Antiemetics and Antidiarrhoeals Flashcards
What is vomiting?
involuntary, forceful of gastric contents through the mouth
it is a protective mechanism
Why is vomiting different to regurgitation?
regurgitation is expulsion of contents from the oesophagus - lots of babies do this
How do we vomit?
1) nausea, salivation and sweating
2) retrograde peristalsis of the upper bowel and stomach
3) deep inspiration
4) closure of glottis to protect airways
5) abdominal muscles contract
6) lower oesophageal sphincter relaxes
Where is the vomiting centre?
in the medulla
What is CTZ and where is it?
the chemoreceptor trigger zone is an area of the medulla oblongata that receives inputs and communicates with other structures in the vomiting centre to initiate vomiting.
located on the base of the floor of the 4th ventricle
What are the inputs to the vomiting centre?
- sensory afferents via the midbrain
- vestibular nuclei (motion sickness - inner ear)
- visceral afferents from the gut (vagus nerve - if problems with gut, CNX sends signals up to CTZ)
- direct triggers (drugs)
What drug agents act on the vestibular nuclei?
H1 receptor antagonists
- Cyclizine
- Levomepromazine
- Cinnarizine
- Promethazine
- Dihenhydramine
Muscarinc receptor antagonists
-Hyoscine hydrobromide
What is the MOA of Cyclizine, Levomepromazine, Cinnarizine, prometazine, dihenhydramine
Acts on vestibular nuclei, inhibits histaminergic signals from vestibular system to CTZ in medulla
What are the uses of Cyclizine, Levomepromazine, Cinnarizine, prometazine, dihenhydramine?
Cinnirazine - motion sickness, non drowsy
promethazine - morning sickness in pregnancy
DON’T GIVE CYCLIZINE TO LITTLE OLD LADIES OR CHILDREN - causes excitation
What is the MOA for Hyoscine hydrobromide?
Works on PSNS
competitive blockade of muscarinic ACh receptor in the vestibular nuclei but also in the CTZ
NOTE - these receptors are everywhere in the body so get side effects potentially everywhere
What are the side effects of H1 receptor antagonists?
- sedation
- excitation
- antimuscarinic - dry mouth, constipation, urinary retention
- cardiac toxicity (long QT interval)
What are the side effects of hyoscine hydrobromide?
- sedation
- memory problems
- glaucoma
- dry mouth and constipation
Who is hyoscine hydrobromide good for?
- people who can’t take tablets (the behind the ear skin patches)
- motion sickness
- gut problems (PNS effect)
- cancer therapy feeling sick
- people with severe diarrhoea
What drug agents act on visceral afferents in the gut?
- 5HT3 receptor antagonists
- D2 receptor antagonists
What is 5HT3 and what is its role and where is it produced?
serotonin
produced by enterochromaffin cells
it excites enteric neurones, increases smooth muscle contraction, motility and increases gut secretion so regulates apeptite
-stops retrograde peristalsis
What are the names of some 5HT3 receptor antagonists?
- Ondansetron
- Granesitron
- Palonestron
What is the MOA of Ondansetron, Granesitron, Palonestron?
reduction of GI motility and GI secretions
-also inhibits CTZ
What is the use of Ondansetron, Granesitron, Palonestron?
good for everyon- often 1st line treatment
What are the side effects of Ondansetron, Granesitron, Palonestron?
UNCOMMON
- constipation
- headache
- elevated liver enzymes
- long QT syndrome
- extra-pyramidal effects - dystonia, Parkinson’s
What are the names of some D2 receptor antagonists that act on visceral afferents in the gut?
Metoclopramide
Domperidone
Why is domperidone less commonly used now?
associated with significant cardiac side effects
What is the MOA of Metoclopramide?
increases ACh at muscarinic receptors in the gut promoting gastric emptying
- increaswes tone at lower oesophageal sphincter so it closes
- increases tone and amplitude of gastric contractions
- decreases tone of pylorus so it opens
ALOS increases peristalsis
What is Metoclopramide used for?
GORD and ileus
What is ileus?
where the gut goes to sleep so gut motility stopped - often occurs after surgery or severe infection
What are the side effects of Metoclopramide and who are they most severe in?
most common in young people and children
- galactorrhoea via prolactin release
- extra-pyramidal effects - dystonia and parkinsonism
What is the MOA of Domperidone?
similar mechanism to metoclopramide
Who is Domperidone used for?
selective cases
- good for babies with reflux
- imporving lactation in breastfeeding mothers
What are the side effects of Domperidone?
- sudden cardiac death (long QT and VT)
- galactorrhea
What agents act on CTZ?
- 5HT3 receptor antagonists
- H1 receptor antagonists
- muscarinic receptor antagonists
- D2 receptor antagonists
- corticosteroids,
- cannabinoids
- NK1 receptor antagonists
What are the names of D2 receptor antagonists?
the zine’s
- metoclopramide
- domperidone
- prochloroperazine
- chlorpromazine
- levomepromazine
- haloperidol
Which drugs are both antipsychotics and antiemetics?
- prochloroperazine
- chlorpromazine
- levomepromazine
- haloperidol
What is the MOA of the zine’s
Act on CTZ
-may also block H1 and muscarinic receptors
What is the MOA of haloperidol?
Act on CTZ
What are the zine’s used for?
motion sickness, vertigo
NOTE - prochlorperazine in pregnancy
What is haloperidol used for?
chemotherapy and palliation
-can also be good to relax anxious patients
What are the side effects of
- metoclopramide
- domperidone
- prochloroperazine
- chlorpromazine
- levomepromazine
- haloperidol
Extra-pyramidal effects - dystonia and parkinsonism
- sedation
- hypotension
What are the names of the corticosteroids used?
Dexametasone
Methylprednisolone
What is the MOA of Dexametasone
Methylprednisolone?
- act on CTZ
- may have action of D2 receptors as antagonists
What are Dexametasone and Methylprednisolone good for?
perioperative nausea and vomiting
chemotherapy
palliation where the patient doesn’t want to eat or can’t stay awake
What are the side effects of Dexametasone and Methylprednisolone?
- insomnia
- increased appetite
- increased blood sugar
What is the name of a cannabinoid?
Nabilone
What is the MOA of nabilone?
assumed to act on CTZ
When is nabilone used?
good for chemotherapy but used as last in line
What are the side effects of nabilone?
dizziness and drowsiness
What are the names of Neurokinin 1 receptor antagonists?
tant’s
Aprepitant
Fosaprepitant
Netupitant
What is the MOA of Aprepitant, Fosaprepitant, Netupitant?
Prevent the action of substance P at CTZ and in peripheral nerves
-also boosts effects of 5HT3 receptor antagonists
- anxiolytic and antidepressant properties
- works better in the presence of these “tron’s”
What is substance P?
a neurotransmitter causing excitation
What are Aprepitant, Fosaprepitant, Netupitant good for?
chemotherapy - particularly for delayed emesis
What are the side effects of Aprepitant, Fosaprepitant, Netupitant?
headache
diarrhoea/constipation
stevens-johnson syndrome
What is stevens-johnson syndrome?
rare but serious disorder that affects the skin, mucous membrane, genitals and eyes
-The syndrome often begins with flu-like symptoms, followed by a red or purple rash that spreads and forms blisters. The affected skin eventually dies and peels off
How would you treat motion sickness?
TAKE BEFORE JOURNEY
1st line - hyoscine hydrobromide
BUT
cinnirazine typically has fewer side effects (better if need to concentrate e.g. you are driving”
Go for favourite side effects
Would you give someone an anti-emetic if you have infective gastroenteritis?
no - need to get rid of the toxins
needed more for other bowel pathologies e.g. reflux, cancers, Chron’s, UC (acute flares), appendicitis
decompressing bowel may be more comfortable e.g. giving NG tube
What are pro kinetics? and when are they good to use?
drugs to help increase drug motility e.g. domperidone and metroclopramide
good to use in GORD and ileus
ALSO chewing gum activates gut to increase motility
When would you not use metoclopramide and domperidone?
with obstruction of the bowels !!! or ischaemic bowel
increased risk of perforation as increase gut motility on dead/obstructed bowel
What is the typical treatment for gut problems?
1st line
Ondansetron and/or cyclizine
ADD dexamethasone is struggling
Try different classes of drugs if they don’t work
What are the direct triggers of CTZ?
Hormones (BHCG in pregnancy) DRUGS -chemo -anaesthetics -opiates etc
What is hyperemesis gravidarum, when does it happen and in what circumstance is it more likely?
severe vomiting, dehydration, weight loss, electrolyte imbalances and urinary ketones in pregnancy where there is a rapid rise in BHCG which stimulates the CTZ
-typically occurs 4-16 weeks but may continue beyond this and there is a higher risk with multiple pregnancies like twins
What is the treatment for hyperemesis gravidarum?
Promethazine/prochlorperazine
then add
metoclopramide (but this works on the gut which isn’t the actual problem)
then add
ondansetron (but there is a increased risk of cleft lip and palate if you use this in 1st trimester of pregnancy
What is the typical treatment for Chemotherapy sickness?
start with dexamethasone
moderate risk - add ondansetron
high risk - add ondansetron and aprepitant too
For rescue use metoclopramide
What are the risk factors for post-operative nausea and vomiting?
- female
- history of motion sickness
- younger
- non-smoker
- general anaesthetic
- laproscopic surgery
- duration of operation
What is the treatment plan for post operative nausea and vomiting?
Low risk - wait and see
Moderate risk - pick 1/2 antiemetic agents
High risk - pick more than 2
if prophylaxis doesn’t work try a different class
What is diarrhoea?
depends on the patient!!
-ask about consistency, frequency and compare to their normal bowel habit
REMEBER - diarrhoea can be osmotic or secretory
How can you treat diarrhoea?
TREAT THE CAUSE !!
- increase transit time (if the stools are in contact with the enterocytes for longer, you will get better absorption
- comfort
- prevent incontinence
What are the drug classes that are used to treat diarrhoea?
- opioid receptor agonists
- osmotic laxatives
- stimulant laxatives
- bulk forming laxative
- stool softeners
What are the names of the opioid receptor agonists?
Loperamide
Codeine
Morphine
What is the MOA of loperamide?
- immodium
- specific to mu receptors in the myenteric plexus
- decreases tone of longitudinal and circular smooth muscle
- reduces peristalsis but increases segmental contractions
- decreases colonic mass movement by suppressing gastrocolic reflex
What is the MOA of codeine and morphine?
acts on mu and delta receptors but not specific to the gut
-can be used for pain too e.g. with appendicitis with pain and diarrhoea
What are the side effects of Loperamide
Codeine
Morphine?
- paralytic ileus
- nausea and vomiting
- sedation and addiction
What are some osmotic laxatives?
Lactulose
Movicol
Cosmocol
What is the MOA of Lactulose
Movicol
Cosmocol?
Lactulose
-laxatives draw fluid in to gut lumen
Macrogels (M and C)
-retain the fluid they came with
What are the names of stimulant laxatives?
Bisacodyl Sodium pico sulphate Senna Co-danthromer Docusate Sodium
What is the MOA of stimulantt laxatives?
increase the intestinal motility
NOTE - docusate sodium acts as a stool softener too
given orally or per rectum (glycerin suppositories help to lubricate too)
What are the names of bulk forming laxatives?
Ispaghula husk
Methylcellulose
What is the MOA of bulk forming laxatives?
- helps bulk the stool
- medicinal fibre
What are the names of some stool softeners?
Docusate sodium
Glycerin suppository
Arachis oil
Liquid paraffin
What is the MOA for stool softeners?
Decrease surface tension of stool
increase penetration of fluid into stool
What is the constipating diet?
used for those with long term loose stools
-IBS, IBS, short bowel, hyper motility
includes eating bananas, white rice/bread
low fibre
less fruit (3 portions)
avoiding caffeine and fizzy drinks
consider probiotics to reinstate balanced intestinal flora
What helps with constipation?
drinking more water
increased fibre intake
regular exercise
toilet routine and positioning
