Antiemetics Flashcards
what is the pathway for vomiting?
1) vomiting centre in medulla signals to vomit
2) retrograde peristalsis
3) nausea, salivation, sweating
4) deep inspiration
5) closure of glottis
6) abdominal muscles contract
7) lower oesophageal sphincter relaxes
which drugs act on the vestibular nuclei?
muscarinic receptor antagonists and H1 receptor antagonists
muscarinic receptor antagonist - name, mechanism, uses, side effects
hyoscine hydrobromide
competitive blockade of muscarinic acetylcholine receptors in VN and at CTZ
good for people who can’t take tablets, motion sickness and for bowel obstruction
sedation, memory problems, glaucoma, dry mouth, constipation
H1 receptor antagonists - names, mechanism, uses, side effects
cyclising, levomepromazine, cinnirazine, promethazine, diphenylhydramine
acts on VN and inhibits histaminergic signals to CTZ in medulla
used for motion sickness and promethazine in morning sickness
sedation, excitation (not good for some old and young people), dry mouth, constipation, urinary retention, and also cardiac toxicity (long QT)
which drugs act on visceral afferent from the gut?
5HT3 receptor antagonists and D2 receptor antagonists
5HT3 receptor antagonists - names, mechanism, side effects
ondansetron, granesitron, palonosetron
serotonin usually secreted by enterochromaffin cells and in response to parasympathetic stimulation, 5HT3 excites enteric neurones causing smooth muscle contraction and increased gut secretion, therefore these drugs decrease motility and secretions, and centrally inhibit CTZ.
uncommon - constipation, headache, increased liver enzymes, long QT syndrome, extrapyramidal effects (dystonia, Parkinsonism)
D2 receptor antagonists acting on visceral afferents in gut - names, mechanisms, side effects
metoclopramide - increases ACH at m receptors in gut which promotes gastric emptying as there is increased tone at LOS, increased tone and amplitude of gastric contractions and decreased tone of pylorus
- good for GORD, ileum
galactorrhea, extrapyramidal effects
domperidone - similar mechanisms, increased cardiac side effects so used less. good for improving lactation in breastfeeding mothers
cardiac death (long QT) and galactorrhea
D2 receptor antagonists acting on CTZ - names, uses, side effects
metoclopramide, domperidone, prochlorperazine, levomepromazine, haloperidol
act on CTZ, good for motion sickness, vertigo, and prochlorperazine in pregnancy, haloperidol is good for chemo and palliation
extrapyramidal, sedation, hypotension
corticosteroids - names, uses, side effects
dexamethasone, methylprednisolone
good for preoperative n&v, chemo, palliation
insomnia, increased appetite, increased blood sugar
cannabinoids - name, use, side effects
nabilone
good for chemo - last line
dizziness, drowsiness
neurokinin 1 receptor antagonists - names, mechanism, uses, side effects
aprepitant, fosaprepitant, netupitant
prevent the action of substance P at CTZ and in peripheral nerves, boost effects of 5HT3 receptor antagonists, anxiolytic and antidepressant properties
good for chemotherapy
headache, diarrhoea/constipation, Steven-johnson syndrome
what is the first line drug for motion sickness?
hyoscine bromie
what happens in hyperemesis gravidarum and how is it treated?
rapid rise in beta-hcg stimulates CTZ, typically between 4-16 weeks but may continue. causes dehydration, 5% weight loss, electrolyte imbalance, urinary ketones
promethazine or prochlorperazine, then add metoclopramide, then ondansetron
which opioid receptor agonist drugs are used to treat diarrhoea and what is the mechanism?
loperamide - specific to m receptor in the myenteric plexus, which causes decreased tone of longitudinal and circular smooth muscle, decreases peristalsis but increases segmental contraction and decrease colonic mass movement by suppressing gastrocolic reflex.
codeine and morphine work on m&d receptors and has similar effects, often used when pain present too
what does a constipating diet consist of and why?
bananas - high in K+, white rice - binds stool, white bread/pasta - low in fibre
