10.1 GI pharmacology Flashcards
When can ulcers be asymptomatic?
Chronic ulcers
What can happen with gastric ulcers?
Bleeding
Perforation
Scarring
Possible obstruction - if scarring occurs around pyloric sphincter
What causes duodenal/gastric ulcers?
- Acid- inability of normal [acid] to inhibit further acid
- Early gastric emptying
- Helicobacter pylori
- NSAIDs
- Smoking and alcohol may delay healing
What are the effects of different molecules on parietal cells?
Stimulation:
- Acetylcholine
- Histamine
- Gastrin
Inhibition:
- Prostaglandins - NSAIDs reduce these ergo increase in production of stomach acid causing ulcers
- PGs also maintain mucosal blood flow, important for removing free H+ ions
What do we use to reduce stomach acid?
Alginates and antacids
PPIs
H2 receptor antagonist
What is an example of an alginate and antacid?
Gaviscon
How do antacids and alginates work?
Antacids buffer stomach acid
Alginic acids increase stomach content viscosity and reduce reflux
They are often taken together as compound mixture
What substances are alginates and antacids?
- Alginic acid - sodium alginate
- Antacid - aluminium hydroxide/magnesium carbonate
What are the adverse effects of using alginates and antacids?
- Magnesium salts can cause diarrhoea
- Aluminium salts can cause constipation
- Gaviscon has both to avoid stop this side effect and balance each other out
What are the contraindications and warnings of alginates and antacids?
- Na+ and K+ containing preparations should be used with caution in renal failure
- High sucrose in some preparations - can cause hyperglycaemia in DM pts
What are the important drug to drug interactions with alginates and antacids?
Reduce absorption of many drugs so should be separated
Increased urine alkalinity can increase aspirin excretion
Can be used to treat aspirin overdose
What are some examples of PPIs?
Lansoprazole
Omeprazole
-prazole suffix
How do proton pump inhibitors work?
Inhibit H+K+ATPase in gastric parietal cells
Final stage in the acid production pathway
Very significant reduction in acid secretion
What are the adverse effects of using PPIs?
GI disturbance
Headache, dizziness
Drowsiness/confusion
What are the contraindications and warnings of using PPIs?
Masks symptoms of oesophageal cancer
Osteoporosis - fracture risk
What are some important drug to drug interactions with PPIs?
Omeprazole is a CYP inhibitor - reduces clopidogrel action
PPIs can also increase effects of warfarin and phenytoin
When are PPIs often prescribed?
With long-term NSAID or steroids
Pericarditis
Give an example of an H2 receptor antagonist
Ranitidine
How do H2 receptor antagonists reduce stomach acid?
Histamine stimulates acid production
Inhibition causes reduced acid production
How effective are H2 receptor antagonists?
Only blocking histamine activation of parietal cells
Can still be stimulated by other molecules
What are the adverse effects of H2 receptor antagonists?
Generally tolerated well - diarrhoea, headache
What are the contraindications and warnings of using H2 receptor antagonists?
Can mask symptoms of gastro-oesophageal cancer
Renal impairment
What are some important drug to drug interactions when using H2 receptor antagonists?
Few common
Reduced exposure to some antivirals and protein kinase inhibitors
Is Ranitidine currently available?
No -currently removed due to containing some carcinogens
Lansoprazole first line alternative
When should you consider a patient may be infected with helicobacter pylori?
All patients with duodenal or gastric ulcers that are not associated with NSAIDs or unresponsive to lifestyle PPIs and antacids
How do we confirm infection of helicobacter pylori?
Urea breath test - C13 isotope use
Urea coverted to ammonia by helicobacter urease
CO2 expired
If breath contains high levels of C13 this means positive H-Pylori infection
How is helicobacter pylori treated?
One week Triple therapy - PPI and two antibacterial agents
Lansoprazole + Clarithromyin + Amoxicillin or Metronidazole
Compliance with full course is important for effectiveness and minimise risk of bacterial resistance
When is metronidazole used over amoxicillin?
If allergic to amoxicillin
What is an example of an amionsalicylate?
Mesalazine
Sulfasalazine
-salazine suffix
When are aminosalicyclates used?
First line treatment for ulcerative colitis
How do aminosalicyclates work?
Release of 5-aminosalsylic acid
Topical action at the colon
Enteric coated tablets which limits gastric breakdown
What aminosalicyclates are used in rheumatoid arthritis?
Sulfasalazine - has sulpha group attached so more beneficial for RA
Mesalazine no role in RA
What are the adverse effects of aminosalicyclates?
GI disturbance - nausea, dyspepsia
Leukopenia - rare
What are some warnings and contraindications when using aminosalicyclates?
Salicyclates are like aspirin - similar hypersensitivity can occur
Do not use in aspirin hypersensitivity
What are some important drug to drug interactions with aminosalicylates?
Enteric coated tablets may break down more quickly if PPIS are being used as this increases the stomach pH
