Laxatives (also known as purgatives or aperients) are foods, compounds, or drugs taken to induce bowel movements or 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 bowel examinations, and may be supplemented by enemas in that circumstance. Sufficiently high doses of laxatives will cause diarrhea. Laxatives work to hasten the elimination of undigested remains of food in the large intestine and colon.[1]
There are several types of laxatives, listed below. Some laxatives combine more than one type of active ingredient to produce a combination of the effects mentioned. Laxatives may be oral or in suppository form.
Constipation with no known organic cause, i.e. no medical explanation, exhibits gender differences in prevalence: females are more often affected than males.[2]
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Some vegetables and foods can be eaten to cure constipation and act as laxatives, although the effectiveness may vary. These include:
Also known as bulking agents or roughage, these include 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 along. Their strength is between that of the bulk producers and the stimulants, and they can be used for patients with occasional constipation or those with anorectal conditions for whom passage of a firm stool is painful.
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.
These cause the intestines to hold more water within, softening the stool. There are two principal types, saline and hyperosmotic.
Saline laxatives attract and retain water in the intestinal lumen, increasing intraluminal pressure and 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.
Lactulose works by the 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.
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, 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.[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 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.[10] They are the most severe among laxatives and should be used with care.
| Preparation(s) | Type | Site of Action | Onset of Action |
|---|---|---|---|
| Cascara (casanthranol) | Anthraquinone | colon | 6-8 hours |
| Buckthorn | Anthraquinone | colon | 6-8 hours |
| Senna extract (senokot) | Anthraquinone | colon | 6-8 hours |
| Aloe vera (aloin) | Anthraquinone | colon | 8-10 hours |
| Phenolphthalein | Diphenylmethane | colon | 8 hours |
| Dulcolax (bisacodyl) (PO) | Diphenylmethane | colon | 6-12 hours |
| Dulcolax (bisacodyl) (suppository) | Diphenylmethane | colon | 60 minutes |
| Microlax | enema | rectum and colon | 15-60 minutes |
| Castor Oil | ricinoleic acid | small intestine | 2-6 hours |
Tegaserod is a motility stimulant that works through activation of 5-HT4 receptors of the enteric nervous system in the gastrointestinal tract. However caution must be taken due to potentially harmful cardiovascular side-effects.
Zelnorm (market name for Tegaserod) was discontinued from marketing on March 30, 2007[13] but is still available for prescription under tight controls.
Laxative abuse is potentially serious since it can lead to intestinal paralysis, irritable bowel syndrome (IBS),[14] pancreatitis, renal failure,[15][16] and other problems, even though recovery is possible with proper treatment.
Physicians generally 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 faeces due to long term overstimulation. The evidence for this was never too strong, and it was always unclear whether the elongated and poorly moving colon of a patient with chronic constipation was a result of or was just a cause for patients' use of stimulant laxatives. A common finding in patients who have used stimulant laxatives is a brown pigment deposited in the intestinal tissue, known as Melanosis coli.
Laxatives are often used by people with an eating disorder. In many cases of bulimia nervosa the patient will abuse laxatives in an attempt to get rid of the calories, to purge themselves of food in the intestines before it becomes digested and absorbed by the body. This will not work, because laxatives hasten the elimination of undigested remains of food in the large intestine and colon. The large intestine and colon do not digest food. They just collect the undigested remains and hold it and absorb water until it is defaecated. Weight loss may be felt, but this is only temporary due to the fact that the person has expelled much of the fluids from their body. The common question of whether or not chronic diarrhea associated with laxative use can promote some degree of true weight loss remains unknown. In any case, this type of laxative misuse causes water to be lost more rapidly than is healthy, potentially leading to dehydration(laxative make osmotic preacher in GIT than body) and electrolyte imbalance(because potassium ion lost) . Prolonged usage of laxatives will actually cause constipation. The sensation of bloating can be significant due to excessive water retention, leading to people with eating disorders to increase the dosage of the laxatives, resulting in dependency and further complicating the constipation. Abusing stimulant-type laxatives can lead to permanent impairment of the bowels, and the constipation problem becomes irreversible. In addition, blood can develop in stools, and excessive blood loss can result in anemia. Patients recovering from laxative abuse often have several months of problematic water retention, resulting in temporary weight gain (not noticeable on the exterior), and sometimes "pitting" edema (in which pressing on the skin leaves an indentation).
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