Pharmacology & Anesthesia: Bowel Regimen

Dietary Fiber

• Mechanism: Increases Colonic Distention to Promote Stool Propulsion
• Recommended Daily Fiber Intake: 20-25 g/Day
• May Take Weeks to See Effects
• Side Effects:
  • Bloating
  • Flatulence

Bulk Forming Laxatives

• Mechanism: Retain Fluid to Increase Fecal Mass
  • Soften Stool & Increase Frequency
• Must Also Sustain Abundant Oral Water Intake
  • Poor Water Intake Can Cause Bloating & Obstruction
• Benefits Debated – Limited Objective Evidence to Support Use
• Forms:
  • Psyllium (Metamucil)
    • PO (Powder) 2.5-30 g/Day
  • Methylcellulose (Citrucel)
    • PO (Powder) 2 g 1-3x/Day
  • Wheat Dextrin (Benefiber)
    • PO (Powder) 4 g 3x/Day
• Side Effects:
  • Bloating
  • Flatulence
  • Nausea

Osmotic Laxatives

• Mechanism: Non-Absorbable Substances Pull Fluid into the Bowel Lumen
• Forms:
  • Polyethylene Glycol (PEG/MiraLAX)
    • PO (Powder Packets) 1-2x 17 g Packets Daily
  • Lactulose
    • PO (Powder Packets) 1-4x 10 g Packets Daily
  • Sorbitol
    • PO (70% Solution) 30-45 cc
    • Rectal Enema (25-30% Solution) 120 cc
  • Magnesium Hydroxide (Milk of Magnesia)
    • PO (Liquid):
      • 400 mg/5 cc: 30-60 cc/Day
      • 800 mg/5 cc: 15-30 cc/Day
      • 1,200 mg/5 cc: 10-20 cc/Day
  • Magnesium Citrate
    • PO (Solution) 195-300 cc Daily
• Lactulose Also Decreases Ammonium Resorption
  • Lactulose Decreases pH Causing Ammonia Uptake by Colonic Bacteria
  • Ammonia (NH3) Converted to Ammonium (NH4)
  • Ammonium Unable to Cross Membrane & Prevents Resorption
• Side Effects:
  • Bloating
  • Flatulence
  • Nausea
  • Magnesium Compounds Can Cause Magnesium Toxicity in Renal Insufficiency

Stimulant Laxatives

• Mechanism: Stimulate the Myenteric & Auerbach Plexuses to Increase Motility
• Forms:
  • Senna (Sennakot)
    • PO (Tablet or Syrup) – Dose Varies
  • Bisacodyl
    • PO 5-15 mg Daily
    • Rectal Suppository 10 mg Daily
• Contraindications:
  • Suspected Complete Bowel Obstruction
  • Recent Anastomosis:
    • 3 Days from Small Bowel Injury
    • 5 Days from Large Bowel Injury
• Side Effects:
  • Abdominal Pain
  • Long Term Use Can Cause Loss of Haustral Folds
  • Melanosis Coli from Senna

Stool Softeners (Surfactants)

• Mechanism: Decrease Surface Tension to Allow Fluid Absorption into Stool
• Forms:
  • Docusate Sodium (Colace)
    • PO 50-360 mg Daily
    • Rectal Enema: 283 mg 1-3x/Day
  • Docusate Calcium
    • PO 240 mg Daily
    • Rectal Enema: 283 mg 1-3x/Day