05 Drugs For Constipation

Drugs for Constipation
(Purgatives or Laxatives )
Prof. Alhaider
Dept. of Pharmacology
H 1434
Definition of Constipation: Too infrequent

passage of stool that may be due to decreased
motility in colon or due to difficulty in
evacuation.
Causes (see Table)
Diet : Decrease in water intake and fiber contents
of diet.
Local Painful Conditions: Anal fissures, piles.

Lack of muscular exercise.
Drugs : Muscle relaxants, Anticholinergics,
Calcium channel blockers

However, Doctors (some times) may consider a
source of chronic constipation. How?
Treatment of Constipation
General Measures :
1. adequate fluid intake.
2. high fiber contents in diet.
3. Regular exercise
4. Regulation of bowel habit.
5. Avoid drugs causing constipation.
Drugs (laxatives, purgatives, cathartics):
Drugs that hasten the transit of food
through the intestine by several methods :
Classification of laxatives or purgatives

1. Bulk Purgatives : Increase volume
of nonabsorbable solid residue.
2. Osmotic Purgatives : Increase water
content in large intestine.
3. Stimulant Purgatives : Increase
motility and secretion.
4. Fecal softeners (lubricants) : Alter
the consistency of feces easier to
pass.
I. Bulk Purgatives
Mechanism of Action
Non absorbed hydrophilic colloids
Increase the bulk of intestinal contents by
water absorption mechanical pressure
on the walls of intestine stimulation of
stretch receptors peristalsis.
Note: 1 gm of Carrot absorbs 20 gm of water.
Members
1. Dietary fibers : undigested polysaccharide
vegetables, fruits, grains, bran, pectin.
2. Natural plant products & semi synthetic
hydrophilic colloids (very important)
Psyllium seed, methyl cellulose
Carboxymethyl cellulose (CMC).
3. Synthetic non absorbed resins
Calcium polycarbophil.
Side Effects
1. Delayed onset of action ( several days 1-3).
2. Intestinal obstruction (should be taken with
enough water).
3. Malabsorption syndrome, abdominal
distention.
4. Interfere with other drug absorption e.g. iron,
calcium, and cardiac glycosides.
Clinical Uses
Hemorrhoids; Pregnancy; Colostomy; ileostomy;
anal fissure; IBS, UC, Chronic diarrhea ass with
diverticular disease.
II - Osmotic Purgatives
Water Soluble but non absorbable compounds
Increase water content in large intestine.
Members
1. Organic (Sugars) : lactulose (semisynthetic
disaccharide of fructose and galactose).
2. Non-organic (Saline purgatives) : Magnesium
salts, sodium or potassium salts.
1. Organic Osmotic (Lactulose)

Metabolized by colonic bacteria into
fructose and galactose.
These sugars are fermented into lactic acid
and acetic acid that function as osmotic
laxatives.
Side Effects
1. Delayed onset of action (2-3 days)
2. Abdominal cramps and flatulence.
3. Electrolyte disturbance.
B.
Why Lactulose is commonly used in liver

?cirrhosis
:Mechanism
Lactulose
Lactic acid + Acetic Acid
acidification of the colon
ammonia
absorption
Dose: 15 ml for constipation and 30 ml for liver cirrhosis
Saline Purgatives (e.g: Magnesium). 2

Mechanism of Action
Are poorly absorbed salts. They remain in
the bowel and retain water by osmosis
thereby increasing the volume of feces
distension peristalsis evacuation of
watery stool.
Rapid effect (within 1-3h ).

Magnesium sulphate (Epsons salt ).
Magnesium oxide (milk of magnesia).
Sodium phosphate.
Uses
1. Treatment of acute constipation
2. Prevention of chronic constipation
Can you mention other uses of magnesium
?sulphate
Side Effects
1. Intravascular volume depletion.
2. Electrolyte fluctuations: severe in childre
Contraindications
1. Elderly patients
2. Renal insufficiency.
3. Sodium salts in CHF.
4. Magnesium salts renal failure, heart block,
CNS depression, neuromuscular block.
Balanced polyethylene glycol (PEG) Movicolc

Balanced isotonic solution of osmotically
active sugar that contain:
polyethyleneglycole and , NaCl, KCl, Na
bicarbonate
No intravascular fluids or electrolyte shifts
No flatus or cramps
Lavage solution
Used for complete cleansing prior to
gastrointestinal endoscopic procedures (4L
over 2-4 hours).
Also, small doses used for treatment or
III - Stimulant Purgatives (cathartics)

Mechanism of Action :
act via direct stimulation of enteric nervous
system peristalsis & purgation.
Members
1. Bisacodyl.
2. Anthraquinone derivatives.
3. Castor oil.
Bisacodyl
- Acts on large intestine ( weak ).
- Onset time 6-10 h, taken at night.
Castor Oil
Fixed oil degraded by lipase in upper small
intestine ricinoleic acid + glycerin
Ricinoleic acid irritates mucosa.
Acts on small intestine (strong ).
5-20 ml on empty stomach in the morning.
O.T. = 4 h.
Anthraquinone derivatives
Senna, Cascara, Aloes
In colon, glycosides are hydrolyzed by

bacteria into emodin + sugar
The absorbed emodin has direct stimulant

action on myenteric plexus smooth
muscle contraction defecation.
Bowel movements in 12 h (orally) or 2 h

(rectally).
Given at night.
Brown pigmentation of the colon (melanosis
coli).
Side Effects of Stimulant Laxative

1. Abdominal cramps may occur.
2. Prolonged use dependence & destruction
of myenteric plexus and atonic colon.
Leading to chronic constipation
Contraindications
3. Senna in lactation
4. Castor oil in pregnancy reflex
contraction of uterus abortion.
IV - Fecal Softeners (Lubricants)

Are non absorbed drugs that soften the feces
thus promoting defecation.
May be given orally or rectally.
Members :
1. Surfactants
decrease surface tension of feces
e.g. Docusate (sodium dioctyl sulfosuccinate).
is given orally or enema.
Is commonly prescribed in hospitalized
patients to minimize straining.
2. Glycerin (Suppository). (Commonly used

after Surgery)
3. Mineral oil (Liquid Paraffin) (good for
radiology preparation)
Side effects of liquid paraffin

1. Not palatable
2. impairs absorption of fat soluble vitamins.
3. Increase activity of oral anticoagulant.
Irritable Bowel Syndrome

It is a functional bowel disorder associated by
characteristic cluster of symptoms in the
absence of detectable structural
abnormalities. However, it is a condition of
diverse pathophysiology associated with
abnormalities in GIT motility (either diarrhea
or constipation). Prevalence is around 15% of
population. Recent work concentrated to the
important role that serotonin plays in such
syndrome. Therefore, many of drugs that
used for Rx of IBS may act by serotonergic
mechanisms (see Table).
1) 5-HT3 receptor antagonists (Alosetron and

Cilanestron) are used for diarrhea associated IBS.
Dose: 1 mg BID
Side Effects: Constipation; Ischemic Colitis
2) 5-HT4 partial agonist (Tegaserod): This is used
for constipation-predominant IBS in women and also
recommended for Rx of chronic constipation.
MOA: Stim. Of 5-HT4 receptor enhances the release
of ACH. The latter increases peristalsis.
Dose: 6 mg BID for 8 weeks.
Side Effects: Diarrhea; Headache
Limitation: does not have significant effect on
symptoms of abdominal pain and discomfort.

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Drugs for Constipation

Definition of Constipation: Too infrequent

Local Painful Conditions: Anal fissures, piles.

Calcium channel blockers

Classification of laxatives or purgatives

1. Organic Osmotic (Lactulose)

Why Lactulose is commonly used in liver

Lactic acid + Acetic Acid

acidification of the colon

Saline Purgatives (e.g: Magnesium). 2

Rapid effect (within 1-3h ).

Balanced polyethylene glycol (PEG) Movicolc

III - Stimulant Purgatives (cathartics)

In colon, glycosides are hydrolyzed by

The absorbed emodin has direct stimulant

Bowel movements in 12 h (orally) or 2 h

Side Effects of Stimulant Laxative

IV - Fecal Softeners (Lubricants)

2. Glycerin (Suppository). (Commonly used

Side effects of liquid paraffin

Irritable Bowel Syndrome

1) 5-HT3 receptor antagonists (Alosetron and

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