Classification of Purgatives | Drugs | Pharmacology

In this article we will discuss about the classification of purgatives that are used to treat the diseases of gastrointestinal system.

These are the drugs, which loosen the bowel and cause its evacuation. Purgatives, as a rule are not the treatment for constipation. The use of purgatives can only be justified in select conditions such as drug induced constipation, after anthelmintic treatment for the expulsion of parasites, hemorrhoids or severe life threatening condition, where straining increases the risk of rectal bleeding or exacerbation of the underlying illness (e.g. myocardial or cerebral ischemia), before surgery or radiological procedures to clear the bowel.

There are large numbers of purgatives, which may be classified as follows:

a. Bulk Purgatives:

Bran, methylcellulose, ispaghula and sterculia.

b. Faecal Softeners:

Docusate sodium.

c. Stimulant Purgatives:

Anthracenes and bisacodyl.

d. Osmotic Purgatives:

Magnesium sulphate and lactulose.

a. Bulk Purgatives:

These act by increasing fecal mass, which stimulates peristalsis. They are useful in the management of patients with colostomy, ileostomy, hemorrhoids, and fissures, chronic diarrhea associated with diverticular disease, irritable bowel syndrome and as adjuncts in ulcerative colitis. Side effects of bulk purgatives include flatulence, distension, intestinal obstruction or fecal impaction and hypersensitivity reactions. Bulk purgatives are contraindicated in intestinal obstruction, colonicatony and fecal impaction.

b. Faecal Softeners:

Docusate sodium acts both by softening the stools and stimulating the colon. It is indicated in painful conditions such as piles or anal fissures to relieve constipation and prior to radiological procedures. Liquid paraffin is rarely used because it may cause anal seepage, lipoid pneumonia (if inhaled), and interference with the absorption of fat soluble vitamins.

c. Stimulant Purgatives:

Anthracenes:

This group contains cascara, senna, rhubarb and aloes, which contain the anthraquinone glycoside, emodin. In the intestines, emodin is released, which gets absorbed into the blood stream and acts on the large intestine, causing increased peristalsis. They take about 6-12 hours to act and are best given at bedtime. Senna is the only anthracene purgative used since other members of the anthraquinone group are powerful stimulants and may cause intestinal cramps. They should be avoided during pregnancy.

Bisacodyl (Dulcolax):

Bisacodyl stimulates the colon and takes about 10-12 hours to act. It can be taken orally in the form of tablets in the night or given as rectal suppositories in the morning for constipation and before radiological procedures and surgery. Side effects are minimal and include griping (tablets) or local irritation (suppositories).

Co-Danthramer:

It is a mixture of a faecal softener and a stimulant purgative (dantron). Because of its teratogenic effect in animals, it is only used in elderly patients with obstinate constipation or those whose constipation is due to opioid analgesics (e.g. terminally ill patients).

Sodium picosulfate:

It is a powerful bowel stimulant and is only used for preparation of patients before surgery or radiology. It is not used for long-term treatment of constipation. Colocynth, jalap and castor oil are other stimulant purgatives, which have a drastic purgative action. Phenolphthalein can cause rashes. They are no longer used.

d. Osmotic Purgatives:

These act by retaining fluid in the bowel or by changing the pattern of water distribution in the feces. Magnesium sulphate (Epson salt) is the most commonly used saline purgative and is useful where rapid bowel evacuation is required. It is effective usually within 1-2 hours. Lactulose is a semisynthetic disaccharide, which is not absorbed from the GIT. It is broken down in the large bowel with the production of various acids. It causes purgation by acting as osmotic purgative and as mild irritant. It prevents the proliferation of ammonia producing organisms and is useful in hepatic encephalopathy.

Adverse effects of purgatives:

The indiscriminate and chronic use of purgatives may be dangerous and can lead to:

i. Loss of fluids and electrolytes

ii. Abdominal pain, rupture of an acutely inflamed appendix

iii. Damage to bowel

iv. Onset of labour pains

v. Lipoid pneumonia with liquid paraffin

vi. Purgative habit

Purgatives should never be given to patients with undiagnosed abdominal pain.