Osmotic laxatives

Osmotic laxatives

These sugar-derived agents (lactulose, its synthetic analogue lactitol, and sorbitol) increase water secretion into the bowel via osmotic action, resulting in increased bulk size, thereby stimulating colonic peristalsis. These agents are often employed in patients with slow peristaltic activity who do not respond to fibre agents.

Lactulose is a synthetic derivative of lactose and is administered orally. Hardly absorbed by the GI tract, colonic microorganisms convert it into organic acids such as lactic acid and acetic acid. The consequent decrease in pH as well as lactulose'sosmotic effects result in increased motility and improved consistency of the faeces. Treatment with lactulose usually results in a softening of the faeces in one to three days.

Sorbitol is a hyperosmotic laxative and has been recommended as a primary agent in the treatment of functional constipation or as a vehicle for rectally administered enemas. In extremely high dosages, oral sorbitol can exert a rapid laxative effect.


Which of the following statements is true?


Lactulose is effective as a laxative agent because