CPT2: GI 7 (Laxatives, anti-spasmics, anti-motilitY) Flashcards
What are the 3 types of laxatives?
- Stimulant
- bulk-forming
- Osmotic
What are examples of bulk-forming laxatives?
How do they work?
Time for effect?
When should this nor be taken?
Important counseling point?
- Bulk Forming Laxatives (Fybogel, Fybogel with mebeverine)
- Contains soluble fibre ispaghula husk – Retains fluid in the faeces. Helps by increasing weight/ bulk of faeses with stimulates the bowel
- Important to have good fluid intake, otherwise can be constipating
- Not recommended in persons taking constipating medication – risk of further constipation
- 2 or 3 days to effect
Examples of osmotic laxatives?
How do they work?
Time to work?
When should these be used and when are they not reccomended?
Important counseling point
- Osmotic laxatives (Macrogols, lactulose)
- Draws water into the faeces due to osmosis
- Avoid lactulose in IBS – can increase bowel gas and therefore bloating
- Important to have good fluid intake due to risk of dehydration
- 1 or 2 days to effect
- Can be used if inadequate response to bulk forming
What are stimulant laxatie examples?
How do they work?
When are they used?
When are they not reccomended?
Time for effect?
- Stimulant Laxatives (Senna, bisacodyl, docusate, picosulfate)
- Cause direct stimulation of the bowel leading to increased colonic motility
- Can cause cramping abdominal pain so potentially limited value in IBS
- Can be used in conjunction if inadequate response to bulk forming/osmotic laxatives or if constipation exacerbated by medication (e.g. opiates)
- Docusate also has a lubricating/stool softening action if stool is hard to pass.
- 6hrs – 1 day to effect
What is linaclotide?
How does it work?
When is it used?
Linaclotide (Constella)
- An agonist of the guanylate cyclase C receptor on the surface of the bowel. Causes a decrease in pain, increase in secretions and an increase in colonic transit.
- Metabolised in the gut and has no systemic activity
- Licensed in IBS, used in patients with predominant constipation
- Indicated for patients who have failed or not tolerated laxative therapy
- Abdominal pain and diarrhoea are common side effects
What are examples of anti-motility agents?
- Codeine
- Loperamide
What does loperamide do?
- Opiate receptor agonist that stimulates opiate receptors in the GI tract
- Reduction of motility. More water is absorbed from faeces.
- Does not cross the blood-brain barrier (at normal doses)
- Extensive first pass metabolism
What does codiene do?
What are the active metabolites and how are these impacted?
- Opiate receptor agonist that stimulates opiate receptors in the GI tract.
- Codeine is metabolised to morphine (10%) and other active metabolites (80%) during first pass
- Reduction of motility. More water is absorbed from faeces.
- Can cross the blood-brain barrier
- CYP2D6 inhibitors (fluoxetine, cimetidine) block conversion to morphine
- Some will not metabolise codeine to morphine
What is 2nd line anti-motility treatment?
How does it work?
When is it used?
What are careful considerations
cousnelling points?
- Amitriptyline
- Tricyclic antidepressant – prevents reuptake of monoamines (serotonin, noradrenaline). Alters pain perception.
- Constipating, so more suitable in patients with pain and diarrhoea predominant IBS. Can be used in constipation predominant IBS if laxative therapy optimised
- Unlicensed in IBS
- Caution in those with existing cardiac disease (QT prolongation), current or previous psychiatric diagnosis (risk of suicide)
- Has an anticholinergic effect (caution in narrow angle glaucoma, risk of urinary retention)
- Take at night due to sedative/hypnotic effect
What are examples of anti-spasmodics?
- Mebeverine, alverine, peppermint oil and Hyoscine butylbromide
How do Mebeverine, alverine, peppermint oil work?
When should they be taken
What are side effects of peppermint oil?
Side effects of Mebeverine and alverine?
- Mebeverine, alverine, peppermint oil
- Direct relaxant action on GI smooth muscle preventing painful muscle spasm. Provides symptomatic relief.
- Peppermint oil can irritate mucous membranes causing a burning sensation –mouth, oesophagus, rectum. Also can cause nausea/vomiting and allergic reactions.
- Alverine and mebeverine can both cause nausea, rash, itch and allergic reactions. Alverine has been reported to have caused jaundice, but the incidence of these adverse effects are not known.
- Usually take before meals, although MR mebeverine is taken BD
How does hysocine butylbromide work?
Side effects?
Contraindications?
- Hyoscine butylbromide (Buscopan)
- Prevents the action of acetylcholine on muscarinic receptors throughout the bowel, resulting in relaxation of GI smooth muscle.
- Side effects more likely than the antispasmodics
- Urinary retention, dry eyes, constipation, dry mouth, tachycardia
- Contra-indicated in patients with myasthenia gravis, narrow angle glaucoma or risk of obstruction.
