Gastrointestinal Pharmacology

Question 1

Antacids

Answer 1

sodium/ aluminium/ magnesium bicarbonate and aluminium/ magnesium hydroxide
Alkylating agents, increase gastric pH to >4.
Can cause wind, constipation and diarrhoea

Question 2

Alginates

Answer 2

Alginic acid combines with saliva to form a viscous foam that floats on the gastric contents and protects the oesophagus

Question 3

H2 antagonists

Answer 3

Include: cimetidine, ranitidine, famotidine
Block activation of Gs-coupled H2 receptors on parietal cells
Reduces gastric acid secretion, giving the lining time to heal
Cimetidine acts as a CYP450 inhibitor → DDIs

Question 4

Proton pump inhibitors (PPIs)

Answer 4

Include: omeprazole, pantoprazole, lansoprazole
Irreversible inhibition of the proton pump, inhibiting 90% of HCl secretion → may cause achlorhydria
Activated in an acidic environment - aids selectivity
Give the ulcer time to heal but increase risk of Campylobacter infection

Question 5

Potassium competitive acid blockers

Answer 5

Vonoprazan - inhibits the proton pump, similarly to PPIs

Question 6

Amoxicillin, clarithromycin, metronidazole

Answer 6

Antibiotics used alongside PPIs and H2 inhibitors for eradication of Helicobacter Pylori, which causes ulceration

Question 7

Misoprostol

Answer 7

Prostaglandin E2 analogue that binds to prostanoid receptors on parietal cells to inhibit acid secretion → given when NSAIDs are used to inhibit gastric side effects

Question 8

Osmotic laxatives

Answer 8

Constipation treatment
Cause fluid retention in the GIT to increase bulk and soften the faeces
Lactulose - converted into lactic and acetic acids by microbiome
Magnesium salts create osmotic pull and may also release CCK to alter motility

Question 9

Bulk laxatives

Answer 9

Constipation treatment
Examples: ispaghula husk, methylcellulose
Increase volume of non-absorbable solid residue

Question 10

Stimulating purgatives

Answer 10

Constipation treatment
Examples: bisacodyl, sodium picosulphate (Dulcolax), senna extracts
Increase smooth muscle contraction and peristalsis

Question 11

D2 antagonists

Answer 11

Constipation treatment
Examples: metoclopramide and domperidone
Inhibit presynaptic Gi-coupled D2 receptors, enhancing ACh release and peristalsis
Prescription only

Question 12

Prucalopride

Answer 12

Constipation treatment
Stimulates presynaptic Gs-coupled 5-HT4 receptors, enhancing ACh release and peristalsis.
Prescription only

Question 13

What is IBS? What are its treatments?

Answer 13

Irritable Bowel Syndrome
Common long-term condition involving pain and bloating which improves with defecation.
Can involve cycles of constipation and diarrhoea, treated with lactulose and loperamide, respectively.
Other treatments include antispasmodics (antimuscarinics). mebeverine (directly relaxes GIT muscles), and antidepressants (amitriptyline, citalopram) to alter sensitivity of sensory nerves.

Question 14

Mebeverine

Answer 14

Direct GI muscle relaxant
Used for IBS

Question 15

What is IBD?

Answer 15

Inflammatory Bowel Disease
Impact terminal ileum and rectum and includes chronic inflammation, Crohn’s disease, and ulcerative colitis.
Causes pain, bloody stool , uveitis, oral lesions, skin rashes, fever, arthritis and weight loss → immune activation and poor nutrient processing involved.
Treated with anti-inflammatory medication and immunosuppressants

Question 16

5-aminosalicylates: Mesalazine , Sulfasalazine

Answer 16

IBD treatment
Release 5-ASA, which inhibits leukotriene and prostanoid formation → anti-inflammatory

Question 16

Infliximab

Answer 16

Severe Crohn’s disease (IBD)
Monoclonal antibody against TNF-α → immunosuppressant

Question 16

Prednisolone

Answer 16

IBD treatment
Corticosteroid, has anti-inflammatory and immunosuppressant actions

Question 17

Immunosuppressants: methotrexate, ciclosporin, azathioprine

Answer 17

Severe Crohn’s disease (IBD)

Question 18

Cholera treatment

Answer 18

Antibiotics such as tetracyclines, macrolides, and fluoroquinolones
Oral vaccine available

Question 19

Loperamide (imodium)

Answer 19

Diarrhoea treatment
Antimotility drug
Opiate, acting at presynaptic μ opioid receptors to have antimuscarinic effects, reducing peristalsis
First choice drug due to low side effects as it does not cross the BBB

Question 20

Muscarinic antagonists

Answer 20

Diarrhoea treatment
Examples: low-dose atropine, dicycloverine
Inhibit postsynaptic receptors, preventing GI motility

Question 21

Absorbents

Answer 21

Diarrhoea treatment
Examples: kaolin, chalk, charcoal, magnesium aluminium silicate, bismuth subsalicylate (Pepto bismol).
Reduce the impact of diarrhoea-causing toxins by providing a protective coating.