Osmotic laxatives The most commonly used osmotic laxatives include magnesium hydroxide, sodium potassium tartrate, lactulose and glycerol.
The hyperosmotic laxatives are glycerin and lactulose (Chronulac, Duphalac), both of which act by holding water within the intestine.
Lactulose may also increase peristaltic action of the intestine.
Lactulose is composed of two sugar molecules; galactose and fructose, and should not be administered to patients who require a low galactose diet.