Irritable Bowel Syndrome (cont.)

The treatment of IBS is a difficult and unsatisfying topic because so few drugs have been studied or have been shown to be effective in treating IBS. Moreover, the drugs that have been shown to be useful have not been substantially effective. This difficult situation exists for many reasons, as follows:

• Life-threatening illnesses (for example, cancer, heart disease , and high blood pressure), capture the public's interest and, more importantly, research funding. IBS is not a life-threatening illness and has received little research funding. Because of the lack of research, an understanding of the physiologic processes (mechanisms) that are responsible for IBS has been slow to develop. Effective drugs cannot be developed until there is an understanding of these mechanisms.
• Research in IBS is difficult. IBS is defined by subjective symptoms, (such as pain), rather than objective signs (for instance, the presence of an ulcer). Subjective symptoms are more unreliable than objective signs in identifying homogenous groups of patients. As a result, groups of patients with IBS who are undergoing treatment are likely to contain some patients who do not have IBS, and this may negatively affect the results of the treatment. Moreover, the results of treatment must be evaluated on the basis of subjective responses (such as improvement in pain). In addition to being unreliable, subjective responses are more difficult to measure than objective responses (such as the healing of an ulcer).
• Different subtypes of IBS (for example, diarrhea-predominant, constipation-predominant, etc.) are likely to be caused by different physiologic processes (mechanisms). It also is possible, however, that the same subtype may be caused by several different mechanisms in different people. What's more, any drug is likely to affect only one mechanism. Therefore, it is unlikely that any one medication can be effective in most-patients with IBS, even patients with similar symptoms. This inconsistent effectiveness makes the testing of drugs difficult. Indeed, it can easily result in drug trials that demonstrate no efficacy (usefulness) when, in fact, the drug is helping a subgroup of patients.
• Subjective symptoms are particularly prone to respond to placebos (inactive drugs, or sugar pills). In fact, in most studies, 20% to 40% of patients with IBS will improve if they receive inactive drugs. Now, all clinical trials of drugs for IBS require a placebo-treated group for comparison. So, the placebo response means that these clinical trials must utilize large numbers of patients to detect meaningful (significant) differences in improvement between the placebo and drug groups. Therefore, such trials are expensive to conduct.

The lack of understanding of the physiologic processes (mechanisms) that cause IBS has meant that treatment cannot be directed at these mechanisms. Instead, treatment usually is directed at the symptoms, which are primarily constipation, diarrhea, and abdominal pain. These symptoms are not mutually exclusive since patients may have abdominal pain with either constipation or diarrhea. Moreover, periods of constipation may alternate with periods of diarrhea. This variation in symptoms over time can make the treatment of symptoms complex. The psychotropic drugs (antidepressants) and psychological treatments (for example, cognitive behavioral therapy) treat hypothetical causes of IBS (such as abnormal function of sensory nerves and the psyche) rather than the symptoms.

Source: MedicineNet.com
http://www.medicinenet.com/irritable_bowel_syndrome/article.htm