Randomized Controlled Trial of Difelikefalin for Chronic Pruritus in Hemodialysis Patients

The efficacy and safety of difelikefalin for pruritus in hemodialysis patients: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Chronic kidney disease-associated pruritus (CKD-ap) is a common complication that negatively affects the quality of life. Difelikefalin has emerged as a novel FDA-approved drug to manage CKD-ap. This systematic review and meta-analysis will assess the efficacy and safety of Difelikefalin versus placebo to manage CKD-ap.

METHODS

PubMed, Scopus, WOS, Central, and Embase were systematically searched until November 2023. RevMan was used to perform meta-analysis. Quality assessment was conducted using the Cochrane RoB 2.0 tool. Results were reported as risk ratio (RR) and mean difference (MD) with a 95% confidence interval (CI). PROSPERO ID: (CRD42023485979).

RESULTS

Five RCTs with a total of 896 participants were included. Difelikefalin significantly decreased the weekly mean WI-NRS score (MD: -0.99 [-1.22, -0.75], p ˂ .00001), 5-D itch scale total score (MD: -1.51 [-2.26, -0.76], p > .0001), and Skindex-10 total score (MD: -7.39 [-12.51, -2.28], p = .005), but showed significantly higher adverse events (RR: 1.26 [1.03, 1.55], p = .03), versus placebo. However, there was no significant difference between both groups in serious adverse events (RR: 1.42 [0.78, 2.57], p = .25) or death (RR: 0.81 [0.19, 3.34], p = .77).

CONCLUSION

Difelikefalin appears to be a promising agent for the management of CKD-induced pruritus in patients with end-stage renal disease. However, evidence is still underpowered due to the paucity of the current data; therefore, more robust RCTs are required to confirm the benefit of Difelikefalin.

Dialysis for Chronic Kidney Failure: A Review

Importance

More than 3.5 million people worldwide and 540 000 individuals in the US receive maintenance hemodialysis or peritoneal dialysis for the treatment of chronic kidney failure. The 5-year survival rate is approximately 40% after initiation of maintenance dialysis.

Observations

Hemodialysis and peritoneal dialysis remove metabolic waste and excess body water and rebalance electrolytes to sustain life. There is no recommended estimated glomerular filtration rate (eGFR) threshold for initiating dialysis, and patient-clinician shared decision-making should help determine when to initiate dialysis. Persistent signs and symptoms of uremia (eg, nausea, fatigue) and volume overload (eg, dyspnea, peripheral edema), worsening eGFR, metabolic acidosis, and hyperkalemia inform the timing of therapy initiation. A randomized clinical trial reported no mortality benefit to starting dialysis at higher eGFR (10-14 mL/min/1.73 m2) vs lower eGFR (5-7 mL/min/1.73 m2) levels. Observational data suggested no differences in 5-year mortality with use of hemodialysis vs peritoneal dialysis. Cardiovascular (eg, arrhythmias, cardiac arrest) and infection-related complications of maintenance dialysis are common. In the US, hemodialysis catheter-related bloodstream infections occur at a rate of 1.1 to 5.5 episodes per 1000 catheter-days and affect approximately 50% of patients within 6 months of catheter placement. Peritonitis occurs at a rate of 0.26 episodes per patient-year and affects about 30% of individuals in the first year of peritoneal dialysis therapy. Chronic kidney failure-related systemic complications, such as anemia, hyperphosphatemia, hypocalcemia, and hypertension, often require pharmacologic treatment. Hypotension during dialysis, refractory symptoms (eg, muscle cramps, itching), and malfunction of dialysis access can interfere with delivery of dialysis.

Conclusions and Relevance

In 2021, more than 540 000 patients in the US received maintenance hemodialysis or peritoneal dialysis for treatment of chronic kidney failure. Five-year survival rate after initiation of maintenance dialysis is approximately 40%, and the mortality rate is similar with hemodialysis and peritoneal dialysis. Decisions about dialysis initiation timing and modality are influenced by patient symptoms, laboratory trajectories, patient preferences, and therapy cost and availability and should include shared decision-making.

[Clinical Research Progress on Using κ-Opioid Receptor Agonists to Treat Uremic Pruritus]

Uremic pruritus, a severe complication in patients with chronic kidney disease, is associated with a high prevalence. It can cause depression and sleep disorders, and seriously affect the quality of life and the social relations of patients. Recently, there is growing evidence showing that κ-opioid receptor agonists, including nalfurafine, difelikefalin, and nalbuphine, can effectively and safely reduce itching symptoms in patients with refractory uremic pruritus. Herein, we reviewed the epidemiology, pathogenesis, clinical symptoms, and treatment strategies of uremic pruritus, and summarized in detail the progress in clinical research on the use of κ-opioid receptor agonists, including nalfurafine, difelikefalin, and nalbuphine, in the management of patients with uremic pruritus.

Information and consensus document for the diagnostic and therapeutic management of pruritus associated with chronic kidney disease in patients on haemodialysis in Spain

Chronic kidney disease-associated pruritus (CKD-aP) is one of the most common and disabling comorbidities in patients with advanced CKD. In addition, it is associated with an increased risk of mortality, poorer quality of life, sleep disorders, mental health disorders, and increased use of health care resources. The clinical presentation of CKD-aP is very heterogeneous, making it difficult to diagnose and treat. Currently, there are no national guidelines on the management of CKD-aP. The aim of this document is to provide national consensus recommendations for the diagnostic and therapeutic management of CKD-aP. The document was prepared in three phases: a diagnostic and therapeutic management algorithm was proposed by a small group of nephrology specialists; the proposal was validated by a larger group of nephrologists; and a second validation by a multidisciplinary group that also included dermatology specialists. The diagnostic and therapeutic management algorithm attempts to cover the current need of a lack of specific guidelines for the adequate management of CKD-aP. At the same time, it introduces the use of difelikefalin, the first and only drug specifically approved for CKD-aP, with a good safety and efficacy profile.

Difelikefalin improves itch-related sleep disruption in patients undergoing haemodialysis

BACKGROUND

Poor sleep quality is associated with higher mortality and lower quality of life in patients with chronic kidney disease-associated pruritus (CKD-aP). Difelikefalin reduces itch in patients with CKD-aP undergoing haemodialysis (HD). This post hoc analysis of the Phase 3 difelikefalin studies (Study 3105 and the pooled dataset from KALM-1 and KALM-2) evaluated whether itch reduction in individuals with CKD-aP improved sleep quality.

METHODS

Itch intensity was assessed in patients undergoing HD who had moderate-to-severe CKD-aP treated with intravenous difelikefalin (0.5 µg/kg, three times weekly) (N = 222, Study 3105; N = 426, KALM-1 and -2) or placebo (N = 425, KALM-1 and -2) for 12 weeks, using the Worst Itch Intensity Numerical Rating Scale (WI-NRS). Sleep quality was assessed using the sleep disability question of the 5-D Itch Scale (5-D SDQ) in all studies and, in Study 3105, with the Sleep Quality Numeric Rating Scale (SQ-NRS).

RESULTS

Greater improvements in sleep quality were observed in patients with ≥3-point versus <3-point WI-NRS improvement using SQ-NRS in Study 3105 [mean (95% confidence interval) -5.2 (-5.6, -4.8) vs -1.5 (-2.0, -1.0)] and 5-D SDQ in KALM-1 and -2 [-1.8 (-2.1, -1.6) vs -0.8 (-1.1, -0.4)]. SQ-NRS and WI-NRS scores were highly correlated at both baseline and Week 12 in Study 3105 (Spearman correlation coefficient: 0.77 and 0.84, respectively). Correlations were also observed between 5-D SDQ and WI-NRS scores in Study 3105 and KALM-1 and -2.

CONCLUSIONS

In patients undergoing HD with moderate-to-severe CKD-aP, itch reduction with intravenous difelikefalin was associated with improved sleep quality. As disturbed sleep may contribute to mortality and morbidity in CKD-aP, difelikefalin may help to address a major clinical burden by improving sleep quality, secondary to itch relief.

TRIAL REGISTRATION

KALM-1 (NCT03422653), KALM-2 (NCT03636269), Study 3105 (NCT03998163).

Efficacy and safety of different systemic drugs in the treatment of uremic pruritus among hemodialysis patients: a network meta-analysis based on randomized clinical trials

Aim

This network meta-analysis was to analyze and rank the efficacy and safety of different systemic drugs in the treatment of uremic pruritus (UP) among hemodialysis patients.

Method

PubMed, Embase, Cochrane Library, and Web of Science databases were searched from inception to 10 July 2023 for randomized controlled trials (RCTs) investigating different drugs in the treatment of UP among hemodialysis patients. Drugs including cromolyn sodium, dexchlorpheniramine, difelikefalin, gabapentin, hydroxyzine, ketotifen, melatonin, montelukast, nalbuphine, nalfurafine, nemolizumab, nicotinamide, pregabalin, sertraline, thalidomide, and placebo were assessed. Outcome measures, including pruritus relief, response, and adverse events, were analyzed. Network plots, forest plots, league tables, and the surface under the cumulative ranking (SUCRA) probabilities were depicted for each outcome.

Results

The network meta-analysis retrieved 22 RCTs. Gabapentin (69.74%) had the highest likelihood to be the most effective drug for pruritus relief in UP patients receiving hemodialysis, followed by cromolyn sodium and hydroxyzine. Thalidomide (60.69%) and gabapentin (58.99%) were associated with significantly more drug responses for treating UP among patients receiving hemodialysis. Patients who were treated with gabapentin (40.01%) were likely to have risks of adverse events and dizziness. Lower risks of adverse events, nausea, and diarrhea were found in patients who received cromolyn sodium and lower risks of somnolence.

Conclusion

This study suggests considering gabapentin treatment when facing a patient suffering from UP. This study provides a reference for the selection of drug therapy for UP patients receiving hemodialysis.

Impact of Difelikefalin on the Health-Related Quality of Life of Haemodialysis Patients with Moderate-To-Severe Chronic Kidney Disease-Associated Pruritus: A Single-Arm Intervention Trial

OBJECTIVE

Chronic kidney disease-associated pruritus (CKD-aP) can have a substantial negative impact on health-related quality of life (HRQoL), including an increased risk of depression, anxiety and sleep disturbance. This trial aimed to assess the impact of intravenous difelikefalin on HRQoL in haemodialysis patients with moderate-to-severe CKD-aP.

METHODS

Post hoc analysis of an open-label, multicentre, single-arm intervention trial assessed pruritus severity and HRQoL at baseline and at 12 weeks of difelikefalin treatment using Worst Itching Intensity Numerical Rating Scale (WI-NRS), Sleep Quality Numeric Rating Scale (SQ-NRS), 5-D itch scale, Skindex-10 scale, EQ-5D-5L with Pruritus Bolt-On (EQ-PSO).

RESULTS

A total of 222 patients received ≥ 1 dose of difelikefalin, and 197 patients completed 12 weeks of difelikefalin treatment. Clinically meaningful changes from baseline to 12 weeks were observed in all disease-specific measures: 73.7% of patients achieved a ≥ 3-point reduction in the weekly mean of 24 h WI-NRS scores and 66% of patients experienced ≥ 3-point improvements in SQ-NRS scores. Improvements were also observed in all Skindex-10 scale and 5-D itch scale domain scores. The percentage of patients reporting no problems in all EQ-PSO domains increased from 1.4 to 24.7% (p < 0.001), respectively. Patients' generic HRQoL EQ-5D-5L mean utility and EQ-5D visual analogue scale scores increased from baseline to 12 weeks: mean changes 0.04 (p = 0.001) and 2.8 (p = 0.046), respectively.

CONCLUSIONS

Patients undergoing haemodialysis with moderate-to-severe CKD-aP receiving difelikefalin reported experiencing clinically meaningful improvements in both their pruritus symptoms and itch-related QoL.

CLINICALTRIALS

gov registration number, NCT03998163; first submitted, 7 May 2019.

Metallic Nanocarriers for Therapeutic Peptides: Emerging Solutions Addressing the Delivery Challenges in Brain Ailments

Peptides and proteins have recently emerged as efficient therapeutic alternatives to conventional therapies. Although they emerged a few decades back, extensive exploration of various ailments or disorders began recently. The drawbacks of current chemotherapies and irradiation treatments, such as drug resistance and damage to healthy tissues, have enabled the rise of peptides in the quest for better prospects. The chemical tunability and smaller size make them easy to design selectively for target tissues. Other remarkable properties include antifungal, antiviral, anti-inflammatory, protection from hemorrhage stroke, and as therapeutic agents for gastric disorders and Alzheimer and Parkinson diseases. Despite these unmatched properties, their practical applicability is often hindered due to their weak susceptibility to enzymatic digestion, serum degradation, liver metabolism, kidney clearance, and immunogenic reactions. Several methods are adapted to increase the half-life of peptides, such as chemical modifications, fusing with Fc fragment, change in amino acid composition, and carrier-based delivery. Among these, nanocarrier-mediated encapsulation not only increases the half-life of the peptides in vivo but also aids in the targeted delivery. Despite its structural complexity, they also efficiently deliver therapeutic molecules across the blood-brain barrier. Here, in this review, we tried to emphasize the possible potentiality of metallic nanoparticles to be used as an efficient peptide delivery system against brain tumors and neurodegenerative disorders. SIGNIFICANCE STATEMENT: In this review, we have emphasized the various therapeutic applications of peptides/proteins, including antimicrobial, anticancer, anti-inflammatory, and neurodegenerative diseases. We also focused on these peptides' challenges under physiological conditions after administration. We highlighted the importance and potentiality of metallic nanocarriers in the ability to cross the blood-brain barrier, increasing the stability and half-life of peptides, their efficiency in targeting the delivery, and their diagnostic applications.

Intravenous difelikefalin for the treatment of hemodialysis pruritus

INTRODUCTION

Patients with chronic kidney disease (CKD) undergoing hemodialysis often experience significant itch secondary to their condition and a subsequent reduction in their overall quality of life. Current treatments are underwhelming, necessitating the search for new, effective therapeutic options to combat itch in this population.

AREAS COVERED

The purpose of this review is to explore the available data for the use of intravenous difelikefalin in patients with CKD undergoing hemodialysis. The pathophysiology of CKD-associated itch is multifactorial, with one proposed mechanism involving an imbalance in the endogenous opioid system, favoring upregulation of itch-activating μ-opioid receptors (MORs) and downregulation of itch-inhibiting κ-opioid receptors (KORs). Dysregulation of the immune system is also involved. Difelikefalin is a recent FDA approved treatment that functions as peripherally acting KOR agonist, targeting this imbalance in the endogenous opioid system seen in CKD patients with itch and having an anti-inflammatory effect on immune cells. Clinical data on intravenous difelikefalin is promising regarding its ability to reduce itch in CKD patients on hemodialysis and improve patient quality of life, with few, mild adverse side effects.

EXPERT OPINION

As intravenous difelikefalin becomes more widely used in the clinical setting, further studies assessing long-term efficacy and safety will be needed.

An update on mechanisms of pruritus and their potential treatment in primary cutaneous T-cell lymphoma

Primary cutaneous T-cell lymphomas (CTCL), which include mycosis fungoides (MF) and Sézary syndrome (SS), are a group of lymphoproliferative disorders characterized by clonal accumulation of neoplastic T-lymphocytes in the skin. Severe pruritus, one of the most common and distressing symptoms in primary CTCL, can significantly impair emotional well-being, physical functioning, and interpersonal relationships, thus greatly reducing quality of life. Unfortunately, effectively managing pruritus remains challenging in CTCL patients as the underlying mechanisms are, as of yet, not fully understood. Previous studies investigating the mechanisms of itch in CTCL have identified several mediators and their corresponding antagonists used for treatment. However, a comprehensive overview of the mediators and receptors contributing to pruritus in primary CTCL is lacking in the current literature. Here, we summarize and review the mediators and receptors that may contribute to pruritus in primary CTCL to explore the mechanisms of CTCL pruritus and identify effective therapeutic targets using the PubMed and Web of Science databases. Studies were included if they described itch mediators and receptors in MF and SS. Overall, the available data suggest that proteases (mainly tryptase), and neuropeptides (particularly Substance P) may be of greatest interest. At the receptor level, cytokine receptors, MRGPRs, and TRP channels are most likely important. Future drug development efforts should concentrate on targeting these mediators and receptors for the treatment of CTCL pruritus.

Safety and effectiveness of HSK21542 for hemodialysis patients: a multiple ascending dose study

Background: HSK21542, a novel selective peripherally-restricted κ-opioid receptor agonist has been proven to be a safe and effective analgesic and antipruritic drug in both in vitro and in vivo studies. We aimed to evaluate its safety, pharmacokinetics and efficacy in hemodialysis patients over a 1-week treatment period, and to establish the optimal dosage for a further 12-week stage 2 trial. Methods: In this multiple ascending dose study, hemodialysis patients were randomly assigned to receive HSK21542 (0.05-0.80 μg/kg), or a placebo three times within 2.5 h at the end of each dialysis session for 1 week. Safety evaluations included reports of treatment-emergent adverse events (TEAEs); pharmacokinetics and efficacy outcomes were also assessed. Results: Among the 44 screened patients, 41 were enrolled and completed the trial. The overall incidence of TEAEs was higher in the HSK21542 group compared to the placebo group, with an incidence of 75.0%, 50.0%, 75.0%, and 88.9% in the range of 0.05-0.80 μg/kg. All TEAEs were grade 1 or 2 in severity. HSK21542 exhibited linear pharmacokinetics characteristics within the dose range 0.05-0.80 μg/kg, without drug accumulation after multiple-doses. Compared to the placebo, a significant decrease of the weekly mean Worst Itching Intensity Numerical Rating Scale was found in the HSK21542-0.30 μg/kg group (p = 0.046), but without significant improvement in the Skindex-16 score. Conclusion: HSK21542 was well tolerated in the dose range 0.05-0.80 μg/kg in hemodialysis patients. HSK21542-0.3 μg/kg exhibited promising efficacy in patients with moderate to severe pruritus and warrants a further Stage 2 trial. Clinical Trial Registration: https://clinicaltrials.gov/, identifier NCT04470154.

Itch: from the skin to the brain - peripheral and central neural sensitization in chronic itch

Similar to chronic pain, chronic itch is frequently linked to neural sensitization, a phenomenon wherein the nervous system becomes hypersensitive to stimuli. This process of neural sensitization of chronic itch is orchestrated by various signaling pathways and mediators in both the peripheral and central nervous systems. At the level of the peripheral nervous system, inflammation and neuroimmune interactions induce plastic changes to peripheral nerve fibers, thereby amplifying the transmission of itch signaling. Neural sensitization in the central nervous system occurs at both the spinal cord and brain levels. At the level of the spinal cord, it involves hyperactivity of itch-activating spinal pathways, dysfunction of spinal inhibitory circuits, and attenuation of descending supraspinal inhibitory pathways. In the brain, neural sensitization manifests as structural and functional changes to itch-associated brain areas and networks. Currently, we have a diverse array of neuroimmune-modulating therapies targeting itch neural sensitization mechanisms to help with providing relief to patients with chronic itch. Itch research is a dynamic and continually evolving field, and as we grow in our understanding of chronic itch mechanisms, so will our therapeutic toolbox. Further studies exploring the peripheral and central neural sensitization mechanisms in the context of chronic itch are needed.

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 Utility of Peripherally Restricted Kappa-Opioid Receptor Agonists for Inhibiting Below-Level Pain After Spinal Cord Injury in Mice

Pain after spinal cord injury (SCI) can be difficult to treat. Drugs that target the opioid receptor (OR) outside the central nervous system (CNS) have gained increasing interest in pain control owing to their low risk of central side effects. Asimadoline and ICI-204448 are believed to be peripherally restricted KOR agonists withlimited access to the CNS. This study examined whether they can attenuate pain hypersensitivity in mice subjected to a contusive T10 SCI. Subcutaneous (s.c.) injection of asimadoline (5, 20 mg/kg) and ICI-204448 (1, 10 mg/kg) inhibited heat hypersensitivity at both doses, but only attenuated mechanical hypersensitivity at the high dose. However, the high-dose asimadoline adversely affected animals' exploratory performance in SCI mice and caused aversion, suggesting CNS drug penetration. In contrast, high-dose ICI-204448 did not impair exploration and remained effective in reducing both mechanical and heat hypersensitivities after SCI. Accordingly, we chose to examine the potential peripheral neuronal mechanism for ICI-204448-induced pain inhibition by conducting in vivo calcium imaging of dorsal root ganglion (DRG) in Pirt-GCaMP6s+/- mice. High-dose ICI-204448 (10 mg/kg, s.c.) attenuated the increased fluorescence intensity of lumbar DRG neurons activated by a noxious pinch (400 g) stimulation in SCI mice. In conclusion, systemic administration of ICI-204448 achieved SCI pain inhibition at doses that did not induce notable side effects and attenuated DRG neuronal excitability which may partly contribute to its pain inhibition. These findings suggest that peripherally restricted KOR agonists may be useful for treating SCI pain, but the therapeutic window must be carefully examined.

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.

Pharmacokinetics, Metabolism, and Excretion of Intravenous [14C]Difelikefalin in Healthy Subjects and Subjects on Hemodialysis

BACKGROUND AND OBJECTIVE

Difelikefalin, a selective kappa-opioid receptor agonist, is the first approved treatment for moderate-to-severe pruritus in patients with end-stage renal disease (ESRD) on hemodialysis (HD) in the USA and Europe. The purpose of this open-label study was to investigate the pharmacokinetics and disposition of [14C]difelikefalin following a single intravenous dose in subjects with normal renal function and subjects on HD.

METHODS

Twelve adult males (n = 6 healthy subjects; n = 6 subjects on HD) received single intravenous doses of [14C]difelikefalin containing 100 µCi (total doses of 1.7-3.0 μg/kg difelikefalin). Blood, urine, feces, and dialysate samples (when applicable) were collected after dosing.

RESULTS

The median time to maximum concentration was similar for HD and healthy subjects, occurring at 5 min post-dose. The mean area under the concentration-time curve (AUC) was approximately 11-fold higher in HD versus healthy subjects; mean plasma half-life was 38.0 h and 2.6 h, respectively. In healthy subjects, 80.5% of the dose was recovered in urine, and 11.3% was recovered in feces. In subjects on HD, 58.8% of the dose was recovered in feces, and 19.5% was recovered in dialysate [for subjects on HD with residual kidney function (n = 3), 11.2% was recovered in urine]. Based on plasma AUClast, parent [14C]difelikefalin was the most abundant analyte in systemic circulation (> 99% of total exposure) for both cohorts. Metabolite profiles in urine and feces suggested minimal metabolism of the parent compound.

CONCLUSION

In subjects on HD, difelikefalin total exposure was higher and plasma half-life was longer compared with subjects with intact renal function. Metabolism was low in both healthy subjects and subjects on HD, with unchanged drug representing > 99% of systemic circulation; however, the route of excretion was primarily into urine versus feces in healthy subjects, and feces versus dialysate in subjects on HD.

REGISTRATION

ClinicalTrials.gov NCT03947970.

Pharmacological interventions for pruritus in adult palliative care patients

BACKGROUND

This is the second update of the original Cochrane review published in 2013 (issue 6), which was updated in 2016 (issue 11). Pruritus occurs in patients with disparate underlying diseases and is caused by different pathologic mechanisms. In palliative care patients, pruritus is not the most prevalent but is a burdening symptom. It can cause considerable discomfort and negatively affect patients' quality of life.

OBJECTIVES

To assess the effects of different pharmacological treatments compared with active control or placebo for preventing or treating pruritus in adult palliative care patients.

SEARCH METHODS

For this update, we searched CENTRAL (the Cochrane Library), MEDLINE (OVID) and Embase (OVID) up to 6 July 2022. In addition, we searched trial registries and checked the reference lists of all relevant studies, key textbooks, reviews and websites, and we contacted investigators and specialists in pruritus and palliative care regarding unpublished data.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) assessing the effects of different pharmacological treatments, compared with a placebo, no treatment, or an alternative treatment, for preventing or treating pruritus in palliative care patients.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed the identified titles and abstracts, performed data extraction and assessed the risk of bias and methodological quality. We summarised the results descriptively and quantitatively (meta-analyses) according to the different pharmacological interventions and the diseases associated with pruritus. We assessed the evidence using GRADE and created 13 summary of findings tables.

MAIN RESULTS

In total, we included 91 studies and 4652 participants in the review. We added 42 studies with 2839 participants for this update. Altogether, we included 51 different treatments for pruritus in four different patient groups. The overall risk of bias profile was heterogeneous and ranged from high to low risk. The main reason for giving a high risk of bias rating was a small sample size (fewer than 50 participants per treatment arm). Seventy-nine of 91 studies (87%) had fewer than 50 participants per treatment arm. Eight (9%) studies had low risk of bias in the specified key domains; the remaining studies had an unclear risk of bias (70 studies, 77%) or a high risk of bias (13 studies, 14%). Using GRADE criteria, we judged that the certainty of evidence for the primary outcome (i.e. pruritus) was high for kappa-opioid agonists compared to placebo and moderate for GABA-analogues compared to placebo. Certainty of evidence was low for naltrexone, fish-oil/omega-3 fatty acids, topical capsaicin, ondansetron and zinc sulphate compared to placebo and gabapentin compared to pregabalin, and very low for cromolyn sodium, paroxetine, montelukast, flumecinol, and rifampicin compared to placebo. We downgraded the certainty of the evidence mainly due to serious study limitations regarding risk of bias, imprecision, and inconsistency. For participants suffering from uraemic pruritus (UP; also known as chronic kidney disease (CKD)-associated pruritus (CKD-aP)), treatment with GABA-analogues compared to placebo likely resulted in a large reduction of pruritus (visual analogue scale (VAS) 0 to 10 cm): mean difference (MD) -5.10, 95% confidence interval (CI) -5.56 to -4.55; five RCTs, N = 297, certainty of evidence: moderate. Treatment with kappa-opioid receptor agonists (difelikefalin, nalbuphine, nalfurafine) compared to placebo reduced pruritus slightly (VAS 0 to 10 cm, MD -0.96, 95% CI -1.22 to -0.71; six RCTs, N = 1292, certainty of evidence: high); thus, this treatment was less effective than GABA-analogues. Treatment with montelukast compared to placebo may result in a reduction of pruritus, but the evidence is very uncertain (two studies, 87 participants): SMD -1.40, 95% CI -1.87 to -0.92; certainty of evidence: very low. Treatment with fish-oil/omega-3 fatty acids compared to placebo may result in a large reduction of pruritus (four studies, 160 observations): SMD -1.60, 95% CI -1.97 to -1.22; certainty of evidence: low. Treatment with cromolyn sodium compared to placebo may result in a reduction of pruritus, but the evidence is very uncertain (VAS 0 to 10 cm, MD -3.27, 95% CI -5.91 to -0.63; two RCTs, N = 100, certainty of evidence: very low). Treatment with topical capsaicin compared with placebo may result in a large reduction of pruritus (two studies; 112 participants): SMD -1.06, 95% CI -1.55 to -0.57; certainty of evidence: low. Ondansetron, zinc sulphate and several other treatments may not reduce pruritus in participants suffering from UP. In participants with cholestatic pruritus (CP), treatment with rifampicin compared to placebo may reduce pruritus, but the evidence is very uncertain (VAS: 0 to 100, MD -42.00, 95% CI -87.31 to 3.31; two RCTs, N = 42, certainty of evidence: very low). Treatment with flumecinol compared to placebo may reduce pruritus, but the evidence is very uncertain (RR > 1 favours treatment group; RR 2.32, 95% CI 0.54 to 10.1; two RCTs, N = 69, certainty of evidence: very low). Treatment with the opioid antagonist naltrexone compared to placebo may reduce pruritus (VAS: 0 to 10 cm, MD -2.42, 95% CI -3.90 to -0.94; two RCTs, N = 52, certainty of evidence: low). However, effects in participants with UP were inconclusive (percentage of difference -12.30%, 95% CI -25.82% to 1.22%, one RCT, N = 32). In palliative care participants with pruritus of a different nature, the treatment with the drug paroxetine (one study), a selective serotonin reuptake inhibitor, compared to placebo may reduce pruritus slightly by 0.78 (numerical analogue scale from 0 to 10 points; 95% CI -1.19 to -0.37; one RCT, N = 48, certainty of evidence: low). Most adverse events were mild or moderate. Two interventions showed multiple major adverse events (naltrexone and nalfurafine).

AUTHORS CONCLUSIONS

Different interventions (GABA-analogues, kappa-opioid receptor agonists, cromolyn sodium, montelukast, fish-oil/omega-3 fatty acids and topical capsaicin compared to placebo) were effective for uraemic pruritus. GABA-analogues had the largest effect on pruritus. Rifampin, naltrexone and flumecinol tended to be effective for cholestatic pruritus. However, therapies for patients with malignancies are still lacking. Due to the small sample sizes in most meta-analyses and the heterogeneous methodological quality of the included trials, the results should be interpreted cautiously in terms of generalisability.

Difelikefalin: A New κ-Opioid Receptor Agonist for the Treatment of Hemodialysis-Dependent Chronic Kidney Disease-Associated Pruritus

OBJECTIVE

To review data for difelikefalin (Korsuva) intravenous solution for management of moderate-to-severe pruritus in hemodialysis (HD) patients.

DATA SOURCES

Literature search of PubMed (January 1946-May 2022) and SCOPUS (January 1946-May 2022) was performed using the terms: Korsuva, CR845, and difelikefalin. Additional information sources include ClinicalTrials.gov, prescribing information, meeting posters, and references of identified articles.

STUDY SELECTION AND DATA EXTRACTION

Clinical trials and articles evaluating difelikefalin for chronic kidney disease-associated pruritis (CKD-aP) in HD patients.

DATA SYNTHESIS

Difelikefalin is a peripherally acting κ-opioid receptor agonist with antipruritic effects for HD patients with moderate-to-severe CKD-aP. A phase 3 study showed significant improvement of patient itch intensity and itch-related quality of life (QOL) when compared with placebo. More patients had decreased pruritus on the 24-hour Worst Itch Intensity Numerical Rating Scale with difelikefalin (49.1%) compared with placebo (27.9%, P < 0.001). A positive effect was seen with or without use of additional antipruritic agents. Common adverse events include diarrhea, dizziness, and vomiting; there were no signs of physical dependence or centrally acting opioid effects (euphoria, hallucinations).

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Difelikefalin reduced itch intensity and improved QOL for patients with CKD-aP. Whether the benefit is continued long-term as well as how it compares with other effective agents is currently unknown.

CONCLUSION

Difelikefalin is the only Food and Drug Administration-approved treatment for moderate-to-severe CKD-aP with additional research into its benefit in this and other types of pruritus ongoing.

How to get rid of itching

Itch is an unpleasant sensation arising from a variety of dermatologic, neuropathic, systemic, and psychogenic etiologies. Various itch pathways are implicated according to the underlying etiology. A variety of pruritogens, or itch mediators, as well as receptors have been identified and provide potential therapeutic targets. Recent research has primarily focused on targeting inflammatory cytokines and Janus kinase signaling, protease-activated receptors, substance P and neurokinin, transient receptor potential-vanilloid ion channels, Mas-related G-protein-coupled receptors (MRGPRX2 and MRGPRX4), the endogenous opioid and cannabinoid balance, and phosphodiesterase 4. Periostin, a newly identified pruritogen, should be further explored with clinical trials. Drugs targeting neural sensitization including the gabergic system and P2X3 are other potential drugs for chronic itch. There is a need for more targeted therapies to improve clinical outcomes and reduce side effects.

Chronic kidney disease-associated pruritus in patients undergoing hemodialysis: Xerosis and topical therapy

Chronic kidney disease-associated pruritus (CKD-aP) is a common and distressing symptom for patients with CKD and a difficult challenge for nephrologists and dermatologists. Recent results showed the multifactorial nature of the pathophysiology, and therapeutic trials were only successful in certain subsets of patients. The clinical manifestations are varied, with xerosis being the most common dermatological manifestation and correlated with the intensity of CKD-aP. A better understanding of the pathophysiology of xerosis in CKD-aP and appropriate topical treatment could correct xerosis to reduce the intensity of CKD-aP and improve the patient's quality of life.

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.).

Uremic pruritus: pathophysiology, clinical presentation, and treatments

Uremic pruritus is one of the most common and bothersome symptoms in patients with end-stage renal disease. Most patients with uremic pruritus experience a prolonged and relapsing course and significant impairments of quality of life. The pathophysiology of uremic pruritus is not completely understood. A complex interplay among cutaneous biology and the nervous and immune systems has been implicated, with the involvement of various inflammatory mediators, neurotransmitters, and opioids. Uremic pruritus treatment outcomes are often unsatisfactory. Clinical trials have mostly been small in scale and have reported inconsistent results. Recent evidence shows that gabapentinoids, nalfurafine, and difelikefalin are effective for relieving uremic pruritus in hemodialysis patients. This review provides an overview of the epidemiology and proposed mechanisms of uremic pruritus, then highlights the manifestations of and clinical approach to uremic pruritus. Current evidence regarding treatment options, including topical treatments, treatment of underlying disease, phototherapy, and systemic treatments, is also outlined. With a better understanding of uremic pruritus, more therapeutic options can be expected in the near future.

Etiopathogenesis of chronic kidney disease-associated pruritus: putting the pieces of the puzzle together

Defined as the unpleasant sensation that causes the desire to scratch, pruritus is the most common skin symptom associated with uremia and appears in almost half of patients with advanced chronic kidney disease (CKD). Beyond its direct impact on quality of life, CKD-associated pruritus (CKD-aP) is an independent predictor of mortality that also has a synergistic effect with other quality of life-related symptoms, such as insomnia, depression, and anxiety. Although different mechanisms have been proposed to explain the origin of Pa-ERC, its etiopathogenesis is still not fully understood. Since new therapeutic targets have been identified and several clinical trials have recently shown promising results, our current understanding of the interrelationships has expanded significantly and the pathophysiological mechanisms underlying CKD-aP are now considered to be multifactorial. The potential triggers of pruritus in patients with CKD are discussed in this review, including hypotheses about skin xerosis, accumulation of uremic toxins, dysregulation of the immune system and systemic inflammation, uremic neuropathy, and imbalances in the endogenous opioid system. Other non-uremic causes of pruritus are also discussed, with the aim of guiding the physicians to apply an adequate aetiopathogenic approach to CKD-aP in their day-to-day clinical practice.

Role of kappa-opioid and mu-opioid receptors in pruritus: Peripheral and central itch circuits

Modern genetic approaches in animal models have unveiled novel itch-specific neural pathways, emboldening a paradigm in which drugs can be developed to selectively and potently target itch in a variety of chronic pruritic conditions. In recent years, kappa-opioid receptors (KORs) and mu-opioid receptors (MORs) have been implicated in both the suppression and promotion of itch, respectively, by acting on both the peripheral and central nervous systems. The precise mechanisms by which agents that modulate these pathways alleviate itch remains an active area of investigation. Notwithstanding this, a number of agents have demonstrated efficacy in clinical trials that influence both KOR and MOR signalling. Herein, we summarize a number of opioid receptor modulators in development and their promising efficacy across a number of chronic pruritic conditions, such as atopic dermatitis, uremic pruritus and beyond.

Nouvelles thérapies dans la prise en charge du patient avec maladie rénale chronique souffrant de prurit : une revue de la littérature New therapies in the management of chronic kidney disease associated pruritus

Chronic Kidney Disease associated Pruritus (CKD-aP) is a well-established and frequent complication observed in patient with CKD, especially in dialysis patients. However, the management of CKD-aP remains a challenge as the pathophysiology and research studies are too small. Finally, there are a few proposed treatment options with significant clinical benefits. This general review will summarize all the available treatments for the CKD-aP and will highlight the clinical efficacy and limits of the current drugs. Notably, we will focus on the implication of the opioid receptor in the pathophysiology of the CKD-aP and the recently Kappa opioid receptor agonist. © 2022 Published by Elsevier Masson SAS on behalf of Société francophone de néphrologie, dialyse et transplantation.

Pruritus in chronic kidney disease

PURPOSE OF REVIEW

Among the many difficult symptoms that patients with kidney disease experience, pruritus is one of the most frequent and troubling. Because a substantial amount of new information has accumulated, we seek here to review the subject.

RECENT FINDINGS

Pruritus is not only a common problematic symptom among patients with kidney disease, but its considerably more frequent than nephrologists recognize. The result for patients is not just uncomfortable itch but degraded quality of life as well. The pathogenesis is increasingly understood, but many aspects remain to be fully resolved. Importantly, research is progressing on treatment, leading to the first approved medication in the United States, difelikefalin, in August, 2021.

SUMMARY

As nephrology is progressing to a greater focus on patient symptoms, recognition of the importance of pruritus has led to increased interest and improved diagnosis and treatment options.

Alleviating symptoms in patients undergoing long-term hemodialysis: a focus on chronic kidney disease-associated pruritus

Since the breakthrough of kidney replacement therapy, increases in life expectancy for patients with end-stage kidney disease have been limited. However, patients have become increasingly vocal that, although mortality and life expectancy matter to them, the quality of their life, and particularly the relief of symptoms associated with their treatment, are in many cases more important. The majority of dialysis-associated symptoms and adverse effects do not currently have any approved treatments in this patient population, with the few treatments that are available used off-label, frequently without proven efficacy, yet still potentially adding further adverse effects to patients' current symptom burden. This article will illustrate how understanding the pathophysiology of a single, particularly burdensome symptom of dialysis (chronic kidney disease-associated pruritus) resulted in the design, development and regulatory approval of a treatment for that symptom. The pathway described here can be applied to other symptoms associated with dialysis, meaning that if we cannot add years to patients' lives, we can at least add life to their remaining years.

A year in pharmacology: new drugs approved by the US Food and Drug Administration in 2021

The second year of the COVID-19 pandemic had no adverse effect on the number of new drug approvals by the US Food and Drug Administration (FDA). Quite the contrary, with a total of 50 new drugs, 2021 belongs to the most successful FDA years. We assign these new drugs to one of three levels of innovation: (1) first drug against a condition ("first-in-indication"), (2) first drug using a novel molecular mechanism ("first-in-class"), and (3) "next-in-class", i.e., a drug using an already exploited molecular mechanism. We identify 21 first-in-class, 28 next-in-class, and only one first-in-indication drugs. By treatment area, the largest group is once again cancer drugs, many of which target specific genetic alterations. Every second drug approved in 2021 targets an orphan disease, half of them being cancers. Small molecules continue to dominate new drug approvals, followed by antibodies and non-antibody biopharmaceuticals. In 2021, the FDA continued to approve drugs without strong evidence of clinical effects, best exemplified by the aducanumab controversy.

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.

Difelikefalin in the Treatment of Chronic Kidney Disease-Associated Pruritus: A Systematic Review

Chronic kidney disease-associated pruritus (CKD-aP) is a chronic condition that significantly reduces the quality of life of patients with end-stage renal disease. The etiology is not fully understood, but imbalance in the activity of the opioid pathways, including downregulation of the kappa-opioid receptor, may contribute to itching sensation. Difelikefalin is a selective, peripherally acting kappa-opioid receptor (KOR) agonist. Recently, difelikefalin has been approved as a first drug for the treatment of pruritus associated with chronic kidney disease (CKD) in adult hemodialysis patients. A systematic review of currently available clinical trials was performed to assess the efficacy and safety of difelikefalin in patients with uremic pruritus. A literature review was conducted in May 2022 based on the PRISMA 2020 guidelines. The analyzed clinical trials showed that difelikefalin was effective in reducing pruritus in patients as assessed by the Worst Itching Intensity Numerical Rating Scale. Improvement in quality of life assessed on the basis of the Skindex score and the 5-D itch scale was also noticed. The most commonly reported side effects were mild and included nausea, vomiting, dizziness, and diarrhea. Due to its proven efficacy and good safety profile, difelikefalin is a promising drug for the treatment of pruritus in patients with chronic kidney disease.

The Kappa Opioid Receptor: A Promising Therapeutic Target for Multiple Pathologies

Kappa-opioid receptors (KOR) are widely expressed throughout the central nervous system, where they modulate a range of physiological processes depending on their location, including stress, mood, reward, pain, inflammation, and remyelination. However, clinical use of KOR agonists is limited by adverse effects such as dysphoria, aversion, and sedation. Within the drug-development field KOR agonists have been extensively investigated for the treatment of many centrally mediated nociceptive disorders including pruritis and pain. KOR agonists are potential alternatives to mu-opioid receptor (MOR) agonists for the treatment of pain due to their anti-nociceptive effects, lack of abuse potential, and reduced respiratory depressive effects, however, dysphoric side-effects have limited their widespread clinical use. Other diseases for which KOR agonists hold promising therapeutic potential include pruritis, multiple sclerosis, Alzheimer's disease, inflammatory diseases, gastrointestinal diseases, cancer, and ischemia. This review highlights recent drug-development efforts targeting KOR, including the development of G-protein-biased ligands, mixed opioid agonists, and peripherally restricted ligands to reduce side-effects. We also highlight the current KOR agonists that are in preclinical development or undergoing clinical trials.

Modulation of the kappa and mu opioid axis for the treatment of chronic pruritus: A review of basic science and clinical implications

Introduction

Treating chronic pruritus is challenging for dermatologists due to the lack of therapeutic options. We review the effects of κ-opioid receptor (KOR) and μ-opioid receptor (MOR) in the modulation of itch, summarize evidence supporting the efficacy and safety of opioid receptor–targeting agents in chronic pruritus, and address clinical considerations.

Results

Preclinical studies have found neural pathways underlying detection, transmission, and modulation of itch signaling and spotlighted the importance of neuronal KOR and MOR in itch perception. Clinical reports suggest that opioid axis modulation may be the basis for the successful treatment of chronic itch. Several agents (MOR antagonist naltrexone; KOR agonists nalfurafine and difelikefalin; dual-acting KOR agonists/MOR antagonists butorphanol and nalbuphine) have been evaluated for treating chronic pruritus in case series, small studies, and clinical trials; nalbuphine has progressed through preliminary (phase II/III) studies in uremic pruritus and prurigo nodularis. The antipruritic efficacy of these agents has been observed across multiple disorders with disparate etiologies, suggesting the potential utility of this class to provide a unified approach to chronic pruritus treatment.

Conclusions

The relative safety of these agents, including a reduced potential for dependence versus MOR-agonist analgesics, should help overcome resistance to the use of opioid receptor–targeting agents in chronic pruritus treatment.

Efficacy and Safety of Difelikefalin in Japanese Patients With Moderate to Severe Pruritus Receiving Hemodialysis: A Randomized Clinical Trial

IMPORTANCE

Patients with pruritus receiving hemodialysis frequently experience oppressive physical and psychiatric symptoms that directly affect their quality of life and increase mortality. However, treatment options are limited.

OBJECTIVE

To determine the clinically recommended dose of difelikefalin, a κ-opioid receptor agonist, based on the efficacy, dose response, safety, and pharmacokinetics.

DESIGN, SETTING, AND PARTICIPANTS

This randomized, double-blind, placebo-controlled, 4-arm phase 2 trial was conducted from February 1, 2019, to October 22, 2019, at 94 sites in Japan. Patients with moderate to severe pruritus receiving hemodialysis were enrolled.

INTERVENTIONS

Difelikefalin (0.25, 0.5, and 1.0 μg/kg) and placebo were intravenously administered 3 times a week at the end of each hemodialysis session for 8 weeks.

MAIN OUTCOME AND MEASURES

The primary end point was the change from baseline in the weekly mean Worst Itching Intensity Numerical Rating Scale (NRS) score at week 8. Secondary outcomes measured changes in itch-related quality-of-life score using the Skindex-16 and 5-D itch scale. Safety was assessed according to adverse events, laboratory tests, vital signs, body weight, and 12-lead electrocardiogram.

RESULTS

A total of 247 Japanese patients (186 male [75%]; mean [SD] age, 64.5 [11.7] years) were randomized to placebo (n = 63), 0.25 μg/kg of difelikefalin (n = 61), 0.5 μg/kg of difelikefalin (n = 61), or 1.0 μg/kg of difelikefalin (n = 62). The changes from baseline in the adjusted mean (SE) of the 24-hour Worst Itching Intensity NRS score at week 8 were -2.86 (0.29) in the placebo group, -2.97 (0.29) in the 0.25 μg/kg of difelikefalin group, -3.65 (0.30) in the 0.5 μg/kg of difelikefalin group, and -3.64 (0.30) in the 1.0 μg/kg of difelikefalin group. Significant differences were found in the 0.5 μg/kg of difelikefalin group (adjusted mean difference, -0.80; 95% CI, -1.55 to -0.04; P = .04) and the 1.0 μg/kg of difelikefalin group (adjusted mean difference, -0.78; 95% CI, -1.54 to -0.03; P = .04) compared with placebo. The Skindex-16 overall score and 5-D itch scale total score indicated an improvement with treatment with 0.5 and 1.0 μg/kg of difelikefalin (adjusted weekly mean [SE] Skindex-16 overall score at week 8, -27.79 [2.05]; 95% CI, -31.83 to -23.74 for 0.5 μg/kg of difelikefalin and -22.69 [2.04]; 95% CI, -26.71 to -18.68 for 1.0 μg/kg of difelikefalin; adjusted weekly mean [SE] 5-D itch scale total score at week 8, -6.5 [0.4]; 95% CI, -7.2 to -5.8 for 0.5 μg/kg of difelikefalin and -6.8 [0.3]; 95% CI, -7.5 to -6.2 for 1.0 μg/kg of difelikefalin). The incidence of adverse events was 67% (42 of 63 patients) in the placebo group, 72% (44 of 61 patients) in the 0.25 μg/kg of difelikefalin group, 77% (47 of 61 patients) in the 0.5 μg/kg of difelikefalin group, and 85% (53 of 62 patients) in the 1.0 μg/kg of difelikefalin group. No dependency was reported.

CONCLUSIONS AND RELEVANCE

The findings of this phase 2 randomized clinical trial of difelikefalin suggest that 0.5 μg/kg of difelikefalin should be the clinically recommended dose as a new option for treating moderate to severe pruritus in patients undergoing hemodialysis because of its efficacy, acceptable tolerability, and manageable safety profile.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT03802617.

Peptide Kappa Opioid Receptor Ligands and Their Potential for Drug Development

Ligands for kappa opioid receptors (KOR) have potential uses as non-addictive analgesics and for the treatment of pruritus, mood disorders, and substance abuse. These areas continue to have major unmet medical needs. Significant advances have been made in recent years in the preclinical development of novel opioid peptides, notably ones with structural features that inherently impart stability to proteases. Following a brief discussion of the potential therapeutic applications of KOR agonists and antagonists, this review focuses on two series of novel opioid peptides, all-D-amino acid tetrapeptides as peripherally selective KOR agonists for the treatment of pain and pruritus without centrally mediated side effects, and macrocyclic tetrapeptides based on CJ-15,208 that can exhibit different opioid profiles with potential applications such as analgesics and treatments for substance abuse.

Novel approach to unpleasant symptom clusters surrounding pruritus in patients with chronic kidney disease and on dialysis therapy

PURPOSE OF REVIEW

Chronic kidney disease-associated-pruritus (CKD-aP) is a common symptom in patients with end-stage kidney disease (ESKD) undergoing dialysis. CKD-aP typically occurs alongside other debilitating symptoms and may comprise so-called 'symptom clusters' which have synergistic effects that adversely impact patient health-related quality of life (HRQoL). Importantly, symptoms in a cluster may share a common biological mechanism. Here we review the clinical impact of CKD-aP and its association with other symptoms reported by dialysis patients. The clinical benefits of treating pruritus and its potential impact on other symptoms are also addressed.

RECENT FINDINGS

Studies have shown CKD-aP significantly impairs HRQoL in patients with ESKD undergoing dialysis and is associated with adverse clinical outcomes, including increased risk of infections, hospitalizations, and mortality. Despite these negative effects, CKD-aP remains underrecognized and undertreated in clinical practice. CKD-aP is frequently associated with other symptoms, including disturbed sleep/poor sleep quality, anxiety, depression, and pain. Clinical studies of antipruritic therapies show that reduction of itch intensity may also alleviate other associated symptoms, such as poor sleep quality.

SUMMARY

CKD-aP and its associated symptoms are inadequately managed in clinical practice. Greater understanding and awareness of CKD-aP and its surrounding symptom clusters in dialysis patients may improve their overall symptom management and HRQoL.

Inhibiting Kiss1 Neurons With Kappa Opioid Receptor Agonists to Treat Polycystic Ovary Syndrome and Vasomotor Symptoms

CONTEXT

Recent evidence suggests that vasomotor symptoms (VMS) or hot flashes in the postmenopausal reproductive state and polycystic ovary syndrome (PCOS) in the premenopausal reproductive state emanate from the hyperactivity of Kiss1 neurons in the hypothalamic infundibular/arcuate nucleus (KNDy neurons).

OBJECTIVE

We demonstrate in 2 murine models simulating menopause and PCOS that a peripherally restricted kappa receptor agonist (PRKA) inhibits hyperactive KNDy neurons (accessible from outside the blood-brain barrier) and impedes their downstream effects.

DESIGN

Case/control.

SETTING

Academic medical center.

PARTICIPANTS

Mice.

INTERVENTIONS

Administration of peripherally restricted kappa receptor agonists and frequent blood sampling to determine hormone release and body temperature.

MAIN OUTCOME MEASURES

LH pulse parameters and body temperature.

RESULTS

First, chronic administration of a PRKA to bilaterally ovariectomized mice with experimentally induced hyperactivity of KNDy neurons reduces the animals' elevated body temperature, mean plasma LH level, and mean peak LH per pulse. Second, chronic administration of a PRKA to a murine model of PCOS, having elevated plasma testosterone levels and irregular ovarian cycles, suppresses circulating levels of LH and testosterone and restores normal ovarian cyclicity.

CONCLUSION

The inhibition of kisspeptin neuronal activity by activation of kappa receptors shows promise as a novel therapeutic approach to treat both VMS and PCOS in humans.

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.

Clinical management of chronic kidney disease-associated pruritus: current treatment options and future approaches

Chronic kidney disease (CKD)-associated pruritus (CKD-aP) is an underdiagnosed yet severely distressing condition that impacts 60% of patients on dialysis and many nondialysis patients with Stages 3–5 CKD. However, despite its high prevalence, there are currently limited treatment options available for these patients and a lack of treatment guidelines for clinicians. In this manuscript, we reviewed the available literature in order to evaluate the current management and treatment options for CKD-aP, including dialysis management, topical treatments, gabapentinoids, opioids and alternative medicine. We also review the available data on CKD-aP treatments in development and propose new guidelines for managing patients with CKD-aP.

Do you feel itchy? A guide towards diagnosis and measurement of chronic kidney disease-associated pruritus in dialysis patients

Chronic kidney disease-associated pruritus (CKD-aP) is a potentially distressing condition that affects a significant proportion of patients with end-stage kidney disease undergoing dialysis. CKD-aP may lead to worsening of patients' physical and mental health-related quality of life (HRQoL) and has also been linked with worse clinical outcomes, including increased mortality. Despite these detrimental effects, evidence from real-world studies shows that CKD-aP still remains overlooked by nephrologists and underreported by patients in clinical practice. Itch is subjective and therefore its diagnosis is often dependent on patients reporting this symptom. There is an opportunity to reduce the burden of CKD-aP on dialysis patients by increasing awareness about this condition and the availability of effective treatments. It is particularly important that nephrologists and other healthcare providers routinely ask their patients if they are experiencing itch. The differential diagnosis of CKD-aP requires a step-by-step identification and exclusion of possible alternative or concomitant causes of itch. Several simple validated self-reported assessment scales are available to evaluate the presence and severity of itch in a time-efficient manner, making them suitable for use in everyday clinical practice. The impact of CKD-aP on haemodialysis patients' HRQoL should also be assessed on a regular basis. This review provides a comprehensive overview of the differential diagnosis of CKD-aP and the diagnostic tools that are available to identify itch and quantify its severity and impact on patient HRQoL. A suggested algorithm to guide the screening, diagnosis and assessment of CKD-aP among dialysis patients in real-world practice is provided.

Chronic Intractable Pruritus in Chronic Kidney Disease Patients: Prevalence, Impact, and Management Challenges - A Narrative Review

Chronic kidney disease (CKD) is recognized as a leading public health problem and causes numerous health complications. One of the most common and burdensome dermatological symptoms affecting patients undergoing dialysis is CKD-associated pruritus (CKD-aP). This condition not only has a negative impact on sleep, mood, daily activities, and quality of life but also increases the mortality risk of hemodialyzed patients. Despite that, this condition is greatly underestimated in clinical practice. Due to the complex and still not fully understood etiopathogenesis of CKD-aP, the choice of an effective therapy remains a challenge for clinicians. Most common therapeutic algorithms use topical treatment, phototherapy, and various systemic approaches. This review aimed to summarize most recent theories about the pathogenesis, clinical features, and treatment of CKD-aP.

Estimation of ZYKR1 in human urine and plasma utilizing LC-MS/MS positive electrospray ionization; a kappa opioid receptor (KOR) agonist

ZYKR1, a short chain novel peptide with selective kappa opioid receptor agonist activity used as analgesics for the treatment of pain management. A sensitive and selective LC-MS/MS assay was developed and validated for estimation of ZYKR1 in human urine and plasma. ZY17258, an analogue compound was used as an internal standard. ZYKR1 was quantified using a selective reaction monitoring in electrospray ionization positive mode. The chromatographic separation was performed using mobile phase consisted of 0.05% v/v formic acid in water and methanol in gradient elution by analytical column Kinetex C₈, 100 A°, 5 µm, 100 × 4.6 mm with 8.0 min analytical run time. Solid Phase extraction technique was used for purification of ZYKR1 and IS from human urine and plasma. The calibration curves were linear over range of 0.300 ng/mL to 300 ng/mL and 0.500 ng/mL to 500 ng/mL for human urine and plasma, respectively. No matrix effect and no significant carryover were observed. The extraction recovery was consistent and ranged from about 85% to 93% in human urine and in plasma respectively. Inter-day and intra-day accuracy (bias, %) and precision (CV, %) was -11.11 to 5.91 % and -2.25 to 6.65 % in human urine and -2.74 to 7.17 % and 2.24 to 15.18 % in plasma respectively were well within the acceptance criteria. Both the assays were devoid of endogenous matrix interference and commonly used concomitant drug interference. The validated assays were used for estimation of ZYKR1 from clinical pharmacokinetic study sample bioanalysis in healthy human subjects.

Difelikefalin: First Approval

Difelikefalin (Korsuva™) is a synthetic peptide agonist of the kappa opioid receptor being developed by Cara Therapeutics for the treatment of pruritus. In August 2021, intravenous difelikefalin was approved in the USA for the treatment of moderate-to-severe pruritus associated with chronic kidney disease (CKD) in adults undergoing haemodialysis. Intravenous difelikefalin has also been evaluated for CKD-associated pruritus in patients undergoing haemodialysis in various other countries, with Marketing Authorization Application under regulatory review in the EU and a phase III trial ongoing in Japan. Clinical studies of an oral formulation of difelikefalin have also been completed or are underway in pruritus indications, including pruritus associated with atopic dermatitis, notalgia paraesthetica or primary biliary cholangitis. This article summarizes the milestones in the development of difelikefalin leading to this first approval for CKD-associated pruritus in adults undergoing haemodialysis.

Evaluation of the abuse potential of difelikefalin, a selective kappa-opioid receptor agonist, in recreational polydrug users

Difelikefalin, a selective kappa‐opioid receptor agonist with limited central nervous system penetration, is being developed for the treatment of chronic pruritic conditions. This randomized, double‐blind, active‐ and placebo‐controlled, four‐way crossover study was designed to evaluate the abuse potential of difelikefalin in healthy recreational polydrug users. Using a 4 × 4 Williams design, nondependent adult users of opioids and hallucinogens (N = 44) were randomized to receive single intravenous (i.v.) injections of difelikefalin at supratherapeutic doses (5 and 15 mcg/kg); pentazocine (0.5 mg/kg), a schedule IV mu‐opioid partial agonist and kappa‐opioid receptor agonist; and placebo. The abuse potential of difelikefalin was compared with pentazocine and placebo using the maximal score (maximum effect [E_max]) of the Drug Liking visual analog scale (VAS; primary end point), along with multiple secondary end points of subject‐rated measures and pupillometry. Difelikefalin produced significantly lower Drug Liking VAS E_max, and lower peak positive, sedative, and perceptual effects compared with pentazocine. These effects of difelikefalin were small, brief, and not dose‐dependent, although marginally greater than those observed with placebo. Neither dose of difelikefalin elicited significant negative or hallucinogenic effects. On end‐of‐session measures of overall drug liking and willingness to take the drug again, difelikefalin did not differ from placebo, indicating subjects neither liked nor disliked the effects overall and did not feel motivated to take the drug again. Consistent with its lack of mu agonist activity, difelikefalin did not induce miosis compared with pentazocine. All treatments were generally well‐tolerated. This study indicates that difelikefalin presents a low potential for abuse.

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.

Chronic Kidney Disease-Associated Pruritus

Pruritus is a distressing condition associated with end-stage renal disease (ESRD), advanced chronic kidney disease (CKD), as well as maintenance dialysis and adversely affects the quality of life (QOL) of these patients. It has been reported to range from 20% to as high as 90%. The mechanism of CKD-associated pruritus (CKD-aP) has not been clearly identified, and many theories have been proposed to explain it. Many risk factors have been found to be associated with CKD-aP. The pruritus in CKD presents with diverse clinical features, and there are no set features to diagnose it.The patients with CKD-aP are mainly treated by nephrologists, primary care doctors, and dermatologists. Many treatments have been tried but nothing has been effective. The search of literature included peer-reviewed articles, including clinical trials and scientific reviews. Literature was identified through March 2021, and references of respective articles and only articles published in the English language were included.

Therapeutic Peptides Targeting PPI in Clinical Development: Overview, Mechanism of Action and Perspectives

Targeting protein-protein interactions (PPIs) has been recently recognized as an emerging therapeutic approach for several diseases. Up today, more than half a million PPI dysregulations have been found to be involved in pathological events. The dynamic nature of these processes and the involvement of large protein surfaces discouraged anyway the scientific community in considering them promising therapeutic targets. More recently peptide drugs received renewed attention since drug discovery has offered a broad range of structural diverse sequences, moving from traditionally endogenous peptides to sequences possessing improved pharmaceutical profiles. About 70 peptides are currently on the marked but several others are in clinical development. In this review we want to report the update on these novel APIs, focusing our attention on the molecules in clinical development, representing the direct consequence of the drug discovery process of the last 10 years. The comprehensive collection will be classified in function of the structural characteristics (native, analogous, heterologous) and on the basis of the therapeutic targets. The mechanism of interference on PPI will also be reported to offer useful information for novel peptide design.