GI Pharmacology

Question 1

How do Alginates and Antacids work?

Name a drug that contains both

Answer 1

• Antacids buffer stomach acid
• Alginates increase stomach content viscosity and reduce reflux
• Gaviscon

Question 2

List 2 ADRs of Gaviscon

Answer 2

• Diarrhoea due to Magnesium in Antacid component

- Constipation due to Aluminium in Antacid component

Question 3

List 2 Contraindications of Gaviscon

Answer 3

• Caution with renal failure

- High sucrose in some preparations so caution with Hyperglycaemia in DM

Question 4

List 2 DDIs of Gaviscon

Answer 4

• Can reduce absorption of many drugs so doses should be separated
• Can increase urine alkalinity, which would lead to increases Aspirin excretion

Question 5

What drug class are Omeprazole and Lansoprazole?

How do they work?

Answer 5

Proton Pump Inhibitors (PPIs)

Irreversibly inhibit H+/ ATPase in Parietal Cells, significantly reducing acid secretion

Question 6

List 4 ADRs of PPIs

Answer 6

• GI Disturbance (Ab pain, Constipation, Diarrhoea)
• Headaches
• Dizziness
• Drowsiness/ confusion

Question 7

List 2 contraindications of PPIs

Answer 7

• Can-> Osteoporosis, increasing fracture risk

- Mask symptoms of Gastro-oesophageal cancer

Question 8

List 3 DDIs of PPIs

Answer 8

• Omeprazole is a CYP inhibitor, preventing Clopidogrel activation

PPIs can increase effects of;

• Warfarin
• Phenytoin (so monitor these if on them)

Question 9

Describe the use of PPIs

Answer 9

• Use for shortest effective duration, at lowest effective dose
• Often prescribed alongside NSAIDs or Steroids

Question 10

What class of drug is Ranitidine?

How does this work?

Answer 10

H2 Receptor Antagonist

Inhibits H2 receptors (Local histamine release normally contributes to proton pump activation)

Question 11

List 2 ADRs of H2 receptor antagonists

Answer 11

• Diarrhoea
• Headache

(But usually well tolerated)

Question 12

List 2 contraindications of H2 Receptor Antagonists

List DDIs

Answer 12

• Can mask symptoms of Gastro-Oesophageal cancer
• Renal impairment

Few DDIs (reduced exposure to some antivirals)

Question 13

Why is there a current large scale recall on Ranitidine containing products?

What’s prescribed instead now?

Answer 13

• Possible carcinogenic contaminant

- Lansoprazole

Question 14

How is H. pylori treated?

Answer 14

One week triple therapy of PPI + 2 Antibacterials

• Lansoprazole + Clarithromycin + Amoxicillin/ Metronidazole (if allergic to Amoxicillin)

Question 15

What class of drugs are Sulfasalazine and Mesalazine?

What are they used to treat?

Answer 15

Aminosalicyclates

Ulcerative colitis

Question 16

Compare use of Mesalazine and Sulfasalazine

Answer 16

Mesalazine;

• Used for UC treatment
• No role in treating RA

Sulfasalazine;

• More side effects so used infrequently for UC
• More useful for treating RA

Question 17

List 2 ADRs of Aminosalicyclates

List 1 Contraindication

List 1 DDI

Answer 17

• GI Disturbance (Nausea, Dyspepsia)
• Leukopenia (rare)
• Are salicylicates like Aspirin, so similar hypersensitivity
• Tablets may break down quicker in presence of PPIs

Question 18

Why are H2 Receptor Antagonists only partially effective in reducing acid secretion, compared to PPIs?

Answer 18

There are other routes to pump activation than via Histamine