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, Pink Lady Enema

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: 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. Safety
      1. Appears safe in children and adults
      2. In 2017, studies initiated to determine if young children absorb Ethylene Glycol with neurotoxicity based on case reports
         1. No evidence at this point that this is a significant concern
         2. (2017) Presc Lett 24(4): 23
   9. References
      1. Gremse (2002) Clin Pediatr 41:225-9 [PubMed]
      2. Pashankar (2003) Arch Pediatr Adolesc Med 157:661-4 [PubMed]
      3. Voskuijl (2004) Gut 53:1590-4 [PubMed]
6. Preparations: Magnesium salt Osmotic Laxatives
   1. Rapid onset (within 3 hours)
   2. Avoid longterm use due to Electrolyte loss risk
      1. These agents are typically used once as part of a bowel regimen
   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 twice daily as needed
      3. Concentration 800 mg/5 ml
         1. Children: 0.5 cc/kg/day divided twice daily as needed
      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 to 10 ounces (240 to 300 ml) orally daily as needed
         2. Child: 4 ml/kg up to 200 ml orally daily as needed
7. Preparations: Poorly-absorbed sugars (may be used in Renal Failure)
   1. Largely replaced by Polyethylene glycol 3350 (PEG, Miralax)
   2. 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 to 30 ml orally daily
         2. Child (10 mg/15 ml): 1-3 cc/kg/day divided daily to twice daily
   3. Lactitol
      1. As effective as Lactulose with less pain and Flatus
      2. Pitzalis (1995) Pediatr Med Chir 17(3):223-6 [PubMed]
   4. 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
8. 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
9. 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. Pink Lady Enema (1/2 Fleet Enema, 100 ml Docusate, 60 ml Mineral Oil, 60 ml Magnesium Citrate)
   4. Alternative agent: Tap Water Enema
   5. 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
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