The placebo effect in irritable bowel syndrome trials: a meta-analysis.

BACKGROUND: Despite the apparent high placebo response rate in randomized placebo-controlled trials (RCT) of patients with irritable bowel syndrome (IBS), little is known about the variability and predictors of this response. OBJECTIVES: To describe the magnitude of response in placebo arms of IBS clinical trials and to identify which factors predict the variability of the placebo response. METHODS: We performed a meta-analysis of published, English language, RCT with 20 or more IBS patients who were treated for at least 2 weeks. This analysis is limited to studies that assessed global response (improvement in overall symptoms). The variables considered as potential placebo modifiers were study design, study duration, use of a run-in phase, Jadad score, entry criteria, number of office visits, number of office visits/study duration, use of diagnostic testing, gender, age and type of medication studied. FINDINGS: Forty-five placebo-controlled RCTs met the inclusion criteria. The placebo response ranged from 16.0 to 71.4% with a population-weighted average of 40.2%, 95% CI (35.9-44.4). Significant associations with lower placebo response rates were fulfillment of the Rome criteria for study entry (P=0.049) and an increased number of office visits (P=0.026). CONCLUSIONS: Placebo effects in IBS clinical trials measuring a global outcome are highly variable. Entry criteria and number of office visits are significant predictors of the placebo response. More stringent entry criteria and an increased number of office visits appear to independently decrease the placebo response.

Heterogeneity in phase I clinical trials: prior elicitation and computation using the continual reassessment method.

Heterogeneity in a phase I clinical trial patient population may lead to distinctly different dose-response relationships along covariate values. For a given target probability of toxicity, this implies different maximum tolerated doses (MTDs) for each distinct subpopulation. Within the framework of O'Quigley, Pepe and Fisher's (1990) continual reassessment method, we propose the notion of average and patient-specific MTDs by augmenting the dose--response model with other covariates to account for such differences. A method to elicit prior distributions on the dose and other covariate parameters are proposed, based on the predictive approach of Ibrahim and Laud (1994), Laud and Ibrahim (1995), and Ibrahim, Ryan and Chen (1998). This approach relies on prior predictions for the response vector y(0) and a quantity a(0) specifying uncertainty in y(0). Then, y(0) and a(0) are used to specify a prior for the regression coefficients in a semi-automatic fashion. The elicitation scheme for y(0) uses results from previous phase I cancer clinical trials. The average and patient-specific MTDs and an elicitation method are demonstrated in logistic regression examples.

The perception of respiratory work and effort can be independent of the perception of air hunger.

Dyspnea in patients could arise from both an urge to breathe and increased effort of breathing. Two qualitatively different sensations, "air hunger" and "respiratory work and effort," arising from different afferent sources are hypothesized. In the laboratory, breathing below the spontaneous level may produce an uncomfortable sensation of air hunger, and breathing above it a sensation of work or effort. Measurement of a single sensory dimension cannot distinguish these as separate sensations; we therefore measured two sensory dimensions and attempted to vary them independently. In five normal subjects we obtained simultaneous ratings of air hunger and of work and effort while independently varying PCO(2) or the level of targeted voluntary breathing. We found a difference in response to the two stimulus dimensions: air hunger ratings changed more steeply when PCO(2) was altered and ventilation was constant; work or effort ratings changed more steeply when ventilation was altered and PCO(2) was constant. We conclude that "air hunger" is qualitatively different from "work and effort" and arises from different afferent sources.

The prognostic value of age and follicle-stimulating hormone levels in women over forty years of age undergoing in vitro fertilization.

PURPOSE: Basal follicle-stimulating hormone (FSH) and age are predictors of successful outcome in in vitro fertilization (IVF). More recently, the clomiphene citrate challenge test (CCCT) has been proposed as a better way to predict IVF outcome than FSH alone. The purpose of this study was to determine which indicator of ovarian reserve--basal (day 3) FSH or the CCCT--is the better predictor of IVF success in the critical age group of women over the age of 40. METHODS: In this retrospective study, basal FSH and clomiphene-stimulated FSH levels from 104 women who underwent 175 cycles of IVF were analyzed. RESULTS: Neither basal FSH level nor stimulated FSH level alone were statistically significant predictors of IVF success; however, no patient with a day 3 FSH level > 11.1 mIU/ml or a stimulated day 10 FSH level > 13.5 mIU/ml conceived and carried a pregnancy. All ongoing pregnancies occurred in the first two cycles of IVF. CONCLUSIONS: Clear prognostic cutoff values were found to predict IVF success in women over age 40. IVF programs should consider limiting the number of cycles of IVF in women above age 40.

Longitudinal design for phase I clinical trials using the continual reassessment method.

The goal of phase I clinical trials is to estimate the maximum tolerated dose (MTD), the highest dose at which a specified probability of toxic response is not exceeded. However, this is not the only piece of information that is useful for the design of phase II and phase III clinical trials. Information on cumulative toxicity is important as well. To study the effect of cumulative toxicity in patients, it is necessary to examine how patients respond to multiple-dose administrations. To this end, we propose a longitudinal dose-response model that accommodates this concern, which is motivated from clearance-rate considerations and from a model proposed by Simon et al. To appropriately titrate an individual's dosage at each time period, we also propose an updating mechanism based on the Bayesian paradigm. We select individual and group MTDs using Legedza and Ibrahim's extension of O'Quigley et al. 's Continual Reassessment Method. Simulations are described to demonstrate the usefulness of our proposal. Control Clin Trials 2000;21:574-588