Pharmacokinetic analysis of capsaicin after topical administration of a high-concentration capsaicin patch to patients with peripheral neuropathic pain

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.

Update on Treating Painful Diabetic Peripheral Neuropathy: A Review of Current US Guidelines with a Focus on the Most Recently Approved Management Options

Painful diabetic peripheral neuropathy (DPN) is a highly prevalent and disabling complication of diabetes that is often misdiagnosed and undertreated. The management of painful DPN involves treating its underlying cause via lifestyle modifications and intensive glucose control, targeting its pathogenesis, and providing symptomatic pain relief, thereby improving patient function and health-related quality of life. Four pharmacologic options are currently approved by the US Food and Drug Administration (FDA) to treat painful DPN. These include three oral medications (duloxetine, pregabalin, and tapentadol extended release) and one topical agent (capsaicin 8% topical system). More recently, the FDA approved several spinal cord stimulation (SCS) devices to treat refractory painful DPN. Although not FDA-approved specifically to treat painful DPN, tricyclic antidepressants, serotonin/norepinephrine reuptake inhibitors, gabapentinoids, and sodium channel blockers are common first-line oral options in clinical practice. Other strategies may be used as part of individualized comprehensive pain management plans. This article provides an overview of the most recent US guidelines for managing painful DPN, with a focus on the two most recently approved treatment options (SCS and capsaicin 8% topical system), as well as evidence for using FDA-approved and guideline-supported drugs and devices. Also discussed are unmet needs for this patient population, and evidence for potential future treatments for painful DPN, including drugs with novel mechanisms of action, electrical stimulation devices, and nutraceuticals.

Novel Therapeutic Hybrid Systems Using Hydrogels and Nanotechnology: A Focus on Nanoemulgels for the Treatment of Skin Diseases

Topical and transdermal drug delivery are advantageous administration routes, especially when treating diseases and conditions with a skin etiology. Nevertheless, conventional dosage forms often lead to low therapeutic efficacy, safety issues, and patient noncompliance. To tackle these issues, novel topical and transdermal platforms involving nanotechnology have been developed. This review focuses on the latest advances regarding the development of nanoemulgels for skin application, encapsulating a wide variety of molecules, including already marketed drugs (miconazole, ketoconazole, fusidic acid, imiquimod, meloxicam), repurposed marketed drugs (atorvastatin, omeprazole, leflunomide), natural-derived compounds (eucalyptol, naringenin, thymoquinone, curcumin, chrysin, brucine, capsaicin), and other synthetic molecules (ebselen, tocotrienols, retinyl palmitate), for wound healing, skin and skin appendage infections, skin inflammatory diseases, skin cancer, neuropathy, or anti-aging purposes. Developed formulations revealed adequate droplet size, PDI, viscosity, spreadability, pH, stability, drug release, and drug permeation and/or retention capacity, having more advantageous characteristics than current marketed formulations. In vitro and/or in vivo studies established the safety and efficacy of the developed formulations, confirming their therapeutic potential, and making them promising platforms for the replacement of current therapies, or as possible adjuvant treatments, which might someday effectively reach the market to help fight highly incident skin or systemic diseases and conditions.

Painful diabetic peripheral neuropathy of the feet: integrating prescription-strength capsaicin into office procedures

Prescription-strength (8%) capsaicin topical system is a US FDA-approved treatment for painful diabetic peripheral neuropathy of the feet. A 30 min application of the capsaicin 8% topical system can provide sustained (up to 3 months) local pain relief by desensitizing and reducing TRPV1-expressing cutaneous fibers. Capsaicin is not absorbed systemically; despite associated application-site discomfort, capsaicin 8% topical system is well tolerated, with no known drug interactions or contraindications, and could offer clinical advantages over oral options. Capsaicin 8% topical system are not for patient self-administration and require incorporation into office procedures, with the added benefit of treatment compliance. This article reviews existing literature and provides comprehensive, practical information regarding the integration of capsaicin 8% topical systems into office procedures.

Antimicrobial Properties of Capsaicin: Available Data and Future Research Perspectives

Capsaicin is a phytochemical derived from plants of the genus Capsicum and subject of intensive phytochemical research due to its numerous physiological and therapeutical effects, including its important antimicrobial properties. Depending on the concentration and the strain of the bacterium, capsaicin can exert either bacteriostatic or even bactericidal effects against a wide range of both Gram-positive and Gram-negative bacteria, while in certain cases it can reduce their pathogenicity by a variety of mechanisms such as mitigating the release of toxins or inhibiting biofilm formation. Likewise, capsaicin has been shown to be effective against fungal pathogens, particularly Candida spp., where it once again interferes with biofilm formation. The parasites Toxoplasma gondi and Trypanosoma cruzi have been found to be susceptible to the action of this compound too while there are also viruses whose invasiveness is significantly dampened by it. Among the most encouraging findings are the prospects for future development, especially using new formulations and drug delivery mechanisms. Finally, the influence of capsaicin in somatostatin and substance P secretion and action, offers an interesting array of possibilities given that these physiologically secreted compounds modulate inflammation and immune response to a significant extent.

Pharmaceutical treatment of osteoarthritis

OBJECTIVE

To review the current state of pharmaceutical treatment recommendations for the management of osteoarthritis.

METHOD

A narrative review was drafted to describe treatment guidelines, mechanism of action, pharmacokinetics, and toxicity for nine classes of pharmaceuticals: 1) oral nonsteroidal anti-inflammatory drugs (NSAIDs), 2) topical NSAIDs, 3) COX-2 inhibitors, 4) duloxetine, 5) intra-articular corticosteroids, 6) intra-articular hyaluronic acid, 7) acetaminophen (paracetamol), 8) tramadol, and 9) capsaicin.

RESULTS

In general, oral and topical NSAIDs, including COX-2 inhibitors, are strongly recommended first-line treatments for osteoarthritis due to their ability to improve pain and function but are associated with increased risks in patients with certain comorbidities (e.g., heightened cardiovascular risks). Intra-articular corticosteroid injections are generally recommended for osteoarthritis management and have relatively minor adverse effects. Other treatments, such as capsaicin, tramadol, and acetaminophen, are more controversial, and many updated guidelines offer differing recommendations.

CONCLUSION

The pharmaceutical management of osteoarthritis is a constantly evolving field. Promising treatments are emerging, and medicines that were once considered conventional (e.g., acetaminophen) are gradually becoming less acceptable based on concerns with efficacy and safety. Clinicians need to consider the latest evidence and recommendations to make an informed decision with their patients about how to optimize treatment plans for patients with knee, hip, polyarticular, or hand osteoarthritis.

Second-degree burn induced by high-concentration topical capsaicin with mobility sequelae: A case report

High-concentration topical capsaicin is used as a second-line treatment for neuropathic pain. Transient, mild burning sensation and erythema are expected adverse drug reactions. Here, we report the first case of second degree burn after the application of a high-concentration topical capsaicin patch with secondary mobility sequelae. Nine months after the application, neuropathic pain still remained and the patient described mobility difficulties in daily activities, preventing her from returning to work. This report aims to raise the question of the benefit/risk ratio of high concentration topical capsaicin.

Evaluation of 8% Capsaicin Patches in Chemotherapy-Induced Peripheral Neuropathy: A Retrospective Study in a Comprehensive Cancer Center

Introduction: Chemotherapy-induced peripheral neuropathy (CIPN) is often painful and can arise during or after the end of oncological treatments. They are mostly induced by platinum salts, taxanes, and immunotherapies. Their incidence is estimated between 19 and 85%. They can require a chemotherapy dose reduction or early termination. The European Society for Medical Oncology (ESMO) recommends high-concentration capsaicin patch (HCCP) in second line for the treatment of painful CIPN. This treatment induces a significative pain relief but only shown by low-powered studies. The objective of this study was to evaluate efficacy and tolerability of HCCP applications in CIPN. Methods: This monocentric observational retrospective real-world-data study of the CERCAN cohort took place in the Western Cancer Institute's Anaesthesiology and Pain Department at Angers, France. Independent pain physicians completed the CGIC (Clinician Global Impression of Change) for each patient who benefited from HCCP applications for painful CIPN starting from 1 January 2014 to 22 December 2021, based on the collected data after every patch application. Results: A total of 57 patients (80.7% women) was treated with HCCP for painful CIPN, and 184 applications were realized, consisting of 296 sessions. CGIC found an important or complete pain relief for 61 applications (33.2%, corresponding to 43.9% patients). We found less efficacy for platinum-salts-induced CIPN compared to others (p = 0.0238). The efficacy was significatively higher for repeated applications when HCCP was used in second line compared to third line (p = 0.018). The efficacy of HCCP was significatively higher starting the third application (p = 0.0334). HCCPs were mainly responsible for local adverse events found in 66.6% patients (65.1% burning or painful sensation, 21.1% erythema). Conclusion: HCCP applications in painful CIPN induce an important pain relief with a global satisfying tolerability.

TRPV1 in chronic pruritus and pain: Soft modulation as a therapeutic strategy

Chronic pain and pruritus are highly disabling pathologies that still lack appropriate therapeutic intervention. At cellular level the transduction and transmission of pain and pruritogenic signals are closely intertwined, negatively modulating each other. The molecular and cellular pathways involved are multifactorial and complex, including peripheral and central components. Peripherally, pain and itch are produced by subpopulations of specialized nociceptors that recognize and transduce algesic and pruritogenic signals. Although still under intense investigation, cumulative evidence is pointing to the thermosensory channel TRPV1 as a hub for a large number of pro-algesic and itchy agents. TRPV1 appears metabolically coupled to most neural receptors that recognize algesic and pruritic molecules. Thus, targeting TRPV1 function appears as a valuable and reasonable therapeutic strategy. In support of this tenet, capsaicin, a desensitizing TRPV1 agonist, has been shown to exhibit clinically relevant analgesic, anti-inflammatory, and anti-pruritic activities. However, potent TRPV1 antagonists have been questioned due to an hyperthermic secondary effect that prevented their clinical development. Thus, softer strategies directed to modulate peripheral TRPV1 function appear warranted to alleviate chronic pain and itch. In this regard, soft, deactivatable TRPV1 antagonists for topical or local application appear as an innovative approach for improving the distressing painful and itchy symptoms of patients suffering chronic pain or pruritus. Here, we review the data on these compounds and propose that this strategy could be used to target other peripheral therapeutic targets.

The role of the capsaicin 8% patch in the treatment of painful diabetic peripheral neuropathy

Treatment of painful diabetic peripheral neuropathy (PDPN) is challenging and often limited by drug tolerability and adverse effects. This review article focuses on the high-dose (8%) capsaicin patch that allows for improved efficacy and reduced application frequency in comparison to low-dose capsaicin formulations. Systemic absorption is minimal resulting in fewer systemic side effects than first-line oral medications. There is evidence that capsaicin patch treatment is well-tolerated, safe and provides effective pain relief maintained for several weeks; well-powered studies are needed to confirm these findings. The capsaicin 8% patch may benefit patients at high risk for adverse effects from oral medication, polypharmacy or inadequate pain relief from first-line therapies.

Capsaicin and TRPV1 Channels in the Cardiovascular System: The Role of Inflammation

Capsaicin is a potent agonist of the Transient Receptor Potential Vanilloid type 1 (TRPV1) channel and is a common component found in the fruits of the genus Capsicum plants, which have been known to humanity and consumed in food for approximately 7000-9000 years. The fruits of Capsicum plants, such as chili pepper, have been long recognized for their high nutritional value. Additionally, capsaicin itself has been proposed to exhibit vasodilatory, antimicrobial, anti-cancer, and antinociceptive properties. However, a growing body of evidence reveals a vasoconstrictory potential of capsaicin acting via the vascular TRPV1 channel and suggests that unnecessary high consumption of capsaicin may cause severe consequences, including vasospasm and myocardial infarction in people with underlying inflammatory conditions. This review focuses on vascular TRPV1 channels that are endogenously expressed in both vascular smooth muscle and endothelial cells and emphasizes the role of inflammation in sensitizing the TRPV1 channel to capsaicin activation. Tilting the balance between the beneficial vasodilatory action of capsaicin and its unwanted vasoconstrictive effects may precipitate adverse outcomes such as vasospasm and myocardial infarction, especially in the presence of proinflammatory mediators.

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.

Evaluation of In Vitro Capsaicin Release and Antimicrobial Properties of Topical Pharmaceutical Formulation

(1) Background: Capsaicin is the main capsaicinoid of the Capsicum genus and it is responsible for the pungent taste. Medical uses of the fruits of chili peppers date from the ancient time until nowadays. Most of all, they are used topically as analgesic in anti-inflammatory diseases as rheumatism, arthritis and in diabetic neuropathy. Reports state that the Capsicum genus, among other plant genera, is a good source of antimicrobial and antifungal compounds. The aim of this study was the preparation of a pharmaceutical Carbopol-based formulation containing capsaicin and the evaluation of its in vitro release and antimicrobial and antifungal properties. (2) Methods: It was first stabilized with an extraction method from the Capsicum annuum fruits with 98% ethanol and then the identification and determination of Capsaicin in this extract was realized by HPLC. (3) Results and Conclusions: Rheological analyses revealed that the selected formulation exhibited a pseudo-plastic behavior. In vitro release studies of capsaicin from a Carbopol-based formulation reported that approximately 50% of capsaicin was release within 52 h. Additionally, the Carbopol-based formulation significantly increased the antimicrobial effects of capsaicin towards all tested bacteria and fungi strains.

Peripheral neuropathic pain

Neuropathic pain (NP) can have either central nervous system causes or ones from the peripheral nervous system. This article will focus on the epidemiology, classifications, pathology, non-invasive treatments and invasive treatments as a general review of NP involving the peripheral nervous system. NP has characteristic symptomatology such as burning and electrical sensations. It occurs in up to 10% of the general population. Its frequency can be attributed to its occurrence in neck and back pain, diabetes and patients receiving chemotherapy. There are a wide range of pharmacologic options to control this type of pain and when such measures fail, numerous interventional methods can be employed such as nerve blocks and implanted stimulators. NP has a cost to the patient and society in terms of emotional consequences, quality of life, lost wages and the cost of assistance from the medical system and thus deserves serious consideration for prevention, treatment and control.

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.

Fight fire with fire: Neurobiology of capsaicin-induced analgesia for chronic pain

Capsaicin, the pungent ingredient in chili peppers, produces intense burning pain in humans. Capsaicin selectively activates the transient receptor potential vanilloid 1 (TRPV1), which is enriched in nociceptive primary afferents, and underpins the mechanism for capsaicin-induced burning pain. Paradoxically, capsaicin has long been used as an analgesic. The development of topical patches and injectable formulations containing capsaicin has led to application in clinical settings to treat chronic pain conditions, such as neuropathic pain and the potential to treat osteoarthritis. More detailed determination of the neurobiological mechanisms of capsaicin-induced analgesia should provide the logical rationale for capsaicin therapy and help to overcome the treatment's limitations, which include individual differences in treatment outcome and procedural discomfort. Low concentrations of capsaicin induce short-term defunctionalization of nociceptor terminals. This phenomenon is reversible within hours and, hence, likely does not account for the clinical benefit. By contrast, high concentrations of capsaicin lead to long-term defunctionalization mediated by the ablation of TRPV1-expressing afferent terminals, resulting in long-lasting analgesia persisting for several months. Recent studies have shown that capsaicin-induced Ca²⁺/calpain-mediated ablation of axonal terminals is necessary to produce long-lasting analgesia in a mouse model of neuropathic pain. In combination with calpain, axonal mitochondrial dysfunction and microtubule disorganization may also contribute to the longer-term effects of capsaicin. The analgesic effects subside over time in association with the regeneration of the ablated afferent terminals. Further determination of the neurobiological mechanisms of capsaicin-induced analgesia should lead to more efficacious non-opioidergic analgesic options with fewer adverse side effects.

Novel Agents in Neuropathic Pain, the Role of Capsaicin: Pharmacology, Efficacy, Side Effects, Different Preparations

PURPOSE OF REVIEW

Capsaicin is a natural substance used to treat neuropathic pain because of its ability to be used in a more direct form on patients and efficiently treat their pain without the amount of side effects seen in the use of oral medications.

RECENT FINDINGS

Currently, the treatments for neuropathic pain are, control of the underlying disease process, then focused on symptomatic relief with pharmacotherapy, topical analgesics, or other interventions. When all pharmacological agents fail to relieve the pain, interventional strategies can be considered, such as neural blocks, spinal cord stimulation, and intrathecal administered medications. The response to current treatment of neuropathic pain is only modest relief of symptoms. Multiple treatment options may be attempted, while ultimately leaving patients with refractory neuropathic pain. For these reasons, a better treatment approach to neuropathic pain is greatly needed. Overall, capsaicin has great potential for becoming a first- or second-line treatment for neuropathic pain, and for becoming a therapeutic option for many other neuropathic pain-related disease states.

Randomized, Double-Blind, Placebo-Controlled Trial of Intraarticular Trans-Capsaicin for Pain Associated With Osteoarthritis of the Knee

Objective

To assess the efficacy and safety of high‐purity synthetic trans‐capsaicin (CNTX‐4975) in patients with chronic moderate‐to‐severe osteoarthritis (OA)–associated knee pain.

Methods

In this phase II multicenter double‐blind study, patients ages 45–80 years who had stable knee OA were randomized in a 2:1:2 ratio to receive a single intraarticular injection of placebo, CNTX‐4975 0.5 mg, or CNTX‐4975 1.0 mg. The primary efficacy end point was area under the curve (AUC) for change from baseline in daily Western Ontario and McMaster Universities Osteoarthritis Index pain with walking score (range 0–10, 0 = none and 10 = extreme) through week 12. Secondary efficacy end points included a similar AUC analysis of outcomes in patients treated with CNTX‐4975 0.5 mg, and evaluations extending to 24 weeks.

Results

Efficacy was evaluated in 172 patients (placebo group, n = 69; CNTX‐4975 0.5 mg group, n = 33; CNTX‐4975 1.0 mg group, n = 70). At week 12, greater decreases in the AUC for the pain score were observed with CNTX‐4975 in the 0.5 mg and 1.0 mg groups versus placebo (0.5 mg group least squares mean difference [LSMD] −0.79, P = 0.0740; 1.0 mg group LSMD −1.6, P < 0.0001). Significant improvements were maintained at week 24 in the 1.0 mg group (LSMD −1.4, P = 0.0002). Treatment‐emergent adverse events were similar in the placebo and CNTX‐4975 1.0 mg groups.

Conclusion

In this study, CNTX‐4975 provided dose‐dependent improvement in knee OA–associated pain. CNTX‐4975 1.0 mg produced a significant decrease in OA knee pain through 24 weeks; CNTX‐4975 0.5 mg significantly improved pain at 12 weeks, but the effect was not evident at 24 weeks.

Capsaicin 8% Dermal Patch: A Review in Peripheral Neuropathic Pain

The adhesive capsaicin dermal patch (Qutenza^®) delivers a high concentration (8% w/w) of synthetic capsaicin, a highly selective agonist of transient receptor potential vanilloid-1 (TRPV-1), directly to the site of pain. The capsaicin 8% dermal patch is indicated in the EU for the treatment of peripheral neuropathic pain (PNP) in adults, either alone or in combination with other medicinal products for pain. In patients with painful diabetic peripheral neuropathy, a single 30-min application of the capsaicin 8% dermal patch provided 12 weeks of pain relief and improved sleep quality compared with placebo. Repeat treatment with the capsaicin 8% dermal patch plus standard of care over 52 weeks provided sustained pain relief, with no negative neurological effects compared with standard of care alone. The capsaicin 8% dermal patch was non-inferior to oral pregabalin in relieving pain in patients with non-diabetic PNP, with a faster onset of action and greater treatment satisfaction. A single 60-min application of the capsaicin 8% dermal patch provided rapid and sustained pain relief in patients with postherpetic neuralgia. Results in patients with HIV-associated neuropathy were equivocal, with a significant improvement in pain intensity observed in one trial, but not in the other. The capsaicin 8% dermal patch was generally well tolerated; transient application-site reactions were the most common adverse events. In conclusion, the capsaicin 8% dermal patch is a useful addition to the treatment options currently available for patients with PNP.

Sex differences in the pharmacology of itch therapies-a narrative review

BACKGROUND

Chronic itch is the most common skin-related condition, associated with a high psychosocial and economic burden. In recent years, increasing evidence of sex differences in the perception, clinical presentation and treatment requirements of itch points towards potential benefits when using sex-adapted therapies. It is well-known that body composition, absorption, metabolism, elimination and adverse drug reactions (ADRs) differ between sexes, but only little is known about the impact of sex in the pharmacology of itch treatments, which could help to rationalise sex-adapted treatment strategies.

AIM

To evaluate and review sex effects in the pharmacokinetics and /-dynamics of drugs used to treat itch.

METHODS

In this narrative review we performed a PubMed and MEDLINE (Ovid) search using the terms (itch OR pruritus) AND (gender OR sex) AND (drug OR medication OR pharmacokinetics OR pharmacodynamics). Additional searches were performed for the topical and systemic drugs recommended by the European Guideline on Chronic Pruritus.

RESULTS

We found numerous reports with variable levels of evidence of sex effects with respect to the pharmacokinetics and/or pharmacodynamics of 14 drug classes used for the treatment of itch, including a total of 19 systemic and 3 topical drugs. Women seem to present higher plasma levels of several drugs used in itch treatment, including tri- and tetracyclic antidepressants (e.g. doxepin, amitriptyline, mirtazapine), serotonin reuptake inhibitors (e.g. paroxetine, sertraline, fluoxetine), immunosuppressive drugs (e.g. cyclosporine, mycophenolate mofetil), serotonin receptor antagonists (e.g. ondansetron) and betablockers (e.g. propranolol). Adverse drug reactions (ADRs) were generally more common in women. Being female was reported to be an independent risk factor for QTc-prolongation associated with antihistamines and tetracyclic antidepressants. Additionally, women seem to be more prone to sedative effects of antihistamines, and to suffer from a higher frequency as well as severity of side effects with systemic calcineurin inhibitors, opioid agonists, and opioid antagonists. Women were also sensitised more often to topically applied drugs. Of note, apart from only one experimental study with capsaicin, none of these reports were designed specifically to assess the effect of sex (and gender) in the treatment of itch.

DISCUSSION/CONCLUSION

Our review supports previous reports that sex is of importance in the pharmacokinetics and /-dynamics of several drugs used to treat itch although those drugs were mostly evaluated for non-itch indications. However, the results are limited by methodological limitations evident in most studies such as underrepresentation of women in clinical trials. This emphasises the need to study the impact of sex (and gender) in future itch trials to yield better outcomes and prevent ADRs in both sexes.

Cannabinoid Hyperemesis

Cannabinoid hyperemesis syndrome (CHS) is a paradoxical condition in which a long-term cannabis user suffers an episode of intractable vomiting that may last days separated by longer asymptomatic periods of weeks or months. Cannabinoids are often utilized for their antiemetic properties, so CHS can be a puzzling condition, and the diagnosis of CHS may be disputed by patients. Unlike other cyclic vomiting syndromes, CHS can be relieved by hot showers or topical capsaicin. Abstinence from cannabinoids causes CHS to resolve, sometimes in a matter of days or hours. Marijuana users as well as many clinicians are not aware of CHS, and patients may undergo unnecessary tests, scans, and other procedures to get an accurate diagnosis. Symptoms may be severe enough to require hospitalization. With liberalization of marijuana laws and favorable public opinion about the healing properties of cannabis, CHS may be more frequently observed in clinical practice.

Assessing and Treating Chronic Pain in Patients with End-Stage Renal Disease

Pain is one of the most common symptoms among patients with end-stage renal disease (ESRD), and is often under recognized and not adequately managed in hemodialysis (HD) patients. Barriers to adequate pain management include poor awareness of the problem, insufficient medical education, fears of possible drug-related side effects, and common misconceptions about the inevitability of pain in elderly and HD patients. Caregivers working in HD should be aware of the possible consequences of inadequate pain assessment and management. Common pain syndromes in HD patients include musculoskeletal diseases and metabolic neuropathies, associated with typical intradialytic pain. Evaluating the etiology, nature, and intensity of pain is crucial for choosing the correct analgesic. A mechanism-based approach to pain management may result in a better outcome. Pharmacokinetic considerations on clearance alterations and possible toxicity in patients with ESRD should drive the right analgesic prescription. Comorbidities and polymedications may increase the risk of drug-drug interactions, therefore drug metabolism should be taken into account when selecting analgesic drugs. Automedication is common among HD patients but should be avoided to reduce the risk of hazardous drug administration. Further research is warranted to define the efficacy and safety of analgesic drugs and techniques in the context of patients with ESRD as generalizing information from studies conducted in the general population could be inappropriate and potentially dangerous. A multidisciplinary approach is recommended for the management of complex pain syndromes in frail patients, such as those suffering from ESRD.

Ultra-diluted Toxicodendron pubescens attenuates pro-inflammatory cytokines and ROS- mediated neuropathic pain in rats

Despite the availability of multiple therapeutic agents, the search for novel pain management of neuropathic pain is still a challenge. Oxidative stress and inflammatory signaling are prominently involved in clinical manifestation of neuropathic pain. Toxicodendron pubescens, popularly known as Rhus Tox (RT) is recommended in alternative medicines as an anti-inflammatory and analgesic remedy. Earlier, we reported anti-inflammatory, anti-arthritic and immunomodulatory activities of Rhus Tox. In continuation, we evaluated antinociceptive efficacy of Rhus Tox in the neuropathic pain and delineated its underlying mechanism. Initially, in-vitro assay using LPS-mediated ROS-induced U-87 glioblastoma cells was performed to study the effect of Rhus Tox on reactive oxygen species (ROS), anti-oxidant status and cytokine profile. Rhus Tox decreased oxidative stress and cytokine release with restoration of anti-oxidant systems. Chronic treatment with Rhus Tox ultra dilutions for 14 days ameliorated neuropathic pain revealed as inhibition of cold, warm and mechanical allodynia along with improved motor nerve conduction velocity (MNCV) in constricted nerve. Rhus Tox decreased the oxidative and nitrosative stress by reducing malondialdehyde (MDA) and nitric oxide (NO) content, respectively along with up regulated glutathione (GSH), superoxide dismutase (SOD) and catalase activity in sciatic nerve of rats. Notably, Rhus Tox treatment caused significant reductions in the levels of tumor necrosis factor (TNF-α), interleukin-6 (IL-6) and interleukin-1β (IL-1β) as compared with CCI-control group. Protective effect of Rhus Tox against CCI-induced sciatic nerve injury in histopathology study was exhibited through maintenance of normal nerve architecture and inhibition of inflammatory changes. Overall, neuroprotective effect of Rhus Tox in CCI-induced neuropathic pain suggests the involvement of anti-oxidative and anti-inflammatory mechanisms.

Capsaicin 8% Patch Repeat Treatment in Nondiabetic Peripheral Neuropathic Pain: A 52-Week, Open-Label, Single-Arm, Safety Study

OBJECTIVES

To investigate the long-term safety and tolerability of capsaicin 8% patch repeat treatment in nondiabetic patients with peripheral neuropathic pain.

METHODS

A prospective, open-label, observational study in patients with postherpetic neuralgia, posttraumatic or postsurgical nerve injury, HIV-associated distal sensory polyneuropathy, or other peripheral neuropathic pain, and average daily pain score ≥4, who received ≤6 capsaicin 8% patch treatments over 52 weeks according to clinical need (retreatment at 9 to 12 wk intervals). Sensory testing and analgesic effectiveness were assessed using "bedside tests" and Brief Pain Inventory (question 5).

RESULTS

Overall, 306 patients received treatment. Treatment-emergent adverse events (TEAEs) and drug-related TEAEs were reported by 252 (82.4%) and 207 (67.6%) patients. Application site pain was the most common drug-related TEAE (n=112, 36.6%); no drug-related serious TEAEs were reported. Sensory category shift analyses from baseline to end of study (EoS) in patients attending at least 2 sensory visits (n=278 for all tests except warm, n=277) found sensory deterioration/loss in at least 1 modality in 50.4% (n=140); deterioration/loss in 1, 2, 3, 4, or 5 modalities occurred in 26.6% (n=74), 14.0% (n=39), 5.8% (n=16), 2.5% (n=7), and 1.4% (n=4) cases. Newly emergent hyperesthesia or allodynia was apparent in 1.1% to 3.6% of the cases (depending on modality) by EoS. Between 25.2% and 32.0% of patients reported improvement in a sensory modality by EoS. Average daily pain was 6.6 and 4.7 at baseline and month 12.

CONCLUSIONS

Generally, capsaicin 8% patch repeat treatment over 52 weeks was well tolerated, with variable alteration in sensory function and minimal chance of complete sensory loss.

Capsaicin-based analgesic balm attenuates the skeletal muscle metaboreflex in healthy humans

The exercise pressor reflex (EPR) is comprised of group III and IV skeletal muscle afferents and is one of the principal mediators of the cardiovascular response to exercise. In animals, capsaicin-based analgesic balm (CAP) attenuates the pressor response to muscle contraction, indicating the transient receptor potential vanilloid 1 (TRPv1) receptor (localized on the group IV afferent neuron) as an important mediator of the EPR. However, whether these findings can be extrapolated to humans remains unknown. Here, we tested the hypothesis that CAP would attenuate blood pressure (BP) and muscle sympathetic nerve activity (MSNA) responses to isolated muscle metaboreflex activation in healthy men. MSNA (microneurography) and beat-to-beat heart hate (HR, by electrocardiography), and BP (finger photoplethysmography) were continuously measured in eight healthy males (23 ± 5 yr) at rest, during isometric handgrip exercise, and during postexercise ischemia (PEI). Trials were performed before and 30 and 60 min after the topical application of CAP (0.1%, CAPZASIN-HP) over the volar forearm of the subject's exercising arm. Isometric exercise evoked increases in mean BP (∆32 ± 4 mmHg) and MSNA (∆26 ± 5 bursts/min; ∆19 ± 5 bursts/100 heart beats). The increases in BP during handgrip were not affected by CAP, but the increase in MSNA was lower after 60 min of CAP application. During PEI, the increases in BP and MSNA were all significantly less than those before CAP (all P < 0.05). In conclusion, CAP attenuated BP and sympathetic responses evoked by PEI in humans. These data provide evidence that transient receptor potential vanilloid 1 receptors potentially contribute to the EPR in humans, via its metabolic component. NEW & NOTEWORTHY We found that topical application of capsaicin-based analgesic balm attenuates arterial blood pressure and muscle sympathetic nerve activity during isolated muscle metaboreflex activation following isometric handgrip exercise in healthy humans. These findings suggest that the transient receptor potential vanilloid 1 may contribute to the exercise pressor reflex in humans via its metabolic component.

Acute effect of different concentrations of cayenne pepper cataplasm on sensory-motor functions and serum levels of inflammation-related biomarkers in healthy subjects

Physical medicine therapies are often used in treating widespread musculoskeletal disorders, such as neck and low back pain. Herbal cataplasms containing rubefacient substances, such as Cayenne pepper, or galenic preparations like Munari cataplasm are commonly used as natural medications to treat painful areas. In this paper we show the effects of a 20-min application of Cayenne pepper and kaolin powder cataplasm (CPC) on healthy subjects. Treatment effects were evaluated by cold/hot feeling on visual analogue scale, blood pressure, body temperature, skin light touch sensations, two-point discrimination, and pain threshold to a mechanical stimulus, before and immediately after, 15 min after and 30 min after different concentration of Cayenne pepper in CPC preparation on healthy subjects. Maximal voluntary trunk extension force and trunk extension submaximal force matching error were also measured. In addition, the resulting optimal CPC mixture was tested for its safety by measuring changes in circulating levels of inflammatory-related biomarkers after 20-min application. The results indicate that the 5% concentration of Cayenne pepper in the preparation of CPC is the best choice, since no additional effects can be obtained with the 10% concentration, and the effects are higher than those observed at the 2.5% concentration. Importantly, 5% CPC application did not induce a significant increase of inflammatory-related biomarkers, suggesting that 20-min application has no negative side effects at systemic levels. Further studies are needed to investigate the immediate and long-term effects of repeated CPC applications as well as to understand the intersecting underlying mechanisms activated by Capsaicin and other identified factors, in order to be more extensively used in the field of physical medicine therapies.

Effects of Capsaicin on Older Patients with Oropharyngeal Dysphagia: A Double-Blind, Placebo-Controlled, Crossover Study

BACKGROUND/AIMS

The standard of care for older patients with oropharyngeal dysphagia (OD) is poor. Stimulation of transient receptor potential vanilloid 1 might become a pharmacological strategy for these patients. This study aimed to compare the therapeutic effect of film food containing 0.75 µg of capsaicin in these patients.

METHODS

In a crossover, randomized trial, 49 patients with OD were provided capsaicin or identical placebo at least 7 days apart. Patients' reported symptoms during repeated swallowing, the volume, pH and substance P (SP) concentrations in saliva, and cervical esophageal wall motion evaluated by ultrasonographic tissue Doppler imaging were obtained before and after capsaicin or placebo administration.

RESULTS

Significantly more patients with OD who took capsaicin experienced improvement in symptoms than those who took placebo. Salivary SP levels were significantly increased after capsaicin administration compared with placebo in the effective group. The duration of cervical esophageal wall opening was significantly shorter in capsaicin administration in the effective group. Furthermore, a significant negative correlation was found between the duration of cervical esophageal wall opening and salivary SP levels.

CONCLUSION

Elevated salivary SP concentrations stimulated by capsaicin greatly improve the safety and efficacy of swallowing, and shorten the swallow response in older patients with OD.

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.

Capsaicin 8% patch treatment for amputation stump and phantom limb pain: a clinical and functional MRI study

Purpose

The aim of this study was to measure the efficacy of a single 60 min application of capsaicin 8% patch in reducing chronic amputation stump and phantom limb pain, associated hypersensitivity with quantitative sensory testing, and changes in brain cortical maps using functional MRI (fMRI) scans.

Methods

A capsaicin 8% patch (Qutenza) treatment study was conducted on 14 patients with single limb amputation, who reported pain intensity on the Numerical Pain Rating Scale ≥4/10 for chronic stump or phantom limb pain. Pain assessments, quantitative sensory testing, and fMRI (for the lip pursing task) were performed at baseline and 4 weeks after application of capsaicin 8% patch to the amputation stump. The shift into the hand representation area of the cerebral cortex with the lip pursing task has been correlated with phantom limb pain intensity in previous studies, and was the fMRI clinical model for cortical plasticity used in this study.

Results

The mean reduction in spontaneous amputation stump pain, phantom limb pain, and evoked stump pain were −1.007 (p=0.028), −1.414 (p=0.018), and −2.029 (p=0.007), respectively. The areas of brush allodynia and pinprick hypersensitivity in the amputation stump showed marked decreases: −165 cm², −80% (p=0.001) and −132 cm², −72% (p=0.001), respectively. fMRI analyses provided objective evidence of the restoration of the brain map, that is, reversal of the shift into the hand representation of the cerebral cortex with the lip pursing task (p<0.05).

Conclusion

The results show that capsaicin 8% patch treatment leads to significant reduction in chronic pain and, particularly, in the area of stump hypersensitivity, which may enable patients to wear prostheses, thereby improving mobility and rehabilitation. Phantom limb pain (“central” pain) and associated brain plasticity may be modulated by peripheral inputs, as they can be ameliorated by the peripherally restricted effect of the capsaicin 8% patch.

Neuroprotective effect of Azadirachta indica standardized extract in partial sciatic nerve injury in rats: Evidence from anti-inflammatory, antioxidant and anti-apoptotic studies

Chronic neuropathic pain is a common and widely recognized pain syndrome for patients and difficult to manage for physicians. Azadirachta indica (AI) possesses analgesic, anti-inflammatory, and antioxidant properties. To evaluate the neuroprotective effect of AI standardized extract in an animal model of peripheral neuropathy induced by partial sciatic nerve ligation (PSNL). PSNL was induced in male Wistar rats (180-200 g) with tight ligation of the nerve. Rats received treatment with either vehicle i.e. distilled water (PSNL control), Pyridoxine (100 mg/kg, p.o.) or AI (100, 200 and 400 mg/kg, p.o.) for 28 days. Various behavioral parameters, biochemical, molecular and histological parameters were evaluated. PSNL resulted in a significant decrease (p < 0.05) in allodynia, hyperalgesia, motor coordination and motor nerve conduction velocity (MNCV) whereas chronic treatment with AI (200 and 400 mg/kg) significantly attenuated (p < 0.05) these behavioral changes. Enhanced activity of oxidative-nitrosative stress, inflammatory mediators (TNF-α, IL-1β, and NF-κB) as well as mRNA expression of Bax, Caspase-3, and iNOs were significantly attenuated (p < 0.05) by AI treatment. It also significantly increased (p < 0.05) peripheral blood oxygen content and Bcl-2 mRNA expression. The flow cytometric analysis revealed that AI (200 and 400 mg/kg) treatment significantly attenuated neural apoptosis and reactive oxygen species levels. PSNL induced histological aberrations were also decreased by AI treatment. Azadirachta indica exerts its neuroprotection against PSNL induced neuropathic pain via inhibition of oxidative-nitrosative stress, the release of pro-inflammatory cytokines and apoptosis to improve MNCV (graphical abstract, Figure 1(Fig. 1)).

Curcumin, Piperine, and Capsaicin: A Comparative Study of Spice-Mediated Inhibition of Human Cytochrome P450 Isozyme Activities

Inhibition of cytochrome P450 (P450) enzymes (CYP) has been shown to lower the metabolism of drugs that are P450 substrates and to consequently alter their pharmacokinetic profiles. Curcumin (CUR), piperine (PIP), and capsaicin (CAP) are spice components (SC) that inhibit the activities of a range of P450 enzymes, but the selection of which SC to be prioritized for further development as an adjuvant will depend on the ranking order of the inhibitory potential of the SCs on specific P450 isozymes. We used common human recombinant enzyme platforms to provide a comparative evaluation of the inhibitory activities of CUR, PIP, and CAP on the principal drug-metabolizing P450 enzymes. SC-mediated inhibition of CYP3A4 was found to rank in the order of CAP (IC₅₀ 1.84 ± 0.71 µM) ∼ PIP (2.12 ± 0.45 µM) > CUR (11.93 ± 3.49 µM), while CYP2C9 inhibition was in the order of CAP (11.95 ± 4.24 µM) ∼ CUR (14.58 ± 4.57 µM) > PIP (89.62 ± 9.17 µM). CAP and PIP were significantly more potent inhibitors of CYP1A2 (IC₅₀ 2.14 ± 0.22 µM and 14.19 ± 4.15 µM, respectively) than CUR (IC₅₀ > 100 µM), while all three SCs exhibited weak activity toward CYP2D6 (IC₅₀ 95.42 ± 12.09 µM for CUR, 99.99 ± 5.88 µM for CAP, and 110.40 ± 3.23 µM for PIP). Of the three SCs, CAP thus has the strongest potential for further development into an inhibitor of multiple CYPs for use in the clinic. Data from this study are also useful for managing potential drug-SC interactions.

Capsaicin 8 % Patch: A Review in Peripheral Neuropathic Pain

The capsaicin 8 % patch (QUTENZA®) is an adhesive patch containing a high concentration (8 % w/w) of synthetic capsaicin, a selective agonist of transient receptor potential vanilloid 1 channel. It is approved for treatment of peripheral neuropathic pain in adults either alone or in combination with other medicinal products for pain in the EU; it is only approved to treat postherpetic neuralgia (PHN) in the USA. In patients with painful diabetic peripheral neuropathy (PDPN), a single 30-min application of the capsaicin 8 % patch significantly improved pain relief and sleep quality compared with placebo in a 12-week double-blind trial. In a 52-week, randomized trial, up to seven consecutive 30-min treatments with the capsaicin 8 % patch (≤7 treatments each at least 8 weeks apart) plus standard of care therapy was associated with sustained pain relief and no negative neurological safety consequences compared with standard of care. In two randomized trials, a single 60-min application of the capsaicin 8 % patch reduced pain scores significantly more than a low-concentration (0.04 %) capsaicin control patch in patients with PHN. Capsaicin 8 % patch treatment was noninferior to pregabalin (optimized dosage) in a randomized trial in patients with nondiabetic peripheral neuropathic pain. Results in two trials in patients with HIV-AN were equivocal, with a significant improvement in pain intensity observed in one trial, but not in the other. The capsaicin 8 % patch was associated with expected, transient, capsaicin-related application-site adverse events such as erythema and pain.

Modulation of signal transduction pathways by natural compounds in cancer

Cancer is generally regarded as the result of abnormal growth of cells. According to World Health Organization, cancer is the leading cause of mortality worldwide. Mother nature provides a large source of bioactive compounds with excellent therapeutic efficacy. Numerous phytochemicals from nature have been investigated for anticancer properties. In this review article, we discuss several natural compounds, which have shown anti-cancer activity. Natural compounds induce cell cycle arrest, activate intrinsic and extrinsic apoptosis pathways, generate Reactive Oxygen Species (ROS), and down-regulate activated signaling pathways, resulting in inhibition of cell proliferation, progression and metastasis of cancer. Several preclinical studies have suggested that natural compounds can also increase the sensitivity of resistant cancers to available chemotherapy agents. Furthermore, combining FDA approved anti-cancer drugs with natural compounds results in improved efficacy. On the basis of these exciting outcomes of natural compounds against several cancer types, several agents have already advanced to clinical trials. In conclusion, preclinical results and clinical outcomes against cancer suggest promising anticancer efficacy of agents from natural sources.

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.

Effectiveness of High-Frequency Electrical Stimulation Following Sensitization With Capsaicin

Although nonnoxious, high-frequency electrical stimulation applied segmentally (ie, conventional transcutaneous electrical nerve stimulation [TENS]) has been proposed to modulate pain, the mechanisms underlying analgesia remain poorly understood. To further elucidate how TENS modulates pain, we examined evoked responses to noxious thermal stimuli after the induction of sensitization using capsaicin in healthy volunteers. We hypothesized that sensitization caused by capsaicin application would unmask TENS analgesia, which could not be detected in the absence of sensitization. Forty-nine healthy subjects took part in a series of experiments. The experiments comprised the application of topical capsaicin (.075%) on the left hand in the C6 dermatome, varying the location of TENS (segmental, left C6 dermatome, vs extrasegmental, right shoulder), and assessing rating of perception (numeric rating scale: 0-10) and evoked potentials to noxious contact heat stimuli. The extrasegmental site was included as a control condition because previous studies indicate no analgesic effect to remote conventional TENS. Conventional TENS had no significant effect on rating or sensory evoked potentials in subjects untreated with capsaicin. However, segmental TENS applied in conjunction with capsaicin significantly reduced sensation to noxious thermal stimuli following a 60-minute period of sensitization.

PERSPECTIVE

The study indicates that sensitization with capsaicin unmasks the analgesic effect of conventional TENS on perception of noxious contact heat stimuli. Our findings indicate that TENS may be interacting segmentally to modulate distinct aspects of sensitization, which in turn results in analgesia to thermal stimulation.

Oxidant-based anticancer activity of a novel synthetic analogue of capsaicin, capsaicin epoxide

OBJECTIVES

Plant-derived natural substances, such as capsaicin, with potent antiproliferative activity against cancer cells in vitro are considered to be promising nutraceuticals in anticancer therapy. Nevertheless, the limited systemic bioavailability of phytochemicals may raise questions regarding the physiological relevance of their phytochemical effects in vivo. Thus, the search for novel phytochemical-based substances with more efficient anticancer action is needed.

METHODS

In the present study, a capsaicin analogue, namely, capsaicin epoxide, was synthesized, and its cytotoxic potential against cancer cells was evaluated and compared to that of capsaicin through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and multi-caspase assays. The abilities of capsaicin and capsaicin epoxide to induce oxidative stress were estimated using redox-sensitive fluorogenic probes: 2',7'-dichlorodihydrofluorescein diacetate (H2DCF-DA) and dihydroethidium.

RESULTS

The structure and purity of the synthesized product were confirmed by nuclear magnetic resonance spectroscopy, electrospray ionization mass spectrometry, and gas chromatography. Normal human dermal fibroblasts were not susceptible to treatment with the agent, whereas a cancer cell type-specific response was observed. Human breast carcinoma cells were found to be the most sensitive to capsaicin epoxide treatment compared with capsaicin treatment, and the action of capsaicin epoxide was oxidant based.

DISCUSSION

Our data indicate that the antiproliferative activity of capsaicin epoxide is potentiated in vitro, when used at much lower concentrations compared with capsaicin at similar concentrations. Thus, the findings of this study may have implications for phytochemical-based anticancer drug development.

Bioavailability of capsaicin and its implications for drug delivery

The dietary compound capsaicin is responsible for the "hot and spicy" taste of chili peppers and pepper extracts. It is a valuable pharmacological agent with several therapeutic applications in controlling pain and inflammation. Emerging studies show that it displays potent anti-tumor activity in several human cancers. On a more basic research level, capsaicin has been used as a ligand to activate several types of ion-channel receptors. The pharmacological activity of capsaicin-like compounds is dependent on several factors like the dose, the route of administration and most importantly on its concentration at target tissues. The present review describes the current knowledge involving the metabolism and bioavailability of capsaicinoids in rodents and humans. Novel drug delivery strategies used to improve the bioavailability and therapeutic index of capsaicin are discussed in detail. The generation of novel capsaicin-mimetics and improved drug delivery methods will foster the hope of innovative applications of capsaicin in human disease.

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.

Antiproliferative effects of TRPV1 ligands on nonspecific and enteroantigen-specific T cells from wild-type and Trpv1 KO mice

BACKGROUND

Treatment with the TRPV1 agonist, capsaicin, was previously shown to protect against experimental colitis in the severe combined immunodeficiency (SCID) T-cell transfer model. Here, we investigate trpv1 gene expression in lymphoid organs and cells from SCID and BALB/c mice to identify a potential target for the anti-inflammatory effect of capsaicin.

METHODS

The trpv1 expression was studied by real-time PCR in lymphoid tissues and gut of untreated and capsaicin-treated colitic SCID mice. Effects of capsaicin and a TRPV1 antagonist on T cells were studied in vitro.

RESULTS

In contrast to BALB/c mice, spleen, lymph nodes, and rectum of colitic and noncolitic SCID mice express trpv1 mRNA. Capsaicin treatment in vivo attenuated T-cell transfer colitis and capsaicin in vitro also attenuated T-cell proliferation induced by enteroantigen, mitogen, and anti-CD3/CD28 beads in BALB/c, C57BL/6 mice, and B6.129X1-trpv1tm1Jul/J trpv1 knockout mice. Proliferation and cytokine secretion were fully comparable in mice with and without trpv1 expression. Likewise, enteroantigen- and mitogen-stimulated T cells from wild-type and trpv1 knockout mice were equally inhibited by capsaicin. Surprisingly, the TRPV1 antagonist BCTC also inhibited enteroantigen- and mitogen-induced T-cell proliferation.

CONCLUSIONS

The trpv1 mRNA expression in lymphoid organs and the rectum of SCID mice suggests that the TRPV1 signaling in these organs could play a role in capsaicin-mediated attenuation of colitis. In addition, capsaicin-induced inhibition of T-cell proliferation of wild-type T cells lacking trpv1 expression suggests that capsaicin inhibits colitogenic T cells in a TRPV1 receptor-independent way, which might be linked to its anti-inflammatory effect.