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Physiology 1 Semester 2 > The Pharmacological Basis of the Treatment of GI Disorders > Flashcards

The Pharmacological Basis of the Treatment of GI Disorders Flashcards

1
Q

State the areas of the GI tract that are pharmacologically important

A
  • Gastric acid secretion - 2.5L of gastric juice secreted a day
  • Vomiting
  • Gut motility
  • Bile formation and excretion
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2
Q

State some examples of H2 receptor antagonists and what they are used for

A

H2 receptor antagonists (ranitidine, cimetidine, famotidine, nizatidine)

Clinical uses of H2 receptor antagonists - peptic ulcers, reflux oesophagitis

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3
Q

State the mechanism of action of H2 receptor antagonists

A
  • They inhibit histamine, acetylcholine and gastrin stimulated acid secretion on parietal cells
  • Reduce gastric acid secretion and as a consequence reduce pepsin secretion
  • Can decrease basal and food stimulated acid secretion by 90%
  • Promote the healing of duodenal ulcers but if treatment stops there is relapse
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4
Q

What are some unwanted effects H2 receptor antagonists produce

A
  • Generally rare but may be diarrhoea, muscle cramps, transient rashed and hypergastrinemia
  • Cimetidine - gynaecomastia in men - decreased sexual function
  • Cimetidine also inhibits P450 enzymes - decreased metabolism of a number of drugs metabolised by P450 enzymes e.g. anticoagulants, tricyclic antidepressants e.g. imipramine, dosulepin and amitriptyline
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5
Q

Compare the effects of ranitidine and cimetidine on inhibition of acid secretion

A
  • Graph shows that as serum concentration of ranitidine and cimetidine increases the % of acid inhibition also increases
  • But ranitidine is more potent than cimetidine as it needs a lesser serum concentration to produce maximum % of acid inhibition
  • IC50 for ranitidine is 0.07 mcg/ml while IC50 for cimetidine is 0.44 mcg/ml - the lower the IC50 the more active the drug
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6
Q

Give examples of proton pump inhibitor drugs

A

Omeprazole, lansoprazole, pantoprazole, rabeprazole

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7
Q

Describe what proton pump inhibitors are used for

A
  • Peptic ulcers, reflux oesophagitis, as a component of therapy for H pylori
  • Can also be used in the treatment of zollinger ellison syndrome
  • Drugs of choice especially if hyper secretion of acid occurs
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8
Q

Describe the mechanism of action of proton pump inhibitors

A
  • They are weak bases that are inactive at a neutral pH and irreversibly inhibit the H+/K+ ATPase pump
  • Decreases the basal and food stimulated gastric acid secretion
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9
Q

What are the unwanted effects of proton pump inhibitors

A

Headache, diarrhoea, mental confusion, rashes, somnolence, impotence, gynaecomastia, dizziness

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10
Q

What type of drugs protect the gastric mucosa?

A

Prostaglandins are gastroprotective

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11
Q

Describe what misoprostol does

A
  • Inhibits basal and food stimulated gastric acid secretion
  • Inhibits histamine and caffeine induced gastric acid secretion
  • Inhibits the activity of parietal cells
  • Increases the mucosal blood flow and can augment the secretion of HCO3- and mucus
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12
Q

Describe the effects of metoclopramide on gastric motility/emptying

A
  • Metoclopramide has mixed effects - inhibits pre and postsynaptic dopamine receptors as well as 5HT3 receptors - inhibits vomiting
  • Also stimulates 5HT4 - prokinetic
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13
Q

Describe the effects of dopamine

A
  • Dopamine acts on different dopamine receptors
  • Dopamine has relaxant effects on the gut by deactivating D2 receptors in the lower oesophageal sphincter and stomach (fundus and antrum)
  • Overall dopamine has mixed effects on the gut - may induce contraction of the proximal small intestine but relaxation in the distal small intestine
  • Dopamine inhibits the release of acetylcholine from intrinsic myenteric cholinergic neurons by activating presynaptic D2 receptors
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14
Q

Explain what inhibition of dopamine by metoclopramide does in the GI tract

A
  • Increases the release of acetylcholine which increases peristalsis of the duodenum, jejunum and ileum
  • The increased acetylcholine leads to increased intragastric pressure due to increased lower oesophageal sphincter tone and increased tone of gastric contractions
  • These improve antroduodenal coordination which accelerates gastric emptying and relaxes the pyloric sphincter
  • Through additional prokinetic effects it stimulates the presynaptic excitatory 5HT receptors and inhibitory nitrergic neurons which leads to coordinated gastric motility
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15
Q

What other areas does metoclopramide have use in?

A
  • Metoclopramide has some antiemetic properties via central effects
  • Metoclopramide relieves headaches via its central effects
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16
Q

State some conditions in which metoclopramide may be used

A
  • Antiemetic - nausea due to surgery or cancer
  • Gastro-oesophageal reflux disease (GORD)
  • Relieve symptoms of gastroparesis - promotes gastric emptying by stimulating gastric motility
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17
Q

Summarise the effects of metoclopramide

A
  1. Inhibits presynaptic and postsynaptic D2 receptors
  2. Stimulates the release of acetylcholine/SP from enteric neurons
  3. Elicits mixed 5HT agonist and antagonist effects e.g. stimulates excitatory 5HT4 receptors and inhibits 5HT3 receptors
  4. Stimulates inhibitory nitrergic neurons - mediate NO release
  5. Increases intragastric pressure - increased lower oesophageal sphincter and gastric tone
  6. Motility stimulant - improves antroduodenal coordination and accelerated gastric emptying
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18
Q

State some examples of antispasmodic drugs and what they do

A
  • Examples - propantheline, dicloxerine, mebeverine
  • Decrease the spasm of the bowel - they have a relaxant action of the GI tract (relax the smooth muscle of the GI tract)
19
Q

What type of drug is propantheline and what is it useful in as a treatment?

A
  • Propantheline is an antimuscarinic agent (muscarinic receptor antagonists inhibit parasympathetic activity to reduce spasm of the bowel)
  • May be useful in irritable bowel syndrome and diverticular disease - a congenital lesion may be a source of bacterial overgrowth
20
Q

State the goals of pharmacological treatment of gastric ulcers

A
  • Reduce acid secretion with H2 receptor antagonists e.g. ranitidine
  • Neutralise secreted acid with antacids e.g. gaviscon
  • Attempt to eradicate H pylori
21
Q

Drugs that inhibit or neutralise acid secretion can be used to treat what?

A
  • Peptic ulcers
  • Reflux oesophagitis - gastric acid secretion can damage the oesophagus
  • Zollinger ellison syndrome - gastrin producing tumour
22
Q

What is the general mechanism of antacids?

A
  • Neutralise gastric acids
  • Increase the pH of gastric acid
  • Prolonged dosage can lead to healing of duodenal ulcers but is less effective for gastric ulcers
23
Q

Describe what bismuth chelate does

A
  • Protects the gastric mucosa
  • Forms a base over crater of the ulcer
  • Absorbs pepsin
  • Increases HCO3- and PG secretion
  • Toxic against H pylori
  • Blackens the stool and tongue
24
Q

How to prostaglandins protect epithelial cells of the stomach against damage?

A
  • Stimulating the secretion of HCO3- which neutralises gastric acid
  • Reducing H+ secretion
  • Stimulating mucus production
  • Promoting vasodilation
25
Q

How is H pylori treated?

A
  • Omeprazole, amoxicillin and metronidazole
  • Omeprazole, clarithromycin and amoxicillin or tetracycline, metronidazole and bismuth chelates
  • Lansoprazole, clarithromycin, tinidazole and bismuth chelates
26
Q

Describe how bismuth chelate has cytoprotective effects

A
  • Provides a physical barrier over the surface/base of the ulcer
  • Enhances local synthesis of prostaglandins
  • Promotes bicarbonate secretion
  • Bismuth chelate has toxic effects on the bacillus - it prevents the adherence of H pylori to the mucosa or inhibit its proteolytic activity - stimulates bicarbonate secretion - increases prostaglandin synthesis and absorbs pepsin
27
Q

State some unwanted effects of bismuth chelate

A

Nausea vomiting blackening of the tongue and faeces

28
Q

What is the patient advice when taking metronidazole?

A
  • Adhere to the treatment
  • Disulfiram like reaction if metronidazole is taken with alcohol - patient will feel severely ill and may stop taking the drug
29
Q

What is normal bowel movement in a day?

A

Normal bowel opening is 1-3 x a day but hugely varies

30
Q

What symptoms can constipation produce?

A

Constipation causes rectal distension which can lead to - headache, loss of appetite, nausea and abdominal distension/stomach pain

31
Q

What are the causes of constipation?

A

Decreased motility of large intestine due to old age or damage to enteric nervous system of the colon

32
Q

What are some factors that increase colonic motility and increase constipation symptoms

A
  • Increases fibre cellulose and complex polysaccharides
  • Bran some fruits and vegetables with high fibre
  • Laxatives
  • Mineral oil - it lubricates the faeces
  • Castor oil - stimulates motility of colon
33
Q

State the causes, alarm signs and management of constipation

A

Causes -
- Diet
- Inactivity
- Drugs

Alarm signs -
- Acute onset constipation in older individuals
- Weight loss
- Blood in the stool
- Anaemia
- Family history of colon cancer or inflammatory bowel disease

Management of constipation -
- Diet, fluid intake and exercise
- Increased fibre intake and increased water intake

34
Q

Describe the drug treatments available for constipation

A

Purgatives -
- Can modulate/hasten food transit in the intestines
- Laxatives, stool softeners and stimulants

35
Q

Describe what bulk and osmotic laxatives do

A

Bulk -
- Bulk laxatives = methylcellulose
- Plant gums e.g. agar, linseed, bran are polysaccharide polymers
- They retain water in the gut lumen to promote peristalsis
- Increase the stools solid content

Osmotic laxatives - e.g. lactulose
- Increases and maintains the volume of fluid in the lumen of bowel by osmosis
- Increases transfer of gut contents into the intestine
- Increases volume of gut content entering the colon - distension and purgation in 1hr
- High doses cause flatulence, cramps, diarrhoea, vomiting and tolerance

36
Q

Describe the mode of action of lactulose in constipation

A
  • The unchaged lactulose reaches the colon
  • The colonic bacteria breaks it down into short fatty acid chains
  • This increases osmotic pressure and increases biomass
  • There is then softening of the faeces/volume of the stool increases
  • Peristalsis is stimulated
  • Colonic transit time is shortened
37
Q

How is diarrhoea treated?

A
  • Maintain body fluid and electrolytes
  • Identify causal organism and if possible treat with antibiotics
  • Modify secretion/absorption balance
38
Q

What are the causes of diarrhoea?

A

Infectious agents
Toxins
Anxiety
Drugs

39
Q

What does diarrhoea do to fluid balance?

A
  • Diarrhoea increases the motility of the GI tract
  • This increases secretion and decreases the absorption of fluid
  • This decreases electrolytes and water
40
Q

State 2 types of drugs used to treat diarrhoea

A
  • Antidiarrhoeal drugs - decreases movement
  • Antispasmodic drugs - decrease movement - relax smooth muscle in GI tract
41
Q

State the main therapeutic strategies to diarrhoea treatment

A
  • Maintain fluid and electrolyte balance through oral rehydration therapy
  • Use of anti-infectives as bacterial infections can resolve with time - if viral these may not be needed
  • Use of non microbial antidiarrheal agents
  • Use of anti motility drugs - absorbents an agents that modify fluid and electrolyte transport
42
Q

Describe what drugs are used to treat travellers diarrhoea

A
  • Most develop diarrhoea while travelling
  • Loperamide- selective on GI tract - decreases passage of faeces and decreases duration of illness
  • Codeine and loperamide - antisecretory action - Decreases intestinal motility
43
Q

Describe the mechanism of action of loperamide

A
  • Mechanism of action of loperamide -
  • An opioid receptor agonist
  • Binds to the u-opioid receptor of the myenteric plexus of the large intestine which inhibits bowel function
  • Controls motility and secretion of GI tract
  • Stimulation of the u-opioid receptor by loperamide inhibits gastric emptying, increases sphincter tone and induces stationary motor patterns and blocks peristalsis
  • Antispasmolytic agent which reduces smooth muscle activity in the GI tract and reduces passage of faeces
  • Reduce force and speed of colonic movement by:
  • Increasing haustral mixing in proximal colon
  • Inhibits propulsive mass movement in distal colon

Physiology 1 Semester 2 (50 decks)

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