Oral difelikefalin reduces moderate to severe pruritus and expression of pruritic and inflammatory biomarkers in subjects with atopic dermatitis

BACKGROUND

Pruritus is the most common and burdensome symptom of atopic dermatitis (AD). Pruritus-targeted treatments in AD are lacking, particularly for patients with milder skin disease.

OBJECTIVE

We sought to evaluate the impact of the selective κ-opioid receptor agonist difelikefalin (DFK) on pruritus intensity and pruritus- and immune-related biomarkers in subjects with moderate to severe AD-related pruritus.

METHODS

A phase 2 clinical trial investigated the efficacy and safety of oral DFK 0.25, 0.5, and 1.0 mg in subjects with moderate to severe AD-related pruritus. A biomarker substudy evaluated the effects of DFK on the expression of pruritus, TH2-associated genes, and skin barrier-related genes.

RESULTS

In the clinical trial (N = 401), all DFK doses reduced itch versus placebo; however, the results were not statistically significant at week 12. In a subgroup of subjects in the trial with mild to moderate skin inflammation and moderate to severe itch (itch-dominant AD phenotype), DFK reduced itch at week 12 versus placebo. In the biomarker substudy, DFK downregulated the expression of key pruritus-related genes (eg, IL-31 and TRPV1) and the AD phenotype (eg, CCL17). Gene set variation analysis confirmed that DFK, but not placebo, downregulated pruritus-related genes and TH2 pathways. DFK improved skin barrier integrity markers and upregulated the expression of claudins and lipid metabolism-associated genes (eg, SEC14L6, ELOVL3, CYP1A2, and AKR1D1).

CONCLUSIONS

DFK treatment reduced itch in subjects with moderate to severe AD-related pruritus, particularly those with an "itch-dominant" AD phenotype, and had an impact on the expression of pruritus, TH2-associated genes, and skin barrier-related genes. DFK is a promising therapy for AD-related pruritus; further clinical studies are warranted.

The Burden of Pruritus Associated With CKD: A Mixed Methods Analysis Among Patients Undergoing Dialysis

Rationale & Objective

Despite its prevalence and distress to patients, chronic kidney disease-associated pruritus (CKD-aP) is poorly characterized, which may contribute to the condition's underdiagnosis and inadequate management. This study aimed to understand the symptom experience of patients with CKD-aP and the extent to which pruritus impacts their lives.

Study Design

Mixed methods study including one-on-one qualitative interviews and completion of the Skindex-10 Questionnaire (measuring itch-related quality of life).

Setting & Participants

A total of 23 patients undergoing hemodialysis and reporting pruritus at 4 dialysis centers in the United States.

Analytical Approach

Interviews followed a semistructured guide that included targeted and follow-up questions to elicit discussion of patients' symptoms of pruritus, including frequency and variability, impact on activities of daily living, and emotional and social functioning. Interviews were digitally audio-recorded. A coding dictionary was developed from transcripts to analyze themes and concepts.

Results

Participants described their itch with various terms, including "numbness," "pain," and "tingling" on their skin. Itch affected multiple areas but especially the back, usually occurred daily, and was often worse at night. For some, itching was a constant experience. Patients relieved their itch through scratching and various off-label treatments; some reported skin damage from excessive scratching and most indicated treatments provided limited relief. Pruritus considerably disrupted physical function, including sleep, daily activities, social functioning and relationships, and emotional and psychological wellbeing. All participants reported being bothered by their itching during the past week on the Skindex-10 Questionnaire.

Limitations

All participants were from the United States, so the findings may not be generalizable to other countries.

Conclusions

Although symptom experience varies considerably, CKD-aP causes severe distress for many patients undergoing hemodialysis and can profoundly impair their quality of life. The results of this study show the impact of itch from patients' perspectives and highlight the need for greater awareness and better management of this condition.

Plain-Language Summary

Patients with chronic kidney disease often experience itching, or pruritus, but its importance to patients is regularly overlooked. This study used one-on-one interviews to investigate patients' experiences of chronic kidney disease-associated pruritus and how it impacts their lives. We found that participants experienced itch on various body areas and used different words to describe their itch (eg, "numbness" and "pain"). Some reported skin damage from excessive scratching, and many used off-label treatments and other interventions (eg, rubbing alcohol and multiple showers daily), which provided limited relief. For many, itching was experienced daily and severely disrupted sleep, daily activities, interactions with others, and mental wellbeing. These findings reveal chronic kidney disease-associated pruritus severely impacts patients and highlights the need for improved management of this condition.

Assessment of the physical dependence potential of difelikefalin: Randomized placebo-controlled study in patients receiving hemodialysis

Difelikefalin is a selective kappa opioid receptor agonist approved for treating moderate-to-severe pruritus in adults undergoing hemodialysis (HD). Difelikefalin is not a controlled substance under the Controlled Substances Act. This study assessed the potential for developing physical dependence on difelikefalin in patients undergoing HD. Eligible patients received open-label difelikefalin after each dialysis session for 3 weeks before entering a 2-week double-blind phase, when they were randomized to either continue difelikefalin or to switch to receiving placebo. Signs of physical withdrawal were assessed using the Clinical Opiate Withdrawal Scale (COWS), several patient-reported scales, and physiological measures. The primary end point was the between-group difference in mean maximum COWS total scores during the double-blind phase; the mean difference (placebo - difelikefalin) was compared against a predefined noninferiority limit (+4). Thirty-five patients (57.1% male; 91.4% Black or African American; median [range] age 58 [28-77] years) were included, of which 30 were randomized (placebo, n = 14; difelikefalin, n = 16). The least squares mean difference in maximum COWS total scores was 0.52 (95% confidence interval [CI]: -0.56, 1.59). The upper CI limit (1.59) was below +4, indicating that patients who discontinued difelikefalin (placebo group) had similar withdrawal scores to patients who continued difelikefalin. Additional assessments supported the COWS results, showing no meaningful differences between groups in physiological measures or in patient-reported measures of sleep or physical withdrawal. These results demonstrate that abruptly discontinuing chronic difelikefalin treatment in patients undergoing HD does not produce signs or symptoms of physical withdrawal.

A Phase 2 Study of Oral Difelikefalin in Subjects With Chronic Kidney Disease and Moderate-to-Severe Pruritus

INTRODUCTION

/Background: Chronic pruritus is burdensome for chronic kidney disease (CKD) patients.

OBJECTIVE

We evaluated difelikefalin efficacy and safety in reducing itch in subjects with non-dialysis-dependent (NDD)-CKD and those undergoing hemodialysis (HD).

METHODS

This phase 2, double-blind, randomized, placebo-controlled, dose-finding study enrolled NDD-CKD (stage 3-5) and HD subjects with moderate-to-severe pruritus. Subjects were equally randomized to oral difelikefalin (0.25, 0.5, 1.0 mg) or placebo once daily for 12 weeks. The primary endpoint was change in weekly mean Worst Itch Numeric Rating Scale (WI-NRS) score at week 12.

RESULTS

269 subjects were randomized (mean [SD] baseline WI-NRS: 7.1 [1.2]). Difelikefalin 1.0 mg significantly reduced weekly mean WI-NRS scores versus placebo at week 12 (P=0.018), with numerical reductions observed with difelikefalin 0.25 and 0.5 mg. At week 12, 38.6% of subjects receiving difelikefalin 1.0 mg achieved complete response (WI-NRS 0-1) versus 14.4% receiving placebo. Difelikefalin resulted in ∼20% improvement in itch-related quality-of-life measures. The most common treatment-emergent adverse events were dizziness, fall, constipation, diarrhea, gastroesophageal reflux disease, fatigue, hyperkalemia, hypertension, and urinary tract infection.

LIMITATIONS

Study duration was 12 weeks.

CONCLUSIONS

Oral difelikefalin significantly reduced itch intensity in stage 3‒5 CKD subjects with moderate-to-severe pruritus, supporting continued development for this condition.

Phase 2 Trial of Difelikefalin in Notalgia Paresthetica

BACKGROUND

Notalgia paresthetica is a neuropathic disorder characterized by pruritus in a circumscribed region of the upper back. Difelikefalin, a selective kappa opioid receptor agonist, has shown efficacy in other chronic pruritic conditions and is being investigated for the treatment of notalgia paresthetica.

METHODS

In this phase 2, double-blind, placebo-controlled trial, we randomly assigned, in a 1:1 ratio, patients with moderate-to-severe pruritus caused by notalgia paresthetica to receive 2 mg of oral difelikefalin or placebo twice daily for 8 weeks. The primary outcome was the change from baseline at week 8 in the weekly mean score on the daily Worst Itch Numeric Rating Scale (WI-NRS; scores range from 0 [no itch] to 10 [worst itch imaginable]). The secondary clinical outcomes were itch-related quality-of-life and itch-related sleep measures.

RESULTS

A total of 126 patients were enrolled; 62 patients were assigned to receive difelikefalin, and 63 were assigned to receive placebo. One patient who had been assigned to receive difelikefalin withdrew consent before the first dose and is not included in the main analyses. The mean baseline WI-NRS score was 7.6 (indicating severe itch) in each group. The change from baseline in the weekly mean WI-NRS score at week 8 was -4.0 points in the difelikefalin group and -2.4 points in the placebo group (difference in change, -1.6 points; 95% confidence interval, -2.6 to -0.6; P = 0.001). The results for the secondary outcomes generally did not support those of the primary analysis. Headache, dizziness, constipation, and increased urine output occurred more frequently in the difelikefalin group than in the placebo group.

CONCLUSIONS

Among patients with notalgia paresthetica, oral treatment with difelikefalin resulted in modestly greater reductions in itch intensity scores than placebo over a period of 8 weeks but was associated with adverse events. Larger and longer trials are needed to assess the efficacy and safety of difelikefalin treatment in this disorder. (Funded by Cara Therapeutics; KOMFORT ClinicalTrials.gov number, NCT04706975.).

Understanding the patient experience of living with notalgia paresthetica: A qualitative interview study

Background

Notalgia paresthetica (NP) is a chronic sensory neuropathy that causes intense pruritus, typically affecting the upper portion of the back and lasting for months to years. The impacts of pruritus and the full symptom experience are not well documented.

Objective

To describe patients’ NP symptom experience and the impacts of living with NP-related itch.

Methods

Semistructured, one-to-one qualitative telephone interviews were conducted in adults living with NP. The worst itch severity during the previous 24 hours was assessed using an 11-point numerical rating scale.

Results

Thirty participants (23 females; aged 41-80 years) completed interviews. Seventeen NP-related symptoms were described, with daily itch being the most common. Participants’ itch ranged from severe to very severe (50%) and was experienced for a median of 2.8 years. Most (73%) participants were not receiving treatment for NP at the time of the study. Other reported symptoms included skin pain or sensitivity and secondary symptoms from itching (skin discoloration, lumps or bumps, bleeding or scabbing). NP-related itch was frequently reported to affect mood, interfere with sleep, and disrupt self-care.

Limitations

Only English-speaking participants living in the United States were included.

Conclusion

This study highlights the patient experience of living with NP and findings reveal that there remains an unmet need for effective therapeutic options to address NP-related itch.

Efficacy of Difelikefalin for the Treatment of Moderate to Severe Pruritus in Hemodialysis Patients: Pooled Analysis of KALM-1 and KALM-2 Phase 3 Studies

Rationale & Objective

Chronic kidney disease–associated pruritus (CKD-aP) in patients treated by hemodialysis (HD) impairs quality of life (QoL). Difelikefalin, a selective κ-opioid receptor agonist, decreased the intensity of CKD-aP in patients undergoing HD. This pooled analysis evaluated difelikefalin’s efficacy and the itch-related QoL overall and in subgroups defined by demographics or disease characteristics.

Study Design

In KALM-1 and KALM-2, participants were randomized (1:1) to receive intravenous difelikefalin or placebo 3 times/wk for 12 weeks, followed by a 52-week open-label extension.

Setting & Participants

Adults with moderate to severe CKD-aP treated by HD in North America, Europe, and the Asia-Pacific region.

Intervention

Intravenous difelikefalin at 0.5 mcg/kg or placebo.

Outcomes

Itch intensity (Worst Itching Intensity Numerical Rating Scale [WI-NRS]) and itch-related QoL (Skindex-10 and 5-D Itch questionnaires).

Results

851 participants were randomized (difelikefalin, n = 426; placebo, n = 425). This pooled analysis demonstrated early     (week 1), sustained difelikefalin efficacy, with significantly greater achievement of ≥3-point WI-NRS reduction with difelikefalin (51.1%) versus placebo (35.2%; P < 0.001). Achievement of a ≥4-point WI-NRS reduction was significantly greater with difelikefalin (38.7%) versus placebo (23.4%; P < 0.001). Difelikefalin reduced itch intensity in subgroups based on age, sex, anti-itch medication use, the presence of specific medical conditions, and gabapentin or pregabalin use. More participants receiving difelikefalin versus placebo achieved clinically meaningful decreases of ≥15 points on the Skindex-10 scale (55.5% vs 40.5%, respectively; P < 0.001) and ≥5 points on the 5-D Itch scale (52.1% vs 42.3%, respectively; P = 0.01), with sustained 5-D Itch effects up to 64 weeks.

Limitations

Subgroup samples were small. The WI-NRS, Skindex-10, and 5-D Itch are not used in routine clinical care of dialysis patients; therefore, findings may not reflect the real-world effectiveness of difelikefalin.

Conclusions

Difelikefalin demonstrated rapid, sustained efficacy, with consistent results in diverse populations of patients treated by HD.

Funding

Cara Therapeutics, Inc.

Trial Registration

The KALM-1 trial is registered as NCT03422653 and the KALM-2 trial is registered as NCT03636269.

Safety and Tolerability of Difelikefalin for the Treatment of Moderate to Severe Pruritus in Hemodialysis Patients: Pooled Analysis From the Phase 3 Clinical Trial Program

Rationale & Objective

We report a pooled safety analysis of intravenous difelikefalin in participants with moderate to severe chronic kidney disease–associated pruritus (CKD-aP) treated by hemodialysis in 4 phase 3 clinical studies.

Study Design

KALM-1 and KALM-2 were randomized, double-blind, placebo-controlled, pivotal phase 3 studies; CLIN3101 (52 weeks) and CLIN3105 (12 weeks) were open-label studies.

Setting & Participants

Adults with moderate to severe CKD-aP treated by hemodialysis in North America, Europe, and the Asia-Pacific region.

Intervention

At least 1 intravenous placebo or difelikefalin dose of 0.5 mcg/kg for up to 64 weeks.

Outcomes

Safety.

Results

Safety analyses were conducted with 848 participants in the placebo-controlled cohort (424 participants each in the difelikefalin and placebo groups) and in 1,306 participants in the all-difelikefalin-exposure cohort. In the placebo-controlled cohort, the most commonly reported treatment-emergent adverse events (TEAEs), occurring in ≥2% of participants receiving difelikefalin and with a ≥1% higher incidence than placebo, were diarrhea (9.0% and 5.7%, respectively); dizziness (6.8% and 3.8%, respectively); nausea (6.6% and 4.5%, respectively); gait disturbances, including falls (6.6% and 5.4%, respectively), hyperkalemia (4.7% and 3.5%, respectively); headache (4.5% and 2.6%, respectively); somnolence (4.2% and 2.4%, respectively); and mental status changes (3.3% and 1.4%, respectively). These were mostly mild or moderate, with few leading to discontinuation. Incidence rates of TEAEs, serious TEAEs, and discontinuations because of TEAEs did not increase with long-term exposure. Three participants (0.7%) in the difelikefalin group and 5 participants (1.2%) in the placebo group died during the study.

Limitations

Pooled data from studies with different designs.

Conclusions

Intravenous difelikefalin demonstrated an acceptable safety profile, was generally well tolerated with long-term use, and may address the unmet treatment need for patients with CKD-aP treated by hemodialysis.

Funding

Cara Therapeutics, Inc.

Trial Registration

KALM-1 is registered as NCT03422653, KALM-2 as NCT03636269, CLIN3101 as NCT03281538, and CLIN3105 as NCT03998163.

Psychometric validation and meaningful change thresholds of the Worst Itching Intensity Numerical Rating Scale for assessing itch in patients with chronic kidney disease-associated pruritus

Background

Chronic kidney disease-associated pruritus (CKD-aP) is characterized by persistent itch that often leads to substantially impaired quality of life. The Worst Itching Intensity Numerical Rating Scale (WI-NRS) is a single-item patient-reported outcome measure in which patients indicate the intensity of the worst itching they experienced over the past 24 h. Here, we evaluated the content validity and psychometric properties of the WI-NRS and confirmed the threshold of meaningful change in hemodialysis patients with moderate-to-severe CKD-aP.

Methods

Content validity interviews were conducted in 23 patients. Psychometric properties of the WI-NRS were assessed using data from one phase 2 (N = 174) and two phase 3 (N = 848) clinical trials investigating an anti-pruritic treatment. Anchor-based methods were used to confirm meaningful within-patient change score thresholds in the phase 3 trial patients and mixed-method exit interviews (N = 70) contributed further insight.

Results

Content validity interviews indicated patients considered the WI-NRS to be straightforward, comprehensive, and relevant. Test–retest reliability was strong in both trial cohorts (intraclass correlation coefficients > 0.75). Construct validity analyses indicated high correlation between the WI-NRS and other measures of itch. Anchor-based analyses showed a reduction of ≥ 3 points from baseline score represented an appropriate clinically meaningful within-patient change on the WI-NRS. In the exit interviews, all patients with a reduction ≥ 3 points considered the change meaningful.

Conclusions

The WI-NRS is a reliable, valid, and responsive measure of itch intensity for patients with moderate-to-severe CKD-aP. These results support its use to assess treatment efficacy and in clinical evaluation and management of pruritus in hemodialysis patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41687-021-00404-z.

Itching is a distressing medical condition common in patients with chronic kidney disease, especially those undergoing hemodialysis. The itch often leads to skin damage due to a continuous and uncontrollable urge to scratch. It affects about 60% of hemodialysis patients and can be severe enough to seriously affect quality of life. At present, there are no approved therapies. To evaluate whether new treatments for itch are effective, clinicians need to assess if the intensity of itch decreases over time. However, because itch intensity can only be measured accurately by the person experiencing it, a measure is required that can be easily understood and used by patients. This study evaluated a scale in which patients mark a number between ‘0’ (corresponding to no itch) and ‘10’ (the worst itching imaginable), to describe the worst itch intensity they experienced over the last 24 hours. Using data from three clinical trials of a novel treatment for itch in patients undergoing hemodialysis with moderate-to-severe pruritus, we found that the scale was reliable in repeat-testing experiments, and mirrored other methods of measuring changes in itch. In interviews, patients said they found the scale straightforward and easy to complete. Our analysis and patients’ opinions showed a 3-point reduction in itch intensity on the scale represented a meaningful improvement. These findings support the use of this scale to assess the efficacy of new treatments and in clinical evaluation and management of pruritus in patients with chronic kidney disease.

FC 022AN OPEN-LABEL, MULTICENTER STUDY TO EVALUATE THE SAFETY AND EFFECTIVENESS OF INTRAVENOUS DIFELIKEFALIN IN PATIENTS WITH MODERATE-TO-SEVERE CKD–ASSOCIATED PRURITUS UNDERGOING HEMODIALYSIS

Background and Aims

Chronic kidney disease–associated pruritus (CKD-aP) is a common and highly distressing condition in patients undergoing hemodialysis (HD). CKD-aP is associated with sleep disturbances, significant quality-of-life (QoL) impairment, and increased morbidity and mortality. Difelikefalin (DFK) is a selective kappa opioid receptor agonist in development for CKD-aP that has minimal central nervous system penetration. In placebo-controlled phase 3 trials of patients with moderate to severe CKD-aP undergoing HD, intravenous (IV) DFK had an acceptable safety profile and demonstrated significant reductions vs placebo in itch intensity. We report safety and effectiveness outcomes, including itch-related QoL and sleep measures, from a phase 3 open-label study of DFK in patients with moderate to severe CKD-aP.

Method

This multicenter, open-label study conducted in the United States and Europe enrolled patients with moderate to severe CKD-aP (mean baseline 24-hour Worst Itching Intensity Numerical Rating Scale [WI-NRS] score ≥5) undergoing HD for ≥3 months. Patients received IV DFK 0.5 mcg/kg 3 times/week at the end of each HD session for up to 12 weeks. Predefined effectiveness endpoints at week 12 included ≥3-point and ≥4-point improvement in the weekly mean of the 24-hour WI-NRS score (range from 0 [no itching] to 10 [worst itching imaginable]). Change from baseline in QoL at week 12 was assessed using the 5-D itch and Skindex-10, multidimensional itch-related questionnaires validated in CKD-aP (higher scores indicate worse QoL). The proportion of patients with no problems (score of 1) on the skin irritation and self-confidence domains of the EQ-PSO questionnaire was evaluated. Post hoc endpoints included complete resolution in WI-NRS (≥75% of week 12 scores 0 or 1) and Sleep Quality Questionnaire total score assessments (range of possible scores, 0 [did not interfere] to 10 [completely interfered]), including ≥3-point and ≥4-point improvement in weekly mean score and complete resolution (all scores of 0) at week 12. Safety assessments and adverse events (AEs) were evaluated. Data were summarized descriptively.

Results

Among 222 patients who received DFK, 197 (88.7%) completed the study. At baseline, mean ±SD age was 58.1 ±12.8 years and 54.5% of patients were male. Baseline mean ±SD WI-NRS score was 7.6 ±1.3, Sleep Quality score was 6.6 ±2.2, 5-D itch score was 17.1 ±3.5, and Skindex-10 score was 32.9 ±14.3. At week 12, the majority of patients achieved ≥3-point and ≥4-point improvement in WI-NRS (73.7% and 59.3%) and Sleep Quality score (66.0% and 56.7%). Complete resolution of WI-NRS and Sleep Quality score was observed in 29.4% and 19.1% of patients, respectively (Figure). DFK was associated with improvements in mean 5-D itch (−7.1 ±4.3) and Skindex-10 (−21.0 ±15.6) scores at week 12. The proportion of patients reporting no problems in the skin irritation EQ-PSO domain increased from 1.4% at baseline to 28.9% at week 12, and self-confidence EQ-PSO domain scores increased from 63.5% at baseline to 73.2% at week 12. Overall, 64.4% (143/222) of patients reported ≥1 treatment-emergent AE (TEAE). The most commonly reported TEAEs (≥4% of patients) were diarrhea (5.0% [11/222]), nausea (4.5% [10/222]), and hyperkalemia (4.1% [9/222]). Serious TEAEs were reported by 20.3% (45/222) of patients; no serious TEAEs were related to study drug.

Conclusion

In this phase 3 open-label study in patients with moderate to severe CKD-aP undergoing HD, DFK was generally well tolerated with an acceptable safety profile. DFK demonstrated effectiveness based on reduction of itch intensity, and improvements in sleep quality and itch-related QoL at week 12. The majority of patients reported ≥3-point or ≥4-point improvement in WI-NRS and Sleep Quality scores, with some reporting complete resolution. Findings from this open-label study provide insight into the potential real-world effectiveness of DFK in moderate to severe CKD-aP.

Randomized Controlled Trial of Difelikefalin for Chronic Pruritus in Hemodialysis Patients

Introduction

There is an unmet medical need for pruritus associated with chronic kidney disease, a distressing complication characterized by generalized and persistent itch affecting 20% to 40% of patients undergoing hemodialysis. Here we report the results of a phase 2 trial evaluating the efficacy and safety of a novel peripherally restricted kappa opioid receptor agonist, difelikefalin, in adult patients undergoing hemodialysis with pruritus.

Methods

In this study, 174 hemodialysis patients with moderate-to-severe pruritus were randomly assigned to receive difelikefalin (0.5, 1.0, or 1.5 μg/kg) or placebo intravenously thrice weekly after each hemodialysis session for 8 weeks in a double-blind, controlled trial. The primary endpoint was the change from baseline at week 8 in the weekly mean of the 24-hour Worst Itching Intensity Numerical Rating Scale score. The secondary efficacy endpoint was the change in itch-related quality of life measured by the Skindex-10 questionnaire. Other endpoints included safety, sleep quality, and additional measures including the 5-D itch scale.

Results

A significant reduction from baseline in itch intensity scores at week 8 favored all difelikefalin doses combined versus placebo (P = 0.002). Difelikefalin also showed improvement over placebo in Skindex-10, 5-D itch, and sleep disturbance scores (P ≤ 0.005). Overall, 78% of patients receiving difelikefalin reported treatment-emergent adverse events versus 42% of patients given placebo, with diarrhea, dizziness, nausea, somnolence, and fall being the most frequent (≥5%).

Conclusion

In this trial, difelikefalin effectively reduced itching intensity and improved sleep and itch-related quality of life.

A Phase 3 Trial of Difelikefalin in Hemodialysis Patients with Pruritus

BACKGROUND

Difelikefalin is a peripherally restricted and selective agonist of kappa opioid receptors that are considered to be important in modulating pruritus in conditions such as chronic kidney disease.

METHODS

In this double-blind, placebo-controlled, phase 3 trial, we randomly assigned patients undergoing hemodialysis who had moderate-to-severe pruritus to receive either intravenous difelikefalin (at a dose of 0.5 μg per kilogram of body weight) or placebo three times per week for 12 weeks. The primary outcome was the percentage of patients with an improvement (decrease) of at least 3 points from baseline at week 12 in the weekly mean score on the 24-hour Worst Itching Intensity Numerical Rating Scale (WI-NRS; scores range from 0 to 10, with higher scores indicating greater itch intensity). The secondary outcomes included the change from baseline in itch-related quality-of-life measures, the percentage of patients with an improvement of at least 4 points in the WI-NRS score at week 12, and safety.

RESULTS

A total of 378 patients underwent randomization. A total of 82 of 158 patients (51.9%) in the difelikefalin group had a decrease of at least 3 points in the WI-NRS score (primary outcome), as compared with 51 of 165 (30.9%) in the placebo group. The imputed percentage of patients with a decrease of at least 3 points in the WI-NRS score was 49.1% in the difelikefalin group, as compared with 27.9% in the placebo group (P<0.001). Difelikefalin also resulted in a significant improvement from baseline to week 12 in itch-related quality of life as measured by the 5-D itch scale and the Skindex-10 scale. The imputed percentage of patients with a decrease of at least 4 points in the WI-NRS score at week 12 was significantly greater in the difelikefalin group than in the placebo group (37.1% [observed data: 64 of 158 patients] vs. 17.9% [observed data: 35 of 165 patients], P<0.001). Diarrhea, dizziness, and vomiting were more common in the difelikefalin group than in the placebo group.

CONCLUSIONS

Patients treated with difelikefalin had a significant reduction in itch intensity and improved itch-related quality of life as compared with those who received placebo. (Funded by Cara Therapeutics; KALM-1 ClinicalTrials.gov number, NCT03422653.).

Identifying optimal dosage regimes under safety constraints: An application to long term opioid treatment of chronic pain

There is growing interest and investment in precision medicine as a means to provide the best possible health care. A treatment regime formalizes precision medicine as a sequence of decision rules, one per clinical intervention period, that specify if, when and how current treatment should be adjusted in response to a patient's evolving health status. It is standard to define a regime as optimal if, when applied to a population of interest, it maximizes the mean of some desirable clinical outcome, such as efficacy. However, in many clinical settings, a high-quality treatment regime must balance multiple competing outcomes; eg, when a high dose is associated with substantial symptom reduction but a greater risk of an adverse event. We consider the problem of estimating the most efficacious treatment regime subject to constraints on the risk of adverse events. We combine nonparametric Q-learning with policy-search to estimate a high-quality yet parsimonious treatment regime. This estimator applies to both observational and randomized data, as well as settings with variable, outcome-dependent follow-up, mixed treatment types, and multiple time points. This work is motivated by and framed in the context of dosing for chronic pain; however, the proposed framework can be applied generally to estimate a treatment regime which maximizes the mean of one primary outcome subject to constraints on one or more secondary outcomes. We illustrate the proposed method using data pooled from 5 open-label flexible dosing clinical trials for chronic pain.

A Subgroup Analysis Found no Diminished Response to Buprenorphine Transdermal System Treatment for Chronic Low Back Pain Patients Classified with Depression

BACKGROUND

Chronic pain (CP) patients with depression typically exhibit worse post-treatment outcomes than nondepressed CP patients. The cause is often assumed to reflect a differential response to treatment, neglecting other potential explanations, such as the continuation of differences in pretreatment outcomes. This post hoc analysis examines whether worse post-treatment outcomes for depressed patients with chronic low back pain (CLBP) are driven by reduced treatment efficacy.

METHODS

Data were from opioid-naïve adult patients with moderate-to-severe CLBP who participated in a randomized, placebo-controlled, double-blind clinical trial of Butrans(®) (buprenorphine) Transdermal System (BTDS) for pain relief. Depression screening was based on baseline SF-36v2 Mental Health subscale scores. Patient-reported measures of pain severity, pain interference, quality of life, sleep problems, and functional disability were administered at screening and during the study. Differential treatment efficacy for each outcome was examined using analysis of covariance models that included interaction terms between treatment arm and depression status.

RESULTS

At baseline, patients classified as depressed showed greater pain interference, lower quality of life, more sleep problems, and greater functional disability than nondepressed patients; the two groups did not differ in pain severity. No statistically significant interactions between treatment arm and depression status were observed. The direction of improvement post-treatment favored the depressed group on nine of seventeen outcomes.

CONCLUSIONS

Results do not support a differential response to BTDS treatment between depressed and nondepressed CLBP patients across a variety of patient-reported outcomes. These findings raise the question of whether depressed mood actually moderates the effectiveness of treatment in CP patients.

Application site adverse events associated with the buprenorphine transdermal system: a pooled analysis

OBJECTIVE

To characterize the profile of application site reactions (ASRs) for patients treated with the buprenorphine transdermal system (BTDS) in chronic pain studies.

METHODS

The incidences of ASRs during treatment with BTDS were examined using (a) integrated data from 16 controlled and uncontrolled Phase III chronic pain studies (N = 6566), (b) a subset of integrated data that focused on the double-blind phases of five enriched, placebo-controlled studies (n = 1806) and (c) data from an international postmarketing drug safety database. These data were compared with the ASR data reported in the full prescribing information of other transdermal patches marketed in the US.

RESULTS

Among the 6566 patients, the overall incidence of ASRs was 23.4%, of which 98.3% were mild to moderate in intensity, none were serious and 4.4% led to treatment discontinuation. Rates of severe and inflammatory ASRs were low. Among the 1806 patients, ASR rates were higher with BTDS (16.6%) than placebo transdermal system (12.7%). Among the 6566 patients, the 1806 patients, and the postmarketing data, the most common ASRs seen were pruritus, erythema and rash. Incidences of most ASRs for other selected transdermal products were 17% or lower.

CONCLUSION

Incidence rates of ASRs in patients treated with BTDS were low and infrequently led to discontinuation. Severe and inflammatory-type ASRs were not common. The ASR profile of BTDS was comparable with those of other transdermal patches.

Considerations for improving assay sensitivity in chronic pain clinical trials: IMMPACT recommendations

A number of pharmacologic treatments examined in recent randomized clinical trials (RCTs) have failed to show statistically significant superiority to placebo in conditions in which their efficacy had previously been demonstrated. Assuming the validity of previous evidence of efficacy and the comparability of the patients and outcome measures in these studies, such results may be a consequence of limitations in the ability of these RCTs to demonstrate the benefits of efficacious analgesic treatments vs placebo ("assay sensitivity"). Efforts to improve the assay sensitivity of analgesic trials could reduce the rate of falsely negative trials of efficacious medications and improve the efficiency of analgesic drug development. Therefore, an Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials consensus meeting was convened in which the assay sensitivity of chronic pain trials was reviewed and discussed. On the basis of this meeting and subsequent discussions, the authors recommend consideration of a number of patient, study design, study site, and outcome measurement factors that have the potential to affect the assay sensitivity of RCTs of chronic pain treatments. Increased attention to and research on methodological aspects of clinical trials and their relationships with assay sensitivity have the potential to provide the foundation for an evidence-based approach to the design of analgesic clinical trials and expedite the identification of analgesic treatments with improved efficacy and safety.

Efficacy and safety of the seven-day buprenorphine transdermal system in opioid-naïve patients with moderate to severe chronic low back pain: an enriched, randomized, double-blind, placebo-controlled study

CONTEXT

This article presents the results of a pivotal Phase 3 study that assesses a new treatment for the management of chronic low back pain: a transdermal patch containing the opioid buprenorphine. In this randomized, placebo-controlled study with an enriched enrollment design, the buprenorphine transdermal system (BTDS) was found to be efficacious and generally well tolerated.

OBJECTIVES

This enriched, multicenter, randomized, double-blind study evaluated the efficacy, tolerability, and safety of BTDS in opioid-naïve patients who had moderate to severe chronic low back pain.

METHODS

Patients who tolerated and responded to BTDS (10 or 20 mcg/hour) during an open-label run-in period were randomized to continue BTDS 10 or 20 mcg/hour or receive matching placebo. The primary outcome was "average pain over the last 24 hours" at the end of the 12-week double-blind phase, collected on an 11-point scale (0=no pain, 10=pain as bad as you can imagine). Sleep disturbance (Medical Outcomes Study subscale) and total number of supplemental analgesic tablets used were secondary efficacy variables.

RESULTS

Fifty-three percent of patients receiving open-label BTDS (541 of 1024) were randomized to receive BTDS (n=257) or placebo (n=284). Patients receiving BTDS reported statistically significantly lower pain scores at Week 12 compared with placebo (least square mean treatment difference: -0.58, P=0.010). Sensitivity analyses of the primary efficacy variable and results of the analysis of secondary efficacy variables supported the efficacy of BTDS relative to placebo. During the double-blind phase, the incidence of treatment-emergent adverse events was 55% for the BTDS treatment group and 52% for the placebo treatment group. Laboratory, vital sign, and electrocardiogram evaluations did not reveal unanticipated safety findings.

CONCLUSION

BTDS was efficacious in the treatment of opioid-naïve patients with moderate to severe chronic low back pain. Most treatment-emergent adverse events observed were consistent with those associated with the use of opioid agonists and transdermal patches.

A randomized, placebo-controlled, double-blinded, parallel-group, 5-week study of buprenorphine transdermal system in adults with osteoarthritis

BACKGROUND

This multicenter, parallel-group, 35-day study in adults with osteoarthritis (OA) pain evaluated the analgesic efficacy and safety of buprenorphine transdermal system (BTDS) designed for 7-day wear.

METHODS

Patients with OA pain inadequately controlled with nonsteroidal antiinflammatory drugs or patients who had taken opioids for OA pain within the past year entered a 7-day run-in period during which they took ibuprofen only. Patients with pain > or = on a 0-10 scale had their ibuprofen discontinued and were randomized into a 28-day double-blinded period to receive either BTDS at 1 of 3 dose levels (5, 10, or 20 microg/b) or placebo. Doses were titrated to effectiveness over a period of 21 days and maintained for 7 days. No rescue medication was allowed during the study. The primary efficacy measure was the proportion of patients who achieved treatment success, defined as a patient satisfaction score of good, very good, or excellent (on day 28 or at early discontinuation) for those who did not discontinue due to ineffective treatment.

RESULTS

More BTDS-treated patients experienced treatment success than placebo TDS-treated patients (44 percent and 32 percent; odds ratio = 1.66, p = 0.036). Fewer patients taking BTDS titrated to the highest dose compared with placebo (p < 0.05). There were two serious adverse events (both in the placebo group) and no deaths. The most common (> or =5 percent) adverse events reported in BTDS-treated patients were nausea, headache, dizziness, somnolence, application site pruritus, and vomiting.

CONCLUSION

Compared with placebo, BTDS treatment was effective in treating patients with moderate to severe pain due to OA of the knee or hip. BTDS was well-tolerated.

Enriched analgesic efficacy studies: An assessment by clinical trial simulation

BACKGROUND AND OBJECTIVE

Enrichment strategies which select subjects who appear to respond to the drug have been used in drug studies to demonstrate clinical efficacy. We have used clinical trial simulation techniques to examine factors that are relevant in clinical trial design based on enrichment where poor responders are excluded from the double-blind phase of the study.

METHODS

Simulations were performed for an analgesic trial design involving an open-dose titration phase (enrichment phase) followed by a double-blind, randomized, placebo-controlled maintenance phase. Enrichment was examined by excluding subjects above a predefined pain score (cutoff) from analysis of efficacy for the maintenance phase. Cutoff pain scores ranging from 4 to 7 on a 0 to 10 categorical scale were examined. A database consisting of chronic pain patients who participated in studies with a new formulation of buprenorphine was used to build the simulation model. Since no data were available for the key model variable "correlation between treatment and placebo response", values of 0.25, 0.5, and 0.75 were used for the simulations.

RESULTS

A correlation between treatment and placebo effect ranging from 0.75 to 0.25 will cause the likelihood of trial success to vary from 50% to 95%. This model also shows that recruitment efficiency will decrease with the use of lower cutoff pain scores.

CONCLUSION

Prior to using enrichment techniques, investigators must consider the correlation between treatment effect and placebo response to optimize clinical trial design.

A trial comparing low-dose, short-course ciprofloxacin and standard 7 day therapy with co-trimoxazole or nitrofurantoin in the treatment of uncomplicated urinary tract infection

The study was undertaken to compare the safety and efficacy of twice-daily ciprofloxacin for 3 days with standard 7 day therapy with either co-trimoxazole or nitrofurantoin in the treatment of women with acute, uncomplicated urinary tract infections (UTI). This multicentre, prospective, randomized, double-blind trial compared oral ciprofloxacin (100 mg bd) for 3 days with co-trimoxazole (160/800 mg bd) or nitrofurantoin (100 mg bd) for 7 days. Bacteriological and clinical evaluations were performed at study entry, during therapy and 4-10 days and 4-6 weeks after the completion of therapy. The primary efficacy parameter was eradication of the causative organism 4- 10 days following treatment. Of 713 women enrolled and evaluable for safety, 521 were evaluable for efficacy (168 ciprofloxacin, 174 co-trimoxazole, 179 nitrofurantoin). Escherichia coli (83%) was the most frequently isolated pathogen in all treatment groups. Bacteriological eradication was reported in 88% of ciprofloxacin patients, 93% of co-trimoxazole patients and 86% of nitrofurantoin patients. At the 4-6 week follow-up, ciprofloxacin had statistically significantly higher eradication rates (91%) than co-trimoxazole (79%; 95% confidence limit (CL) = −20.6%, −3.9%) and nitrofurantoin (82%; 95% CL = −17.1%, −0.9%). Clinical resolution 4- 10 days after therapy and at the 4- 6 week follow-up was similar among the three treatment groups. The overall incidence of treatment-emergent adverse events was not significantly different (P= 0.093) among the three drug regimens, althousgh co-trimoxazole was associated with a greater number of adverse events than ciprofloxacin (P ≤0.05). Ciprofloxacin also caused fewer episodes of nausea than either of the other agents (P ≤0.01).

A trial comparing low-dose, short-course ciprofloxacin and standard 7 day therapy with co-trimoxazole or nitrofurantoin in the treatment of uncomplicated urinary tract infection

The study was undertaken to compare the safety and efficacy of twice-daily ciprofloxacin for 3 days with standard 7 day therapy with either co-trimoxazole or nitrofurantoin in the treatment of women with acute, uncomplicated urinary tract infections (UTI). This multicentre, prospective, randomized, double-blind trial compared oral ciprofloxacin (100 mg bd) for 3 days with co-trimoxazole (160/800 mg bd) or nitrofurantoin (100 mg bd) for 7 days. Bacteriological and clinical evaluations were performed at study entry, during therapy and 4-10 days and 4-6 weeks after the completion of therapy. The primary efficacy parameter was eradication of the causative organism 4-10 days following treatment. Of 713 women enrolled and evaluable for safety, 521 were evaluable for efficacy (168 ciprofloxacin, 174 co-trimoxazole, 179 nitrofurantoin). Escherichia coli (83%) was the most frequently isolated pathogen in all treatment groups. Bacteriological eradication was reported in 88% of ciprofloxacin patients, 93% of co-trimoxazole patients and 86% of nitrofurantoin patients. At the 4-6 week follow-up, ciprofloxacin had statistically significantly higher eradication rates (91%) than co-trimoxazole (79%; 95% confidence limit (CL) = -20.6%, -3.9%) and nitrofurantoin (82%; 95% CL = -17.1%, -0.9%). Clinical resolution 4-10 days after therapy and at the 4-6 week follow-up was similar among the three treatment groups. The overall incidence of treatment-emergent adverse events was not significantly different (P = 0.093) among the three drug regimens, although co-trimoxazole was associated with a greater number of adverse events than ciprofloxacin (P < or = 0.05). Ciprofloxacin also caused fewer episodes of nausea than either of the other agents (P < or = 0.01).