¹University of Ottawa, Faculty of Medicine, Ottawa, ON, Canada
²Dermatrials Research Inc. & Venderm Innovations in Psoriasis, Hamilton, ON, Canada

Conflict of interest:
Ryan Gotesman has no conflicts of interest to disclose. Ron Vender has been a consultant, and/or scientific advisor, and/or investigator, and/or speaker for Amgen, AbbVie, Astellas, Bausch Health/Valeant, BMS, Boehringer Ingelheim, Celgene, Dermira, Eli Lilly, Galderma, GSK, Janssen, Leo Pharma, Merck (MSD), Merck Serono, Novartis, Pfizer, Regeneron, Roche, Sanofi-Aventis/Genzyme, Sun Pharma, Takeda and UCB.

Abstract:
Psoriasis is an immune-mediated inflammatory skin disease that affects about 2% of the population and is associated with many comorbidities. Recent advances have demonstrated interleukin (IL)-17 signaling plays a crucial role in the pathogenesis of psoriasis. Bimekizumab is a novel monoclonal antibody treatment for psoriasis that uses a single binding site to inhibit IL-17A and IL-17F. Here we will discuss the safety and efficacy of bimekizumab in the treatment of moderate-to-severe plaque psoriasis.

Key Words:
plaque psoriasis, IL-17, interleukin-17A, interleukin-17F, bimekizumab

Table of Contents:

1. Introduction
2. IL-17 in Psoriasis
3. Phase I Trials
4. Phase II Trials
5. Phase III Trials
6. Conclusion

Introduction

Psoriasis is a chronic, auto-immune inflammatory skin condition with a worldwide prevalence of about 2%.¹ The most common manifestation is plaque psoriasis, presenting as well-delineated, erythematous, scaly and itchy plaques that may appear anywhere on the body but are usually found on the extensor surfaces of the elbows and knees.² Plaque psoriasis may be described as moderate-to-severe when it covers 3% or more of the body’s surface or has a significant effect on a patient’s quality of life. About 1 in 5 psoriasis patients report moderate or severe disease.³

The systemic inflammation in psoriasis can affect multiple systems beyond the skin. Psoriatic arthritis is an erosive arthritis that develops in about 30% of psoriatic patients and causes joint pain as well as stiffness.⁴ Psoriasis has also been linked with cardiovascular disease, diabetes, lymphoma and depression.^5-7 The prevalence of comorbidities increases with disease severity, and men and women with severe psoriasis experience a 3.5 and 4.4 year reduction in life-expectancy, respectively.⁸

Multiple therapies are available for treating psoriasis. The mainstay for combating mild psoriasis is topical therapy composed of corticosteroids, vitamin D3 analogues, retinoids, anthralin and coal tar.⁹ Topical treatments are ineffective in managing moderate-to-severe disease though they may be used as adjuncts. Instead, moderate-to-severe psoriasis is treated using systemic therapy that includes phototherapy, corticosteroids, retinoids, methotrexate, cyclosporine, and biologics.¹⁰ Biologic agents target specific inflammatory molecules implicated in the pathogenesis of psoriasis and have proven particularly effective. Biologics have been developed against tumor necrosis factor-alpha (TNF-α), interleukin (IL)-12, IL-23, IL-17 and the IL-17 receptor.¹¹ Recent advances have revealed the fundamental role that IL-17 pathways play in the development of psoriasis.

IL-17 in Psoriasis

The IL-17 family is comprised of six members, IL-17A, IL-17B, IL-17C, IL-17D, IL-17E and IL-17F.¹² Among the members, IL-17A and IL-17F share the greatest structural similarity and are secreted as homodimers or IL-17A/F heterodimers. IL-17 plays an essential part in defending against microbial invaders at mucosal and epithelial sites by stimulating production of inflammatory cytokines that attract neutrophils, monocytes and lymphocytes. T helper 17 (Th17) T cells are a major source of IL-17, as are gamma delta (γδ) T cells in the skin, neutrophils, natural killer cells and mast cells.¹³ IL-17 signaling is dysregulated in psoriasis.

The trigger for psoriasis is thought to be a foreign antigen, perhaps introduced through infection or trauma.¹⁴ Activated inflammatory cells release IL-23, which stimulates the production of inflammatory cytokines, including IL-17A, IL-17F and IL-17A/F. The activity of the IL-17A homodimer is about 30 times more than the IL-17F homodimer, with the activity of the IL-17A/F heterodimer lying somewhere in-between.¹⁵ All three induce the keratinocyte and vascular hyperproliferation underlying psoriasis. Indeed, IL-17A and IL-17F, along with their receptors, are highly expressed in psoriatic plaques.¹⁶ In addition, IL-17 can attract inflammatory cells to infiltrate psoriatic lesions and further contribute to the inflammatory state. Moreover, IL-17 can act in concert with TNF-α to create a positive feedback loop that maintains and exacerbates inflammation of the dermis.¹⁷

Biologics aimed at the IL-17 pathway have demonstrated impressive efficacy in treating moderate-to-severe psoriasis. Two of the three currently approved biologics, secukinumab and ixekizumab, inhibit IL-17A, while the remaining, brodalumab, antagonizes the IL-17 receptor A subunit. These inhibitors have proven to be more effective in clearing psoriasis than TNF-α inhibitors and many of the new IL-23 targeted therapies, thereby cementing IL-17 as a key component of plaque pathogenesis.^18,19 Bimekizumab is a novel monoclonal antibody treatment for psoriasis that distinguishes itself by using a single binding site to neutralize two members of the IL-17 family, IL-17A and IL-17F.²⁰ A number of Phase I, II and III trials have evaluated the efficacy and safety of bimekizumab.

Phase I Trials

In 2016, the first in-human double-blind, placebo-controlled study of bimekizumab randomized 39 patients with mild-tomoderate plaque psoriasis to receive a single dose of intravenous infusion of bimekizumab or placebo.²¹ The primary objective was to investigate the safety of bimekizumab and secondary objectives were to characterize the drug’s pharmacokinetic profile and clinical benefit. The tested doses of bimekizumab were 8mg, 40mg, 160mg, 480mg or 640mg and patients were evaluated over a 20-week period. Treatment emergent adverse events (TEAEs) were observed in 84.6% of those receiving bimkezumab compared to 76.9% on placebo. Most of the TEAEs were classified as mild, 61.5% in the bimekizumab cohort and 53.8% in the placebo group.

The TEAEs experienced by 10% or more of those on bimekizumab were headache, oropharyngeal pain, nasopharyngitis and site reactions from using medical devices. Only one serious adverse event, vomiting, was reported and not thought to be related to the medication. There were no severe TEAEs or deaths and no patients left the study due to an adverse event. Bimekizumab’s plasma concentration increased with dose in a linear fashion and the half-life ranged from 17-26 days. Five patients developed antibodies against bimekizumab during the trial, but they had no effect on pharmacokinetic parameters.

Bimekizumab elicited a dose-dependent improvement in disease severity. The biologic’s impact was most rapid at the higher doses of 480mg and 640mg, reducing baseline scores by over 65% at week 2. Maximal effect in all measures of disease activity were observed between weeks 8-12 in subjects receiving 160mg-640mg of the drug and the effect was maintained up to weeks 12-20. Focusing on Psoriasis Area and Severity Index (PASI) scores, the 160mg group experienced a maximal effect of over 85% reduction in PASI at week 6. Maximal effect of over 94% reduction in PASI score was reached by week 6 in the 480mg group and week 4 in the 640mg group, and the effect was maintained through weeks 12-20.

Phase II Trials

Soon after, bimekizumab was evaluated in the multicenter, double-blind, placebo-controlled Phase IIb BE ABLE I trial.²² The 250 patients with moderate-to-severe plaque psoriasis were randomized (1:1:1:1:1:1) to receive subcutaneous bimekizumab every 4 weeks at doses of 64mg, 160mg, 160mg with 320mg loading dose, 320mg, 480mg, or placebo. The primary endpoint was achieving PASI90 (90% reduction in PASI) at week 12.

Secondary endpoints were reaching PASI90 at week 8, PASI75 (75% reduction in PASI) at week 2, and PASI100 (complete skin clearance) at week 2, as well as achieving an Investigator’s Global Assessment (IGA) score of clear or almost clear skin (IGA0/1) with two or more categories of improvement from baseline. Bimekizumab elicited a swift clinical response, significantly improving disease activity across all doses by week 4. By week 8, substantially more patients on bimekizumab reached PASI90 (41%-86% vs. 0%, p<0.0001) and IGA0/1 (46%-86% vs. 5%, p≤0.0003) across doses compared with placebo. The primary endpoint, PASI90 response at week 12, was significantly related to bimekizumab dose (p<0.0001) and was reached by 46% of patients using 64mg, 67% using 160mg, 75% using 160mg and 320mg loading dose, 79% using 320mg and 72% using 480mg of bimekizumab compared to 0% on placebo (Figure 1).

Significantly more patients also achieved PASI75 (62%-93% vs. 5%, p<0.0001), PASI100 (28%-60% vs. 0%, p≤0.0002) and IGA0/1 (51%-86% vs. 5%, p≤0.0001) at week 12 across all doses compared to placebo.

The safety profile of bimekizumab did not change with dose, though TEAEs were more frequently reported in patients treated with bimekizumab than placebo (61% vs. 36%). The common TEAEs that occurred in 5% or more of patients in any treatment group were nasopharyngitis, upper respiratory tract infection, arthralgia, γ-glutamyltransferase increase, neutropenia, rhinitis, tonsillitis, oral candidiasis, headache, leukopenia and vomiting. Worth highlighting, 4.3% of bimekizumab patients developed fungal infections compared to no cases in the placebo group.

In addition, adverse events led to 4.8% of bimekizumab patients and 2.4% in the placebo group leaving the study; however, no serious events were thought to be related to the treatment. Importantly, no cases of anaphylactic reactions, inflammatory bowel disease, neuropsychiatric complications or systemic infections were reported.

Phase III Trials

Full results for the Phase III clinical trials BE VIVID and BE READY were published in early 2021 and confirmed bimekizumab to be a safe, effective therapy for moderate-to-severe plaque psoriasis. BE VIVID, was a 52-week trial that randomized 567 patients in a ratio of 4:2:1 to receive bimekizumab 320mg every 4 weeks, ustekinumab 45mg or 90mg (baseline weight-dependent dosing) at weeks 0 and 4, then every 12 weeks or placebo every 4 weeks.²³ At week 16, the placebo group was switched to bimekizumab 320mg every 4 weeks. In BE VIVID, 85% of patients receiving bimekizumab reached PASI90 after 16 weeks of therapy, far more than the 50% of patients receiving ustekinumab and 5% of patients taking placebo.²³ By the 52nd week, 82% of patients treated with bimekizumab had achieved PASI90 relative to 56% in the ustekinumab group.

Safety of the drug corresponded to the Phase II BE ABLE I trial. The safety profiles of bimekizumab and ustekinumab were comparable, with 6% of patients on bimekizumab experiencing serious TEAEs compared to 7% of those on ustekinumab.

Data from BE READY demonstrated bimekizumab’s impressive long-term efficacy. BE READY spanned 55 weeks and randomized 435 patients in a ratio of 4:1 to receive bimekizumab 320mg every 4 weeks or placebo every 4 weeks.²⁴ Bimekizumab-treated patients who achieved PASI90 at week 16 were re-allocated (1:1:1) to receive bimekizumab 320mg every 4 weeks, every 8 weeks or placebo until week 56. At week 16, 91% of patients receiving bimekizumab 320mg every 4 weeks achieved PASI90 relative to 1% in the placebo arm. As well, IGA0/1 was achieved in 93% of patients receiving bimekizumab 320mg every 4 weeks relative to 1% in the placebo arm.

Patients randomized to placebo following the initial 16 weeks of therapy only relapsed after a median time of 32 weeks had elapsed since their last treatment. In addition, doubling the period between bimekizumab treatments did not reduce the drug’s effectiveness: About 91% of patients randomized to receive bimekizumab every 8 weeks following week 16 reached PASI90 by the end of the study, relative to the 87% in the group that received monthly bimekizumab for the entirety of the trial. With respect to safety, there were two cases of malignancy, one a basal cell carcinoma detected in the 320mg every 4 weeks group during the initial treatment phase, and a case of prostate cancer in the placebo group during the randomized withdrawal period. There were no serious hypersensitivity reactions across any of the bimekizumab groups.

Hepatic events occurred in 3% of the bimekizumab 320mg every 4 weeks group and 1% of the placebo group in the initial treatment period, and in 8% of the bimekizumab 320mg every 4 weeks group and 3% of the bimekizumab 320mg every 8 weeks group in the randomized withdrawal period. The majority of these cases were transient elevated liver function tests that self resolved without dose adjustment and none led to treatment discontinuation. Three serious infections (enterovirus, pneumonia, otitis media chronic) occurred in the bimekizumab 320mg every 4 weeks group and no opportunistic infections or active tuberculosis were reported.

A third Phase III clinical trial, BE SURE, randomized 478 patients to receive bimekizumab or adalimumab through an active-controlled initial treatment period of 24 weeks followed by a dose-blind maintenance treatment period until week 56.²⁵ At week 16, bimekizumab was superior to adalimumab in achieving PASI90 and IGA0/1.²⁶ Bimekizumab was also better at reaching PASI100 at weeks 16 and 24 and led to a more rapid response. High levels of skin clearance were achieved with bimekizumab during the dose-blind maintenance period through week 56 and no new safety concerns were identified. Importantly, BE SURE results have yet to be published in a peer-reviewed journal and are expected in 2021.

Conclusion

Bimekizumab is a novel treatment for moderate-to-severe plaque psoriasis that has shown promising efficacy and safety in clinical trials. By simultaneously targeting two components of the IL-17 pathway, IL-17A and IL-17F, the biologic can downregulate proinflammatory signaling and rapidly improve patients’ skin.

Based on strong Phase III trial results, 2020 saw the US Food and Drug Administration accept a biologics licence application and the European Medicine Agency accept a marketing authorization application for bimekizumab as a treatment of adults with moderate-to-severe plaque psoriasis. Though no serious adverse events were associated with the drug, its long-term safety must still be demonstrated. Due to IL-17’s role in preventing microbial invasion, particular attention should be paid to any increase in opportunistic infection. Further investigations are warranted to compare bimekizumab against biologics like secukinumab or ixekizumab that only target a single component of the IL-17 pathway.

Given the drug’s impressive efficacy, bimekizumab may become first-line therapy for moderate-to severe plaque psoriasis and the dermatology community eagerly awaits its approval.

Purchase Article PDF for $1.99

¹Faculty of Medicine, University of Toronto, Toronto, ON, Canada
²Division of Dermatology, University of Toronto, Toronto, ON, Canada
³The Lynde Institute of Dermatology, Markham, ON, Canada

Conflict of interest:
All of the authors declare no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Abstract:
Prurigo nodularis (PN) is a chronic, recalcitrant inflammatory skin condition characterized by the presence of pruritic nodules. The exact pathogenesis of the disease is unknown, although immune and neural dysregulation are indicated in driving the itch-scratch cycle. Specifically, interleukin-4 and interleukin-31 pathways have been recently implicated in transmission of the pruritic sensation. There are currently no US FDA-approved targeted therapies for the treatment of PN. This article aims to review our present understanding of the disease pathogenesis and treatments, with a focus on emerging therapeutics. Specifically, this article explores the developing use of monoclonal antibodies nemolizumab and dupilumab, opioid receptor modulation and cannabinoids as potential treatments for PN.

Key Words:
prurigo nodularis, nemolizumab, dupilumab, chronic pruritus

Clinical Presentation

Prurigo nodularis (PN) is a chronic inflammatory skin condition characterized by the presence of pruritic nodules. Lesions vary in size from a few millimeters to 2-3 cm in diameter, and range in number from a few to hundreds.¹ Nodules may be flesh-colored, erythematous, or hyperpigmented (depending on skin type), and are typically located in symmetric linear arrangements along extensor surfaces.¹ PN has some predilection for elderly patients and individuals with dark skin, particularly persons of African ancestry.^2,3 Although the disease affects patients of either sex, some research suggests women may be disproportionately affected in terms of frequency, age of onset, and severity.⁴ Numerous risk factors have been elucidated prior to development of PN, including eczemas, psychiatric diagnoses, and chronic medical diseases such as malignancy, liver failure, chronic renal failure, diabetes and human immunodeficiency virus (HIV) infection.^3,5-7

Pathophysiology

The pathogenesis of PN is thought to be characterized by a cutaneous reaction pattern due to chronic itching and repeated scratching, otherwise termed the “itch-scratch cycle.” Although the exact pathogenesis of PN is unknown, immune and neural dysregulation drive the pruritic cycle.⁸

Histopathologic studies investigating the immune response of PN have demonstrated increased infiltrate in the dermis of PN lesions consisting of increased T lymphocytes, mast cells and eosinophilic granulocytes.^8,9 The intense itch is created by an inflammatory response in the skin through mediators such as interleukin (IL)-31, tryptase, eosinophil cationic protein, histamine, prostaglandins and neuropeptides.^8,9 Specifically, eosinophils and IL-31 are particularly implicated in the pathogenesis of the disease through their increased expression and pathologic mechanisms in the dermis of PN lesioned skin.^8-13

Neuronal dysregulation has also been demonstrated in PN; studies have shown differences in nerve fiber density between the dermis and epidermis in individuals with PN.¹¹ Further, dysregulation of neuropeptides has been implicated in the pathogenesis, with particular increases in calcitonin gene-related peptide and substance P in dermal PN skin.^8-11,14 Although these changes may be secondary to repeated mechanical scratching, they still contribute to the pruritic cycle through regulation of eosinophils, mast cells, effects on endorphins and mu- and kappa-opioid receptors.^8,9,11

Regardless of the aforementioned potential triggering pathologies, central nervous system functioning is essential for transmitting the itch signal from the periphery. Recent seminal findings by Oetjen and colleagues have demonstrated that the IL-4 receptor is directly expressed on sensory neurons in the dorsal root ganglia of both humans and mice. This receptor is directly activated by expression of type 2 cytokines, such as IL-4, IL-13 and IL-31.¹⁵ Most importantly, the authors demonstrated that ablating the IL-4 receptor in a mouse model significantly diminished chronic pruritus, and treating human patients with recalcitrant chronic itch that failed other immunosuppressive therapies with inhibitors of the type 2 cytokine pathway (Janus kinase – JAK – inhibitors) markedly improved their symptoms.¹⁵ Taken together, therapeutics targeting the inhibition of this central nervous system pathway may potentially be groundbreaking in the treatment of PN.

Current Treatments

Currently, there are no US Food and Drug Administration (FDA) approved targeted treatments for PN. Although the treatment goal is to break the itch-scratch cycle to allow the nodules to heal, there is a high degree of variability between providers and treatment regimens in the use of off-label therapies.^8,16 A recent systematic review assigned level of evidence ratings to the current treatment options for PN (Table 1). The review found that many current therapies have low efficacy or a high frequency of side effects, limiting their effectiveness. Further, there was a paucity of randomized control trials (8 RCTs, with only 3/8 having >22 participants with PN) and quality studies looking at treatment of PN. Overall, topical agents, including corticosteroids, calcineurin inhibitors, calcipotriol, and capsaicin, had the highest evidence ratings, with some beneficial effects.¹⁷ The majority of studies investigating phototherapy and photochemotherapy reported mild side effects and demonstrated good partial response rates, as did thalidomide, although it had poorer quality studies and a large side effect profile. Antiepileptics and antidepressants, such as pregabalin, amitriptyline, paroxetine, fluvoxamine, and neurokinin-1 receptor antagonists had strong evidence ratings with promising treatment results and low risks of side effects. Lastly, systemic immunomodulatory therapies, such as cyclosporine and methotrexate, demonstrated some benefit in a limited number of low evidence level studies. However, these systemic treatments had poor safety profiles.¹⁷

The lack of success with current treatments is likely due to the heterogeneity of disease and dearth of regimens addressing the immunologic and neural pathophysiologic components of PN.^8,17

Emerging Treatments

Currently, several new treatments are being explored for itch pathogenesis in PN (Table 2).

Nemolizumab

Nemolizumab is a new drug designed to interrupt the itch-scratch cycle in PN. Considering that up-regulation of IL-31 messenger RNA has been reported in PN lesions compared to healthy skin biopsies, a drug interrupting this increase could be beneficial.¹³ Nemolizumab was designed as a humanized anti-human IL-31 receptor A monocloncal antibody. This monoclonal antibody disrupts the binding of IL-31 to its receptor, and in doing so inhibits part of the cascade of inflammatory events causing the itch sensation.^18,19

Results of a phase 2 trial of nemolizumab on adults with moderate-to-severe PN were recently published. Moderate-to-severe PN was defined as 20 or more nodules, while severe PN was characterized as a mean score of at least 7 (range 0-10) for the worst daily intensity of pruritus. PN patients were randomly equally assigned to receive subcutaneous injections of nemolizumab 0.5 mg/kg (n=34), or matching placebo (n=36).²⁰ Three total injections were administered at baseline, week 4 and week 8, with three more visits at weeks 12, 16 and 18. At week 4 there was a 53% reduction from baseline in peak pruritus score (4.5 points) in the nemoluzimab group, compared to a 20% reduction in the placebo group (1.7 points). Reductions were maintained throughout the trial period.²⁰ The mean number of prurigo lesions decreased by a greater proportion in the nemolizumab group compared to the placebo group at week 12. Other secondary outcome measures such as assessments investigators’ global assessments, sleep quality and Dermatology Life Quality Index also demonstrated greater improvements in the nemolizumab group compared to placebo.²⁰ Nemolizumab was associated with more side effects than placebo, namely abdominal symptoms such as abdominal pain and diarrhea, as well as nonspecific musculoskeletal symptoms.²⁰

Based on these strong and promising results for treatment of PN, the FDA recently approved nemolizumab for Breakthrough Therapy status, thus expediting its development and approval process.²¹ Phase 3 trials are currently underway (NCT03989206).

Dupilumab

Similar to nemolizumab, dupilumab is a monoclonal antibody antagonist of the IL-4 receptor, another integral component of the neural pathway for pruritus.¹⁵ Further, it has already been approved by the FDA for three indications including treatment of moderate-to-severe atopic dermatitis.²²

The largest recently published case series has demonstrated the benefit of dupilumab in the treatment of chronic pruritus. Twenty recalcitrant pruritus patients at a tertiary care center were treated with off-label dupilumab at standard atopic dermatitis dosing. Promising results were observed, with complete resolution obtained in 12/20 patients and an overall mean reduction of 7.⁵⁵ points on the numeric rating scale for itch intensity (range 0-10). Specifically, 9 patients in this series had PN, and reported a mean reduction in itch ratings of 7.89. Further, the drug was well tolerated in all patients and no significant adverse events were reported.²² The same authors have also reported success in its specific use for PN in a previously published case series.²³ Several other case series and reports all published within the last year have also described the benefit of dupilumab for treatment of PN.^24-28

Further, a recent retrospective cohort study examined the effectiveness of dupilumab in treating adults affected by persistent atopic dermatitis with clinical features of generalized PN. A total of 90 atopic dermatitis patients were treated, of which 9 patients demonstrated generalized PN. Significant improvements in Eczema Area and Severity Index, Dermatology Quality of Life Index, and pruritus visual analogue scale score were observed after treatment.²⁹ Another recent retrospective cohort study of 16 adult patients with chronic PN refractory to multimodal treatment regimens reported similar results.³⁰ Taken together with the evidence from the case series, the use of dupilumab in treatment of PN shows promise, and warrants further research with randomized control trials.

Opioid Receptor Modulation: Nalbuphine, Butorphanol, Naloxone and Naltrexone

Other research has examined the efficacy of opioid receptor modulating drugs in the treatment of pruritus. Considering that imbalances between mu- and kappa-opioid signalling have been indicated in generalized itch pathogenesis, mixed kappa-opioid agonist/mu-opioid antagonists may interrupt this cycle.³¹ The mechanisms of nalbuphine and butorphanol both act as such, and each have been demonstrated to have some beneficial effects on reducing pruritus. Specifically, one study examined the effects of nalbuphine in hemodialysis patients on treating uremic pruritus, and found discernable reductions in measures of itch severity with increasing dosage.³² Further, case investigations examining the effects of butorphanol on intractable pruritus have also demonstrated its benefit.³¹ Importantly, a recent multicenter, double-blind randomized control trial examined the effects of nalbuphine on itch severity in PN, as well as evaluated the safety and tolerability of the drug in this population. Phase 2 results have been released, but not yet published, and demonstrated promising beneficial effects of nalbuphine in reducing pruritus (NCT02174419).

Intravenous naloxone and oral naltrexone, both mu-opioid receptor antagonists, have also demonstrated antipruritic effects in select PN patients.^33,34 A double-blind, randomized control trial investigating the use of naloxone infusions in patients with pruritus of cholestasis (n=29) found that it was associated with reduced pruritic perception and actual reduction of scratching.³⁵ Further, another trial of 65 patients examined the effects of naltrexone on pruritus, and found significant benefits including lesion healing and symptom reduction.³⁶ Further studies examining the efficacy of opioid receptor modulation in pruritic pathways are warranted given these promising combined results.

Cannabinoids

Cannabinoid receptor (CB)1 and CB2 are expressed on cutaneous nerve fibers, with agonists of these receptors diminishing histamine-induced excitation and leading to reduction of itch.^37,38 As such, these cannabinoid receptors are thought to contribute to the pruritic sensation. A recent systematic review examined the efficacy of cannabinoids for the treatment of chronic refractory pruritus. Only 5 studies were included in the analysis, but all reported a reduction in itch intensity following cannabinoid therapy.³⁹ Considering the recent growth in acceptance of use and favorable legislation of medical marijuana, further research is warranted to explore its potential use in PN.⁴⁰

Conclusion

Novel therapeutics are currently being explored for the treatment of PN. It is important for treatments to consider targeting both the neural and immunologic components of the itch-scratch cycle. Nemolizumab and dupilumab both demonstrate promise in inhibiting specific central nervous system pathways responsible for transmission of the pruritic sensation. Moving forward it is important for clinicians to better understand the pathogenesis of PN, and apply an integrated approach to treatment of this chronic, recalcitrant condition.

Purchase Article PDF for $1.99

Binimetinib tablets + encorafenib capsules

Encapsulated cell therapy for Fabry disease

Oritavancin IV injection

Purchase PDF for $1.99