Laxatives are products that promote bowel movements.
Laxatives may be grouped by mechanism of action.
Saline cathartics include dibasic sodium phosphate (Phospo-Soda), magnesium citrate, magnesium hydroxide (milk of magnesia), magnesium sulfate (Epsom salts), sodium biphosphate, and others. They act by attracting and holding water in the intestinal lumen, and may produce a watery stool. Magnesium sulfate is the most potent of the laxatives in this group.
Stimulant and irritant laxatives increase the peristaltic movement of the intestine. Examples include cascara and bisadocyl (Dulcolax). Castor oil works in a similar fashion.
Bulk producing laxatives increase the volume of the stool, and will both soften the stool and stimulate intestinal motility. Psyillium (Metamucil, Konsil) and methylcellulose (Citrucel) are examples of this type. The overall effect is similar to that of eating high-fiber foods, and this class of laxative is most suitable for regular use.
Docusate (Colace) is the only representative example of the stool softener class. It holds water within the fecal mass, providing a larger, softer stool. Docusate has no effect on acute constipation , since it must be present before the fecal mass forms to have any effect, but may be useful for prevention of constipation in patients with recurrent problems, or those who are about to take a constipating drug, such as narcotic analgesics .
Mineral oil is an emollient laxative. It acts by retarding intestinal absorption of fecal water, thereby softening the stool.
The hyperosmotic laxatives are glycerin and lactulose (Chronulac, Duphalac), both of which act by holding water within the intestine. Lactulose may also increase peristaltic action of the intestine.
Laxatives are used to treat constipation—the passage of small amounts of hard, dry stools, usually fewer than three times a week. Constipation may be caused by several conditions, some of which are potentially serious, and require medical attention:
- Neurologic—caused by failure of nerves to stimulate movement of the muscles of the intestines.
- Obstructive—failure of the muscles in the intestine to open, or presence of a mass that's blocking passage of the feces through the intestine.
- Endocrine/metabolic—caused by some diseases including hypothyroidism.
- Medicinal—caused by some drugs, including narcotic analgesics, iron, and some drugs used in cancer treatment.
Chronic constipation occurs in 1–4% of children between the ages of four and 10. If constipation continues, it should be treated by a physician.
A reasonable first step is to assure that there is enough fiber in the diet. This may be done by switching to a high fiber breakfast cereal. If this doesn't lead to improvement, then medical attention is necessary.
Short term use of laxatives is generally safe except in appendicitis , fecal impaction, or intestinal obstruction. Lactulose is composed of two sugar molecules; galactose and fructose, and should not be administered to patients who require a low galactose diet.
Chronic use of laxatives may result in fluid and electrolyte imbalances, steatorrhea, osteomalacia, diarrhea , cathartic colon, and liver disease. Excessive intake of mineral oil may cause impaired absorption of oil soluble vitamins , particularly A and D. Excessive use of magnesium salts may cause hypermanesemia.
Excessive use of laxatives may result in dependency on these products. This may cause a condition known as cathartic colon.
Excessive use of laxatives that contain sodium or magnesium may result in dangerously high blood levels of these elements.
Mineral oil and docusate should not be used in combination. Docusate is an emulsifying agent which will increase the absorption of mineral oil.
Bisacodyl tablets are enteric coated, and so should not be used in combination with antacids. The antacids will cause premature rupture of the enteric coating.
Preventing side effects
Used properly, laxatives are very safe. Do not overuse or give in doses larger than those labeled. If constipation persists, obtain medical help.
Laxatives should not be used too frequently. Bulk laxatives such as psyllium should be the normal first choice.
Mineral oil should not be given to infants or other children while laying down. This may result in the oil going into the lungs.
Carbohydrates —Compounds, such as cellulose, sugar, and starch, that contain only carbon, hydrogen, and oxygen, and are a major part of the diets of people and other animals.
Cathartic colon —A poorly functioning colon, resulting from the chronic abuse of stimulant cathartics.
Colon —The part of the large intestine that extends from the cecum to the rectum. The sigmoid colon is the area of the intestine just above the rectum; linking the descending colon with the rectum. It is shaped like the letter S.
Diverticulitis —Inflammation of the diverticula (small outpouchings) along the wall of the colon, the large intestine.
Fiber —Carbohydrate material in food that cannot be digested.
Hyperosmotic —Hypertonic, containing a higher concentration of salts or other dissolved materials than normal tissues.
Osteomalacia —A bone disease that occurs in adults due to a prolonged period of vitamin D deficiency. It is characterized by softening of the bone and is sometimes referred to as adult rickets.
Steatorrhea —An excessive amount of fat in the feces due to poor fat absorption in the gastrointestinal tract.
Stool —The solid waste that is left after food is digested. Stool forms in the intestines and passes out of the body through the anus.
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Samuel Uretsky, PharmD