Laxatives, Anti-Motility agents, Anti-spasmodics

Question 1

Bulk Forming Laxatives:
example
mode of action
contraindication
days to effect
classification

Answer 1

• Ispaghula husk (+mebevirine) - Fybogel
• Soluble fibre, ispaghula husk, retains fluid in the faeces
• need good fluid intake otherwise constipating
• • Not reccomeneded in pt taking constipation meds - risk of further constipation
• 2-3 days to effect
• Class - GSL

Question 2

Osmotic laxatives
example
mode of action
contraindications
days to effect
classification

Answer 2

• Macrogols, Lactulose
• draws water into the faeces via osmosis
• Avoid lactulose in IBS - increases bowel gas therefore bloating
• risk of dehydration - good fluid intake
• 1-2 days to effect
• use if inadequate response to bulk forming
• P

Question 3

Stimulant laxatives
examples
mode of action
contraindications
days to effect
classification

Answer 3

• Senna, Bisacodyl, Docusate, picosulfate
• Causes direct stimulation of the bowels increasing colonic motility
• can cause cramping, abdominal pain so potentialy limited value in IBS
• can be used in conjunction if inadequate response to bulk-forming/osmotic, or in opiod induced constipation
• docusate also has lubricating/stool softening action if stool is hard to pass
• 6hrs-1day to effect
• P

Question 4

Linaclotide:
MOA
Indication
Side effects

Answer 4

Linaclotide:
* Guanylate cyclase C receptor agonist.
* Agonises guanylate cyclase C receptors on the surface of the bowel
* Causes decrease in pain, increase in secretions and an increase in colonic transition
* Metabolised in the gut - no systematic activity
* IBS - failed or not tolerated previous laxative therapy
* Side effects: abdominal pain and diarrhoea

Question 5

Loperamide - Anti-motility agents
Drug class
MOA
Side effects

Answer 5

• Opiate receptor agonist - stimulates opiate receptors in GI tract
• causes reduction of motility as more water absorbed from the faeces
• does not cross BBB at normal dose
• Extensive first pass metabolism
• side effects: GI disorders, headache, nausea

Question 7

Codeine - Anti-motility agents

Answer 7

• Opiate receptor agonist - stimulates opiate receptors in GI tract
• metabolised to morphine (10%) and other active metabolites (80%) via first pass
• Reduced motility - more water absorbed from the faeces
• Can cross BBB
• CYP2D6 inhibitors - fluoxetine (block conversion to morphine)
• some pt will not metabolsie codeine to morphien
• Respiratory depression, dependence, overdose

Question 8

Amitryptiline - Anti-motility agents

Answer 8

• Tryciclic antidepressant
• prevents reuptake of monoamines (seratonin, noradrenaline). alters pain reception
• constipating, so more suitable in patients with pain/diarrhoea IBS.
• Unlisenced in IBS
• Caution in pt’s with existing cardiac issues / current or previous psychiatric disorders
• anti-cholonergic effect - risk of urinary incontenence
• Take at night due to sedative/hypnotic effect

Question 9

Anti-spasmodics

Answer 9

• Mebeverine, Alverine, Peppermint oil
  direct relaxant action on GI smooth muscle preventing painful muscle spasm - symptomatic releif
• Peppermint oil can irritate mucous membrane causing burning sensation in mouth, oesophagus, rectum. can also cause nausea, vomitting, alergic reactions
• Alverine and Mebeverine can cause nausea, rash, itch and allergic reactions.
• Take before meals, except MR mebevrine BD.

Question 10

Anti-spasmodics

Answer 10

• Hyoscine Butylbromide (Buscopan)
• Prevents the action of Ach on muscaranic receptors throughout the bowel, resulting in relaxation of GI smooth muscle.
• Side effects: urinary retention, dry eyes, constipation, dry mouth, tachycardia
• contraindicated ion patients with myasthenia gravid, narrow angle glaucoma or risk of obstruction