VPT 311: General and Systemic Veterinary Pharmacology (2+1)

BULK PURGATIVES

• Bulk laxatives (e.g: methylcellulose, agar, psyllium, wheat bran)
• Dietary fibres consists of unabsorbable cell wall and other constituents of vegetable food – cellulose, pectins, glycoproteins and other polysaccharides.
• Bran is a byproduct of flour industry consists of 40% dietary fibre. It absorbs water in the intestines, swells, increases water content of feces.- softens it and facilitates colonic transit.
• Osmotically active products may be formed in the colon by bacterial degradation of pectins etc., which act to retain water.
• Dietary fibre supports bacterial growth in colon which contribute to the fecal mass.
• Certain dietary fibres (gums, lignins, pectins) bind bile acids and promote their excretion in feces leading to enhancement of degradation of cholesterol in liver and thereby plasma LDL cholesteol is lowered.
• Increased intake of dietary fibres is the most appropriate method for prevention and treatment of functional constipation.
• It is the first line approach for most dogs and cats in the treatment of simple constipation.
• Prolonged intake of bran and other bulk forming agents reduces rectosigmoid intraluminal pressure – relives symptoms of irritable bowel disease and colonic diverticulosis.
• It is also useful when tenesmus at stools has to be avoided.

Demerits

• Unpalatable, 20-40g/day needs to be ingested.
• Full effect requires daily administration for at least 3-4 days.
• It does not soften feces already present in colon or rectum.
• Flatulence may occur.

Psyllium (Plantago) and Ispaghula

• Contain natural colloid mucilage, which forms a gelatinous mass by absorbing water, 3-12 g of refined husk freshly mixed with water or milk and taken daily acts in 1-3 days.
• It should not be swallowed dry (may lead to oesophageal impaction)
• Ispaghula husk (refined)
  
• Plantago husk

Methylcellulose and carboxymethylcellulose are semi-synthetic colloidal hydrophilic derivatives of cellulose; 4-6 g/day is satisfactory to produce laxative effect.

Mechanism of action

• Bulk laxatives contain hydrophilic colloids, which absorb water and increae bulk.
• Bulk stimulatives large bowel peristalsis
• Wheat bran is administered orally by adding to the diet.
• The laxative effect occurs within 1-3 days.
• Generous amount of water must be given with all bulk forming agents.
• It should not be used in patients with gastric ulcerations, adhesions, stenosis and when fecal impaction is a possibility