Vomiting: emetics and anti-emetics Flashcards
define haematemesis
V blood
emetic vs anti-emetic
stimulates/ inhibits V
what are the 3 causes of V? give examples of each
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
what is dysphagia?
failure to prehend/ swallow food
what is expectoration?
coughing up phlegm
what is regurgitation?
passive reflux of oesophageal contents
where is the V centre
the medulla
where does the medulla receive inputs from?
vagus and glossopharyngeal nerves mediate control of closure of airway and motor changes of GI tract
name 5 afferent inputs to the V centre
higher brain centres, vestibular, CRTZ, V centre, peripheral receptors
how do higher brain centres influence V?
Psychogenic - fear, stress, excitement
How do vestibular inputs influence the V centre?
motion sickness/ labyrinthitis
how does the CRTZ influence V?
outside BBB so exposed to blood.
drugs e.g. digoxin, morphine
metabolic - acidoses, toxins etc
How might the V centre influence V?
CNS inflammation, raised intracranial pressure; hydrocephalus/ brain tumour
What about peripheral receptors?
CNX/ CNIX - inflammation, irritation, distension
anatomy of where nerves are?? think
what are the stages of the V reflex?
prodromal, retching, expulsion, relaxation
describe the prodromal stage
nausea. restlessness, depression, salivation, relaxation of LES
describe the retching stage
uncoordinated contractions of resp muscles. inhibition salivation, duodenal retroperistalsis, mixing of gastric contents
describe the expulsion phase
coordinated abdominal contractions, stomach squeezed, inhibition of breathing, closure of glottis and nasopharynx to protect airway. reduced LES and UES tone.
describe the relaxation phase
abdominal muscles, resp and diaphragm relax, nasopharynx and glottis relax and breathing resumes
give 2 consequences of V
dehydration due loss of Na and water
acid-base disturbances
describe a metabolic acidosis
more common. loss of duodenal juice therefore HCO3.
GI loss of K so hypokalaemia
describe a metabolic alkalosis
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
what are emetics used for? give examples of contra-indications
to induce vomiting of substances that are safe to be vomited back.
sharps, detergents, batteries, some medicines
what is the main problem with emetic/ anti-emetic drugs?
species differences in receptor location so some drugs may only work in certain situations in some species
define V
forceful, reflex ejection of gastric (and upper intestinal) content from the stomach. ACTIVE PROCESS with forceful contraction of abdominal muscles
give 3 examples of emetic drugs
ipecacuanha, apomorphine, xylazine (alpha-2 agonist)
how does Ipecacuanha work?
contains emetine, stimulates gastric chemoreceptors
how does apomorphine work?
stimulates dopaminergic receptors in CRTZ - powerful in dogs (not cats)
how does xylazine work?
stimulated adrenergic receptors in V centre. rapid induction in cats but sedation (inhalation)
name other chemicals known to induce V
salt, hydrogen peroxide, washing soda (sodium carbonate) no longer recommended as most also contain caustic sodium hydroxide
how might chemotherapy drugs stimulate V?
fear/ anticipation (higher brain), direct action CRTZ, serotonin receptors GI/ damage to ep
describe the properties of maropitant
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
describe the properties of metoclopramide
licensed oral and injectable forms, CRI puppies and kittens. lower doses D2, higher 5HT3 antagonists. also a prokinetic, urinary excretion (dose). SE = hyper CNS
how do anti-histamines work?
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)
how do anti-muscarinics work?
inhibit parasymp. antagonise M1 Ach receptors. unlicensed and SE = dry mouth, tachycardia, mydriasis and constipation
e.g. scopolamine
how do serotonin antagonists work?
antagonise 5HT3 receptors, unlicensed. often used for chemo induced vom as expensive e.g. Ondansetron
how do phenothiazines work?
dopamine receptor antagonists. unlicensed + antagonise other receptors. SE = sedation, vasodilation (sedatives)
what other drugs can be used to inhibit V?
glucocorticoids, cannabinoids
name 6 drug groups used as anti-emetics
maropitant, metoclopramide, anti-histamines, anti-muscarinics, serotonin antagonists, phenothiazides
