Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
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
Life-threatening illnesses (for example,
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