Gut Motility Flashcards
What neurotransmitters are involved in emesis, classify by location
Vestibular apparatus: Ach, H1
Medullary centre: Ach, H1, 5HT
Vomiting centre: dopamine
Name the classifications of anti-emetic drugs
Dopamine D2 receptor antagonists (e.g. Metoclopramide, domperidone)
5HT3 receptor antagonists (e.g. Ondansetron)
Anti-muscarinics (e.g. Hyocine)
H1 receptor antiagonists (e.g. Cyclizine)
Other agents (e.g. Cannabinoids, benzodiazepines)
Domperidone: Class Mechanism of action Indications ADRs
D2 receptor antagonist
Acts on postrema (ependymal cells) on 4th ventricle floodr and in stomach to increase gastric emptying
Used in acute nausea and vomiting (admin orally)
ADRs: prolactin release (galactorrhoea)
Ondamsteron: Class Mechanism of action Indications ADRs
5HT3 receptor antagonist
Acts on medullary centres and reducing vagal afferent nerves from GIT
used in radiation sickness and chemo (given IV)
ADRs: headaches, constipation, flushing
Metoclopramide: Class Mechanism of action Indications ADRs
D2 receptor antagonist
Acts on postrema on 4th ventricle floor
Also some anti-cholinergic effects and blocking of vagal afferents
First line for mild nausea and vomiting (safe/easy to admin)
ADRs: extra-pyramidal (avoid in PD)
Cyclizine:
Class
Indications
ADRs
H1 receptor antagonist
Used in acute nausea and vomiting (oral, IV, IM)
ADR: prolong QT interval
What are the main classes of laxatives
Give examples and what they are used for
Osmotic laxatives (e.g. Movicol) Hard faeces
Bulk laxatives and Faecal softeners (e.g. Islaghula)
Hard faeces
Stimulant/irritants (e.g anthraquinone group: Senna, Bisacodyl)
For soft faeces
Bulk laxatives and faecal softeners:
Mechanism of action
ADRs
Bulk laxatives: Act as non-degradable veg fibres, giving bulk to gut and aiding peristalsis
Faecal softeners: lubricating and softening stokl
Flatulence; do not give to patients with adhesions or ulceration
Osmotically active laxatives:
Mechanism of action
Indications
Cause water retention in small and large bowel; increase peristalsis
Used for ‘resistant’ constipation or urgent relief
Stimulant / irritant laxatives:
Mechanism of action
Indications
ADRs in abuse
Excite sensory nerves, leading to water and electrolyte retention, therefore peristaltic action
Used for rapid treatment (impaction, surgical prep)
Melanosis coli (benign pigmentation of colon wall)
What are the main classes of anti-diarrhoea drugs
Give examples
Anti-motility drugs
(E.g. Loperamide)
Bulk forming agents
(E.g. Ispaghula)
Loperamide:
Mechanism of action
Indications
ADRs
Opiate analogue that reduces GI motility
Used in chronic diarrhoea
Avoid in IBD: risk toxic megacolon
Name the 2 sites involved in the vomiting reflex pathway
Area postrema (in 4th ventricle; outside BBB)
Vomiting centre (in lateral reticular formation of medulla)
