Laxatives

LAXATIVES


LAXATIVES

  • Used for preventing constipation, by promoting evacuation of bowels.
  • Also referred to as “Aperients, Purgatives, Cathartics”.

Other best measures:

  • High fiber diet, adequate fluid intake & regular exercise.
  • Unresponsive patients require laxatives.

Classification of laxative drugs:

Luminal active agents Stimulant purgative Prokinetics New agents
Subdivided into

  • Bulk-forming.
  • Surfactant.
  • Osmotic

1. Bulk-forming agents:

  • Dietary agents
  • Brain
  • Psyllium
  • Methylcellulose

2. Surfactant (Stool softner):

  • Docusate (DOSS)
  • Liquid paraffin
  • Mineral oil

3. Osmotic:

Subdivided into: Saline laxatives & non-digestive sugars & alcohols.

  • Saline laxatives:
    • (Mg(OH)2, MgSO4)
    • Sodium phosphate
  • Non-digestive sugars & alcohols:
    • Lactulose
    • Sorbitol
    • Mannitol
    • Polyethylene glycol
1. Diphenylmethanes:

  • Bisacodyl
  • Sodium picosulfate
  • Phenolphthalein

2. Anthraquinones:

  • Senna
  • Cascara

3. Castro oil.

1. 5HT4 agonists:

  • Prucalopride

2. D2 antagonists:

  • Metoclopramide
  • Domperidone
  • Macrolides (mainly erythromycin)
This section is a separate module.
1. Chloride secretory agents:

  • Lubiprostone
  • Linaclotide

2. Opioid receptor antagonists (For opioid-induced constipation):

  • Methylnaltrexone Alvimopan

Important drugs:

1. Chloride secretory agents:

  • Drugs: Lubiprostone & Linaclotide.
  • MOA:
    • Stimulate Cl channel opening in intestine.
    • Increase liquid secretion in gut.
    • Decrease transit time.
  • Used for chronic constipation.
  • Linaclotide:
    • Guanylate cyclase agonist.
    • Indicated for oral treatment of idiopathic constipation & IBS with constipation.

2. Non-digestive sugars & alcohols:

  • Lactulose:
  • MOA:
    • Acts by conversion to short chain fatty acids in colon.
    • Fatty acids –> result in decreased intestinal juice pH.
    • At low pH, ammonia becomes ionized (NH4+) & cannot be absorbed.

Contraindications:

  • In presence of megacolon – Bulk-forming agents.
  • In chronic renal failure – Saline purgatives.
  • In presence of intestinal obstruction – Stimulant purgatives.

Adverse effects:

  • Melanosis coli (brown pigmentation of colon) – Chronic use of anthraquinone derivatives (senna & cascara).
  • Risk of potential carcinogenicity – Phenolphthalein.
  • Deficiency of fat-oluble vitamins – Liquid paraffin.
  • Hypokalemia & causes constipation itself – Associated with laxative abuse.
Laxative/purgative abuse:
  • Obsession for regular purgative usage.
  • Maybe reflection of psychological problem.

Effects of purgative abuse:

  • Constipation itself.
  • Flaring of intestinal pathology (rupture of inflamed appendix).
  • Fluid & electrolyte imbalance (especially hypokalaemia).
  • Steatorrhoea
  • Malabsorption syndrome.
  • Protein-losing enteropathy.
  • Spastic colitis.

Exam Important

  • Laxatives used for preventing constipation, by promoting evacuation of bowels.
  • Laxatives also referred to as “Aperients, Purgatives, Cathartics”.
  • Senna & Cascara are including under stimulant purgative & are used as laxatives.
  • Opioid receptor antagonists like Methylnaltrexone & Alvimopan are useful for opioid-induced constipation.
  • Docusate (DOSS), liquid paraffin & mineral oil are all stool softner/surfactant.
  • Lubiprostone & Linaclotide are chloride secretory agents.
  • Luminal active agents useful as laxatives are further subdivided into bulk-forming, surfactant & osmotic agents.
  • Phenolphthalein is a stimulant purgative.
  • Lubiprostone & Linaclotide stimulates Cl channel opening in intestine, increases liquid secretion in gut & decreases transit time, hence useful in chronic constipation.
  • Linaclotide is a guanylate cyclase agonist, indicated for oral treatment of idiopathic constipation & IBS with constipation.
  • Chronic use of anthraquinone derivatives (senna & cascara) causes Melanosis coli (brown pigmentation of colon).
  • Phenolphthalein shows risk of potential carcinogenicity.
  • Liquid paraffin result in deficiency of fat-soluble vitamins.
  • Laxative/purgative abuse is assocaited with hypokalemia & causes constipation itself.
  • Effects of laxative/purgative abuse include steatorrhoea, malabsorption syndrome, protein-losing enteropathy & spastic colitis.
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