Placebos in clinical trials: unravelling a complex phenomenon

Clinical Trials in Alzheimer's Disease: A Hurdle in the Path of Remedy

Human clinical trials seek to ameliorate the disease states and symptomatic progression of illnesses that, as of yet, are largely untreatable according to clinical standards. Ideally, clinical trials test "disease-modifying drugs," i.e., therapeutic agents that specifically modify pathological features or molecular bases of the disease and would presumably have a large impact on disease progression. In the case of Alzheimer's disease (AD), however, this approach appears to have stalled progress in the successful development of clinically useful therapies. For the last 25 years, clinical trials involving AD have centered on beta-amyloid (Aβ) and the Aβ hypothesis of AD progression and pathology. According to this hypothesis, the progression of AD begins following an accumulation of Aβ peptide, leading to eventual synapse loss and neuronal cell death: the true overriding pathological feature of AD. Clinical trials arising from the Aβ hypothesis target causal steps in the pathway in order to reduce the formation of Aβ or enhance clearance, and though agents have been successful in this aim, they remain unsuccessful in rescuing cognitive function or slowing cognitive decline. As such, further use of resources in the development of treatment options for AD that target Aβ, its precursors, or its products should be reevaluated. The purpose of this review was to give an overview of how human clinical trials are conducted in the USA and to assess the results of recent failed trials involving AD, the majority of which were based on the Aβ hypothesis. Based on these current findings, it is suggested that lowering Aβ is an unproven strategy, and it may be time to refocus on other targets for the treatment of this disease including pathological forms of tau.

Placebo Response in Rheumatoid Arthritis Clinical Trials

OBJECTIVE

Understanding the placebo response is critical to interpreting treatment efficacy, particularly for agents with a ceiling to their therapeutic effect, where an increasing placebo response makes it harder to detect potential benefit. The objective of this study is to assess the change in placebo responses over time in rheumatoid arthritis (RA) randomized placebo-controlled trials (RCT) for drug licensing authorization.

METHODS

The Cochrane Controlled Trials Register database was searched to identify RCT of biological or targeted synthetic disease-modifying antirheumatic drugs (DMARD) in RA. Studies were excluded if patients were conventional synthetic DMARD (csDMARD)-naive, not receiving background csDMARD therapy, or were biologic experienced. Metaregression model was used to evaluate changes in American College of Rheumatology (ACR) 20, ACR50, and ACR70 treatment response over time.

RESULTS

There were 32 trials in total: anti-tumor necrosis factor therapy (n = 15), tocilizumab (n = 4), abatacept (n = 2), rituximab (n = 2), and Janus kinase inhibitors (n = 9). From 1999 to 2018, there was no significant trend in the age or sex of patients in the placebo arm. Disease duration, swollen joint count, and 28-joint count Disease Activity Score using erythrocyte sedimentation rate at baseline all significantly declined over time. There was a statistically significant increase in placebo ACR50 and ACR70 responses (ACR50 β = 0.41, 95% CI 0.09-0.74, p = 0.01; ACR70 β = 0.18, 95% CI 0.04-0.31, p = 0.01) that remained significant after controlling for potential confounders.

CONCLUSION

There has been a rise in the placebo response in RA clinical trials over the last 2 decades. Shifting RA phenotype, changes in trial design, and expectation bias are possible explanations for this phenomenon. This observation has important implications when evaluating newer novel agents against established therapies.