Laxatives - Osmotic Flashcards
What are examples of osmotic laxatives?
- Lactulose
- Macrogel
- Phosphate enema
What are indications for the use of stimulant laxatives?
- Constipation and faecal impaction
- Bowel Prep prior to surgery/endoscopy
- Hepatic encephalopathy
What is the mechanism of action of stimulant laxatives?
Based on osmotically active substances which stay in gut lumen - hold water in stool maintaining volume and stimulating peristalsis.
Why is lactulose used in hepatic encephalopathy?
Reduces ammonia absorption by increasing gut transit rate and acidifying the stool, which inhibits the proliferation of ammonia-producing bacteria
What are important adverse side effects of osmotic laxatives?
- Flatulence
- Abdominal cramps
- Nausea
- Diarrhoea
- Phosphate enema - local irritation and electrolyte disturbances
When should you not use osmotic laxatives?
- Intestinal obstruction - risk of perforation
- Phosphate enema - heart failure, ascites and electrolyte disturbances
How would you prescribe lactulose to treat constipation with impaction?
15mL twice daily and titrate to effect
How many doses of phosphate enema would you prescribe per day to treat faecal impaction?
One per 24 hours
What should you advise if giving stimulant laxatives?
Drink plenty of water
When treating faecal impaction rectally, what would be your first line choice?
Glycerol suppository first, then phostphate enema
