IBS Treatment: Anticonstipation Medications

IBS Treatment: Anticonstipation Medications

“Normal” frequency of bowel movements in the general population is three to twelve a week.  So constipation to one person can mean normal bowel patterns to another person.  Constipation is entirely dependent on the individual and generally is considered a decrease in the usual bowel pattern.  Medically, however, constipation refers to when someone has two or less bowel movements a week or has excessive straining with defecation.  There are many different causes of constipation in adults.  Most common is low fiber in the diet, but others include anatomic structural problems (e.g., hemorrhoids), systemic disorders (e.g., hypothyroidism), medications, or generalized disorders (such as IBS) that can slow colonic transit.

Just as there is a multitude of factors that can cause constipation, there are many remedies used to treat constipation.  These anticonstipation agents can be divided into bulking agents and laxatives.  The bulking agents include psyllium, methylcellulose, and polycarbophil.  There are several types of laxatives and they are divided according to how they work: 1) osmotics, 2) stimulants, 3) emollients, and 4) 5-HT4 agonists (Tegaserod).

Bulking Agents
It has been traditionally recommended to treat constipation with a trial of fiber supplements.  This recommendation is now controversial because some studies suggest that 40-70% of people with constipation-predominant IBS had improvement with placebo.  It is now recommended to evaluate and treat the individual rather than follow strict generic protocols.  Psyllium (also known as Metamucil, Fiberall, Reguloid, or Konsyl) is often used as fiber supplementation.  This agent can function as a laxative.  It empties the bowels by absorbing water into the large intestine (colon), increasing fecal bulk, which induces peristalsis (waves that move the feces to the rectum).  It is usually started after the person has been unresponsive to dietary fiber.  Psyllium is available over-the-counter in doses of 4 grams taken one to three times a day.  It should be avoided if there are any allergic reactions or any signs of obstruction, such as acute abdominal pain, nausea, or vomiting. Methylcellulose, polycarbophil, ispaghula husk, and corn fiber are other bulking agents that work in a similar manner to psyllium and are helpful in treating constipation-predominant IBS.

Osmotic laxatives
The osmotic laxatives include 1) milk of magnesia, 2) magnesium citrate, 3) sodium phosphate, 4) lactulose, 5) polyethylene gel and 6) sorbitol.  These agents function by causing water to be drawn into the intestines.  It softens the stools and leads to a watery diarrhea.  All of these medications are in fluid form.

Stimulant Laxatives
These include cascara sagrada, senna, riconelic acid, and diphenylmethane derivatives.  These agents cause diarrhea (secretory diarrhea rather than osmotic diarrhea).

Emollients includes docusates and mineral oil.  They help prevent constipation by soothing the mucosal surfaces of the intestine, making it easier to defecate.

5-HT4 agonist: Tegaserod
Tegaserod is considered a prokinetic agent.  It promotes bowel motility and decreases visceral hypersensitivity.  It works by stimulating the release of neurotransmitters.  March of 2007, Tegaserod was temporarily withdrawn from the United States store shelves after long term safety issues.  It has been associated with ischemic colitis, a potentially fatal condition.  July of 2007, Tegaserod was allowed back on the market albeit with severe restrictions.  It is now only approved for up to twelve weeks of treatment in women younger than 55 years with constipation-predominant IBS.

Videlock EJ, Chang L. Irritable bowel syndrome: current approach to symptoms, evaluation, and treatment. Gastroenterol Clin North Am. Sep 2007;36(3):665-685, x.