Osmotic Laxative

Aka: Osmotic Laxative, Osmotic Cathartic, Magnesium Hydroxide, Milk of Magnesia, Magnesium Citrate, Polyethylene glycol, PEG, Miralax, Sorbitol, Fleets Enema, Fleet Enema, Phospho-Soda

1. See Also
   1. Laxative
   2. Constipation
   3. Functional Constipation
   4. Pediatric Constipation
2. Mechanism
   1. Poorly absorbed, they act as hyperosmolar agents
   2. Stimulate colonic activity (via cholecystokinin)
3. Complications
   1. Hypermagnesemia (in patients with Renal Failure)
   2. Hypocalcemia (phosphate overdose)
4. Contraindications
   1. Renal Failure (except Lactulose and Sorbitol)
5. Preparations: Poorly-absorbed sugars (may be used in Renal Failure)
   1. Lactulose (Chronulac)
      1. Easier to administer to young children
      2. May cause abdominal cramping and flatus
      3. More expensive then Sorbitol ($10-30 per 480 ml)
      4. Onset of action within 24-48 hours
      5. Dose
         1. Adults: 15-60 ml PO daily
         2. Child (10 mg/15 ml): 1-3 cc/kg/day divided qd-bid
   2. Lactitol
      1. As effective as Lactulose with less pain and flatus
      2. Pitzalis (1995) Pediatr Med Chir 17(3):223-6
   3. Sorbitol 70%
      1. Less expensive than Lactulose ($7 per 480 ml)
      2. Sweet taste
      3. Dosing
         1. Adult: 15-60 ml PO daily
         2. Child: 1-3 ml/kg/day divided twice daily
6. Preparations: Magnesium salt Osmotic Laxatives
   1. Rapid onset (within 3 hours)
   2. Avoid longterm use due to electrolyte loss risk
   3. Milk of Magnesia (Magnesium Hydroxide)
      1. Cost: $3 per 360 ml
      2. Concentration: 400 mg/5 ml
         1. Adults: 15-60 ml PO qd prn
         2. Children: 1-3 cc/kg/day divided bid prn
      3. Concentration 800 mg/5 ml
         1. Children: 0.5 cc/kg/day divided bid prn
      4. Adverse effects
         1. May cause abdominal cramping in higher doses
   4. Magnesium Citrate (Citroma)
      1. Cost: $1.50 per 300 ml
      2. Dose
         1. Adult: 8 ounces PO daily prn
         2. Child: 4 ml/kg up to 200 ml PO daily prn
7. Preparations: Mineral Oil
   1. Child: 1-3 cc/kg/day divided daily to twice daily
   2. Contraindicated if aspiration risk
   3. Not recommended under age 18 months
   4. Give chilled in juice to maximize tolerability
   5. Coadminister multivitamin daily if used chronically
8. Preparations: Sodium salt Osmotic Laxatives
   1. Phopho-Soda (Osmoprep, Visicol) 2 tablespoons in 4 ounces water orally
   2. Fleets Enema (sodium phosphate) 120 ml enema
   3. Alternative agent: Tap Water Enema
   4. Precaution: Acute phosphate nephropathy (FDA Black Box Warning)
      1. Risk of permanent impact on Renal Function following use
      2. Risk Factors
         1. Diabetes Mellitus
         2. Age over 65 years
         3. Dehydration
         4. Concurrent NSAID, ACE Inhibitor, ARB or Diuretic
      3. Prevention of Renal Function impact
         1. Consider alternative Bowel Preparation if risk factors above
         2. Maintain clear fluid intake to replace fluid losses from Diarrhea
9. Preparations: Polyethylene glycol 3350 (PEG, Miralax)
   1. Similar to bowel prep solution (GoLytely, Colyte)
   2. Onset of action with 24-48 hours
   3. No salty taste
   4. More expensive then Sorbitol: $2/day
   5. Preparation
      1. Use PEG powder 17 grams (one capful)
      2. Dissolve in 240 ml (8 ounces) water or juice
      3. May chill PEG solution or mix with flavoring (e.g. Crystal Light) to improve taste
         1. If for Colonoscopy prep, avoid colored flavoring that might interfere with visibility
   6. Dose:
      1. Adult: 17 grams (1 capful) daily
      2. Child
         1. Start 0.8-1 g/kg/day (15 ml/kg/day) divided bid
         2. Adjust dose for two soft painless stools per day
         3. Taper dose over time
   7. Efficacy
      1. Safe, well tolerated and effective
      2. More effective and better tolerated than Lactulose
   8. References
      1. Gremse (2002) Clin Pediatr 41:225-9
      2. Pashankar (2003) Arch Pediatr Adolesc Med 157:661-4
      3. Voskuijl (2004) Gut 53:1590-4
10. Preparations: Not recommended
    1. Castor oil or Ricinoleic Acid (Purge)
       1. Avoid due to electrolyte disturbance
       2. Adult: 15-30 ml PO qhs
       3. Child: 5-15 ml PO qhs
    2. Soapsuds Enemas (never use)
       1. Risk of irritation or hemorrhagic colitis