Scientific and ethical issues in the use of placebo and active controls in clinical trials

Challenges and opportunities: what we are learning from the clinical natalizumab experience

The approval of natalizumab for relapsing forms of multiple sclerosis, and the subsequent voluntary suspension of its use due to an unexpected viral infection, is a cautionary tale of how much we have to learn about how to prioritize and perform the necessary research and development of novel therapeutics for human diseases, the ethics of placebo-controlled trials and the relationships between researchers, regulatory authorities and the pharmaceutical industry.

The network meta-analytic-predictive approach to non-inferiority trials

In non-inferiority clinical trials, a test treatment is compared to an active-control rather than to placebo. Such designs are considered when placebo is unethical or not feasible. The critical question is whether the test treatment would have been superior to placebo, had placebo been used in the non-inferiority trial. This question can only be addressed indirectly, based on information from relevant historical trials with data on active-control and placebo. The network meta-analytic-predictive approach to non-inferiority trials is based on a network meta-analysis of the data from the historical trials and the non-inferiority trial, and the prediction of the putative test vs. placebo effect in the non-inferiority trial. The approach extends previous work by incorporating between-trial variability for all relevant parameters and focusing on the parameters in the non-inferiority trial rather than on population means. Two prominent examples with binary outcomes are used to illustrate the approach.

Clinical evaluation of novel bisphosphonate dosing regimens in osteoporosis: The role of comparative studies and implications for future studies

BACKGROUND

Daily nitrogen-containing bisphosphonates have shown antifracture efficacy in many studies of postmenopausal osteoporosis. However, current dosing schedules are often inconvenient or impractical for patients. Efforts to reduce dosing frequency to improve adherence (ie, compliance and persistence), and therefore treatment outcomes, are ongoing. Although a number of trial designs can be used to consider the efficacy of therapy, comparing the efficacy of different regimens should only be undertaken in purposefully designed head-to-head studies.

OBJECTIVE

This article summarizes the design and conduct of clinical studies that have investigated alternative bisphosphonate regimens and those that have directly compared different approved bisphosphonates. It also explores the implications for future studies of postmenopausal osteoporosis treatment.

METHODS

Using the terms bisphosphonate, daily, weekly, and monthly, a search (completed in 2006) of the PubMed database was conducted to identify primary English-language publications of pertinent studies comparing either novel with established regimens of the same bisphosphonates or different established bisphosphonates.

RESULTS

The first option is the equivalence or noninferiority bridging study for comparison of new treatment regimens versus the established regimen of the same bisphosphonate, known as the active comparator. Four such studies have led to the registration of novel bisphosphonate dosing regimens designed to provide easier dosing alternatives for patients. The second option is the active comparator study, which compares one bisphosphonate with the most prescribed weekly bisphosphonate. Weekly dosed oral alendronate has previously been shown to be superior (for bone mineral density gains) to daily and weekly dosed oral risedronate. An ongoing noninferiority study, Monthly Oral Therapy with Ibandronate for Osteoporosis Intervention, is comparing weekly alendronate with ibandronate, a monthly oral bisphosphonate.

CONCLUSIONS

The exploration of new dosing schedules and formulations aims to identify the optimal bisphosphonate regimen for postmenopausal osteoporosis. To achieve this, careful consideration must be given to the choice of a scientifically valid study design that effectively, and ethically, meets the study objectives. Given the concerns regarding placebo-controlled antifracture studies, 2 alternative study designs should be considered, both using validated surrogate end points (bone mineral density and biochemical markers of bone turnover) as the principal mode of assessment.

How useful are measures of BMD and bone turnover?

Measurements of bone mineral density (BMD) and biochemical markers of bone turnover are useful in the diagnosis and management of osteoporosis, as well as in research relating to the pathogenesis and treatment of the disease. Recent challenges to the utility of these measures have resulted in some confusion among both researchers and clinicians. BMD accounts for the great majority of bone strength and is the current gold standard for the diagnosis of osteoporosis, as well as for prediction of fracture risk. Although bone turnover increases sharply after menopause, biochemical markers of bone turnover have limited usefulness in fracture risk prediction. Persistently elevated bone turnover throughout the menopause is associated with structural decrements, cannot be measured routinely and non-invasively. In research applications, both BMD and markers of bone turnover are used to identify candidate agents in preclinical and clinical studies. In addition, head-to-head comparisons of treatments utilize these measures, because fracture endpoint trials would need to be extraordinarily large and complex. Analyses that have suggested that change in BMD or bone turnover 'explains' little of change in fracture risk with treatment appear to be flawed. Although neither can perfectly predict fracture, they are our current best alternatives.