Laxative
Laxative
King Cobra
Category="Gastroenterology"A laxative is a preparation used for encouraging Defecation, or the elimination of Feces. Laxatives are most often taken to treat Constipation. Certain stimulant, lubricant, and saline laxatives are used to evacuate the colon for rectal and bowel examinations. They are sometimes supplemented by enemas.Laxatives are often abused by bulimics or anorexics. Laxative abuse is a problem that is potentially very serious since it can lead to problems such as intestinal paralysis, Irritable bowel syndrome (IBS), and Pancreatitis, among others.
There are several types of laxatives, listed below. A type not listed is the combination laxative, which simply means that the laxative has more than one ingredient, with a combination of effects. Laxatives may be oral or in Suppository form.
It is interesting to note that, while there is no gender based medicine to ease Constipation, advertisers tend to promote some brands as being "More for a lady" than others.
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. Examples: psyllium husk (Metamucil), methylcellulose (Citrucel), polycarbophil, apples. They should be taken with plenty of water. Bulk-producing agents have the gentlest of effects among laxatives and can be taken just for maintaining regular bowel movements.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. Many of these quickly produce a tolerance effect and so become ineffective with prolonged use. Their strength lies in between the fibers and the stimulants and can be used for patients with occasional Constipation or those with anorectal conditions in which passage of a firm stool is painful. Stool softeners include Docusate (Colace, Diocto).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. An example is Mineral oil, which also retards colonic absorption of water, softening the stool. Note: Mineral oil may decrease the absorption of fat-soluble vitamins (A, D, E and K).Hydrating agents (osmotics)
These cause the intestines to concentrate more water within, softening the stool. There are two principal types, saline and hyperosmotic. Examples: Milk of Magnesia, Epsom salt.Saline
- Site of Action: Small and large intestine
- Onset of Action: 0.5 - 3 hours
Saline laxatives attract and retain water in the intestinal lumen increasing intraluminal pressure, thus softening the stool. They will also cause the release of Cholecystokinin, which stimulates the digestion of fat and protein. Saline laxatives may alter a patient's fluid and electrolyte balance. Examples: Dibasic sodium phosphate, Magnesium citrate, Magnesium hydroxide (Milk of Magnesia), Magnesium sulphate, Monobasic sodium phosphate, Sodium biphosphate. Note: sulphate salts are considered the most potent.Hyperosmotic agents
- Site of Action: Colon
- Onset of Action: 0.5 - 3 hours
Hyperosmotic laxatives include Glycerin suppositories and Lactulose. Lactulose works by osmotic effect which retains water in the colon, lowering the pH and increasing colonic peristalsis. Lactulose is also indicated in Portal-systemic encephalopathy. Glycerin suppositories work mostly by hyperosmotic action, but also the sodium stearate in the preparation causes local irritation to the colon.Stimulant / Irritant
These stimulate peristaltic action, and can be dangerous under certain circumstances. Stimulant laxatives act on the intestinal mucosa or nerve plexus, they also alter water and electrolyte secretion. They are the most severe among laxatives and should be used only in extreme conditions. Note: Castor oil may be preferred when more complete evacuation is required.Examples:
Miscellaneous
Castor Oil
- Site of Action: Small intestine
- Onset of Action: 2 - 6 hours
Castor oil acts directly on intestinal mucosa or nerve plexus and alters water and electrolyte secretion. It is converted into ricinoleic acid (the active component) in the gut.See also