Constipation and Diarrhea

  • Definition: typically fewer than 3 BM per week 
  • Classification of chronic constipation into 3 categories
    • normal transit, 
    • isolated slow transit (assessment for slow transit is done ONLY after defecatory disorders are ruled out or do not respond to pelvic floor training)
    • defecatory disorders 

  1. Laxatives
    1. Bulk Forming Laxatives or Fiber
      1. Indigestible, hydrophilic colloids that absorb water, forming a bulky, emollient gel that distends the colon and promotes peristalsis 
      2. Eg. Natural (Psyllium, Methylcellulose) Synthetic Fibers (Polycobophil) 
      3. Side effects: Bacterial Digestion of plant fibers leads to bloating and flatus
    2. Osmotic Laxatives
      1. Colon can neither concentrate nor dilute fecal fluid. Fecal water is isotonic throughout the colon. Osmotic laxatives are soluble but  non absorbable compound that result in increased stool liquidity due to obligate increase in fecal fluid
      2. Non-absorbable Sugars (Sorbitol and Lactulose) or Salts  MgOH (Milk of Magenesia) Mag Citrate, Sulfate Solution, Sodium Phosphate 
        1. Used for the treatment of acute constipation or prevent chronic constipation
        2. When taking the purgatives, patient should maintain adequate hydration 
      3. Balanced Polyethylene Glycol : PEG is an inert, non absorbable, osmotically active sugar with sodium sulfate, sodium chloride, sodium bicarbonate, potassium chloride
        1. PEG is designed such that no significant intravascular fluid or electrolyte shift occurs 
        2. Does not produce significant cramps or flatus 
    3. Stimulant Laxatives or Cathartics
      1. Multiple poorly understood mechanisms 
        1. Direct stimulant of enteric nervous system, colonic electrolytes or fluid secretion
        2. Useful for patient who are neurologically impaired and  in bed-bound patients in long-term care facilities 
      2. Anthraquinone Derivatives
        1. Aloe, Senna, Cascara 
          1. Produce BM in 6-12 hrs when given orally and within 2 hrs when given rectallly
          2. Chronic use causes "melanosis coli"
      3. Diphenylmethane Derivatives 
        1. Bisacodyl
          1. Tab or suppository 
          2. Acute or Chronic Constipation
  2. Stool Softner
    1. Soften stool material, permitting water and lipids to penetrate
    2. Oral or Rectal administration
    3. Eg. Docusate (oral or enema), Glycerin suppository, 
  3. Lubricant: Mineral Oil : Coates the stool and makes it lubricated, thus prevents water absorption from stool. Useful for patient with fecal impaction. Aspiration can lead to severe lipid pneumonitis, Long term use causes fat soluble vitamin deficiency. NOT palatable
  4. Chloride Channel Activators
    1. Lubiprostone: Prostanoic acid derivatives labeled for use in IBS-C
      1. Stiumulates ClC-2 in SI
      2. Causes N in upto 30 % of patients due to delayed gastric emptying 
    2. Linaclotide: Different mechanism of Cl secretion than Lubiprostone 
  5. Opioid receptor antiagonists
    1. Methylnatrexone Bromide
    2. Alvimopan
  6. Serotonin 5-HT4 R agonists
    1. Tegaserod 
Ref: Basic and Clinical Pharmacology, 13th edition. 

Acute Diarrhea

Chronic Diarrhea


Lancet 2012; 379: 2466–76 

Lancet 2012; 379: 2466–76