Laxative
Laxatives, purgatives, or aperients are substances that loosen stools and increase bowel movements. They are used to treat and prevent constipation.
Laxatives vary as to how they work and the side effects they may have. Certain stimulant, lubricant, and saline laxatives are used to evacuate the colon for rectal and bowel examinations, and may be supplemented by enemas under certain circumstances. Sufficiently high doses of laxatives may cause diarrhea. Some laxatives combine more than one active ingredient, and may be administered orally or rectally.
Types
Bulk-forming agents
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 they can pass more easily through the intestines.Properties
- Site of action: small and large intestines
- Onset of action: 12–72 hours
- Examples: dietary fiber, Metamucil, Citrucel, FiberCon
Dietary fiber
Foods that help with laxation include fiber-rich foods. Dietary fiber includes insoluble fiber and soluble fiber, such as:- Fruits, such as bananas, though this depends on their ripeness, kiwifruits, prunes, apples, pears, and raspberries
- Vegetables, such as broccoli, string beans, kale, spinach, cooked winter squash, cooked taro and poi, cooked peas, and baked potatoes
- Whole grains
- Bran products
- Nuts
- Legumes, such as beans, peas, and lentils
Emollient agents (stool softeners)
Properties
- Site of action: small and large intestines
- Onset of action: 12–72 hours
- Examples: Docusate, Gibs-Eze
Lubricant agents
laxatives are substances that coat the stool with slippery lipids and decrease colonic absorption of water so the stool slides through the colon more easily. Lubricant laxatives also increase the weight of stool and decrease intestinal transit time.Properties
- Site of action: colon
- Onset of action: 6–8 hours
- Example: mineral oil
Hyperosmotic agents
laxatives cause the intestines to hold more water, creating an osmotic gradient, which adds more pressure and stimulates bowel movement.Properties
- Site of action: colon
- Onset of action: 12–72 hours, 0.25–1 hour
- Examples: glycerin suppositories, sorbitol, lactulose, and polyethylene glycol
Solutions of polyethylene glycol and electrolytes 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, Cosmocol, CoLyte, Miralax, Movicol, NuLytely, Suprep, and Fortrans. Solutions of sorbitol have similar effects.
Saline laxative agents
Saline laxatives are nonabsorbable, osmotically active 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.Properties
- Site of action: small and large intestines
- Onset of action: 0.5–3 hours, 2–15 minutes
- Examples: sodium phosphate, magnesium citrate, magnesium hydroxide, and magnesium sulfate
Stimulant agents
Properties
Prolonged use of stimulant laxatives can create drug dependence by damaging the colon's haustral folds, making users less able to move feces through their 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.
Miscellaneous
is a glyceride that is hydrolyzed by pancreatic lipase to ricinoleic acid, which produces laxative action by an unknown mechanism.Properties
- Site of action: colon, small intestine
- Onset of action: 2–6 hours
- Examples: castor oil
Serotonin agonist
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 was removed from the general U.S. and Canadian markets in 2007, due to reports of increased risks of heart attack or stroke. It is still available to physicians for patients in emergency situations that are life-threatening or require hospitalization.
Prucalopride is a current drug approved for use in the EU since October 15, 2009, in Canada since December 7, 2011, and in the United States since December 2018.
Chloride channel activators
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.Comparison of available agents
Effectiveness
For adults, a randomized controlled trial found PEG 17 grams once per day to be superior to tegaserod at 6 mg twice per day. A randomized controlled trial found greater improvement from two sachets of PEG versus two sachets of lactulose. 17 g per 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.For children, PEG was found to be more effective than lactulose.
Problems with use
Laxative abuse
Some of the less significant adverse effects of laxative abuse include dehydration, low blood pressure, fast heart rate, postural dizziness and fainting; however, laxative abuse can lead to potentially fatal acid-base, and electrolyte imbalances. For example, severe hypokalaemia has been associated with distal renal tubular acidosis from laxative abuse. Metabolic alkalosis is the most common acid-base imbalance observed. Other significant adverse effects include rhabdomyolysis, steatorrhoea, inflammation and ulceration of colonic mucosa, pancreatitis, kidney failure, factitious diarrhea and other problems. The colon will need more quantities of laxatives to keep functioning, this will result in a lazy colon, infections, irritable bowel syndrome, and potential liver damage.Although some patients with eating disorders such as anorexia nervosa and bulimia nervosa abuse laxatives in an attempt to lose weight, laxatives act to speed up the transit of feces through the large intestine, which occurs after the absorption of nutrients in the small intestine is already complete. Thus, studies of laxative abuse have found that effects on body weight reflect primarily temporary losses of body water rather than energy loss.