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.