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Laxatives

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Laxatives

Laxatives (purgatives, aperients) are foods, compounds and/or drugs taken to loosen the stool, most often taken to treat constipation. Certain stimulant, lubricant and saline laxatives are used to evacuate the colon for rectal and/or bowel examinations, and may be supplemented by enemas under certain circumstances. Sufficiently high doses of laxatives may cause diarrhea. Laxatives work to increase the movement of feces along the colon.

Some laxatives combine more than one active ingredient. Laxatives may be oral and/or in suppository form.

Foods

Foods that help with laxation include fruits, especially banana,[1] kiwifruit[2] and prunes,[3] bran products, aloe vera, blackstrap molasses, pear, and nuts (especially almonds and walnuts).Template:Medcn

Bulk-producing agents

A bulk-forming agent is a substance, such as fiber in food, that adds bulk and water to stools so that they can pass more easily through the intestines (lower part of the digestive tract).[4]

Also known as bulking agents or roughage, these include insoluble dietary fibre. 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. 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
  • Examples: docusate (Colace, Diocto), Gibs-Eze

Act as a surfactant, enabling additional water and fats to be incorporated in the stool, making it easier to move.

Lubricants or 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. Mineral oil may decrease the absorption of fat-soluble vitamins and some minerals.

Hydrating agents (osmotics)

These cause the intestines to hold more water within, softening the stool. There are two principal types, saline and hyperosmotic.

Saline

Saline laxatives attract and retain water in the intestinal lumen, thus softening the stool. They 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.

Hyperosmotic agents

Lactulose works by the osmotic effect, which retains water in the colon, lowering the pH through bacterial fermentation to lactic, formic and acetic acid, and increasing colonic peristalsis. Lactulose is also indicated in Portal-systemic encephalopathy. Glycerin suppositories work mostly by hyperosmotic action, but the sodium stearate in the preparation also causes local irritation to the colon.

Solutions of polyethylene glycol and electrolytes (sodium chloride, sodium bicarbonate, potassium chloride, and sometimes sodium sulfate) are used for whole bowel irrigation, a process designed to prepare the bowel for surgery or colonoscopy and to treat certain types of poisoning. Brand names for these solutions include GoLytely, GlycoLax, CoLyte, Miralax, Movicol, NuLytely, SUPREP, Fortrans, and others. Solutions of sorbitol have similar effects as the aforementioned. Brand name SoftLax.

Effectiveness

For adults, a randomized controlled trial found PEG [MiraLax or GlycoLax] 17 grams once per day to be superior to tegaserod at 6 mg twice per day.[5] A randomized controlled trial found greater improvement from 2 sachets (26 grams) of PEG versus 2 sachets (20 grams) of lactulose.[6] 17 grams/day of PEG has been effective and safe in a randomized controlled trial for six months.[7] Another randomized controlled trial found no difference between sorbitol and lactulose.[8]

For children, PEG was found to be more effective than lactulose.[9]

Stimulant or irritant

Stimulant laxatives (also called "contact laxatives") act on the intestinal mucosa or nerve plexus, altering water and electrolyte secretion.[10] They also stimulate peristaltic action and can be dangerous under certain circumstances.[11] They are the most powerful among laxatives and should be used with care.

Common Stimulant Laxatives[12][13]
Preparation(s) Type Site of action Onset of
Cascara (casanthranol) Anthraquinone colon 36–8 hours
Buckthorn Anthraquinone colon 36–8 hours
Senna extract (senna glycoside) Anthraquinone colon 36–8 hours
Aloe vera (aloin) Anthraquinone colon 58–10 hours
Phenolphthalein Triphenylmethane colon 48 hours
bisacodyl (oral) Triphenylmethane colon 66–12 hours
bisacodyl (suppository) Triphenylmethane colon 160 minutes
Microlax enema rectum and colon 015–60 minutes
Castor oil ricinoleic acid small intestine 22–6 hours

Serotonin agonist

These are motility stimulants that work through activation of 5-HT4 receptors of the enteric nervous system in the gastrointestinal tract. However, some have been discontinued or restricted due to potentially harmful cardiovascular side-effects.

Tegaserod (brand name Zelnorm) was discontinued from marketing in the United States on March 30, 2007. It is still available to physicians for patients in emergency situations that are life-threatening or require hospitalization.[14]

Cisapride (brand name Prepulsid) was voluntarily removed from the U.S. market on July 14, 2000 for the same reason as Tegaserod. Its use in many other countries is discontinued or restricted. It is still available for veterinary use as a compound to treat GI tract problems.

Prucalopride (brand name Resolor) is a current drug approved for use in the EU October 15, 2009[15] and in Canada (brand name Resotran) on December 7, 2011.[16] It has not been approved by the Food and Drug Administration for use in the United States, but it is in development by Shire PLC.[17]

Chloride channel activators

Lubiprostone (brand name Amitiza) is used in the management of chronic idiopathic constipation and irritable bowel syndrome. It causes the intestines to produce a chloride-rich fluid secretion that softens the stool, increases motility, and promotes spontaneous bowel movements (SBM).

Uses

  • Bowel preparation
  • Chronic constipation
  • Chronic immobility

Problems with use

Laxative abuse

Laxative abuse can lead to potentially fatal fluid and electrolyte imbalances (especially dehydration, hypokalaemia and a metabolic acidosis) as well as intestinal paralysis, irritable bowel syndrome (IBS),[18] pancreatitis,[19] renal failure,[20][21] factitious diarrhea[22] and other problems.

Although patients with eating disorders such as anorexia nervosa and bulimia nervosa frequently abuse laxatives in an attempt to lose weight, laxatives act to speed up the transit of faeces through the large intestine, which occurs subsequent to the absorption of nutrients in the small intestine. Thus, studies of laxative abuse have found that effects on body weight reflect primarily temporary losses of body water rather than energy (calorie) loss [23] http://www.uptodate.com/contents/acid-base-and-electrolyte-abnormalities-with-diarrhea-or-ureteral-diversion

Laxative gut

Physicians warn against the chronic use of stimulant laxatives due to concern that chronic use causes the colonic tissues to get worn out over time and not be able to expel feces due to long-term overstimulation. A common finding in patients having used stimulant laxatives is a brown pigment deposited in the intestinal tissue, known as melanosis coli.

Historical & non-mainstream medical use

Laxatives, then called physicks or purgatives, were used extensively in pre-modern medicine to treat a wide range of conditions for which they are now generally regarded as ineffective in modern evidence-based medicine. Likewise, laxatives (often termed colon cleanses), continue to be promoted by practitioners of complementary medicine for a range of conditions, including conditions that are not medically recognized, e.g. mucoid plaque.

See also

References

External links

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