Osmotic Purgatives: Lactulose, Polyethylene Glycol etc

Osmotic Purgatives: Lactulose, Polyethylene Glycol etc

January 5, 2020 0 By Bertrand Dibbert


Hey welcome back guys. In this video we will see osmotic purgatives. So, let’s start… Among osmotic purgatives are various saline
purgatives like Magnesium sulphate, Magnesium hydroxide, Magnesium citrate, Sodium sulphate
and Sodium phosphate. Then we have, polyethylene glycol and nonabsorbable
sugars like lactose, sorbitol and mannitol. Intestinal bacteria degrade these sugars to
short chain fatty acids which are osmotically more active. Now let’s see their mechanism of action. They retain water in the lumen by their osmotic
activity. This causes distention of bowel. Magnesium containing preparations also cause
release of cholecystokinin on top of this. All of these results in increased peristaltic
activity leading to bowel evacuation. Saline and polyethylene glycol produce watery
stool within 1-3 hours. Whereas lactulose soft stool. And its effect appears after 1-3 days. As water is lost along with osmotic purgatives,
it is important to maintain adequate water intake when using them. So, this was mechanism of action. Now let’s see uses of osmotic purgatives. They are used in acute and chronic constipations. Saline is used clear the bowel after food
or drug poisoning and after some anthelmintic drugs like niclosamide to flush out worms. Saline and polyethylene glycol are used to
prepare bowel for radiologic or endoscopic examination and for surgery. Lactulose is used in hepatic encephalopathy. Increased ammonia level is a major problem
in hepatic encephalopathy. Now we have just seen that intestinal bacteria
degrade lactulose into short chain fatty acids. This makes the lumen more acidic which leads
to conversion of ammonia into ammonium. As its polar, it cannot be absorbed. This effect along with purgative action of
lactulose results in increased elimination of ammonia. This reduces ammonia level in blood. So, these were uses of osmotic purgatives. Now let’s move to adverse events. Cramping is a common side effect with osmotic
purgatives. Repeated use of saline purgatives can cause
fluid and electrolyte imbalance. Lactulose causes flatus and cramping due to
bacterial digestion. Magnesium and phosphate containing preparations
should be used cautiously in patient with renal or cardiac disease or pre-existing electrolyte
abnormality. Sodium preparations should be avoided in patients
of congestive heart failure. Thats its friends for osmotic purgatives. If you liked this video. Please spread it among your friends and colleagues. If you are a visual learner, you will love
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