Response-adaptive decision-theoretic trial design: operating characteristics and ethics

Bayesian adaptive decision-theoretic designs for multi-arm multi-stage clinical trials

Multi-arm multi-stage clinical trials in which more than two drugs are simultaneously investigated provide gains over separate single- or two-arm trials. In this paper we propose a generic Bayesian adaptive decision-theoretic design for multi-arm multi-stage clinical trials with K (K≥2) arms. The basic idea is that after each stage a decision about continuation of the trial and accrual of patients for an additional stage is made on the basis of the expected reduction in loss. For this purpose, we define a loss function that incorporates the patient accrual costs as well as costs associated with an incorrect decision at the end of the trial. An attractive feature of our loss function is that its estimation is computationally undemanding, also when K > 2. We evaluate the frequentist operating characteristics for settings with a binary outcome and multiple experimental arms. We consider both the situation with and without a control arm. In a simulation study, we show that our design increases the probability of making a correct decision at the end of the trial as compared to nonadaptive designs and adaptive two-stage designs.

The Performance of Fixed-Horizon, Look-Ahead Procedures Compared to Backward Induction in Bayesian Adaptive-Randomization Decision-Theoretic Clinical Trial Design

Designing optimal, Bayesian decision-theoretic trials has traditionally required the use of computationally-intensive backward induction. While methods for addressing this barrier have been put forward, few are both computationally tractable and non-myopic, with applications of the Gittins index being one notable example. Here we explore the look-ahead approach with adaptive-randomization, with designs ranging from the fully myopic to the fully informed. We compare the operating characteristics of the look-ahead designed trials, in which decision rules are based on a fixed number of future blocks, with those of trials designed using traditional backward induction. The less-myopic designs performed well. As the designs become more myopic or the trials longer, there were disparities in regions of the decision space that are transition zones between continuation and stopping decisions. The more myopic trials generally suffered from early stopping as compared to the less myopic and backward induction trials. Myopic trials with adaptive randomization also saw as many as 28 % of their continuation decisions change to a different randomization ratio as compared to the backward induction designs. Finally, early stages of myopic-designed trials may have disproportionate effect on trial characteristics.

Clinical trials in acute respiratory distress syndrome: challenges and opportunities

This year is the 50th anniversary of the first description of acute respiratory distress syndrome (ARDS). Since then, much has been learned about the pathogenesis of lung injury in ARDS, with an emphasis on the mechanisms of injury to the lung endothelium and the alveolar epithelium. In terms of treatment, major progress has been made in reducing mortality from ARDS with lung-protective ventilation, using a tidal volume of 6 mL per kg of predicted bodyweight and a plateau airway pressure of less than 30 cm H₂O. In more severely hypoxaemic patients with ARDS, neuromuscular blockade and prone positioning have further reduced mortality, probably by extending the therapeutic effects of lung protective ventilation. Fluid-conservative therapy has also increased ventilator-free days in patients with ARDS. The lack of success of pharmacological therapies for ARDS, however, presents a continued challenge in the field. In addition to presenting a brief summary of previous experience with clinical trials in ARDS, we focus in this Review on future opportunities to improve clinical trial design to maximise the likelihood of identifying beneficial pharmacological therapies. In view of the heterogeneity in ARDS, both prognostic and predictive enrichment strategies are needed that target therapies toward specific subgroups of patients with ARDS on the basis of both severity and biology. Approaches to reducing heterogeneity in ARDS clinical trials include using physiological, radiographic, and biological criteria to select patients for both phase 2 and 3 trials. Additionally, interest is growing in the design of preventive clinical trials in ARDS and to initiate early treatment of patients with acute lung injury before the need for endotracheal intubation. We also present promising new approaches to treating ARDS, including combination therapies, cell-based therapies, and generic pharmacological compounds with low-risk profiles that are already in routine clinical use for other clinical indications.

"You can't always get what you want": from doctrine to practicability of study designs for clinical investigation in endometriosis

BACKGROUND

Patients, now generally well informed through dedicated websites and support organizations, are beginning to look askance at clinical experimentation. We conducted a survey investigation to verify whether women with endometriosis would still accept to participate in a randomized controlled trial (RCT) on treatment for pelvic pain.

METHODS

A total of 500 patients consecutively self-referring to an academic outpatient endometriosis clinic, were asked to compile two questionnaires focused on hypothetical comparisons between a new drug and a standard drug, and between medical and surgical treatment, for endometriosis-associated pelvic pain. The main outcome measure was the percentage of patients willing to participate in a theoretical RCT.

RESULTS

A total of 239 (48 %) women would decline participation in a comparative study on a new drug and a standard drug, as 204 (41 %) would prefer the former medication, and 35 (7 %) the latter. Fifty women (10 %) would participate in a RCT, but only 24 (5 %) would accept blinding. The most frequently chosen option was the patient preference trial (211; 42 %). No significant differences were observed in demographic and clinical characteristics between the 50 women who would accept and the 450 who would decline to be enrolled in a RCT. A total of 229 women (46 %) would decline participation in a comparative study on medical versus surgical treatment, as 186 (37 %) would prefer pharmacological therapy and 43 (9 %) a surgical procedure. Only 11 (2 %) women would participate in such a RCT. More than half of the women (260; 52 %) selected the patient preference trial. No significant variations in distributions of answers were observed between women who did or did not undergo a previous surgical procedure.

CONCLUSION

Only a small minority of the women included in our study sample would accept randomization, and even less so blinding. Patient preference appears to play a central role when planning interventional trials on endometriosis-associated pelvic pain. Adequately designed observational analytic studies could be considered when recruitment in a RCT appears cumbersome.

The Potential of Adaptive Design in Animal Studies

Clinical trials are the backbone of medical research, and are often the last step in the development of new therapies for use in patients. Prior to human testing, however, preclinical studies using animal subjects are usually performed in order to provide initial data on the safety and effectiveness of prospective treatments. These studies can be costly and time consuming, and may also raise concerns about the ethical treatment of animals when potentially harmful procedures are involved. Adaptive design is a process by which the methods used in a study may be altered while it is being conducted in response to preliminary data or other new information. Adaptive design has been shown to be useful in reducing the time and costs associated with clinical trials, and may provide similar benefits in preclinical animal studies. The purpose of this review is to summarize various aspects of adaptive design and evaluate its potential for use in preclinical research.

Predicting geriatric falls following an episode of emergency department care: a systematic review

BACKGROUND

Falls are the leading cause of traumatic mortality in geriatric adults. Despite recent multispecialty guideline recommendations that advocate for proactive fall prevention protocols in the emergency department (ED), the ability of risk factors or risk stratification instruments to identify subsets of geriatric patients at increased risk for short-term falls is largely unexplored.

OBJECTIVES

This was a systematic review and meta-analysis of ED-based history, physical examination, and fall risk stratification instruments with the primary objective of providing a quantitative estimate for each risk factor's accuracy to predict future falls. A secondary objective was to quantify ED fall risk assessment test and treatment thresholds using derived estimates of sensitivity and specificity.

METHODS

A medical librarian and two emergency physicians (EPs) conducted a medical literature search of PUBMED, EMBASE, CINAHL, CENTRAL, DARE, the Cochrane Registry, and Clinical Trials. Unpublished research was located by a hand search of emergency medicine (EM) research abstracts from national meetings. Inclusion criteria for original studies included ED-based assessment of pre-ED or post-ED fall risk in patients 65 years and older with sufficient detail to reproduce contingency tables for meta-analysis. Original study authors were contacted for additional details when necessary. The Quality Assessment Tool for Diagnostic Accuracy Studies (QUADAS-2) was used to assess individual study quality for those studies that met inclusion criteria. When more than one qualitatively similar study assessed the same risk factor for falls at the same interval following an ED evaluation, then meta-analysis was performed using Meta-DiSc software. The primary outcomes were sensitivity, specificity, and likelihood ratios for fall risk factors or risk stratification instruments. Secondary outcomes included estimates of test and treatment thresholds using the Pauker method based on accuracy, screening risk, and the projected benefits or harms of fall prevention interventions in the ED.

RESULTS

A total of 608 unique and potentially relevant studies were identified, but only three met our inclusion criteria. Two studies that included 660 patients assessed 29 risk factors and two risk stratification instruments for falls in geriatric patients in the 6 months following an ED evaluation, while one study of 107 patients assessed the risk of falls in the preceding 12 months. A self-report of depression was associated with the highest positive likelihood ratio (LR) of 6.55 (95% confidence interval [CI] = 1.41 to 30.48). Six fall predictors were identified in more than one study (past falls, living alone, use of walking aid, depression, cognitive deficit, and more than six medications) and meta-analysis was performed for these risk factors. One screening instrument was sufficiently accurate to identify a subset of geriatric ED patients at low risk for falls with a negative LR of 0.11 (95% CI = 0.06 to 0.20). The test threshold was 6.6% and the treatment threshold was 27.5%.

CONCLUSIONS

This study demonstrates the paucity of evidence in the literature regarding ED-based screening for risk of future falls among older adults. The screening tools and individual characteristics identified in this study provide an evidentiary basis on which to develop screening protocols for geriatrics adults in the ED to reduce fall risk.

Managing competing demands in the implementation of response-adaptive randomization in a large multicenter phase III acute stroke trial

It is well known that competing demands exist between the control of important covariate imbalance and protection of treatment allocation randomness in confirmative clinical trials. When implementing a response-adaptive randomization algorithm in confirmative clinical trials designed under a frequentist framework, additional competing demands emerge between the shift of the treatment allocation ratio and the preservation of the power. Based on a large multicenter phase III stroke trial, we present a patient randomization scheme that manages these competing demands by applying a newly developed minimal sufficient balancing design for baseline covariates and a cap on the treatment allocation ratio shift in order to protect the allocation randomness and the power. Statistical properties of this randomization plan are studied by computer simulation. Trial operation characteristics, such as patient enrollment rate and primary outcome response delay, are also incorporated into the randomization plan.

Precision medicine clinical trials: defining new treatment strategies

OBJECTIVES

To discuss the role of clinical trials in the changing landscape of cancer care resulting in individualized cancer treatment plans including a discussion of several innovative randomized studies designed to evaluate multiple targeted therapies in molecularly defined subsets of individuals.

DATA SOURCES

Medical and nursing literature, research articles, and clinicaltrials.gov.

CONCLUSION

Recent advancements in cancer biomarkers and biomedical technology have begun to transform fundamentals of cancer therapeutics and clinical trials through innovative adaptive trial designs. The goal of these studies is to learn not only if a drug is safe and effective but also how it is best delivered and who will derive the most benefit.

IMPLICATIONS FOR NURSING PRACTICE

Implementation of clinical trials in the cancer biomarker era requires knowledge, skills, and expertise related to the use of biomarkers and molecularly defined processes underlying a malignancy, as well as an understanding of associated ethical, legal, and social issues to provide competent, safe, and effective health care and patient communication.