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).
The pharmacokinetic properties of hyperosmolar
laxatives vary.
Glycerin is placed directly into the colon by enema
or suppository and isn’t absorbed systemically.
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.
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.
PEG is a nonabsorbable solution that acts as an
osmotic drug, but doesn’t alter electrolyte balance.
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.
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.
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.)
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