Although constipation is a frequent complaint among the elderly, the use of laxatives is not always warranted. Increases in physical activity, fluid intake, and dietary fiber may be sufficient measures to control constipation.
Laxatives are the most frequently prescribed drugs in personal care homes in Manitoba, Canada. From April 1987 to April 1988, 13% of the total drug costs was for laxatives.1 In addition to the costs involved in using laxatives is the time factor. Nurses and aides spend considerable time distributing laxatives, time that could be spent evaluating and meeting other residents' needs.
This article will review the use of laxatives specifically relating to their use in elderly individuals who reside in a personal care home. Although laxatives may also be used for diagnostic studies, treatment of irritable bowel syndrome, hemorrhoids, and medical or surgical illness, these uses will not be addressed. Both pharmacological and non-pharmacological methods of treating constipation will be discussed.
ORIGIN OF CONSTIPATION
To understand laxatives, their mode of action, and possible side effects, it is necessary to review the mechanism of defecation.
Normal activity in the colon involves mixing and propulsive movements. The mixing movements cause segmentation of the lumen, which exposes the colonic contents to the surface of the large intestine. The main force propelling the contents through Mhe intestine is peristalsis, the wormlike wave motion that occurs involuntarily and is induced by distention of the intestinal lumen. These waves consist of contraction followed by relaxation of the circular layers of the smooth muscle fibers of the wall of the intestine. The rate of elimination of the colonic contents depends on water absorption in the large intestine: increased water absorption results in constipation whereas diarrhea may occur if water absorption is decreased.
The urge to defecate is felt when a mass of feces accumulates in the rectum. Regular bowel movements are initiated by nerve impulses that relax the internal and external sphincters. Simultaneous contractions of the muscles of the abdominal wall tend to expel the feces out of the rectum.
A complex interplay of factors such as gastric, sympathetic, and parasympathetic innervation, local neuronal effects, and central nervous system integration influence peristaltic movements. Meals and physical activity, for example, stimulate peristaltic movement, whereas certain drugs, such as morphine, decrease peristaltic movement.
Constipation is defined as a decrease in the frequency of bowel movements accompanied by a prolonged and difficult passage of stool. This is usually followed by a sensation of incomplete evacuation.2 It is important to note that constipation is not solely defined by the number of bowel movements within a certain period. In healthy individuals, the frequency can vary from one bowel movement every 24 hours to one every 3 to 4 days. Thus, constipation does not exist merely because the resident failed to have a daily evacuation of the bowel. In constipation, mean colonic transit time (the time required for the fecal mass to travel the length of the colon) is significantly slowed, but gastric emptying time and small intestine transit time do not change.2
MAJOR CAUSES OF CONSTIPATION*
Because bowel function can vary significantly from person to person, it is important that a history of the resident's bowel habits be obtained on admission to the facility. Some questions to ask residents include how many times a week do they usually move their bowels? What method(s), if any, did they use at home for keeping their bowels regular? Once this information has been ascertained, the resident's routine should be followed, not the facility's.
Constipation is prevalent among the elderly for numerous reasons. In many elderly persons, constipation developed in early life and has simply worsened with age; in others, it has developed in their later years. Pathophysiologically, the aging bowel has diminished contractual muscle tone and loss of neuronal sensitivity. Anatomically, the aging bowel may develop diverticula that contribute to uncoordinated contractions of colonic muscle. The other major causes of constipation in the elderly include neglecting to respond to the defecation urge; failure to acquire the habit of regular defecation; faulty eating habits; environmental changes; psychological stress; decreased food intake or increased intake of highly processed, low-bulk foods; metabolic disorders; depressions; and prolonged use of constipating drugs such as aluminum hydroxide, opiates, and calcium channel blocking agents. Causes of constipation in the elderly are summarized in Table 1.
The main objectives in managing constipation are to empty the rectum of its fecal contents and restore normal habits of defecation.3 Before drug therapy for constipation is initiated, it is important to rule out the presence of any disorders that can cause constipation. Also, a review of medication use, including use of over-the-counter drugs, may identify contributing medicines that could be changed or discontinued. However, modifications of the medication regimen are often impossible or impractical. Psychological influenees also cannot be ignored. In a double-blind study of 20 patients with chronic constipation, 14 obtained relief with the use of a placebo.4 Discussion and treatment of psychological problems may be all the treatment that is necessary.
ACTION OF LAXATIVES ON THE BOWEL*
Constipation should first be treated by non-pharmacological measures. This may include increases in physical activity, fluid intake, and dietary fiber.
Regular exercise is an important part of a bowel management program because it stimulates gut motility. For some elderly residents who are immobile due to neuromuscular disorder, arthritic joints, or generalized weakness, a regular exercise program may not be possible. However, even a small increase in activity has been shown to stimulate the bowel. Lor example, such modest activity as sitting up in bed or turning or twisting in a chair causes some distinct changes in colonic motility.5 If the patient is able, walking 20 to 30 minutes a day is a good form of exercise.5
Liquids are natural stool softeners; therefore, a glass or two of water on rising, between meals, and at bedtime should be prescribed. Coffee, tea, or juice, especially grapefruit, are not substitutes as they act as diuretics and thus decrease body fluids.5 Therefore, their use should be limited.
Dietary fiber is also extremely important in preventing constipation. Because fiber holds water, stools tend to be softer, bulkier, and heavier in persons with a higher fiber intake. Fiber also speeds slow passage through the intestine and slows rapid transit time.5 Raisins, broccoli, beans, dried apricots, and sweet potatoes contain generous helpings of fiber. Wheat bran is one of the top constipation preventives and is now available in many cereals and breads. Ten to 20 g (approximately 3 tbsp) of wheat bran supplies roughly 10 g of dietary fiber.6 A 100 g portion of bran flakes contains between 2.7 g and 6.5 g of crude fiber, and one slice of whole wheat bread contains between 1 g and 2 g. It is recommended that residents should receive at least 6 g to 10 g of dietary fiber per day. Although prunes and prune juice are often recommended as a source of fiber, prunes contain 2 g of fiber and prune juice has almost none. Prunes also contain Phenolphthalein and may cause cathartic colon if used long-term.7 Even more important, when a person who is used to eating prunes suddenly stops, constipation may result.
Another area that is often overlooked in the management of constipation is the establishment of a regular bowel routine. Most authorities recommend attempting defecation after breakfast as this is when the strongest propulsive contractions occur. Bowel retraining may also be necessary; however, this can be a very difficult and timeconsuming process.
If these non-pharmacological methods fail after being tried for an appropriate time, such as 2 to 4 weeks, then laxatives may be used. It must be stressed, however, that the habit oil regular drug use (except for the bulkforming type) to produce daily bowel movements is proscribed.
CLASSES OF LAXATIVES
Laxative, cathartic, and purgative describe agents that act on the large intestine (colon, bowel) to promote defecation, but these terms have evolved to represent different degrees of action. A laxative produces soft stools with a minimal incidence of abdominal cramping. A cathartic produces a soft to fluid stool and may also cause abdominal cramping. A purgative produces a watery stool and violent cramping to such an extent that shock and hemorrhaging may result.
Purgatives are no longer used in medical practice, and only some cathartics, also called stimulant or contact laxatives, are commonly used. Traditionally, laxatives are classified as bulk forming, osmotic, surfactant (wetting agent), contact (stimulant, irritant), lubricant (emollient), or suppositories and enemas. The action of these laxatives on the bowel is shown in Figure 1 .
Valid indications for the use of laxatives are limited. The need is clear in patients with disorders that require avoidance of straining, such as coronary artery disease, aortic aneurysm, or stroke. In the absence of such disorders, the prospective use of laxatives should be carefully evaluated as constipation can lead to fecal incontinence, intestinal obstruction, mental disturbances, retention of urine, or rectal bleeding. Therefore, appropriate use of laxatives must be followed.
This class of laxatives includes bran, methylcellulose, polycarbophil, and psyllium hydrophilic mucilloid. These laxatives act by retaining water so that the stool remains large and soft. Peristalsis is also stimulated. Bacterial metabolism of these products may further promote defecation by the production and accumulation of osmotically active acidic metabolites.4
It has been found that increasing the dietary fiber by 25% to 40% with the addition of bran can reportedly eliminate and prevent constipation in up to 60% of patients as well as reduce the mean intestinal transit time from 126 hours to 86 hours.7 Unprocessed bran, apparently because of its superior water-holding effect, provides greater laxative effect than processed bran.8 Cereals such as 100% Bran or Allbran have about half as much bran as the same weight of unprocessed bran.
The amount of bran required (usually 10 g to 20 g daily), however, may produce erratic bowel habits, gaseousness, and abdominal discomfort during the first few weeks of therapy. Bran may also worsen hypocalcemia and reduce serum iron and should be used with caution in these disorders. The use of bran and other bulk-forming laxatives is contraindicated in bedbound constipated residents because it may compound the problem by increasing bulk in the already distended colon. These agents are also contraindicated in residents with intestinal stricture because they may hasten intestinal obstruction.
The effects of bulk-forming laxatives are generally seen within 24 hours, but sometimes may not manifest for as long as 3 days. These laxatives should be given with large amounts (at least 8 oz. with each dose) of water to prevent intestinal obstruction.
Bulk-forming laxatives should not be administered concomitantly with drugs such as digoxin or salicylates as these laxatives may inhibit their absorption (Table 2). Special care should also be taken with diabetic residents and those receiving sodium restricted diets. Most bulk laxatives that contain psyllium also contain up to 50% dextrose. Diabetics often have decreased gastric emptying and other motor disturbances of the bowel that may complicate the use of bulk laxatives. Individuals receiving sodium restricted diets should avoid using Metamucil instant mix, which contains 200 mg of sodium per pack.
DRUG INTERACTIONSWITH LAXATIVES*
Polycarbophil (Mitrolan) is a synthetic hydrophilic polyacrylic resin, which can absorb up to 60 times its weight in water. Comparative clinical trials are required to document its effectiveness compared with other bulkforming laxatives.
Methylcellulose (Citrucil) is a new bulk laxative. Its advantages over Metamucil are that it is less gritty and it does not contain sodium. However, it contains 5 g of sugar per dose.
Osmotic (Saline) Laxatives
This group of laxatives consists of magnesium, sulfate, phosphate, and tartrate ions. They act by attracting water osmotically into the lumen of the large intestine, and the resulting bulk stimulates peristalsis. More recent findings suggest that saline cathartics stimulate the release of cholecystokinin, which inhibits the absorption of fluid and electrolytes from the jejunum and ileum.9 Osmotic laxatives empty the bowel in 2 to 6 hours. The sulfate salts are considered to be the most potent of this group of laxatives, followed by magnesium salts. Phosphates or tartrates are the weakest.
Residents with poor kidney function should not receive salts of magnesium, sulfate, or phosphate (ie, magnesium hydroxide or sulfate, sodium phosphate) because they cannot excrete the extra salt load from the small fraction of the salt that is absorbed systemically. In addition, an accumulation of magnesium, sulfate, and phosphate ions may occur. For example, serum magnesium levels may rise to toxic levels in residents with renal impairment and cause central nervous system depression, hypotension, muscle weakness and electrocardiographic changes.4 The use of phosphate salts has reportedly produced hyperphosphatemia, hypocalcemia, tetany, hypernatremia, and dehydration.4
Lactulose, also an osmotic agent, is a synthetic disaccharide that is not hydrolyzed by intestinal enzymes and is not absorbed. Instead, lactulose is degraded by bacteria in the colon to short-chain organic acids, which are also not absorbed but act as osmotic agents. The net effect is a moderate fluid accumulation in the colon and the formation of a soft stool. Some of the disadvantages of using lactulose, however, are that it is unpalatably sweet for some residents; it should be used with caution in residents with diabetes because it contains some digestible sugars; it may take 24 hours to 48 hours after a dose for a normal bowel movement to occur; and the cost is considerably higher than other laxatives. In addition, in higher than recommended doses, lactulose may cause flatulence, cramps, diarrhea, and electrolyte imbalance and tolerance may develop with prolonged use. 10
With the osmotic laxatives, the resident should be given at least a full glass of water so that no net fluid loss occurs. Without adequate fluid replacement, osmotic laxatives can produce dehydration.
Surfactants (Wetting Agents)
The dioctyl sulfosuccinates are anionic surface active agents that have detergent activity. They lower surface tension at the oil-water interface of the stool, thereby allowing the fecal material to be penetrated by water and fat. Recent findings suggest that in addition to acting directly on the stool, these drugs might change intestinal morphology and interfere with cellular function. They also appear to cause fluid and electrolyte accumulation in the colon.8 They are recommended for residents with hard, dry stools who have normal intestinal tone or for those who must avoid straining. When used on a chronic, routine basis, they appear to be of little value in the prevent tion of constipation.11
The dioctyl sulfosuccinates are available as sodium or calcium salts; however, not enough sodium or calcium is contained in these products to be of clinical concern. It is recom-, mended that drugs with a low therapeutic index and relatively poor absorption characteristics, such as digoxin and aspirin, not be administered at the same time as these surfactants. In controlled laboratory studies, these agents have been found to facilitate the absorption of poorly absorbable substances and they may increase the toxicity of such substances.11
Contact (Stimulant) Laxatives
There are three basic types of stimulant laxatives: castor oil; anthraquinones (Senekot); and diphenylmethanes (Dulcolax). The stimulant laxatives can induce a relatively mild laxative action, or in high dosages can produce severe cramping. Their chronic use may result in fluid and electrolyte disturbances, malabsorption, enteric loss of protein, cathartic colon, and a darkened pigmentation of the colonic mucosa.
Castor oil is a potent laxative but has no use in the treatment of chronic constipation. It is hydrolyzed in the proximal small intestine by pancreatic lipase enzymes to produce the active metabolite, ricinoleic acid. Ricinoleic acid induces defecation by the stimulation of an influx of fluid into the lumen of the gut while inhibiting salt and water absorption. Chronic use is discouraged because it may cause morphologic damage to the intestinal mucosa, erosion of villi, and malabsorption of nutrients.
Anthraquinones include senna, cascara sagrada, and aloe. These laxatives pass mostly unchanged through the small intestine to the colon. A portion of the dose is absorbed and subsequently acts on the colon. Their exact mechanism of action is unknown; direct stimulant activity, stimulation of the myenteric plexus, and altered sodium transport may be involved. Because their action is mainly limited to the colon, the onset of action is from 6 hours to 12 hours. Senna preparations are more irritating than cascara and often produce colic and discomfort. Senna and cascara color an acid urine yellow-brown and an alkaline urine red. Because aloe is a powerful irritant laxative causing griping and pelvic vascular congestion, it is not recommended.
Diphenylmethanes include bisacodyl and Phenolphthalein, both of which supposedly act directly on the mucosal nerve plexus of the colon. Phenolphthalein enters the enterohepatic circulation and may be effective for several days. Therefore, it is not recommended for geriatric individuals. Excessive and prolonged use of this particular laxative can also induce osteomalacia secondary to impaired absorption of vitamin D and calcium.
Bisacodyl is chemically related to Phenolphthalein, but only 5% is absorbed compared with 15% for Phenolphthalein.4 No systemic toxicity has yet been reported. Bisacodyl tablets are available in the enteric coated form to avoid release of the active ingrethent in the stomach. Bisacodyl is irritating to the gastric mucosa and may cause abdominal distress. Tablets should not be taken concurrently with or within 1 hour of antacid medication or H2 blockers because an increase in gastric pH will cause a dissolution of the enteric coating of the tablet. These tablets also should not be chewed.
Lubricant (Emollient) Laxatives
The most commonly used lubricant laxative is mineral oil, obtained from petroleum and consists of a mixture of liquid hydrocarbons. The oil is indigestible, but minute quantities are absorbed from the intestinal tract. Mineral oil exerts its laxative effect by lubricating fecal content, thus preventing excessive dehydration. The feces remains son and its passage is facilitated. Mineral oil should not be used as a laxative for a number of reasons. It may interfere with the absorption of fat soluble vitamins (A, D, E, and K), calcium, phosphate, and other nutrients. Lipid pneumonia, localized granuloma, and pulmonary fibrosis may occur following aspiration of mineral oil. Large doses of the oil may also cause leakage through the anal sphincter, soiling clothing and bed linen.
BOWEL REGULATION TREATMENT PLAN*
Suppositories and Enemas
Although most laxatives are available in oral form, suppositories and enemas are also commonly employed. Glycerin suppositories, for example, have been in use for many years. Glycerin is ineffective when taken orally because it is rapidly absorbed and metabolized. Elderly residents experiencing mild and infrequent constipation can usually obtain relief from a glycerin suppository. It induces defecation within 30 minutes of use by stimulating retention of fluid in the rectum. Rectal irritation can occur with its use.
Bisacodyl is also available in suppository form. It takes from 15 minutes to 1 hour to produce its effects. Again, as with glycerin suppositories, a mild burning sensation may occur in the rectum following administration.
Enemas should not be routinely prescribed for the elderly but reserved for only the most difficult cases of constipation. Incorrect use can produce fluid and electrolyte imbalances and, sometimes, even colonic perforation.12 The mechanism that induces defecation varies with the enema fluid used. Sodium phosphate/biphosphate (Fleet) adds bulk by osmotic effects; mineral oil softens and lubricates hardened stool. Regardless of the enema fluid chosen, only the distal colon will be evacuated when an enema is properly administered. This closely approximates a normal bowel movement.
The use of suppositories requires less nursing time than enemas and is aesthetically more pleasing to the resident. One drawback, however, is that suppositories are not very effective if hard, dry stool is present.
CHOICE OF LAXATIVES
As stated previously, before a laxative is prescribed, it is very important to determine whether a laxative is necessary at all. There is a tendency to indiscriminately prescribe laxatives for every resident in a long-term care facility whether they are needed or not.
In active, ambulatory elderly residents who fail to respond to increased dietary fiber and hydration, a bulk laxative should be tried first. Nonresponders are likely to be sedentary or debilitated, chronic abusers of stimulant laxatives, or residents with reduced colonic peristalsis for other reasons. In these residents, bulk agents alone may produce a large collection of soft stool in the descending and sigmoid colon that is difficult to pass. These residents will often require the addition of a mild stimulant to the bulk agent. Alternatively, an osmotic laxative with colonic stimulating properties such as Milk of Magnesia may be added. In residents who cannot tolerate bulk laxatives or those on fluid restriction, a combination stool softener and stimulant should be tried.
Stool softeners or bulk agents with increased hydration are useful in residents whose constipation is characterized by regular but hard and difficultto-pass stools. Stool softeners are also useful in residents with hemorrhoids or medical problems where straining is detrimental. Stool softeners are not of much value in elderly residents with hypotonic constipation. The colon in these residents is full of putty-like stool that cannot be evacuated. Those who do not respond adequately to a high fiber diet or bulk laxatives may require a contact laxative in addition.
In residents with acute constipation and stool present in the rectum, a glycerin or bisacodyl suppository will usually produce prompt results. Alternatively, an enema may be used.
Figure 2 is a stepwise approach to constipation based on the previous principles.
Laxatives are agents that relieve constipation through several mechanisms. Laxatives may act as stimulants, lubricants, bulk-producers, or fecalsofteners.
The use of laxatives is widespread not only in Manitoba personal care homes but throughout North American hospitals and long-term care facilities. The occasional use of a laxative is not harmful; however, the daily use of these drugs for achieving a bowel movement may be detrimental because of the side effects they can produce and possible drug interactions (Table 2). Therefore, more discriminant use is warranted not only for the residents' welfare but also because of the cost factors.
Potential solutions to the overuse of laxative agents include the use of dietary bran. In addition, there should be less regular administration of stimulant and osmotic agents, more regular or daily administration of bulk-forming laxatives and stoolsofteners, and no use of lubricant agents. Finally, an increase in the awareness of normal gastrointestinal physiology and the role of non-drug factors needs to be emphasized.
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MAJOR CAUSES OF CONSTIPATION*
DRUG INTERACTIONSWITH LAXATIVES*