A 3-way Cross-over Study of Pregabalin, Placebo, and the Histamine 3 Receptor Inverse Agonist AZD5213 in Combination With Pregabalin in Patients With Painful Diabetic Neuropathy and Good Pain-reporting Ability

Test-retest and interrater reliability of experimental within-subject variability of pain reports as assessed by the focused analgesia selection test

Introduction

Within-subject variability (WSV) of pain intensity reports has been shown to predict the placebo response. The focused analgesia selection test (FAST), which allows to experimentally assess WSV of pain reports, has been used as a screening tool to identify participants who are likely to have a strong placebo response in drug-development clinical trials. Yet, the reliability of FAST has not been reported.

Objectives

To assess test-retest and interrater reliability of the FAST outcomes. To mimic pharma-sponsored clinical trials, we enlisted inexperienced assessors who underwent limited training.

Methods

Healthy volunteers performed the FAST twice within a week and were randomly assigned to either the test-retest group or the interrater group. T-tests, partial Pearson correlations, intraclass correlations (ICC), and Bland-Altman plots were generated to assess FAST outcomes' reliability.

Results

Sixty-three participants completed the study and were assigned to the test-retest (N = 33) or interrater (N = 30) arms. No statistically significant differences in the FAST outcomes were detected between the 2 sessions, except for the FAST covariance (FAST CoV) in the interrater assessment (P = 0.009). Test-retest reliabilities of the FAST-main outcomes were r = 0.461, ICC = 0.385 for the FAST R 2 and r = 0.605, ICC = 0.539 for the FAST ICC and in the interrater cohort, they were FAST R 2: r = 0.321, ICC = 0.337 and FAST ICC: r = 0.355, ICC = 0.330.

Conclusion

Using inexperienced assessors, the FAST outcomes test-retest ranged from moderate to strong, whereas the interrater reliability ranged from weak to poor. These results highlight the importance of adequately training study staff members before using this tool in multicentre clinical trials.

Evaluating the Effect of Pregabalin in the Treatment of Carpal Tunnel Syndrome: A Prospective, Randomized, Triple-Blinded, Placebo-controlled Trial

OBJECTIVE

This study aimed to determine the effectiveness of pregabalin for the control of symptoms in mild to moderate idiopathic Carpal tunnel syndrome (CTS).

METHODS

In this randomized, placebo-controlled trial, 146 mild to moderate idiopathic CTS patients were randomized into pregabalin (n=74) and placebo groups (n=72). Per protocol, analysis was conducted with 131 patients; pregabalin (n=65) and placebo (n=66). The drug titration dose was 50 mg once daily for the first week, twice daily for the second week and thrice daily for the next 6 weeks. The primary outcome included a change in the Symptom Severity Scale and Functional Status Scale (FSS) of the Boston Carpal Tunnel Questionnaire after the eighth week. The secondary outcome was the change in clinical and electrophysiological grading after 8 weeks of therapy.

RESULTS

There was a statistically significant improvement in the mean Symptom Severity Scale (14.92±3.72 vs. 16.55±4.45; P =0.025) and FSS (10.77±2.64 vs. 12.0±2.55; P =0.007) in the pregabalin group after 8 weeks. Mean clinical and electrophysiological grading changed significantly from 2.3±0.7 to 2.1±0.8 ( P =0.001) and 1.9±0.7 to 1.8±0.8 ( P =0.020), respectively in the pregabalin group but not in the placebo group.

DISCUSSION

The results of this study demonstrates that pregabalin is effective in ameliorating symptoms and improving functional outcomes in mild to moderate idiopathic CTS.

On the Relationship Between Pain Variability and Relief in Randomized Clinical Trials

Previous research reports suggest greater baseline variability is associated with greater pain relief in those who receive a placebo. However, studies that evidence this association do not control for confounding effects from regression to the mean and natural history. In this report, we analyzed data from two randomized clinical trials (Placebo I and Placebo II, total N = 139) while adjusting for the effects of natural history and regression to the mean via a no treatment group. Results agree between the two placebo groups in each study: both placebo groups showed negligible semi-partial correlations between baseline variability and adjusted response [r_sp (CI_95%) = 0.22 (0.03, 0.42) and 0 (−0.07, 0.07) for Placebo I and II, respectively]. The no treatment group in Placebo I showed a negative correlation [−0.22 (−0.43, −0.02)], but the no treatment and drug groups in Placebo II's correlations were negligible [−0.02 (−0.08, 0.02) and 0.00 (−0.10, 0.12) for the no treatment and drug groups, respectively]. When modeled as a linear covariate, baseline pain variability accounted for <1% of the variance in post-intervention pain across both studies. Even after adjusting for baseline pain and natural history, the inability of baseline pain variability to account for substantial variance in pain response highlights that previous results concerning pain variability and treatment response may be inconsistent. Indeed, the relationship appears to be neither consistently specific nor sensitive to improvements in the placebo group. More work is needed to understand and establish the prognostic value of baseline pain variability—especially its placebo specificity and generalizability across patient populations.