Laxatives and Purgatives
They are substances that regulate fecal consistency and stimulate or promote defecation. The uses of these agents as aperients, laxatives, cathartics or purgatives depend on the intensity and severity of their actions.
- Laxatives ease defecation
- Cathartics accelerate defecation while
- Aperients is a mild laxatives
Classification of laxatives or purgatives
- Bulk Purgatives: These increase volume of non absorbable solid residue.
- Osmotic Purgatives: These increase water content in large intestine.
- Stimulant Purgatives: These increase motility and secretion.
- Fecal Softeners: These alter the consistency of feces leading to easier to pass.
- Lubricants purgatives
Pharmacodynamics of Bulk purgatives
- They are natural and semisynthetic polysaccharides and cellular derivatives
- Their hydrophilic undigested portion in the colon swells in the presence of water
- This increases the bulk of intestinal contents which stimulates mechanical pressure on the walls of intestine.
- The mechanical pressure stimulates the stretch receptors in the GIT leading to peristalsis.
Types of bulk purgatives
- Dietary fibers: Undigested polysaccharide vegetables, fruits, grains, bran, pectin.
- Natural plant products – Psyllium seed,
- Semi-synthetic hydrophilic colloids – Methyl and carboxy methyl cellulose
- Synthetic non absorbed resins -Calcium polycarbophil
Side effects of bulk purgatives
- Intestinal obstruction (They should be taken with enough water to prevent this from occurring).
- Malabsorption syndrome
- Abdominal distention.
They interfere with the absorption of the following drugs
- calcium and
- cardiac glycosides etc
Osmotic or Saline purgatives
- They are soluble, but non absorbable inorganic salts that are retained in the GIT.
- Because of their osmotic actions, they attract water from tissues and increase the bulk of contents in large intestine
- They induce peristalsis and produce watery stool.
- They have rapid effects within 1-3 hours
Types of saline purgatives
- Magnesium salts: Examples of these include: Magnesium citrate, magnesium hydroxide, magnesium sulphate. Magnesium salts also stimulate cholecystokinin from the duodenum which causes accumulation of fluid and electrolytes in the intestine.
- Sodium salts: Examples include Sodium sulphate and sodium phosphate Glycerin: They lubricate passage and stimulate rectal contraction
- Sorbitol: It is given by rectal route as an enema or orally
Side effects and contraindication
- Intravascular volume depletion.
- Electrolyte fluctuations: Severe in children.
- Sodium salts are contraindicated in congestive heart failure and renal disease
- Magnesium salt are contraindicated in patients with renal impairment, heart block, CNS depression and neuromuscular block
Stimulant purgatives (Cathartics)
- Stimulant purgatives increase GIT peristalsis by irritating the GIT mucosa or direct stimulation of enteric nervous system
- They increase mucus production, reduce electrolyte and water absorption and increase fluidity of stool
- Prolonged use of stimulant purgatives may inhibit the functions of the colon (non functioning colon).
Types of stimulant laxatives
- Its onset of action is in 20-60min after adminstration and the duration can last for 10-12hrs after rectal dose
- It’s useful for bowel evacuation prior to surgery and radiological exam.
- Dose 5-10mg orally or 10mg rectally.
- It is degraded by lipase in upper small intestine to ricinoleic acid + glycerin
- The ricinoleic acid irritates mucosa and stimulates peristalsis within 30 min – 2hours of adminstration.
- The dose is 5-20 ml on empty stomach in the morning.
- These are of plant origin: Cassia acutifolia, Cassia angustifolia, Cascara sagrada, and Rhamnus frangula
- In the colon anthraquinone derivatives are hydrolyzed to active anthraquinone
- This stimulates the mysenteric plexus which increases smooth muscle contraction leading to defecation.
- Bowel movement occurs in 12 h (orally) or 2 h (rectally) after adminstration.
- It is given at night
- Abdominal cramps may occur.
- Prolonged use will cause dependence & destruction of mysenteric plexus and atonic colon.
- Senna is contraindicated in lactation
- Castor oil is contraindicated in pregnancy as it may cause reflex contraction of uterus leading to abortion.
- These are non absorbed able drugs that soften the feces thus promoting defecation by reducing the surface tension of fecal mass.
- The decrease in surface tension of fecal mass allows the penetration of intestinal fluid.
- Some fecal softeners increase mucosal cAMP which will stimulate fluid accumulation in the lumen
- They can be given orally or rectally.
Types of fecal softeners
- Docusate calcium (calcium dioctyl sulfosuccinate)
- Docusate sodium (sodium dioctyl sulfosuccinate)
They are used in the treatment of constipation in geriatrics and obstetrics.
Docusate sodium 240mg daily
Docusate calcium 50-500mg daily.
- Dehydrocholic acid : It is a bile salt which reduces the absorption of electrolytes and water from the GIT.
750mg -150g daily in 3 doses
Liquid Paraffin is a lubricant purgative
- It is oily and a mixture of aliphatic hydrocarbon
- It tasteless and odorless and used as a mild purgative
- It lubricates intestinal tract, softens stool and makes defecation very easy
- It prevents straining in patients with hemorrhoids
Side effects of Liquid Paraffin
- Impairs absorption of fat soluble vitamins.
- Increase activity of oral anticoagulant.