Factors Associated With Placebo Treatment Response in Functional Dyspepsia Clinical Trials.

INTRODUCTION: Controlling for potential placebo effects is an important aspect of gaining an accurate estimate of how much the therapy alone changes patient symptoms or other end points. When the placebo effect is large, this can lead to only a small fraction of changes seen in the active therapy group being attributed to the therapy itself. This problem has been well studied in some disorders of brain-gut interaction but not in functional dyspepsia where placebo response rates of 40% and higher have been reported. Understanding risk factors for placebo response might lead to changes in trial design that could reduce the magnitude of the problem. This study sought to identify risk factors for the placebo effect in a functional dyspepsia clinical trial with a longer-term aim of suggesting trial design changes that might minimize the problem. METHODS: A secondary analysis of the clinical trial data was undertaken using 2 arms deemed to involve placebo therapy. Potential predictors were drawn from a wide range of patient characteristics including psychological, clinical, and physiological features. RESULTS: Predictors of a stronger placebo effect on the gastrointestinal symptom rating scale included higher functional dyspepsia symptom burden at baseline ( b = -0.101), coexisting irritable bowel syndrome ( b = -0.436), and higher scores on the Nepean Dyspepsia Index eat/drink domain (-0.005). Baseline symptom burden and coexisting irritable bowel syndrome were found to be independent placebo predictors, explaining 13% of the variance in change in gastrointestinal symptom rating scale. Anxiety, childhood sexual abuse, sleep amount, and frequent abdominal pain were also found to be predictors of change in individual symptom scores. DISCUSSION: The findings of this study yield actionable insights into trial methodology that may help to reduce the magnitude of the placebo effect in future functional dyspepsia treatment trials.

The Nepean Dyspepsia Index is a valid instrument for measuring quality-of-life in functional dyspepsia.

BACKGROUND: The Nepean Dyspepsia Index (NDI) has been in widespread use since its publication in 1999 and the addition of a short form in 2001. The NDI was one of the first disease-specific quality-of-life instruments created for functional dyspepsia (FD). However, its psychometric properties have never been validated in an independent sample. AIM: This study aimed to evaluate the validity and reliability of the NDI in an a-priori driven approach in an independent population. PATIENTS AND METHODS: In 289 individuals who fulfilled the Rome criteria for FD enrolled in a randomized placebo-controlled trial (FD treatment trial), we examined construct validity, convergent validity, and internal consistency. RESULTS: Construct validity was supported in its 25-item unweighted and weighted forms as well as the 10-item short form. All items in the 25-item form yielded considerable (>0.5) standardized loadings on their respective latent variables and all reached statistical significance (P<0.0001), supporting their relationships with the hypothesized domains. Convergent validity was strongly supported, with every domain being correlated with multiple external instruments; the majority of correlations were in the range 0.3-0.5 (in absolute values). The items comprising each domain showed good internal consistency, with the lowest value of Chronbach α at 0.80. Scores based on the short form (10-item) version of the NDI correlated strongly with the full 25-item form (tension ρ=0.88, interference ρ=0.94, eat/drink ρ=0.95, knowledge ρ=0.84 and work/study ρ=0.97; all P<0.0001). CONCLUSION: The NDI is a valid instrument that can be used to measure the disease-specific impact of FD on quality of life.