Study design features affecting outcome in antidepressant trials

Nocebo and lessebo effects

The power of placebos is commonly associated with the placebo effect. In contrast, detrimental effects related to the use of a placebo are little studied and less well recognized. This chapter covers the nocebo and lessebo effects defined, respectively, as expectation of harm in the form of adverse events in a placebo arm and reduction of therapeutic benefit due to the uncertainty of being allocated to placebo. The lessebo effect is a more recent concept and has been described only in depression, schizophrenia and Parkinson's disease. The nocebo response was evaluated in many neurological diseases, including epilepsy, multiple sclerosis, Parkinson's disease, Alzheimer's disease, restless leg syndrome, among others. Meta-analyses of randomized controlled trials in these conditions reveal a significant variability of the magnitude of the nocebo response and that factors related to study design, study participants or neurological disease can be associated with a nocebo response, although with the opposing findings across conditions. The knowledge about neurobiological mechanisms of the nocebo effect is poor for neurological diseases, and most of the information has been generated in pain. Functional neuroimaging suggests the existence of a distinct network for the anticipation and the experience of a hyperalgesia nocebo response. Different types of neurotransmitters have been involved, including cholecystokinin, dopamine and opioids. Recognizing the potential impact of nocebo and lessebo effects, mitigating strategies are in development with application to clinical research and clinical practice, such as a contextualized informed consent process, alternative study designs and enhancement of patient-physician communication.

Design considerations for handling dropouts in anti-depressant drug trials

BACKGROUND

In clinical trials, statistical analysis often requires certain assumptions about missing data for a valid statistical inference. If the dropout rate is high, a wrong assumption about the missing data may compromise the validity of statistical inferences.

PURPOSE

To mitigate the high dropout rates commonly observed in psychiatry clinical trials, we consider two design approaches for short-term controlled trials submitted in support of marketing applications for drug products for the major depressive disorder (MDD) indication: (1) shortening the trial duration and (2) treating time to treatment discontinuation as an alternative primary efficacy endpoint.

METHODS

Subject-level efficacy data from 45 trials for drugs approved for an MDD indication between 1997 and 2014 were collected. We analyzed change from baseline in Hamilton Depression Rating Scale (HAMD-17) total score using the mixed model repeated measures approach. We compared the least squares means and the 95% confidence intervals of the treatment effect among three different trial durations, 4, 6, and 8weeks. We considered two definitions of discontinuation: (i) all-cause discontinuation, (ii) discontinuation due to lack of efficacy. We compared the two-sided log-rank p-values with the p-values from the protocol-specified primary analysis.

CONCLUSIONS

Our findings suggest that MDD trials in the acute setting may be shortened to 6weeks provided that the treatment difference between drug and placebo on HAMD-17 total score reaches approximately 2units at Week 6. However, our exploratory analyses of available data do not support the use of time to treatment discontinuation as an alternative primary efficacy endpoint.

Declining efficacy in controlled trials of antidepressants: effects of placebo dropout

Drug-placebo differences (effect-sizes) in controlled trials of antidepressants for major depressive episodes have declined for several decades, in association with selectively increasing clinical improvement associated with placebo-treatment. As these trends require adequate explanation, we tested the hypothesis that decreasing trial-dropout rates may be an important contributor. We gathered reports of peer-reviewed, placebo-controlled trials of antidepressants (1980-2011) by computerized literature searching, and applied meta-analysis, meta-regression and multiple linear regression methods to evaluate associations of dropout rates and other factors of interest, to reporting year and reported efficacy [standardized mean drug-placebo difference (SMD) as Hedges' g-statistic]. In 56 trials meeting inclusion and exclusion criteria, we confirmed significant overall efficacy of antidepressants but declining drug-placebo contrasts over the past three decades. Among other changes, there was a corresponding increase in placebo-associated improvement with a decline in placebo-dropout rate, mainly for lack of efficacy. These effects were found only when last-observation-carried-forward (LOCF) analyses were used. Other trial-design and subject factors, including drug-responses and drug-dropout rates, were much less associated with efficacy. We propose that declining placebo-dropout rates ascribed to inefficacy combined with use of LOCF analyses led to increasing improvement in placebo-arms that contributed to declining antidepressant-placebo contrasts in controlled treatment trials since the 1980s.

Another face of placebo: the lessebo effect in Parkinson disease: meta-analyses

OBJECTIVE

To study the impact of negative expectation related to receiving a placebo (the "lessebo effect") on efficacy outcome measures of symptomatic treatments in Parkinson disease (PD).

METHODS

We conducted meta-analyses of double-blind randomized controlled trials (RCTs) of dopamine agonists in PD and compared the pooled mean score change of the motor section of the Unified Parkinson's Disease Rating Scale (mUPDRS) across active treatment arms according to the presence of a placebo arm or the probability of placebo assignment (0%, <50%, and 50%) of the original RCT. A mixed-effects model was used. Heterogeneity was assessed by subgroup analyses and meta-regression modeling.

RESULTS

A total of 28 study arms were extracted from active-controlled trials (3,277 patients) and 42 from placebo-controlled trials (4,554 patients). The overall difference between groups in the pooled mean score change in the mUPDRS was 1.6 units (95% confidence interval [CI] 0.2, 3.0; p = 0.023), in favor of the active-controlled group. In subgroup analyses, this difference was of higher magnitude in the early PD group without motor fluctuations (3.3 mUPDRS units, 95% CI 1.1, 5.4; p = 0.003) and for study duration ≤ 12 weeks (4.1 mUPDRS units, 95% CI 1.0, 7.2; p = 0.009). There was no between-group difference using probability of placebo assignment as criterion.

CONCLUSIONS

This study shows that the use of a placebo can be associated with a clinically significant reduction in the magnitude of change of the mUPDRS after an active treatment in RCTs for PD. These new findings have potential implications in the development of new treatments and appraisal of current treatment options for PD and possibly for other neurologic disorders.

Publication bias, with a focus on psychiatry: causes and solutions

Publication bias undermines the integrity of the evidence base by inflating apparent drug efficacy and minimizing drug harms, thus skewing the risk-benefit ratio. This paper reviews the topic of publication bias with a focus on drugs prescribed for psychiatric conditions, especially depression, schizophrenia, bipolar disorder, and autism. Publication bias is pervasive; although psychiatry/psychology may be the most seriously afflicted field, it occurs throughout medicine and science. Responsibility lies with various parties (authors as well as journals, academia as well as industry), so the motives appear to extend beyond the financial interests of drug companies. The desire for success, in combination with cognitive biases, can also influence academic authors and journals. Amid the flood of new medical information coming out each day, the attention of the news media and academic community is more likely to be captured by studies whose results are positive or newsworthy. In the peer review system, a fundamental flaw arises from the fact that authors usually write manuscripts after they know the results. This allows hindsight and other biases to come into play, so data can be "tortured until they confess" (a detailed example is given). If a "publishable" result cannot be achieved, non-publication remains an option. To address publication bias, various measures have been undertaken, including registries of clinical trials. Drug regulatory agencies can provide valuable unpublished data. It is suggested that journals borrow from the FDA review model. Because the significance of study results biases reviewers, results should be excluded from review until after a preliminary judgment of study scientific quality has been rendered, based on the original study protocol. Protocol publication can further enhance the credibility of the published literature.