8.1 anti-emetics Flashcards
what is the difference between vomiting and regurgitation?
vomiting = involuntary forceful expulsion of gastric contents through the mouth
regurgitation = not as forceful, mechanical and effortless
what causes vomiting?
retrograde peristalsis and abdominal muscle contracture + nausea, salivation and sweat = vomit
the vomiting centre is in the medulla
what stimulates the vomiting centre in the medulla?
- direct triggers e.g chemotherapy, drugs, hormones
- sensory afferent via midbrain e.g gross things
- vestibular nuclei disturbance e.g motion sickness
- visceral afferents from gut e.g stretched/inflamed
what agents act on vestibular nuclei?
muscarinic receptor antagonists
H1 receptor antagonists
how do muscarinic receptor antagonists work and what are they good for?
they act on vestibular nuclei
competitive blockade of muscarinic acetylcholine receptors (parasympathetic nervous system)
good for people who can’t take tablets, motion sickness and bowel obstruction
give an example of a muscarinic receptor antagonist and give its side effects.
Hyoscine hydrobromide
side effects
- sedation
- memory problems
- glaucoma
- dry mouth and constipation
how do H1 receptor antagonists work and what are they good for?
act on the vestibular nuclei
inhibit histaminergic signs from vestibular system to the Chemotherapy Trigger Zone in the medulla (essentially antihistamines)
good for motion sickness, promethazine is good for morning sickness in pregnancy). Not good for elderly and children as side effects are more prominent.
what are the side effects of H1 receptor antagonists? give an example of a few.
examples
- cyclizine
- promethazine
side effects
- sedation
- excitation
- antimuscarinic (dry mouth,constipation, urinary retention)
- cardiac toxicity (long QT interval)
what agents act on visceral afferents of the gut?
- 5HT3 (serotonin) receptor antagnoists
- D2 receptor antagnoists
what role does serotonin play in the gut?
- most serotonin in the body is located in the gut
- produced by enterochromaffin cells
- excites enteric neurones in response to parasympathetic stimulation (get smooth muscle contraction and increased gut secretions)
- regulates appetite
how do 5HT3 receptor antagonists affect the gut?
they act on visceral afferents of the gut
peripherally
- reduce GI motility
- reduces GI secretions
centrally
- acts to inhibit the chemoreceptor trigger zone (which makes the vomiting centre go)
what are benefits and the side effects of 5HT3 receptor antagonists? give an example of one.
Ondansetron is an example.
its good for almost anyone, and it often the first line treatment
side effects
- constipation
- headache
- elevated liver enzyme
- long QT syndrome
- extra pyramidal effects: dystonia, Parkinsonism
what is metaclopramide and how does it effect the gut?
metaclopramide
acts on visceral afferents of the gut
a D2 receptor antagonist
increases Ach at muscarinic receptors in the gut and promotes gastric emptying
- increase tone at Lower oesophageal sphincter so it closes
- increase tone and amplitude of gastric contractions
- decreased tone of pylorus so it opens (gastric contents can get further down in the gut)
what are the side effects of metaclopramide and what is it good for?
good for
- GORD
- Ileus (gut is paralysed = lack of peristaltic movements)
side effects
- galactorrhea via prolactin release
- extra-pyramidal effects: dystonia, Parkinsonism
what is domperidone and how does it effect the gut? what is it good for?
acts on visceral afferents in the gut
a D2 receptor antagonist
similar mechanism as metoclopramide
good for improving lactation in breastfeeding mothers
what are the side effects of domperidone?
- sudden cardiac death (Long QT and VT)
- glactorrhoea
what D2 receptor antagonists are also antipsychotics?
prochlorperazine
chlorpromazine
levomepromazine
THE ZINES
and haloperidol
the zines
are good for motion sickness and vertigo. act on chemoreceptor trigger zone.
haloperidol
is good for chemotherapy and palliation. acts on chemotherapy trigger zone.
how can corticosteroids help nausea and what are their side effects?
they act on the chemoreceptor trigger zone good for - preoperative nausea - chemotherapy - palliation
side effects
- insomina
- increased appetite (good for chemo)
- increased blood sugar
how can cannabinoids help nausea? what are the side effects?
act on Chemoreceptor trigger zone
good for chemotherapy
e.g Nabilone
side effects
- dizziness
- drowsiness
what are neurokinin 1 receptor antagonists and how do they work?
they act on the Chemoreceptor trigger zone
prevent the action of substance P (an excitatory neurotransmitter) at CTZ and in peripheral nerves
Boosts effects of 5HT3 receptor antagonists
anxiolytic and antidepressant properties
good for chemotherapy
what are the side effects of neurokinin 1 receptor antagonists? name an example.
- headache
- diarrhoea/ constipation
example = aprepitant, fosaprepitant, netupitant (THE TANTS)
what is used first line for motion sickness?
hydrocine hydrobromide (but its a sedative so don’t take if you’re driving)
cinnirazine has fewer side effects (so if you’re driving take this so you can concentrate)
what are pro kinetics and what are they good and bad for?
pro kinetics = drugs that enhance GI motility
useful for
- GORD
- Ileus
don’t use in
- obstructions
- risks in perforations
name 2 pro kinetic drugs.
domperidone metaclopramide (cisapride)
what are some direct triggers on the chemoreceptor trigger zone?
hormones e.g hyperemesis gravidarum
drugs
- chemotherapy
- anaesthetics
- opiates
what is hyperemesis gravidarum?
rapid rise in Bhcg stimulates CTZ
typically weeks 4-16 of pregnancy
higher risk with multiple pregnancies
get
- dehydration
- weight loss
- electrolyte imbalance
- urinary ketones
what drugs could you use to treat hyperemesis gravidarum in pregnancy?
promethazine (H1 receptor antagonist)/ prochlorperazine (D2 receptor antagonists)
then add
metaclopramide
then add
ondansetron
how many anti emetics would you use for post operative nausea and vomiting when there is a -
low risk
medium risk
high risk
low risk - wait and see
medium - 1/2 agents
high risk - 2+ agents
how can loperamide help diarrhoea?
An opioid receptor agonist
specific to U receptors in the myenteric plexus
decreases tone of longitudinal and circular smooth muscle
reduces peristalsis but increases segmental contractions (so poo is pushed into a bigger more solid stool due to more contact with enterocytes)
decreases colonic mass movement by suppressing gastrocolic reflex
how can codeine and morphine help diarrhoea and what are their side effects?
they’re opioid receptor agonists
they have similar effects to loperamide
more often used when patients have pain also
side effects
- paralytic ileus
- nausea and vomiting
- sedation and addiction
what are the components of a constipating diet and to who would you recommend it to?
for those with long term loose stools e.g IBS, IBD, short bowel, drug side effects
components
- bananas (potassium and fibre)
- white rice (binds stool)
- white bread/pasta (low fibre)
NB: too much fibre = fluid stool. Have a little only just to bulk it up. too little and you won’t poo.
avoid caffeine, fatty or spicy foods and fizzy drinks
what diet and lifestyle changes can be made to relieve constipation?
- more water
- increase fibre intake: fruit, veg, nuts, wholegrains
- regular exercise
- toilet routine and positioning
what two main categories of medicines can be used for constipation?
laxatives and enemas
what are osmotic laxatives? name an example.
increase the amount of water in the large bowel
e. g lactulose draws fluid in from gut wall
e. g macrogols retain the fluid bowel comes in with
what are stimulant laxatives? name 2 examples.
increase intestinal motility and peristalsis
can be given orally or per rectum
e.g bisacodyl, glycerin suppositories
what are bulk forming laxatives?
medicinal fibre
what are the use of stool softeners?
decrease surface tension of stool and increase penetration of fluid of stool = make it runnier
e.g glycerin suppository, liquid parafin enemas, docusate sodium etc.
