Gefapixant, a P2X3 receptor antagonist, for the treatment of refractory or unexplained chronic cough: a randomised, double-blind, controlled, parallel-group, phase 2b trial

Camlipixant in Refractory Chronic Cough: A Phase 2b, Randomized, Placebo-controlled Trial (SOOTHE)

Rationale: There is no broadly accessible treatment for patients with refractory chronic cough, a disease characterized by chronic cough that persists despite treatment for other cough-related etiologies or has no identified underlying cause. Objectives: SOOTHE (NCT04678206), a phase 2b, randomized, placebo-controlled trial, evaluated the efficacy and safety of P2X3 antagonist camlipixant in adults with refractory chronic cough (cough duration, ⩾1 yr; baseline awake cough frequency, ⩾25 coughs/h). Methods: After a single-blind, 16-day placebo run-in, patients were randomized (1:1:1:1) to receive camlipixant 12.5, 50, or 200 mg twice daily or placebo for 4 weeks. The primary endpoint was change from baseline to Day 28 in objective 24-hour cough frequency. Secondary endpoints included cough severity and cough-related quality of life. Measurements and Main Results: Overall, 310 patients were randomized. A statistically significant reduction in placebo-adjusted 24-hour cough frequency was seen in the 50 mg (-34.4%; 95% confidence interval, -50.5 to -13.3; P = 0.0033) and 200 mg (-34.2%; 95% confidence interval, -50.7 to -12.2; P = 0.0047) camlipixant arms. All camlipixant arms showed a trend for greater improvement in cough severity visual analog scale and Leicester Cough Questionnaire scores over placebo. Camlipixant was well tolerated with no serious treatment-emergent adverse events reported. Taste alteration occurred in 4.8-6.5% of patients in camlipixant arms (vs. 0% with placebo); these were usually mild-moderate. Conclusions: Camlipixant treatment reduced cough frequency and improved patient-reported outcomes in patients with refractory chronic cough, with an acceptable safety profile. Clinical trial registered with www.clinicaltrials.gov (NCT04678206).

Channel synapse mediates neurotransmission of airway protective chemoreflexes

Neural reflexes to chemicals in the throat protect the airway from aspiration and infection. Mechanistic understanding of these reflexes remains premature, exemplified by chronic cough-a sensitized cough reflex-being a prevalent unmet clinical need. Here, in mice, a whole-body search for channel synapses-featuring CALHM1/3 channel-mediated neurotransmitter release-and single-cell transcriptomics uncovered subclasses of the Pou2f3+ chemosensory cell family in the throat communicating with vagal neurons via this synapse. They express G protein-coupled receptors (GPCRs) for noxious chemicals, T2Rs, which upon stimulation trigger swallow and cough-like expulsive reflexes in the hypopharynx and larynx, respectively. These reflexes were abolished by Calhm3 and Pou2f3 knockout and could be triggered by targeted optogenetic stimulation. Furthermore, aeroallergen exposure augmented CALHM3-dependent expulsive reflex. This study identifies Pou2f3+ epithelial cells with channel synapses as chemosensory end organs of airway protective reflexes and sites of their hyperresponsiveness, advancing mechanistic understanding of airway defense programs with distinct therapeutic potential.

Cough Reflex Hypersensitivity as a Key Treatable Trait

Cough reflex hypersensitivity is emerging as a key treatable trait in chronic cough and other cough-associated respiratory conditions. This review examines the neurological basis of cough, highlighting the complex interplay between peripheral and central mechanisms. The concept of cough hypersensitivity aims to address unmet clinical needs by recognizing chronic cough as a distinct disorder rather than merely a symptom. Evidence from clinical trials supports cough hypersensitivity as a treatable trait in chronic cough, with opiates, gabapentinoids, and novel P2X3 antagonists showing efficacy. Cough hypersensitivity is also relevant in conditions presenting with persistent cough, such as asthma, bronchiectasis, and idiopathic pulmonary fibrosis, though more research is needed. Recognizing cough reflex hypersensitivity as a treatable trait offers new avenues for management, particularly for patients with persistent cough despite etiology-targeted therapies. We propose redefining chronic cough as a distinct disease entity in which cough hypersensitivity is a common feature and key therapeutic target, potentially leading to better patient care and the development of novel therapies.

The Clinical Approach to Chronic Cough

Chronic cough remains a significant clinical challenge, affecting approximately 10% of the population and leading to significant impairment in psychological, social, and physical quality of life. In recent years, efforts have intensified to elucidate the mechanisms underlying chronic cough and to focus on investigating and treating refractory chronic cough (RCC). A "treatable trait" approach, which focuses on identifying and addressing the specific associated causes of chronic cough, has gained traction. In some patients, RCC is likely driven by a neuropathic mechanism due to dysregulation of the neuronal pathways involved in the cough reflex, often clinically described as cough hypersensitivity syndrome. Although the initial treatment of underlying conditions remains central to managing treatable traits, the therapeutic options for RCC have expanded to include targeting cough hypersensitivity. First-line treatments now include neuromodulators and speech therapy with one P2X3 receptor antagonist (gefapixant) recently licensed in the European Union, United Kingdom, and Japan. Despite these advances, patient responses remain variable, underscoring the ongoing need for research into the pathophysiology and treatment of RCC. This article reviews current investigations and management options in treating chronic cough and RCC.

Reframing Refractory Chronic Cough: The Role of Interoception

Refractory chronic cough (RCC) remains a persistent clinical challenge, often resistant to traditional treatments. Emerging evidence now positions RCC as a disorder rooted in hypersensitivity, driven primarily by central neural processes rather than external physiological causes. Central to this understanding is the concept of interoception-the brain's ability to perceive and interpret internal bodily signals. Neuroimaging research has identified abnormalities in brain regions associated with interoception and inhibitory control among RCC patients. Interestingly, RCC shares neurophysiological characteristics with other disorders like overactive bladder and urinary urge incontinence (OAB/UUI), which also involve dysregulated interoceptive and inhibitory mechanisms. Behavioral treatments for OAB/UUI are highly effective and are regarded as the first-line treatment in many consensus guidelines. OAB/UUI behavioral treatments have been shown to induce central neuroplastic changes, further underscoring their efficacy and potential parallel for RCC interventions. Behavioral cough suppression therapy (BCST), an efficacious treatment for RCC, may leverage similar neuroplastic adaptations, enhancing interoceptive processing and inhibitory control. Given the multi-dimensional nature of interoception, which encompasses sensory perception shaped by learning, memory, and emotional context, BCST's engagement of multiple neural pathways offers an alternative therapeutic option compared to single-mechanism pharmacological treatments. Future research should prioritize exploring the mechanistic underpinnings of BCST and other interoception-based therapies for developing more comprehensive and effective treatment options. Such research holds promise for improving patient outcomes, alleviating the significant healthcare burden associated with RCC, and advancing our understanding of central hypersensitivity disorders.

Refractory Chronic Cough: A State-of-the-Art Review for Otolaryngologists

OBJECTIVE

Patients with refractory chronic cough (RCC) are being seen in increasing numbers within otolaryngology clinics. Identifying the next steps in the evaluation and management of cough in patients who have had first-line treatment for gastroesophageal reflux, sinonasal disease, pulmonary disease, and angiotensin-converting enzyme inhibitor-related cough is paramount. This state-of-the-art review focuses on emerging treatments for RCC from an otolaryngology perspective.

DATA SOURCES

Pubmed.

REVIEW METHODS

The available literature on chronic cough, with a focus on RCC, emerging paradigms concerning pathophysiology, and evolving treatment approaches was reviewed and summarized.

CONCLUSIONS

Guided by a more detailed understanding of refractory cough physiology, a myriad of new treatment options have been developed to treat RCC. These are primarily aimed at disrupting what is thought to be a hypersensitive cough reflex, whether by a dampening of its sensory inputs or an alteration in motor activity, and are inclusive of neuromodulator treatments, superior laryngeal nerve blockade, vocal fold augmentation, botulinum toxin injection, topical capsaicin, and potentially the eventual use of P2X3 antagonists. Improved laryngopharyngeal reflux diagnosis and management, as well as the potential benefit of behavioral cough suppression therapy, are also discussed.

IMPLICATIONS FOR PRACTICE

The literature supporting each of these strategies is growing-and as more patients with RCC seek otolaryngology care, knowledge of these various approaches may improve the overall treatment of this condition.

Randomized, controlled, proof-of-concept trial of gefapixant for endometriosis-related pain

OBJECTIVE

To evaluate the P2X3 receptor antagonist, gefapixant, for treating moderate-to-severe endometriosis-related pain.

DESIGN

Randomized, double-blind, phase 2, and proof-of-concept trial.

SUBJECTS

Premenopausal women age 18-49 years with moderate-to-severe endometriosis-related pain who were not using hormonal treatment.

INTERVENTION(S)

Gefapixant (45-mg twice daily) or placebo over two menstrual cycles.

MAIN OUTCOME MEASURE(S)

Participants rated peak pelvic pain severity daily on a 0 (no pain) - 10 (extremely severe pain) scale. The primary endpoint was change from baseline in average daily peak pelvic pain severity during treatment cycle 2.

RESULT(S)

All 187 participants randomized (gefapixant, N = 94; placebo, N = 93) took ≥1 dose of investigational treatment and all but six in each treatment group completed the trial. The model-based least-squares mean reduction from baseline in average daily peak pelvic pain severity during treatment cycle 2 was -2.2 for gefapixant and -1.7 for placebo (difference, -0.5; 95% confidence interval, -1.01 to 0.03). In secondary analyses, the difference between gefapixant and placebo in peak pelvic pain severity reduction from baseline on menstrual days was -0.6 (95% confidence interval, -1.18 to -0.06) and -0.5 (95% confidence interval, -1.04 to 0.03) on nonmenstrual days. Taste-related adverse events were reported in 31.9% of participants for gefapixant vs. 4.3% for placebo. Pharmacokinetic assessments at months 1 and 2 clinic visits indicated that of the 94 participants in the gefapixant group, 39 had detectable levels of gefapixant in the blood for both assessments although 38 had no detectable levels for ≥1 assessment.

CONCLUSION(S)

Gefapixant (45-mg twice daily) was not shown to be superior to placebo in reducing endometriosis-related pain, although the results directionally favored gefapixant. This trial result should be considered inconclusive given possible issues with treatment compliance.

CLINICAL TRIAL REGISTRATION NUMBER

NCT03654326.

20S-Ginsenoside Rh2, the major bioactive saponin in Panax notoginseng flowers, ameliorates cough by inhibition of NaV1.7 and TRPV1 channel currents and downregulation of TRPV1 expression

ETHNOPHARMACOLOGICAL RELEVANCE

Panax notoginseng flowers, which are the buds of the traditional Chinese medicinal herb Sanqi, are widely used in China for their cough-ameliorating properties, with demonstrated therapeutic effects in the treatment of both acute and chronic coughs. However, both the antitussive mechanism and active compound basis of P. notoginseng flowers remain poorly understood.

AIM OF THE STUDY

We investigated the antitussive effects of P. notoginseng flowers, identified the bioactive constituents responsible for alleviating cough symptoms, and elucidated the underlying pharmacological mechanisms.

MATERIALS AND METHODS

We analyzed the major chemical constituents of aqueous extracts of P. notoginseng flowers using liquid chromatography-mass spectrometry and quantitatively analyzed the key component, 20S-ginsenoside Rh2, using high-performance liquid chromatography. Using a cough reflex model in healthy mice and an ovalbumin-induced, highly sensitive guinea pig cough model, we verified the suppressive effects of P. notoginseng flowers and their saponin constituents on coughing. Furthermore, we explored the mechanisms of action of the key ion channels, NaV1.7 and TRPV1, using whole-cell patch-clamp techniques and molecular docking. Finally, the therapeutic mechanisms of P. notoginseng flowers on pathological cough were revealed using hematoxylin and eosin staining, immunohistochemistry, and western blotting.

RESULTS

The active components of P. notoginseng flowers were primarily protopanaxadiol-type saponins, among which 20S-ginsenoside Rh2 had the highest content (51.46 mg/g). In the mouse model, P. notoginseng flowers exhibited antitussive effects comparable to those of pentoxyverine citrate. Although its main saponin component, 20S-ginsenoside Rh2, showed slightly weaker effects, it still demonstrated concentration-dependent inhibition of channel activity. The whole-cell patch-clamp technique and virtual molecular docking showed that Rh2 might exert its effects by directly binding to the NaV1.7 and TRPV1 channels. In the guinea pig model, P. notoginseng flowers and their saponin components not only reduced cough frequency and prolonged the latency period before cough onset, but also significantly inhibited tracheal and pulmonary inflammation and the overexpression of TRPV1.

CONCLUSIONS

20S-Ginsenoside Rh2, the major bioactive saponin in P. notoginseng flowers, exhibits potent antitussive effects. The potential mechanism of action of 20S-Ginsenoside Rh2 in the treatment of cough may involve inhibiting NaV1.7 and TRPV1 channel currents through direct binding to core protein active sites and downregulating TRPV1 expression.

Gefapixant as a P2X3 receptor antagonist treatment for obstructive sleep apnea: a randomized controlled trial

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is a highly prevalent disorder with serious health consequences but limited therapeutic options. For a subset of those with OSA, a key underlying mechanism is hypersensitive chemoreflex control of breathing. There is no approved therapy that targets this endotypic trait. Here we determine whether the P2X3 receptor antagonist gefapixant, which is predicted to attenuate hypersensitive carotid chemoreflexes, reduces OSA severity in patients with chemoreflex-dependent OSA.

METHODS

In a randomized placebo-controlled crossover study, 24 patients with moderate-to-severe OSA (aged 39-68 years, non-continuous positive airway pressure users) whose disorder was partially responsive to supplemental oxygen (chemoreflex-dependent OSA) were treated with gefapixant 180 mg (or placebo) administered as tablets taken orally before bedtime for 7 days and assessed via overnight polysomnography. The primary analysis examined whether gefapixant treatment resulted in a greater reduction in the apnea-hypopnea index from baseline than placebo.

RESULTS

Gefapixant did not lower the apnea-hypopnea index significantly more than placebo; the estimated ratio of the apnea-hypopnea index on gefapixant vs placebo was 0.92 (90% confidence interval: 0.73, 1.17). Notably, nocturnal hypoxemia was increased (ratio of total sleep time with saturated peripheral oxygen < 90% on gefapixant vs placebo = 2.08 [90% confidence interval: 1.53, 2.82]), consistent with reduced chemoreflex output. Commonly reported adverse events with gefapixant included ageusia, dysgeusia, oral hypoaesthesia, nausea, somnolence, and taste disorders.

CONCLUSIONS

Gefapixant, while generally well tolerated, did not reduce OSA severity in patients with chemoreflex-dependent OSA. P2X3 receptor antagonism is unlikely to provide an avenue for therapeutic intervention in OSA.

CLINICAL TRIAL REGISTRATION

Registry: ClinicalTrials.gov; Name: Safety and Tolerability of Gefapixant (MK-7264) in Participants with Obstructive Sleep Apnea (MK-7264-039); URL: https://clinicaltrials.gov/study/NCT03882801; Identifier: NCT03882801.

CITATION

Robbins JA, Sands S, Maganti L, et al. Gefapixant as a P2X3 receptor antagonist treatment for obstructive sleep apnea: a randomized controlled trial. J Clin Sleep Med. 2024;20(12):1905-1913.

Benefit-Risk Profile of P2X3 Receptor Antagonists for Treatment of Chronic Cough: Dose-Response Model-Based Network Meta-Analysis

BACKGROUND

Refractory or unexplained chronic cough disrupts quality of life and burdens health care systems around the world. The P2X3 receptor antagonist gefapixant is approved in many countries for its antitussive effects, but taste disturbances are a common adverse effect. Four newer, more selective P2X3 receptor antagonists have been developed to address this problem.

RESEARCH QUESTION

How does the benefit-risk profile vary across the five available P2X3 receptor antagonists?

STUDY DESIGN AND METHODS

A systematic review and network meta-analysis was conducted to evaluate the efficacy of P2X3 receptor antagonists, including gefapixant, sivopixant, eliapixant, camlipixant, and filapixant. Primary outcomes were a reduction rate in 24-hour cough frequency and incidence of taste disturbance. Dose-response curves and median effective dose (ED50) were calculated. Effect size at ED50 was ranked according to the surface under the cumulative ranking curve. The confidence was evaluated by Confidence In Network Meta-Analysis.

RESULTS

Sixteen randomized controlled trials involving 4,904 participants were analyzed. The gefapixant regimen demonstrated an ED50 of 90.7 mg/d for cough frequency reduction. Gefapixant showed the highest antitussive effectiveness at ED50 (reduction rate in 24-hour cough frequency: median, 28.1%; 95% credible interval [CrI], 21.0%-35.6%; ranked 1 of 5; moderate certainty) but the highest prevalence of taste disturbance (absolute risk difference per 100 patients: median, 38; 95% CrI, 27-51; ranked 5 of 5; high certainty) and the highest prevalence of discontinuation. Camlipixant had a well-balanced profile (reduction rate in 24-hour cough frequency: median, 14.7%; 95% CrI, 5.4%-26.0%; ranked 3 of 5; low certainty; and taste disturbance; absolute risk difference per 100 patients; median, 2; 95% CrI, 1-6; ranked 2 of 5; low certainty). Placebo had a mean of 33.1% reduction in 24-hour cough frequency.

INTERPRETATION

When used at safe doses, gefapixant had a favorable risk-benefit profile compared with the other four agents. Camlipixant showed initial promise, which may be further investigated by phase III trials currently underway.

CLINICAL TRIAL REGISTRATION

University Hospital Medical Information Network Center (UMIN-CTR); No. UMIN000050622; URL: https://center6.umin.ac.jp.

Cough severity visual analog scale scores and quality of life in patients with refractory or unexplained chronic cough

BACKGROUND

Refractory chronic cough (RCC) and unexplained chronic cough (UCC) adversely affect patients' quality of life (QoL). This multicenter, non-interventional study evaluates the relationship between cough severity and QoL and other patient-reported outcomes (PROs) in Spanish outpatients.

METHODS

RCC/UCC patients self-administered a printed survey comprising the cough-severity visual analog scale (VAS), adapted Cough Severity Diary (CSD), and Leicester Cough Questionnaire (LCQ), plus purpose-designed items regarding the physical and everyday-life impact of cough. Patients were stratified into VAS score tertiles. The impact of cough on QoL and other PROs in each tertile, and relationships between LCQ scores and the tertiles, were assessed.

RESULTS

The VAS was completed by 189 patients, and VAS score tertiles were identified as 0-50, 60-70, and 80-100 mm. The only between-tertile difference in demographic or cough characteristics was cough duration. VAS score tertiles were linearly associated with mean LCQ domain and total scores, as well as the proportion of patients with the highest scores on all adapted CSD items, and almost all physical and everyday-life impact items. In multiple linear-regression models, an increase of one tertile in the VAS score was associated with a decrease of 2.23 points in the LCQ total score, indicating poorer cough-related QoL.

CONCLUSION

As self-assessed in patients with RCC/UCC, cough-severity VAS scores were strongly associated with the impact of cough on QoL and everyday life. Patients with VAS scores of 60-100 mm reported the greatest impact and thus may benefit the most from targeted cough therapies.

Productive cough, a forgotten phenotype of refractory chronic cough

BACKGROUND

Refractory chronic cough (RCC) patients typically complain of a dry cough. Sputum production in these patients has rarely been described in the literature. However, sputum production in RCC may be common, troublesome and particularly challenging to manage.

AIMS

We aimed to characterise patients referred to our regional specialist cough clinic who have significant sputum production (≥1 teaspoon of sputum daily) and compare their demographics, symptomatology and investigation results to those presenting with a dry RCC.

METHODS

A retrospective case note analysis of all consecutive referrals to a tertiary cough clinic identified as having a productive cough (≥1 teaspoon of sputum daily) was performed over a 12-month period. They were compared to a paired number of patients with dry RCC.

RESULTS

Patients with productive cough represented nearly a quarter (98/398, 24.6 %) of new patient referrals to the clinic. Demographic information, symptomatology and investigation results were comparable to those with a dry RCC. Over a third, 35.8 % of patients with a productive cough reported expectorating an egg-cupful of sputum or more a day. Nearly half, 40% of those with high volume sputum production (≥egg-cupful daily) had both a normal CT thorax and normal spirometry.

CONCLUSIONS

Patients with RCC can expectorate significant volumes of sputum in the absence of underlying lung disease. This group have similar demographics to those with dry RCC. This is the first piece of work to our knowledge to describe this cohort. Future work needs to acknowledge this forgotten phenotype to ensure that they receive comprehensive evaluation and evidenced based treatment.

The discovery and development of gefapixant as a novel antitussive therapy

INTRODUCTION

Gefapixant, a P2X 3 receptor antagonist, shows considerable potential in managing refractory or unexplained chronic cough. Clinical trials have consistently demonstrated its efficacy in significantly reducing cough frequency and alleviating associated symptoms. However, its adverse effect profile, particularly taste disturbances such as dysgeusia and hypogeusia, the incidence of which is dose-dependent, poses a significant challenge to patient compliance and overall treatment satisfaction.

AREAS COVERED

The authors review the mechanism of action of gefapixant, the dose-dependent nature of its adverse effects and the findings from various clinical trials, including Phase 1, Phase 2, and Phase 3 studies. The authors also cover its regulatory status, post-marketing data, and its main competitors.

EXPERT OPINION

Gefapixant represents a significant advancement in treating chronic cough. However, balancing efficacy and tolerability is crucial. Lower effective doses and potential combination therapies may mitigate taste disturbances. Patient education and close monitoring during treatment are also important for optimal outcomes. Further research is needed to refine dosing strategies to minimize side effects while maintaining therapeutic efficacy. This research and personalized treatment approaches are key to optimizing gefapixant therapy, ensuring improved management of chronic cough while reducing adverse effects. However, pharmaceutical trials and proposals must be adapted to align with each regulatory body's specific requirements and concerns.

Release of ATP in the lung evoked by inhalation of irritant gases in rats

Adenosine triphosphate (ATP) can be released into the extracellular milieu from various types of cells in response to a wide range of physical or chemical stresses. In the respiratory tract, extracellular ATP is recognized as an important signal molecule and trigger of airway inflammation. Chlorine (Cl2), sulfur dioxide (SO2), and ammonia (NH3) are potent irritant gases and common industrial air pollutants due to their widespread uses as chemical agents. This study was carried out to determine if acute inhalation challenges of these irritant gases, at the concentration and duration simulating the accidental exposures to these chemical gases in industrial operations, triggered the release of ATP in the rat respiratory tract; and if so, whether the level of ATP in bronchoalveolar lavage fluid (BALF) evoked by inhalation challenge of a given irritant gas was elevated by chronic allergic airway inflammation. Our results showed: 1) inhalation of these irritant gases caused significant increases in the ATP level in BALF, and the magnitude of evoked ATP release was in the order of Cl2 > SO2 > NH3. 2) Chronic airway inflammation induced by ovalbumin-sensitization markedly elevated the ATP level in BALF during baseline (breathing room air) but did not potentiate the release of ATP in the lung triggered by inhalation challenges of these irritant gases. These findings suggested a possible involvement of the ATP release in the lung in the regulation of overall airway responses to acute inhalation of irritant gases and the pathogenesis of chronic allergic airway inflammation.NEW & NOTEWORTHY Extracellular adenosine triphosphate (ATP) is a contributing factor and signaling molecule of airway inflammation. This study demonstrated for the first time that the ATP release in the lung was markedly elevated after acute inhalation challenges of three common industrial air pollutants; the order of the response magnitude was chlorine > sulfur dioxide > ammonia. These findings provided new information and improved our understanding of the adverse pulmonary effects caused by accidental inhalation exposures to these irritant gases.

What causes cough in pulmonary fibrosis, and how should we treat it?

PURPOSE OF REVIEW

To review the current understanding of the impact, mechanisms and treatments for cough in patients with interstitial lung disease (ILD). Evidence suggests that cough is a prevalent symptom in patients with ILD and has a significant impact on patients.

RECENT FINDINGS

There is increasing interest in the role of cough hypersensitivity as seen in chronic refractory cough in patients with ILD, and encouraging recent results suggest that ILD-associated cough responds to opiate therapy.

SUMMARY

Understanding the aetiology of cough in patients with ILD is crucial to continue to develop therapies which might be effective in reducing cough and increasing quality of life.

Decoding the impact of the placebo response in clinical trials for chronic cough

Chronic cough is a prevalent and challenging condition, with limited treatment options available. The interpretation of clinical trial results for antitussive drugs is complicated by the presence of the placebo response, which can confound outcomes and impede regulatory approval. This review aims to explore the impact of the placebo response on clinical trials for cough medications and elucidate the underlying mechanisms involved. The multifaceted nature of antitussive effects, including pharmacological, psychological/neurobiological and nonspecific effects, is discussed. Additionally, potential solutions to address the placebo response in future cough medication development, such as strategic study design, appropriate choice of end-points and meticulous patient selection, are proposed. More progress to harness this issue is urgently needed.

Single- and Multiple-Dose Pharmacokinetics of Gefapixant (MK-7264), a P2X3 Receptor Antagonist, in Healthy Adults

Gefapixant (MK-7264, RO4926219, AF-219) is a first-in-class P2X3 antagonists being developed to treat refractory or unexplained chronic cough. The initial single- and multiple-dose safety, tolerability, and pharmacokinetics of gefapixant at doses ranging from 7.5 to 1800 mg were assessed in four clinical trials. Following single-dose administration of 10-450 mg, the pharmacokinetic (PK) profile of gefapixant in plasma and urine demonstrated low inter-subject variability and a dose-proportional exposure. Following administration of multiple doses twice daily, the plasma exposures were dose-proportional at doses ranging from 7.5 to 50 mg and less than dose-proportional at doses ranging from 100 to 1800 mg. The time to mean peak drug concentration ranged from 2 to 3 h post-dose, and steady state was achieved by 7 days after dosing, with an accumulation ratio of approximately 2, comparing data from day 1 to steady state. The mean apparent terminal half-life ranged from 8.2 to 9.6 h. Gefapixant was primarily excreted unmodified in urine. Gefapixant was well tolerated following single-dose administration up to 1800 mg and multiple doses up to 1800 mg twice daily; there were no serious adverse events (AEs) reported. The most common AE reported was dysgeusia. The PK profile supports a twice-daily dosing regimen.

Drugs Targeting Cough Receptors: New Therapeutic Options in Refractory or Unexplained Chronic Cough

Refractory chronic cough is a disabling disease with very limited therapeutic options. A better understanding of cough pathophysiology has led to the development of emerging drugs targeting cough receptors. Recent strides have illuminated novel therapeutic avenues, notably centred on modulating transient receptor potential (TRP) channels, purinergic receptors, and neurokinin receptors. By modulating these receptors, the goal is to intervene in the sensory pathways that trigger cough reflexes, thereby providing relief without compromising vital protective mechanisms. These innovative pharmacotherapies hold promise for improvement of refractory chronic cough by offering improved efficacy and potentially mitigating adverse effects associated with current recommended treatments. A deeper comprehension of their precise mechanisms of action and clinical viability is imperative for optimising therapeutic interventions and elevating patient care standards in respiratory health. This review delineates the evolving landscape of drug development in this domain, emphasising the significance of these advancements in reshaping the paradigm of cough management.

Development of an Italian version of the Leicester cough questionnaire and its relationship with other symptom-specific measures for patients with chronic cough

OBJECTIVE

To implement subjective methods for measuring the impact of chronic cough on patients' daily life, including an Italian version of the symptom-specific, health status measure for patients with chronic cough, i.e. the Leicester Cough Questionnaire (LCQ).

METHODS

Sixty-five chronic cough patients attended a tertiary cough clinic on two separate occasions 8 weeks apart. The visual analogue scale for cough severity (VAS), the LCQ and the cough disturbance score (CDS) were administered on both occasions. The LCQ was adapted for Italian conditions following a forward-backward translation procedure. Concurrent validation, internal consistency, repeatability and responsiveness were determined.

RESULTS

The CDS, VAS and LCQ were correlated (r coefficients ranging from 0.69 to 0.94, p < 0.01). The internal consistency for each LCQ domain was high (alpha coefficient range 0.87-0.93), as was the 8-week repeatability of the LCQ in the patients (n = 36, 60 %) who displayed no change in CDS and VAS (intra-class correlation coefficient = 0.86, p < 001) over the same period. Patients who reported an improvement in CDS and VAS after 8 weeks (n = 29) also demonstrated significant improvements in each LCQ domain. The mean difference in LCQ total score before and after improvements was 2.26 (95 % CI: 1.58-4.47).

CONCLUSIONS

The Italian version of the LCQ appears to be just as valid as the other language versions of the questionnaire. In addition, the CDS appears to be a clinically useful, symptom-specific measure of the overall disturbance provoked by cough.

P2X3 Receptor Antagonist Eliapixant in Phase I Clinical Trials: Safety and Inter-ethnic Comparison of Pharmacokinetics in Healthy Chinese and Japanese Participants

BACKGROUND

Afferent neuronal hypersensitization via P2X3 receptor signaling has been implicated as a driver of several disorders, including refractory chronic cough, endometriosis, diabetic neuropathic pain, and overactive bladder. Eliapixant, a selective P2X3 receptor antagonist, has been in clinical development for all four disorders.

OBJECTIVE

This paper describes pharmacokinetic (PK) and safety data from two phase I studies of eliapixant in healthy Japanese and Chinese participants and compares those data within the two populations and with previous multiple dose data from Caucasian participants.

METHODS

Two separate phase I, single-center, randomized, placebo-controlled studies were conducted with healthy male participants. The Japanese study was single-blind and the Chinese study was double-blind. Eliapixant was administered as an oral amorphous solid dispersion immediate-release tablet in strengths of 25 mg, 75 mg, and 150 mg. PK characteristics after a single dose (SD) and at steady state (multiple dose [MD], twice daily), adverse events (AEs), and tolerability were evaluated. A post hoc comparison of PK characteristics after SD of eliapixant in Japanese and Chinese participants, and after MD of eliapixant in Japanese, Chinese, and Caucasian participants, was performed.

RESULTS

Overall, 36/39 participants enrolled in the Japanese/Chinese studies, respectively (mean [standard deviation] age 25.4 [6.5] and 26.7 [5.0] years, respectively). After SD administration, maximum plasma concentration (Cmax) was higher among Japanese than Chinese participants in the 25 mg and 75 mg dose groups, but comparable in the 150 mg dose group. The area under the concentration-time curve (AUC) was comparable between Japanese and Chinese participants in the 25 mg and 75 mg dose groups, but lower among Japanese participants in the 150 mg group. Half-lives after SD and MD administration were also comparable in Japanese and Chinese participants. The post hoc analysis included 26 Japanese, 30 Chinese, and 50 Caucasian participants. Comparable exposure (Cmax,md and AUC[0-12]md) was observed after MD administration of eliapixant in Chinese and/or Japanese compared with Caucasian participants (geometric mean inter-ethnic ratios close to 1). The trough plasma concentration after eliapixant 150 mg MD, which was assumed to be relevant to eliapixant efficacy, was comparable across all ethnicity groups. Most AEs reported in the Japanese (eliapixant 75 mg SD, n = 2; eliapixant 150 mg MD, n = 2) and Chinese participants (eliapixant 25 mg SD, n = 7; eliapixant 75 mg SD, n = 6; eliapixant 150 mg SD, n = 7; eliapixant 150 mg MD, n = 9; placebo SD, n = 5; placebo MD, n = 1) were of mild intensity. Higher incidences of AEs in the Chinese population were likely due to differing standards of AE reporting between investigators.

CONCLUSION

Eliapixant was well tolerated by Japanese and Chinese participants. The inter-ethnic evaluation demonstrated similar PK characteristics across Japanese, Chinese, and Caucasian participants.

REGISTRATION

ClinicalTrials.gov identifier numbers: NCT04265781 and NCT04802343.

The bumpy road of purinergic inhibitors to clinical application in immune-mediated diseases

ABSTRACT

Purinergic signaling plays important roles throughout the body in the regulation of organ functions during and following the disruption of homeostasis. This is also reflected by the widespread expression of two families of purinergic receptors (P1 and P2) with numerous subtypes. In the last few decades, there has been increasing evidence that purinergic signaling plays an important role in the regulation of immune functions. Mainly, signals mediated by P2 receptors have been shown to contribute to immune system-mediated pathologies. Thus, interference with P2 receptors may be a promising strategy for the modulation of immune responses. Although only a few clinical studies have been conducted in isolated entities with limited success, preclinical work suggests that the use of P2 receptor inhibitors may bear some promise in various autoimmune diseases. Despite the association of P2 receptors with several disorders from this field, the use of P2 receptor antagonists in clinical therapy is still very scarce. In this narrative review, we briefly review the involvement of the purinergic system in immunological responses and clinical studies on the effect of purinergic inhibition on autoimmune processes. We then open the aperture a bit and show some preclinical studies demonstrating a potential effect of purinergic blockade on autoimmune events. Using suramin, a non-specific purinergic inhibitor, as an example, we further show that off-target effects could be responsible for observed effects in immunological settings, which may have interesting implications. Overall, we believe that it is worthwhile to further investigate this hitherto underexplored area.

Chronic cough: more than just a persistent cough: a systematic literature review to understand the impact of chronic cough on quality of life

PURPOSE

Chronic cough (CC), defined as a cough persisting ≥ 8 weeks, can have a substantial negative impact on health-related quality of life (HRQoL). This is exacerbated by challenges with timely diagnosis and a lack of approved therapies. A systematic literature review (SLR) was conducted to identify evidence on HRQoL and health state utility values associated with refractory CC or unexplained CC.

METHODS

Electronic database searches were supplemented with searches of conference proceedings and health technology assessment body websites. Two independent reviewers assessed all citations for inclusion based on predefined inclusion/exclusion criteria. Key inclusion criteria were patient populations with CC and reporting of patient-reported outcomes or utilities using generic or disease-specific measures.

RESULTS

Following screening, 65 studies were identified for inclusion in the SLR. Of these, 23 studies assessed HRQoL among patients with CC who were not treated or treated with unspecified interventions, and 42 studies in patients who were treated with specified interventions. The studies indicated a substantial decrement to HRQoL as a result of CC, characterized by generic and disease-specific patient-reported outcome measures. HRQoL was impacted across multiple domains, including physical, psychological, and social functioning. The studies also demonstrated the potential for treatments to have a significant positive impact on HRQoL.

CONCLUSIONS

CC can substantially affect HRQoL in patients, across physical, psychological, and social domains. Although treatments can improve HRQoL in these patients, the available evidence is limited. There remains an unmet need for approved pharmacological treatments to alleviate CC and improve HRQoL for these patients.

Safety and Pharmacokinetics of HRS-2261, a P2X3 Receptor Antagonist, in Healthy Subjects: A Randomized, Double-Blind, Placebo-Controlled Phase 1 Study

BACKGROUND

P2X3 receptor antagonists hold promising potential as a therapeutic option for patients with refractory or unexplained chronic cough, a condition lacking approved therapies. This study assessed the safety, tolerability, and pharmacokinetics (PK) of HRS-2261, a novel selective P2X3 receptor antagonist, in healthy subjects.

METHODS

This randomized, double-blinded, placebo-controlled phase 1 trial of HRS-2261 consisted of three phases: the single ascending dose (SAD) study phase, the food-effect study phase, and the multiple ascending dose (MAD) study phase. In the SAD phase, healthy subjects were randomly assigned to receive a single oral dose of HRS-2261 (25, 100, 200, 400, 800, and 1200 mg) or placebo. Subjects in the 200 mg group of the SAD phase progressed directly to the food-effect phase following safety evaluation. In the MAD phase, healthy subjects were randomized to receive HRS-2261 (50, 200, and 400 mg) or placebo twice daily for 14 consecutive days. The primary endpoints were safety and tolerability.

RESULTS

A total of 62 and 30 subjects were enrolled in the SAD and MAD phases, respectively, with 12 subjects from the SAD phase transitioning to the food-effect phase. The incidence and severity of adverse events (AEs) were not dose dependent, and most AEs were mild except for one moderate AE (epididymitis, which was not related to treatment) in the 400 mg group. Dysgeusia was reported in nine subjects, including two from the SAD phase, one from the food-effect phase, and six from the MAD phase. The median Tmax and geometric mean t1/2 were 0.9-2.0 h and 4.1-8.5 h in the SAD, and 2.0-2.7 h and 4.6-5.0 h on day 14 in the MAD, respectively. Drug exposures in the SAD and MAD phases were both less than dose proportional. The accumulation of the drug was slight with repeated twice-daily dosing. Food-effect study results showed that food intake did not affect the plasma exposure of HRS-2261.

CONCLUSIONS

HRS-2261 demonstrated good tolerability, with a low incidence of dysgeusia. The PK profile was favorable. This study supports further development of HRS-2261 as a potential P2X3 receptor antagonist for chronic cough.

TRIAL REGISTRATION NUMBER

Clinical trials.gov, identifier: NCT05274516. Trial registration date: March 10, 2022.

Diagnosis and treatment of taste disorders in Japan

Though 270,000 patients with complaints of taste abnormalities visited medical institutions annually in 2019 survey, there are no drugs for the treatment of taste disorders that are covered by health insurance in Japan. In the survey, the number of patients with taste disorders was correlated with age, and the need for medical treatment for taste disorders is expected to increase in the future because of the super-aging society. The pathophysiology of taste disorders varies widely. There is an obvious need to decide the site and the causes of the disorder and understand the mechanism, by performing various examinations. It needs to first adjust the causative systemic diseases and medications in the treatment for taste disorder. Damage of taste cells due to zinc deficiency is the main pathophysiological mechanism of taste disorders, and zinc supplementation is a standard treatment in Japan. Oral zinc therapy is the treatment for taste disorders due to zinc deficiency or idiopathic taste disorder; though a double-blind study was conducted, it was considered low-level evidence in a clinical review. In Japan, the off-label use of polaprezinc for taste disorders was approved in 2011, and zinc acetate hydrate was approved for hypozincemia in March 2017, making it easier to use oral zinc therapy in general. In some cases, psychotherapy or herbal medicine therapy has been used with remarkable success, although its effectiveness has not been clearly tested. It might be expected to offer some help to patients. In the treatment of elderly patients with taste disorders, physicians need to consider the difference between "age-related changes in taste in healthy people" and "taste disorders in elderly persons", and they should separate them. Aggressive treatment is desirable regardless of age, because no significant difference in the efficacy of various treatments was found between patients older and younger than 65 years.

The Therapeutic Landscape in Chronic Cough

In recent years, there has been a substantial increase in the development of antitussive therapies and the first new therapy, gefapixant has been licenced in Europe. This review describes current unlicenced treatments for chronic cough and details treatments currently in development for refractory chronic cough and cough in idiopathic pulmonary fibrosis, as well as compounds previously explored.

Patient preferences for the treatment of chronic cough: a discrete choice experiment

BACKGROUND

Chronic cough is common, negatively affects quality of life and has limited treatment options. Inhibition of purinergic signalling is a promising therapeutic approach but is associated with taste-related adverse effects. Little is known about treatment preferences from the perspective of patients with chronic cough, such as trade-offs between efficacy and side effect.

METHODS

Patients with chronic cough completed an online discrete choice experiment survey in which they answered a series of questions requiring a choice between two constructed treatment options characterised by varying attribute levels. Selection of cough and taste-related attributes was informed by qualitative interviews and clinical trial data. Logit-based models were used to analyse resulting choice data.

RESULTS

The discrete choice experiment survey was completed by 472 participants with chronic cough. Among study attributes, frequency of intense cough attacks was the most important to participants, followed by taste change, frequency of night-time coughing and frequency of daytime coughing. To accept the least preferred taste disturbance of a bitter, metallic, chalky or oily taste change, participants required either: (1) elimination of night-time cough along with a slight reduction in daytime cough; (2) elimination of daytime cough along with a pronounced reduction in night-time or (3) reduction in intense cough attacks from 7 to 2 times per week. Two distinct preference patterns were identified, each placing different importance on efficacy versus side effect trade-offs.

CONCLUSIONS

Participants with chronic cough were willing to accept some taste disturbances in exchange for improved efficacy of chronic cough treatments. Knowledge of patient preferences can facilitate shared decision-making.

Efficacy and Safety of Eliapixant in Overactive Bladder: The 12-Week, Randomised, Placebo-controlled Phase 2a OVADER Study

BACKGROUND

Effective, well-tolerated novel treatments for overactive bladder (OAB) are lacking. The P2X3 receptor antagonist eliapixant demonstrated potential to reduce OAB symptoms in preclinical studies.

OBJECTIVE

To evaluate the safety, tolerability, and efficacy of eliapixant in patients with OAB with urgency urinary incontinence (UUI).

DESIGN, SETTING AND PARTICIPANTS

OVADER was a 12-wk, randomised, placebo-controlled, double-blind, parallel-group, multicentre, phase 2a study (NCT04545580) conducted between 2020 and 2022 in private and institutional clinical practices. Eligible patients were aged ≥18 yr with wet OAB symptoms (urgency, urinary frequency, and urinary incontinence) for ≥3 mo before screening.

INTERVENTION

Randomisation (1:1 ratio) to oral eliapixant 125 mg or placebo twice daily.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The primary endpoint was the mean change from baseline in the mean number of UUI episodes/24 h over weeks 4, 8, and 12 according to an electronic bladder diary, evaluated using a repeated-measurement model in a Bayesian framework.

RESULTS AND LIMITATIONS

Of 202 patients enrolled, 85 were valid for per-protocol analysis. The primary efficacy endpoint was not met. The posterior probability for eliapixant superiority over placebo was 40% (point estimate 0.05, 95% credible interval -∞ to 0.38), which did not meet the predefined criterion of ≥90% probability. Secondary and exploratory endpoints were not met. The incidence of adverse events was similar in the eliapixant (n = 32, 63%) and placebo (n = 27, 56%) groups; most were mild and five led to discontinuation of eliapixant.

CONCLUSIONS

OVADER did not meet its clinical efficacy endpoints. Potential reasons include the nonspecific OAB symptom complex, the poorly understood pathophysiology, and the coinciding COVID-19 pandemic.

PATIENT SUMMARY

We tested whether a new drug called eliapixant would reduce symptoms of overactive bladder in comparison to placebo. We found that the drug did not work. More knowledge on how overactive bladder occurs is needed to find new drugs to treat this condition.

Patient-reported experiences with refractory or unexplained chronic cough: a qualitative analysis

BACKGROUND

Chronic cough, defined as a cough lasting 8 or more weeks, affects up to 10% of adults. Refractory chronic cough (RCC) is a cough that is uncontrolled despite comprehensive investigation and treatment of comorbid conditions while unexplained chronic cough (UCC) is a cough with no identifiable cause despite extensive evaluation of comorbid conditions. RCC and UCC are often poorly controlled. Understanding individuals' lived experience of the symptoms and impacts of these conditions may guide therapeutic strategies.

OBJECTIVES

The primary objectives of this study were to assess respondents' perceptions of the key symptoms of RCC and UCC and the impacts of RCC and UCC and their symptoms on well-being, health-related quality of life, work productivity, and social relationships.

DESIGN

Qualitative study.

METHODS

This study enrolled 30 adults with physician-diagnosed RCC or UCC. Two trained qualitative researchers conducted individual, in-depth telephone interviews using a semi-structured interview guide. Interviews were audio-recorded, transcribed, coded, and systematically analyzed to identify content themes.

RESULTS

A total of 15 respondents with RCC and 15 with UCC were included in the study. Many respondents had RCC or UCC for a long duration (median 9 years, range: 0-24). Half of the respondents reported having a coughing episode at least once daily. Only 40% of respondents reported that medication had improved their symptoms. In over half of the respondents, RCC or UCC hindered communication, caused embarrassment, frustration, and worry, and lowered quality of life. Perceptions of meaningful treatment benefits in RCC or UCC varied widely across respondents.

CONCLUSION

RCC and UCC remained poorly managed in many individuals and were associated with a wide range of symptoms and cough triggers that hindered daily activities and reduced emotional well-being. Understanding individuals' lived experiences may inform the development of RCC and UCC therapeutic strategies.

Safety and efficacy of P2X3 receptor antagonist for the treatment of refractory or unexplained chronic cough: A systematic review and meta-analysis of 11 randomized controlled trials

BACKGROUND AND OBJECTIVES

Chronic refractory cough is a challenging condition that requires a thorough evaluation and management approach. P2X3 receptors that are ATP-dependent play an important part in nerve fiber sensitization and pathological pain pathways. We conducted this systematic review and meta-analysis to determine the long-term safety and efficacy of P2X3 receptor antagonist drugs in chronic cough.

METHODS

We systematically searched PubMed, Scopus, Web of Science, and Embase to identify all relevant published studies through January 15, 2023 that assessed P2X3 antagonists in chronic cough. The protocol was registered in the PROSPERO database with ID: CRD42023422408. Efficacy outcomes were awake (daytime) cough frequency, night cough frequency, 24-h cough frequency, Cough Severity Diary, and total Leicester Cough Questionnaire score. We used the random-effect model to pool the data using RStudio and CMA software.

RESULTS

A total of 11 randomized controlled trials comprising 1350 patients receiving a p2x3 antagonist compared to the placebo group were included in this meta-analysis. A significant decrease in 24-h cough frequency (MD = -4.99, 95% CI [-7.15 to -2.82], P < 0.01), awake (daytime) cough frequency (MD = -7.18, 95% CI [-9.98 to 4.37], P < 0.01), and total Leicester Cough Questionnaire score (MD = 1.74, 95% CI [1.02 to 2.46], P < 0.01) exhibited between the P2X3 antagonist and placebo groups. The frequency of the night cough showed an insignificant difference between the two groups. According to the safety, drug-related adverse events, dysgeusia, hypogeusia, and ageusia significantly increased between the P2X3 antagonist and placebo groups.

CONCLUSION

P2X3 receptor antagonists are promising drugs for treating chronic cough by significantly reducing the frequency, severity, and quality. Some potential side effects may include drug-related adverse events such as hypogeusia, ageusia, and dysgeusia.

Illuminating Airway Nerve Structure and Function in Chronic Cough

Airway nerves regulate vital airway functions including bronchoconstriction, cough, and control of respiration. Dysregulation of airway nerves underlies the development and manifestations of airway diseases such as chronic cough, where sensitization of neural pathways leads to excessive cough triggering. Nerves are heterogeneous in both expression and function. Recent advances in confocal imaging and in targeted genetic manipulation of airway nerves have expanded our ability to visualize neural organization, study neuro-immune interactions, and selectively modulate nerve activation. As a result, we have an unprecedented ability to quantitatively assess neural remodeling and its role in the development of airway disease. This review highlights our existing understanding of neural heterogeneity and how advances in methodology have illuminated airway nerve morphology and function in health and disease.

Burden of chronic cough on social participation, healthcare resource utilisation and activities of daily living in the Canadian Longitudinal Study on Aging (CLSA)

BACKGROUND

Chronic cough is a common troublesome condition, but it is unclear whether dry or productive chronic cough and sex, impacts the burden of cough differently.

METHODS

The Canadian Longitudinal Study on Aging is a nationally generalizable, stratified random sample of adults aged 45-85 years. Chronic cough was identified based on a self-reported daily cough in the last 12 months assessed at baseline (2011-2015) and follow-up (2015-2018). Odds ratios (95 % CI) for cough status and change in social participation activities (SPA), healthcare resource utilisation (HCRU), basic activities of daily living (ADLs) and instrumental activities of daily living (IADLs) were estimated using a weighted generalised estimating equation (WGEE). Results were stratified by sex, and adjusted for age, sex, smoking, body mass index, education, respiratory diseases and retirement status.

RESULTS

Overall, chronic cough was associated with less SPA, greater HCRU and impaired ADL/IADLs. Productive chronic cough in males was associated with SPA limited by health, ED visits and hospitalisation. Females with productive chronic cough was associated with reduced frequency of SPA and ED visit. Dry chronic cough in females was associated with SPA limited by health and ED visits. Both types of cough was associated with at least 1 impaired basic ADL, but only in females with productive chronic cough was there an association with any impairment in IADLs.

CONCLUSION

Chronic cough is associated with a greater burden on social participation, healthcare use and personal care.

Efficacy and Tolerability of Gefapixant for Treatment of Refractory or Unexplained Chronic Cough: A Systematic Review and Dose-Response Meta-Analysis

Importance

Gefapixant represents an emerging therapy for patients with refractory or unexplained chronic cough.

Objective

To evaluate the efficacy and tolerability of gefapixant for the treatment of adults with refractory or unexplained chronic cough.

Data Sources

MEDLINE, Embase, Cochrane Central Register of Controlled Trials, and Web of Science from November 2014 to July 2023.

Study Selection

Two reviewers independently screened for parallel and crossover randomized clinical trials (RCTs) that compared, in patients with refractory or unexplained chronic cough, either gefapixant with placebo, or 2 or more doses of gefapixant with or without placebo.

Data Extraction and Synthesis

Two reviewers independently extracted data. A frequentist random-effects dose-response meta-analysis or pairwise meta-analysis was used for each outcome. The GRADE (Grading of Recommendations, Assessment, Development, and Evaluation) approach was used to rate the certainty in whether patients would perceive the effects as important (greater than the minimal important difference [MID]) or small (less than the MID).

Main Outcomes and Measures

Cough frequency (measured using the VitaloJAK cough monitor; MID, 20%), cough severity (measured using the 100-mm visual analog scale [VAS]; higher score is worse; MID, 30 mm), cough-specific quality of life (measured using the Leicester Cough Questionnaire [LCQ]; score range, 3 [maximal impairment] to 21 [no impairment]; MID, 1.3 points), treatment-related adverse events, adverse events leading to discontinuation, and taste-related adverse events.

Results

Nine RCTs including 2980 patients were included in the primary analysis. Compared with placebo, gefapixant (45 mg twice daily) had small effects on awake cough frequency (17.6% reduction [95% CI, 10.6%-24.0%], moderate certainty), cough severity on the 100-mm VAS (mean difference, -6.2 mm [95% CI, -4.1 to -8.4]; high certainty), and cough-specific quality of life on the LCQ (mean difference, 1.0 points [95% CI, 0.7-1.4]; moderate certainty). Compared with placebo, gefapixant (45 mg twice daily) probably caused an important increase in treatment-related adverse events (32 more per 100 patients [95% CI, 13-64 more], moderate certainty) and taste-related adverse events (32 more per 100 patients [95% CI, 22-46 more], high certainty). High-certainty evidence suggests that gefapixant (15 mg twice daily) had small effects on taste-related adverse events (6 more per 100 patients [95% CI, 5-8 more]).

Conclusions and Relevance

Compared with placebo, gefapixant (45 mg orally twice daily) led to modest improvements in cough frequency, cough severity, and cough-specific quality of life but increased taste-related adverse events.

Potential applications of P2X3 receptor antagonists in the treatment of refractory cough

Refractory chronic cough is defined as a clinical condition in which the cause of the cough remains unclear after comprehensive examination and treatment, or the cause is clear but symptomatic treatment is ineffective. Patients with refractory chronic cough experience a variety of physiological and psychological issues that significantly lower their quality of life and place a significant socio-economic burden on society. As a result, research both domestically and internationally has turned heavily toward these patients. Recently, several studies have identified P2X3 receptor antagonists for the treatment of refractory chronic cough, and this paper reviews the background, mechanism of action, evidence-based proof and application prospects of this class of drugs. KEY MESSAGE: There were plenty of studies about P2X3 receptor antagonists in the past, and in recent years this series of drugs are effective in refractory chronic cough. Although review articles summarizing have been published previously, most have focused on their chemical properties rather than their clinical aspects, with some omitting drugs that have been in clinical studies for nearly two years such as Eliapixant and Sivopixant. Focusing on four P2X3 receptor antagonists with proven efficacy in clinical studies, we analyzed the characteristics and disadvantages of each drug by comparing their clinical results of them and theoretically explained the common side effects of these drugs, as well as their potential for treating refractory chronic cough. This article can be used as a reference for the follow-up studies of P2X3 receptor antagonists in chronic cough. Additionally, it also has implications for the clinical focus of the drug and the approaches to relieve some side effects.

Chronic cough relief by allosteric modulation of P2X3 without taste disturbance

P2X receptors are cation channels that sense extracellular ATP. Many therapeutic candidates targeting P2X receptors have begun clinical trials or acquired approval for the treatment of refractory chronic cough (RCC) and other disorders. However, the present negative allosteric modulation of P2X receptors is primarily limited to the central pocket or the site below the left flipper domain. Here, we uncover a mechanism of allosteric regulation of P2X3 in the inner pocket of the head domain (IP-HD), and show that the antitussive effects of quercetin and PSFL2915 (our nM-affinity P2X3 inhibitor optimized based on quercetin) on male mice and guinea pigs were achieved by preventing allosteric changes of IP-HD in P2X3. While being therapeutically comparable to the newly licensed P2X3 RCC drug gefapixant, quercetin and PSFL2915 do not have an adverse effect on taste as gefapixant does. Thus, allosteric modulation of P2X3 via IP-HD may be a druggable strategy to alleviate RCC.

Burden of refractory and unexplained chronic cough on patients' lives: a cohort study

Background

Chronic cough (cough lasting for ≥8 weeks) can lead to significant impairment in quality of life (QoL). Using patient-reported outcomes, this cohort study assessed the perceived impact of chronic cough on QoL and everyday life in patients from outpatient hospital clinics with refractory chronic cough (RCC) or unexplained chronic cough (UCC).

Methods

This was a multicentre, non-interventional survey study. Cough severity was assessed on a 0-100 mm Visual Analogue Scale (VAS). Frequency, intensity and disruptiveness of cough were assessed using an adaptation of the Cough Severity Diary. The impact of cough on QoL was assessed using the Leicester Cough Questionnaire (LCQ). The physical impact of cough and associated impact on everyday life activities were explored using purpose-designed questions.

Results

191 patients responded to the survey; 121 (63.4%) had RCC and 149 were women (78.0%). Mean score on the cough severity VAS was 62.9 mm. Mean LCQ total score of 11.9 indicated reduced QoL. Cough impaired patients' everyday life, including the inability to speak fluently (58.0% of patients) and feeling tired/drained (46.6%). Women perceived poorer chronic cough-related QoL than men, as reflected by lower LCQ scores, and greater impairment of physical health, including cough-related stress urinary incontinence, and psychological health.

Conclusions

Patients with RCC/UCC experience a significant burden in their everyday life, including impaired QoL, and perceive a negative impact on physical and psychological health and everyday activities, affecting work, relationships and leisure activities. The impact appears to be greater in women than men for several of the aspects studied.

Efficacy and safety of pharmacotherapy for refractory or unexplained chronic cough: a systematic review and network meta-analysis

Background

Refractory chronic cough (RCC) has a significant impact on patient's health-related quality of life and represents a challenge in clinical management. However, the optimal treatment for RCC remains controversial. This study aimed to investigate and compare the efficacy and safety of the current pharmacological therapeutic options for RCC.

Methods

A systematic review was performed by searching PubMed, Web of Science, Embase, and Ovid databases from January 1, 2008 to March 1, 2023. All randomised control trials (RCTs) reporting outcomes of efficacy or/and safety were included in the Bayesian network meta-analysis. Here, we compared the effects on Leicester Cough Questionnaire (LCQ), Visual Analogue Scale (VAS), and objective cough frequency of patients with RCC. Besides, we also compared the incidence of adverse events (AEs) for analysis of safety. PROSPERO registration: CRD42022345940.

Findings

19 eligible RCTs included 3326 patients and 7 medication categories: P2X3 antagonist, GABA modulator, Transient Receptor Potential (TRP) modulator, NK-1 agonist, opioid analgesic, macrolide, and sodium cromoglicate. Compared with placebo, mean difference (MD) of LCQ and 24 h cough frequency for P2X3 antagonist relief were 1.637 (95% CI: 0.887-2.387) and -11.042 (P = 0.035). Compared with placebo, effect sizes (MD for LCQ and cough severity VAS) for GABA modulator were 1.347 (P = 0.003) and -7.843 (P = 0.003). In the network meta-analysis, gefapixant is the most effective treatment for patients with RCC (The Surface Under the Cumulative Ranking Curves (SUCRA) is 0.711 in LCQ, 0.983 in 24 h cough frequency, and 0.786 in cough severity VAS). Lesogaberan had better efficacy than placebo (SUCRA: 0.632 vs. 0.472) in 24 h cough frequency. Eliapixant and lesogaberan had better efficacy than placebo in cough severity VAS. However, TRP modulator had worse efficacy than placebo. In the meta-analysis of AEs, the present study found P2X3 antagonist had a significant correlation to AEs (RR: 1.129, 95% CI: 1.012-1.259), especially taste-related AEs (RR: 6.216, P < 0.05).

Interpretation

In this network meta-analysis, P2X3 antagonist showing advantages in terms of efficacy is currently the most promising medication for treatment of RCC. GABA modulator also showed potential efficacy for RCC but with AEs of the central system. Nevertheless, the role of TRP modulator needed to be revisited. Further research is needed to determine the potential beneficiary population for optimizing the pharmacological management of chronic cough.

Funding

National Natural Science Foundation of China (81870079), Guangdong Science and Technology Project (2021A050520012), Incubation Program of National Science Foundation for Distinguished Young Scholars (GMU2020-207).

From bench to bedside: The role of cough hypersensitivity in chronic cough

BACKGROUND

Chronic cough is a burdensome condition characterized by persistent cough lasting longer than 8 weeks. Chronic cough can significantly affect quality of life, physical function and productivity, with many people troubled with a cough that lasts for months or even years. People with chronic cough commonly report a persistent urge to cough with frequent bouts of coughing triggered by innocuous stimuli, which has led to the concept of cough hypersensitivity.

MAIN BODY

Both central and peripheral neural pathways regulate cough, and although mechanisms driving development of cough hypersensitivity are not fully known, sensitization of these neural pathways contributes to excessive cough triggering in cough hypersensitivity. Effective therapies that control chronic cough are currently lacking. Recent therapeutic development has focused on several ion channels and receptors involved in peripheral activation of cough (e.g., transient receptor potential channels, P2 × 3 receptors and voltage-gated sodium channels) or central cough processing (e.g., neurokinin-1 [NK-1] receptors and nicotinic acetylcholine receptors).

CONCLUSION

These targeted therapies provide novel insights into mechanisms underlying cough hypersensitivity and may offer new treatment options for people with chronic cough. In this review, we explore preclinical and clinical studies that have improved our understanding of the mechanisms responsible for chronic cough and discuss the most promising targeted approaches to date, including trials of P2 × 3-receptor antagonists and NK-1-receptor antagonists.

Population pharmacokinetic analysis of the P2X3-receptor antagonist gefapixant

Gefapixant, a P2X3-receptor antagonist, demonstrated objective and subjective efficacy in individuals with refractory or unexplained chronic cough. We report a population pharmacokinetic (PopPK) analysis that characterizes gefapixant pharmacokinetics (PKs), quantifies between- and within-participant variability, and evaluates the impact of intrinsic and extrinsic factors on gefapixant exposure. The PopPK model was initially developed using PK data from six phase I studies. Stepwise covariate method was utilized to identify covariates impacting PK parameters; the model was re-estimated and covariate effects were re-assessed after integrating PK data from three phase II and III studies. Simulations were conducted to evaluate the magnitude of covariate effects on gefapixant exposure. Of 1677 participants included in this data set, 1618 had evaluable PK records. Age, body weight, and sex had statistically significant, but not clinically relevant, effects on exposure. Degree of renal impairment (RI) had statistically significant and clinically relevant effects on exposure; exposure was 17% to 89% higher in those with versus without RI. Simulation results indicated that gefapixant 45 mg administered once daily to patients with severe RI has similar exposure to gefapixant 45 mg administered twice daily to patients with normal renal function. There were no significant effects of proton pump inhibitors or food. Of evaluated intrinsic and extrinsic factors, only RI had a clinically relevant effect on gefapixant exposure. Patients with mild or moderate RI do not require dosage adjustments; however, for patients with severe RI who are not on dialysis, gefapixant 45 mg once daily is recommended.

The Severity of Chronic Cough Diary (SCCD): development and content validation of a novel patient-reported outcome instrument for evaluating the symptom experience of chronic cough

BACKGROUND

Refractory chronic cough (RCC), a cough lasting longer than 8 weeks with an unexplained underlying etiology and unresponsive to conventional treatment, can have substantial effects on patients' quality of life. For assessment of the efficacy of antitussive medication in clinical trials in RCC, patient-reported outcome (PRO) instruments should be fit for purpose with appropriate content validity. Here we describe the qualitative testing of a newly developed PRO instrument: the Severity of Chronic Cough Diary (SCCD).

METHODS

The SCCD was developed to assess patients' symptom experience of cough in patients with RCC. A preliminary version was tested and refined based on an iterative process in a qualitative study. In total, three rounds of interviews were conducted with adult participants diagnosed with RCC in the USA (n = 19) and UK (n = 10). Rounds 1-3 consisted of hybrid concept elicitation (CE) interviews and cognitive interviews (CIs), with Round 3 also including interviews in a subset of participants (n = 5) about the usability of the SCCD as administered on an electronic handheld device.

RESULTS

The CE interviews identified concepts important to patients' experiences related to RCC that were broadly in line with the concepts in the preliminary version of the SCCD. Participants provided positive feedback on the draft SCCD across all CI rounds, reporting the instrument to be relevant and straightforward to complete, and containing a comprehensive set of concepts to evaluate their symptom experience of RCC. Participants demonstrated a good understanding of proposed item wording, response options, and the 24-hour recall period, and thought completion of the SCCD on the electronic device was easy. Following revisions based on results from each interview round, the SCCD at the end of this qualitative research study had 14 items assessing the concepts of: cough symptoms (five items), symptoms related to cough (four items), disruption to activities due to cough (three items), and disruption to sleep due to cough (two items).

CONCLUSIONS

The results of this study provide qualitative evidence supporting the content validity of the SCCD as a PRO instrument for evaluating outcomes of therapies for RCC in clinical trials.

Efficacy and safety of gefapixant for chronic cough: a meta-analysis of randomised controlled trials

BACKGROUND

The efficacy and safety of gefapixant in adults with chronic cough remain unclear. Our objective was to assess the efficacy and safety of gefapixant using updated evidence.

METHODS

MEDLINE, Cochrane Central Register of Controlled Trials (CENTRAL) and Embase databases were searched from inception through September 2022. Subgroup analysis based on dose of gefapixant (i.e. ≤20, 45-50 and ≥100 mg twice daily for low, moderate and high doses, respectively) was performed to explore a potential dose-dependent effect.

RESULTS

Five studies involving seven trials showed the efficacy of moderate- or high-dose gefapixant for reducing objective 24-h cough frequency (estimated relative reduction 30.9% and 58.5%, respectively) (i.e. primary outcome) and awake cough frequency (estimated relative reduction 47.3% and 62.8%, respectively). Night-time cough frequency was only reduced with high-dose gefapixant. Consistently, the use of moderate- or high-dose gefapixant significantly alleviated cough severity and improved cough-related quality of life, but increased the risk of all-cause adverse events (AEs), treatment-related AEs and ageusia/dysgeusia/hypogeusia. Subgroup analysis showed dose dependency in both efficacy and AEs with a cut-off dose being ≥45 mg twice daily.

CONCLUSIONS

This meta-analysis revealed dose-dependent efficacy and adverse effects of gefapixant against chronic cough. Further studies are required to investigate the feasibility of moderate-dose (i.e. 45-50 mg twice daily) gefapixant in clinical practice.

Bronchial thermoplasty improves cough hypersensitivity and cough in severe asthmatics

BACKGROUND

Cough is a troublesome symptom of asthma because it is associated with disease severity and poor asthma control. Bronchial thermoplasty (BT) may be effective in improving cough severity and cough-related quality of life in severe uncontrolled asthma.

OBJECTIVE

To evaluate the efficacy of BT for cough in severe uncontrolled asthma.

METHODS

Twelve patients with severe uncontrolled asthma were enrolled in this study between 2018 May and March 2021 and arbitrarily divided into cough-predominant [cough severity Visual Analog Scale (VAS) ≥ 40 mm, n = 8] and typical asthma (cough VAS <40 mm, n = 4) groups. Clinical parameters, such as capsaicin cough sensitivity [C-CS: the concentrations to inhaled capsaicin required to induce at least two (C2) and five (C5) coughs], lung function, and type-2-related biomarkers (fractional nitric oxides and absolute eosinophil counts) and cough-related indices [cough severity VAS and the Leicester Cough Questionnaire (LCQ)] were evaluated before and 3 months after performing BT.

RESULTS

BT significantly improved both cough-related indices and C-CS in the cough-predominant group. Changes in C-CS were significantly correlated with changes in the LCQ scores (C5: r = 0.65, p = 0.02 for all patients, and r = 0.81, p = 0.01 for the cough-predominant group).

CONCLUSIONS

BT may be effective for cough in severe uncontrolled asthma by improving C-CS. However, further larger cohort studies are necessary to confirm the effect of BT for cough in asthma.

CLINICAL TRIAL REGISTRATION

This study was registered in the UMIN Clinical Trials Registry (Registry ID UMIN: 000031982).

Efficacy and Safety of Eliapixant in Refractory Chronic Cough: The Randomized, Placebo-Controlled Phase 2b PAGANINI Study

INTRODUCTION

The PAGANINI study evaluated the efficacy and safety of the selective P2X3 antagonist eliapixant in patients with refractory chronic cough (RCC).

METHODS

PAGANINI was a randomized, double-blind, parallel-group, placebo-controlled, multicenter, dose-finding, phase 2b study. Adults with RCC lasting ≥ 12 months and cough severity ≥ 40 mm on a visual analog scale at screening were enrolled. Participants were randomized 1:1:1:1 to twice-daily 25 mg, 75 mg, or 150 mg oral eliapixant or placebo for 12 weeks. The primary endpoint was change from baseline in 24-h cough count after 12 weeks of intervention.

RESULTS

Overall, 310 participants were randomized to twice-daily eliapixant 25 mg (n = 75), 75 mg (n = 78), 150 mg (n = 80), or placebo (n = 77). A statistically significant dose-response signal with eliapixant was detected for the primary endpoint (all dose-response models, adjusted p < 0.1; one-sided). Adverse events (AEs) were reported in 39 (51%) participants with placebo and 43-51 (57-65%) participants receiving eliapixant. The most common AE was dysgeusia, occurring in 1% (n = 1) of the placebo group and 1-16% (n = 1-13) of the eliapixant groups in a dose-related manner. One case of a moderate drug-induced liver injury occurred in a participant receiving 150 mg twice-daily eliapixant.

CONCLUSION

Eliapixant demonstrated efficacy and a favorable taste tolerability profile in RCC. However, a drug-induced liver injury contributed to intensified liver monitoring in clinical trials with eliapixant and discontinuation of the entire development program in all indications by Bayer AG.

TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT04562155; registered September 18, 2020.

Guidelines for the management of chronic cough in adults. Endorsed by the French speaking society of respiratory diseases (Société de Pneumologie de Langue Française, SPLF), the Société Française d'Oto-Rhino-Laryngologie et de Chirurgie de la Face et du Cou (SFORL), the Société Française de Phoniatrie et de Laryngologie (SFPL), the Société Nationale Française de Gastro-entérologie (SNFGE)

Patients with chronic cough experience a high alteration of quality of life. Moreover, chronic cough is a complex entity with numerous etiologies and treatments. In order to help clinicians involved in the management of patients with chronic cough, guidelines on chronic cough have been established by a group of French experts. These guidelines address the definitions of chronic cough and the initial management of patients with chronic cough. We present herein second-line tests that might be considered in patients with cough persistence despite initial management. Experts also propose a definition of unexplained or refractory chronic cough (URCC) in order to better identify patients whose cough persists despite optimal management. Finally, these guidelines address the pharmacological and non-pharmacological interventions useful in URCC. Thus, amitryptilline, pregabalin, gabapentin or morphine combined with speech and/or physical therapy are a mainstay of treatment strategies in URCC. Other treatment options, such as P2 × 3 antagonists, are being developed.

[Guidelines for the management of chronic cough in adults]

Patients with chronic cough experience major alteration in their quality of life. Given its numerous etiologies and treatments, this disease is a complex entity. To help clinicians involved in patient management of patients, guidelines have been issued by a group of French experts. They address definitions of chronic cough and initial management of patients with this pathology. We present herein the second-line tests that might be considered in patients whose coughing has persisted, notwithstanding initial management. The experts have also put forward a definition of unexplained or refractory chronic cough (URCC), the objective being to more precisely identify those patients whose cough persists despite optimal management. Lastly, these guidelines indicate the pharmacological and non-pharmacological interventions of use in URCC. Amitriptyline, pregabalin, gabapentin or morphine combined with speech and/or physical therapy are mainstays in treatment strategies. Other treatment options, such as P2X3 antagonists, are being developed and have generated high hopes among physicians and patients alike.

Emerging drugs in the treatment of chronic cough

INTRODUCTION

Chronic cough is a debilitating condition that is among the most common reasons for seeking medical attention yet remains challenging to manage. Identifying an underlying respiratory, nasal or upper gastrointestinal disease triggering cough is the first step in assessment, but once this has been ruled out or adequately treated, many patients remain troubled with chronic cough.

AREAS COVERED

This narrative review discusses the role of existing treatments and describes the current research landscape for the development of new therapies for chronic cough greater than 8 weeks that is refractory (RCC) or unexplained (UCC). The literature search includes published studies found on pubmed and conference abstracts until 2023.

EXPERT OPINION

RCC/UCC can occur due to neuronal dysregulation of the vagus nerve or central nervous system. Hence, novel anti-tussives have targeted ion channels involved in the neuronal signaling which triggers cough. Although some therapies targeting receptors such as TRPV1 have failed to show efficacy, P2X3 antagonists have emerged as the most promising therapy for patients impacted by chronic cough. Disease specific therapies such as for idiopathic pulmonary fibrosis are in early development.

The P2X3 receptor antagonist filapixant in patients with refractory chronic cough: a randomized controlled trial

BACKGROUND

P2X3 receptor antagonists seem to have a promising potential for treating patients with refractory chronic cough. In this double-blind, randomized, placebo-controlled study, we investigated the efficacy, safety, and tolerability of the novel selective P2X3 receptor antagonist filapixant (BAY1902607) in patients with refractory chronic cough.

METHODS

Following a crossover design, 23 patients with refractory chronic cough (age: 60.4 ± 9.1 years) received ascending doses of filapixant in one period (20, 80, 150, and 250 mg, twice daily, 4-days-on/3-days-off) and placebo in the other. The primary efficacy endpoint was the 24-h cough frequency on Day 4 of each dosing step. Further, subjective cough severity and health-related quality of life were assessed.

RESULTS

Filapixant at doses ≥ 80 mg significantly reduced cough frequency and severity and improved cough health-related quality of life. Reductions in 24-h cough frequency over placebo ranged from 17% (80 mg dose) to 37% (250 mg dose), reductions over baseline from 23% (80 mg) to 41% (250 mg) (placebo: 6%). Reductions in cough severity ratings on a 100-mm visual analog scale ranged from 8 mm (80 mg) to 21 mm (250 mg). No serious or severe adverse events or adverse events leading to discontinuation of treatment were reported. Taste-related adverse events occurred in 4%, 13%, 43%, and 57% of patients treated with filapixant 20, 80, 150, and 250 mg, respectively, and in 12% treated with placebo.

CONCLUSIONS

Filapixant proved to be efficacious, safe, and-apart from the occurrence of taste disturbances, especially at higher dosages-well tolerated during the short therapeutic intervention. Clinical trial registration EudraCT, eudract.ema.europa.eu, 2018-000129-29; ClinicalTrials.gov, NCT03535168.