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, sodium 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 metabolized 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.
Warning!
Adverse reactions to hyperosmolar laxatives
Adverse reactions to most hyperosmolar laxatives involve fluid and electrolyte imbalances.
Glycerin
- Weakness
- Fatigue
Lactulose
- Abdominal distention and cramps, gas
- Nausea and vomiting
- Diarrhea
- Hypokalemia
- Hypovolemia
- Increased blood glucose level
Saline compounds
- Weakness
- Lethargy
- Dehydration
- Hypernatremia
- Hypermagnesemia
- Hyperphosphatemia
- Hypocalcemia
- Cardiac arrhythmias
- Shock
Polyethylene glycol
- Nausea
- Explosive diarrhea
- Bloating
Drug interactions
Hyperosmolar laxatives don’t interact significantly with other drugs. However, oral drugs given 1 hour before administering PEG have significantly decreased absorption.
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