Antiemetics & Antidiarrhoeals Flashcards
What is hyperemesis gravidarum?
Not just morning sickness, but also involves dehydration, weight loss, electrolyte imbalance and urinary ketones. It’s caused by the rapid rise in beta hcg, which stimulates the CTZ.
What is the difference between vomiting and regurgitation?
Vomiting is a forceful expulsion, regurgitation is not forceful and is due to mechanical problems at the lower end of the oesophagus.
Name 4 things that can trigger the chemoreceptor trigger zone (CTZ).
- vestibular nuclei - receive signals from inner ear and semicircular canals
- direct triggers e.g. Drugs/hormones
- sensory afferents e.g. Sight/taste/smell
- visceral afferents from gut due to damage or inflammation
Describe the process of vomiting.
- CTZ is triggered
- retrograde peristalsis in gut
- deep inspiration
- closure of glottis
- abdominal muscles contract
- lower oesophageal sphincter relaxes
Name 2 drug classes that act on the vestibular nuclei.
- mAChr antagonists
- H1 antagonists
Name 2 drug classes that act on the visceral afferents in gut.
- 5HT3 antagonists
- D2 antagonists
Name all the drug classes that act directly on the CTZ (7).
- mAChr antagonists
- H1 antagonists
- D2 antagonists
- 5HT3 antagonists
- corticosteroids
- cannabinoids
- NK1 antagonists
Name a mAChr drug used as an antiemetic.
Hyoscine hydrobromide - used for motion sickness.
What are the typical anticholinergic side effects of drugs?
Constipation
Dry mouth
Name 2 H1 receptor antagonists used as antiemetics.
Cyclizine
Promethazine
What is promethazine and what is it often used for?
H1 antagonist - used for motion sickness, but especially morning sickness during pregnancy.
Why should you be careful when prescribing cyclizine?
Has side effects of sedation and excitement - these side effects can be very prominent in old ladies and children who are smaller.
Name a 5HT3 antagonist used as an antiemetic.
Ondansetron
Which cells produce serotonin?
Enterochromaffin cells in response to parasympathetic stimulation.
Name 2 D2 antagonists that act directly on the visceral afferents of the gut.
Metacloperamide
Domperidone
What is the MOA of metacloperamide and domperidone?
D2 antagonists - block D2 receptors in gut, speeding up stomach emptying, can be useful for GORD or ileus.
Name a side effect of metacloperamide and domperidone.
-galactorrhoea (inappropriate/excessive production of milk)
Name 2 D2 antagonists that act directly on the CTZ.
Chlorpromazine
Haloperidol
What is haloperidol used for?
Often used for chemotherapy and palliative care as it is slightly sedative, so can help patients to relax.
Name a corticosteroid used as an antiemetic.
Dexamethasone
What is dexamethasone used for?
Palliative care
Chemotherapy
Perioperative nausea
Name a cannabinoid used as an antiemetic.
Nabilone
Name a neurokinin 1 receptor antagonist used as an antiemetic.
Aprepitant
Name 2 things that the D2 antagonists chlorpromazine and haloperidol can be used for.
Antipsychotics
Antiemetics
What is the MOA of NK1 antagonists?
Prevents the action of substance P at the CTZ, acts as an antiemetic.
Name a side effect of aprepitant.
Stevens Johnson Syndrome
What is Stevens Johnson Syndrome?
A condition that is a disorder of the immune system, but is often triggered by drugs or infections (type IV hypersensitivity reaction). Starts with a severe skin reaction, fever and flu-like symptoms. Can lead to blindness.
What drugs are used for GORD or ileus?
Domperidone or metacloperamide (not suitable for obstruction).
What is the specific treatment for gut problems e.g. Ileus, obstruction, appendicits, cancer, GORD?
Ondansetron
And/or cyclizine
Then add dexamethasone
What is the specific drug treatment for hyperemesis gravidarum?
Promethazine or prochlorperazine
Then add metacloperamide
Then add ondansetron
What specific drug treatment can be used for chemotherapy sickness?
Dexamethasone
Then add ondansetron
Then add aprepitant
Use metacloperamide for rescue
What drugs can be used for post-operative nausea and vomiting?
Pick 1 or 2 antiemetics (any).
Name the 2 types of diarrhoea.
Osmotic - due to reduced absorption there is excess osmotic material in gut.
Secretory - excess secretion of ions into gut lumen.
Name 3 opioid receptor antagonists used for diarrhoea.
Loperamide
Codeine
Morphine
How do opioids treat diarrhoea?
Reduce peristalsis and slow down gut movement, allowing more time for water absorption.
What lifestyle modifications can help relieve constipation.
- more fibre in diet - ‘constipation diet’
- drink more water
- more exercise
What are the 3 types of laxatives that can be used for constipation?
- osmotic
- stimulant
- bulk forming
Name 2 osmotic laxatives and explain their MOA?
Lactulose, macrogol
Contain sugar that osmotically draws fluid into the gut.
Name 2 stimulant laxatives and explain their MOA.
Docusate sodium, senna
Increase intestinal motility and increase water and electrolyte transfer into the gut.
What is the MOA of bulk forming laxatives?
Increase faecal bulk, causing increased water retention in the gut lumen (fibre keeps liquid in the stool).
How do stool softeners work?
Lubricate and break down stool, aids passing.
How do enemas work?
Decrease surface tension of stool and increases penetration of fluid into stool
