Laxatives/Purgatives - Mechanism of action, Indications, Contraindication, Adverse effects and Drug interactions



These drugs are combinedly knows as purgatives, which includes laxatives and cathartics these drugs are used to overcome the constipation and proper evacuation of bowels.

Mechanism of action

Osmotic laxatives (Magnesium hydroxide) draw water into the intestine to increase the mass of stool, stretching musculature which results in peristalsis.

Stimulant laxatives result in stimulation of intestinal peristalsis.

Lubricant laxatives increase water retention in the stool, prevent water absorption from the stool, and lubricate as well as soften intestinal contents.

Stool softener allow more fluid are fat to penetrate the faeces, producing a softer fecal mass.

Drug example and doses

Bilk forming laxatives (Methyl Cellulose) - 2 tablets 1000mg orally with 8oz of liquid up to 6times a day.

Lubricant laxatives include mineral oil (Kondremal, Fleet mineral oil enema.

Hyperosmotic laxatives include lactulose. - 10mg BD

Stimulant laxatives (Bisacodyl, Castor oil) – 5 -10 mg sodium Pico sulfate 15-20 ml

Stool softener (Docusate Calcium, Docusate potassium) - 240mg 50-400mg orallyb1to 4 equally divided dose each day.

Indications / Uses

To treat or prevent constipation.

To prepare the bowel for radiologic or endoscopic procedures.

Short term treatment of constipation caused high dose of opioid use.

Osmotic laxatives are used to rapid evacuation of the bowel after ingestion of poison or following anti-helminthic therapy to rid of the body from dead parasites.

Methyl cellulose and psyllium are used to many chronic diarrhoea.

Contraindication / Precautions

Contraindicated if patient with parasites.

Severe abdominal pain of unknown cause.

Adverse effects

GI irritation.

Rectal burning sensation.

Osmotic laxatives may causes Dehydration.

Long term use and abuse of laxatives may cause permanent loss of colonic motility.

Laxative dependence and electrolyte imbalances.

Nutritional deficiencies (with lubricant laxatives).

Belching (with osmotic laxatives)

Electrolyte imbalance. (With saline laxatives)

Drug interactions

Laxative decrease intestinal transit time and reduce absorption of orally administer drug.

Laxatives/Purgatives Notes PDF

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