Saline and Osmotic Laxatives

Saline and Osmotic Laxatives

Introduction. Agents that act as osmotic laxatives include various Mg2+ salts; the sulfate, phosphate, and tartrate salts of Na+ and K+; the disaccharide lactulose; glycerin; sorbitol and mannitol; and polyethylene glycol-electrolyte solutions. They are poorly and slowly absorbed and act by their osmotic properties in the luminal fluid.

Osmotic Laxatives (Unabsorbed Carbohydrates: Lactulose, Glycerin, Sorbitol, and Mannitol). Osmotic laxatives, whose structures are shown below, are not absorbed and are resistant to digestion in the small intestine. The primary osmotic effect of lactulose may be augmented in the distal ileum and colon by bacterial metabolism of the disaccharide to fructose and galactose, then to lactate, acetate, and formate. These metabolites add osmotic strength and are only partially absorbed. The concomitant reduction in luminal pH also may enhance motility and secretion.