Effect of difelikefalin, a selective kappa opioid receptor agonist, on respiratory depression: A randomized, double-blind, placebo-controlled trial.

Difelikefalin, a selective kappa opioid receptor agonist designed to limit central nervous system (CNS) penetration, is under development for the treatment of pruritus. Its hydrophilic, small-peptidic structure limits CNS entry, minimizing potential CNS-mediated adverse events (AEs). This study assessed the effect of difelikefalin on key relevant measures of respiratory depression in healthy volunteers. This single-center, randomized, double-blind, placebo-controlled, three-way crossover study enrolled healthy, nonsmoking volunteers. Subjects were randomized to 1 of 3 treatment sequences of difelikefalin (1.0 or 5.0 mcg/kg i.v.) or placebo on sequential days with an intervening 24 (±2) h washout period. The primary end points included incidence of increased end-tidal carbon dioxide (ETCO2 ) greater than or equal to 10 mm Hg versus baseline or a level greater than 50 mm Hg sustained greater than or equal to 30 seconds, and incidence of reduction in saturation of peripheral oxygen (SpO2 ) to less than 92% sustained greater than or equal to 30 seconds. Secondary end points included incidence of reduced respiratory rate and other safety assessments. Fifteen subjects were randomized and completed the study. No subject on placebo or difelikefalin met the increased ETCO2 or reduced SpO2 primary end point criteria for respiratory depression. All respiratory measures in each group remained near baseline values during 4-h postdose observations. No subject met the reduced respiratory rate criterion or experienced clinically significant changes in ETCO2 , SpO2 , or respiratory rate. The most commonly reported treatment-emergent AEs (TEAEs; ≥20% of subjects) were paresthesia, hypoesthesia, and somnolence in the difelikefalin arms. All TEAEs were mild and resolved without intervention. Difelikefalin 1.0 and 5.0 mcg/kg i.v. did not produce respiratory depression.

Research design considerations for single-dose analgesic clinical trials in acute pain: IMMPACT recommendations.

This article summarizes the results of a meeting convened by the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) on key considerations and best practices governing the design of acute pain clinical trials. We discuss the role of early phase clinical trials, including pharmacokinetic-pharmacodynamic (PK-PD) trials, and the value of including both placebo and active standards of comparison in acute pain trials. This article focuses on single-dose and short-duration trials with emphasis on the perioperative and study design factors that influence assay sensitivity. Recommendations are presented on assessment measures, study designs, and operational factors. Although most of the methodological advances have come from studies of postoperative pain after dental impaction, bunionectomy, and other surgeries, the design considerations discussed are applicable to many other acute pain studies conducted in different settings.

Research designs for proof-of-concept chronic pain clinical trials: IMMPACT recommendations.

Proof-of-concept (POC) clinical trials play an important role in developing novel treatments and determining whether existing treatments may be efficacious in broader populations of patients. The goal of most POC trials is to determine whether a treatment is likely to be efficacious for a given indication and thus whether it is worth investing the financial resources and participant exposure necessary for a confirmatory trial of that intervention. A challenge in designing POC trials is obtaining sufficient information to make this important go/no-go decision in a cost-effective manner. An IMMPACT consensus meeting was convened to discuss design considerations for POC trials in analgesia, with a focus on maximizing power with limited resources and participants. We present general design aspects to consider including patient population, active comparators and placebos, study power, pharmacokinetic-pharmacodynamic relationships, and minimization of missing data. Efficiency of single-dose studies for treatments with rapid onset is discussed. The trade-off between parallel-group and crossover designs with respect to overall sample sizes, trial duration, and applicability is summarized. The advantages and disadvantages of more recent trial designs, including N-of-1 designs, enriched designs, adaptive designs, and sequential parallel comparison designs, are summarized, and recommendations for consideration are provided. More attention to identifying efficient yet powerful designs for POC clinical trials of chronic pain treatments may increase the percentage of truly efficacious pain treatments that are advanced to confirmatory trials while decreasing the percentage of ineffective treatments that continue to be evaluated rather than abandoned.

Abuse liability measures for use in analgesic clinical trials in patients with pain: IMMPACT recommendations.

Assessing and mitigating the abuse liability (AL) of analgesics is an urgent clinical and societal problem. Analgesics have traditionally been assessed in randomized clinical trials (RCTs) designed to demonstrate analgesic efficacy relative to placebo or an active comparator. In these trials, rigorous, prospectively designed assessment for AL is generally not performed. The Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) convened a consensus meeting to review the available evidence and discuss methods for improving the assessment of the AL of analgesics in clinical trials in patients with pain. Recommendations for improved assessment include: (1) performing trials that include individuals with diverse risks of abuse; (2) improving the assessment of AL in clinical trials (eg, training study personnel in the principles of abuse and addiction behaviors, designing the trial to assess AL outcomes as primary or secondary outcome measures depending on the trial objectives); (3) performing standardized assessment of outcomes, including targeted observations by study personnel and using structured adverse events query forms that ask all subjects specifically for certain symptoms (such as euphoria and craving); and (4) collecting detailed information about events of potential concern (eg, unexpected urine drug testing results, loss of study medication, and dropping out of the trial). The authors also propose a research agenda for improving the assessment of AL in future trials.

Core outcome measures for opioid abuse liability laboratory assessment studies in humans: IMMPACT recommendations.

A critical component in development of opioid analgesics is assessment of their abuse liability (AL). Standardization of approaches and measures used in assessing AL have the potential to facilitate comparisons across studies, research laboratories, and drugs. The goal of this report is to provide consensus recommendations regarding core outcome measures for assessing the abuse potential of opioid medications in humans in a controlled laboratory setting. Although many of the recommended measures are appropriate for assessing the AL of medications from other drug classes, the focus here is on opioid medications because they present unique risks from both physiological (e.g., respiratory depression, physical dependence) and public health (e.g., individuals in pain) perspectives. A brief historical perspective on AL testing is provided, and those measures that can be considered primary and secondary outcomes and possible additional outcomes in AL assessment are then discussed. These outcome measures include the following: subjective effects (some of which comprise the primary outcome measures, including drug liking; physiological responses; drug self-administration behavior; and cognitive and psychomotor performance. Before presenting recommendations for standardized approaches and measures to be used in AL assessments, the appropriateness of using these measures in clinical trials with patients in pain is discussed.

Determining the clinically important difference in visual analog scale scores in abuse liability studies evaluating novel opioid formulations.

PURPOSE: This study determined how the magnitude of change in positive subjective responses predicts clinical outcome in a treatment setting. Specifically, we attempted to define what constitutes a clinically important difference (CID) in subjective responses. METHODS: A 100-mm visual analog scale (VAS) measured subjective ratings of drug "high," calculated via an anchor-based method with published data from participants receiving sustained-release naltrexone (NTX) and heroin in a laboratory setting. The data were then compared to clinical outcomes in a treatment trial with sustained-release naltrexone. A distribution-based method subsequently analyzed data from participants who received ALO-01 (extended-release morphine with sequestered NTX) to predict its abuse liability. RESULTS: Differences in ratings of drug high of approximately 10 mm on a 100-mm line were clinically significant. By extrapolation, CIDs were also found between crushed or intact ALO-01 and immediate-release morphine sulfate (IRMS). No CIDs were found between intact and crushed ALO-01. CONCLUSIONS: From laboratory and treatment trial data involving naltrexone, calculation of CIDs in subjective ratings of high is possible. Consequently, crushing/swallowing or injecting ALO-01 produces clinically significantly less drug high than oral or intravenous morphine alone, suggesting that ALO-01 has lower abuse liability by those routes than morphine formulations.

Research design considerations for confirmatory chronic pain clinical trials: IMMPACT recommendations.

There has been an increase in the number of chronic pain clinical trials in which the treatments being evaluated did not differ significantly from placebo in the primary efficacy analyses despite previous research suggesting that efficacy could be expected. These findings could reflect a true lack of efficacy or methodological and other aspects of these trials that compromise the demonstration of efficacy. There is substantial variability among chronic pain clinical trials with respect to important research design considerations, and identifying and addressing any methodological weaknesses would enhance the likelihood of demonstrating the analgesic effects of new interventions. An IMMPACT consensus meeting was therefore convened to identify the critical research design considerations for confirmatory chronic pain trials and to make recommendations for their conduct. We present recommendations for the major components of confirmatory chronic pain clinical trials, including participant selection, trial phases and duration, treatment groups and dosing regimens, and types of trials. Increased attention to and research on the methodological aspects of confirmatory chronic pain clinical trials has the potential to enhance their assay sensitivity and ultimately provide more meaningful evaluations of treatments for chronic pain.

Analyzing multiple endpoints in clinical trials of pain treatments: IMMPACT recommendations. Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials.

The increasing complexity of randomized clinical trials and the practice of obtaining a wide variety of measurements from study participants have made the consideration of multiple endpoints a critically important issue in the design, analysis, and interpretation of clinical trials. Failure to consider important outcomes can limit the validity and utility of clinical trials; specifying multiple endpoints for the evaluation of treatment efficacy, however, can increase the rate of false positive conclusions about the efficacy of a treatment. We describe the use of multiple endpoints in the design, analysis, and interpretation of pain clinical trials, and review available strategies and methods for addressing multiplicity. To decrease the probability of a Type I error (i.e., the likelihood of obtaining statistically significant results by chance) in pain clinical trials, the use of gatekeeping procedures and other methods that correct for multiple analyses is recommended when a single primary endpoint does not adequately reflect the overall benefits of treatment. We emphasize the importance of specifying in advance the outcomes and clinical decision rule that will serve as the basis for determining that a treatment is efficacious and the methods that will be used to control the overall Type I error rate.

Interpreting the clinical importance of treatment outcomes in chronic pain clinical trials: IMMPACT recommendations.

UNLABELLED: A consensus meeting was convened by the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) to provide recommendations for interpreting clinical importance of treatment outcomes in clinical trials of the efficacy and effectiveness of chronic pain treatments. A group of 40 participants from universities, governmental agencies, a patient self-help organization, and the pharmaceutical industry considered methodologic issues and research results relevant to determining the clinical importance of changes in the specific outcome measures previously recommended by IMMPACT for 4 core chronic pain outcome domains: (1) Pain intensity, assessed by a 0 to 10 numerical rating scale; (2) physical functioning, assessed by the Multidimensional Pain Inventory and Brief Pain Inventory interference scales; (3) emotional functioning, assessed by the Beck Depression Inventory and Profile of Mood States; and (4) participant ratings of overall improvement, assessed by the Patient Global Impression of Change scale. It is recommended that 2 or more different methods be used to evaluate the clinical importance of improvement or worsening for chronic pain clinical trial outcome measures. Provisional benchmarks for identifying clinically important changes in specific outcome measures that can be used for outcome studies of treatments for chronic pain are proposed. PERSPECTIVE: Systematically collecting and reporting the recommended information needed to evaluate the clinical importance of treatment outcomes of chronic pain clinical trials will allow additional validation of proposed benchmarks and provide more meaningful comparisons of chronic pain treatments.

What is sufficient evidence for the reliability and validity of patient-reported outcome measures?

This article focuses on the necessary psychometric properties of a patient-reported outcomes (PROs) measure. Topics include the importance of reliability and validity, psychometric approaches used to provide reliability and validity estimates, the kinds of evidence needed to indicate that a PRO has a sufficient level of reliability and validity, contexts that may affect psychometric properties, methods available to evaluate PRO instruments when the context varies, and types of reliability and validity testing that are appropriate during different phases of clinical trials. Points discussed include the perspective that the psychometric properties of reliability and validity are on a continuum in which the more evidence one has, the greater confidence there is in the value of the PRO data. Construct validity is the type of validity most frequently used with PRO instruments as few "gold standards" exist to allow the use of criterion validity and content validity by itself only provides beginning evidence of validity. Several guidelines are recommended for establishing sufficient evidence of reliability and validity. For clinical trials, a minimum reliability threshold of 0.70 is recommended. Sample sizes for testing should include at least 200 cases and results should be replicated in at least one additional sample. At least one full report on the development of the instrument and one on the use of the instrument are deemed necessary to evaluate the PRO psychometric properties. Psychometric testing ideally occurs before the initiation of Phase III trials. When testing does not occur prior to a Phase III trial, considerable risk is posed in relation to the ability to substantiate the use of the PRO data. Various qualitative (e.g., focus groups, behavioral coding, cognitive interviews) and quantitative approaches (e.g., differential item functioning testing) are useful in evaluating the reliability and validity of PRO instruments.

Core outcome domains for chronic pain clinical trials: IMMPACT recommendations.

OBJECTIVE: To provide recommendations for the core outcome domains that should be considered by investigators conducting clinical trials of the efficacy and effectiveness of treatments for chronic pain. Development of a core set of outcome domains would facilitate comparison and pooling of data, encourage more complete reporting of outcomes, simplify the preparation and review of research proposals and manuscripts, and allow clinicians to make informed decisions regarding the risks and benefits of treatment. METHODS: Under the auspices of the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT), 27 specialists from academia, governmental agencies, and the pharmaceutical industry participated in a consensus meeting and identified core outcome domains that should be considered in clinical trials of treatments for chronic pain. CONCLUSIONS: There was a consensus that chronic pain clinical trials should assess outcomes representing six core domains: (1) pain, (2) physical functioning, (3) emotional functioning, (4) participant ratings of improvement and satisfaction with treatment, (5) symptoms and adverse events, (6) participant disposition (e.g. adherence to the treatment regimen and reasons for premature withdrawal from the trial). Although consideration should be given to the assessment of each of these domains, there may be exceptions to the general recommendation to include all of these domains in chronic pain trials. When this occurs, the rationale for not including domains should be provided. It is not the intention of these recommendations that assessment of the core domains should be considered a requirement for approval of product applications by regulatory agencies or that a treatment must demonstrate statistically significant effects for all of the relevant core domains to establish evidence of its efficacy.