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

Constipation can be because of the following reasons weakness of intestines, intestinal spasms, emotional tension improper diet, lack of physical exercise or work, side effects of the drugs etc.

In constipation, fecal material becomes hard and dry, the use of laxatives and purgatives provides relief from constipation by elimination of bowel contents.

How Saline Cathartics Work

The mechanism behind saline cathartics is relatively simple. When ingested, these substances increase the osmotic pressure in the intestines, which in turn draws water into the bowel. The increased water content softens the stool and facilitates its passage, ultimately leading to more comfortable and regular bowel movements.

Cathartics or laxatives can be considered under the following class:

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

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

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

2. Strong purgatives: Cause complete evacuation of the bowel and bowel becomes inactive and also given to remove the solid particles from the 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 the intestine by absorbing large quantities 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 the laboratory, it is prepared by treating a solution of magnesium carbonate with dilute sulphuric acid. The mixture is stirred well and carbon dioxide 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 is filtrated and the 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 taste, insoluble in boiling water and practically soluble in alcohol

Storage: Store protected from moisture

Medicinal uses:

 Saline cathartic as an osmotic laxative

• Electrolyte replacement

Sodium Ortho Phosphate

Synonyms: Disodium Hydrogen Phosphate, Sodium orthophosphate

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

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

Method of preparation: It is prepared by treating sodium carbonate with a hot phosphoric acid solution. The solution is neutralized, 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


1. Are saline cathartics safe for regular use?

Saline cathartics are generally safe for short-term use to relieve constipation. However, prolonged or excessive use can lead to complications. Consult a healthcare professional for guidance.

2. How quickly do saline cathartics work?

Saline cathartics typically work within a few hours to induce bowel movements.

3. Can I use saline cathartics during pregnancy?

Pregnant individuals should consult their healthcare provider before using saline cathartics or any other medication.

4. Are there age restrictions for saline cathartics?

Age restrictions may vary depending on the product. Always follow the product’s recommended age guidelines.

5. What should I do if I experience side effects from saline cathartics?

If you experience severe side effects, such as severe diarrhea, dehydration, or cramping, seek immediate medical attention.

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