Vomiting: emetics and anti-emetics

Question 1

define haematemesis

Answer 1

V blood

Question 2

emetic vs anti-emetic

Answer 2

stimulates/ inhibits V

Question 3

what are the 3 causes of V? give examples of each

Answer 3

primary gastric conditions - gastritis, ulcer, foreign body, obstruction, neoplasia
intestinal conditions - enteritis, colitis, obstruction, constipation
secondary to systemic (non-GI) causes - toxaemia, motion sickness, CNS disease, otitis media, hepatitis, peritonitis, drugs e.g. digoxin

Question 4

what is dysphagia?

Answer 4

failure to prehend/ swallow food

Question 5

what is expectoration?

Answer 5

coughing up phlegm

Question 6

what is regurgitation?

Answer 6

passive reflux of oesophageal contents

Question 7

where is the V centre

Answer 7

the medulla

Question 8

where does the medulla receive inputs from?

Answer 8

vagus and glossopharyngeal nerves mediate control of closure of airway and motor changes of GI tract

Question 9

name 5 afferent inputs to the V centre

Answer 9

higher brain centres, vestibular, CRTZ, V centre, peripheral receptors

Question 10

how do higher brain centres influence V?

Answer 10

Psychogenic - fear, stress, excitement

Question 11

How do vestibular inputs influence the V centre?

Answer 11

motion sickness/ labyrinthitis

Question 12

how does the CRTZ influence V?

Answer 12

outside BBB so exposed to blood.
drugs e.g. digoxin, morphine
metabolic - acidoses, toxins etc

Question 13

How might the V centre influence V?

Answer 13

CNS inflammation, raised intracranial pressure; hydrocephalus/ brain tumour

Question 14

What about peripheral receptors?

Answer 14

CNX/ CNIX - inflammation, irritation, distension

anatomy of where nerves are?? think

Question 15

what are the stages of the V reflex?

Answer 15

prodromal, retching, expulsion, relaxation

Question 16

describe the prodromal stage

Answer 16

nausea. restlessness, depression, salivation, relaxation of LES

Question 17

describe the retching stage

Answer 17

uncoordinated contractions of resp muscles. inhibition salivation, duodenal retroperistalsis, mixing of gastric contents

Question 18

describe the expulsion phase

Answer 18

coordinated abdominal contractions, stomach squeezed, inhibition of breathing, closure of glottis and nasopharynx to protect airway. reduced LES and UES tone.

Question 19

describe the relaxation phase

Answer 19

abdominal muscles, resp and diaphragm relax, nasopharynx and glottis relax and breathing resumes

Question 20

give 2 consequences of V

Answer 20

dehydration due loss of Na and water

acid-base disturbances

Question 21

describe a metabolic acidosis

Answer 21

more common. loss of duodenal juice therefore HCO3.

GI loss of K so hypokalaemia

Question 22

describe a metabolic alkalosis

Answer 22

loss of HCl (hypochloraemia) due to pyloric blockage therefore retention of HCO3.
renal excreation of NaHCO3 to compensate and Na/K exchange to compensate for Na loss. Also leads to hypokalaemia

Question 23

what are emetics used for? give examples of contra-indications

Answer 23

to induce vomiting of substances that are safe to be vomited back.
sharps, detergents, batteries, some medicines

Question 24

what is the main problem with emetic/ anti-emetic drugs?

Answer 24

species differences in receptor location so some drugs may only work in certain situations in some species

Question 25

define V

Answer 25

forceful, reflex ejection of gastric (and upper intestinal) content from the stomach. ACTIVE PROCESS with forceful contraction of abdominal muscles

Question 26

give 3 examples of emetic drugs

Answer 26

ipecacuanha, apomorphine, xylazine (alpha-2 agonist)

Question 27

how does Ipecacuanha work?

Answer 27

contains emetine, stimulates gastric chemoreceptors

Question 28

how does apomorphine work?

Answer 28

stimulates dopaminergic receptors in CRTZ - powerful in dogs (not cats)

Question 29

how does xylazine work?

Answer 29

stimulated adrenergic receptors in V centre. rapid induction in cats but sedation (inhalation)

Question 30

name other chemicals known to induce V

Answer 30

salt, hydrogen peroxide, washing soda (sodium carbonate) no longer recommended as most also contain caustic sodium hydroxide

Question 31

how might chemotherapy drugs stimulate V?

Answer 31

fear/ anticipation (higher brain), direct action CRTZ, serotonin receptors GI/ damage to ep

Question 32

describe the properties of maropitant

Answer 32

effective drug, broad spectrum drug. blocks substance P receptors (NK). licensed in D and C, will inhibit V due to chemo agents, motion sickness and gastroenteritis. Highly protein-bound so once daily dose. given IV, SC (pain) and PO (poor bio so double dose) metabolised by liver (disease) store in fridge

Question 33

describe the properties of metoclopramide

Answer 33

licensed oral and injectable forms, CRI puppies and kittens. lower doses D2, higher 5HT3 antagonists. also a prokinetic, urinary excretion (dose). SE = hyper CNS

Question 34

how do anti-histamines work?

Answer 34

H1 receptor antagonists in vestibular and CRTZ. less effective in animals than people. some efficacy in motion sickness and vestibular disease in dogs, no vet licensed products and mostly used in allergic skin disease. SE = drowsiness H2 antagonists block gastric acid production e.g. promethazine (human)

Question 35

how do anti-muscarinics work?

Answer 35

inhibit parasymp. antagonise M1 Ach receptors. unlicensed and SE = dry mouth, tachycardia, mydriasis and constipation e.g. scopolamine

Question 36

how do serotonin antagonists work?

Answer 36

antagonise 5HT3 receptors, unlicensed. often used for chemo induced vom as expensive e.g. Ondansetron

Question 37

how do phenothiazines work?

Answer 37

dopamine receptor antagonists. unlicensed + antagonise other receptors. SE = sedation, vasodilation (sedatives)

Question 38

what other drugs can be used to inhibit V?

Answer 38

glucocorticoids, cannabinoids

Question 39

name 6 drug groups used as anti-emetics

Answer 39

maropitant, metoclopramide, anti-histamines, anti-muscarinics, serotonin antagonists, phenothiazides