Hyperosmolar laxatives

Hyperosmolar laxatives

Hyperosmolar laxatives work by drawing water into the intestine,thereby promoting bowel distention and peristalsis. They include:

§    glycerin

§    lactulose

§    saline compounds (magnesium salts, sodium biphosphate, sodi-um phosphate, polyethylene glycol [PEG], and electrolytes).

Pharmacokinetics

The pharmacokinetic properties of hyperosmolar laxatives vary.

Direct placement

Glycerin is placed directly into the colon by enema or suppository and isn’t absorbed systemically.

Minimal absorption

Lactulose enters the GI tract orally and is minimally absorbed. As a result, the drug is distributed only in the intestine. It’s metabo-lized by bacteria in the colon and excreted in stool.

Introducing ions

After saline compounds are introduced into the GI tract orally or as an enema, some of their ions are absorbed. Absorbed ions are excreted in urine, the unabsorbed drug in stool.

Pegging PEG

PEG is a nonabsorbable solution that acts as an osmotic drug, but doesn’t alter electrolyte balance.

Pharmacodynamics

Hyperosmolar laxatives produce a bowel movement by drawing water into the intestine. Fluid accumulation distends the bowel and promotes peristalsis, resulting in a bowel movement.

Pharmacotherapeutics

The uses of hyperosmolar laxatives vary.

§    Glycerin is helpful in bowel retraining.

§    Lactulose is used to treat constipation and to reduce ammonia production and absorption from the intestines in the patient with an elevated ammonia level, as occurs in cirrhosis and liver failure.

§    Saline compounds are used when prompt and complete bowel evacuation is required.

Drug interactions

Hyperosmolar laxatives don’t interact significantly with other drugs. However, oral drugs given 1 hour before administering PEG have significantly decreased absorption. (See Adverse reactions tohyperosmolar laxatives.)