Laxatives, osmotically acting

Lactulose (e.g., Chronulac) Cramps, flatulance, nausea, vomiting. PO. Metabolized in intestine to lactate which acts as a laxative osmotically and by lowering pH. 

Bisacodyl is a stimulant laxative that does not take long to act and is therefore useful in acute constipation. The bulk-forming laxative ispaghula husk takes longer to act when compared with bisacodyl but is useful for long-term administration. Lactulose, which is an osmotic laxative, has a lag time of about 48 hours before onset of action. Loperamide and kaolin and morphine mixture are antidiarrhoeals used in acute diarrhoea. 

Lactulose is an osmotic laxative acting by retaining fluid in the bowel. It takes a long time to act, generally up to 48 hours, and may cause abdominal discomfort. 

Saline laxatives like MgS04, Mg(OH)2, Mg2 Citrate and Na+ Phosphates act via their osmotic pressure to retain water in the colon. Other osmotic laxatives are carbohydrates such as lactulose, glycerin, sorbitol, and mannitol. They are not absorbed and are resistant to digestion in the small intestine. Most agents are orally administered. It should be noted however that glycerin, sodium phosphates and sorbitol are formulated for rectal use. From lactulose lactic and acetic acids are formed by intestinal bacteria and apart from its osmotic effects it thus acidifies the content of the colon. The reduction of the pH stimulates motility and secretion. 

Since the disaccharide lactulose cannot be hydrolyzed by digestive enzymes, it also acts as an osmotic laxative. Fermentation of lactulose by colon bacteria leads to acidification of bowel contents and a reduced number of bacteria. Lactulose is used in liver failure to forestall hepatic coma by preventing bacterial production of ammonia and its subsequent absorption (absorbable NH3 —< nonabsorbable NH4 ). Another disaccharide, lac-titol, produces a similar effect. 

Lactulose is a synthetic disaccharide. Taken orally, it is unaffected by small intestinal disaccharidases, is not absorbed and thus acts as an osmotic laxative. Tolerance may develop. Lactulose is also used in... 

It is broken down by colonic bacteria, mainly to lactic acid, to produce a local osmotic effect and therefore takes much longer to act than inorganic osmotic laxatives. 

Osmotic laxatives are salts that act osmotically by retaining the water they are given with, or by drawing water into the bowel from the body. This accelerates transfer of gut... 

Various ideas have been considered by which lactose promotes its laxative effect. Perhaps the most probable one is that the sugar acts as a hy-dragog and, as such, results in a water purgation. Possibly this is due to slow hydrolysis and absorption of lactose, thus maintaining a high osmotic pressure in the lumen of the intestines. This increases the water content and distends the intestines which, in turn, stimulates peristaltic action. The subject has been extensively reviewed 34) ... 

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