gastrointestinal disorders
Constipation
Treatment of Constipation
Possibly discontinuation of causative drugs (some may be necessary) Increase in dietary fiber Possibly trial with a brief course of osmotic laxatives Any identified conditions should be treated. See table Agents Used to Treat Constipation for a summary. Laxatives should be used judiciously. Some (eg, phosphate, bran, cellulose) bind drugs and interfere with absorption. Rapid fecal transit may rush some drugs and nutrients beyond their optimal absorptive locus. Contraindications to laxative and cathartic use include acute abdominal pain of unknown origin, inflammatory bowel disorders, intestinal obstruction, gastrointestinal bleeding, and fecal impaction. The diet should contain enough fiber (typically 15 to 20 g/day) to ensure adequate stool bulk. Vegetable fiber, which is largely indigestible and unabsorbable, increases stool bulk. Certain components of fiber also absorb fluid, making stools softer and facilitating their passage. Fruits and vegetables are recommended sources, as are cereals containing bran. Fiber supplementation is particularly effective in treating normal-transit constipation but is not very effective for slow-transit constipation or defecatory disorders. Behavioral changes may help. Patients should try to move their bowels at the same time daily, preferably 15 to 45 minutes after breakfast, because food ingestion stimulates colonic motility. Initial efforts at regular, unhurried bowel movements may be aided byglycerinsuppositories. Patients with obsessive-compulsive disorder require treatment for that disorder. In addition, physicians must explain that daily bowel movements are not essential, that the bowel must be given a chance to function, and that frequent use of laxatives or enemas (>once every 3 days) denies the bowel that chance. Bulking agents(eg,psyllium, calciumpolycarbophil,methylcellulose) act slowly and gently and are the safest agents for promoting elimination. Proper use involves gradually increasing the dose—ideally taken 3 or 4 times a day with sufficient liquid (eg, 500 mL/day of extra fluid) to prevent impaction—until a softer, bulkier stool results. Bloating may be reduced by gradually titrating the dose of dietary fiber to the recommended dose, or by switching to a synthetic fiber preparation such asmethylcellulose. Osmotic agentscontain poorly absorbed polyvalent ions (eg, magnesium, phosphate, sulfate), polymers (eg,polyethylene glycol), or carbohydrates (eg,lactulose,sorbitol) that remain in the bowel, increasing intraluminal osmotic pressure and thereby drawing water into the intestine. The increased volume stimulates peristalsis. These agents usually work within 3 hours. In general, osmotic laxatives are reasonably safe even when used regularly. However, sodium phosphate should not be used for bowel cleansing because it may rarely cause acute renal failure even after a single use for bowel preparation. These events occurred primarily in older patients, those with preexisting renal disease, and those who were taking drugs that affect renal perfusion or function (eg, diuretics, angiotensin-converting enzyme inhibitors,angiotensin IIreceptor blockers). Also, magnesium and phosphate are partially absorbed and may be detrimental in some conditions (eg, renal insufficiency). Sodium (in some preparations) may exacerbate heart failure. In large or frequent doses, these drugs may upset fluid and electrolyte balance. Another approach to cleansing the bowel for diagnostic tests or surgery or sometimes for chronic constipation uses large volumes of a balanced osmotic agent (eg,polyethylene glycol–electrolyte solution) given orally or via nasogastric tube. Secretory or stimulant cathartics(eg, phenolphthalein,bisacodyl, anthraquinones,castor oil, anthraquinones) act by irritating the intestinal mucosa or by directly stimulating the submucosal and myenteric plexus. Although phenolphthalein was withdrawn from the US market after animal studies suggested the compound was carcinogenic, there is no epidemiologic evidence of this in humans.Bisacodylis an effective rescue drug for chronic constipation. The anthraquinonessenna, cascara sagrada, aloe, and rhubarb are common constituents of herbal and over-the-counter laxatives. They pass unchanged to the colon where bacterial metabolism converts them to active forms. Adverse effects include allergic reactions, electrolyte depletion, melanosis coli, and cathartic colon. Melanosis coli is a brownish black colorectal pigmentation of unknown composition. Cathartic colon refers to alterations in colonic anatomy observed on barium enema in patients with chronic stimulant laxative use. Cathartic colon can cause constipation that leads to more laxative use and thus more constipation, creating a vicious circle. It is unclear whether cathartic colon, which has been attributed to destruction of myenteric plexus neurons by anthraquinones, is caused by currently available agents or other neurotoxic agents (eg, podophyllin), which are no longer available. There does not seem to be an increased risk of colon cancer with long-term anthraquinone use. Enemascan be used, including tap water and commercially prepared hypertonic solutions. Emollient agents(eg,docusate,mineral oil) act slowly to soften stools, making them easier to pass. However, they are not potent stimulators of defecation.Docusateis a surfactant, which allows water to enter the fecal mass to soften and increase its bulk. Peripherally acting mu-opioid receptor antagonists(PAMORAs; eg,methylnaltrexone,naloxegol,naldemedine) can be used to treat opioid-induced constipation that does not resolve with other measures.Alvimopanis a mu-opioid antagonist that is available for short-term hospital use in surgical patients for the treatment of postoperative ileus. Fecal impaction is treated initially with enemas of tap water followed by small enemas (100 mL) of commercially prepared hypertonic solutions. If these do not work, manual fragmentation and disimpaction of the mass may be necessary. This procedure is painful, so perirectal and intrarectal application of local anesthetics (eg,lidocaine5% ointment ordibucaine1% ointment) is recommended. Some patients require sedation. 