Constipation Flashcards
Bulk-forming Laxatives
Common indications
(Ispaghula husk, methylcellulose)
- Constipation and faecal impaction- particularly in patients who cannot increase their dietary fibre intake
- Mild Chronic diarrhoea- associated with diverticular disease or IBS
Bulk-forming Laxatives
MOA
- Bulk-forming laxatives contain a hydrophilic substance, such as polysaccharide or cellulose, which is not absorbed or broken down by the gut.
- Like dietary fibre, this attracts water into the stool and increases its mass
- Adequate fluid intake is therefore important to the action of bulk-forming laxatives
- Increased stool bulk stimulates peristalsis and helps releive constipation
- It can also help in chronic diarrhoea or when stoma output needs managing
Bulk-forming Laxatives
Important adverse effects
- These drugs are generally well tolerated, with mild abdominal distension and flatulence being the most common side effect.
- Rarely, they can cause GI obstruction and faecal impaction
Bulk-forming Laxatives
Warnings
- They should not be used in patients with subacute or established intestinal obstruction or faecal impaction
- And in general should not be used in patients with ileus
Bulk-forming Laxatives
Administration
- Bulk-forming laxatives may be provided in the form of granules or powder to be dissolved in water or tablets
- Importantly, they should be taken with plenty of water (300mL)
Bulk-forming Laxatives
Communication and monitoring
- Explain that you are offering a laxative that works as a fibre supplement
- This will hopefully make there stools easier to pass
- Outline the common side effects
- Tell them the dose can be adjusted according to there symptoms
- Take at mealtimes
- When treating inpatients, a stool chart is useful to monitor efficacy of treatment
Osmotic Laxatives (lactulose, macrogol, phosphate enema)
Common indications
- Constipation and faecal impaction
- Bowel preparation prior to surgery or endoscopy
- Hepatic encephalopathy
Osmotic Laxatives (lactulose, macrogol, phosphate enema)
MOA
- These medicines are based on osmotically active substances (sugars or alcoho.ls) that are not absorbed or digested, therefore remain in the gut lumen.
- They hold water in the stool, maintaining its volume and stimulating peristalsis.
- Lactulose, in particular also reduces ammonia absorption (Hepatic encephalopathy)
- It does this by increasing gut transit rate and acidifying the stool, which inhibits the proliferations of ammonia-producing bacteria, hence is helpful in people in liver failure
Osmotic Laxatives (lactulose, macrogol, phosphate enema)
Important adverse effects
- Flatulence, abdominal cramps and nausea are common
- Diarrhoea
- Local irritation
- Electrolyte disturbances
Osmotic Laxatives (lactulose, macrogol, phosphate enema)
Warnings
- Lactulose is contra-indicated in Intestinal obstruction as there is a risk of proliferation
- Phosphate enemas can cause significant fluid shift so should be used with caution in those patients with HF, ascites and when electrolyte disturbances are present
Osmotic Laxatives (lactulose, macrogol, phosphate enema)
Important interactions
- There are no significant interactions
- However the effects of warfarin may be slightly increased
Osmotic Laxatives (lactulose, macrogol, phosphate enema)
Communication
- Explain that you are offering treatment with a laxative that will hopefully make their stool softer and easier to pass
- To work, it requires them to drink plenty of water. They should aim for 6-8 glasses a day
- Mention ab cramps and flatulence can occur but should get better over time
Stimulant laxatives (bisacodyl, senna, glycerol, docusate)
Common indications
- Constipation
- Faecal impation- only in suppository form
Stimulant laxatives (bisacodyl, senna, glycerol, docusate)
MOA
- Stimulant laxatives increase water and electrolyte secretion from the colon mucosa, thereby increasing volume of colonic content and stimulating peristalsis
- They also have a direct pro-peristalsis action with the mechanisms varying between formulations
- Senna gets metabolised by bacteria with the metabolite have a direct action of the enteric nervous system
- Docusate has both stimulant and faecal softening actions
Stimulant laxatives (bisacodyl, senna, glycerol, docusate)
Adverse effects
- Ab pain/cramps
- Prolonged use can cause melanosis coli (reversible pigmentation of intestinal wall)
- Prolonged use can also cause lazy bowel
