Topical capsaicin treatment of chronic postherpetic neuralgia

Adenosine Monophosphate as a Metabolic Adjuvant Enhances Antibiotic Efficacy against Drug-Resistant Bacterial Pathogens

Global bacterial infections are on the rise, and drug resistance to bacteria is gradually rendering existing antibiotics ineffective. Therefore, the discovery of new strategies is urgently needed. Cellular metabolism is a key factor in the regulation of bacterial drug resistance, which cannot be separated from the utilization of energetic substances, suggesting that energetic substances may be associated with bacterial drug resistance. In this study, we found that adenosine monophosphate (AMP) can enhance the bactericidal effect of gentamicin against gentamicin-resistant Staphylococcus aureus. This synergistic effect can be generalized for use with different antibiotics and Gram-positive or Gram-negative bacteria. We also validated that the mechanism of AMP reversal of antibiotic resistance involves enhancing the proton motive force via the tricarboxylic acid cycle to increase antibiotic uptake. Simultaneously, AMP increases oxidative stress-induced cell death. This study presents a strategy for adopting low-dose antibiotics to control drug-resistant bacteria, which is important for future drug development and bacterial control.

Medicinal Plants for the Treatment of Neuropathic Pain: A Review of Randomized Controlled Trials

Neuropathic pain is a disabling condition caused by various diseases and can profoundly impact the quality of life. Unfortunately, current treatments often do not produce complete amelioration and can be associated with potential side effects. Recently, herbal drugs have garnered more attention as an alternative or a complementary treatment. In this article, we summarized the results of randomized clinical trials to evaluate the effects of various phytomedicines on neuropathic pain. In addition, we discussed their main bioactive components and potential mechanisms of action to provide a better view of the application of herbal drugs for treating neuropathic pain.

Analgesic Treatment Approach for Postherpetic Neuralgia: A Narrative Review

Post-herpetic neuralgia (PHN) is an entity derived from peripheral nerve damage that occurs during the reactivation of the Varicella Zoster Virus (VZV), which manifests itself through pain with neuropathic characteristics. This can prove to be very difficult to manage in the chronic stages of disease reappearance. There currently exists a multitude of treatment alternatives for PHN, however, prevention through the early initiation of antiviral regimens is vital. There are various pharmacological options available, but it is important to individualize each patient to maximize efficacy and minimize adverse effects. Interventional procedures have become a cornerstone in difficult-to-manage cases, and have shown promising outcomes when used in a multimodal approach by experienced specialists. It is necessary to make an objective diagnosis of PHN and start early treatment. Additionally there is current evidence that vouches for interventional therapies as well as individualization, with a clear establishment of therapeutic objectives according to the needs of each patient.

Complex Regional Pain Syndrome: Practical Diagnostic and Treatment Guidelines, 5th Edition

There have been some modest recent advancements in the research of Complex Regional Pain Syndrome, yet the amount and quality of the work in this complicated multifactorial disease remains low (with some notable exceptions; e.g., the recent work on the dorsal root ganglion stimulation). The semi-systematic (though in some cases narrative) approach to review is necessary so that we might treat our patients while waiting for "better research." This semi-systematic review was conducted by experts in the field, (deliberately) some of whom are promising young researchers supplemented by the experience of "elder statesman" researchers, who all mention the system they have used to examine the literature. What we found is generally low- to medium-quality research with small numbers of subjects; however, there are some recent exceptions to this. The primary reason for this paucity of research is the fact that this is a rare disease, and it is very difficult to acquire a sufficient sample size for statistical significance using traditional statistical approaches. Several larger trials have failed, probably due to using the broad general diagnostic criteria (the "Budapest" criteria) in a multifactorial/multi-mechanism disease. Responsive subsets can often be identified in these larger trials, but not sufficient to achieve statistically significant results in the general diagnostic grouping. This being the case the authors have necessarily included data from less compelling protocols, including trials such as case series and even in some instances case reports/empirical information. In the humanitarian spirit of treating our often desperate patients with this rare syndrome, without great evidence, we must take what data we can find (as in this work) and tailor a treatment regime for each patient.

Topical Treatment of Localized Neuropathic Pain in the Elderly

The prevalence of neuropathic pain in the older population has been reported to be very high and is most commonly localized to a circumscribed area. Treatment failure is frequent in neuropathic pain and is accompanied by central side effects with recommended oral drugs acting on the central nervous system. A number of topical pharmaceuticals are available on prescription and also sold over the counter. This review in persons aged older than 60 years shows the efficacy of lidocaine 5% and capsaicin 8% for localized neuropathic pain while results with other pharmaceuticals are rather inconsistent. Local application of drugs has a very limited systemic effect and the pharmacological advantages of local over systemic treatment are particularly interesting in older persons who often have comorbidities and take multiple medications. However, more information is needed on the efficacy and safety of lidocaine 5% and capsaicin 8% in older old persons and on the long-term effects of these pharmaceuticals. These studies should also pave the way for research and development in the field of topical analgesics with a satisfactory level of evidence-based medicine.

Postherpetic Neuralgia: Current Evidence on the Topical Film-Forming Spray with Bupivacaine Hydrochloride and a Review of Available Treatment Strategies

PURPOSE OF REVIEW

This is a comprehensive review of the literature about the use of bupivacaine hydrochloride for the treatment of post-herpetic neuralgia (PHN). It briefly reviews the background, biology, diagnosis and conventional treatment for PHN, and then introduces and compares the recent evidence for the use of topical bupivacaine.

RECENT FINDINGS

PHN is defined by pain lasting 90 days or more after the initial presentation of herpes zoster ("Shingles", HZ) rash and is the most common complication of this disease. A product of re-activation of the Varicella-Zoster virus (VZV), HZ is diagnosed more than 1 million times annually in the United States. Approximately 20% of patients with HZ will experience PHN and will continue to suffer intermittent neuropathic symptoms, including itching and pain, that is sharp, stabbing, throbbing or burning, with the pain localized to the site of their original rash. This long-lasting pain compares with the severity of long-standing rheumatics and osteo-arthritis and is accompanied by severe allodynia causing significant suffering, and a financial burden that is manifested in both healthcare costs and loss of quality-adjusted life years. Prevention of PHN may be achieved with the Zoster vaccine, although there is still a large segment of unvaccinated population. Moreover, the Zoster vaccine is not always effective for prevention. Current treatment includes medical (systemic tricyclic antidepressants, anticonvulsants and opioids, topical lidocaine and capsaicin) and interventional (subcutaneous Botox injections, nerve blocks and nerve stimulation) therapies. These therapies are not always effective, and each carries their own profile of side effects and risks. Moreover, up to 50% of patients with PHN are refractory to management. Recent evidence is emerging to support the use of topical local anesthetics for the treatment of PHN. Two small studies recently found topical lidocaine spray to be effective in treating paroxysmal pain attacks associated with PHN. Bupivacaine is a longer-lasting local anesthetic, and a film-forming formulation allows easy and durable application to the affected skin. Recent studies show that topical film-forming bupivacaine is safe and as effective as lidocaine for the treatment of PHN. PHN is an important though common complication of HZ and can cause long-lasting pain and disability. Current treatment for PNH is limited by efficacy and safety profiles of individual therapies. Recent evidence points to topical local anesthetics as an effective and safe alternative to conventional therapy. Film-forming bupivacaine may offer a durable and safe option for this otherwise difficult to treat syndrome.

Method to determine the impact of substantivity on ex vivo skin-permeation

Topical formulations are the most common therapeutic agents in the treatment of skin diseases. They contain one or more active pharmaceutical ingredients (API) which need to penetrate or permeate the skin in order to exert their effect. However, after application a part of the formulation is removed from the skin due to contact with the environment. Therefore, a part of the active is then not available for penetration and thus, a loss in therapeutic effect will result. To achieve the desired therapeutic outcome a sufficient fraction of the formulation must remain on the skin. The extent to which the loss of preparation affects penetration and permeation is less investigated. This work presents a method to examine the influence of mechanical stress and formulation loss on skin permeation. A movable punch with a defined weight simulated contact between clothing or skin and the applied formulation. Weight of the tool, number of contacts and speed settings were variable and were investigated. Ex vivo permeation experiments were performed in Franz diffusion cells using porcine skin. Three preparations with nonivamide as active ingredient were chosen as model formulations: A semisolid cream, an oil-in-oil emulsion and a film-forming formulation. The last two show sustained permeation profiles. The method uses skin-to-formulation and clothing-to-formulation contact to simulate the removal of the formulations from the skin.

Biological Activities of Red Pepper (Capsicum annuum) and Its Pungent Principle Capsaicin: A Review

Capsaicin, the pungent alkaloid of red pepper (Capsicum annuum) has been extensively studied for its biological effects which are of pharmacological relevance. These include: cardio protective influence, antilithogenic effect, antiinflammatory, and analgesia, thermogenic influence, and beneficial effects on gastrointestinal system. Therefore, capsaicinoids may have the potential clinical value for pain relief, cancer prevention and weight loss. It has been shown that capsaicinoids are potential agonists of capsaicin receptor (TRPV1). They could exert the effects not only through the receptor-dependent pathway but also through the receptor-independent one. The involvement of neuropeptide Substance P, serotonin, and somatostatin in the pharmacological actions of capsaicin has been extensively investigated. Topical application of capsaicin is proved to alleviate pain in arthritis, postoperative neuralgia, diabetic neuropathy, psoriasis, etc. Toxicological studies on capsaicin administered by different routes are documented. Capsaicin inhibits acid secretion, stimulates alkali and mucus secretion and particularly gastric mucosal blood flow which helps in prevention and healing of gastric ulcers. Antioxidant and antiinflammatory properties of capsaicin are established in a number of studies. Chemopreventive potential of capsaicin is evidenced in cell line studies. The health beneficial hypocholesterolemic influence of capsaicin besides being cardio protective has other implications, viz., prevention of cholesterol gallstones and protection of the structural integrity of erythrocytes under conditions of hypercholesterolemia. Beneficial influences of capsaicin on gastrointestinal system include digestive stimulant action and modulation of intestinal ultrastructure so as to enhance permeability to micronutrients.

The Effectiveness and Safety of Topical Capsaicin in Postherpetic Neuralgia: A Systematic Review and Meta-analysis

In particular, neuropathic pain is a major form of chronic pain. This type of pain results from dysfunction or lesions in the central and peripheral nervous system. Capsaicin has been traditionally utilized as a medicine to remedy pain. However, the effectiveness and safety of this practice is still elusive. Therefore, this systematic review aimed to investigate the effect of topical capsaicin as a pain-relieving agent that is frequently used in pain management. In brief, all the double-blinded, randomized placebo- or vehicle-controlled trials that were published in English addressing postherpetic neuralgia were included. Meta-analysis was performed using Revman^® version 5.3. Upon application of the inclusion and exclusion criteria, only six trials fulfilled all the criteria and were included in the review for qualitative analysis. The difference in mean percentage change in numeric pain rating scale score ranges from -31 to -4.3. This demonstrated high efficacy of topical capsaicin application and implies that capsaicin could result in pain reduction. Furthermore, meta-analysis was performed on five of the included studies. All the results of studies are in favor of the treatment using capsaicin. The incidence of side effects from using topical capsaicin is consistently higher in all included studies, but the significance of safety data cannot be quantified due to a lack of p-values in the original studies. Nevertheless, topical capsaicin is a promising treatment option for specific patient groups or certain neuropathic pain conditions such as postherpetic neuralgia.

Alternative methods of pain management for the older adult population: Review of topical pain medications

The older adult population is one of the fastest growing age groups in the United States. As this population continues to expand, determining the safest way to provide pain management has become increasingly important. More than 50% of community-dwelling older adults experience pain on a daily basis, and up to 83% of those in assisted living facilities experience persistent pain. Pain is exceedingly challenging to treat safely and effectively in the elderly because of the physiologic changes that occur as people age. In addition, many nonnarcotic medications with analgesic properties are listed in both the 2012 American Geriatrics Society Beers Criteria for Potentially Inappropriate Medication Use in Older Adults and the Pharmacy Quality Alliance high-risk medications lists. An approach to the growing challenge of managing pain in the elderly that is gaining popularity among community-dwelling patients is the use of topical pain medications. The goal of this article is to review some of the available literature regarding the use of various topical analgesics alone or in combination, and to discuss their known or theoretical mechanisms of peripheral pain modulation. Commercially available or compounded topical pain medications may be used to replace or augment doses of oral medications in an effort to decrease the risk of adverse drug events for older adult patients. When prescribing topical pain medications physicians should consider the nature of the pain targeted, the type of analgesia expected from each ingredient, the potential for systemic absorption, and related side effects.

Topical and Intranasal Analgesic Therapy in a Woman with Refractory Postherpetic Neuralgia

A patient-specific, stepped approach to topical and intranasal analgesic pharmacotherapy was effective in reducing refractory postherpetic neuralgia (PHN) not responding to the current standard of care for PHN. The use of topical analgesic therapy allowed for higher concentrations of medication locally while reducing the likelihood of systemic side effects common to the drugs used. No adverse effects were noted for either topical or intranasal drug therapy. The patient-specific, stepped approach resulted in clinically significant decreases in pain on visual analog scale (VAS), with the use of intranasal ketamine 10% solution and topical gabapentin 6%, ketoprofen 10%, lidocaine 5%, and ketamine 10% cream.

Systematic review and meta-analysis of pharmacological therapies for pain associated with postherpetic neuralgia and less common neuropathic conditions

OBJECTIVE

To estimate the relative efficacy of pharmacological therapies for the treatment of postherpetic neuralgia (PHN), multiple sclerosis (MS)-related pain, posttraumatic pain, central poststroke pain (CPSP) and human immunodeficiency virus (HIV)-related neuropathic pain (NeP).

METHODS

This systematic review (through June 2011) identified randomised, controlled trials of treatments for these conditions. Bayesian mixed treatment comparison (MTC) methods were used to determine the relative efficacy and safety among the treatments within each pain condition.

RESULTS

Fifty studies were identified: 33 PHN, 2 MS-related pain, 3 CPSP, 3 posttraumatic pain and 9 HIV-related NeP. Data from 28 PHN studies including 21 interventions and 4317 patients were included into the PHN MTC. Of treatments studied in ≥ 50 patients, opioids had the greatest mean pain reduction of -1.70 vs. placebo on an 11-point numeric rating scale. Pregabalin ≥ 300 mg/day was most effective for ≥ 30% and ≥ 50% pain reduction [relative risk (RR) vs. placebo = 2.44 and 2.13, respectively]. Data identified for MS-related pain, CPSP, posttraumatic pain and HIV-related NeP were sparse; only 7 of 17 studies had ≥ 50 patients. Adverse events (AEs) and discontinuations for most treatments were not significantly greater than placebo except in PHN, where 8 of 12 treatments had higher risks of AEs compared with placebo and tricyclic antidepressants and opioids had higher risk of discontinuation compared with placebo.

CONCLUSIONS

Guideline-recommended treatments for PHN were more effective than placebo on the pain NRS and for ≥ 30% and ≥ 50% pain reduction. Although guidelines exist for the management of less common NeP conditions, little published evidence supports them. These results highlight the need for additional evaluations and more complete reporting of outcomes to help guide physicians' treatment selections.

Riot control agents: the tear gases CN, CS and OC-a medical review

INTRODUCTION

2-Chloroacetophenone (CN), o-chlorobenzylidene malonitrile (CS) and oleoresin capsicum (OC) are common riot control agents. While serious systemic effects are uncommon, exposure to high concentrations may lead to severe complications and even death. The aim of this narrative review is to summarise all main aspects of the riot control agents CN, CS and OC toxicology, including mechanisms of toxicity, clinical features and management.

METHODS

OVID MEDLINE and ISI Web of Science were searched for terms associated with CN, CS and OC toxicity in humans and those describing the mechanism of action, clinical features and treatment protocols.

RESULTS

CN, CS and OC are effective lacrimating agents; evidence for toxicity, as measured by the threshold for irritation, is greatest for CN, followed by CS and OC. Typically, ocular and respiratory tract irritation occurs within 20-60 s of exposure. Ocular effects involve blepharospasm, photophobia, conjunctivitis and periorbital oedema. Following inhalation, effects may include a stinging or burning sensation in the nose, tight chest, sore throat, coughing, dyspnoea and difficulty breathing. Dermal outcomes are variable, more severe for CN and include dermal irritation, bulla formation and subcutaneous oedema. Removal from the contaminated area and fresh air is a priority. There is no antidote; treatment consists of thorough decontamination and symptom-directed supportive care. Ocular exposure requires thorough eye decontamination, an eye exam and appropriate pain management. Monitoring and support of respiratory function is important in patients with significant respiratory symptoms. Standard treatment protocols may be required with patients with pre-existing respiratory conditions. Dermal exposures may require systemic steroids for patients who develop delayed contact dermatitis.

CONCLUSIONS

CN, CS and OC are effective riot control agents. In the majority of exposures, significant clinical effects are not anticipated. The irritant effects can be minimised both by rapid evacuation from sites of exposure, decontamination and appropriate supportive care.

Thermo-sensitive TRP channels in peripheral nerve injury: a review of their role in cold intolerance

One of the sensory complications of traumatic peripheral nerve injury is thermal intolerance, which manifests in humans mainly as cold intolerance. It has a major effect on the quality of life, and adequate therapy is not yet available. In order to better understand the pathophysiological background of thermal intolerance, we focus first on the various transient receptor potential (TRP) channels that are involved in temperature sensation, including their presence in peripheral nerves and in keratinocytes. Second, the role of thermo-sensitive TRP channels in cold and heat intolerance is described showing three different mechanisms that contribute to thermal intolerance in the skin: (a) an increased expression of TRP channels on nerve fibres and on keratinocytes, (b) a lower activation threshold of TRP channels and (c) the sprouting of non-injured nerve fibres. Finally, the data that are available on the effects of TRP channel agonists and antagonists and their clinical use are discussed. In conclusion, TRP channels play a major role in temperature sensation and in cold and heat intolerance. Unfortunately, the available pharmaceutical agents that successfully target TRP channels and counteract thermal intolerance are still very limited. Yet, our focus should remain on TRP channels since it is difficult to imagine a reliable treatment for thermal intolerance that will not involve TRP channels.

New and developing drugs for the treatment of neuropathic pain in diabetes

A number of agents from diverse pharmacological classes are used to treat neuropathic pain associated with diabetic peripheral neuropathy. Only three of these have regulatory approval for this indication in the U.S. In this focused article, I will discuss selected drugs, newly approved or in development, to treat neuropathic pain in patients with diabetic neuropathy. These will include agonists and antagonists of the transient receptor potential channels, a family of receptor proteins that play a role in the transduction of physical stress; sodium channel isoform specific antagonists; a recently approved dual-action opioid receptor agonist-norepinephrine reuptake inhibitor; gene therapy for neuropathic pain; and anti-nerve growth factor molecules. Mechanisms of action, preclinical supporting data, clinical trial evidence, and adverse effects will be reviewed.

Therapeutic options for the treatment of postherpetic neuralgia: a systematic review

Postherpetic neuralgia (PHN) is a chronic and painful condition that may result in significant disturbances to normal activities and decreases in the quality of life for those affected. Despite the availability of several first- and second-line treatment options, many patients may experience refractory pain. The objectives of this review were to summarize evidence for Food and Drug Administration (FDA)-approved and off-label therapies for the treatment of PHN and to present gaps in the current literature for future research focus. Several agents, including pregabalin, gabapentin, and opioids, have been shown to significantly improve pain when compared with placebo. However, evidence regarding the comparative effectiveness of these treatment alternatives is lacking. In order to choose the optimal treatment, providers should consider issues related to efficacy, safety, and tolerability in conjunction with patient goals, preferences, and adherence issues. Evidence from randomized or observational studies that directly compare agents with each other should help to inform treatment choices.

Complex regional pain syndrome: practical diagnostic and treatment guidelines, 4th edition

OBJECTIVE

This is the fourth edition of diagnostic and treatment guidelines for complex regional pain syndrome (CRPS; aka reflex sympathetic dystrophy).

METHODS

Expert practitioners in each discipline traditionally utilized in the treatment of CRPS systematically reviewed the available and relevant literature; due to the paucity of levels 1 and 2 studies, less rigorous, preliminary research reports were included. The literature review was supplemented with knowledge gained from extensive empirical clinical experience, particularly in areas where high-quality evidence to guide therapy is lacking.

RESULTS

The research quality, clinical relevance, and "state of the art" of diagnostic criteria or treatment modalities are discussed, sometimes in considerable detail with an eye to the expert practitioner in each therapeutic area. Levels of evidence are mentioned when available, so that the practitioner can better assess and analyze the modality under discussion, and if desired, to personally consider the citations. Tables provide details on characteristics of studies in different subject domains described in the literature.

CONCLUSIONS

In the humanitarian spirit of making the most of all current thinking in the area, balanced by a careful case-by-case analysis of the risk/cost vs benefit analysis, the authors offer these "practical" guidelines.

Diagnosing and managing postherpetic neuralgia

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

Capsaicin for neuropathic pain: linking traditional medicine and molecular biology

Capsaicin has long been used as a traditional medicine to treat pain and, recently, its mechanism of analgesic action has been discovered. This review article documents the clinical development of capsaicin to demonstrate that pharmacognosy still has a profound influence on modern-day drug development programs. Capsaicin is a highly selective agonist for the transient receptor potential channel vanilloid-receptor type 1 (TRPV1), which is expressed on central and peripheral terminals of nociceptive primary sensory neurons. Knockout studies have revealed the importance of TRPV1 as a molecular pain integrator and target for novel analgesic agents. Topical application of capsaicin at the peripheral terminal of TRPV1-expressing neurons superficially denervates the epidermis in humans in a highly selective manner and results in hypoalgesia. In three recent randomized controlled trials, a patch containing high-concentration capsaicin demonstrated meaningful efficacy and tolerability relative to a low-concentration capsaicin control patch in patients with peripheral neuropathic pain. Data from clinical practice will determine if the high-concentration capsaicin patch is effective in real-world settings.

Topical capsaicin (low concentration) for chronic neuropathic pain in adults

BACKGROUND

Topical creams with capsaicin are used to treat pain from a wide range of chronic conditions including neuropathic pain. Following application to the skin capsaicin causes enhanced sensitivity to noxious stimuli, followed by a period with reduced sensitivity and, after repeated applications, persistent desensitisation. There is uncertainty about the efficacy and tolerability of capsaicin for treating painful chronic neuropathies. This is an update of an earlier review of topical capsaicin for chronic neuropathic pain in adults that looked at all doses and formulations of capsaicin. The original review has now been split: here we consider only formulations using a low concentration of capsaicin (< 1%) applied several times daily over several weeks, while another review will consider a single application of capsaicin at a high concentration.

OBJECTIVES

To review the evidence from controlled trials on the efficacy and tolerability of topically applied low-concentration (< 1%) capsaicin in chronic neuropathic pain in adults.

SEARCH METHODS

Cochrane CENTRAL, MEDLINE, EMBASE and Oxford Pain Relief Database, searched to July 2012.

SELECTION CRITERIA

Randomised, double-blind, placebo-controlled studies of at least six weeks' duration, using low-concentration (< 1%) topical capsaicin to treat neuropathic pain.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed study quality and validity, and extracted data. Information was extracted on numbers of participants with pain relief (clinical improvement) after at least six weeks, and with local skin reactions, and used to calculate relative risk (or risk ratio, RR) and numbers needed to treat to benefit (NNT) and harm (NNH). Details of definition of pain relief and specific adverse events were sought.

MAIN RESULTS

No additional studies were identified for this update of low concentration capsaicin. Included studies were published before 1996. Six studies (389 participants in total) compared regular application of low dose (0.075%) capsaicin cream with placebo cream. There was substantial heterogeneity in results, probably as a result of the small number of studies each with small numbers of participants, as well as the different pain conditions studied and different definitions of "clinical success" reported. Only two studies reported data for the preferred primary outcome of at least 50% pain relief, and there were too few data for pooled analysis. Local skin reactions were more common with capsaicin, usually tolerable, and attenuated with time; the NNH for repeated low-dose application was 2.5 (95% confidence interval (CI) 2.1 to 3.1). All studies satisfied minimum criteria for quality and validity, but maintenance of blinding remains a potential problem.

AUTHORS' CONCLUSIONS

There were insufficient data to draw any conclusions about the efficacy of low-concentration capsaicin cream in the treatment of neuropathic pain. The information we have suggests that low-concentration topical capsaicin is without meaningful effect beyond that found in placebo creams; given the potential for bias from small study size, this makes it unlikely that low-concentration topical capsaicin has any meaningful use in clinical practice. Local skin irritation, which was often mild and transient but may lead to withdrawal, was common. Systemic adverse effects were rare.

A randomized, prospective study of efficacy and safety of oral tramadol in the management of post-herpetic neuralgia in patients from north India

OBJECTIVE

To evaluate the safety and efficacy of oral tramadol therapy (50 to 200 mg/day) in the treatment for post-herpetic neuralgia (PHN).

METHODS

The study was a prospective, single-blind, non-responder vs. responder, randomized trial conducted in 100 outpatients of PHN after oral administration of tramadol for 4 weeks. Those patients who had achieved 50% or greater pain relief after 14 days of oral tramadol treatment were categorized as responders and those reporting < 50% pain relief were categorized as non-responders. Rescue analgesia was provided by the topical application of a cream consisting of the combination of 3.33% doxepin and 0.05% capsaicin to the affected areas of PHN patients of both groups for at least 14 days, along with tramadol therapy. The rescue analgesia was extended to 4 weeks in patients of the non-responder group. The primary endpoints were measured using a numerical rating scale (NRS) at rest and with movement. Secondary endpoints included additional pain ratings such as global perceived effect (GPE), Neuropathic Pain Symptom Inventory scores (NPSI), daily sleep interference score (DSIS), quality of life (QOL) as per WHO QOL-BREF Questionnaire scores, patient and clinician ratings of global improvement. The 2 groups were compared on the basis of pain intensity scores, encompassing primary as well as secondary endpoints, and QOL after 28 days of the treatment regimen.

RESULTS

Pain intensity scores measured by NRS (at resting and with movement), NPSI, and DSIS were consistently reduced (P < 0.001) over 28 days at varying intervals in both the groups, but the magnitude of reduction was higher in responders than non-responders. A concomitant improvement (P < 0.001) was observed in GPE on days 3, 14, and 28 as compared to the respective baseline scores in both the groups. Although the WHO QOL-BREF scores showed significant (P < 0.001) improvement in QOL of PHN patients at days 14 and 28 in both the groups, the magnitude of improvement was higher in responders as compared to non-responders. Significant improvement in pain intensity scores and QOL in non-responders is mainly attributed to the use of rescue analgesia for 28 days rather than recommended tramadol therapy.

CONCLUSIONS

Treatment with tramadol 50 to 200 mg per day was associated with significant pain reduction in terms of enhanced pain relief, reduced sleep interference, greater global improvement, diminished side-effect profile, and improved QOL in PHN patients from North India. Further categorization of PHN patients may be helpful so that additional or alternative therapy may be prescribed to non-responders.

Multimodal approach for the management of Hunan hand syndrome: a case report

Hunan hand syndrome, a form of painful contact dermatitis, is a rare case finding. It is usually seen in people with continuous and prolonged exposure to chili peppers. The main ingredient in chili peppers is capsaicin that leads to the clinical condition, Hunan hand syndrome. This is paradoxical to the use of capsaicin as local application for relief of pain in various clinical situations, such as diabetic neuropathy and postherpetic neuralgia. We report a case of Hunan hand syndrome, managed successfully by using a multimodal approach comprised of a continuous stellate ganglion block, gabapentin, local ice water, and fluocinonide application.

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

OBJECTIVES

Analyses of integrated data from 4 controlled postherpetic neuralgia studies evaluated the effect of NGX-4010, a capsaicin 8% patch, administered alone or together with systemic neuropathic pain medications.

METHODS

Patients recorded their “average pain for the past 24 hours” daily for 12 weeks using an 11-point Numeric Pain Rating Scale (NPRS). Efficacy assessment included the percentage NPRS score reduction from baseline during weeks 2 to 8 and 2 to 12, the proportion of patients responding during weeks 2 to 8 and 2 to 12 and the Patient Global Impression of Change (PGIC) at weeks 8 and 12.

RESULTS

During the studies, 302 NGX-4010 and 250 control (capsaicin, 0.04% wt/wt) patients were using at least 1 systemic neuropathic pain medication; 295 NGX-4010 and 280 control patients were not. During weeks 2 to 8, NGX-4010 patients reported greater reductions in NPRS scores compared with control both in patients using systemic neuropathic pain medications (26.1% vs. 18.1%, P=0.0011) and in patients not using these medications (36.5% vs. 26.2%, P=0.0002). Patients not using systemic neuropathic pain medications reported a greater reduction in pain compared with patients using these medications in both, NGX-4010 and control groups, resulting in comparable treatment differences between NGX-4010 and control regardless of systemic neuropathic pain medication use. Similar results were seen during weeks 2 to 12, for the responder and PGIC analyses. Transient, capsaicin-related application site reactions were the most common adverse events and not affected by systemic neuropathic pain medication use.

CONCLUSION

A single 60-minute NGX-4010 treatment reduces PHN for up to 12 weeks regardless of concomitant systemic neuropathic pain medication use.

Systematic review and meta-analysis of efficacy, safety, and tolerability data from randomized controlled trials of drugs used to treat postherpetic neuralgia

OBJECTIVE

To conduct a systematic review of available data from reports of randomized controlled trials on the efficacy, safety, and tolerability of drugs used to treat postherpetic neuralgia (PHN), a common type of neuropathic pain.

DATA SOURCES

The MEDLINE (1950-June 30, 2009) and EMBASE (1974-June 30, 2009) databases were used to identify source studies, in conjunction with a review of reference citations from identified published reports.

STUDY SELECTION AND DATA EXTRACTION

We selected all English-language reports of randomized placebo-controlled trials of the efficacy, tolerability, and safety of drugs (oral or transdermal) used for treatment in patients with PHN. Studies with treatment duration less than 4 weeks were excluded. From each identified trial, we extracted information on (1) placebo-corrected percentage reductions in pain intensity from randomization to end of active treatment; (2) relative risks of withdrawal due to lack of efficacy; (3) relative risks of various adverse events; and (4) relative risks of withdrawal due to adverse events.

DATA SYNTHESIS

Twelve reports of randomized controlled trials in patients with PHN were identified, involving 8 different agents (amitriptyline, capsaicin, divalproex sodium, gabapentin, morphine, nortriptyline, pregabalin, tramadol). Most studies were small, involving fewer than 200 patients. Pain intensity was reported to have been reduced significantly with all drugs (range: 13.8% [tramadol] to 42.4% [amitriptyline]); data were pooled using techniques of meta-analysis when information was available from more than 1 trial. No clinical trial reported a significant reduction in risk of withdrawal as a result of lack of efficacy. Analysis of adverse events was greatly limited by erratic and inconsistent reporting and wide variation in sample sizes.

CONCLUSIONS

While available literature establishes the efficacy of 8 drugs in treatment of PHN, it does not provide adequate guidance as to which agents are best to treat this condition, in part because of inadequate reporting of data on tolerability and safety.

Review of current guidelines on the care of postherpetic neuralgia

An unfortunate minority of patients with acute herpes zoster (AHZ) experience pain beyond the typical 4-week duration, and roughly 10% develop the distressing complication of postherpetic neuralgia (PHN), often defined as pain persisting for > 4 months after the onset of the rash. Elderly patients are at increased risk of PHN. The pathophysiology of PHN is complex, likely involving both peripheral and central processes. This complexity may create opportunities for pharmacologic interventions with multiple differing mechanisms of action. Consequently, complementary combinations of pharmacologic agents are frequently more effective than any monotherapy. Current US and international guidelines on the care of patients with PHN are reviewed and interpreted here to facilitate their effective incorporation into the practice of primary care physicians, acknowledging the contrasts that often exist between the clinical trial populations analyzed to craft so-called evidence-based medicine and the individual patients seen in daily practice, many of whom may not have been candidates for those clinical trials. First-line treatments for PHN include tricyclic antidepressants, gabapentin and pregabalin, and the topical lidocaine 5% patch. Opioids, tramadol, capsaicin cream, and the capsaicin 8% patch are recommended as either second- or third-line therapies in different guidelines. Therapies that have demonstrated effectiveness for other types of neuropathic pain are discussed, such as serotonin-norepinephrine reuptake inhibitors, the anticonvulsants carbamazepine and valproic acid, and botulinum toxin. Invasive procedures such as sympathetic blockade, intrathecal steroids, and implantable spinal cord stimulators have been studied for relief of PHN, mainly in patients refractory to noninvasive pharmacologic interventions. The main guidelines considered here are those issued by the American Academy of Neurology for the treatment of postherpetic neuralgia (2004) and general guidelines for the treatment of neuropathic pain issued by the Special Interest Group on Neuropathic Pain of the International Association for the Study of Pain (2007) and the European Federation of Neurological Societies (2010).

Gynecologic management of neuropathic pain

Obstetrician/gynecologists often are the initial management clinicians for pelvic neuropathic pain. Although treatment may require comprehensive team management and consultation with other specialists, there are a few critical and basic steps that can be performed during an office visit that offer the opportunity to improve quality of life significantly in this patient population. A key first step is a thorough clinical examination to map the pain site physically and to identify potentially involved nerves. Only limited evidence exists about how best to manage neuropathic pain; generally, a combination of surgical, manipulative, or pharmacologic methods should be considered. Experimental methods to characterize more precisely the nature of the nerve dysfunction exist to diagnose and treat neuropathic pain; however, additional scientific evidence is needed to recommend these options unanimously. In the meantime, an approach that was adopted from guidelines of the International Association for the Study of Pain has been tailored for gynecologic pain.

5% lidocaine-medicated plaster vs other relevant interventions and placebo for post-herpetic neuralgia (PHN): a systematic review

Several pharmacological treatments are used to manage post-herpetic neuralgia (PHN). The use of topical analgesics, such as 5% lidocaine-medicated plaster (5% LMP), may be preferable to systemic treatments in that they are formulated to produce a local pain relieving effect with minimal systemic absorption. However, direct head-to-head comparisons are relatively few, and a rigorous assessment of the relative efficacy and safety of the various treatment options is lacking. The objective of this study was to compare 5% LMP for the relief of PHN with other relevant interventions and placebo. Six databases were searched up to May 2010. Quantitative methods for data synthesis were used, and a network meta-analysis was conducted. Twenty unique studies (32 publications) were included. Placebo-controlled studies showed 5% LMP to be effective in providing pain relief and reducing allodynia while adverse event rates were generally low. A comparison between 5% LMP and pregabalin indicated the non-inferiority of 5% LMP for pain reduction and showed greater improvement of quality of life for 5% LMP. Adverse events (AE) were significantly fewer with 5% LMP. In the network meta-analysis, only 5% LMP and gabapentin were associated with a greater change in pain from baseline than placebo [-15.50 (95% CI -18.85 to -12.16) and -7.56 (95% CI -12.52 to -2.59) respectively]. 5% LMP was shown to be more effective than capsaicin [-16.45 (95% CI -20.04 to -12.86)], gabapentin [-7.95 (95% CI -13.29 to -2.61)] and pregabalin [-13.45 (95% CI -19.19 to -7.71)]. For pain relief, two comparators were more effective than placebo [mean pain relief, gabapentin: 32.77 (95% CI 15.57-49.97); 5% LMP: 26.77 (95% CI 9.11-44.43)]. 5% LMP was shown to be comparable to gabapentin [-6.00 (95% CI -25.32-13.32)]. The results suggest that 5% LMP and gabapentin have similar effects on pain relief and that 5% LMP is more effective than capsaicin and pregabalin (change in pain from baseline). Topical agents, such as 5% LMP, are associated with fewer and less clinically significant AE than is the case for systemic agents. However, small numbers, and limited size and quality of included studies should be taken into account. Further studies are needed.

[Types of topical treatment for peripheral neuropathic pain : Mechanism of action and indications]

The term "peripheral neuropathic pain syndromes" summarizes several chronic pain syndromes, which can occur focally or generalized in the peripheral nervous system in the course of an impairment of afferent neurons. Controlled clinical trials gave distinct indications for systemic treatments with antidepressants, anticonvulsants and opioid analgesics in several neuropathic pain syndromes. In addition to these systemic therapies, there are also two topical treatment options: topical application of lidocaine and capsaicin. An important cause of sensitization phenomena of afferent nociceptors is the upregulation of sodium channels and thermosensor channels. In the context of a partial nerve lesion that leaves behind partially preserved or regenerated afferent nerve fibres, just these channels could be used as target structures for topical medications. Topically applied drugs are absorbed systemically only in minute quantities, so systemic side effects are negligible. Pharmacological interactions with systematically acting substances are also virtually absent; thus, topically applied substances are especially appropriate for add-on therapy in addition to systemic pain medication.

A multicenter, randomized, double-blind, controlled study of NGX-4010, a high-concentration capsaicin patch, for the treatment of postherpetic neuralgia

OBJECTIVES

To confirm the efficacy, tolerability, and safety of NGX-4010, an 8% capsaicin dermal patch (capsaicin 640 µg/cm(2) ), in patients with postherpetic neuralgia (PHN). PHN is a chronic pain disorder that can be difficult to treat and for which current treatment options are often limited by poor tolerability.

DESIGN

A total of 418 patients were randomized to receive a single 60-minute application of NGX-4010 or a 0.04% capsaicin control patch (3.2 µg/cm(2) ) in a multicenter, double-blind, confirmatory, phase 3 study.

PATIENTS

Patients were 18-90 years old with a diagnosis of PHN, pain for at least 6 months, and an average baseline Numeric Pain Rating Scale (NPRS) score of 3-9.

OUTCOME MEASURES

The primary efficacy end point was the percentage change in NPRS score from baseline to weeks 2-8.

RESULTS

NGX-4010 recipients had a significantly greater mean reduction from baseline in pain during weeks 2-8 compared with the control group (32.0% vs 24.4%; P=0.011). A ≥ 30% reduction in mean NPRS scores was achieved in 46% of NGX-4010 recipients compared with 34% of controls (P=0.02). Pain was significantly lower in NGX-4010 recipients than controls by week 2, and greater pain reduction was maintained throughout the remaining 12-week study period. Most treatment-emergent adverse events were application site specific (notably erythema and pain), transient, and generally mild to moderate in severity.

CONCLUSIONS

In patients with PHN, a single 60-minute application of NGX-4010 produced significant reduction in pain that was maintained over a 12-week period.

Effect of duration of postherpetic neuralgia on efficacy analyses in a multicenter, randomized, controlled study of NGX-4010, an 8% capsaicin patch evaluated for the treatment of postherpetic neuralgia

BACKGROUND

Postherpetic neuralgia (PHN) is a painful and difficult to treat complication of acute herpes zoster. Current treatment options provide only partial relief and are often limited by poor tolerability. We evaluated the safety and efficacy of a single 60-minute application of NGX-4010, an 8% capsaicin patch, in patients with PHN.

METHODS

This multicenter, double-blind, controlled study randomized 155 patients 2:1 to receive either NGX-4010 or a 0.04% capsaicin control patch. Patients were at least 18 years old with PHN for at least 3 months, and an average Numeric Pain Rating Scale (NPRS) score of 3 to 9. The primary efficacy endpoint was the percentage change in NPRS score from baseline to weeks 2-8.

RESULTS

The mean percent reduction in "average pain for the past 24 hours" NPRS scores from baseline to weeks 2-8 was greater in the NGX-4010 group (36.5%) compared with control (29.9%) although the difference was not significant (p = 0.296). PGIC analysis demonstrated that more NGX-4010 recipients considered themselves improved (much, or very much) compared with control at weeks 8 and 12, but the differences did not reach statistical significance. Post hoc analyses of patients with PHN for at least 6 months showed significantly greater reductions in "average pain for the past 24 hours" NPRS scores from baseline to weeks 2-8 in NGX-4010 patients compared to controls (37.6% versus 23.4%; p = 0.0291). PGIC analysis in this subgroup demonstrated that significantly more NGX-4010 recipients considered themselves much or very much improved compared with control at week 12 (40% versus 20%; p = 0.0403;).

CONCLUSIONS

Although treatment appeared to be safe and well tolerated, a single 60-minute application of NGX-4010 failed to show efficacy in this study which included patients with PHN for less than 6 months. Large reductions in pain observed among control patients with pain for less than 6 months may have been due to spontaneous resolution of PHN, may have confounded the results of the prespecified analyses, and should be taken into account when designing PHN studies.

TRIAL REGISTRATION

NCT00068081.

A multicenter, randomized, double-blind, controlled dose finding study of NGX-4010, a high-concentration capsaicin patch, for the treatment of postherpetic neuralgia

Postherpetic neuralgia (PHN) is a painful complication of acute herpes zoster. This multicenter, double-blind, controlled study randomized 299 PHN patients to receive either NGX-4010, a high-concentration capsaicin (8%) patch, or a low-concentration capsaicin (0.04%) control patch for 30, 60, or 90 minutes. The mean percent reductions in NPRS score from baseline to weeks 2 through 8 were significantly greater in the total NGX-4010 group (26.5%, P = .0286) and the 90-minute NGX-4010 group (27.8%, P = .0438) compared to the pooled control group (17.3%). After review of the data suggested a difference between genders in reporting of pain scores and a higher proportion of males (61%) in the 60-minute NGX-4010 group, post hoc gender-stratified analyses were performed and showed that the 60-minute NGX-4010 group also had a significantly larger mean percent reduction in average pain scores (28.0%, P = .0331). Pain reduction in the 30-minute NGX-4010 group, although similar in magnitude to the other doses, was not significantly different from control in either of these analyses. Similar results were observed during weeks 2 through 12. Most treatment-emergent adverse events were application-site specific, transient and mostly mild to moderate in severity.

PERSPECTIVE

This article reports the safety and efficacy of NGX-4010 applied for 3 different durations (30, 60, or 90 minutes) in patients with PHN. The results identified the 60-minute duration as the dose to be evaluated in subsequent studies and identified a gender effect on reported changes in pain.

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.

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.

Topical capsaicin for chronic neuropathic pain in adults

BACKGROUND

Topical creams with capsaicin are used to treat pain from a wide range of chronic conditions including neuropathic pain. Following application to the skin capsaicin causes enhanced sensitivity to noxious stimuli, followed by a period with reduced sensitivity and, after repeated applications, persistent desensitisation. There is uncertainty about the efficacy and tolerability of capsaicin for treating painful chronic neuropathies.

OBJECTIVES

To review the evidence from controlled trials on the efficacy and tolerability of topically applied capsaicin in chronic neuropathic pain in adults.

SEARCH STRATEGY

Cochrane CENTRAL, MEDLINE, EMBASE and Oxford Pain Relief Database, searched in May 2009.

SELECTION CRITERIA

Randomised, double blind, placebo controlled studies of at least six weeks' duration, using topical capsaicin to treat neuropathic pain.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and validity, and extracted data. Information was extracted on numbers of participants with pain relief (clinical improvement) after at least six weeks, and with local skin reactions, and used to calculate relative risk and numbers needed to treat to benefit (NNT) and harm (NNH). Details of definition of pain relief and specific adverse events were sought.

MAIN RESULTS

Six studies (389 participants in total) compared regular application of low dose (0.075%) capsaicin cream with placebo cream; the NNT for any pain relief over six to eight weeks was 6.6 (4.1 to 17). Two studies (709 participants in total) compared a single application of high dose (8%) capsaicin patch with placebo patch; the NNT for >/= 30% pain relief over twelve weeks was 12 (6.4 to 70). Local skin reactions were more common with capsaicin, usually tolerable, and attenuated with time; the NNH for repeated low dose application was 2.5 (2.1 to 3.1). There were insufficient data to analyse either data set by condition or outcome definition. All studies satisfied minimum criteria for quality and validity, but maintenance of blinding remains a potential problem.

AUTHORS' CONCLUSIONS

Capsaicin, either as repeated application of a low dose (0.075%) cream, or a single application of a high dose (8%) patch may provide a degree of pain relief to some patients with painful neuropathic conditions. Local skin irritation, which is often mild and transient but may lead to withdrawal, is common. Systemic adverse effects are rare. Estimates of benefit and harm are not robust due to limited amounts of data for different neuropathic conditions and inconsistent outcome definition.

Pharmacological management of neuropathic pain in older adults: an update on peripherally and centrally acting agents

The burden of neuropathic pain in older adults is great and the practitioner is challenged to reduce symptoms and improve quality of life. Many common neuropathic pain syndromes are more prevalent in the older population, and older adults also carry greater sensitivity to certain side effects. The health care professional should have a thorough familiarity with all medications available to treat this difficult group of disorders.

Instilled or injected purified natural capsaicin has no adverse effects on rat hindlimb sensory-motor behavior or osteotomy repair

BACKGROUND

A novel formulation of > or = 98% pure capsaicin (4975) is currently undergoing clinical investigation using novel routes of delivery to provide selective analgesia lasting weeks to months with a single dose. We conducted this study to assess the safety and effects of instilled and injected 4975 in rat models of wound healing osteotomy repair and sensory-motor nerve function.

METHODS

Adult male and female Sprague-Dawley rats were used. To assess the effects of 4975 on nerve or muscle, 0.0083 or 0.025 mg 4975 or vehicle (25% polyethylene glycol-300) was applied to exposed sciatic nerve, or 0.1 mg 4975 or vehicle was injected into the surrounding muscle (Group 1). To assess the effect of 4975 on bone healing, an osteotomy was made in one femur and 0.5 mg of 4975 or vehicle was instilled into the site (Group 2). Behavioral testing was performed on both groups of rats and histological evaluation of the sciatic nerve, and surrounding soft tissue and bone was done at days 3, 14, and 28 after surgery. Femurs from osteotomy rats were assessed using peripheral quantitative computed tomography and biomechanical testing. Standard statistical tests were used to compare groups.

RESULTS

Rats with direct application of 4975 to the sciatic nerve and surrounding muscle were no different from the controls in nociceptive sensory responses (F = 0.910, P = 0.454), grip strength (F = 0.550, P = 0.654), or histology of the muscle or sciatic nerve. In osteotomy rats, there were no statistical differences between 4975 and vehicle-treated rats for bone area (H = 2.858, P = 0.414), bone mineral content (F = 0.945, P = 0.425), or bone mineral density (F = 0.87, P = 0.462) and no difference in soft tissue healing. There were neither differences in bone stiffness (F = 1.369, P = 0.268) nor were there noticeable differences in the macro- or microscopic appearance of the right femur osteotomy healing site and surrounding soft tissues between the control group and the 4975-treated animals.

CONCLUSION

A single, clinically relevant application of instilled or injected 4975 has no observable adverse effect on wound and bone healing after osteotomy or on the structural integrity of exposed muscle and nerve.