An open-label pilot study of high-concentration capsaicin patch in painful HIV neuropathy

Treating neuropathic pain and comorbid affective disorders: Preclinical and clinical evidence

INTRODUCTION

Neuropathic pain (NP) significantly impacts quality of life and often coexists with affective disorders such as anxiety and depression. Addressing both NP and its psychiatric manifestations requires a comprehensive understanding of therapeutic options. This study aimed to review the main pharmacological and non-pharmacological treatments for NP and comorbid affective disorders to describe their mechanisms of action and how they are commonly used in clinical practice.

METHODS

A review was conducted across five electronic databases, focusing on pharmacological and non-pharmacological treatments for NP and its associated affective disorders. The following combination of MeSH and title/abstract keywords were used: "neuropathic pain," "affective disorders," "depression," "anxiety," "treatment," and "therapy." Both animal and human studies were included to discuss the underlying therapeutic mechanisms of these interventions.

RESULTS

Pharmacological interventions, including antidepressants, anticonvulsants, and opioids, modulate neural synaptic transmission to alleviate NP. Topical agents, such as capsaicin, lidocaine patches, and botulinum toxin A, offer localized relief by desensitizing pain pathways. Some of these drugs, especially antidepressants, also treat comorbid affective disorders. Non-pharmacological techniques, including repetitive transcranial magnetic stimulation, transcranial direct current stimulation, and photobiomodulation therapy, modulate cortical activity and have shown promise for NP and mood disorders.

CONCLUSIONS

The interconnection between NP and comorbid affective disorders necessitates holistic therapeutic strategies. Some pharmacological treatments can be used for both conditions, and non-pharmacological interventions have emerged as promising complementary approaches. Future research should explore novel molecular pathways to enhance treatment options for these interrelated conditions.

Is the Capsaicin 179 mg (8% w/w) Cutaneous Patch an Appropriate Treatment Option for Older Patients with Peripheral Neuropathic Pain?

Introduction

Capsaicin 179 mg (8% weight per weight) cutaneous patch ("capsaicin patch") is a recommended topical treatment for peripheral neuropathic pain (PNP). In older patients, topical treatments may be preferred over systemic treatments, but data specific to the older population are scarce.

Methods

We conducted pooled analyses of multiple clinical trials to evaluate efficacy and safety of capsaicin patch in older patients. The analysis of efficacy included four randomized, double-blind, 12-week studies with similar trial design comparing a single treatment of capsaicin 179 mg cutaneous patch vs low-dose control patch in post-herpetic neuralgia. For the safety evaluation, data were pooled from 18 interventional studies in which capsaicin patch was used in PNP with varying etiologies.

Results

Capsaicin patch had similar analgesic efficacy in elderly (n=582) and non-elderly patients (n=545) in terms of change from baseline to 2-12 weeks in the 11-point numeric pain rating scale (NPRS) score for average pain over the previous 24 hours. In both age groups, decrease in NPRS score was significantly greater with capsaicin patch vs control. Older patients treated with capsaicin patch were significantly more likely than those in the control group to achieve responder status (ie mean decrease in NPRS score from baseline to week 2-12 of at least 30% or ≥2 points): 36.1% vs 27.1% (odds ratio [OR] [95% CI] 1.52 [1.06, 2.18]; P=0.0231) and 33.1% vs 20.9% (OR [95% CI] 1.90 [1.30, 2.78]; P=0.0009) for active treatment vs control group, respectively. Similar proportions of non-elderly patients (n=2,311) and elderly patients (n=537) treated with capsaicin patch experienced treatment-emergent adverse events (TEAEs) (81.6% and 78.1%, respectively) and serious TEAEs (8.2% and 7.2%), with application-site reactions the most common TEAEs in both groups.

Conclusion

The capsaicin patch was equally efficacious and well tolerated in older patients as in younger patients.

Traditional processing increases biological activities of Dendrobium offificinale Kimura et. Migo in Southeast Yunnan, China

The orchid Dendrobium officinale grows throughout southeast China and southeast Asian countries and is used to treat inflammation and diabetes in traditional Chinese medicine. Tie pi feng dou is a well-known traditional Chinese medicine made from the dried D. officinale stems. Processing alters the physicochemical properties of TPFD; however, it is unclear how processing affects the quality and medicinal value of this plant. Here, we analyzed and compared the chemical composition of fresh stems of D. officinale and TPFD and explored possible explanations for the enhanced medicinal efficacy of processed D. officinale stems using qualitative and quantitative methods. To identify the components of FSD and TPFD, we used ultra-high-performance liquid chromatography combined with mass spectrometry in negative and positive ion modes and interpreted the data using the Human Metabolome Database and multivariate statistical analysis. We detected 23,709 peaks and identified 2352 metabolites; 370 of these metabolites were differentially abundant between FSD and TPFD (245 more abundant in TPFD than in FSD, and 125 less abundant), including organooxygen compounds, prenol lipids, flavonoids, carboxylic acids and their derivatives, and fatty acyls. Of these, 43 chemical markers clearly distinguished between FSD and TPFD samples, as confirmed using orthogonal partial least squares discriminant analysis. A pharmacological activity analysis showed that, compared with FSD, TPFD had significantly higher levels of some metabolites with anti-inflammatory activity, consistent with its use to treat inflammation. In addition to revealing the basis of the medicinal efficacy of TPFD, this study supports the benefits of the traditional usage of D. officinale.

Dermatopharmacokinetic and pharmacodynamic evaluation of a novel nanostructured formulation containing capsaicinoids for treating neuropathic pain

The in vivo skin penetration by dermal microdialysis and the pharmacological efficacy of a chitosan hydrogel containing capsaicinoids-loaded nanocapsules (CHNC_Caps) was evaluated in this study. Such gel has previously been proven to control capsaicinoids release and decrease the drugs side effects in humans. The nanocapsules containing capsaicinoids had an average size around 150 nm, with a low polydispersity index, positive zeta potential, and high encapsulation efficiency of the drugs. The CHNC_Caps showed intact nanocapsules, a slightly acid pH value, and a pseudoplastic behavior suitable for topical application. Microdialysis experiments showed a 1.6-fold increase in the concentration of capsaicinoids in the dermis (after 12 h of its application) when CHNC_Caps was administered compared to a chitosan hydrogel containing capsaicinoids in hydroethanolic solution (CHET_Caps) and the commercial cream. The CHNC_Caps showed antiallodynic and antihyperalgesic effects from 6 h to 96 h after treatment initiation, whereas CHET_Caps and the commercial cream showed antiallodynic and antihyperalgesic effects only at 48 h and 96 h after treatment initiation, respectively. CHNC_Caps and the commercial cream maintained antihyperalgesic activity for 6 days after treatment interruption. For mechanical allodynia, the antinociceptive effect was maintained for 48 h after treatment interruption only with CHNC_Caps. In conclusion, CHNC_Caps is a promising formulation for treating peripheral neuropathic pain.

Human immunodeficiency virus-related peripheral neuropathy: A systematic review and meta-analysis

BACKGROUND AND PURPOSE

Human immunodeficiency virus (HIV)-associated neurological syndromes occur in affected individuals as a consequence of primary HIV infection, opportunistic infections, inflammation and as an adverse effect of some forms of antiretroviral treatment (ART). The aim of this systematic review was to establish the epidemiological characteristics, clinical features, pathogenetic mechanisms and risk factors of HIV-related peripheral neuropathy (PN).

METHODS

A systematic, computer-based search was conducted using the PubMed database. Data regarding the above parameters were extracted. Ninety-four articles were included in this review.

RESULTS

The most commonly described clinical presentation of HIV neuropathy is the distal predominantly sensory polyneuropathy. The primary pathology in HIVPN appears to be axonal rather than demyelinating. Age and treatment with medications belonging in the nucleoside analogue reverse transcriptase class are risk factors for developing HIV-related neuropathy. The pooled prevalence of PN in patients naïve to ARTs was established to be 29% (95% CI: 9%-62%) and increased to 38% (95% confidence interval [CI]: 29%-48%) when looking into patients at various stages of their disease. More than half of patients with HIV-related neuropathy are symptomatic (53%, 95% CI: 41%-63%). Management of HIV-related neuropathy is mainly symptomatic, although there is evidence that discontinuation of some types of ART, such as didanosine, can improve or resolve symptoms.

CONCLUSIONS

Human immunodeficiency virus-related neuropathy is common and represents a significant burden in patients' lives. Our understanding of the disease has grown over the last years, but there are unexplored areas requiring further study.

Identification of the dietary supplement capsaicin as an inhibitor of Lassa virus entry

The limited treatment options for the increasing occurrence of Lassa hemorrhagic fever in West Africa poses an urgent need for the discovery and development of novel therapeutics. Dietary supplements, especially natural products that are edible and safe for human use, are a good source of drug discovery with potential for uncovering novel applications. In this study, we tested 40 natural products of dietary supplements and identified capsaicin, a common dietary supplement abundant in chili peppers, as an inhibitor of Lassa virus (LASV) entry with EC50 of 6.9-10.0 μmol/L using an HIV based pseudovirus platform. Capsaicin inhibits the entry of five LASV strains but not against the Old World arenavirus lymphocytic choriomeningitis virus (LCMV), showing a preferential activity against LASV. Capsaicin inhibits LASV entry by blocking the pH dependent viral fusion through affecting the stable signal peptide (SSP)-GP2 transmembrane (GP2TM) region of the LASV surface glycoprotein. Mutational study revealed the key residues Ala25, Val431, Phe434 and Val435 in SSP-GP2TM region in capsaicin's antiviral effect. This study for the first time reveals a direct acting antiviral effect of capsaicin against the hemorrhagic fever causing LASV, providing detailed interaction hot spots in the unique SSP-GP2TM interface of LASV glycoprotein that is crucial in fusion inhibition, and offering a new strategy in discovering and developing antivirals from natural products that are safe for human use.

Plant-derived medicines for neuropathies: a comprehensive review of clinical evidence

Neuropathy is defined as the damage to the peripheral or central nervous system accompanied by pain, numbness, or muscle weakness, which can be due to congenital diseases or environmental factors such as diabetes, trauma, or viral infections. As current treatments are not sufficiently able to control the disease, studies focusing on the identification and discovery of new therapeutic agents are necessary. Natural products have been used for a long time for the management of different neurological problems including neuropathies. The aim of the present study is to review the current clinical data on the beneficial effects of medicinal plants in neuropathy. Electronic databases including PubMed, Scopus, and Cochrane Library were searched with the keywords ‘neuropathy’ in the title/abstract and ‘plant’ or ‘extract’ or ‘herb’ in the whole text from inception until August 2017. From a total of 3679 papers, 22 studies were finally included. Medicinal plants were evaluated clinically in several types of neuropathy, including diabetic neuropathy, chemotherapy-induced peripheral neuropathy, carpal tunnel syndrome, and HIV-associated neuropathy. Some studies reported the improvement in pain, nerve function, nerve conduction velocity, and quality of life. Cannabis sativa (hemp), Linum usitatissimum (linseed oil), capsaicin, and a polyherbal Japanese formulation called Goshajinkigan had the most evidence regarding their clinical efficacy. Other investigated herbal medicines in neuropathy, such as Matricaria chamomilla (chamomile), Curcuma longa (turmeric), and Citrullus colocynthis (colocynth), had only one clinical trial. Thus, future studies are necessary to confirm the safety and efficacy of such natural medicines as a complementary or alternative treatment for neuropathy.

Sensitized vasoactive C-nociceptors: key fibers in peripheral neuropathic pain

Introduction

Multiple mechanisms are involved in the development and persistence of neuropathic pain. Some patients with nerve damage will remain painless and develop a "loss of function" phenotype, whereas others develop painful neuropathies.

Objectives

The aim of this study is to investigate the role of a peripheral nervous system sensitization by analyzing patients with and without pain.

Methods

The topical application of capsaicin was investigated in peripheral nociceptors. Two groups of patients (painful vs painless) with length-dependent neuropathies and small-fiber impairment were tested. Quantitative sensory testing was assessed before and after topical application of 0.6% capsaicin in the affected skin. In addition, blood perfusion measurements and an axon reflex flare assessment were performed.

Results

Quantitative testing revealed that heat hyperalgesia was induced in all patients and volunteers (P < 0.01) without observing any significant differences between patient groups. By contrast, the extent of the axon reflex flare reaction (P < 0.01) as well as the blood perfusion (P < 0.05) was significantly greater in patients with pain than in neuropathy patients not experiencing pain.

Conclusion

Hyperexcitable vasoactive nociceptive C fibers might contribute to pain in peripheral neuropathies and therefore may serve as a key player in separating into a painless or painful condition.

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.

Antinociceptive effects of topical mepivacaine in a rat model of HIV-associated peripheral neuropathic pain

Background

A consequence of HIV infection is sensory neuropathy, a debilitating condition that degrades the quality of life of HIV patients. Furthermore, life-extending antiretroviral treatment may exacerbate HIV sensory neuropathy. Analgesics that relieve other neuropathic pains show little or no efficacy in ameliorating HIV sensory neuropathy. Thus, there is a need for analgesics for people with this particular pain. While lidocaine is used in the management of painful peripheral neuropathies, another local anesthetic mepivacaine, with a potentially improved bioavailability, could be utilized for the management of HIV neuropathic pain.

Methods

The efficacy of topical anesthetics was evaluated in a preclinical rodent model of painful peripheral neuropathy induced by epineural administration of the HIV envelope protein gp120 delivered using saturated oxidized cellulose implanted around the sciatic nerve. Beginning at 2 weeks following gp120 administration, the effects of local anesthetics topically applied via gauze pads were tested on heat and mechanical hyperalgesia in the hind paw. Rats were tested using several concentrations of mepivacaine or lidocaine during the following 2 weeks.

Results

By 2 weeks following epineural gp120 implantation, the ipsilateral hind paw developed significant hypersensitivity to noxious pressure and heat hyperalgesia. A short-lasting, concentration-dependent amelioration of pressure and heat hyperalgesia was observed following topical application of mepivacaine to the ipsilateral plantar hind paw. By contrast, topical lidocaine ameliorated heat hyperalgesia in a concentration-dependent manner but not pressure hyperalgesia. Equipotent concentrations of mepivacaine and lidocaine applied topically to the tail of mice significantly increased tail withdrawal latencies in the tail flick test, demonstrating that both local anesthetics attenuate responding to a brief noxious stimulus.

Conclusion

These findings showed that mepivacaine, rather than lidocaine, consistently attenuated two distinct symptoms of neuropathic pain and suggest that topical formulations of this local anesthetic could have utility in the alleviation of clinical HIV neuropathic pain.

Cutaneous drug delivery of capsaicin after in vitro administration of the 8% capsaicin dermal patch system

OBJECTIVE

Epicutaneous application of capsaicin causes a long-lasting analgesic effect by binding to the membrane transient receptor potential vanilloid 1 (TRPV1) on mechanoheat-sensitive C and Aδ fibres, changing axonal integrity and inhibiting neurogenic inflammatory processes. To date, no information is available regarding the cutaneous drug delivery of capsaicin following patch application.

METHODS

Using a Franz diffusion cell, the cutaneous concentration-time profiles 30, 60 and 90 min after application of a patch containing 8% capsaicin (640 µg/cm(2)) on ex vivo thin (mamma) and thick (plantar) human skin were investigated at 32 °C, and additionally at 42 °C for thin skin and 10 °C for thick skin. An HPLC-MS method was used for the analytic detection of capsaicin.

RESULTS

The results show that already after a 30-min application of the 8% capsaicin patch, an equilibrium reservoir can be found in the stratum corneum in both thick and thin skin. Under physiological temperature conditions, a sufficient bioavailability of capsaicin in the cutaneous target compartments can be found. Raising the temperature to 42 °C has no relevant impact on the concentration-time profile, while reducing the temperature to 10°C leads to a significantly lower bioavailability.

CONCLUSION

After 30 min of application, a sufficient cutaneous bioavailability of capsaicin is reached in thick as well as thin skin. Whether shorter application times may suffice to achieve therapeutic effectiveness requires further investigation.

Capsaicin-based therapies for pain control

The TRPV1 receptor is known to play a role in nociceptive transmission in multiple organ systems, usually in response to the pain of inflammation. TRPV1 antagonism has so far shown limited benefit in antinociception. Capsaicin, a TRPV1 agonist, has been shown to induce a refractory period in the nerve terminal expressing TRPV1 and even, in sufficient dosing, to create long-term nerve terminal defunctionalization. This has led to research into topical capsaicin as a treatment for multiple painful conditions. The majority of work has focused on musculoskeletal pain and neuropathic pain and has revealed that although low-dose topical capsaicin has limited effectiveness as an analgesic, high-dose capsaicin, when tolerated, has the potential for long-term analgesia in certain types of neuropathic pain.

Insulin-like growth factor-1 prevents dorsal root ganglion neuronal tyrosine kinase receptor expression alterations induced by dideoxycytidine in vitro

Dideoxycytidine (zalcitabine, ddC) produces neurotoxic effects. It is particularly important to understand the toxic effects of ddC on different subpopulations of dorsal root ganglion (DRG) neurons which express distinct tyrosine kinase receptor (Trk) and to find therapeutic factors for prevention and therapy for ddC-induced peripheral sensory neuropathy. Insulin-like growth factor-1 (IGF-1) has been shown to have neurotrophic effects on DRG sensory neurons. However, little is known about the effects of ddC on distinct Trk (TrkA, TrkB, and TrkC) expression in DRG neurons and the neuroprotective effects of IGF-1 on ddC-induced neurotoxicity. Here, we have tested the extent to which the expression of TrkA, TrkB, and TrkC receptors in primary cultured DRG neurons is affected by ddC in the presence or absence of IGF-1. In this experiment, we found that exposure of 5, 25, and 50 μmol/L ddC caused a dose-dependent decrease of the mRNA, protein, and the proportion of TrkA-, TrkB-, and TrkC-expressing neurons. IGF-1 (20 nmol/L) could partially reverse the decrease of TrkA and TrkB, but not TrkC, expression with ddC exposure. The phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 (10 μmol/L) blocked the effects of IGF-1. These results suggested that the subpopulations of DRG neurons which express distinct TrkA, TrkB, and TrkC receptors were affected by ddC exposure. IGF-1 might relieve the ddC-induced toxicity of TrkA- and TrkB-, but not TrkC-expressing DRG neurons. These data offer new clues for a better understanding of the association of ddC with distinct Trk receptor expression and provide new evidence of the potential therapeutic role of IGF-1 on ddC-induced neurotoxicity.

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.

A randomized, double-blind, controlled study of NGX-4010, a capsaicin 8% dermal patch, for the treatment of painful HIV-associated distal sensory polyneuropathy

INTRODUCTION

Effective treatment of HIV-associated distal sensory polyneuropathy remains a significant unmet therapeutic need.

METHODS

In this randomized, double-blind, controlled study, patients with pain due to HIV-associated distal sensory polyneuropathy received a single 30-minute or 60-minute application of NGX-4010--a capsaicin 8% patch (n = 332)--or a low-dose capsaicin (0.04%) control patch (n = 162). The primary endpoint was the mean percent change from baseline in Numeric Pain Rating Scale score to weeks 2-12. Secondary endpoints included patient global impression of change at week 12.

RESULTS

Pain reduction was not significantly different between the total NGX-4010 group (-29.5%) and the total control group (-24.5%; P = 0.097). Greater pain reduction in the 60-minute (-30.0%) versus the 30-minute control group (-19.1%) prevented intended pooling of the control groups to test individual NGX-4010 treatment groups. No significant pain reduction was observed for the 30-minute NGX-4010 group compared with 30-minute control (-26.2% vs.-19.1%, respectively, P = 0.103). Pain reductions in the 60-minute NGX-4010 and control groups were comparable (-32.8% vs. -30.0%, respectively; P = 0.488). Posthoc nonparametric testing demonstrated significant differences favoring the total (P = 0.044) and 30-minute NGX-4010 groups (P = 0.035). Significantly, more patients in the total and 30-minute NGX-4010 group felt improved on the patient global impression of change versus control (67% vs. 55%, P = 0.011 and 65% vs. 45%, P = 0.006, respectively). Mild to moderate transient application site pain and erythema were the most common adverse events.

CONCLUSIONS

Although the primary endpoint analyses were not significant, trends toward pain improvement were observed after a single 30-minute NGX-4010 treatment.

Tolerability of NGX-4010, a capsaicin 8% patch, in conjunction with three topical anesthetic formulations for the treatment of neuropathic pain

BACKGROUND

The objective of this study was to assess the safety, tolerability, and preliminary efficacy of NGX-4010, a capsaicin 8% patch, following pretreatment with three different topical anesthetics in patients with peripheral neuropathic pain.

METHODS

This open-label, multicenter study enrolled 117 patients with post-herpetic neuralgia, HIV-associated distal sensory polyneuropathy, or painful diabetic neuropathy. Patients received pretreatment with one of three lidocaine 4%-based topical anesthetics (L.M.X.4(®) [Ferndale Laboratories Inc, Ferndale, MI], Topicaine(®) Gel [Estela Basso, Jupiter, FL], or Betacaine Enhanced Gel 4 [Tiberius Inc, Tampa, FL]) for 60 minutes followed by a single 60- or 90-minute NGX-4010 application, and were followed for 12 weeks. Tolerability and safety measures included "pain now" Numeric Pain Rating Scale (NPRS) scores, dermal assessments, medication use for treatment-related pain, adverse events (AEs), clinical laboratory parameters, physical examinations, and vital signs. The primary efficacy variable was the percentage change in mean NPRS scores for "average pain for the past 24 hours" from baseline to weeks 2 through 12.

RESULTS

Treatment with NGX-4010 following pretreatment with any of the three topical anesthetics was generally safe and well tolerated. Nearly all patients completed ≥90% of the planned NGX-4010 application duration. The most common treatment-related AEs, application-site burning and application-site pain, were transient, mostly mild or moderate, and could be adequately managed by local cooling or short-acting oral opioid analgesics. Although slightly more patients used medication for treatment-related discomfort following pretreatment with Topicaine compared with L.M.X.4 or Betacaine, there were no statistical differences between the topical anesthetics. Neuropathic pain reduction from baseline to weeks 2 through 12 was approximately 30% and was similar among the topical anesthetics; the proportion of responders ranged from 45% to 50%.

CONCLUSION

Treatment with NGX-4010 following pretreatment with any of the three topical anesthetics was generally safe and well tolerated; no significant differences in the parameters measured were noted between the pretreatment groups.

Efficacy, safety, and tolerability of NGX-4010, capsaicin 8% patch, in an open-label study of patients with peripheral neuropathic pain

AIMS

To assess efficacy, safety, and tolerability of NGX-4010, capsaicin 8% patch, in patients with peripheral neuropathic pain.

METHODS

This open-label, uncontrolled, 12-week study enrolled 25 patients with postherpetic neuralgia (PHN), one with HIV-distal sensory polyneuropathy, and 91 with painful diabetic neuropathy (PDN). Patients received pre-treatment with one of three 4% lidocaine topical anesthetics (L.M.X.4¹, Topicaine Gel², or Betacaine Enhanced Gel 4³) followed by a single 60- or 90-min NGX-4010 application. The primary efficacy variable was the percentage change in Numeric Pain Rating Scale scores from baseline to Weeks 2-12. Adverse events (AEs), laboratory parameters, vital signs, neurosensory examinations, dermal assessments, treatment-related pain scores, and medication use for treatment-related pain were collected.

RESULTS

PDN and PHN patients achieved a 31% and 28% mean pain decrease from baseline during Weeks 2-12, respectively, and 47% and 44%, respectively, were responders (≥30% pain decrease). Mild or moderate treatment-site-related burning and pain were the most common AEs and there was no evidence of impaired neurosensory function.

CONCLUSIONS

NGX-4010 in conjunction with any of the three topical anesthetics tested was generally safe and well tolerated and reduced pain over a 12-week period in patients with PDN and PHN.

Capsaicin 8% topical patch (Qutenza)--a review of the evidence

Qutenza is a high-potency capsaicin (8%) topical patch, labeled for treating pain associated with postherpetic neuralgia (PHN). Qutenza decreases pain sensation by reducing transient receptor potential vanilloid 1 (TRPV1) expression and decreasing the density of epidermal nerve fibers in the application area. Systemic absorption from Qutenza is low. Qutenza has not been directly compared to any other medications for the treating PHN. Two pivotal clinical trials compared Qutenza to a control patch (0.04% capsaicin) in PHN. The primary endpoint of both trials was the reduction in numeric pain rating scale (NPRS) score. Qutenza reduced pain from baseline to weeks 2 to 8 (29.6% and 32% reductions) compared to control (19.9% and 24.4% reductions; P ≤ .01). The improvement in NPRS scores persisted, with score reductions greater with Qutenza (29.9% and 32.3% reductions) compared to control (20.4% and 25% reductions; P ≤ .03) for the period 2 to 12 weeks. Safety and efficacy of capsaicin 8% has been demonstrated in open-label trials for up to 48 weeks. The most common adverse drug reactions occurring with capsaicin 8% are application site erythema (63%) and application site pain (42%). Some patients experienced transient increases in blood pressure during Qutenza application. Qutenza must be administered by a physician or under the close supervision of a physician. Prior to application, pretreat the affected area with a topical anesthetic to reduce application site pain. Some patients may require systemic analgesics during and after treatment for treatment-associated pain. Applications of Qutenza can be repeated no sooner than once every 3 months, as needed.

Pharmacological treatment of painful HIV-associated sensory neuropathy: a systematic review and meta-analysis of randomised controlled trials

BACKGROUND

Significant pain from HIV-associated sensory neuropathy (HIV-SN) affects ∼40% of HIV infected individuals treated with antiretroviral therapy (ART). The prevalence of HIV-SN has increased despite the more widespread use of ART. With the global HIV prevalence estimated at 33 million, and with infected individuals gaining increased access to ART, painful HIV-SN represents a large and expanding world health problem. There is an urgent need to develop effective pain management strategies for this condition.

METHOD AND FINDINGS

OBJECTIVE

To evaluate the clinical effectiveness of analgesics in treating painful HIV-SN.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

Medline, Cochrane central register of controlled trials, www.clinicaltrials.gov, www.controlled-trials.com and the reference lists of retrieved articles.

SELECTION CRITERIA

Prospective, double-blinded, randomised controlled trials (RCTs) investigating the pharmacological treatment of painful HIV-SN with sufficient quality assessed using a modified Jadad scoring method.

REVIEW METHODS

Four authors assessed the eligibility of articles for inclusion. Agreement of inclusion was reached by consensus and arbitration. Two authors conducted data extraction and analysis. Dichotomous outcome measures (≥ 30% and ≥ 50% pain reduction) were sought from RCTs reporting interventions with statistically significant efficacies greater than placebo. These data were used to calculate RR and NNT values.

RESULTS

Of 44 studies identified, 19 were RCTs. Of these, 14 fulfilled the inclusion criteria. Interventions demonstrating greater efficacy than placebo were smoked cannabis NNT 3.38 95%CI(1.38 to 4.10), topical capsaicin 8%, and recombinant human nerve growth factor (rhNGF). No superiority over placebo was reported in RCTs that examined amitriptyline (100mg/day), gabapentin (2.4 g/day), pregabalin (1200 mg/day), prosaptide (16 mg/day), peptide-T (6 mg/day), acetyl-L-carnitine (1g/day), mexilitine (600 mg/day), lamotrigine (600 mg/day) and topical capsaicin (0.075% q.d.s.).

CONCLUSIONS

Evidence of efficacy exists only for capsaicin 8%, smoked cannabis and rhNGF. However,rhNGF is clinically unavailable and smoked cannabis cannot be recommended as routine therapy. Evaluation of novel management strategies for painful HIV-SN is urgently needed.

Long-term safety of NGX-4010, a high-concentration capsaicin patch, in patients with peripheral neuropathic pain

CONTEXT

Postherpetic neuralgia (PHN) and painful human immunodeficiency virus-associated distal sensory polyneuropathy (HIV-DSP) are peripheral neuropathic pain syndromes that are difficult to treat. Current treatment options are often limited by poor tolerability.

OBJECTIVES

The objective of the current open-label study was to assess the safety of repeated applications of NGX-4010, a high-concentration capsaicin patch (capsaicin 8%), over one year, in patients with moderate to severe PHN or HIV-DSP.

METHODS

Patients had successfully completed a previous NGX-4010 study and had a pain level appropriate for further treatment. Eligible patients had not been treated with NGX-4010 within 12 weeks of study initiation. Patients received pretreatment with a topical local anesthetic (lidocaine 4%) for 60 minutes followed by either a 60-minute (PHN and HIV-DSP patients) or a 90-minute (HIV-DSP patients) treatment with NGX-4010. Patients could receive up to three additional treatments at intervals of > or = 12 weeks. Regardless of the number of treatments received, all patients were followed up for 48 weeks except for those withdrawing early.

RESULTS

A total of 106 patients were enrolled and received a total of 293 NGX-4010 treatments. The most frequently reported treatment-emergent adverse events were transient, mild-to-moderate application site erythema, pain, edema, and papules. Small, transient pain-related increases in blood pressure during and immediately after NGX-4010 application were observed. There was no evidence of an increased incidence of adverse events, dermal irritation, intolerability, or impaired neurological function with repeated treatments.

CONCLUSION

It is concluded that repeated treatments with NGX-4010 administered over a one-year period are generally safe and well tolerated.

Ion channel blockers for the treatment of neuropathic pain

Neuropathic pain, a severe chronic pain condition characterized by a complex pathophysiology, is a largely unmet medical need. Ion channels, which underlie cell excitability, are heavily implicated in the biological mechanisms that generate and sustain neuropathic pain. This review highlights the biological evidence supporting the involvement of voltage-, proton- and ligand-gated ion channels in the neuropathic pain setting. Ion channel modulators at different research or development stages are reviewed and referenced. Ion channel modulation is one of the main avenues to achieve novel, improved neuropathic pain treatments. Voltage-gated sodium and calcium channel and glutamate receptor modulators are likely to produce new, improved agents in the future. Rationally targeting subtypes of known ion channels, tackling recently discovered ion channel targets or combining drugs with different mechanism of action will be primary sources of new drugs in the longer term.

Novel insights on diagnosis, cause and treatment of diabetic neuropathy: focus on painful diabetic neuropathy

Diabetic neuropathy is common, under or misdiagnosed, and causes substantial morbidity with increased mortality. Defining and developing sensitive diagnostic tests for diabetic neuropathy is not only key to implementing earlier interventions but also to ensure that the most appropriate endpoints are employed in clinical intervention trials. This is critical as many potentially effective therapies may never progress to the clinic, not due to a lack of therapeutic effect, but because the endpoints were not sufficiently sensitive or robust to identify benefit. Apart from improving glycaemic control, there is no licensed treatment for diabetic neuropathy, however, a number of pathogenetic pathways remain under active study. Painful diabetic neuropathy is a cause of considerable morbidity and whilst many pharmacological and nonpharmacological interventions are currently used, only two are approved by the US Food and Drug Administration. We address the important issue of the 'placebo effect' and also consider potential new pharmacological therapies as well as nonpharmacological interventions in the treatment of painful diabetic neuropathy.

NGX-4010, a high-concentration capsaicin patch, for the treatment of postherpetic neuralgia: a randomized, double-blind, controlled study with an open-label extension

OBJECTIVES

To assess the efficacy, tolerability, and safety of NGX-4010, a high-concentration capsaicin dermal patch (capsaicin 640 microg/cm(2), 8%) in patients with postherpetic neuralgia (PHN).

METHODS

Patients were randomized to receive NGX-4010 or control patch in a 4-week, double-blind study. This was followed by an open-label extension phase (up to 48 weeks total) where patients could receive up to three additional treatments no sooner than 12 weeks after initial treatment. The primary efficacy variable was mean change from baseline in mean morning and evening numerical pain rating scale (NPRS) scores.

RESULTS

During days 8-28 after the double-blind treatment, NGX-4010 patients had a mean change in NPRS scores from baseline of -32.7% compared with -4.4% for control patients (P = 0.003). Mean NPRS scores decreased from baseline during week 1 in both treatment groups, remained relatively stable through week 12 in NXG-4010 patients, but returned to near baseline during weeks 2-4 in controls. Mean change in NPRS scores from baseline during weeks 2-12 was -33.8% for NGX-4010 and +4.9% for control recipients. A similar decrease in NPRS scores from baseline was maintained with subsequent NGX-4010 treatments, regardless of the number of treatments received. Transient increases in application site pain were adequately managed with analgesics. No increases in application site reactions or adverse events were observed with repeated treatments. No patients discontinued the study due to an adverse event.

CONCLUSION

NGX-4010 is a promising topical treatment for PHN patients, which appears to be tolerable, generally safe, and effective.

NeuroAIDS: an evolving epidemic

Over 60,000 Canadians are infected with human immunodeficiency virus (HIV). Greater than 50% of these individuals will develop a neurological disorder despite the availability of highly active antiretroviral therapy. HIV causes nervous system disease at all stages of infection with adverse effects on quality of life, adherence to medications, employment and survival. These disorders include opportunistic infections in addition to distinct HIV-associated neurological syndromes and undesirable treatment-related effects. The latter two groups of disorders are often undiagnosed and untreated in both adolescents and adults. Direct HIV infection of central nervous system causes HIV-associated dementia, which is a progressive subcortical dementia. HIV infection of the peripheral nervous system produces a painful sensory neuropathy termed distal sensory polyneuropathy, which may be exacerbated by several antiretroviral drugs. Other important HIV-induced neurological disorders include vacuolar myelopathy and an increased risk of seizures. Future issues that will confound the presentation and treatment of HIV-induced nervous system disorders include the increasing prevalence of drug-resistant HIV strains, increasing age of HIV-infected patients, hepatitis C virus co-infection and the Immune Reconstitution Inflammatory Syndrome. Herein, we review the clinical presentations, underlying pathogenesis and treatments of this burgeoning group of neurological disorders.

NGX-4010, a high-concentration capsaicin patch, for the treatment of postherpetic neuralgia: a randomised, double-blind study

BACKGROUND

The limitations of current treatments for postherpetic neuralgia (PHN) have led to the investigation of localised, non-systemic alternatives. NGX-4010, a high-concentration (8%) capsaicin dermal patch, was developed to treat patients with neuropathic pain. We report the results of a randomised, double blind, 12-week study of the efficacy and safety of one application of NGX-4010 in patients with PHN.

METHODS

In this multicentre, double-blind, parallel-group trial, 402 patients were randomly assigned to one 60-min application of NGX-4010 (640 microg/cm(2) [8% capsaicin]) or a low-concentration capsaicin control patch (3.2 microg/cm(2) [0.04% capsaicin]). Patients were aged 18-90 years, had had postherpetic neuralgia for at least 6 months, and had an average baseline numeric pain rating scale (NPRS) score of 3 to 9. The primary efficacy endpoint was percentage change in NPRS score from baseline to weeks two to eight. Analysis was by intention to treat. This trial is registered with ClinicalTrials.gov, number NCT00115310.

FINDINGS

Patients who were randomly assigned to NGX-4010 (n=206) had a significantly greater reduction in pain during weeks two to eight than did patients who had the control patch (n=196). The mean changes in NPRS score were -29.6%vs -19.9% (difference -9.7%, 95% CI -15.47 to -3.95; p=0.001). 87 (42%) patients who received NGX-4010 and 63 (32%) controls had a 30% or greater reduction in mean NPRS score (odds ratio [OR] 1.56, 95% CI 1.03 to 2.37; p=0.03). The patients who had NGX-4010 had significant improvements in pain during weeks two to 12 (mean change in NPRS score -29.9%vs -20.4%, difference -9.5, -15.39 to -3.61; p=0.002). Transient blood pressure changes associated with changes in pain level were recorded on the day of treatment, and short-lasting erythema and pain at the site of application were common, self-limited, and generally mild to moderate in the NGX-4010 group and less frequent and severe in the controls.

INTERPRETATION

One 60-min application of NGX-4010 provided rapid and sustained pain relief in patients with postherpetic neuralgia. No adverse events were associated with treatment except for local reactions at the site of application and those related to treatment-associated pain.

Natural products to drugs: natural product-derived compounds in clinical trials

Natural product and natural product-derived compounds that are being evaluated in clinical trials or are in registration (as at 31st December 2007) have been reviewed, as well as natural product-derived compounds for which clinical trials have been halted or discontinued since 2005. Also discussed are natural product-derived drugs launched since 2005, new natural product templates and late-stage development candidates.