Cathartics are drugs used to relieve constipation. The term laxative is used for mild cathartics whereas purgatives is used for strong cathartics. They are also given for the expulsion of intestinal parasite and also for clearing the bowels before surgery if necessary.

Constipation can be because of following reasons like weakness of intestinal, intestinal spasm, emotional tension improper diet, lack of physical exercise or work, side effect of the drugs etc. In constipation fecal material becomes hard and dry, use of laxative and purgative provides relief from constipation by elimination of bowel contents.

Cathartics or laxatives can be considered under the following class:

1. Mild laxatives: are those drugs, which promote evacuation of bowel with minimum adverse effects. Drugs included in this group are:

• Bulk producing drugs: Which promote evacuation of bowel by increasing the stools bulk volume and water contents. Eg; Isapgol, agar- agar methyl cellulose etc.

• Stool softeners (Emollient):  Which penetrate and soften the stool.  Eg:  D-soctyl sodium sulphosuccinate, liquid paraffin, etc.

2. Strong purgatives: Cause complete evacuation of the bowel and bowel become in active and also given to remove the solid particles from intestine before certain x-ray examination or surgery. There are two kinds of strong purgatives.

• Irritant or stimulant: These are drugs or chemicals, which act by local irritation or intestinal tract and bring about stimulation of peristaltic activity. Eg Phenolphthalein, senna, etc.

Saline cathartics: These act by increasing the osmotic load of intestine by absorbing large quantity of water and they’re by stimulating peristalsis.Eg: magnesium compounds.

Magnesium sulphate

Synonym: Epsom Salt

Chemical formula: MgSO4 .7H 2O

Method of Preparation:

Laboratory: In laboratory it is prepared by treating a solution of magnesium carbonate with dilute sulphuric acid. The mixture is stirred well and carbon di oxide is removed, then the solution is evaporated to get the crystals of magnesium sulphate.

Chemical reactions:

MgCO3 + H2SO4→MgSO4+ CO2+ H2O

Commercially: Dolomite

It is prepared by reacting Sulphuric acid with dolomite. Dolomite is a mixture of magnesium and calcium carbonate. The magnesium sulphate being water soluble remains in the solution while the impurities such as calcium carbonate undergo precipitation, thus the solution id filtrated and filtrate is subjected to evaporation to get the crystals of magnesium sulphate.

Chemical reactions:

MgCO3.CaCO3 + 2 H2SO4 →MgSO4 + CaSO4+ 2CO2+2 H2O

Description: Colourless crystals or a white, crystalline powder with bitter and saline in tatse, soluble in boiling water and practically in soluble in alcohol

Storage: Store protected from moisture

Medicinal uses:

    Saline cathartic as osmotic laxative

    Electrolyte replacement

Sodium Ortho Phosphate

Synonyms: Disodium Hydrogen Phosphate,Sodium ortho phosphate

Chemical formula: Na2HPO4  nH2O (n=12, 10, 8, 7, 5, 2 or 0)

Description: Colourless, transparent crystals; very efflorescent, Soluble in water and practically in soluble in alcohol

Method of preparation: It is prepared by treating sodium carbonate with a hot solution of phosphoric acid. The solution is neutralised, concentrated and crystals are separated, centrifuged, washed and dried

Chemical reactions:

H3PO4 + Na2CO3→ Na2HPO4 + H2O+ CO2

Storage: Store protected from moisture

Medicinal uses:

     Saline cathartic

     Electrolyte replacement

     Standard buffer solution

    Softening hard water

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