laxative - Bulk-producing agents, Stool softeners / Surfactants, Lubricants / Emollient, Hydrating agents (osmotics)

A drug which causes emptying of the bowels; also known as a purgative. Laxatives are overused for the treatment of constipation, which is usually cured by a high fibre diet. Except when medically recommended, authorities believe, they do more harm than good. Examples include castor oil and diphenylmethane.

Laxatives are often abused by bulimics or anorexics (nervosa).

There are several types of laxatives, listed below.

Bulk-producing agents

Site of Action: Small and large intestine Onset of Action: 12 - 72 hours

Also known as bulk-forming or bulking agents, these include dietary fiber. Bulk-producing agents cause the stool to be bulkier and to retain more water, as well as forming an emollient gel, making it easier for peristaltic action to move it along.

Stool softeners / Surfactants

Site of Action: Small and large intestine Onset of Action: 12 - 72 hours

These cause water and fats to penetrate the stool, making it easier to move along.

Lubricants / Emollient

Site of Action: Colon Onset of Action: 6 - 8 hours

These simply make the stool slippery, so that it slides through the intestine more easily.

Hydrating agents (osmotics)

These cause the intestines to concentrate more water within, softening the stool.

Saline

Site of Action: Small and large intestine Onset of Action: 0.5 - 6 hours

Saline laxatives attract and retain water in the intestinal lumen, increasing intraluminal pressure and thus softening the stool.

Hyperosmotic agents

Site of Action: Colon Onset of Action: 0.5 - 3 hours

Hyperosmotic laxatives include Glycerin suppositories and Lactulose. Glycerin suppositories work mostly by hyperosmotic action, but also the sodium stearate in the preparation causes local irritation to the colon.

Stimulant / Irritant

Site of Action: Colon

These stimulate peristaltic action, and can be dangerous under certain circumstances. Castor oil may be preferred when more complete evacuation is required.
Examples:

Onset of Action	Laxative Name
6 - 8 hours	Cascara Phenolphthalein (Formerly in Ex-lax but phased out because of carcinogenicity concerns)
6 - 10 hours	Bisacodyl tablets (Dulcolax) Casanthranol Senna (Ex-lax) Aloe Vera
2 - 6 hours	Castor oil
15 min - 1 hour	Bisacodyl suppository

Castor oil

Site of Action: Small intestine Onset of Action:

Castor oil acts directly on intestinal mucosa or nerve plexus and alters water and electrolyte secretion.

Other

Tegaserod is a motility stimulant that works through activation of 5-HT4 receptors of the enteric nervous system in the gastrointestinal tract.