Laxatives, bulk-forming
Key examples
- Ispaghula husk
- Methylcellulose
- Sterculia
Common indications
- Constipation and faecal impaction, particularly in patients who cannot increase their dietary fibre intake.
- Mild chronic diarrhoea associated with diverticular disease or irritable bowel syndrome.
Mechanisms of action
- Bulk-forming laxatives contain a hydrophilic substance, such as a polysaccharide or cellulose, which is not absorbed or broken down in 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 to relieve constipation. It can also help in chronic diarrhoea. This can be useful for some patients with diverticular disease, irritable bowel syndrome, or when managing stoma output.
Important adverse effects
- These drugs are generally well tolerated, with mild abdominal distension and flatulence being the most common side effects. Rarely, but more seriously, they may cause faecal impaction and gastrointestinal obstruction.
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.
Important interactions
- There are no clinically significant adverse drug interactions with bulk-forming laxatives.
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