'Laxatives' are foods, compounds, or drugs taken to induce bowel movements, 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. Often, taking powerful laxatives can cause
diarrhea, accompanied by massive
flatulence attacks, due to the overworking of the
bowels. Some people who experienced these side effects produced more than three times the average daily amount of
flatulence in just one bowel release.
Laxatives are often abused by people with
bulimia nervosa or
anorexia nervosa. Laxative abuse is potentially serious since it can lead to
intestinal paralysis,
Irritable Bowel Syndrome (IBS),
pancreatitis,
renal failure,
[ Renal failure associated with laxative abuse, Copeland P, , , Psychother Psychosom, 1994 ][ Renal injury associated with laxative abuse, Wright L, DuVal J, , , South Med J, 1987 ] and other problems.
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.
[ Gender, age, society, culture, and the patient's perspective in the functional gastrointestinal disorders, Chang L, Toner B, Fukudo S, Guthrie E, Locke G, Norton N, Sperber A, , , Gastroenterology, 2006 ] 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.
Tobacco smoking has a laxative effect.
[1]
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 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. 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 & 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 (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.
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, monobasic sodium phosphate,
sodium biphosphate,
Epsom salt
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 greater improvement from 2 sachets (26 grams) of
PEG [MiraLax or GlycoLax] versus or 2 sachets (20 grams) of
lactulose [ Comparison of a low dose polyethylene glycol electrolyte solution with lactulose for treatment of chronic constipation., 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, , , Gut, 1999 ]. 17 grams/day of
PEG has been effective and safe in a randomized controlled trial for six months.
[2] Another
randomized controlled trial found no difference between
sorbitol and
lactulose [ Cost-effective treatment of constipation in the elderly: a randomized double-blind comparison of sorbitol and lactulose., Lederle F, Busch D, Mattox K, West M, Aske D, , , Am J Med, 1990 ].
For children,
PEG was found to be more effective than
lactulose.
[3]
Stimulant / Irritant
★ Site of Action: Colon
★ Examples:
These stimulate
peristaltic action and can be dangerous under certain circumstances. Long term use can lead to 'cathartic colon'.
[ Alterations in colonic anatomy induced by chronic stimulant laxatives: the cathartic colon revisited., Joo J, Ehrenpreis E, Gonzalez L, Kaye M, Breno S, Wexner S, Zaitman D, Secrest K, , , J Clin Gastroenterol, 1998 ] 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.
References
1. Nicotine withdrawal symptoms:Constipation
2. A randomized, multicenter, placebo-controlled trial of polyethylene glycol laxative for chronic treatment of chronic constipation, Dipalma JA, Cleveland MV, McGowan J, Herrera JL, , , Am. J. Gastroenterol., 2007
3. BestBETs: Is polyethylene glycol safe and effective for chro...
See also
★
ATC code A06
External links
★
Oral laxatives -
MedlinePlus.
★
Laxative overdose -
MedlinePlus.
★
Metamucil psyllium fiber laxative
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