Osmotic purgatives work by retaining water osmotically in the intestine, distending the bowel and indirectly increasing peristalsis. Common osmotic purgatives include magnesium and sodium salts like magnesium sulfate, magnesium hydroxide, sodium sulfate, and sodium phosphate. Lactulose is also an osmotic purgative, as the bacteria in the colon break it down into products that retain water osmotically. Osmotic purgatives differ in dose, palatability, and risk of systemic toxicity. Their main uses are in preparing the bowel before surgery or colonoscopy and in food/drug poisoning.

1. PURGATIVES-
Classification& Osmotic
Purgatives

2. CLASSIFICATION
• 1)Bulk forming
Dietary fibre: Bran,phyllium(plantago)
Isphagula,Methyl cellulose
• 2)Stool softener
Docusates(DOSS),Liquid paraffin
• 3)Stimulant purgatives
A.Diphenylmethanes-
Phenolphthalein,Bisacodyl,Sodium picosulfate
B.Anthraquinones(Emodins)-

3. Contd....
-Senna,Cascara sagrada
C) 5-HT4 agonist
Tegaserod
D) Fixed oil
Castor oil
• 4)Osmotic purgatives
Mg salts- Mg(SO)4,Mg(OH)2
Na salts-Na2(SO)4,Na3(PO)4
Na.K.tartarate
LACTULOSE

4. Osmotic Purgatives
Solutes not absorbed in the intestine→Retain
H2O osmotically→distent the
bowel→increasing peristalsis indirectly(basis
of osmotic purgatives)
All inorganic salts used as osmotic pugatives
have similar action- differ only in
dose,palatability&risk of systemic toxicity

5. Mg++ ions release cholecystokinin which may aid
purgative action of Mg salts.
• Mg(SO)4(Epsom salt):5-15g,bitter in taste
• Mg(OH)2(as 8% w/w suspn-milk of magnesia)
:30 ml , bland in taste, also used as antacid
• Na2(SO)4(Glauber’s salt):10-15g,bad in taste.
• Na3(PO)4:6-12g, taste is not unpleasant.
• Na.K.tartrate(Rochelle salt):8-15g, relatively
pleasant tasting.

6. LACTULOSE
A semi synthetic disaccharide of fructose and
lactose.
Neither digested nor absorbed in the small
intestine.
It is broken down in the colon by bacteria to
osmotically more active products
• Dose-10g BD taken with planty of water

7. The breakdown products of lactulose are
acidic→NH3 produced by bacteria in colon is
converted to ionised NH4+ salts and is not
absorbed
So it causes redn in bld NH3 conc. By 25-50%
in patients with hepatic encephalopathy.
(for this purpose,dose shud b increased to 20g
TDS or more)

8. • C/I of osmotic purgatives:-
Mg. Salts are contr. Indicated in RENAL INSUFFICIENCY
Na. Salts shud not b given to patients of CONGESTIVE
HEART FAILURE and other Na+
retaining states.
• Uses-preparation of bowel b4 surgery& colono-
scopy,in food/drug poisoning& as after purge in
treatment of tapeworm infestation.
They r practically not used 4 the treatment of
constipation bcoz afterconstipation is common.

9. THANK U....