GI Drugs

Question 1

List drugs commonly used for GI disorders

Answer 1

Alginates and Antacids
Proton pump inhibitors (PPI)
H2 receptor antagonists
Amionsalicylates

Question 2

List the following for: Alginates and Antacids

• Use
• Example drugs
• Drug class
• Mechanism of action
• Adverse effects
• Warnings / contraindications
• Important drug reactions

Answer 2

Alginic acid - increase stomach viscosity and reduce reflux
Antacids - buffer stomach acid

Gaviscon

Alginates and Antacids

Alginic acid - Increase stomach viscosity and reduce reflux
Antacids - Buffer stomach acid

• Magnesium salts can cause diarrhoea
• Aluminium salts can cause constipation
• Renal failure (caution)
• Hyperglycaemia in diabetes - high sucrose in some preparations
• Can reduce absorption of many drugs - doses should be separated
• Increased urine alkalinity can increase aspirin excretion

Question 3

List the following for: Proton pump inhibitors (PPI)

• Use
• Example drugs
• Drug class
• Mechanism of action
• Adverse effects
• Warnings / contraindications
• Important drug reactions

Answer 3

Reduce gastric acid secretion

Lansoprazole
Omeprazole

Proton pump inhibitors

• Irreversibly inhibit H/K ATPase in gastric parietal cells
• Final stage in the pathway - very significant reduction in acid secretion
• GI disturbance – abdominal pain, constipation diarrhoea
• Headache, dizziness
• Drowsiness/confusion
• Mask symptoms of gastro-oesophageal cancer
• Osteoporosis - fracture risk
• Omeprazole CYP inhibitor - reduced clopidogrel action
• PPIs can increase effects of warfarin and phenytoin - monitor

Question 4

List the following for: H2 receptor antagonists

• Use
• Example drugs
• Drug class
• Mechanism of action
• Adverse effects
• Warnings / contraindications
• Important drug reactions (recall)

Answer 4

Reduce gastric acid secretion

Ranitidine

H2 receptor antagonists

• Inhibition of H2 receptors
• Reduce local histamine release, reduced proton pump activation
• Other routes to pump inhibition mean only partial reduction in acid secretion

Generally well tolerated

• Diarrhoea
• Headache
• Mask symptoms of gastro-oesophageal cancer
• Renal impairment
• Current large scale recall on most ranitidine containing products due to possible carcinogenic contaminant

Question 5

List the following for: Amionsalicylates

• Use
• Example drugs
• Drug class
• Mechanism of action
• Adverse effects
• Warnings / contraindications
• Important drug reactions

Answer 5

First line treatment in ulcerative colitis (UC)

Mesalazine

Amionsalicylates

• Release of 5-aminosalsylic acid
• Topical action at the colon (enteric coated tablets limit gastric breakdown)
• GI disturbance - nausea, dyspepsia
• Leukopenia (rare)
• Like aspirin (salicylates) - similar hypersensitivity
• Enteric coated tablets may break down quicker in presence of PPI (because of increased pH / more alkaline)