Laxatives

Definition

Laxatives are products that promote bowel movements.

Purpose

Laxatives are used to treat constipation—the passage of small amounts of hard, dry stools, usually fewer than three times a week. Before recommending use of laxatives, differential diagnosis should be performed. Prolonged constipation may be evidence of a significant problem, such as localized peritonitis or diverticulitis. Complaints of constipation may be associated with obsessive-compulsive disorder. Use of laxatives should be avoided in these cases. Patients should be aware that patterns of defecation are highly variable, and may vary from two to three times daily to two to three times weekly.Laxatives may also be used prophylacticly for patients, such as those recovering from a myocardial infarction or those who have had recent surgery, who should not strain during defecation.Laxatives are also used to cleanse the lower bowel before a colonoscopy or similar diagnostic procedure.

Description

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. Psyllium (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. Many primary care physicians suggest that patients try laxatives in this category before using saline or stimulant laxatives.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.Some newer options for the treatment of chronic constipation are being developed by various groups of researchers. These include such alternative therapies as biofeedback; newer drugs like tegaserod (Zelnorm) and prucalopride, which stimulate peristalsis; a nerve growth factor known as neurotrophin-3; and electrical stimulation of the colon.

Recommended dosage

See specific products.

Precautions

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.Lactulose and magnesium sulfate are pregnancy category B. Casanthranol, cascara sagrada, danthron, docusate sodium, docusate calcium, docusate potassium, mineral oil and senna are category C. Casanthranol, cascara sagrada and danthron are excreted in breast milk, resulting in a potential increased incidence of diarrhea in the nursing infant.The American College of Toxicology states that cathartics should not be used as a means of clearing poisons from the digestive tract of a poisoning victim. Although some physicians have administered these laxatives along with activated charcoal in order to reduce the body's absorption of the poison, this treatment is no longer recommended.

Interactions

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.

Key terms

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 large intestine.Diverticulitis — Inflammation of the part of the intestine known as the diverticulum.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 disease of adults, characterized by softening of the bone. Similar to rickets which is seen in children.Pregnancy category — A system of classifying drugs according to their established risks for use during pregnancy. Category A: Controlled human studies have demonstrated no fetal risk. Category B: Animal studies indicate no fetal risk, but no human studies, or adverse effects in animals, but not in well-controlled human studies. Category C: No adequate human or animal studies, or adverse fetal effects in animal studies, but no available human data. Category D: Evidence of fetal risk, but benefits outweigh risks. Category X: Evidence of fetal risk. Risks outweigh any benefits.Steatorrhea — An excess of fat in the stool.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.

Resources

Books

Beers, Mark H., MD, and Robert Berkow, MD., editors. "Diarrhea and Constipation." In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2004.Karch, A. M. Lippincott's Nursing Drug Guide. Springhouse, PA: Lippincott Williams & Wilkins, 2003.

Organizations

American Society of Health-System Pharmacists (ASHP). 7272 Wisconsin Avenue, Bethesda, MD 20814. (301) 657-3000. http://www.ashp.org.National Digestive Diseases Information Clearinghouse. 2 Information Way, Bethesda, MD 20892-3570. nddic@aerie.com. http://www.niddk.nih.gov/Brochures/NDDIC.htm.United States Food and Drug Administration (FDA). 5600 Fishers Lane, Rockville, MD 20857-0001. (888) INFO-FDA. 〈http:/www.fda.gov〉.

单词	laxatives
释义	laxatives laxatives Used to promote easy defecation. EncyclopediaSeelaxative Laxatives Laxatives Definition Laxatives are products that promote bowel movements. Purpose Laxatives are used to treat constipation—the passage of small amounts of hard, dry stools, usually fewer than three times a week. Before recommending use of laxatives, differential diagnosis should be performed. Prolonged constipation may be evidence of a significant problem, such as localized peritonitis or diverticulitis. Complaints of constipation may be associated with obsessive-compulsive disorder. Use of laxatives should be avoided in these cases. Patients should be aware that patterns of defecation are highly variable, and may vary from two to three times daily to two to three times weekly.Laxatives may also be used prophylacticly for patients, such as those recovering from a myocardial infarction or those who have had recent surgery, who should not strain during defecation.Laxatives are also used to cleanse the lower bowel before a colonoscopy or similar diagnostic procedure. Description 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. Psyllium (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. Many primary care physicians suggest that patients try laxatives in this category before using saline or stimulant laxatives.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.Some newer options for the treatment of chronic constipation are being developed by various groups of researchers. These include such alternative therapies as biofeedback; newer drugs like tegaserod (Zelnorm) and prucalopride, which stimulate peristalsis; a nerve growth factor known as neurotrophin-3; and electrical stimulation of the colon. Recommended dosage See specific products. Precautions 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.Lactulose and magnesium sulfate are pregnancy category B. Casanthranol, cascara sagrada, danthron, docusate sodium, docusate calcium, docusate potassium, mineral oil and senna are category C. Casanthranol, cascara sagrada and danthron are excreted in breast milk, resulting in a potential increased incidence of diarrhea in the nursing infant.The American College of Toxicology states that cathartics should not be used as a means of clearing poisons from the digestive tract of a poisoning victim. Although some physicians have administered these laxatives along with activated charcoal in order to reduce the body's absorption of the poison, this treatment is no longer recommended. Interactions 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. Key terms 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 large intestine.Diverticulitis — Inflammation of the part of the intestine known as the diverticulum.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 disease of adults, characterized by softening of the bone. Similar to rickets which is seen in children.Pregnancy category — A system of classifying drugs according to their established risks for use during pregnancy. Category A: Controlled human studies have demonstrated no fetal risk. Category B: Animal studies indicate no fetal risk, but no human studies, or adverse effects in animals, but not in well-controlled human studies. Category C: No adequate human or animal studies, or adverse fetal effects in animal studies, but no available human data. Category D: Evidence of fetal risk, but benefits outweigh risks. Category X: Evidence of fetal risk. Risks outweigh any benefits.Steatorrhea — An excess of fat in the stool.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. Resources Books Beers, Mark H., MD, and Robert Berkow, MD., editors. "Diarrhea and Constipation." In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2004.Karch, A. M. Lippincott's Nursing Drug Guide. Springhouse, PA: Lippincott Williams & Wilkins, 2003. Organizations American Society of Health-System Pharmacists (ASHP). 7272 Wisconsin Avenue, Bethesda, MD 20814. (301) 657-3000. http://www.ashp.org.National Digestive Diseases Information Clearinghouse. 2 Information Way, Bethesda, MD 20892-3570. nddic@aerie.com. http://www.niddk.nih.gov/Brochures/NDDIC.htm.United States Food and Drug Administration (FDA). 5600 Fishers Lane, Rockville, MD 20857-0001. (888) INFO-FDA. 〈http:/www.fda.gov〉. AcronymsSeeLX
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