American College of Physicians: Internal Medicine — Doctors for Adults ®


Special Focus: Irritable Bowel Syndrome

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From the November/December ACP Observer, copyright © 2007 by the American College of Physicians.

Mark Pimentel, MD, isn't surprised when he takes a patient with irritable bowel syndrome (IBS) off of a half-dozen drugs that others have prescribed to treat the condition—from antispasmodics to laxatives to antidiarrheals—and finds the symptoms don't get worse.

Colored X-ray of the sigmoid colon (far right to center) and rectum (lower center) of a patient with IBS. The rectum, seen at lower center, is distended with gas.

Colored X-ray of the sigmoid colon (far right to center) and rectum (lower center) of a patient with IBS. The rectum, seen at lower center, is distended with gas.

"Just throwing drugs at [IBS] isn't the right option," said Dr. Pimentel, director of the Gastrointestinal Motility Program and Laboratory, Cedars-Sinai Medical Center, Los Angeles, and an editorial consultant for the PIER module on IBS. But he acknowledged that physicians, often frustrated with treating this chronic condition, try to do something for their equally frustrated patients. "It's easy to pull out the prescription pad instead of figuring it out," he said.

Yet recent study findings have pointed to other solutions, based on thinking of IBS as a GI-centric or organic disease rather than one focused on a psychological brain-gut connection. Specifically, the ideas that food poisoning can lead to protracted IBS and that bacteria may be to blame open the door to other treatment options.

Still, physicians should not get complacent about treating their patients with IBS but should continue to monitor the patient for red flag symptoms that might indicate more serious conditions. Patients who continue to present with IBS may still develop colon or pancreatic cancer, Dr. Pimentel cautioned. "IBS is so common, we get lazy. Don't forget other things can happen," he said.


A history and physical exam are the primary ways to evaluate IBS in patients. Typical IBS symptoms include abdominal pain, prominent gastrocolic reflex and excessive gas and flatulence. IBS can be classified as diarrhea-predominant, constipation-predominant or mixed with alternating diarrhea and constipation. These symptoms can wax and wane for years and may be exacerbated by psychological stress.

The Rome and Manning criteria are based on symptoms and do a good job of discriminating IBS from other gastrointestinal disorders.

To apply the Rome criteria, ask about recurrent abdominal pain or discomfort at least three days per month in the past three months, with onset at least six months before diagnosis, associated with two or more of the following:

  • improvement with defecation,
  • onset with change in frequency of stool, or
  • onset associated with a change in the form and appearance of stool.

To use the Manning criteria, look for three or more of the following:

  • pain relief with defecation, often,
  • looser stools at pain onset, often,
  • more frequent stools at pain onset, often,
  • visible abdominal distention,
  • mucus per rectum, or
  • feeling of incomplete evacuation.

Having at least three of the Manning criteria has an average sensitivity of approximately 60% and a specificity of approximately 80% in making the diagnosis of IBS. These criteria are more accurate in women, younger patients and when more criteria are fulfilled.

Clinicians can rely on the Rome or Manning criteria if no red flag symptoms are present to suggest more serious organic disease. Red flags include:

  • significant weight loss,
  • frequent nocturnal awakenings due to gastrointestinal symptoms,
  • fever,
  • blood mixed in the stool,
  • progressively worsening symptoms,
  • new symptoms after age 50,
  • recent antibiotic use, and
  • family history of colon cancer or inflammatory bowel disease.

The physical exam is usually normal in IBS patients except for mild abdominal tenderness or a palpable tender loop of colon. However, neither is sensitive nor specific for IBS. Physical findings not associated with IBS but indicating the need to look for another diagnosis include fever, weight loss, lymph node enlargement, abdominal mass and hepatosplenomegaly.

There are no specific diagnostic tests for IBS. As a result, use laboratory testing to exclude other gastrointestinal disorders.

Consider flexible sigmoidoscopy to exclude colitis or obstructing lesions of the colon. If patients are young, fulfill the Rome criteria and have no red flag symptoms, a presumptive diagnosis of IBS can be made without endoscopy, but they should be revaluated depending on the course of their symptoms over time.

A CBC and ESR can be used to evaluate for anemia and more serious underlying disease. Serum amylase and liver enzyme levels may be useful if pancreatic or biliary disease is suspected.

In the differential diagnosis of constipation-predominant IBS, consider partial colonic obstruction or non-IBS causes of colonic dysmotility due to medications, neurologic disease, hypothyroidism, pelvic floor dysfunction or colonic inertia, in which transit through the colon can take more than five days. For patients under age 45 with mild, chronic, constipation-predominant symptoms and no red flags, recommend fiber and osmotic laxative treatment before performing any tests other than a CBC. However, obtain colonoscopy in patients over age 45 or those with new onset, severe or refractory symptoms or with family history of colon cancer.

In working through the differential diagnosis of diarrhea-predominant IBS, consider examining the stools for Clostridium difficile if the patient has recently taken antibiotics. In general, bacterial cultures are unlikely to be helpful in patients with chronic diarrhea. For younger patients with mild, chronic diarrhea-predominant symptoms, clinicians should consider examining the stools for ova and parasites, especially if the patient has recently traveled where there may have been exposure to parasites. For patients older than 45 years or with refractory, severe or new-onset symptoms, evaluating the entire colon may be warranted to exclude neoplasm.

Patients with pain-predominant symptoms may have partial or intermittent small intestinal obstruction, Crohn's disease, aerophagia or pancreatico-biliary disease. A flat and upright abdominal radiograph during a pain episode may reveal unrecognized bowel obstruction, aerophagia or retained stool. Other rare conditions that may cause pain-predominant abdominal symptoms with some bowel dysfunction include intestinal angina and endometriosis. Use clinical judgment to determine the extent of the evaluation.

Remember that the risk of overlooking a serious condition other than IBS is as low as 1% to 3% if:

  • the history and physical suggest IBS,
  • the Rome or Manning criteria have been satisfied,
  • the stool occult blood test is negative,
  • red flag symptoms are absent, and
  • CBC and ESR are normal.


Consider referral to a gastroenterologist in cases of diagnostic uncertainty—when patients do not fit Rome or Manning criteria, when patients have red flag symptoms, when patients do not respond to initial management or when more specialized diagnostic procedures such as endoscopy are needed. Also, consider consulting mental health professionals, primarily psychologists, for patients with comorbid psychosocial stressors or disorders.


Non-drug therapy

Reassure patients that their symptoms are not due to a life-threatening disorder or just due to stress. IBS is a real illness and patients will benefit from adopting a healthy lifestyle and learning to avoid symptom triggers. The importance of the physician-patient relationship is underscored by the high placebo response in IBS. Many patients benefit from keeping a daily diary of symptoms, including stressors, mood, events and thoughts. The physician can then use the diary to help patients develop self-management techniques.

The diary should also include diet. Although diet modification has not been proven to work and major exclusion diets should be discouraged, consider looking for specific foods that seem to trigger symptoms. It is also important to:

  • evaluate for lactose intolerance,
  • evaluate consumption of caffeine, fructose, sorbitol, sucralose or other zero-calorie sugars that cause bloating and can have a laxative effect,
  • ask about laxative-containing herbal products,
  • ask if patients with gas and bloating are drinking too much carbonated beverages, drinking with a straw or chewing gum, all of which can lead to aerophagia,
  • advise against excessive intake of fats, which can lead to gas retention,
  • advise against eating certain carbohydrates, such as beans, cabbage, broccoli and cauliflower, which may lead to fermentation and gas in the colon, and
  • encourage patients with constipation to increase fiber intake. Studies suggest this can help relieve constipation but not relieve pain.

Drug therapy

Consider drug therapy to reduce pain and diarrhea or constipation even though the effectiveness of most pharmacologic agents may be limited. In a study of 350 patients with IBS, more than half (55%) taking prescription drugs for IBS felt that they were ineffective or only somewhat effective. More than 60% reported adverse effects, and 40% taking over-the-counter medications reported they were ineffective.

The FDA has only approved two drugs, tegaserod maleate and alosetron hydrochloride, both of which now have restricted use. Tegaserod, a 5-HT4-receptor agonist, was approved for treatment of constipation-predominant IBS but is restricted because of an association with myocardial infarction and stroke. Alosetron, a 5-HT3-receptor antagonist, was approved for diarrhea-predominant IBS but has been restricted because of a 1 in 700 risk of ischemic colitis. Prescribing physicians must register with the manufacturer and patients must sign a consent form to begin therapy.

Other drugs may provide relief for some patients with IBS. These include antispasmodics, laxatives, antidiarrheals, antidepressants and antibiotics. (See table, "Drug treatment for irritable bowel syndrome".)

Consider antispasmodics as a first-line agent for pain since they reduce contractions in the colon. The two available in the U.S. are dicyclomine and hyoscyamine. They should be taken before meals if postprandial urgency, diarrhea and cramping are problems.

Saline-type laxatives may help patients with constipation that is not responsive to increased fiber intake. One study showed that daily administration of low-dose polyethylene glycol laxatives increases bowel frequency and decreases symptoms in chronic constipation. Expert consensus suggests that osmotic laxatives such as magnesium citrate or sodium phosphate are safe and effective for severe constipation when used daily or as needed. Regular use of stimulant cathartics such as senna, cascara and phenolphthalein should be avoided because they can cause cramps.

Loperamide is a first-line agent for diarrhea symptoms. It can be taken as needed or on a scheduled basis depending on severity and frequency. Other opioid antidiarrheal agents, such as diphenoxylate hydrochloride combined with atropine sulfate, also may be effective.

IBS symptoms may be related to intestinal bacterial overgrowth. Several double blind studies have shown that the antibiotics rifaximin and neomycin improve IBS symptoms. However, neomycin only works in 25% of patients and has side effects that limit its use, making rifaximin the preferred choice.

In addition, IBS patients with preexisting psychiatric problems such as depression may benefit from tricyclic antidepressants. Best results are obtained with a low starting dose, then gradual increases as tolerated. Using selective serotonin reuptake inhibitors may increase the quality of life for patients with severe IBS and associated psychological distress.


Patient education can help patients with IBS. Explain the connection between IBS and previous gastrointestinal infection and bacterial overgrowth. Explain that IBS generally is a chronic condition and that patients can help themselves by taking medication as needed, eliminating diet triggers and understanding psychological triggers.


Reassess patients with IBS over time to ensure that a more serious disorder is not being overlooked. Determine that symptoms are not progressive and that red flag symptoms have not developed. Reassure the patient that there are no long-term complications or risk of cancer associated with IBS even though IBS symptoms are typically chronic and fluctuating in severity. Carefully consider the need for diagnostic tests or referral if symptoms are refractory and persistent.

The information included herein should never be used as a substitute for clinical judgment and does not represent an official position of ACP.

This information comes from the PIER module "Irritable Bowel Syndrome".


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