Laxative

Fleet is a common brand of laxative.

Laxatives (or purgatives) 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 only work to hasten the elimination of undigested remains of food in the large intestine and colon.

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.^[1] Not surprisingly, some advertisers promote their brands as being more feminine and thereby tailor their message to the market. The way laxatives function in males and females, however, does not exhibit significant differences.

Vegetables and foods

Some vegetables and foods can be eaten to cure constipation and act as laxatives, although the effectiveness may vary. These include:

Bulk-producing agents

• Site of Action: Small and large intestine
• Onset of Action: 12 - 72 hours
• Examples: psyllium husk (Metamucil), methylcellulose (Citrucel), polycarbophil, dietary fiber, apples

Also known as bulking agents or roughage, 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. 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)

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 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.

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. Mineral oil may decrease the absorption of fat-soluble vitamins and 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

• Site of Action: Small and large intestine
• Onset of Action: 0.5 - 6 hours
• Examples: Dibasic sodium phosphate, magnesium citrate, magnesium hydroxide (Milk of magnesia), magnesium sulfate (which is Epsom salt) , monobasic sodium phosphate, sodium biphosphate.

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.

Sulfate salts are considered the most potent.

Hyperosmotic agents

• Site of Action: Colon
• Onset of Action: 0.5 - 3 hours
• Examples: Glycerin suppositories, Sorbitol, Lactulose, and Polyethylene glycol (PEG).

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, NuLytely, and others.

Effectiveness

For adults, a randomized controlled trial found PEG [MiraLax or GlycoLax] 17 grams once per day better than tegaserod 6 mg twice per day.^[2] A randomized controlled trial found greater improvement from 2 sachets (26 grams) of PEG versus 2 sachets (20 grams) of lactulose ^[3]. 17 grams/day of PEG has been effective and safe in a randomized controlled trial for six months.^[4] Another randomized controlled trial found no difference between sorbitol and lactulose ^[5].

For children, PEG was found to be more effective than lactulose.^[6]

Stimulant / Irritant

• Site of Action

Colon

These stimulate peristaltic action and can be dangerous under certain circumstances. Long term use can lead to 'cathartic colon'.^[7] 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. Castor oil may be preferred when more complete evacuation is required.

Castor oil

• Site of Action

Small intestine

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.

Serotonin agonist

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^[8] but is still available for prescription under tight controls.

Uses

Bowel Prep. Chronic constipation. Chronic immobility.

Problems with use

Laxative Abuse

Laxative abuse is potentially serious since it can lead to intestinal paralysis, Irritable Bowel Syndrome (IBS),^[9] pancreatitis, renal failure,^[10][11] and other problems.

Laxative gut

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 feces 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.

Eating disorders

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 purge themselves of food in the intestines before it becomes digested. Frequently, patients with eating disorders had chronic digestive problems in childhood and found laxatives an effective treatment. The laxative use later may substitute of more appropriate treatment such as a better diet. Treatment of patients with eating disorders and gastrointestinal illnesses can be challenging.

References

1. ↑ Chang L, Toner B, Fukudo S, Guthrie E, Locke G, Norton N, Sperber A (2006). "Gender, age, society, culture, and the patient's perspective in the functional gastrointestinal disorders". Gastroenterology 130 (5): 1435–46. doi:10.1053/j.gastro.2005.09.071. PMID 16678557. 
2. ↑ Di Palma JA, Cleveland MV, McGowan J, Herrera JL (2007). "A randomized, multicenter comparison of polyethylene glycol laxative and tegaserod in treatment of patients with chronic constipation". Am. J. Gastroenterol. 102 (9): 1964–71. doi:10.1111/j.1572-0241.2007.01365.x. PMID 17573794. 
3. ↑ Attar A, Lémann M, Ferguson A, Halphen M, Boutron M, Flourié B, Alix E, Salmeron M, Guillemot F, Chaussade S, Ménard A, Moreau J, Naudin G, Barthet M (1999). "Comparison of a low dose polyethylene glycol electrolyte solution with lactulose for treatment of chronic constipation.". Gut 44 (2): 226–30. PMID 9895382. 
4. ↑ Dipalma JA, Cleveland MV, McGowan J, Herrera JL (2007). "A randomized, multicenter, placebo-controlled trial of polyethylene glycol laxative for chronic treatment of chronic constipation". Am. J. Gastroenterol. 102 (7): 1436–41. doi:10.1111/j.1572-0241.2007.01199.x. PMID 17403074. 
5. ↑ Lederle F, Busch D, Mattox K, West M, Aske D (1990). "Cost-effective treatment of constipation in the elderly: a randomized double-blind comparison of sorbitol and lactulose.". Am J Med 89 (5): 597–601. doi:10.1016/0002-9343(90)90177-F. PMID 2122724. 
6. ↑ "BestBETs: Is polyethylene glycol safe and effective for chro...". Retrieved on 2007-09-06.
7. ↑ Joo J, Ehrenpreis E, Gonzalez L, Kaye M, Breno S, Wexner S, Zaitman D, Secrest K (1998). "Alterations in colonic anatomy induced by chronic stimulant laxatives: the cathartic colon revisited.". J Clin Gastroenterol 26 (4): 283–6. doi:10.1097/00004836-199806000-00014. PMID 9649012. 
8. ↑ FDA Announces Discontinued Marketing of GI Drug, Zelnorm, for Safety Reasons
9. ↑ "Laxative Abuse: Some Basic Facts". National Eating Disorders Association (2005). Retrieved on 2008-09-07.
10. ↑ Copeland P (1994). "Renal failure associated with laxative abuse". Psychother Psychosom 62 (3-4): 200–2. doi:10.1159/000098619. PMID 7531354. 
11. ↑ Wright L, DuVal J (1987). "Renal injury associated with laxative abuse". South Med J 80 (10): 1304–6. doi:10.1097/00007611-198710000-00024. PMID 3660046. 

See also

• ATC code A06

External links

• Laxative overdose - MedlinePlus.