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Purgatives and Laxatives


Laxatives are milder in action and deal with evacuation of rectum. With use of laxatives, there is elimination of formed stools.


Cathartics are severe in action and deal with evacuation of colon. With their use, liquid form of stool is eliminated.


In between the two.

Functions Of Colon
  • Modification of consistency

Maintenance of consistency of stool through reabsorption of water. More water is reabsorbed, stool will harder.

  • Storage of fecal material
  • Evacuation takes place only when it is convenient for person.
Factors affecting function of colon

1.      Diet

Diet rich in fiber content will produce a softer consistency of stool

2.      Water intake

Also plays important role

What is constipation ?

Different in different parts of world. It is based on culture as well e.g. in west, passing 2 stool/week is no constipation, but in the east, passing 1 stool in one day is constipation.

If person is straining hard and consistency of stool is also hard, it is constipation and usually is said that 2 stools /week are constipation.

  1. Diet

Diet lacking fiber content will lead to constipation

  1. Structural abnormalities

Hemorrhoids and anal fissure. In these, patient is reluctant to pass stool.

  1. Tumors of colon can cause constipation
  2. Intestinal obstruction
  3. Drugs

a.      Opioids
b.      Anticholinergics
c.       TCAs
d.      Calcium channel blockers

  1. Systemic diseases
  • Hypothyroidism
  • Diabetes mellitus
  • Parkinsonism
  1. Idiopathic
Management of constipation
  1. To remove the cause
  2. Diet changes
  3. Use of drugs –mostly wrongly described.


Bulk Purgatives

Hydrophilic colloids

  • Ispaghula Husk
  • Bran
  • Methylcellulose
  • Psyllium seed
Stimulant Purgatives

Anthraquinone derivatives

  • Senna
  • Cascara
  • Aloe

Diphyenyl methane derivatives

  • Bisacodyl
  • Phenolphthalein –withdrawn due to cardiotoxicity

Castor oil

Osmotic Laxatives

Saline Purgatives

  • Magnesium sulfate
  • Magnesium Hydroxide
  • Sodium Phosphate

Non-absorbable Sugars

  • Lactulose
  • Sorbitol


  • Glycerin
Stool Softeners
  • Sodium docusate,
  • Calcium docusate,
  • Potassium docusate
  • Mineral Oil
5 HT4 Receptor Agonist


Bulk Forming Purgatives

Mechanism of Action

Fiber  in our diet is:

A. Partly fermented

B. Unfermented

Fermented portion is converted into short chain fatty acids which have got prokinetic activity (they increase motility and secretion)

Unfermented portion imbibes water and increases bulk of stool due to this there is distention and increase in peristalsis.

Side Effects

  1. Abdominal discomfort
  2. Allergic reaction (with psyllium seeds)


  1. Mainly constipation
  2. Irritable bowel syndrome
  3. Diverticulosis
  4. When staining of stool is to be avoided

Stimulant Purgatives

Powerful purgatives

Anthraquinone Purgatives

Mechanism of Action

Contain active principle EMODIN which is a glycoside. It is passed into colon where it is acted upon by bacteria and they liberate ANTHROL which has prokinetic activity

Take a few hours (5-6 hours) to produce their actions.

Side Effects

1.      Melanosis coli

Harmless pigmentation of colonic mucosa. It may be due to use of these drugs or due to pigment rich bacteria.

2.      Cathartic colon

when used for long period of time, abnormal dilation of colon occurs and haustrations are lost. Damage to muscularis mucosae and neurons of myenteric plexus takes place.

These two adverse effects are reversible in some persons.

Diphenylyl methane Derivatives


Mechanism of Action

Hydrolysed in gut through deacetylation and converted to active form which produces low grade inflammation as a result of which motility and secretions are increased.

Take 5-6 hours for action to occur.


  1. Constipation
  2. Prepration of bowel for Radiographic Studies

Side Effects

  1. Abdominal pain/discomfort
  2. Few allergic reactions (rarely Steven’s Johnsons syndrome)

Castor Oil

Oldest purgative largely used by quacks.

—  02 components

a.      Triglyceride – Glycerol & Ricinoleic acid
b.      Proteins

Triglyceride component is acted upon by pancreatic lipases as result of which glycerol and ricinoleic acid is formed. Ricinoleic acid has prokinetic activity.

Prolonged use is prohibited, it can damage intestinal mucosa as well as intestinal neurons.

Fecal Softeners


Softens stool

Cause accumulation of water in the lumen of colon because of which they soften the stool.

Motility of gut

Increased by stimulating cAMP

Emulsifies colonic contents by increasing the penetration of water into stool.

Disrupts mucosal barrier

Interfere with absorption of fat soluble vitamins (A, E and K)

—  Can interfere with absorption of different drugs

Side Effects

—  Mainly GIT

—  Abdominal Cramps, Pain, Nausea, Bitter In Taste

—  Hepatotoxicity has been feared on prolonged use

Liquid Paraffin

A viscous mixture of petroleum hydrocarbons with a lubricant action

Introduced as laxative at start of 19th century and largely used then.

Taken for about 2-3 days.


Helps in relieving constipation as it coats the stool.

Side Effects

—  Unpleasant to swallow

—  Interference with absorption of fat soluble vitamin

Osmotic Purgatives

—  Not absorbed in small intestine & retain water due to osmolar action

—  By absorbing water, increase the bulk of stool because of which there is distention of colon and increase in motility

—  Magnesium salts can increase secretion of CCK, which aids in purgative action of Mg.


  1. Preparation of bowel before surgery
  2. Preparation of bowel before colonoscopy
  3. In food and drug poisoning
  • Glycerine

Given in form of suppository. Acts in 02 ways

  1. Osmotic action
  2. Lubricant action
  • Lactulose

Neither digested nor absorbed. Converted into organic acid, decrease pH of colon, converts ammonium into non-absorbable ammonium ion and thus decreases ammonia absorption.


Hepatic encephalopathy


Mg salts in renal diseases

Na salts in congestive heart failure and patients suffering from Na retaining conditions

Prolonged use

Electrolyte and fluid imbalance.

—  Side Effects

  • Renal and cardiac disease
  • Abdominal distension
  • Flatulence


—  Partial agonist at serotonin 4 receptors and has high affinity for these receptors as compared with 5HT3 receptors.

—  Resembles serotonin and increases release of Acetylcholine and  calcitonin Gene Related Peptides by acting on pre-junctional serotonin 4 receptors.

—  Increases cAMP dependent chloride efflux thus increases secretion, motility

—  Prokinetic activity is seen in stomach and small/large intestine.


  • In chronic constipation when all other remedies fail.
  • Gastropharesis
  • Irritable bowel syndrome

Adverse Effects

  • Diarrhea
  • Abdominal discomfort
  • Flatulence
  • Headache

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