Laxatives (purgatives, aperients) are substances that loosen stools and increase bowel movements. They are used to treat and prevent constipation. Laxatives vary based on how they work and the side effects they have. 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.
- 1 Uses
- 2 Types of non-prescription laxatives
- 3 Types of prescription laxatives
- 4 Comparison of available agents
- 5 Problems with use
- 6 Historical & non-mainstream medical use
- 7 See also
- 8 References
- 9 External links
- Acute and chronic constipation
- Bowel preparation
- Chronic immobility
Types of non-prescription laxatives
Bulk-forming laxatives, also known as roughage, are substances, such as fiber in food and hydrophilic agents in over-the-counter drugs, that add bulk and water to stools so that they can pass more easily through the intestines (lower part of the digestive tract).
- Site of action: small and large intestines
- Onset of action: 12–72 hours
- Examples: dietary fiber, Metamucil, Citrucel, FiberCon
Bulk-forming agents absorb water and should be taken with plenty of water. Bulk-forming agents generally have the gentlest of effects among laxatives and can be taken for long-term maintenance of regular bowel movements.
Foods that help with laxation include fiber-rich foods. Dietary fiber includes insoluble fiber and soluble fiber, such as:
- Fruits, such as bananas, kiwifruits, prunes, apples (with skin), pears (with skin), and raspberries
- Vegetables, such as broccoli, string beans, kale, spinach, cooked winter squash, cooked green peas, and baked potatoes (with skin)
- Whole grains
- Bran products
- Legumes, such as beans, peas, and lentils
Emollient agents (stool softeners)
Emollient laxatives, also known as stool softeners, are anionic surfactants that enable additional water and fats to be incorporated in the stool, making it easier to move through the gastrointestinal tract.
- Site of action: small and large intestines
- Onset of action: 12–72 hours
- Examples: docusate (Colace, Diocto), Gibs-Eze
Emollient agents should be taken with plenty of water. Emollient agents prevent constipation rather than treat long-term constipation.
Hyperosmotic laxatives are substances that cause the intestines to hold more water within and create an osmotic effect that stimulates a bowel movement.
- Site of Action: colon
- Onset of Action: 12-72 hours (oral) 0.25 - 1 hour (rectal)
- Examples: glycerin suppositories, sorbitol, lactulose, and PEG (Colyte, MiraLax)
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 (SoftLax) have similar effects as the aforementioned.
Stimulant laxatives are substances that 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. Prolonged use of stimulant laxatives can create drug dependence by damaging the colon's haustral folds, making a user less able to move feces through the colon on their own. A study of patients with chronic constipation found that 28% of chronic stimulant laxative users lost haustral folds over the course of one year, while none of the control group did.
Saline laxative agents
Saline laxatives are non-absorbable osmotic substances that attract and retain water in the intestinal lumen, increasing intraluminal pressure that mechanically stimulates evacuation of the bowel. Magnesium-containing agents also cause the release of cholecystokinin, which increases intestinal motility and fluid secretion. Saline laxatives may alter a patient's fluid and electrolyte balance.
- Site of Action: small and large intestines
- Onset of Action: 0.5–3 hours (oral), 2–15 minutes (rectal)
- Examples: sodium phosphate (and variants), magnesium citrate, magnesium hydroxide (Milk of magnesia), magnesium sulfate (Epsom salt)
Saline laxatives should be taken with plenty of water.
[See also - Lubricants] Lubricant laxatives are substances that coat the stool with slippery lipids and retard colonic absorption of water so that the stool slides through the colon more easily. Lubricant laxatives also increase the weight of stool and decrease intestinal transit time.
Mineral oil is the only nonprescription lubricant. Mineral oil may decrease the absorption of fat-soluble vitamins and some minerals.
Castor oil is a glyceride that is hydrolyzed by pancreatic lipase to ricinoleic acid, which produces laxative action by an unknown mechanism.
Long-term use of castor oil may result in loss of fluid, electrolytes, and nutrients.
Types of prescription laxatives
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 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.
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).
Comparison of available agents
|Preparation(s)||Type||Site of action||Onset of|
|Cascara (casanthranol)||Anthraquinone||colon||6–8 hours|
|Senna extract (senna glycoside)||Anthraquinone||colon||6–8 hours|
|Aloe vera (aloin)||Anthraquinone||colon||8–10 hours|
|bisacodyl (oral)||Triphenylmethane||colon||6–12 hours|
|bisacodyl (suppository)||Triphenylmethane||colon||60 minutes|
|Microlax||enema||rectum and colon||15–60 minutes|
|Castor oil||ricinoleic acid||small intestine||2–6 hours|
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.
Problems with use
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), pancreatitis, renal failure, factitious diarrhea 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 feces 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.
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.
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