Osmotic laxatives Flashcards
Give the 3 main clinical indications for the use of osmotic laxatives.
1) Constipation and faecal impaction.
2) Bowel preparation prior to surgery and endoscopy. ]
3) Hepatic encephalopathy.
What substances are osmotic laxatives based upon?
osmotically active substances such as sugars or alcohols that are not digested or absorbed and so stay in the gut lumen.
What is the main action of osmotic laxatives?
They hold water in the stool, maintaining its volume and stimulating peristalsis.
Give the 4 osmotic laxative P-drugs.
lactulose
macrogols
magnesium salts
sodium acid phosphate
Why are osmotic laxatives helpful in hepatic encephalopathy?
They increase gut transit rate and acidify the stool, inhibiting the proliferation of ammonia forming bacteria. This means less ammonia is produced which is helpful as hepatic encephalopathy is caused by ammonia boil up.
1) Give 4 possible adverse effects of osmotic laxatives.
2) What can phosphate enemas cause?
1) flatulence, abdominal cramps, nausea and diarrhoea.
2) Local irritation and electrolyte disturbances.
1) Why are osmotic laxatives contraindicated in intestinal obstruction?
2) When should phosphate enemas be used with caution and why?
1) There is a risk of perforation.
2) heart failure, ascites, electrolyte disturbances. This is because they can cause significant fluid shifts.
What is the main aim when treating a patient with osmotic laxatives?
To get the patient to be able to pass about 3 soft/ loose stools per day. Any more and the dose should be reduced.
Before prescribing a phosphate enema, what treatment might be considered first and why?
Glycerol suppository because they are less likely to cause electrolyte disturbances. Phosphate enemas are also quite uncomfortable and can cause irritation so should be reserved for second line treatment.
