Wednesday, December 19, 2012


Stimulant/irritant purgatives/cathartics

How do they act?
They basically act on intestinal mucosa or nerve plexuses to
  • Decrease water absorption from the bowel lumen
  • Increase secretions of fluid into the bowel
  • Stimulate bowel motility 
They are thought to inhibit Na+ K+ ATPase in the basolateral membrane
Secretion is enhanced by activation of cAMP in the crypt cells
& increased prostaglandin synthesis :)

They act on the colon rather than the ileum and produce evacuation within 8-10 hours after administration
This makes them particularly suitable for administration at night ^__^

Examples: Anthraquinone Derivatives, Diphenylmethane Derivatives, Castor Oil, Aloe

When are they used?
They are used to treat constipation in bed ridden patients
Also used to treat constipation due to chronic morphine administration

When are they contraindicated?
Spastic constipation (irritable bowel)
Subacute or chronic intestinal obstruction
Pregnancy (They can reflexly contract the gravid uterus)

Long term use is discouraged due to adverse effects
Larger doses may lead to excessive purgation and electrolyte imbalance (Hypokalemia may occur)
Cramps, skin rashes and fixed drug eruptions are other side effects
Colonic atony, melanosis - On prolonged use
Amount secreted in milk is sufficient to cause purgation in suckling infant

Did you know?
With use of cascara sagrada or senna a pink-red, red-violet, redbrown, yellow-brown, or black discoloration of urine may occur - But that's nothing to worry about :)


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