Laxatives And Other Therapies For Constipation
Laxatives are considered a first-line medical therapy for constipation. Many people are concerned about the use of laxatives, believing that laxatives are addictive or that their long-term use will compromise the person’s ability to have normal bowel movements.
The function of laxatives is to speed the passage of intestinal contents through the gastrointestinal tract or provide the bulk needed for normal stool formation.
Studies designed to evaluate whether laxatives and fiber therapies improve symptoms and the frequency of bowel movements in adults with chronic constipation have generally shown that fiber and laxatives decreased abdominal pain and improved stool consistency compared with placebo.
The four classes of laxatives are bulk-forming, osmotic, stimulant, and emollient.
Bulk-forming laxatives. Bulk-forming laxatives are the most commonly recommended initial treatments for constipation. Bulk-forming laxatives may work as quickly as 12 hours after use or take as long as 3 days to be effective. Some bulk-forming laxatives are derived from natural sources such as agar, psyllium, kelp, and plant gum. Others are synthetic cellulose compounds such as methylcellulose and carboxymethylcellulose. Natural and synthetic bulk-forming laxatives act similarly. They dissolve or swell in the intestines, lubricate and soften the stool, and make the passage of bowel movements easier and more frequent. Bulk-forming laxatives are not absorbed from the intestines into the body and are safe for long-term use. They are also safe for elderly patients to use (Klaschik 2003; Pietrusko 1977; Rousseau 1988; Yakabowich 1990).
Psyllium is a bulk-forming laxative that is high in fiber. Psyllium seeds contain 10 to 30 percent mucilage. The laxative properties of psyllium are caused by the swelling of the husk when it comes in contact with water. This forms a gelatinous mass and keeps the feces hydrated and soft. The resulting bulk stimulates a reflex contraction of the walls of the bowel, causing them to empty (McRorie 1998). Studies have shown that psyllium fiber is more effective than lactulose and other laxatives, and causes more frequent and bulkier bowel movements. It has also been documented to result in a lower incidence of adverse effects (Klaschik 2003; McRorie 1998).
Osmotic laxatives. Osmotic laxatives work by increasing the amount of water in the small intestine and colon, which increases the size and pliability of the stool. When ingested on an empty stomach, they may take only 1 to 2 hours to take effect. Common osmotic laxatives include milk of magnesium, sorbitol, magnesium citrate, and polyethylene glycol–based formulations. Lactulose is a prescription carbohydrate osmotic laxative that is partially broken down by bacteria in the colon into acids that cause water to accumulate in the colon. Osmotic laxatives can cause severe diarrhea and dehydration, so a physician should carefully monitor their use. In some cases, too much fluid can accumulate in the colon, causing electrolyte disorders. Polyethylene glycol does not contain electrolytes and is suggested for use in patients with heart and kidney disease.
Stimulant laxatives. Stimulant laxatives increase motor activity of the bowels by directly stimulating the nerve plexus in the intestinal wall, causing increased movement and the stimulation of local reflexes (Doughty 2002; Klaschik 2003; Schiller 2004; Wald 2003). Stimulant laxatives should only be used when osmotic laxatives have been ineffective, or in preparation for rectal or bowel examinations. Results occur in 6 to 10 hours. Examples of stimulant laxatives include senna, bisacodyl, and dehydrocholic acid. Stimulant laxatives can cause dehydration and electrolyte problems, in addition to structural and muscular changes in the colon (such as cathartic colon) with long-term use (Joo 1998). In some products, stimulant laxatives are combined with bulk-forming laxatives. Studies have shown that these combination products may be safe to use for up to a year (Phillips 2001).
Emollient laxatives. Emollient laxatives are generally divided into two groups: mineral oil and docusates. Mineral oil works by coating the inside of the colon with a thin layer of oil, which helps retain water in the colon and adds moisture and bulk to the stool. It is often used to prevent straining in patients for whom it would be dangerous to strain (Doughty 2002; Klaschik 2003; Wald 2003). Generally, if physicians recommend mineral oil supplementation for constipation, they advise taking 5 to 30 milliliters (mL) at bedtime. However, chronic mineral oil ingestion can result in malabsorption of fat-soluble vitamins and minerals (and, in some cases, can cause inflammation of the lungs). Physicians do not recommend mineral oil for continuous treatment of constipation.
Docusates promote water retention in the fecal mass, thus softening the stool. They are generally used to prevent straining and are most beneficial when the stool is hard. However, it may be 3 days before a patient experiences results. Fecal softeners should not be used exclusively but may be useful in combination with stimulant laxatives.
Prucalopride is a novel, selective and specific serotonin (5-HT4) receptor agonist that belongs to a new class of medications known as benzofurancarboxamides. Prucalopride may increase the frequency of bowel movements and improve colonic transit, which are key factors in the treatment of chronic constipation (Coremans 2003; Emmanuel 2002; Sloots 2002). It works by operating on serotonin receptors in the gut that stimulate motility.
Tegaserod is a serotonin subtype 4 receptor partial agonist for patients who have chronic constipation. Tegaserod treatment produces significant improvements in the symptoms of chronic constipation and is safe and well-tolerated (Farup 2004; Fisher 2004; Johanson 2004).