Gastrointestinal Flashcards
Give examples of anti-emetic drugs:
Cyclizine, metoclopramide and prochlorperazine
What is the mechanism of action of prochlorperazine?
Penothiazine anti-psychotic drug used as an anti-emetic
Dopamine (D2) receptor antagonist
Causes increased dopamine turnover (in mesolimbic and chemoreceptor trigger zone)
When would prochlorperazine be prescribed?
For nausea and vomiting or as an adjunct in some psychotic disorders
What are side effects of prochlorperazine?
Dry mouth
Tachycardia
Restlessness
Drowsiness
What are the types of anti-emetics?
A. Anti-cholinergics (Hyoscine hydrobromide).
Blocks acetylcholine neurotransmitters in the CNS and the PNS
B. Anti-histamines (Cyclizine)
H1 histamine receptor antagonist
C. Serotonin antagonists (Ondansetron)
Block serotonin receptors in the CNS and the GIT
D. Phenothiazines (Prochlorperazine).
Dopamine receptor antagonist (D2 receptor antagonist)
E. Motility stimulants (Metoclorpramide).
Dopamine receptor antagonist (D2 receptor antagonist)
What is the mechanism of action of metoclopramide?
Dopamine (D2) receptor antagonist
Raises activity in the chemoreceptor trigger zone} reducing input from afferent visceral nerves
Also increases gastric emptying and intestinal transit
Reduced esophageal reflux
When is metaclopramide administered?
To treat nausea, vomiting and increase gastric emptying
What are side effects of metoclopramide?
Dystonia (due to dopamine antagonism) Confusion Dizziness Diarrhoea Parkinsonism with long term use
What is the mechanism of action of cyclizine?
Histamine H1 receptor antagonist
Acts on vomiting center in the medullary region
Mild anti-cholinergic and anbti-muscarinic effects
When would cyclizine be given?
Nausea and vomiting
Motion sickness
Vertigo and dizziness
Prophylaxis alongside chemotherapy and opiate analgesic use
What are side effects of cyclizine?
Headache, sedation, diarrhoea
Give examples of laxatives:
Lactulose, senna
What is the mechanism of action of lactulose?
Reduces water absorption in the intestine, pulling water into the bowel and promoting distention and movement
What is the mechanism of action of senna?
It is a stimulant/irritant agent
When are laxatives prescribed?
For constipation, pregnancy and prophylaxis in opiate analgesic use
What are the side effects of laxatives?
Dehydration
Salt loss
Abdominal cramps
Fatigue
What are the types of laxatives?
A. Bulk producing agent - adds more substance so that they can pass through intestine easily (lactulose)
B. Stool softeners - adds mole water and fat into the stool
C. Stimulant or irritant - acts on intestinal mucosa and alters water and electrolyte secretion (senna)
D. Hydrating agents - intestines hold more water (milk of magnesia)
Give examples of H2 receptor antagonists:
Ranitidine
Cimetidine
Famotidine
Nizatidine
What is the mechanism of action of H2 receptor antagonists?
Histamine binds to H2 receptors on gastric parietal cells stimulating gastric acid secretion
Drugs antagonise the effect of histamine at these H2 receptors
Reduced cAMP and hence reduced activity of H/K ATPase pump
When are H2 receptor antagonists prescribed?
Peptic ulcer, GORD, Zollinger-Ellison syndrome
What are the side effects of H2 receptor antagonists?
Headache Dizziness Diarrhoea Reduced B12 absorption Gynaecomastia
What is a specific side effect of cimetidine?
It inhibits cytochrome p450 enzymes
Give examples of PPIs:
Omeprazole
Lansoprazole
Pantoprazole
What is the mechanism of action of PPIs?
Bind to H/K ATPase pump on gastric parietal cells
Reduces HI production and hence reduced gastric acidity
