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Laxatives (purgatives, aperients) are foods, compounds 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.
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.
These enable additional water and fats to be incorporated in the stool, making it easier to move.
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.
Saline laxatives attract and retain water in the intestinal lumen, increasing intraluminal pressure and 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.
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 also the sodium stearate in the preparation 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, NuLytely, SUPREP, Fortrans and others.
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. A randomized controlled trial found greater improvement from 2 sachets (26 grams) of PEG versus 2 sachets (20 grams) of lactulose. 17 grams/day of PEG has been effective and safe in a randomized controlled trial for six months. Another randomized controlled trial found no difference between sorbitol and lactulose.
Stimulant laxatives act on the intestinal mucosa or nerve plexus, altering water and electrolyte secretion. They also stimulate peristaltic action and can be dangerous under certain circumstances. They are the most powerful among laxatives and should be used with care.
|Preparation(s)||Type||Site of Action||Onset of|
|Cascara (casanthranol)||Anthraquinone||colon||6–8 hours|
|Senna extract (senokot)||Anthraquinone||colon||6–8 hours|
|Aloe vera (aloin)||Anthraquinone||colon||8–10 hours|
|Dulcolax (bisacodyl) (PO)||Triphenylmethane||colon||6–12 hours|
|Dulcolax (bisacodyl) (suppository)||Triphenylmethane||colon||60 minutes|
|Microlax||enema||rectum and colon||15–60 minutes|
|Castor oil||ricinoleic acid||small intestine||2–6 hours|
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.
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 which was approved for use in the EU October 15, 2009 and in Canada (brand name Resotran) on December 7, 2011. 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.
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 which soften the stool, increases motility, and promotes spontaneous bowel movements (SBM).
Laxative abuse is potentially serious since it can lead to intestinal paralysis, irritable bowel syndrome (IBS), pancreatitis, renal failure, factitious diarrhea and other problems, even though recovery is possible with proper treatment.
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 who have used stimulant laxatives is a brown pigment deposited in the intestinal tissue, known as melanosis coli.
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. Similarly, laxatives (often termed colon cleanses), continue to be promoted by practitioners of complementary medicine for a range of conditions, including conditions which are not medically recognized, e.g. mucoid plaque.
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