Week 5.4 - Gastro-Intestinal Pharmacology

Question 1

What is important to rememeber when administering drugs particularly in GI?

Answer 1

• many illnesses affect absorption, metabolism and transit time of drugs
• consider dosage carefully to avoid toxicity

Question 2

What are the main drug classes in GI?

Answer 2

• acid suppression
• drugs affecting motility
• laxatives
• drugs treating IBD
• drugs affecting biliary secretions

Question 3

What is the neuronal control of GI?

Answer 3

• ENS controls gut.
• contains 2 plexuses - inner meissner’s and outer myenteric/ausbach’s plexus

Question 4

What nervous fibres does the ENS receive?

Answer 4

pre-ganglionic parasympathetic nerve fibres from vagus mostly - excitatory - ACh and substance P

Question 5

What are sympathetic fibres in the GI?

Answer 5

• sympathetic fibres mostly from post-ganglionic
• supply smooth muscle in gut and vasculature
• also sympathetic fibres that terminate within the plexus and have inhibitory effect on secretion, motility

Question 6

What are some neurotransmitters that are involves in gut control?

Answer 6

ACh, noradrenaline, substance P, vasoactive intestinal peptide

Question 7

What is hormonal control of the GI?

Answer 7

• endocrine hormones like gastrin and CCK
• paracrine hormones like histamine and somatostatin - act on nearby cells

Question 8

What is the action of substance P?

Answer 8

participates in peristalsis by activating smooth muscle either directly as a paracrine or through activation of cholinergic neurones as a neurotransmitter

Question 9

What are different acid suppression medications?

Answer 9

aim to prevent reflux by neutralising acid
- antacids (maalox)
- alginates (gaviscon)
- combination of both effective

Question 10

Which drugs inhibit gastric secretion?

Answer 10

• PPI’s - omeprazole - oral/IV
• H2RA - ranitidine - oral/IV
• prostaglandins like misoprostol
• somatostatin

Question 11

What is the mechanism of H2RA and PPI?

Answer 11

• H2RA blocks histamine receptor H2. CYP2C19 metabolises it and there are different variations so figure out variation in individual to avoid hepatotoxicity.
• PPI inhibits H+K+ase proton pump.
• both over-used and can lead to long term acid suppression

Question 12

What is an issue with long term acid suppression medication?

Answer 12

can cause higher pH which is favourable to infections like C.Difficile. also causes B12 deficiency and kidney disease

Question 13

What controls vomiting?

Answer 13

• emetic centre in the medulla. causes salivation, secretion and smooth muscle control so increase pressure below and decrease pressure above
• vestibular system - dizziness

Question 14

How do you treat nausea?

Answer 14

• difficult to control
• low dose antidepressants (tricyclics)
• anti-epileptic (gabapentin)
• olanzipine (antispychotic)

Question 15

What drugs are used to treat constipation?

Answer 15

• purgatives
• include bulk laxatives and osmotic laxatives
• bulk take few days to work but few side effects. osmotic work immediately but lead to electrolyte disrutbances
  also faecal softeners

Question 16

What are examples of anti-constipation drugs?

Answer 16

• bulk laxatives - methylcellulose
• osmotic laxatives - Saline/lactulose
• docusate sodium faecal softeners

Question 17

What is the action of purgatives?

Answer 17

increase water content of faeces - draws water into stool. several days to work.

Question 18

What are laxatives?

Answer 18

drugs which increase electrolytes and therefore water secretion in the gut. quick mechanisms but causes cramps

Question 19

How do we treat diarrhoea?

Answer 19

• anti-spasmodics which reduce smooth muscle tone
• anti-muscarinics reduce motility
• opioids - loperamide - decrease ACh release and smooth muscle contraction

Question 20

What are some drugs that directly affect motility in constipation?

Answer 20

• domperidone - increases LoS pressure, gastric empying and peristalsis
• metoclopramide - increases gastric emotying and gastric motility

Question 21

What are some laxatives?

Answer 21

• bisocodyl
• sodium picosulfate
• senna; dantron

Question 22

Which drug types do we use for IBD?

Answer 22

• 5ASA’s (aminosalicytates)
• steroids
• immunosuppressants
• biologics

Question 23

What are examples of immunosuppressants?

Answer 23

• azathioprine
• cyclosporin
• 6-mercaptopurine
• methotrexate

Question 23

What are biologics and examples?

Answer 23

• Anti TNFa - inflixamab
• Anti IL25/36 - (vedolizumab, ustekinumab)

Question 24

What drugs are used for symptomatic relief of IBS?

Answer 24

• Antispasmodics (buscopan)
• anti-cholinergics
• CCB’s - peppermint supplements
• antidepressants for diarrhoea/constipation

Question 25

How do we treat gallstones?

Answer 25

• surgically but may be pharmaceutically
• UDSA dissolves smaller stones
• GTN for pain caused by stones
• bile acid sequestriants keep bile acids in gut to reduce cholesterol levels