Gastrointestinal System Flashcards
Alginates/Antacids
Mechanism of Action
Antacids: buffer stomach acids
Alginate: increase viscosity of contents and create floating raft to separate acidic contents from GOJ
Alginates/Antacids
Indications
GORD, Dyspepsia
Alginates/Antacids
Contraindications and Side Effects
C/I: Thickened milk preparations can lead to bloating, caution in electrolyte imbalance and diabetics (some have Na/K, others sucrose)
Side Effects: Diarrhoea (from free Mg salts), Constipation (from free Al salts)
Alginates/Antacids
Interactions
May bind to other drugs
Antacids can reduce concentration of ACEi, Abx, bisphosphonates, digoxin, levothyroixine, PPIs
Alginates/Antacids
Prescription advice
Proprietary only (Gaviscon, Rennies), PRN, alongside lifestyle measures, suspend 2/52 before H.pylori test
H2-Receptor Antagonsists
Mechanism of Action
Reduce gastric acid secretion by inhibiting histamine from binding to parietal cells
H2-Receptor Antagonists
Indications
PUD, GORD/Dyspepsia, Zollinger-Ellison Syndrome
H2-Receptor Antagonists
Contraindications and Side Effects
C/I - renal failure, can mask symptoms of gastric cancer
S/E - bowel disturbance, headache/dizziness
H2-Receptor Antagonists
Interactions and Prescription advice
NKDI Rapid onset (good for pre-op/bariatrics), look out for other gastric cancer symptoms
Proton Pump Inhibitors
Mechanism of Action
Irrersible inhibition of H+/K+-ATPase pump of gastric parietal cells almost completely suppresses acid secretion
Proton Pump Inhibitors
Indications
PUD, Dyspepsia, GORD, H.pylori eradication therapy
Proton Pump Inhibitors
Contraindications and Side Effects
C/I - can disguise gastric cancers, increased risk of fracture
S/E - increased pH reduces immunity
Proton Pump Inhibitors
Interactions
Clopidogrel - reduces effectiveness (less so lansoprazole)
Proton Pump Inhibitors
H.pylori eradication therapy
1g amoxicillin + 500mg clarithromycin (or 400mg metronidazole) with PPI
Anti-motility (non-CNS opioid) - Loperamide
Brief details
MoA: Reduces propulsive contractions via u-receptors
I: Diarrhoea
C/I: acute UC exacerbation (megacolon), C.diff colitis, acute dysentery
S/E - constipation, cramping, flatulance
Interactions: risk of toxicity with other CNS active opioids
Elimination: Bile
Prescription - must have negative C.diff sceen
3 Different Laxative Mechanisms
- Bulk-forming - hydrophilic, attracts water and stimulates peristalsis
- Osmotic - holds water in stool to maintain volume and reduces ammonia absorption by acidifying stool
- Stimulant - increases water/electrolyte secretion to increase volume of colonic contents
Laxatives
Indications
Constipation, hepatic encephalopathy (lactulose)
Laxatives
Contraindications
Intestinal obstruction, ileus, dehydration, UC/Crohn’s, fluid levels, N&V, haemorrhoids, anal fissure
Aminosalicylates
Mesalazine/Sulfasalazine
Mechansim of Action
Release 5-aminosalicyclic acid (5-ASA) which is anti-inflammatory against COX-2 and cytokines, breakdown product of sulfapyridine is active in RA
Aminosalicylates
Indications
UC, RA
Aminosalicylates
Contraindications
Aspirin hypersensitivity, folic acid deficiency (must be co-prescribed)
Aminosalicylates
Side Effects
GI upset/headache
Rare - leucopenia/thrombocytopenia, irrecersible oligospermia
Antiemetics - Dopamine receptor antagonist
Metoclopramide/Domperidone
Mechanism
D2 in chemoreceptor trigger zone is blocked so emetogenic substances in blood do not trigger vomiting, also pro-kinetic
Metoclopramide
Indications
Prophylactic of N&V
Metoclopramide
Contraindications
Extrapyramidal effects in <20, bowel obstruction/perforation
Metoclopramide
Side effects
Diarrhoea, extrapyramidal syndromes, drowsiness, increased prolactin secretion
Metoclopramide
Interactions
Dopaminergics - Parkinsons medications
Alternative antiemetics
Cyclizine (H1r antagonist)
Hyoscine Hydrobromide (anti-muscarinic)
Ondansetron (5HT3-r antagonist - used post-op/chemo)
Senna
Brief Description
MoA - bacterial activation leads to pro-motility improves transit, inhibits absorption of water and elextrolyte, increases secretions
I - constipation
C/I - obstruction, IBD, appendicitis, dehydration, <6
S/E - hypersensitivity, adbo pain/spasm, discoloured urine
Interactions - anything that lowers potassium over long term/cardiac glycosides
