Osmotic PurgativesSolutes not absorbed in the intestine→RetainH2O osmotically→distent thebowel→increasing peristalsis indirectly(basisof osmotic purgatives)All inorganic salts used as osmotic pugatives have similar action- differ only indose,palatability&risk of systemic toxicity
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.
LACTULOSEA 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
The breakdown products of lactulose are acidic→NH3 produced by bacteria in colon is converted to ionised NH4+ salts and is not absorbedSo 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)
• 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.