q

What determines the choice of antiemetic drugs?

A

etiology

27
Q

What are the most common 2 serotonin antagonists used and antiemetics? What is their mechanism of action?

A
  1. Ondansetron (Zofran)
  2. Granisetron

block 5-HT3 receptors in VC and CTZ

28
Q

What are 2 common situations where serotonin antagonists are used as antiemetics? What is it used in combination with?

A
  1. chemotherapy-induced nausea and vomiting (Cisplatin)
  2. post-radiation and post-operative nausea and vomiting

increases effect when used with corticosteroids and NK1 antagonists

29
Q

Serotonin antagonists are pretty well-tolerated antiemetics. What are 5 possible adverse effects?

A
  1. mild headache
  2. dizziness
  3. itching
  4. constipation/diarrhea
  5. minor ECG abnormalities
30
Q

What are the 2 types of dopamine (D2) antagonists used as antiemetics?

A
  1. prokinetic drugs - Metoclopramide (Reglan), Domperidone
  2. neuroleptics (antipsychotics) - Chlorpromazine, Droperidol
31
Q

What is the mechanism of action of Metoclopramide and Domperidone? In what 3 situations are they commonly used?

A

block D2 receptors and serotonin receptors in CTZ

  1. non-specific nausea and vomiting
  2. drug responses
  3. post-operative
32
Q

What are 4 possible adverse effects of Metoclopramide and Domperidone?

A

(D2 antagonists)
1. dyskinesia (involuntary movements)
2. sedation
3. postural hypotension
4. extrapyramidal symptoms: tremor, rigidity

33
Q

What are 2 common substance P antagonists used as antiemetics? What is their mechanism of action?

A
  1. Cerenia* (PO, SC, IV)
  2. Aprepitant (PO)

competitively binds to the neurokinin1 (NK1) receptor in VC and other areas

34
Q

In what situation is Cerenia most commonly used?

A
  • given 2 hours before travel for motion sickness
  • pain management
35
Q

What are 3 common situations where substance P antagonists are used? What is it commonly combined with?

A
  1. treat motion sickness
  2. prevention of acute and delayed chemotherapy-induced nausea and vomiting
  3. post-operative nausea and vomiting

combined with serotonin antagonists and corticosteroids

36
Q

What are 5 common adverse effects of substance P antagonists?

A
  1. dyskinesia
  2. sedation
  3. dizziness
  4. hiccups
  5. hypotension
37
Q

What are 2 common antihistamines used as antiemetics? What is their mechanism of action?

A
  1. Diphenhydramine (Benadryl)
  2. Dimenhydrinate (Gravol)

block histamine at H1 receptor (dogs) and block ACh at muscarinic M1 receptors (cats)

38
Q

What are 2 common uses for antihistamines as antiemetics?

A
  1. motion sickness (dogs, poor response in cats)
  2. morning sickness (not common in animals)
39
Q

What are 2 possible adverse effects of antihistamines as antiemetics?

A
  1. prominent sedation, hypotension, and confusion
  2. anticholinergic effects: dry mouth, dilated pupils, urinary retention, constipation
40
Q

What are 2 common anticholinergics used as antiemetics? What is their mechanism of action?

A
  1. Hyoscine Butylbromide (Hysomide)
  2. Dicyclomine
    (PO, injections, patches)

block Ach at the muscarinic M1 receptor

41
Q

What are the 2 common situations that anticholinergics are used as antiemetics? When is it specifically NOT used?

A
  1. motion sickness (patches behind ears)
  2. morning sickness (Dicyclomide)
  • chemotherapy-induced nausea and vomiting
42
Q

What are 5 possible adverse effects of anticholinergics as antiemetics?

A
  1. tachycardia
  2. blurred vision
  3. dry mouth
  4. constipation
  5. urinary retention
43
Q

What 3 benzodiazepines are commonly used as antiemetics? What is their mechanism of action?

A
  1. Lorazepam (PO, IV)
  2. Diazepam (PO, IV, PR)
  3. Midazolam (PO, IV, PR, IN, SL)

enhances the effects of GABA by binding to receptors in the brain

44
Q

What are 3 situations where benzodiazepines are used as antiemetics?

A
  1. psychotropic medication
  2. calming effect (GABAa)
  3. anticipatory nausea and vomiting (chemotherapy)
45
Q

What are 4 possible adverse effects of benzodiazepines as antiemetics?

A
  1. sedation
  2. dry mouth
  3. dizziness
  4. paradoxical agitation
46
Q

What 2 corticosteroids are used as antiemetics? What is their mechanism of action?

A
  1. Dexamethasone
  2. Methylprednisolone

not well-understood - anti-inflammatory effects

47
Q

When are corticosteroids commonly used as antiemetics? What is it commonly used in combination with?

A

chemotherapy-induced vomiting

serotonin antagonists or NK1 antagonists

48
Q

What are 7 possible adverse effects of corticosteroids as antiemetics?

A
  1. hyperglycemia
  2. hypertension
  3. osteoperosis
  4. insomnia
  5. increased intraocular pressure
  6. increased susceptibility to infection
  7. increased appetite and obesity
49
Q

What are 2 cannabinoids used as antiemetics? What is their mechanism of action?

A
  1. Nabilone
  2. Dronabinol

not well-understood - act on CB1 receptors in VC

50
Q

Cannabinoids are not commonly used as antiemetics. When can it be used? What are some possible adverse effects?

A

anticancer drug-induced vomiting

  • euphoria/dysphoria
  • sedation
  • agitation
  • hallucination
  • withdrawal syndrome: restless, insomnia, irritibility
  • autonomic effects: tachycardia, palpitation
51
Q

Antiemetic drugs and their actions in the brain:

A
52
Q

What pneumonic is used for causes of emesis?

A

V = Vestibular - motion sickness, benign paroxysmal positional vertigo, Meniere’s disease, tumor, inner ear infection/inflammation
O = Obstruction - constipation, ileus, intestinal pseudo-onbstruction, partial/full bowel obstruction, ascites, adhesion
M = Motility disorder - gastroparesis, neurological, IBS, medications, hypo/hyperthyroidism, GERD, gastroenteritis, scleoderma
I - Infection, Inflammation, Increased ICP - bacteria/virus, strock, concussion, brain tumor, radiation/chemotherapy, gastroenteritis, pancreatitis, cholecystitis
T = toxins - metabolic disorders, medications, organ failure, poisoning, substance abuse

Introduction to Pharmacology (39 decks)

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