Benefit-risk assessment and reporting in clinical trials of chronic pain treatments: IMMPACT recommendations.

ABSTRACT: Chronic pain clinical trials have historically assessed benefit and risk outcomes separately. However, a growing body of research suggests that a composite metric that accounts for benefit and risk in relation to each other can provide valuable insights into the effects of different treatments. Researchers and regulators have developed a variety of benefit-risk composite metrics, although the extent to which these methods apply to randomized clinical trials (RCTs) of chronic pain has not been evaluated in the published literature. This article was motivated by an Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials consensus meeting and is based on the expert opinion of those who attended. In addition, a review of the benefit-risk assessment tools used in published chronic pain RCTs or highlighted by key professional organizations (ie, Cochrane, European Medicines Agency, Outcome Measures in Rheumatology, and U.S. Food and Drug Administration) was completed. Overall, the review found that benefit-risk metrics are not commonly used in RCTs of chronic pain despite the availability of published methods. A primary recommendation is that composite metrics of benefit-risk should be combined at the level of the individual patient, when possible, in addition to the benefit-risk assessment at the treatment group level. Both levels of analysis (individual and group) can provide valuable insights into the relationship between benefits and risks associated with specific treatments across different patient subpopulations. The systematic assessment of benefit-risk in clinical trials has the potential to enhance the clinical meaningfulness of RCT results.

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

Although certain risk factors can identify individuals who are most likely to develop chronic pain, few interventions to prevent chronic pain have been identified. To facilitate the identification of preventive interventions, an IMMPACT meeting was convened to discuss research design considerations for clinical trials investigating the prevention of chronic pain. We present general design considerations for prevention trials in populations that are at relatively high risk for developing chronic pain. Specific design considerations included subject identification, timing and duration of treatment, outcomes, timing of assessment, and adjusting for risk factors in the analyses. We provide a detailed examination of 4 models of chronic pain prevention (ie, chronic postsurgical pain, postherpetic neuralgia, chronic low back pain, and painful chemotherapy-induced peripheral neuropathy). The issues discussed can, in many instances, be extrapolated to other chronic pain conditions. These examples were selected because they are representative models of primary and secondary prevention, reflect persistent pain resulting from multiple insults (ie, surgery, viral infection, injury, and toxic or noxious element exposure), and are chronically painful conditions that are treated with a range of interventions. Improvements in the design of chronic pain prevention trials could improve assay sensitivity and thus accelerate the identification of efficacious interventions. Such interventions would have the potential to reduce the prevalence of chronic pain in the population. Additionally, standardization of outcomes in prevention clinical trials will facilitate meta-analyses and systematic reviews and improve detection of preventive strategies emerging from clinical trials.

Interpretation of chronic pain clinical trial outcomes: IMMPACT recommended considerations.

Interpreting randomized clinical trials (RCTs) is crucial to making decisions regarding the use of analgesic treatments in clinical practice. In this article, we report on an Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) consensus meeting organized by the Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks, the purpose of which was to recommend approaches that facilitate interpretation of analgesic RCTs. We review issues to consider when drawing conclusions from RCTs, as well as common methods for reporting RCT results and the limitations of each method. These issues include the type of trial, study design, statistical analysis methods, magnitude of the estimated beneficial and harmful effects and associated precision, availability of alternative treatments and their benefit-risk profile, clinical importance of the change from baseline both within and between groups, presentation of the outcome data, and the limitations of the approaches used.

Improving Study Conduct and Data Quality in Clinical Trials of Chronic Pain Treatments: IMMPACT Recommendations.

The estimated probability of progressing from phase 3 analgesic clinical trials to regulatory approval is approximately 57%, suggesting that a considerable number of treatments with phase 2 trial results deemed sufficiently successful to progress to phase 3 do not yield positive phase 3 results. Deficiencies in the quality of clinical trial conduct could account for some of this failure. An Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials meeting was convened to identify potential areas for improvement in trial conduct in order to improve assay sensitivity (ie, ability of trials to detect a true treatment effect). We present recommendations based on presentations and discussions at the meeting, literature reviews, and iterative revisions of this article. The recommendations relate to the following areas: 1) study design (ie, to promote feasibility), 2) site selection and staff training, 3) participant selection and training, 4) treatment adherence, 5) data collection, and 6) data and study monitoring. Implementation of these recommendations may improve the quality of clinical trial data and thus the validity and assay sensitivity of clinical trials. Future research regarding the effects of these strategies will help identify the most efficient use of resources for conducting high quality clinical trials. PERSPECTIVE: Every effort should be made to optimize the quality of clinical trial data. This manuscript discusses considerations to improve conduct of pain clinical trials based on research in multiple medical fields and the expert consensus of pain researchers and stakeholders from academia, regulatory agencies, and industry.

Number Of Clinical Trial Study Sites Impacts Observed Treatment Effect Size: An Analysis Of Randomized Controlled Trials Of Opioids For Chronic Pain.

BACKGROUND: Many aspects of study conduct impact the observed effect size of treatment. Data were utilized from a recently published meta-analysis of randomized, double-blind, placebo-controlled, clinical trials performed for the United States Food and Drug Administration (FDA) approval of full mu-agonist opioids for the treatment of chronic pain. METHODS: The number of study sites in each clinical trial and standardized effect size (SES) were extracted and computed. Standardized effect size was plotted against number of sites, and a two-piece linear model was fit to the plot. Ten studies were included. RESULTS: The SES decreased linearly by 0.13 units for every 10 sites (p=0.037), from 0.75 to 0.36, until an inflection point of 60 sites, after which SES did not decline further. The total number of subjects required for 90% power to discriminate drug from placebo increased from 78 to 336 subjects going from 30 to 60 sites. CONCLUSION: Results showed that the number of sites was a source of loss of assay sensitivity in clinical trials, which may contribute to the well-known problem of failure to successfully transition from Phase 2 to Phase 3 clinical development. Potential solutions include minimizing the number of sites, more rigorous and validated training, central statistical monitoring with rapid correction of performance issues, and more rigorous subject and site selection.

Opioid Pharmacology: Developmental Effects on Opioid Metabolism.

AIMS/OBJECTIVES/BACKGROUND: Children represent a patient demographic composed of multiple, unique subpopulations differentiated by rapidly changing age-related physiology, which includes the means of metabolizing opioids. Opioids are an important part of the pharmacological treatment of both acute and chronic pain. In both clinical medicine and clinical research, it is necessary to understand the differences in drug handling by age cohort in order to appropriately dose children to effect, and to avoid exacerbating deleterious adverse events with potentially grave sequelae. METHODS: Topical review using data from a targeted PubMed literature search. RESULTS: Protein binding, tissue solubility, weight, size (body mass, surface area), blood flow, drug metabolism, and renal function are key determinants of dosing across the different pediatric age cohorts. Each variable functions to elicit a change in drug exposure and therefore varying clinical effect. CONCLUSIONS: Understanding how these variables change the pharmacokinetics and pharmacodynamics of each opioid is critical to the successful and safe management of pain in children.

Evaluation of the oral human abuse potential of Oxycodone DETERx® formulation (Xtampza® ER).

OBJECTIVE: To further characterize the human abuse potential and pharmacokinetics (PK) of Oxycodone DETERx (Xtampza® ER) after intact and chewed oral administration. DESIGN: Randomized, double-blind, triple-dummy, active- and placebo-controlled, single-dose, six-period, crossover comparison study. SETTING: Clinical research unit. SUBJECTS: Adult, nondependent recreational opioid users who liked the effects of crushed immediate-release (IR) oxycodone in solution and were able to differentiate the effects from placebo solution. INTERVENTIONS: Oral administration of intact Oxycodone DETERx (fasted and fed), chewed Oxycodone DETERx (fasted and fed), crushed IR oxycodone (fasted), and placebo (fed). MAIN OUTCOME MEASURES: Subject ratings (100-point visual analog scales) of Drug Liking (primary measure) and Take Drug Again (key secondary measure). RESULTS: The pharmacodynamic (PD) analysis included 52 subjects who completed the study; the PK analysis included 71 subjects. Compared with crushed IR oxycodone fasted, the least-squares mean maximum effect (Emax) was statistically significant (p < 0.01) for Drug Liking and Take Drug Again, respectively, for chewed Oxycodone DETERx fasted (LS mean difference ± standard error of the mean: 13.1 ± 2.2 and 10.0 ± 3.2 points) and fed (10.9 ± 2.2 and 9.7 ± 3.3 points) and intact Oxycodone DETERx fasted (12.2 ± 2.2 and 9.3 ± 3.3 points) and fed (10.3 ± 2.2 and 9.2 ± 3.3 points). Results were consistent for other PD measures (Good Effects, Feeling High). Chewed Oxycodone DETERx fasted and fed treatments were bioequivalent to the respective intact treatments based on PK parameters. CONCLUSIONS: This study showed that when chewed or swallowed intact, under fasted or fed conditions, Oxycodone DETERx had statistically significantly lower abuse potential via the oral route compared with IR oxycodone.

Analgesic efficacy, safety, and tolerability of a long-acting abuse-deterrent formulation of oxycodone for moderate-to-severe chronic low back pain in subjects successfully switched from immediate-release oxycodone.

OBJECTIVES: This post hoc analysis of data from a randomized, double-blind, placebo-controlled, enriched-enrollment randomized-withdrawal Phase III study evaluated the safety, tolerability, and analgesic efficacy of Oxycodone DETERx extended-release (ER), abuse-deterrent capsules (Xtampza® ER) in subjects with chronic low back pain who were successfully transitioned from immediate-release (IR) oxycodone. METHODS: Continuous outcomes were analyzed using a mixed-model repeated-measures approach; binomial outcomes were analyzed using chi-squared; and time-to-event outcomes using Kaplan-Meier analyses. RESULTS: A total of 110 subjects previously prescribed IR oxycodone entered the Open-label Titration Phase. Forty-four subjects were randomized to Oxycodone DETERx (n=22) or placebo (n=22) in the 12-week Double-blind Maintenance Phase. Efficacy results in this subgroup showed a statistically significant difference between Oxycodone DETERx and placebo in average pain intensity scores from Randomization Baseline to Week 12 (least squares mean [± standard error], -1.88 [0.70]; P=0.0078). Additional efficacy results indicated that Oxycodone DETERx vs placebo was associated with a statistically significant benefit in durability of effect from Week 2 through Week 12 (P<0.01), numbers of subjects with a ≥30% (n [%] 10 [45.5%] vs 0 [0%]; P=0.0004) and ≥50% (10 [45.5%] vs 0 [0%]; P=0.0004) improvement in pain intensity, longer time-to-exit (P=0.0014), a greater number of subjects who completed the study (14 [63.6%] vs 4 [18.2%]), and less rescue medication use (acetaminophen; mean [SD], 163.5 [337.8] mg) vs 216.2 [377.3] mg). Adverse event profiles were consistent with opioid class effects and results from the original study; Oxycodone DETERx was well tolerated in subjects previously treated with short-acting oxycodone. CONCLUSIONS: Oxycodone DETERx resulted in clinically meaningful and statistically significant efficacy in subjects with chronic low back pain who were previously prescribed IR oxycodone and were successfully switched to ER Oxycodone DETERx.

Clinical trial designs and models for analgesic medications for acute pain in neonates, infants, toddlers, children, and adolescents: ACTTION recommendations.

Clinical trials to test the safety and efficacy of analgesics across all pediatric age cohorts are needed to avoid inappropriate extrapolation of adult data to children. However, the selection of acute pain models and trial design attributes to maximize assay sensitivity, by pediatric age cohort, remains problematic. Acute pain models used for drug treatment trials in adults are not directly applicable to the pediatric age cohorts-neonates, infants, toddlers, children, and adolescents. Developmental maturation of metabolic enzymes in infants and children must be taken into consideration when designing trials to test analgesic treatments for acute pain. Assessment tools based on the levels of cognitive maturation and behavioral repertoire must be selected as outcome measures. Models and designs of clinical trials of analgesic medications used in the treatment of acute pain in neonates, infants, toddlers, children, and adolescents were reviewed and discussed at an Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks (ACTTION) Pediatric Pain Research Consortium consensus meeting. Based on extensive reviews and continuing discussions, the authors recommend a number of acute pain clinical trial models and design attributes that have the potential to improve the study of analgesic medications in pediatric populations. Recommendations are also provided regarding additional research needed to support the use of other acute pain models across pediatric age cohorts.

The comparative pharmacokinetics of physical manipulation by crushing of Xtampza® ER compared with OxyContin®.

AIM: To further characterize the pharmacokinetics of Xtampza® ER. SUBJECTS & METHODS: This was an open-label, randomized, active-controlled, five-treatment, five-period, naltrexone-blocked, cross-over study. Healthy subjects received five equivalent oxycodone doses: Xtampza ER (intact or crushed), OxyContin® (intact or crushed) or immediate-release (IR) oxycodone (crushed). Blood samples were collected to assess oxycodone concentrations. RESULTS: Crushed and intact Xtampza ER resulted in lower peak plasma concentrations compared with crushed oxycodone IR; crushed and intact Xtampza ER were bioequivalent. Crushed OxyContin exhibited a rapid increase in plasma oxycodone and was bioequivalent to crushed oxycodone IR. CONCLUSION: This second pharmacokinetic study demonstrated that Xtampza ER maintains its ER properties after crushing, unlike OxyContin, which failed to retain its ER properties after crushing. ANZCTR registration number: ACTRN12614000613606.

Tolerability, Safety, and Effectiveness of Oxycodone DETERx in Elderly Patients ≥65 Years of Age with Chronic Low Back Pain: A Randomized Controlled Trial.

TRIAL DESIGN: This was a phase III, randomized withdrawal, double-blind, placebo-controlled, enriched enrollment, parallel-group, multicenter study intended to demonstrate the safety, tolerability, and analgesic efficacy of oxycodone DETERx® (Xtampza™ ER) compared with matching placebo. METHODS: This post hoc analysis was performed using data from a subpopulation of enrolled patients who were ≥65 years of age. The study enrolled male and female patients with a clinical diagnosis of moderate-to-severe chronic low back pain for a minimum of 6 months prior to screening who required around-the-clock opioid therapy. To be eligible for enrollment, patients were required to have an average 24-h pain intensity score of ≥5 and ≤9 on an 11-point (0-10) Pain Intensity-Numerical Rating Scale at the screening visit. The study enrolled both opioid-experienced and opioid-naïve patients. The study consisted of an open-label titration phase followed by a 12-week double-blind maintenance phase. The dose range was 40-160 mg oxycodone hydrochloride equivalent per day. This post hoc analysis evaluated the safety, tolerability, and effectiveness of oxycodone DETERx among patients ≥65 years of age. The effectiveness of oxycodone DETERx was evaluated based on average pain intensity scores, Patient Global Impression of Change, responder analysis, and Kaplan-Meier survival analysis. The safety and tolerability of oxycodone DETERx were also evaluated. Patients were randomized to either oxycodone DETERx or placebo using a blocked randomization scheme in a 1:1 ratio. Randomization was stratified by previous opioid use (naïve or experienced). The study drug was coded in a manner that maintained the blinding. Study personnel and patients remained blinded to the assigned treatments throughout the study. RESULTS: For this post-hoc analysis, the intent-to-treat and randomized safety populations included 52 patients ≥65 years old, 26 each in the oxycodone DETERx and placebo groups, who participated in the study during the titration phase and were randomized to the double-blind maintenance phase. Clinically important pain reduction from screening was achieved with oxycodone DETERx, with the median pain intensity score decreasing from 7.50 at screening to 2.69 at Week 12. A clinically meaningful treatment difference of -0.9 in pain score between oxycodone DETERx and placebo was observed. All 18 elderly patients who completed the study reported improvement in pain, with 62% showing ≥30% improvement and 54% showing ≥50% improvement in pain intensity compared with patients on placebo (p = 0.0128 and p = 0.0501, respectively). Patients on oxycodone DETERx remained in the study longer than those on placebo. Of the 26 patients ≥65 years old randomized to continue oxycodone DETERx during the double-blind maintenance phase, 18 (69%) completed the study; only two patients (8%) in the oxycodone DETERx group discontinued due to adverse events. The safety and tolerability profiles showed no new or unexpected safety concerns. The adverse event profiles were similar between the titration and double-blind maintenance phases. CONCLUSIONS: Oxycodone DETERx was efficacious and generally well tolerated in patients ≥65 years old. TRIAL REGISTRATION: The study was registered with ClinicalTrials.gov (NCT01685684).

Measures That Identify Prescription Medication Misuse, Abuse, and Related Events in Clinical Trials: ACTTION Critique and Recommended Considerations.

Accurate assessment of inappropriate medication use events (ie, misuse, abuse, and related events) occurring in clinical trials is an important component in evaluating a medication's abuse potential. A meeting was convened to review all instruments measuring such events in clinical trials according to previously published standardized terminology and definitions. Only 2 approaches have been reported that are specifically designed to identify and classify misuse, abuse, and related events occurring in clinical trials, rather than to measure an individual's risk of using a medication inappropriately: the Self-Reported Misuse, Abuse, and Diversion (SR-MAD) instrument and the Misuse, Abuse, and Diversion Drug Event Reporting System (MADDERS). The conceptual basis, strengths, and limitations of these methods are discussed. To our knowledge, MADDERS is the only system available to comprehensively evaluate inappropriate medication use events prospectively to determine the underlying intent. MADDERS can also be applied retrospectively to completed trial data. SR-MAD can be used prospectively; additional development may be required to standardize its implementation and fully appraise the intent of inappropriate use events. Additional research is needed to further demonstrate the validity and utility of MADDERS as well as SR-MAD. PERSPECTIVE: Identifying a medication's abuse potential requires assessing inappropriate medication use events in clinical trials on the basis of a standardized event classification system. The strengths and limitations of the 2 published methods designed to evaluate inappropriate medication use events are reviewed, with recommended considerations for further development and current implementation.

The Potential Role of Sensory Testing, Skin Biopsy, and Functional Brain Imaging as Biomarkers in Chronic Pain Clinical Trials: IMMPACT Considerations.

Valid and reliable biomarkers can play an important role in clinical trials as indicators of biological or pathogenic processes or as a signal of treatment response. Currently, there are no biomarkers for pain qualified by the U.S. Food and Drug Administration or the European Medicines Agency for use in clinical trials. This article summarizes an Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials meeting in which 3 potential biomarkers were discussed for use in the development of analgesic treatments: 1) sensory testing, 2) skin punch biopsy, and 3) brain imaging. The empirical evidence supporting the use of these tests is described within the context of the 4 categories of biomarkers: 1) diagnostic, 2) prognostic, 3) predictive, and 4) pharmacodynamic. Although sensory testing, skin punch biopsy, and brain imaging are promising tools for pain in clinical trials, additional evidence is needed to further support and standardize these tests for use as biomarkers in pain clinical trials. PERSPECTIVE: The applicability of sensory testing, skin biopsy, and brain imaging as diagnostic, prognostic, predictive, and pharmacodynamic biomarkers for use in analgesic treatment trials is considered. Evidence in support of their use and outlining problems is presented, as well as a call for further standardization and demonstrations of validity and reliability.

Oral Human Abuse Potential of Oxycodone DETERx® (Xtampza® ER).

Oxycodone DETERx® (Collegium Pharmaceutical Inc, Canton, Massachusetts) is an extended-release, microsphere-in-capsule, abuse-deterrent formulation designed to retain its extended-release properties after tampering (eg, chewing/crushing). This randomized, double-blind, placebo-controlled, triple-dummy study evaluated the oral abuse potential of intact and chewed oxycodone DETERx capsules compared with crushed immediate-release oxycodone. Subjects with a history of recreational opioid use who were nondependent/nontolerant to opioids were enrolled. Treatments included intact oxycodone DETERx (high-fat, high-calorie meal and fasted), chewed oxycodone DETERx (high-fat, high-calorie meal and fasted), crushed immediate-release oxycodone (fasted), and placebo (high-fat, high-calorie meal). Plasma samples were collected to determine pharmacokinetic parameters. The primary endpoint was drug liking at the moment; other endpoints included drug effects questionnaire scores, Addiction Research Center Inventory/Morphine Benzedrine Group score, pupillometry measurements, and safety. Thirty-eight subjects completed the study. Chewed and intact oxycodone DETERx were bioequivalent, unlike crushed immediate-release oxycodone, which yielded higher peak oxycodone plasma concentrations compared with all methods of oxycodone DETERx administration. The mean maximum (peak) effect (Emax ) for drug liking was significantly lower for chewed and intact oxycodone DETERx than for crushed immediate-release oxycodone (P < .01). The time to Emax was significantly longer for chewed and intact oxycodone DETERx than for crushed immediate-release oxycodone (P < .0001). Scores for feeling high and Addiction Research Center Inventory/Morphine Benzedrine Group scores demonstrated lower abuse potential for chewed and intact oxycodone DETERx compared with crushed immediate-release oxycodone. Study treatments were well tolerated; no subjects experienced serious adverse events. These results demonstrate the lower oral abuse potential of chewed and intact oxycodone DETERx than crushed immediate-release oxycodone.

An abuse-deterrent, microsphere-in-capsule formulation of extended-release oxycodone: alternative modes of administration to facilitate pain management in patients with dysphagia.

BACKGROUND: Patients with chronic pain may experience difficulty swallowing, in part due to worsening disease, comorbid conditions, iatrogenic etiology, or age. Patients or caregivers may manipulate extended-release (ER) opioid formulations to facilitate oral dosing due to a lack of therapeutic options that allow for sprinkle or enteral feeding tube administration. If crushed or broken, current oral ER opioids can be associated with adverse sequelae, including risk of potentially fatal overdose. OBJECTIVE: To review the safety, in vitro dissolution data, and in vivo pharmacokinetic data that support alternative modes of administration of oxycodone DETERx (Xtampza ER) via sprinkling onto soft foods for oral ingestion or via enteral feeding tubes. METHODS: A review of oxycodone DETERx data from in vitro and in vivo studies was conducted to demonstrate support for alternative routes and modes of administration. RESULTS: There was no difference in the dissolution profile when administered with various soft foods or when mixed with various liquid vehicles and administered via nasogastric (NG) or gastrostomy (G) tubes, based on in vitro studies. When sprinkled onto applesauce and administered orally, the microspheres were bioequivalent to the intact oxycodone capsules. When crushed or chewed, the formulation maintained its pharmacokinetic profile; no bolus dose of opioid was released. The sprinkle-dose study was limited by the single-dose study design, as well as the small sample size. CONCLUSIONS: Oxycodone DETERx is the first ER oxycodone formulation that can be administered either intact, sprinkled onto soft foods, or via NG/G tubes, thereby providing options for treating pain in patients who have difficulty swallowing.

Participant Preferences for Pharmacologic Chronic Pain Treatment Trial Characteristics: An ACTTION Adaptive Choice-Based Conjoint Study.

Barriers to clinical trial recruitment can delay study completion, potentially resulting in increased costs and an unrepresentative sample. In the current study of 150 participants with chronic pain, we used a computerized adaptive choice-based conjoint survey that included 8 characteristics that may affect enrollment in pharmacologic pain treatment trials (ie, treatment allocation, frequency of pain ratings, treatment administration method, current medications, number of study visits, availability of evening and weekend visits, invasiveness of laboratory procedures, payment). These data were analyzed using Sawtooth Software ver. 8.4.8 (Sawtooth Software, Inc, Orem, UT), which identifies the characteristics that dominate participants' decisions across multiple sets of potential trials. Three characteristics had the largest relative importance in participants' trial preferences: 1) invasiveness of required laboratory procedures (ie, 22%), with no procedures or blood tests preferred over ice-water sensory testing or skin biopsy; 2) ability to continue current pain medications (21%); and 3) payment for study participation (21%), with higher payment preferred. The fourth most important characteristic was number of study visits (13%), with participants preferring fewer in-person visits and more phone contacts. Understanding the preferences of potential participants is an important step toward enhancing enrollment in pain treatment trials. PERSPECTIVE: This article presents the preferences of individuals with chronic pain conditions regarding modifiable pain treatment trial characteristics (eg, number of study visits, payment, treatment allocation). These findings may help to improve enrollment into analgesic clinical trials and in turn accelerate the development of new pain treatments.

Patient phenotyping in clinical trials of chronic pain treatments: IMMPACT recommendations.

There is tremendous interpatient variability in the response to analgesic therapy (even for efficacious treatments), which can be the source of great frustration in clinical practice. This has led to calls for "precision medicine" or personalized pain therapeutics (ie, empirically based algorithms that determine the optimal treatments, or treatment combinations, for individual patients) that would presumably improve both the clinical care of patients with pain and the success rates for putative analgesic drugs in phase 2 and 3 clinical trials. However, before implementing this approach, the characteristics of individual patients or subgroups of patients that increase or decrease the response to a specific treatment need to be identified. The challenge is to identify the measurable phenotypic characteristics of patients that are most predictive of individual variation in analgesic treatment outcomes, and the measurement tools that are best suited to evaluate these characteristics. In this article, we present evidence on the most promising of these phenotypic characteristics for use in future research, including psychosocial factors, symptom characteristics, sleep patterns, responses to noxious stimulation, endogenous pain-modulatory processes, and response to pharmacologic challenge. We provide evidence-based recommendations for core phenotyping domains and recommend measures of each domain.

Pain intensity rating training: results from an exploratory study of the ACTTION PROTECCT system.

Clinical trial participants often require additional instruction to prevent idiosyncratic interpretations regarding completion of patient-reported outcomes. The Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks (ACTTION) public-private partnership developed a training system with specific, standardized guidance regarding daily average pain intensity ratings. A 3-week exploratory study among participants with low-back pain, osteoarthritis of the knee or hip, and painful diabetic peripheral neuropathy was conducted, randomly assigning participants to 1 of 3 groups: training with human pain assessment (T+); training with automated pain assessment (T); or no training with automated pain assessment (C). Although most measures of validity and reliability did not reveal significant differences between groups, some benefit was observed in discriminant validity, amount of missing data, and ranking order of least, worst, and average pain intensity ratings for participants in Group T+ compared with the other groups. Prediction of greater reliability in average pain intensity ratings in Group T+ compared with the other groups was not supported, which might indicate that training produces ratings that reflect the reality of temporal pain fluctuations. Results of this novel study suggest the need to test the training system in a prospective analgesic treatment trial.

Assessment of physical function and participation in chronic pain clinical trials: IMMPACT/OMERACT recommendations.

Although pain reduction is commonly the primary outcome in chronic pain clinical trials, physical functioning is also important. A challenge in designing chronic pain trials to determine efficacy and effectiveness of therapies is obtaining appropriate information about the impact of an intervention on physical function. The Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) and Outcome Measures in Rheumatology (OMERACT) convened a meeting to consider assessment of physical functioning and participation in research on chronic pain. The primary purpose of this article is to synthesize evidence on the scope of physical functioning to inform work on refining physical function outcome measurement. We address issues in assessing this broad construct and provide examples of frequently used measures of relevant concepts. Investigators can assess physical functioning using patient-reported outcome (PRO), performance-based, and objective measures of activity. This article aims to provide support for the use of these measures, covering broad aspects of functioning, including work participation, social participation, and caregiver burden, which researchers should consider when designing chronic pain clinical trials. Investigators should consider the inclusion of both PROs and performance-based measures as they provide different but also important complementary information. The development and use of reliable and valid PROs and performance-based measures of physical functioning may expedite development of treatments, and standardization of these measures has the potential to facilitate comparison across studies. We provide recommendations regarding important domains to stimulate research to develop tools that are more robust, address consistency and standardization, and engage patients early in tool development.