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).