Laxatives
Bulk laxatives (e.g. ispaghula husk) – polysaccharide polymers that are not broken down by digestion and thereby increase stool volume....
Laxatives...
- EXAMPLES: Lactulose, Egycosate.
- MECHANISM OF ACTION
- Bulk laxatives (e.g. ispaghula husk) – polysaccharide polymers that are not broken down by digestion and thereby increase stool volume. This stimulates intestinal peristalsis (via the stretch reflex) as well as softening faeces.
- Osmotic laxatives (e.g. lactulose, Movicol) – these poorly absorbed solutes increase the volume of water in the bowel lumen by osmosis hence increasing transit.
- Stimulant laxatives (e.g. senna, docusate sodium) – the primary effect is via direct stimulation of myenteric plexus resulting in smooth muscle contraction and increased peristalsis.
- Faecal softeners (e.g. arachis oil) – these are surfactants that reduce surface tension and allow water to penetrate and soften faeces.
- Constipation.
- Hepatic encephalopathy (lactulose).
- Bowel obstruction.
- Galactosaemia (lactulose only).
- Acute inflammatory bowel disease.
- Severe dehydration.
- Flatulence.
- Diarrhea.
- Abdominal cramps.
- Electrolyte disturbances.
- Variable – most are broken down locally in the GI tract with minimal absorption.
- No specific drug monitoring required.
- Lactulose may enhance warfarin effects in severe liver disease.
- Before prescribing a laxative ensure constipation is not secondary to an underlying pathology such as bowel cancer.
- It requires at least 2–3 days for osmotic or bulking laxatives to take full effect.
- Avoid laxatives if bowel obstruction is suspected due to risk of perforation.
- Lactulose reduces ammonia-producing organisms and is used in the treatment of hepatic encephalopathy.
- Chronic laxative use can cause tolerance (stimulant laxatives).
