Sunday, January 15, 2006

laxatives

(see Tables 19, 20) Laxatives are mild cathartics that loosen the bowels without pain. They are classified in several different categories including bulk-forming, stimulant, saline, emollient (stool softner), hyperosmotic (increased osmosis), and surfactant laxatives.
Laxative use is prevalent in the elderly, but only in a few cases must laxatives be taken chronically. Between 15 percent and 30 percent of the population older than 60 years of age take at least one dose of laxative per week. Most constipation should be relieved with diet. A good intake of fruit (prunes, apples), high-fiber foods (bran, vegetables), and fluids help most elderly regulate bowel function. An acute episode of fecal impaction or constipation can usually be treated safely with a saline enema. Once acute constipation has been relieved, dietary manipulation, suppositories, and even weekly enemas may be used.
Bulk-forming laxatives are effective through absorption and retention of large amounts of water and are also useful in treating diarrhea. Effects are normally seen within 12 to 24 hours but could take up to three days for a full effect. These laxatives must be taken with water. Special care should be taken with diabetics and those on a salt restricted diet, although side effects are infrequent. An example of a bulk-forming laxative is Metamucil®.
Stimulant laxatives are the type most abused by the public. They can induce a mild laxative action or, in high doses, produce severe cramping and fluid and electrolyte imbalance. With chronic abuse enteric loss of protein and malabsorption can occur. When used correctly, stimulants are useful for acute constipation secondary to other medication, due to prolonged bed rest or hospitalization, and as preparation for abdominal X-rays. Castor oil is in this group of laxatives. Chronic use of castor oil can cause erosion of the intestinal villi, leading to malabsorption of nutrients.
Saline laxatives include sulfate and magnesium salts. People are advised to drink at least eight ounces of water with the laxative to avoid dehydration. Effects are usually produced in three to six hours. In an elderly person, especially one with renal failure, toxic serum levels of magnesium can result. This is characterized by central nervous system depression, hypotension, muscle weakness, and electrocardiographic changes. An example is magnesium sulfate (Milk of Magnesia). Mineral oil is an emollient laxative and should not be used in elderly patients. Most problems occur from chronic mineral oil aspiration. Aspiration can produce acute and chronic pneumonitis (inflammation of the lungs), localized granuloma, and pulmonary fibrosis. Patients taking oral anticoagulants and mineral oil will find the anticoagulants (agents preventing clotting) absorbed poorly. Hyperosmotic laxatives include glycerin and lactulose. Glycerin in suppository form is usually effective within a half hour. Because it is rapidly absorbed and broken down systemically it is ineffective when taken orally. Lactulose is especially useful in treating the elderly. Glycerin suppositories are ineffective if fecal impaction with hard dry stools is present.
Surfactant laxatives work by a detergent activity and are especially effective for conditions where straining should be avoided, such as after abdominal surgery. Surfactants appear to be of little value in preventing constipation, however.
See also FECAL IMPACTIONS.
Covington, T., and Walker, J. Current Geriatric Therapy. Philadelphia: W. B. Saunders, 1984.



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