NGX-4010, a capsaicin 8% dermal patch, administered alone or in combination with systemic neuropathic pain medications, reduces pain in patients with postherpetic neuralgia

Capsaicin Improves Systemic Inflammation, Atherosclerosis, and Macrophage-Derived Foam Cells by Stimulating PPAR Gamma and TRPV1 Receptors

BACKGROUND

Capsaicin, a bioactive compound found in peppers, is recognized for its anti-inflammatory, antioxidant, and anti-lipidemic properties. This study aimed to evaluate the effects of capsaicin on atherosclerosis progression.

METHODS

Apolipoprotein E knockout mice and their C57BL/6 controls were utilized to assess blood lipid profile, inflammatory status, and atherosclerotic lesions. We also examined the influence of capsaicin on cholesterol influx and efflux, and the role of TRPV1 and PPARγ signaling pathways in bone marrow-derived macrophages.

RESULTS

Capsaicin treatment reduced weight gain, visceral adiposity, blood triglycerides, and total and non-HDL cholesterol. These improvements were associated with a reduction in atherosclerotic lesions in the aorta and carotid. Capsaicin also improved hepatic oxidative and inflammatory status. Systemic inflammation was also reduced, as indicated by reduced leukocyte rolling and adhesion on the mesenteric plexus. Capsaicin decreased foam cell formation by reducing cholesterol influx through scavenger receptor A and increasing cholesterol efflux via ATP-binding cassette transporter A1, an effect primarily linked to TRPV1 activation.

CONCLUSIONS

These findings underscore the potential of capsaicin as a promising agent for atherosclerosis prevention, highlighting its comprehensive role in modulating lipid metabolism, foam cell formation, and inflammatory responses.

An extract of phase II and III trials on recent developments in managing neuropathic pain syndromes: diabetic peripheral neuropathy, trigeminal neuralgia, and postherpetic neuralgia

INTRODUCTION

Neuropathic pain (NP) conditions involve lesions to the somatosensory nervous system leading to chronic and debilitating pain. Many patients suffering from NP utilize pharmacological treatments with various drugs that seek to reduce pathologic neuronal states. However, many of these drugs show poor efficacy as well as cause significant adverse effects. Because of this, there is a major need for the development of safer and more efficacious drugs to treat NP.

AREAS COVERED

In this review, we analyzed current treatments being developed for a variety of NP conditions. Specifically, we sought drugs in phase II/III clinical trials with indications for NP conditions. Various databases were searched including Google Scholar, PubMed, and clinicaltrials.gov.

EXPERT OPINION

All the mentioned targets for treatments of NP seem to be promising alternatives for existing treatments that often possess poor side effect profiles for patients. However, gene therapy potentially offers the unique ability to inject a plasmid containing growth factors leading to nerve growth and repair. Because of this, gene therapy appears to be the most intriguing new treatment for NP.

Are We Ready to Recommend Capsaicin for Disorders Other Than Neuropathic Pain?

Capsaicin, a lipophilic, volatile compound, is responsible for the pungent properties of chili peppers. In recent years, a significant increase in investigations into its properties has allowed the production of new formulations and the development of tools with biotechnological, diagnostic, and potential therapeutic applications. Most of these studies show beneficial effects, improving antioxidant and anti-inflammatory status, inducing thermogenesis, and reducing white adipose tissue. Other mechanisms, including reducing food intake and improving intestinal dysbiosis, are also described. In this way, the possible clinical application of such compound is expanding every year. This opinion article aims to provide a synthesis of recent findings regarding the mechanisms by which capsaicin participates in the control of non-communicable diseases such as obesity, diabetes, and dyslipidemia.

Capsaicin 8% Patch for Spinal Cord Injury Focal Neuropathic Pain, a Randomized Controlled Trial

BACKGROUND

Neuropathic pain (NP) after spinal cord injury (SCI) exacerbates disability, decreases quality of life (QOL), and is often refractory to available therapies. Patients report willingness to trade potential recovery of strength, bowel, bladder, or sexual function for pain relief. One proposed mechanism causing NP is up-regulation of transient receptor potential vanilloid 1 (TRPV 1) proteins in uninjured C fibers and dorsal root ganglia causing neuronal excitability. Recent studies have found up-regulation of TRPV 1 proteins after SCI.

OBJECTIVE

We hypothesize the application of capsaicin 8% patch (C8P), FDA approved for NP in diabetic peripheral neuropathy and post-herpetic neuralgia, will improve pain, function and QOL in persons with SCI.

METHODS

Randomized single-blind crossover design in which 11 persons with SCI and NP refractory to two oral pain medications received C8P or a control low dose Capsaicin 0.025% patch (CON) over two 12-week periods. Pain (VAS, MPI-SCI), quality of life (WHO-QOL), and functional status (SCIM) were measured at 2-4-week intervals.

RESULTS

There was a main treatment effect of C8P over CON on VAS and MPI-SCI outcomes with pain reduction of 35% and 29% at weeks 2 and 4, respectively. C8P also demonstrated a main treatment effect over CON on the SCIM mobility subscale. WHO-QOL scores did not improve with C8P.

CONCLUSIONS

C8P improves pain and mobility for patients with SCI and refractory NP. Larger studies should be performed to evaluate impact of repeat applications and QOL outcomes.

Combination Therapy for Neuropathic Pain: A Review of Recent Evidence

Pharmacological treatment is not very effective for neuropathic pain (NP). A progressive decrease in the estimated effect of NP drugs has been reported, giving rise to an increase in the use of the multimodal analgesic approach. We performed a new independent review to assess whether more and better-quality evidence has become available since the last systematic review. We evaluated the efficacy, tolerability, and safety of double-blinded randomized controlled trials involving only adult participants and comparing combination therapy (CT: ≥2 drugs) with a placebo and/or at least one other comparator with an NP indication. The primary outcome assessed was the proportion of participants reporting ≥50% pain reductions from baseline. The secondary outcome assessed was the proportion of drop-outs due to treatment-emergent adverse events. After removing duplicates, 2323 citations were screened, with 164 articles assessed for eligibility, from which 16 were included for qualitative analysis. From the latter, only five lasted for at least 12 weeks and only six complied with the required data for complete analysis. CT has been adopted for years without robust evidence. Efforts have been made to achieve better-quality evidence, but the quality has not improved over the years. In this regard, guidelines for NP should attempt to make recommendations about CT research, prioritizing which combinations to analyze.

Capsaicin 8% patch Qutenza and other current treatments for neuropathic pain in chemotherapy-induced peripheral neuropathy (CIPN)

PURPOSE OF REVIEW

Current oral treatments for neuropathic pain associated with chemotherapy-induced peripheral neuropathy (CIPN) have limited clinical efficacy, and undesirable side-effects. Topically delivered treatments have the advantage of avoiding CNS side-effects, while relieving pain. We have reviewed treatments of neuropathic pain associated with CIPN, focusing on the Capsaicin 8% patch, which can provide pain relief for up to 3 months or longer after a single 30-60-min application.

RECENT FINDINGS

Capsaicin 8% patch is a licensed treatment in the EU/UK for neuropathic pain and shown to be safe and effective in providing pain relief for patients with CIPN. Repeated daily oral or topical administrations are not required, as with other current treatments. The side-effects are transient and restricted to the time around patch application. New evidence suggests the Capsaicin 8% patch can promote the regeneration and restoration of skin nerve fibres in CIPN, in addition to the pain relief.

SUMMARY

The Capsaicin 8% patch is now often a preferred a treatment option for localised neuropathic pain conditions, including the feet and hands in patients with CIPN. Capsaicin 8% patch can be repeated three-monthly, if needed, for a year. In addition to pain relief, it may have a disease-modifying effect.

Herbal Medicine for Pain Management: Efficacy and Drug Interactions

Complementary and alternative medicines such as herbal medicines are not currently part of the conventional medical system. As the popularity of and global market for herbal medicine grows among all age groups, with supporting scientific data and clinical trials, specific alternative treatments such as herbal medicine can be reclassified as a practice of conventional medicine. One of the most common conditions for which adults use herbal medicine is pain. However, herbal medicines carry safety concerns and may impact the efficacy of conventional therapies. Unfortunately, mechanisms of action are poorly understood, and their use is unregulated and often underreported to medical professionals. This review aims to compile common and available herbal medicines which can be used as an alternative to or in combination with conventional pain management approaches. Efficacy and safety are assessed through clinical studies on pain relief. Ensuing herb–drug interactions such as cytochrome modulation, additive and synergistic effects, and contraindications are discussed. While self-management has been recognized as part of the overall treatment strategy for patients suffering from chronic pain, it is important for practitioners to be able to also optimize and integrate herbal medicine and, if warranted, other complementary and alternative medicines into their care.

A critical review of the capsaicin 8% patch for the treatment of neuropathic pain associated with diabetic peripheral neuropathy of the feet in adults

INTRODUCTION

Diabetes is an increasingly prevalent disorder affecting nearly 1-in-5 adults, of which half will experience diabetic peripheral neuropathy (DPN) and a quarter will suffer from diabetic peripheral nerve pain (DPNP), severely impacting quality of life. The currently approved treatment options are typically centrally acting agents whose use is limited by systemic effects and drug interactions. The capsaicin 8% dermal patch was recently approved by the U.S. FDA for the treatment of DPNP.

AREAS COVERED

The authors review the available literature regarding the use of high-concentration capsaicin 8% patch for the treatment of diabetic peripheral neuropathy and neuropathic pain and discuss implementing its use in clinical practice.

EXPERT OPINION

The high-concentration capsaicin 8% patch is an effective and well-tolerated treatment option for treating DPNP. Capsaicin 8% patch may be used alone or in combination with other oral therapies and can provide rapid and sustained neuropathic pain relief following a single application and is safe and effective when used long term.

Expert Opinion: Exploring the Effectiveness and Tolerability of Capsaicin 179 mg Cutaneous Patch and Pregabalin in the Treatment of Peripheral Neuropathic Pain

Background and Objective

Treatment of peripheral neuropathic pain (PNP) remains a challenge. In the absence of clear predictors of response, clinical decision-making involves trial and error. While many classes of pharmacological agent are used and have shown efficacy, one of the most commonly used first-line treatments is pregabalin. However, in the 60% of PNP cases in which the pain is localized, a local treatment may be more suitable. This article will summarize the evidence for the relative effectiveness and tolerability of the capsaicin 179 mg patch and pregabalin in the treatment of PNP and highlight the expert opinion of the authors based on their own clinical experiences.

Results

When compared in a head-to-head trial in patients with PNP, capsaicin 179 mg patch provided non-inferior pain relief compared with an optimized dose of pregabalin, as well as a reduction in dynamic mechanical allodynia, faster onset of action, fewer systemic side effects, and greater treatment satisfaction. Adverse events associated with capsaicin patch are mainly application site reactions, compared with systemic and central nervous system effects with pregabalin. Studies indicate that capsaicin 179 mg patch is associated with a lower burden of therapy than pregabalin in terms of improved tolerability, lack of a daily pill burden, lack of drug-drug interactions, and increased regimen flexibility.

Conclusion

In localized neuropathic pain, evidence supports a pragmatic approach of using a local treatment before considering a systemic treatment. For treatment selection, the patient profile (eg, concomitant medication use, age) and the treatments' efficacy and tolerability profiles should be considered.

Lidocaine medicated plaster, an additional potential treatment option for localized post-surgical neuropathic pain: efficacy and safety results of a randomized, placebo-controlled trial

OBJECTIVE

To assess the efficacy and safety of lidocaine 700 mg medicated plaster (lidocaine plaster) compared to placebo in patients with moderate to severe chronic post-surgical neuropathic pain (PSNP).

METHODS

Patients (n = 363) with a diagnosis of PSNP for a minimum of 3 months to 36 months were randomized (1:1) to lidocaine plaster or placebo for a 12 week double-blind treatment period. Randomization was stratified as "plaster-only" (no concomitant medication for PSNP) or as "add-on" (stable systemic medication for PSNP). The primary efficacy endpoint was the change from baseline in 24 hour average pain intensity at Week 12, assessed by 11 point numerical rating scale (NRS). The trial was registered in ClinicalTrials.gov (NCT01752322) and EudraCT (2012-000347-28).

RESULTS

Treatment with lidocaine or placebo plaster led to a clinically relevant reduction in average pain intensity. Pain reduction (least squares mean [LS mean] standard error [SE], [95% confidence interval, CI]) with lidocaine plaster (-1.70 [0.16], [-2.03, -1.38]) was numerically higher than with placebo (-1.47 [0.16], [-1.78, -1.15]) but the difference was not statistically significant (-0.23 [0.23], [-0.69, 0.22]). Pre-specified exploratory subgroup analyses showed the largest differentiation between lidocaine and placebo in patients without concomitant pain medication, and in patients with more than 1 year between surgery and enrollment. Many secondary outcomes showed a numerically larger improvement in favor of lidocaine. The most commonly reported adverse events were administration site reactions linked to topical administration.

CONCLUSIONS

A clinically relevant pain reduction was observed with lidocaine plaster in patients with PSNP. The safety and tolerability profile is consistent with current knowledge.

QAPSA: post-marketing surveillance of capsaicin 8% patch for long-term use in patients with peripheral neuropathic pain in France

OBJECTIVE

To describe the characteristics of patients treated with the capsaicin 8% patch, prescribing conditions, long-term effects of repeat treatment on pain intensity and perception, quality of life, and impact on concomitant medication.

METHODS

A national, longitudinal, prospective, non-interventional, post-marketing open study was conducted in 50 French pain centers. Adult volunteer non-diabetic patients with peripheral neuropathic pain receiving capsaicin 8% patch treatment were consecutively enrolled. Treatment could be repeated over a 12-month period, with 6 months' follow-up after last application.

RESULTS

A total of 684 patients (age: 53.0 ± 14.9 years, mean ± standard deviation; post-traumatic/surgical peripheral neuropathic pain: 76.3%; pain intensity: 6.2 ± 1.7; pain duration: 3.0 years, median) were treated with 1 to 5 patches at 3/4 month intervals; 70.3% were naive to capsaicin 8% patch treatment at inclusion. Six months after last application, treatment was considered as successful for 21.8% (95% confidence interval: 17.5%-26.7%) of patients by a stringent criterion combining improvement according to the patient's global impression of change (PGIC) and at least 30% improvement on a numerical pain rating scale (NPRS). Clinically relevant improvement in health-related quality of life was observed at end-of-study. No unexpected safety concerns were observed with capsaicin 8% patch repeat treatment.

CONCLUSIONS

The data of this post-marketing study meets the request by the French authorities for additional data on conditions of use in everyday practice. They confirmed the tolerance and long-term effect of capsaicin 8% patch in patients with peripheral neuropathic pain in real-world conditions.

The Role of Qutenza® (Topical Capsaicin 8%) in Treating Neuropathic Pain from Critical Ischemia in Patients with End-Stage Renal Disease: An Observational Cohort Study

Objective

Current treatment strategies for painful critical ischemia in patients with end-stage renal disease (ESRD) are suboptimal. A drug that is non-renally excreted has minimal systemic absorption and does not require dose adjustment in renal failure is attractive. The aim of this study was to evaluate the safety and efficacy of Qutenza® (topical capsaicin 8%) for chronic neuropathic pain from critical ischemia in patients with ESRD.

Design and Setting

A prospective cohort study was conducted in a single-center, university teaching hospital.

Patients

Twenty patients with ESRD were treated with Qutenza® for neuropathic pain from critical limb ischemia.

Methods

Patients were followed-up at 1, 6 and 12 weeks post-treatment. The primary end point was the difference in visual analog scale (VAS) between baseline and week 12. Secondary end points were Brief Pain Inventory questionnaire (BPI) scores, quality of life assessment (EQ-5D) and patient global impression of change (PGIC). Safety and tolerability data were also collected. The trial was prospectively registered with clinical trials databases (EudraCT: 2012-001586-32; NCT01704313).

Results

There was significant reduction in VAS from baseline to week 12 (-20+/-7%; P = 0.02). There was a significant reduction in all seven domains of the BPI. Quality of life also improved at 12 weeks following treatment in two of the EQ-5D domains (mobility and pain). Qutenza® was well tolerated with no significant side effects in this patient cohort, which included 20% diabetics.

Conclusions

In this small, observational study Qutenza® treatment has been shown to be effective and well-tolerated to treat neuropathic pain from critical ischemia in patients with ESRD.

Management of chronic neuropathic pain with single and compounded topical analgesics

The goal of our review was to emphasize important aspects that physicians should take into consideration when prescribing topical analgesics as part of chronic neuropathic pain treatment. We discuss the dermatopharmacokinetics and microstructural components of the skin, differences between topical and transdermal drug delivery, and topical medication effects on peripheral neuropathy and central sensitization. Even though the US FDA approved topical analgesics are 8%-capsaicin and 5%-lidocaine patches for treating postherpetic neuralgia, there are many other studies conducted on the efficacy of topical ketamine cream, clonidine gel, topical gabapentin, topical baclofen and topical phenytoin for peripheral neuropathic pain, either alone or in combination with other formulations. Furthermore, we discuss new compounded topical analgesics that are becoming more popular and that are showing promising results in the management of chronic peripheral neuropathies. However, more studies are needed for elucidation of the role of topical analgesics and their effects, especially when combined with other treatments.

Localized neuropathic pain: an expert consensus on local treatments

BACKGROUND

Pain localization is one of the hallmarks for the choice of first-line treatment in neuropathic pain. This literature review has been conducted to provide an overview of the current knowledge regarding the etiology and pathophysiology of localized neuropathic pain (LNP), its assessment and the existing topical pharmacological treatments.

MATERIALS AND METHODS

Literature review was performed using Medline from 2010 to December 2016, and all studies involving LNP and treatments were examined. A multidisciplinary expert panel of five pain specialists in this article reports a consensus on topical approaches that may be recommended to alleviate LNP and on their advantages in clinical practice.

RESULTS

Successive international recommendations have included topical 5% lidocaine and 8% capsaicin for LNP treatment. The expert panel considers that these compounds can be a first-line treatment for LNP, especially in elderly patients and patients with comorbidities and polypharmacy. Regulatory LNP indications should cover the whole range of LNP and not be restricted to specific etiologies or sites. Precautions for the use of plasters must be followed cautiously.

CONCLUSION

Although there is a real need for more randomized controlled trials for both drugs, publications clearly demonstrate excellent risk/benefit ratios, safety, tolerance and continued efficacy throughout long-term treatment. A major advantage of both plasters is that they have proven efficacy and may reduce the risk of adverse events such as cognitive impairment, confusion, somnolence, dizziness and constipation that are often associated with systemic neuropathic pain treatment and reduce the quality of life. Topical modalities also may be used in combination with other drugs and analgesics with limited drug-drug interactions.

Combination treatment of neuropathic pain: Danish expert recommendations based on a Delphi process

BACKGROUND

Current Danish treatment algorithms for pharmacological treatment of neuropathic pain (NeP) are tricyclic antidepressants (TCA), gabapentin and pregabalin as first-line treatment for the most common NeP conditions. Many patients have insufficient pain relief on monotherapy, but combination therapy had not been included in guidelines until recently. Based on clinical empiricism and scientific evidence, a Delphi consensus process provided a consolidated guidance on pharmacological combination treatment of NeP.

METHODS

A two-round virtual internet-based Delphi process with 6 Danish pain specialists was undertaken. In the first round, questions were answered individually and anonymously, whereas in the second round, the panel openly discussed first round's summary of outcomes. Combinations of pharmacological pain treatments, that is, pregabalin/gabapentin, TCAs, serotonin-norepinephrine reuptake inhibitors (SNRIs), selective serotonin reuptake inhibitors, opioids, other antiepileptics and cutaneous patches, were assessed based on both scientific and clinical practice experiences. The Centers for Disease Control and Prevention (CDC) grading system was used for evidence rating.

RESULTS

Combination of pregabalin/gabapentin with TCA is useful in patients who do not gain sufficient pain relief or tolerate either drug in high doses, or to improve sleep disturbance. Also, combination of pregabalin/gabapentin and SNRIs is reasonably well documented and experienced by some experts to result in sufficient pain relief and fewer side effects than monotherapy. Good evidence on efficacy was found for the combination of pregabalin/gabapentin or TCAs and opioids, which was also frequently used in clinical practice. The evidence for combining TCAs and SNRIs is insufficient, although sometimes used in clinical practice despite the risk of serotonin syndrome. For localized NeP, combination therapy with cutaneous patches should be considered. There was insufficient scientific evidence for any pharmacologic combination therapies with selective serotonin reuptake inhibitors - as well as for other potential combinations.

CONCLUSIONS

The study revealed that combination therapy is widely used in clinical practice and supported by some scientific evidence. However, further studies are needed.

Capsaicin, Nociception and Pain

Capsaicin, the pungent ingredient of the hot chili pepper, is known to act on the transient receptor potential cation channel vanilloid subfamily member 1 (TRPV1). TRPV1 is involved in somatic and visceral peripheral inflammation, in the modulation of nociceptive inputs to spinal cord and brain stem centers, as well as the integration of diverse painful stimuli. In this review, we first describe the chemical and pharmacological properties of capsaicin and its derivatives in relation to their analgesic properties. We then consider the biochemical and functional characteristics of TRPV1, focusing on its distribution and biological effects within the somatosensory and viscerosensory nociceptive systems. Finally, we discuss the use of capsaicin as an agonist of TRPV1 to model acute inflammation in slices and other ex vivo preparations.

Profile of the capsaicin 8% patch for the management of neuropathic pain associated with postherpetic neuralgia: safety, efficacy, and patient acceptability

Capsaicin is a naturally occurring irritant active ingredient found in hot peppers. It is a ligand for transient receptor potential channel vanilloid receptors, which are found in nociceptive nerve terminals in the skin. Initial exposure to topical capsaicin leads to excitation of these receptors, release of vasoactive mediators, erythema, intense burning, pain, and thereafter desensitization of sensory neurons resulting in inhibition of pain transmission. Capsaicin 8% has been licensed for the treatment of postherpetic neuralgia pain in recent years. A single application of high-concentration capsaicin for 60 minutes for postherpetic neuralgia has been robustly evaluated. Capsaicin 8% patches are applied to the most painful areas of healthy skin and allowed to remain for 60 minutes. Treatment can be repeated every 90 days if the pain persists or returns. The patches are usually applied in specialist pain clinics where patients can be pretreated and monitored. Health care staff need to take certain precautions before administering these patches to avoid unintentional contact. Common adverse effects of the capsaicin 8% patch are transient mild-to-moderate self-limiting application-site burning, pain, erythema, pruritus, papules, swelling, dryness, and hypertension. To manage local pain from capsaicin application, the skin is pretreated with a local anesthetic such as topical lidocaine or an oral analgesic such as oxycodone for up to 5 days. A transient increase in pain is usually seen within 48 hours of patch application before the pain-relieving effect starts. Systemic absorption is minimal and clinically insignificant. The nature of administration and relatively high cost of capsaicin patches can significantly limit their use to a small number of patients with severe refractory symptoms. This review highlights recent evidence related to the use and effectiveness of the 8% capsaicin patch for Postherpetic Neuralgia and discusses its safety and side-effect profiles.

Topical analgesics for neuropathic pain in the elderly: current and future prospects

Neuropathic pain (NeP) is a significant medical and socioeconomic burden with limited therapeutic options. Elderly patients exhibit a higher incidence of several NeP conditions and pose a particular challenge due to age-related pharmacokinetic and pharmacodynamic issues, comorbid conditions, and polypharmacy, as well as frailty and cognitive decline. Topical analgesics are of interest because of their comparable efficacy to oral agents, good tolerability and safety, and potential to be add-on therapies to oral treatments. In recent years, two topical formulations for NeP have been approved (5% lidocaine medicated plaster, 8% capsaicin patch) but are not available in all countries. There are controlled trials and a growing body of open-label reports on their use in clinical care. Some studies provide a post hoc analysis of data in relation to older age (≥65 years), which is useful. The body of evidence relating to topical investigational agents is growing and involves controlled trials as well as individual cases. The largest single body of information is for topical ketamine, administered either alone or combined with other agents (particularly amitriptyline), and some large randomized controlled trials report efficacy. Other large trials involve topical clonidine and further ketamine combinations. Compounding analgesics involves challenges, including uncertain composition (two to five ingredients are used) and concentrations (range 0.5-5%), as well as the heterogeneity of data that support choices. Nevertheless, case reports and acceptable response rates in larger cohorts are intriguing, and this area merits further investigation in controlled settings as well as continued documentation of clinical experiences.

Experimental evidence for alleviating nociceptive hypersensitivity by single application of capsaicin

The single application of high-concentration of capsaicin has been used as an analgesic therapy of persistent pain. However, its effectiveness and underlying mechanisms remain to be further evaluated with experimental approaches. The present study provided evidence showing that the single application of capsaicin dose-dependently alleviated nociceptive hypersensitivity, and reduced the action potential firing in small-diameter neurons of the dorsal root ganglia (DRG) in rats and mice. Pre-treatment with capsaicin reduced formalin-induced acute nocifensive behavior after a brief hyperalgesia in rats and mice. The inhibitory effects of capsaicin were calcium-dependent, and mediated by the capsaicin receptor (transient receptor potential vanilloid type-1). We further found that capsaicin exerted inhibitory effects on the persistent nociceptive hypersensitivity induced by peripheral inflammation and nerve injury. Thus, these results support the long-lasting and inhibitory effects of topical capsaicin on persistent pain, and the clinic use of capsaicin as a pain therapy.

Application of the capsaicin 8% cutaneous patch in neuropathic pain of the head and face: A case series

INTRODUCTION

Treatment of neuropathic or neuralgic head and facial pain due to dental, traumatic or surgical nerve lesions or post-herpetic neuropathy is often challenging.

CASES

We are reporting on four patients with neuropathic pain syndromes successfully treated with a capsaicin 8% patch in the affected area of the head or face.

DISCUSSION

Treatment with the capsaicin 8% patch seems to be effective and safe for application to the facial and head region. The capsaicin 8% patch might be an additional treatment option if first-line treatment with anticonvulsants or antidepressants was ineffective or limited by side effects.

Topical capsaicin formulations in the management of neuropathic pain

This chapter reviews the scientific and clinical evidence supporting the use of topical formulations containing the pungent principle of chili peppers--capsaicin, for the treatment of peripheral neuropathic pain. Given the limitations of current oral and parenteral therapies for the management of pain arising from various forms of nerve injury, alternate therapeutic approaches that are not associated with systemic adverse events that limit quality of life, impair function, or threaten respiratory depression are critically needed. Moreover, neuropathic conditions can be complicated by progressive changes in the central and peripheral nervous system, leading to persistent reorganization of pain pathways and chronic neuropathic pain. Recent advances in the use of high-dose topical capsaicin preparations hold promise in managing a wide range of painful conditions associated with peripheral neuropathies and may in fact help reduce suffering by reversing progressive changes in the nervous system associated with chronic neuropathic pain conditions.

Evidence-based guidance for the management of postherpetic neuralgia in primary care

This article aims to help primary care physicians negotiate gaps in current guidelines for postherpetic neuralgia (PHN). The objectives of this article are to: 1) briefly review the available guidelines and identify their strengths and weaknesses; 2) review the gaps in the guidelines; 3) review new data that were not included in the most recent guidelines; 4) provide expert opinion on how the new data and current guidelines can be used to make treatment decisions; and 5) review several important dimensions of care (eg, tolerability, dosing) and provide guidance. In general, all guidelines recognize the α2δ ligands, tricyclic antidepressants (TCAs), opioids, and tramadol as efficacious systemic options, with topical lidocaine serving as an efficacious nonsystemic approach for localized PHN treatment. The first-line treatment options typically recommended in the guidelines are α2δ ligands and TCAs, while opioids and tramadol are often recommended as second- or third-line options. Since the latest guidelines were published, newer agents (eg, topical capsaicin [8%] patch and gastroretentive gabapentin) have met the standard as first-line therapy with the publication of ≥ 1 randomized controlled trial. However, gabapentin enacarbil has not met this standard due to a lack of a published randomized controlled trial in PHN.

A phase 2a, randomized, crossover trial of gabapentin enacarbil for the treatment of postherpetic neuralgia in gabapentin inadequate responders

OBJECTIVE

To compare the efficacy of high-dose (3,600 mg/day) vs low-dose (1,200 mg/day) oral gabapentin enacarbil (GEn) on pain intensity in adults with postherpetic neuralgia (PHN) and a history of inadequate response to ≥1,800 mg/day gabapentin.

DESIGN

Multicenter, randomized, double-blind, crossover study (NCT00617461).

SETTING

Thirty-five outpatient centers in Germany and the United States.

SUBJECTS

Subjects aged ≥18 years with a diagnosis of PHN.

METHODS

During a 2-week baseline period, subjects received open-label treatment with 1,800 mg/day gabapentin. Subjects who had a mean 24-hour average pain intensity score ≥4 during the last 7 days of the baseline period were randomized to receive GEn (1,200 or 3,600 mg/day) for treatment period 1 (28 days), followed by GEn 2,400 mg/day (4 days), and the alternate GEn dose for treatment period 2 (28 days).

RESULTS

There was a modest but significant improvement in pain intensity scores with GEn 3,600 mg vs 1,200 mg (adjusted mean [90% confidence interval] treatment difference, -0.29 [-0.48 to -0.10]; P = 0.013). The difference in efficacy between doses was observed primarily in subjects who received the higher dose during treatment period 2; certain aspects of the study design may have contributed to this outcome. Plasma steady-state gabapentin exposure during GEn treatment was as expected and consistent between treatment periods. No new safety signals or adverse event trends relating to GEn exposure were identified.

CONCLUSIONS

While the overall results demonstrated efficacy in a PHN population, the differences between treatment periods confound the interpretation. These findings could provide insight into future trial designs.

Neuropathic pain: a pathway for care developed by the British Pain Society

Neuropathic pain is a common chronic pain condition that can be challenging to treat, particularly for non-specialists. The development of the Map of Medicine care pathway for the management of neuropathic pain was led by the British Pain Society. Focusing on treatment by non-specialists, this pathway is based on new evidence, consensus, and the interests of service users. This paper presents the care pathway and accompanying evidence base, highlighting its salient features, and discussing important treatment points. After initial assessment, the pathway progresses through first-, second-, and third-line drug treatment, includes advice on topical treatment and opioids (in specific circumstances), and describes non-pharmacological approaches. Importantly, timely review of patients and referral to specialist secondary or tertiary care must be considered as vital components of the pathway. Although the emphasis was not on specialist treatment, advice is given on existing interventions, including neural stimulation and multi-disciplinary care. These, and other steps on the pathway, will be subject to further review as more evidence becomes available. In the meantime, the pathway represents a straightforward, valuable and accessible approach for healthcare professionals managing the distress and impact of neuropathic pain.

Prospective, non-interventional study on the tolerability and analgesic effectiveness over 12 weeks after a single application of capsaicin 8% cutaneous patch in 1044 patients with peripheral neuropathic pain: first results of the QUEPP study

BACKGROUND

Reversible defunctionalisation of nociceptors by the TRPV1 agonist capsaicin in high concentration is an emerging new concept for the treatment of peripheral neuropathic pain.

OBJECTIVES

The capsaicin 8% cutaneous patch with a long-lasting effect for up to 3 months after a single application is available in Germany by prescription since October 2010. The aim of this study was to monitor its usage and therapeutic performance in clinical practice.

METHODS

Patients had a single patch application with up to 4 patches and were followed up after 7-14 days, 4, 8, and 12 weeks. Average pain intensity (NPRS-11), pain attacks, neuropathy symptoms, sleep parameters, quality of life, working capacity and concomitant neuropathic pain medication were assessed during at least two visits.

RESULTS

A total of 509 females (48.8%; effectiveness population N = 1044) and 531 males (50.9%) were included; the mean age was 61.2 ± 14.4 (SD) years. Postherpetic neuralgia was the most frequent diagnosis (31.9%), followed by postsurgical neuralgia (22.8%), post-traumatic neuropathy (12.4%), polyneuropathy (14.3%), and mixed pain syndromes (16.6%). Thirty and 50% responder rates were 42.7% and 23.7%, respectively, with a mean relative reduction of pain intensity during weeks 1-12 of 24.7% (1.1 SEM) and significant improvements in pain attacks, sleep duration and sleep quality, while the consumption of opioids and antiepileptics decreased significantly. In 106 patients (10.0%; safety population n = 1063) 146 adverse drug reactions (ADRs) were reported, mainly application site reactions (erythema, pain). A total of 27 serious ADRs were documented in 17 patients (1.6%).

CONCLUSIONS

Analgesic treatment of peripheral neuropathic pain with the capsaicin 8% cutaneous patch is safe and effective.

LIMITATIONS

The study did not include a control group; therefore, a comparison of the results with that of therapeutic alternatives is not justified.

Mechanism- and experience-based strategies to optimize treatment response to the capsaicin 8% cutaneous patch in patients with localized neuropathic pain

The capsaicin 8% cutaneous patch is an emergent new treatment option for patients with peripheral neuropathic pain. In randomized controlled clinical studies relevant pain relief for 12 weeks was achieved in about one third of patients following a single application. The first part of this paper is a review of the pathophysiology, pharmacology, and published clinical trials with the capsaicin 8% cutaneous patch. The second part reports on outcomes of an interdisciplinary expert workshop, where new treatment results of three major German pain centers were presented and reviewed with the objectives of obtaining responder rates for different pain syndromes, assessing maintenance of effect under real-life conditions, and giving recommendations for practical care. The 12 week responder rates with pain relief of ≥ 30% were comparable in patients with mononeuropathies (37.9%) and postherpetic neuralgia (38.8%). Similar responder rates were seen in a subgroup of patients with cervical spine radiculopathy and back pain (46.7%). In HIV-associated neuropathy the responder rates were high (47.8%) but lower in patients with other polyneuropathies (17.6%). Response rates were nearly identical after 1 week (46.6%) and 4 weeks (43.3) and dropped only slightly at 12 weeks (37.4%). In a subgroup of 54 patients who underwent a second treatment, efficacy was maintained. Response rates in patients with or without lidocaine pretreatment were comparable. Treatment with the capsaicin 8% cutaneous patch was generally safe and well tolerated. The workshop panel recommended further investigation of opportunities to improve the application procedure and to perform studies on the skin penetration and distribution of capsaicin. A modified quantitative sensory testing (QST) should be developed for clinical practice in order to better understand the correlation of sensory profiles and response to capsaicin treatment.

Unravelling the mystery of capsaicin: a tool to understand and treat pain

A large number of pharmacological studies have used capsaicin as a tool to activate many physiological systems, with an emphasis on pain research but also including functions such as the cardiovascular system, the respiratory system, and the urinary tract. Understanding the actions of capsaicin led to the discovery its receptor, transient receptor potential (TRP) vanilloid subfamily member 1 (TRPV1), part of the superfamily of TRP receptors, sensing external events. This receptor is found on key fine sensory afferents, and so the use of capsaicin to selectively activate pain afferents has been exploited in animal studies, human psychophysics, and imaging studies. Its effects depend on the dose and route of administration and may include sensitization, desensitization, withdrawal of afferent nerve terminals, or even overt death of afferent fibers. The ability of capsaicin to generate central hypersensitivity has been valuable in understanding the consequences and mechanisms behind enhanced central processing of pain. In addition, capsaicin has been used as a therapeutic agent when applied topically, and antagonists of the TRPV1 receptor have been developed. Overall, the numerous uses for capsaicin are clear; hence, the rationale of this review is to bring together and discuss the different types of studies that exploit these actions to shed light upon capsaicin working both as a tool to understand pain but also as a treatment for chronic pain. This review will discuss the various actions of capsaicin and how it lends itself to these different purposes.

Transient receptor potential vanilloid 1 as a therapeutic target in analgesia

INTRODUCTION

The selective excitatory action of capsaicin followed by long-term chemoanalgesia due to an action on the 'capsaicin receptor' of C-polymodal nociceptors, cloned 15 years ago, opened up fascinating perspectives for a class of nociceptor blocking analgesics.

AREAS COVERED

The TRPV1/capsaicin receptor is an integrative, chemoceptive, noxious heat-gated cation channel also gated by several endogenous ligands and sensitized by phosphorylation through intracellular cascades triggered from receptors of bradykinin, prostanoids, NGF and interactions with TRPA1. In this review, types of sensory receptors and unique mechanisms for blocking nociceptor action, e.g., 'pore dilation' intracellular acidosis and the long-term function-related mitochondrial swelling at the nerve terminals and sensory neurons are summarized. In humans the 8% capsaicin dermal patch is already in usage for nondiabetic neuropathic pain and two topical preparations of civamide have also been approved recently for cluster headache and osteoarthritis. Evidence for epidermal nerve terminal loss in humans after topical applications and misleading results on sensory neuron death evoked by TRPV1 agonism in animals are discussed.

EXPERT OPINION

The unique 'multisteric' gating of TRPV1 channel which is opened and modulated in various conformational changes to natural stimuli differs from the operation of canonical ligand-gated channels and makes it suitable to initiate development of second generation of TRPV1 antagonists without on-target side effects of hyperthermia and risk of burn injury.

Vaccination against herpes zoster in developed countries: state of the evidence

Although progress has been made in the treatment of herpes zoster (HZ) and postherpetic neuralgia (PHN), available therapeutic options are only partially effective. Given evidence that a live-attenuated varicella-zoster-virus vaccine is effective at reducing the incidence of HZ, PHN and the burden of illness, policymakers and clinicians are being asked to make recommendations regarding the use of the zoster vaccine. In this report, we summarize the evidence regarding the: (1) burden of illness; (2) vaccine efficacy and safety; and (3) cost-effectiveness of vaccination, to assist evidence-based policy making and guide clinicians in their recommendations. First, there is general agreement that the overall burden of illness associated with HZ and PHN is substantial. Second, the safety and efficacy of the zoster vaccine at reducing the burden of illness due to HZ and the incidence of PHN have been clearly demonstrated in large placebo-controlled trials. However, uncertainty remains about the vaccine's duration of protection. Third, vaccination against HZ is likely to be cost-effective when the vaccine is given at approximately 65 y of age, if vaccine duration is longer than 10 y.

Diagnosing and managing postherpetic neuralgia

Postherpetic neuralgia (PHN) represents a potentially debilitating and often undertreated form of neuropathic pain that disproportionately affects vulnerable populations, including the elderly and the immunocompromised. Varicella zoster infection is almost universally prevalent, making prevention of acute herpes zoster (AHZ) infection and prompt diagnosis and aggressive management of PHN of critical importance. Despite the recent development of a herpes zoster vaccine, prevention of AHZ is not yet widespread or discussed in PHN treatment guidelines. Diagnosis of PHN requires consideration of recognized PHN signs and known risk factors, including advanced age, severe prodromal pain, severe rash, and AHZ location on the trigeminal dermatomes or brachial plexus. PHN pain is typically localized, unilateral and chronic, but may be constant, intermittent, spontaneous and/or evoked. PHN is likely to interfere with sleep and daily activities. First-line therapies for PHN include tricyclic antidepressants, gabapentin and pregabalin, and the lidocaine 5 % patch. Second-line therapies include strong and weak opioids and topical capsaicin cream or 8 % patch. Tricyclic antidepressants, gabapentinoids and strong opioids are effective but are also associated with systemic adverse events that may limit their use in many patients, most notably those with significant medical comorbidities or advanced age. Of the topical therapies, the topical lidocaine 5 % patch has proven more effective than capsaicin cream or 8 % patch and has a more rapid onset of action than the other first-line therapies or capsaicin. Given the low systemic drug exposure, adverse events with topical therapies are generally limited to application-site reactions, which are typically mild and transient with lidocaine 5 % patch, but may involve treatment-limiting discomfort with capsaicin cream or 8 % patch. Based on available clinical data, clinicians should consider administering the herpes zoster vaccine to all patients aged 60 years and older. Clinicians treating patients with PHN may consider a trial of lidocaine 5 % patch monotherapy before resorting to a systemic therapy, or alternatively, may consider administering the lidocaine 5 % patch in combination with a tricyclic antidepressant or a gabapentinoid to provide more rapid analgesic response and lower the dose requirement of systemic therapies.

Positive allosteric modulation of TRPV1 as a novel analgesic mechanism

Background

The prevalence of long-term opiate use in treating chronic non-cancer pain is increasing, and prescription opioid abuse and dependence are a major public health concern. To explore alternatives to opioid-based analgesia, the present study investigates a novel allosteric pharmacological approach operating through the cation channel TRPV1. This channel is highly expressed in subpopulations of primary afferent unmyelinated C- and lightly-myelinated Aδ-fibers that detect low and high rates of noxious heating, respectively, and it is also activated by vanilloid agonists and low pH. Sufficient doses of exogenous vanilloid agonists, such as capsaicin or resiniferatoxin, can inactivate/deactivate primary afferent endings due to calcium overload, and we hypothesized that positive allosteric modulation of agonist-activated TRPV1 could produce a selective, temporary inactivation of nociceptive nerve terminals in vivo. We previously identified MRS1477, a 1,4-dihydropyridine that potentiates vanilloid and pH activation of TRPV1 in vitro, but displays no detectable intrinsic agonist activity of its own. To study the in vivo effects of MRS1477, we injected the hind paws of rats with a non-deactivating dose of capsaicin, MRS1477, or the combination. An infrared diode laser was used to stimulate TRPV1-expressing nerve terminals and the latency and intensity of paw withdrawal responses were recorded. qRT-PCR and immunohistochemistry were performed on dorsal root ganglia to examine changes in gene expression and the cellular specificity of such changes following treatment.

Results

Withdrawal responses of the capsaicin-only or MRS1477-only treated paws were not significantly different from the untreated, contralateral paws. However, rats treated with the combination of capsaicin and MRS1477 exhibited increased withdrawal latency and decreased response intensity consistent with agonist potentiation and inactivation or lesion of TRPV1-containing nerve terminals. The loss of nerve endings was manifested by an increase in levels of axotomy markers assessed by qRT-PCR and colocalization of ATF3 in TRPV1⁺ cells visualized via immunohistochemistry.

Conclusions

The present observations suggest a novel, non-narcotic, selective, long-lasting TRPV1-based approach for analgesia that may be effective in acute, persistent, or chronic pain disorders.

Combination pharmacotherapy for the treatment of neuropathic pain in adults

BACKGROUND

Pharmacotherapy remains an important modality for the treatment of neuropathic pain. However, as monotherapy current drugs are associated with limited efficacy and dose-related side effects. Combining two or more different drugs may improve analgesic efficacy and, in some situations, reduce overall side effects (e.g. if synergistic interactions allow for dose reductions of combined drugs).

OBJECTIVES

This review evaluated the efficacy, tolerability and safety of various drug combinations for the treatment of neuropathic pain.

SEARCH METHODS

We identified randomised controlled trials (RCTs) of various drug combinations for neuropathic pain from CENTRAL, MEDLINE, EMBASE and handsearches of other reviews and trial registries. The most recent search was performed on 9 April 2012.

SELECTION CRITERIA

Double-blind, randomised studies comparing combinations of two or more drugs (systemic or topical) to placebo and/or at least one other comparator for the treatment of neuropathic pain.

DATA COLLECTION AND ANALYSIS

Data extracted from each study included: proportion of participants a) reporting ≥ 30% pain reduction from baseline OR ≥ moderate pain relief OR ≥ moderate global improvement; b) dropping out of the trial due to treatment-emergent adverse effects; c) reporting each specific adverse effect (e.g. sedation, dizziness) of ≥ moderate severity. The primary comparison of interest was between study drug(s) and one or both single-agent comparators. We combined studies if they evaluated the same drug class combination at roughly similar doses and durations of treatment. We used RevMan 5 to analyse data for binary outcomes.

MAIN RESULTS

We identified 21 eligible studies: four (578 participants) evaluated the combination of an opioid with gabapentin or pregabalin; two (77 participants) evaluated an opioid with a tricyclic antidepressant; one (56 participants) of gabapentin and nortriptyline; one (120 participants) of gabapentin and alpha-lipoic acid, three (90 participants) of fluphenazine with a tricyclic antidepressant; three (90 participants) of an N-methyl-D-aspartate (NMDA) blocker with an agent from a different drug class; five (604 participants) of various topical medications; one (313 participants) of tramadol with acetaminophen; and another one (44 participants) of a cholecystokinin blocker (L-365,260) with morphine. The majority of combinations evaluated to date involve drugs, each of which share some element of central nervous system (CNS) depression (e.g. sedation, cognitive dysfunction). This aspect of side effect overlap between the combined agents was often reflected in similar or higher dropout rates for the combination and may thus substantially limit the utility of such drug combinations. Meta-analysis was possible for only one comparison of only one combination, i.e. gabapentin + opioid versus gabapentin alone. This meta-analysis involving 386 participants from two studies demonstrated modest, yet statistically significant, superiority of a gabapentin + opioid combination over gabapentin alone. However, this combination also produced significantly more frequent side effect-related trial dropouts compared to gabapentin alone.

AUTHORS' CONCLUSIONS

Multiple, good-quality studies demonstrate superior efficacy of two-drug combinations. However, the number of available studies for any one specific combination, as well as other study factors (e.g. limited trial size and duration), preclude the recommendation of any one specific drug combination for neuropathic pain. Demonstration of combination benefits by several studies together with reports of widespread clinical polypharmacy for neuropathic pain surely provide a rationale for additional future rigorous evaluations. In order to properly identify specific drug combinations which provide superior efficacy and/or safety, we recommend that future neuropathic pain studies of two-drug combinations include comparisons with placebo and both single-agent components. Given the apparent adverse impact of combining agents with similar adverse effect profiles (e.g. CNS depression), the anticipated development and availability of non-sedating neuropathic pain agents could lead to the identification of more favourable analgesic drug combinations in which side effects are not compounded.

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

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