Clinical Trial Issues

The methodologies of many of the clinical trials that have assessed potential drug treatments for patients with IBS have been flawed,132'133 and several factors complicate IBS study design. Because IBS is a multiple-symptom complex, the mix of patients enrolled in trials is often heterogeneous, potentially complicating the interpretation of results.134'135 It is also likely that the undetected presence of pelvic floor dysfunction negatively biases the results of IBS-C studies.134

Another challenge is the existence of a large placebo response rate in IBS trials.135 An analysis of 27 randomized controlled trials evaluating the efficacy of various therapeutic options for patients with IBS found that the median placebo response was 47% (range, 0-84%).132 A more recent analysis of 45 studies with a well-defined global response outcome found a mean placebo response of 40.2% (range, 16-71%). Several factors may contribute to these high placebo rates. IBS is a chronic episodic disorder that waxes and wanes over long periods, and symptomatic cycles may alternate with symptom-free intervals of 1-3 months.133 Symptoms therefore may lessen or resolve spontaneously during the course of a clinical trial. In addition, the positive interactive environment of a clinical trial may help relieve patients' stress and anxiety about their condition and give them better insight into the nature of IBS, resulting in

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Conquering Fear In The 21th Century

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