Chapter 162 - antiemetics & prokinetics

Question 1

anti-emetic class most effective in the face of GI obstruction

Answer 1

NK-1 receptor antagonists (maropitant)

Question 2

MOA of maropitant

Answer 2

neurokinin-1 receptor antagonist - blocks the action of substance P in the CNS and PNS in the GI tract

Question 3

maropitant contraindications

Answer 3

puppies

Question 4

effect of IV maropitant on amount of sevoflurane required during anaesthesia?

Answer 4

reduces MAC (minimum alveolar concentration)

Question 5

name 3 5-HT3 receptor antagonists

Answer 5

ondansetron, dolasetron, granisetron

Question 6

MOA of ondansetron

Answer 6

competitively block serotonin 5-HT3 receptors centrally (CRTZ, MVC) and peripherally (intestinal vagal afferents)

Question 7

side effects of 5-HT3 receptor antagonists in people

Answer 7

somnolence, diarrhoea, constipation, prolongation of QT interval, decreased efficacy of tramadol (with ondansetron)

Question 8

MOA of metoclopramide

Answer 8

dopamine receptor antagonist, 5-HT3 receptor antagonist - potent blocker of CRTZ, decreases gastroesophageal reflux, increases gastric emptying

Question 9

why might metoclopramide be less effective in cats cf dogs

Answer 9

paucity of dopamine receptors

Question 10

contraindications to metoclopramide

Answer 10

severely decreased GFR (renally excreted)

Question 11

side effects of metoclopramide overdose

Answer 11

extrapyramidal signs (behavioural signs, apparent hallucinations), similiar to amphetamine intoxication (hyperactivity, frenzied behaviour)

Question 12

suggested dose of metoclopramide for gastrokinesis and gastroesophageal reflux

Answer 12

0.4mg/kg IV followed by 0.3mg/kg/h CRI

Question 13

chlorpromazine drug class

Answer 13

promazine derivatives, antidopaminergic, antihistaminic, blocks the CRTZ (and MVC at higher doses), anticholinergic, antispasmodic, a-adrenergic blocking effects

Question 14

side effects of promazine derivatives

Answer 14

sedation, vasodilation –> hypotension, increased CVP, changes in HR, lower the seizure threshold (now doubted), CNS signs of severe hepatic dysfunction, may potentiate extrapyramidal side effects when given with metoclopramide

Question 15

most effective prokinetic drug class in vet med?

Answer 15

5-HT4 receptor agonists (eg cisapride)

Question 16

why is cisapride not necessarily a good choice for treatment of megaesophagus

Answer 16

not effective on striated muscle, increases gastroesophageal sphincter tone which may make regurgitation worse

Question 17

MOA of erythromycin as a prokinetic

Answer 17

motilin receptor agonist (increases lower oesophageal sphincter tone, increases small and large bowel peristalsis)

Question 18

use for misoprostol as a prokinetic

Answer 18

increased colonic motility