Constipation is an often-overlooked problem in primary care practice. It deserves careful evaluation, including consideration of the many possible causes and appropriate diagnostic testing. Fortunately, most patients respond well to conservative measures.
Constipation prompts a visit to a physician by 1.2% of the US population every year (although most persons with constipation do not seek the assistance of a physician).What You Should Know About Constipation,” is included with this article. (For your convenience, it may be freely duplicated and distributed.)
Suggested lifestyle changes include moderate physical activity, increased fluid intake, increased dietary fiber, and sitting on the toilet about 15–20 minutes after breakfast (taking advantage of the gastrocolic reflex). In selected patients, these changes may be useful, although specific benefits of moderate physical activity and increased fluid intake have not been conclusively proven.
Wheat bran is one of the best and least expensive bulk laxatives. Methylcellulose (eg, Citrucel), psyllium (eg, Metamucil), and polycarbophil (eg, FiberCon) are bulk laxatives that are safe, more refined, and more concentrated than wheat bran, but they are also more expensive. Combined with diet and liquids, bulk laxatives are the most effective and “natural” long-term treatment for constipation. However, their slow onset of action (between 12 and 72 hours) limits their usefulness in acute management of constipation.
The saline laxatives include magnesium citrate (eg, Citroma) and magnesium hydroxide (eg, Milk of Magnesia). These agents decrease colonic transit time by stimulating cholecystokinin and draw fluid into the colon by their osmotic effect. Their rapid onset of action (between 30 minutes and 3 hours) makes saline laxatives an excellent choice for acute management of constipation. These laxatives commonly cause abdominal cramping and, in patients with renal failure, may cause magnesium toxicity. Nevertheless, saline laxatives are generally safe and effective.
Polyethylene glycol (eg, MiraLax) is an effective new osmotic laxative. Rapid onset of action (between 24 and 48 hours) makes an osmotic a good choice for patients who have chronic constipation that fails to respond to bulk and saline laxatives. Polyethylene glycol is equally effective, but better tolerated than the older osmotics, lactulose and sorbitol.16 Because it is not fermented, gas and cramps are minimal. Lactulose (eg, Chronulac) and sorbitol, which are poorly absorbed sugars, likewise have rapid onset of action, but flatulence and abdominal distention may limit tolerance. Sorbitol is generally less expensive than lactulose.
The oral stimulant laxatives include diphenylmethanes, the anthraquinones, and castor oil (eg, Emulsoil). They are more potent than bulk or osmotic laxatives, but long-term use is safe if limited to 3 days per week. Bisacodyl (eg, Dulcolax), a diphenylmethane, alters electrolyte transportation within intestinal mucosa and stimulates peristalsis. These actions may cause abdominal cramping and hypokalemia. Cascara (mildest), senna (eg, Senokot), and aloe (strongest) are anthraquinones, which are laxatives with actions and side effects similar to bisacodyl. These agents may cause a benign, reversible pigmentation of the colon (melanosis coli). It has been suggested that chronic use of these agents may damage the enteric nervous system, but a causal relationship has not been clearly established. The most prudent approach is to limit use of stimulant laxatives to constipation that is refractory to other laxatives.
Enemas and suppositories
Enemas and suppositories stimulate colonic contractions and soften stools. Water, saline, soap suds, hypertonic sodium phosphate, and mineral oil are used as enemas. Acute water intoxication can occur with water enemas, especially in infants, children, and the elderly, if they have difficulty evacuating the water. Phosphate enemas may cause hyperphosphatemia and hypocalcemic tetany in these patients and should therefore be used with caution in most patients and should not be used in children 3 years of age or younger. Glycerin and bisacodyl are stimulant suppositories that are clinically effective. Bisacodyl and soap suds enemas cause changes in the epithelium of the rectum, and the effect of glycerin on rectal mucosa is unclear. Therefore, these agents should only be used episodically. Mineral oil enemas are used to soften hardened stool in the rectal ampulla.
Other treatment options
More aggressive measures may be necessary for specific types of constipation. These include behavioral therapy and biofeedback for pelvic floor dysfunction, and surgery for slow-transit constipation or Hirschsprung’s disease.
Investigative pharmacologic treatments for constipation include agents that increase colonic contractions (prokinetic drugs) and prostaglandins. These agents have had limited efficacy and troublesome side effects. Therefore, at this time these drugs have limited usefulness in the treatment of constipation.
The management of fecal impaction begins with complete evacuation of the colon. Initially, patients with hard stool in the rectum may be given mineral oil retention enemas followed by manual disimpaction. Prior to further treatment, it is important to obtain an abdominal radiograph to rule out mechanical bowel obstruction. If there is no mechanical bowel obstruction, evacuation of the impaction can be accomplished with oral polyethylene glycol (eg, GoLytely) until clear (up to 8 liters or more may be required for complete evacuation).16 Administration of twice-daily enemas for 3 days or more is an acceptable alternative to oral polyethylene glycol. Lifestyle changes, bulk laxatives, saline, osmotic laxatives, and enemas should be used to maintain regular defecation after the colon has been cleansed. It is reasonable to attempt to withdraw laxatives after several months of regular bowel habits.