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Clinician’s Corner: Laxatives that cause softening of feces in 1-3 days

Generic Representative Brand Dosage
          Docusate sodium Colace® 50, 100 50-360mg/day
          Docusate calcium Surfak 240mg 50-360mg/day
MINERAL OIL Kondremul® 15-30ml
LACTULOSE Chronulac®, Constulose® 15-30ml
SORBITOL 30-50gm
PEG 3350 soln Miralax® 1 cap 17gm in 8oz water

Stool softeners

USE: : Beneficial in rectal conditions, like surgery and hemorrhoids in which passage of a firm stool is painful.  Generally used for prevention of constipation, not treatment.

HOW IT WORKS: docusate increasing wetting efficiency of intestinal fluid, acting like a soap, thereby softening fecal mass.  Helps fat and water to mix together to soften feces. If you are curious, cut open a capsule, add to a small prescription vial, add water and shake. Looks like dishwashing soap.


  • Take with fill glass of water.
  • Do not take with any mineral oil containing laxatives, as this will lead to the oil’s absorption and cause hepatotoxicity.

Available as:

  • Colace® 100mg is expensive, have our staff show you the docusate sodium, which is a generic for Colace.
  • Surfak® (docusate calcium) 240mg    1 capsule daily

Emollients  (lubricants)

USE : prophylactically in patients who should not strain (rectal surgery, post heart attack)

HOW IT WORKS: Softens fecal contents by coating them, thereby preventing the colonic absorption of water.


  • Do NOT give with stool softeners (Colace, Surfak)
  • Avoid if you have the potential to aspirate such as GI reflux, as this could cause lipid pneumonia
  • May cause anal leakage leading to anal itching. May stain clothes/furniture.
  • If used long term, supplement with fat soluble vitamins (ADEK) as this will impair their absorption.
  • Take on an empty stomach

Available as:

  • Mineral oil: dose 15-45ml HS
  • Kondremul® ( mineral oil emulsion) dose : 30-75ml HS

Lactulose – Chronulac® (Rx only)

USE : useful particularly in elderly patients.  Not usually first line.  Takes at least 24-48 hours for action.

HOW IT WORKS: it is two sugar molecules linked together and is used orally or rectally. Broken down by bacteria in the colon to form lactic acid, formic acid, acetic acid and carbon dioxide.  Increase osmotic pressure and acid levels in  the colonic contents, thus increasing stool water content and softening.


  • Give with fruit juice, water or milk to increase palatability.
  • Will cause significant gas, leading to -flatulence, abdominal pain and cramping.
  • May also cause diarrhea and electrolyte imbalances.
  • Because it contains galactose & lactose, use with caution in diabetics.
  • If used over 6 months in elderly measure: electrolytes (K & Cl) & carbon dioxide periodically.

Available as: Chronulac® (lactulose) 10gm / 15ml available in pints and quarts

Dosage 15-30ml daily.  Increase to 60ml if necessary. Prescription only.


These are alcohol sugars that are used as sweeteners.  Ingesting excessive sugar free candy or sugar free gum can cause diarrhea to occur. 

Polyethylene glycol laxatives

Indication:  Used for colon cleansing before diagnostic procedures or colorectal operations.  Can also be used in lower doses for chronic constipation.

Mechanism: is an osmotic laxative that large molecules draw water into the gut, and increased volume results in distention of the intestines, increasing peristalsis and bowel motility, and softening stools.

FYI: the number 3350 is the molecular weight of this particular polyethylene glycol.

Patient information

  • May cause abdominal cramping, flatulence, rectal irritation and incontinence.
  • Miralax : contains PEG 3350 (this product for long term management of constipation)

Dosage: 1 capful (17gm) in 8 oz of water once daily.

  • Available prescription sizes: 255gm (2 weeks supply) and 527gm as (1 month supply).
  • Caution: some generic caps are “oversized” and have a fill line inside. May cause over dosage—more than 17 grams. You can measure 17 grams by using a “heaping” tablespoonful.
  • Also available over the counter in 7-day, 14-day and 28-day packaging.