Topical capsaicin for chronic neuropathic pain in adults

Unlocking the potential of capsaicin in oral health (Review)

Capsaicin is a bioactive compound found prominently in Capsicum annuum L. plants and takes on a pivotal role in their characteristic spiciness. Previous studies have delved into the potential analgesic effect of capsaicin in various oral conditions, such as oral neuropathic pain, trigeminal neuralgia, oral mucositis, temporomandibular joint disorders and burning mouth syndrome. Capsaicin has also demonstrated promise in inhibiting the proliferation of different oral cancer cell lines. Its antimicrobial properties have also been shown to inhibit the growth of oral pathogens associated with dental caries, periodontitis and oral candidiasis. However, to harness its benefits effectively, more studies are required to establish optimal dosages for pain relief while minimizing adverse effects. In addition, investigation of the effect of capsaicin on nonpathogenic oral bacteria and viruses is warranted. Human-based research is crucial for elucidating the biomolecular mechanisms underlying the properties of capsaicin, potentially leading to the development of more effective interventions for oral health problems.

Herpes Zoster and Post-Herpetic Neuralgia-Diagnosis, Treatment, and Vaccination Strategies

INTRODUCTION

Herpes zoster is caused by the reactivation of latent varicella infection within the sensory ganglia, caused by the varicella-zoster virus (VZV). The disease is classically characterized by a painful unilateral vesicular eruption. Complications of the disease include herpes zoster ophthalmicus, Ramsay Hunt syndrome, acute retinal necrosis, and post-herpetic neuralgia. In this paper, we discuss the epidemiology, pathogenesis, clinical features, diagnosis, management, and vaccination strategies of herpes zoster and post-herpetic neuralgia.

METHOD

This paper was developed with input from specialists from Singapore's public sectors-dermatologists, family physicians, and infectious diseases specialists.

RESULTS

The diagnosis of herpes zoster is clinical and can be aided with laboratory investigations. Early initiation of antivirals, within 72 h of onset, can reduce the severity and duration of the condition and decrease the intensity of pain. In patients with a high risk of post-herpetic neuralgia, early initiation of anticonvulsants or tricyclic antidepressants can be considered. Herpes zoster is highly preventable, with the advent of the recombinant zoster vaccine (RZV) providing an overall vaccine efficacy of 97.2%. Procedures such as epidural blocks and subcutaneous or intracutaneous injections of local anesthetics and steroids can be considered for patients with a high risk of post-herpetic neuralgia to reduce its incidence.

CONCLUSION

This article serves as a guideline for clinicians in the diagnosis, investigations, management, and prevention of herpes zoster. With the majority of adults in Singapore currently at risk of developing herpes zoster due to varicella immunization being only introduced in 2020, it is important for clinicians to recognize and manage herpes zoster appropriately.

Efficacy and safety of topical capsaicin in the treatment of osteoarthritis pain: A systematic review and meta-analysis

Osteoarthritis (OA) affects hundreds of millions of people worldwide. The objective was to critically appraise the efficacy and safety of topical capsaicin in reducing pain in OA. MEDLINE (PubMed) and Embase (Ebsco) were searched from inceptions until February 2023. The eligibility criteria included randomized controlled trials (RCTs), evaluating topical capsaicin in OA patients. Standard Cochrane methods were used to extract data and to appraise eligible studies. Eight double-blind RCTs involving 498 patients were included. Five trials (62.5%) were at an overall low risk of bias, and three (37.5%) were at a high risk of bias. Meta-analysis showed that, in various OA patients, compared with placebo, topical capsaicin (0.0125%-5%) may reduce pain severity measured with visual analog scale (standardized mean difference = -0.84, 95% confidence intervals [CIs] = -1.48 to -0.19, p = 0.01; eight studies). However, topical capsaicin may increase burning sensation at the application site (risk ratio = 5.56, 95% CI = 1.75-17.69, p = 0.004, numbers needed to harm = 3; five studies) when compared with placebo. Limitations include short study durations, small sample sizes, high heterogeneity, and overall low-to-very-low certainty of the evidence. Topical capsaicin may reduce OA pain at follow-ups of up to 3 months. Larger trials, potentially evaluating capsaicin in combination with phytopharmaceuticals having anti-inflammatory effects, with longer follow-ups might be needed to reduce the existing uncertainties. Topical capsaicin might be recommended for short-term management of pain in OA patients intolerant to nonsteroidal anti-inflammatory drugs.

Identification of compounds that cause axonal dieback without cytotoxicity in dorsal root ganglia explants and intervertebral disc cells with potential to treat pain via denervation

Low back pain, knee osteoarthritis, and cancer patients suffer from chronic pain. Aberrant nerve growth into intervertebral disc, knee, and tumors, are common pathologies that lead to these chronic pain conditions. Axonal dieback induced by capsaicin (Caps) denervation has been FDA-approved to treat painful neuropathies and knee osteoarthritis but with short-term efficacy and discomfort. Herein, we propose to evaluate pyridoxine (Pyr), vincristine sulfate (Vcr) and ionomycin (Imy) as axonal dieback compounds for denervation with potential to alleviate pain. Previous literature suggests Pyr, Vcr, and Imy can cause undesired axonal degeneration, but no previous work has evaluated axonal dieback and cytotoxicity on adult rat dorsal root ganglia (DRG) explants. Thus, we performed axonal dieback screening using adult rat DRG explants in vitro with Caps as a positive control and assessed cytotoxicity. Imy inhibited axonal outgrowth and slowed axonal dieback, while Pyr and Vcr at high concentrations produced significant reduction in axon length and robust axonal dieback within three days. DRGs treated with Caps, Vcr, or Imy had increased DRG cytotoxicity compared to matched controls, but overall cytotoxicity was minimal and at least 88% lower compared to lysed DRGs. Pyr did not lead to any DRG cytotoxicity. Further, neither Pyr nor Vcr triggered intervertebral disc cell death or affected cellular metabolic activity after three days of incubation in vitro. Overall, our findings suggest Pyr and Vcr are not toxic to DRGs and intervertebral disc cells, and there is potential for repurposing these compounds for axonal dieback compounds to cause local denervation and alleviate pain.

Neuropathic Pain in Aged People: An Unresolved Issue Open to Novel Drug Approaches, Focusing on Painful Diabetic Neuropathy

A majority of older patients suffer from neuropathic pain (NP) that significantly alters their daily activities and imposes a significant burden on health care. Multiple comorbidities and the risk of polypharmacy in the elderly make it challenging to determine the appropriate drug, dosage, and maintenance of therapy. Age-dependent processes play a contributing role in neuropathy given that diabetic neuropathy (DN) is the most common form of neuropathy. This narrative review is mainly focused on the drug treatment approach for neuropathy-associated pain in aged people including both drugs and dietary supplements, considering the latter as add-on mechanism-based treatments to increase the effectiveness of usual treatments by implementing their activity or activating other analgesic pathways. On one hand, the limited clinical studies assessing the effectiveness and the adverse effects of existing pain management options in this age segment of the population (> 65), on the other hand, the expanding global demographics of the elderly contribute to building up an unresolved pain management problem that needs the attention of healthcare providers, researchers, and health authorities as well as the expansion of the current therapeutic options.

Nociceptors protect sickle cell disease mice from vaso-occlusive episodes and chronic organ damage

Sickle cell disease (SCD) is a common hereditary hematologic disorder. SCD patients suffer from acute vaso-occlusive episodes (VOEs), chronic organ damage, and premature death, with few therapeutic options. Although severe pain is a major clinical manifestation of SCD, it remains unknown whether nociception plays a role in SCD pathogenesis. To address this question, we generated nociceptor-deficient SCD mice and found, unexpectedly, that the absence of nociception led to more severe and more lethal VOE, indicating that somatosensory nerves protect SCD mice from VOE. Mechanistically, the beneficial effects of sensory nerves were induced by the neuropeptide calcitonin gene–related peptide (CGRP), which acted on hematopoietic cells. Additionally, oral capsaicin consumption, which can activate somatosensory nerves by binding to TRPV1, dramatically alleviated acute VOE and significantly prevented chronic liver and kidney damage in SCD mice. Thus, the manipulation of nociception may provide a promising approach to treat SCD.

[Perioperative analgesia with nonopioid analgesics : Joint interdisciplinary consensus-based recommendations of the German Pain Society, the German Society of Anaesthesiology and Intensive Care Medicine and the German Society of Surgery]

BACKGROUND

Nonopioid analgesics are frequently used for perioperative analgesia; however, insufficient research is available on several practical issues. Often hospitals have no strategy for how to proceed, e.g., for informing patients or for the timing of perioperative administration of nonopioid analgesics.

METHODS

An expert panel representing the German national societies of pain, anaesthesiology and intensive care medicine and surgery developed recommendations for the perioperative use of nonopioid analgesics within a formal, structured consensus process.

RESULTS

The panel agreed that nonopioid analgesics shall be part of a multimodal analgesia concept and that patients have to be informed preoperatively about possible complications and alternative treatment options. Patients' history of pain and analgesic intake shall be evaluated. Patients at risk of severe postoperative pain and possible chronification of postsurgical pain shall be identified. Depending on the duration of surgery, nonopioid analgesics can already be administered preoperatively or intraoperatively so that plasma concentrations are sufficient after emergence from anesthesia. Nonopioid analgesics or combinations of analgesics shall be administered for a limited time only. An interdisciplinary written standard of care, comprising the nonopioid analgesic of choice, possible alternatives, adequate dosing and timing of administration as well as surgery-specific policies, have to be agreed upon by all departments involved. At discharge, the patient's physician shall be informed of analgesics given and those necessary after discharge. Patients shall be informed of possible side effects and symptoms and timely discontinuation of analgesic drugs.

CONCLUSION

The use of nonopioid analgesics as part of a perioperative multimodal concept should be approved and established as an interdisciplinary and interprofessional concept for the adequate treatment of postoperative pain.

[Perioperative analgesia with nonopioid analgesics : Joint interdisciplinary consensus-based recommendations of the German Pain Society, the German Society of Anaesthesiology and Intensive Care Medicine and the German Society of Surgery]

BACKGROUND

Nonopioid analgesics are frequently used for perioperative analgesia; however, insufficient research is available on several practical issues. Often hospitals have no strategy for how to proceed, e.g., for informing patients or for the timing of perioperative administration of nonopioid analgesics.

METHODS

An expert panel representing the German national societies of pain, anaesthesiology and intensive care medicine and surgery developed recommendations for the perioperative use of nonopioid analgesics within a formal, structured consensus process.

RESULTS

The panel agreed that nonopioid analgesics shall be part of a multimodal analgesia concept and that patients have to be informed preoperatively about possible complications and alternative treatment options. Patients' history of pain and analgesic intake shall be evaluated. Patients at risk of severe postoperative pain and possible chronification of postsurgical pain shall be identified. Depending on the duration of surgery, nonopioid analgesics can already be administered preoperatively or intraoperatively so that plasma concentrations are sufficient after emergence from anesthesia. Nonopioid analgesics or combinations of analgesics shall be administered for a limited time only. An interdisciplinary written standard of care, comprising the nonopioid analgesic of choice, possible alternatives, adequate dosing and timing of administration as well as surgery-specific policies, have to be agreed upon by all departments involved. At discharge, the patient's physician shall be informed of analgesics given and those necessary after discharge. Patients shall be informed of possible side effects and symptoms and timely discontinuation of analgesic drugs.

CONCLUSION

The use of nonopioid analgesics as part of a perioperative multimodal concept should be approved and established as an interdisciplinary and interprofessional concept for the adequate treatment of postoperative pain.

Topical Capsaicin for the Treatment of Neuropathic Pain

BACKGROUND

Neuropathic pain (NP) is an egregious problem worldwide. Due to the side-effects of oral drugs, drugs delivered directly to the affected area of pain are preferred.

OBJECTIVE

Capsaicin, a chemical compound isolated from chili peppers, is used as an analgesic in topical ointments and dermal patches to alleviate pain. Objective of the study is to review the application and functionality of topical capsaicin in treatment of neuropathic pain.

DATA SOURCES

To systematically review capsaicin's functions on NP, we retrieved articles from the PubMed database published in the last ten years.

STUDY ELIGIBILITY CRITERIA

The inclusion criteria were capsaicin and the use of capsaicin for the treatment of NP; on the other hand, articles were excluded according to the mentioned criteria such as abstracts, articles written in any language other than English, incomplete articles, and conference papers.

PARTICIPANTS AND INTERVENTIONS

Out of 265 articles, 108 articles were selected after filtering through the inclusion and exclusion criteria. The data and knowledge currently existing for capsaicin treatment in NP are summarized.

RESULTS

This review indicates that capsaicin effectively improves NP treatment without affecting the motor and large nerve fibres involved in sensory function. Transient receptor potential channel vanilloid type 1 (TRPV1) is the capsaicin receptor expressed in central and peripheral terminals of a sensitive primary nerve cell. Conclusions and implications of key findings: Topical capsaicin has a sensible safety profile and is effective in reducing NP. Therefore, studies over the last decade suggest that capsaicin might be a potential drug for NP treatment.

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.

Regulation of Pain Genes-Capsaicin vs Resiniferatoxin: Reassessment of Transcriptomic Data

Emerging evidence has shown a strong association between neuropathic pain and chronic diseases. In recent years, the treatment of neuropathic pain has attracted more attention. Natural products, such as capsaicin and resiniferatoxin, have been well utilized to treat this disease. In this study, we aim to compare the regulatory effects of capsaicin and resiniferatoxin on pain-related genes as well as on genes with no direct association with pain. Public transcriptomic and microarray data on gene expression in the dorsal root ganglia and genes associated with TRPV1 (+) neurons were obtained from the GEO database and then analyzed. Differentially expressed genes were selected for further functional analysis, including pathway enrichment, protein-protein interaction, and regulatory network analysis. Pain-associated genes were extracted with the reference of two pain gene databases and the effects of these two natural drugs on the pain-associated genes were measured. The results of our research indicate that as compared to capsaicin, resiniferatoxin (RTX) regulates more non pain-associated genes and has a negative impact on beneficial genes (off-targets) which are supposed to alleviate nociception and hypersensitivity by themselves. So, based on this study, we may conclude that capsaicin may be less potent when compared to RTX, but it will elicit considerably less adverse effects too. Thereby confirming that capsaicin could be used for the efficient alleviation of neuropathic pain with possibly fewer side effects.

Herbal Dentifrices: Emerging Trends and Patterns

Background:

Herbal extracts have been employed since ages in dentistry as tooth cleansing and antimicrobial agents. The use of herbal medicines continues to expand and trend rapidly across the world. Herbal extracts have been used in dentistry for multiple uses as reducing inflammation, as antimicrobial plaque agents, for preventing release of histamine and as antiseptics, antioxidants, antimicrobials and analgesics. They also aid in healing process and are very effective in controlling microbial plaque and other disorders related to gums.

Objective:

The present review aims towards the combined review as well as compilation of available herbs under the category of various dental associated problems.

Materials and Methods:

The herbs were studied by sectioning them as for looking after different works or findings done against dental caries, tooth ache, scouring teeth, gum troubles and herbs as mouth fresheners.

Results:

Herbal extracts have been used on a large scale in dentistry as tooth cleansing and antimicrobial plaque agents. Many people take herbal derived medicines or herbal based products for the purpose of reducing inflammation, as antimicrobial agents, for preventing release of histamine and as antiseptics, antioxidants, antifungals, antibacterials, antivirals and analgesics. Herbal extracts are used in dentistry for treatment of various dental disorders.

Conclusion:

The use of herbal medicines are blooming rapidly across the world. Herbal extracts and the various herbs on the whole or their specific parts have been used in dentistry. They relieve the problems of gums and act as excellent mouth fresheners. The natural herbal remedies act as an effective substitute to antibiotics and represent a promising approach for prevention and as therapeutic strategies for various oral infections as they are natural, eradicate the problem from its root and provide long lasting relief. The herbal remedies are advantageous over conventional treatment.

A Randomized, Double-Blind, Placebo- and Active Comparator-Controlled Phase I Study of Analgesic/Antihyperalgesic Properties of ASP8477, a Fatty Acid Amide Hydrolase Inhibitor, in Healthy Female Subjects

Objectives

To evaluate the analgesic/antihyperalgesic effect of ASP8477.

Design

Randomized, double-blind, double-dummy, cross-over, placebo- and active comparator-controlled study.

Setting

HPR Dr. Schaffler GmbH, Munich, Germany.

Subjects

Healthy female subjects aged 18–65 years.

Methods

Eligible subjects were randomly assigned to one of six treatment sequences and received multiple ascending doses of ASP8477, duloxetine, and placebo over three treatment periods (each consisting of 21-day dosing separated by 14-day washout periods). On the last day of each dose level, laser evoked potentials (LEPs) and visual analog scales (VAS pain) on capsaicin-treated skin at baseline and at multiple postdose time points were assessed. The primary end point was the difference in LEP N2-P2 peak-to-peak (PtP) amplitudes for ASP8477 100 mg vs placebo.

Results

Twenty-five subjects were randomized. In all subjects, LEP N2-P2 PtP amplitudes were numerically lower for ASP8477 100 mg vs placebo (P = 0.0721); in subjects who demonstrated positive capsaicin skin effects, a greater mean difference of –2.24 µV (P = 0.0146) was observed. Across all doses, LEP N2-P2 PtP amplitudes were lower for duloxetine compared with ASP8477 (mean difference –3.80 µV; P < 0.0001) or placebo (mean difference –5.21 µV; P < 0.0001). The effect of ASP8477 (all doses) on down-scoring the VAS pain score was significant compared with placebo (mean difference –2.55%; P < 0.0007).

Conclusions

ASP8477 was well tolerated in this study. Analysis of all subjects did not demonstrate a significant difference in LEP for ASP8477 100 mg over placebo but did in subjects who demonstrated positive capsaicin skin effects.

Efficacy of Capsaicin for the Treatment of Cannabinoid Hyperemesis Syndrome: A Systematic Review

Objective: Cannabinoid hyperemesis syndrome (CHS) is characterized by cyclic vomiting, abdominal pain, and alleviation of symptoms via hot showers in chronic cannabinoid users. Capsaicin is recommended as a reasonable first-line treatment approach for CHS despite limited clinical evidence regarding its use. The objective of this study is to systematically review the efficacy data for capsaicin in CHS. Data Sources: A literature search using keywords related to cannabinoids, emesis, and capsaicin was performed in MEDLINE, CINAHL, and EMBASE from inception through March 31, 2019. Study Selection and Data Extraction: Studies and published abstracts in which capsaicin was used for CHS and clinical outcomes were reported were eligible for inclusion. Data Synthesis: A total of 241 articles were screened, of which 5 full-text articles and 6 conference abstracts were included. Full-text case reports (n = 3) and case series (n = 2) found capsaicin to be effective in a total of 18 patients. Published abstracts were in the form of case reports (n = 1), case series (n = 3), and retrospective cohort studies (n = 2). Relevance to Patient Care and Clinical Practice: Capsaicin use was described as beneficial in all case series and case reports; however, both retrospective cohort studies were unable to find a significant benefit for capsaicin on primary outcomes (emergency department length of stay). Conclusion: Current data for capsaicin efficacy in CHS is of low methodological quality. However, the limited data on alternative antiemetic therapies and capsaicin’s favorable risk-benefit profile make it a reasonable adjunctive treatment option.

Herbal medicinal products or preparations for neuropathic pain

BACKGROUND

Neuropathic pain is a consequence of damage to the central nervous system (CNS), for example, cerebrovascular accident, multiple sclerosis or spinal cord injury, or peripheral nervous system (PNS), for example, painful diabetic neuropathy (PDN), postherpetic neuralgia (PHN), or surgery. Evidence suggests that people suffering from neuropathic pain are likely to seek alternative modes of pain relief such as herbal medicinal products due to adverse events brought about by current pharmacological agents used to treat neuropathic pain. This review includes studies in which participants were treated with herbal medicinal products (topically or ingested) who had experienced neuropathic pain for at least three months.

OBJECTIVES

To assess the analgesic efficacy and effectiveness of herbal medicinal products or preparations for neuropathic pain, and the adverse events associated with their use.

SEARCH METHODS

We searched CENTRAL and the Cochrane Database of Systematic Reviews, MEDLINE, Embase, CINAHL and AMED to March 2018. We identified additional studies from the reference lists of the retrieved papers. We also searched trials registries for ongoing trials and we contacted experts in the field for relevant data in terms of published, unpublished or ongoing studies.

SELECTION CRITERIA

We included randomised controlled trials (including cross-over designs) of double-blind design, assessing efficacy of herbal treatments for neuropathic pain compared to placebo, no intervention or any other active comparator. Participants were 18 years and above and had been suffering from one or more neuropathic pain conditions, for three months or more.We applied no restrictions to language or gender. We excluded studies monitoring effects of isolated, single chemicals derived from the plant or synthetic chemicals based on constituents of the plant, if they were not administered at a concentration naturally present within the plant.We excluded studies monitoring the effects of traditional Asian medicine and Cannabinoids as well as studies looking at headache or migraine as these treatments and conditions are addressed in distinct reviews.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. Two review authors independently considered trials for inclusion, assessed risk of bias, and extracted data. We calculated the risk ratio (RR) and number needed to treat for an additional beneficial outcome (NNTB). The primary outcomes were participant-reported pain relief of 30%, or 50%, or greater, and participant-reported global impression of clinical change (PGIC). We also collected information on adverse events. We assessed evidence using GRADE and created a 'Summary of findings' table.

MAIN RESULTS

We included two studies (128 participants). Both diabetic neuropathy and non-diabetic neuropathic pain conditions were investigated across these two studies.Two herbal medicinal products, namely nutmeg (applied topically as a 125 mL spray for four weeks, containing mace oil 2%, nutmeg oil 14%, methyl salicylate 6%, menthol 6%, coconut oil and alcohol) and St John's wort (taken in capsule form containing 900 μg total hypericin each, taken three times daily, giving a total concentration of 2700 mg for five weeks). Both studies allowed the use of concurrent analgesia.Both reported at least one pain-related outcome but we could not carry out meta-analysis of effectiveness due to heterogeneity between the primary outcomes and could not draw any conclusions of effect. Other outcomes included PGIC, adverse events and withdrawals. There were no data for participant-reported pain relief of 50% or greater or PGIC (moderate and substantial) outcomes.When looking at participant-reported pain relief of 30% or greater over baseline, we observed no evidence of a difference (P = 0.64) in response to nutmeg versus placebo (RR 1.12, 95% confidence interval (CI) 0.69 to 1.85; 48.6% vs 43.2%). We downgraded the evidence for this outcome to very low quality.We observed no change between placebo and nutmeg treatment when looking at secondary pain outcomes. Visual analogue scale (VAS) scores for pain reduction (0 to 100, where 0 = no pain reduction), were 44 for both nutmeg and placebo with standard deviations of 21.5 and 26.5 respectively. There was no evidence of a difference (P = 0.09 to 0.33) in total pain score in response to St John's wort compared to placebo, as there was only a reduction of 1 point when looking at median differences in change from baseline on a 0 to 10-point numeric rating scale.There was a total of five withdrawals out of 91 participants (5%) in the treatment groups compared to six of 91 (6.5%) in the placebo groups, whilst adverse events were the same for both the treatment and placebo groups.We judged neither study as having a low risk of bias. We attributed risk of bias to small study size and incomplete outcome data leading to attrition bias. We downgraded the evidence to very low quality for all primary and secondary outcomes reported in this review. We downgraded the quality of the evidence twice due to very serious limitations in study quality (due to small study size and attrition bias) and downgraded a further level due to indirectness as the included studies only measured outcomes at short-term time points. The results from this review should be treated with scepticism as we have very little confidence in the effect estimate.

AUTHORS' CONCLUSIONS

There was insufficient evidence to determine whether nutmeg or St John's wort has any meaningful efficacy in neuropathic pain conditions.The quality of the current evidence raises serious uncertainties about the estimates of effect observed, therefore, we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect.

Next-Gen Therapeutics for Skin Cancer: Nutraceuticals

Growing modernization and lifestyle changes with limited physical activity have impacted diet and health, leading to an increased cancer mortality rate worldwide. As a result, there is a greater need than before to develop safe and novel anticancer drugs. Current treatment options such as chemotherapy, radiotherapy and surgery, induce unintended side effects, compromising patient's quality of life, and physical well-being. Therefore, there has been an increased global interest in the use of dietary supplements and traditional herbal medicines for treatment of cancer. Recently, nutraceuticals or "natural" substances isolated from food have attracted considerable attention in the cancer field. Emerging research suggests that nutraceuticals may indeed prevent and protect against cancer. The intent of this article is to review some of the current spice-derived nutraceuticals in the treatment of melanoma and skin cancer.

Assessing and treating primary headaches and cranio-facial pain in patients undergoing rehabilitation for neurological diseases

BACKGROUND

Pain is a very common condition in patient undergoing rehabilitation for neurological disease; however the presence of primary headaches and other cranio-facial pains, particularly when they are actually or apparently independent from the disability for which patient is undergoing rehabilitation, is often neglected. Diagnostic and therapeutic international and national guidelines, as well as tools for the subjective measure of head pain are available and should also be applied in the neurorehabilitation setting. This calls for searching the presence of head pain, independently from the rehabilitation needs, since pain, either episodic or chronic, interferes with patient performance by affecting physical and emotional status. Pain may also interfere with sleep and therefore hamper recovery.

METHODS

In our role of task force of the Italian Consensus Conference on Pain in Neurorehabilitation (ICCPN), we have elaborated specific recommendations for diagnosing and treating head pains in patients undergoing rehabilitation for neurological diseases.

RESULTS AND CONCLUSION

In this narrative review, we describe the available literature that has been evaluated in order to define the recommendations and outline the needs of epidemiological studies concerning headache and other cranio-facial pain in neurorehabilitation.

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.

Systematic review of management of chronic pain after surgery

BACKGROUND

Pain present for at least 3 months after a surgical procedure is considered chronic postsurgical pain (CPSP) and affects 10-50 per cent of patients. Interventions for CPSP may focus on the underlying condition that indicated surgery, the aetiology of new-onset pain or be multifactorial in recognition of the diverse causes of this pain. The aim of this systematic review was to identify RCTs of interventions for the management of CPSP, and synthesize data across treatment type to estimate their effectiveness and safety.

METHODS

MEDLINE, Embase, PsycINFO, CINAHL and the Cochrane Library were searched from inception to March 2016. Trials of pain interventions received by patients at 3 months or more after surgery were included. Risk of bias was assessed using the Cochrane risk-of-bias tool.

RESULTS

Some 66 trials with data from 3149 participants were included. Most trials included patients with chronic pain after spinal surgery (25 trials) or phantom limb pain (21 trials). Interventions were predominantly pharmacological, including antiepileptics, capsaicin, epidural steroid injections, local anaesthetic, neurotoxins, N-methyl-d-aspartate receptor antagonists and opioids. Other interventions included acupuncture, exercise, postamputation limb liner, spinal cord stimulation, further surgery, laser therapy, magnetic stimulation, mindfulness-based stress reduction, mirror therapy and sensory discrimination training. Opportunities for meta-analysis were limited by heterogeneity. For all interventions, there was insufficient evidence to draw conclusions on effectiveness.

CONCLUSION

There is a need for more evidence about interventions for CPSP. High-quality trials of multimodal interventions matched to pain characteristics are needed to provide robust evidence to guide management of CPSP.

Topical phenytoin for the treatment of neuropathic pain

We developed and tested a new putative analgesic cream, based on the anticonvulsant phenytoin in patients suffering from treatment refractory neuropathic pain. The use of commercial topical analgesics is not widespread due to the facts that capsaicin creams or patches can give rise to side effects, such as burning, and analgesic patches (e.g., lidocaine 5% patches) have complex handling, especially for geriatric patients. Only in a few countries, compounded creams based on tricyclic antidepressants or other (co-)analgesics are available. Such topical analgesic creams, however, are easy to administer and have a low propensity for inducing side effects. We, therefore, developed a new topical cream based on 5% and 10% phenytoin and described three successfully treated patients suffering from neuropathic pain. All patients were refractory to a number of other analgesics. In all patients, phenytoin cream was effective in reducing pain completely, without any side effects, and the tolerability was excellent. The onset of action of the phenytoin creams was within 30 minutes. Phenytoin cream might become a new treatment modality of the treatment of neuropathic pain.

Quantitative Thermal Testing Profiles as a Predictor of Treatment Response to Topical Capsaicin in Patients with Localized Neuropathic Pain

There are no reliable predictors of response to treatment with capsaicin. Given that capsaicin application causes heat sensation, differences in quantitative thermal testing (QTT) profiles may predict treatment response. The aim of this study was to determine whether different QTT profiles could predict treatment outcomes in patients with localized peripheral neuropathic pain (PeLNP). We obtained from medical records QTT results and treatment outcomes of 55 patients treated between 2010 and 2013. Warm sensation threshold (WST) and heat pain threshold (HPT) values were assessed at baseline at the treatment site and in the asymptomatic, contralateral area. Responders were defined as those who achieved a > 30% decrease in pain lasting > 30 days. Two distinct groups were identified based on differences in QTT profiles. Most patients (27/31; 87.1%) with a homogenous profile were nonresponders. By contrast, more than half of the patients (13/24, 54.2%) with a nonhomogenous profile were responders (p = 0.0028). A nonhomogenous QTT profile appears to be predictive of response to capsaicin. We hypothesize patients with a partial loss of cutaneous nerve fibers or receptors are more likely to respond. By contrast, when severe nerve damage or normal cutaneous sensations are present, the pain is likely due to central sensitization and thus not responsive to capsaicin. Prospective studies with larger patient samples are needed to confirm this hypothesis.

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.

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

BACKGROUND

This review is an update of 'Topical capsaicin (high concentration) for chronic neuropathic pain in adults' last updated in Issue 2, 2013. Topical creams with capsaicin are used to treat peripheral neuropathic pain. Following application to the skin, capsaicin causes enhanced sensitivity, followed by a period with reduced sensitivity and, after repeated applications, persistent desensitisation. High-concentration (8%) capsaicin patches were developed to increase the amount of capsaicin delivered; rapid delivery was thought to improve tolerability because cutaneous nociceptors are 'defunctionalised' quickly. The single application avoids noncompliance. Only the 8% patch formulation of capsaicin is available, with a capsaicin concentration about 100 times greater than conventional creams. High-concentration topical capsaicin is given as a single patch application to the affected part. It must be applied under highly controlled conditions, often following local anaesthetic, due to the initial intense burning sensation it causes. The benefits are expected to last for about 12 weeks, when another application might be made.

OBJECTIVES

To review the evidence from controlled trials on the efficacy and tolerability of topically applied, high-concentration (8%) capsaicin in chronic neuropathic pain in adults.

SEARCH METHODS

For this update, we searched CENTRAL, MEDLINE, Embase, two clinical trials registries, and a pharmaceutical company's website to 10 June 2016.

SELECTION CRITERIA

Randomised, double-blind, placebo-controlled studies of at least 6 weeks' duration, using high-concentration (5% or more) topical capsaicin to treat neuropathic pain.

DATA COLLECTION AND ANALYSIS

Two review authors independently searched for studies, extracted efficacy and adverse event data, and examined issues of study quality and potential bias. Where pooled analysis was possible, we used dichotomous data to calculate risk ratio and numbers needed to treat for one additional event, using standard methods.Efficacy outcomes reflecting long-duration pain relief after a single drug application were from the Patient Global Impression of Change (PGIC) at specific points, usually 8 and 12 weeks. We also assessed average pain scores over weeks 2 to 8 and 2 to 12 and the number of participants with pain intensity reduction of at least 30% or at least 50% over baseline, and information on adverse events and withdrawals.We assessed the quality of the evidence using GRADE and created a 'Summary of findings' table.

MAIN RESULTS

We included eight studies, involving 2488 participants, two more studies and 415 more participants than the previous version of this review. Studies were of generally good methodological quality; we judged only one study at high risk of bias, due to small size. Two studies used a placebo control and six used 0.04% topical capsaicin as an 'active' placebo to help maintain blinding. Efficacy outcomes were inconsistently reported, resulting in analyses for most outcomes being based on less than complete data.For postherpetic neuralgia, we found four studies (1272 participants). At both 8 and 12 weeks about 10% more participants reported themselves much or very much improved with high-concentration capsaicin than with 'active' placebo, with point estimates of numbers needed to treat for an additional beneficial outcome (NNTs) of 8.8 (95% confidence interval (CI) 5.3 to 26) with high-concentration capsaicin and 7.0 (95% CI 4.6 to 15) with 'active' placebo (2 studies, 571 participants; moderate quality evidence). More participants (about 10%) had average 2 to 8-week and 2 to 12-week pain intensity reductions over baseline of at least 30% and at least 50% with capsaicin than control, with NNT values between 10 and 12 (2 to 4 studies, 571 to 1272 participants; very low quality evidence).For painful HIV-neuropathy, we found two studies (801 participants). One study reported the proportion of participants who were much or very much improved at 12 weeks (27% with high-concentration capsaicin and 10% with 'active' placebo). For both studies, more participants (about 10%) had average 2 to 12-week pain intensity reductions over baseline of at least 30% with capsaicin than control, with an NNT of 11 (very low quality evidence).For peripheral diabetic neuropathy, we found one study (369 participants). It reported about 10% more participants who were much or very much improved at 8 and 12 weeks. One small study of 46 participants with persistent pain following inguinal herniorrhaphy did not show a difference between capsaicin and placebo for pain reduction (very low quality evidence).We downgraded the quality of the evidence for efficacy outcomes by one to three levels due to sparse data, imprecision, possible effects of imputation methods, and susceptibility to publication bias.Local adverse events were common, but not consistently reported. Serious adverse events were no more common with active treatment (3.5%) than control (3.2%). Adverse event withdrawals did not differ between groups, but lack of efficacy withdrawals were somewhat more common with control than active treatment, based on small numbers of events (six to eight studies, 21 to 67 events; moderate quality evidence, downgraded due to few events). No deaths were judged to be related to study medication.

AUTHORS' CONCLUSIONS

High-concentration topical capsaicin used to treat postherpetic neuralgia, HIV-neuropathy, and painful diabetic neuropathy generated more participants with moderate or substantial levels of pain relief than control treatment using a much lower concentration of capsaicin. These results should be interpreted with caution as the quality of the evidence was moderate or very low. The additional proportion who benefited over control was not large, but for those who did obtain high levels of pain relief, there were usually additional improvements in sleep, fatigue, depression, and quality of life. High-concentration topical capsaicin is similar in its effects to other therapies for chronic pain.

Capsaicin: Current Understanding of Its Mechanisms and Therapy of Pain and Other Pre-Clinical and Clinical Uses

In this review, we discuss the importance of capsaicin to the current understanding of neuronal modulation of pain and explore the mechanisms of capsaicin-induced pain. We will focus on the analgesic effects of capsaicin and its clinical applicability in treating pain. Furthermore, we will draw attention to the rationale for other clinical therapeutic uses and implications of capsaicin in diseases such as obesity, diabetes, cardiovascular conditions, cancer, airway diseases, itch, gastric, and urological disorders.

Capsaicin and Its Role in Chronic Diseases

A significant number of experimental and clinical studies published in peer-reviewed journals have demonstrated promising pharmacological properties of capsaicin in relieving signs and symptoms of non-communicable diseases (chronic diseases). This chapter provides an overview made from basic and clinical research studies of the potential therapeutic effects of capsaicin, loaded in different application forms, such as solution and cream, on chronic diseases (e.g. arthritis, chronic pain, functional gastrointestinal disorders and cancer). In addition to the anti-inflammatory and analgesic properties of capsaicin largely recognized via, mainly, interaction with the TRPV1, the effects of capsaicin on different cell signalling pathways will be further discussed here. The analgesic, anti-inflammatory or apoptotic effects of capsaicin show promising results in arthritis, neuropathic pain, gastrointestinal disorders or cancer, since evidence demonstrates that the oral or local application of capsaicin reduce inflammation and pain in rheumatoid arthritis, promotes gastric protection against ulcer and induces apoptosis of the tumour cells. Sadly, these results have been paralleled by conflicting studies, which indicate that high concentrations of capsaicin are likely to evoke deleterious effects, thus suggesting that capsaicin activates different pathways at different concentrations in both human and rodent tissues. Thus, to establish effective capsaicin doses for chronic conditions, which can be benefited from capsaicin therapeutic effects, is a real challenge that must be pursued.

Treatment of painful diabetic neuropathy

Painful diabetic neuropathy (PDN) is a debilitating consequence of diabetes that may be present in as many as one in five patients with diabetes. The objective assessment of PDN is difficult, making it challenging to diagnose and assess in both clinical practice and clinical trials. No single treatment exists to prevent or reverse neuropathic changes or to provide total pain relief. Treatment of PDN is based on three major approaches: intensive glycaemic control and risk factor management, treatments based on pathogenetic mechanisms, and symptomatic pain management. Clinical guidelines recommend pain relief in PDN through the use of antidepressants such as amitriptyline and duloxetine, the γ-aminobutyric acid analogues gabapentin and pregabalin, opioids and topical agents such as capsaicin. Of these medications, duloxetine and pregabalin were approved by the US Food and Drug Administration (FDA) in 2004 and tapentadol extended release was approved in 2012 for the treatment of PDN. Proposed pathogenetic treatments include α-lipoic acid (stems reactive oxygen species formation), benfotiamine (prevents vascular damage in diabetes) and aldose-reductase inhibitors (reduces flux through the polyol pathway). There is a growing need for studies to evaluate the most potent drugs or combinations for the management of PDN to maximize pain relief and improve quality of life. A number of agents are potential candidates for future use in PDN therapy, including Nav 1.7 antagonists, N-type calcium channel blockers, NGF antibodies and angiotensin II type 2 receptor antagonists.

Screening and treatment by the primary care provider of common diabetes complications

Diabetes is the leading cause of end-stage renal disease, blindness, and nontraumatic lower-limb amputation. The largest reductions in cardiovascular events are seen when multiple risk factors are addressed simultaneously. The benefit of aspirin as secondary prevention in patients with previous stroke or myocardial infarction has been well established. Regular, dilated eye examinations are effective in detecting sight-threatening diabetic retinopathy and have been shown to prevent blindness. The use of appropriate tools and clinical examination/inspection provides greater than 87% specificity in detecting diabetic peripheral neuropathy. Early treatment of risk factors, including hypertension, hyperglycemia, and dyslipidemia can delay or prevent diabetic nephropathy.

Capsaicin and dihydrocapsaicin determination in chili pepper genotypes using ultra-fast liquid chromatography

Research was carried out to estimate the levels of capsaicin and dihydrocapsaicin that may be found in some heat tolerant chili pepper genotypes and to determine the degree of pungency as well as percentage capsaicin content of each of the analyzed peppers. A sensitive, precise, and specific ultra fast liquid chromatographic (UFLC) system was used for the separation, identification and quantitation of the capsaicinoids and the extraction solvent was acetonitrile. The method validation parameters, including linearity, precision, accuracy and recovery, yielded good results. Thus, the limit of detection was 0.045 µg/kg and 0.151 µg/kg for capsaicin and dihydrocapsaicin, respectively, whereas the limit of quantitation was 0.11 µg/kg and 0.368 µg/kg for capsaicin and dihydrocapsaicin. The calibration graph was linear from 0.05 to 0.50 µg/g for UFLC analysis. The inter- and intra-day precisions (relative standard deviation) were <5.0% for capsaicin and <9.9% for dihydrocapsaicin while the average recoveries obtained were quantitative (89.4%–90.1% for capsaicin, 92.4%–95.2% for dihydrocapsaicin), indicating good accuracy of the UFLC method. AVPP0705, AVPP0506, AVPP0104, AVPP0002, C05573 and AVPP0805 showed the highest concentration of capsaicin (12,776, 5,828, 4,393, 4,760, 3,764 and 4,120 µg/kg) and the highest pungency level, whereas AVPP9703, AVPP0512, AVPP0307, AVPP0803 and AVPP0102 recorded no detection of capsaicin and hence were non-pungent. All chili peppers studied except AVPP9703, AVPP0512, AVPP0307, AVPP0803 and AVPP0102 could serve as potential sources of capsaicin. On the other hand, only genotypes AVPP0506, AVPP0104, AVPP0002, C05573 and AVPP0805 gave a % capsaicin content that falls within the pungency limit that could make them recommendable as potential sources of capsaicin for the pharmaceutical industry.

Recent advances in cancer pain management

Pain is the most feared symptom of cancer. New oncological cancer treatments are improving survival, but advanced cancer presents challenges that have not been seen before, often with pain that is very difficult to manage because of a recurrent tumour that is invading the central nervous system. In some of the older interventional techniques of destroying nerve pathways, expertise has diminished or has been deemed unnecessary with the development of specialist palliative care. Not all pain is managed adequately with the analgesic ladder. Knowledge of pain mechanisms, careful assessment and selection of the right technique at the right time will enhance cancer pain management. New techniques include intrathecal drug therapy, vertebroplasty, cordotomy, ultra-sound guided nerve blocks, neuromodulation and advances in drug therapies.

Capsaicin-based therapies for pain control

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

TRPs: modulation by drug-like compounds

Drug-like compounds that exert biological activity towards TRP channels are either being used as cell biological tools or further developed into pharmacological lead structures aiming at therapeutic use in diseased states. Although drug-likeliness is not easy to predict, common rules include a relatively low molecular weight, physicochemical constraints, and the absence of known reactive or otherwise toxic groups. Small molecules that exert a biological activity to block, activate, or modulate TRP channels are intensely sought. Such tool compounds may be useful to assign native currents to a certain TRP channel and to validate the channel as a candidate target for future pharmacological intervention. Depending on the TRP channel isotype, these activities have reached different levels, with only few TRP channels modulators already being clinically tested in humans, whereas other compounds only underwent a preliminary validation. For some TRP channels, reliable low molecular weight inhibitors are not yet available. Hence, further efforts need to be undertaken in order to explore the physiological impact and possible therapeutic potential of TRP channel targeting with drug-like compounds.

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.

Health economic evidence of 5% lidocaine medicated plaster in post-herpetic neuralgia

BACKGROUND

Post-herpetic neuralgia (PHN) is the most common and most debilitating complication of herpes zoster, and involves considerable associated costs.

OBJECTIVE

This paper presents results from nine health economic studies undertaken in eight European countries that compared lidocaine medicated plaster with gabapentin and/or pregabalin in PHN. It aims to support the increasing need for published cost-effectiveness data for health care decision-making processes in Europe.

METHODS

All studies were based on a similar core Markov model with data derived from clinical trials, local Delphi panels, and official national price and tariff lists. The main outcome measure was cost per quality-adjusted life year gained; time without pain or intolerable adverse events was also included as a secondary outcome measure. All studies focused on an elderly population of patients with PHN who had insufficient pain relief with standard analgesics and could not tolerate or had contraindications to tricyclic antidepressants.

RESULTS

Despite considerable differences in many of the variables used, the results showed remarkable similarity and suggested that use of lidocaine medicated plaster offered cost-savings in many of the countries studied, where it proved a highly cost-effective alternative to both gabapentin and pregabalin.

CONCLUSION

Lidocaine medicated plaster is a cost-effective alternative to gabapentin and pregabalin in the treatment of PHN. These savings are largely the result of the superior safety profile of the lidocaine medicated plaster.

Options for treating postherpetic neuralgia in the medically complicated patient

Patients with postherpetic neuralgia (PHN) are often of advanced age or immunocompromised and likely to have ≥1 comorbid medical condition for which they receive ≥1 medication (polypharmacy). Comorbidities affecting renal or hepatic function can alter pharmacokinetics, thereby impacting the efficacy or tolerability of PHN analgesic therapies. Cardiovascular, cerebrovascular, or psychiatric comorbidities may increase patient vulnerability to potential adverse events associated with some PHN analgesic therapies. Because PHN is a localized condition, localized therapy with a topical analgesic (lidocaine patch 5% and capsaicin 8% patch or cream) may provide adequate efficacy while mitigating the risk of systemic adverse events compared with oral analgesics (eg, tricyclic antidepressants, anticonvulsants, opioids). However, combined therapy with a topical and an oral analgesic or with >1 oral analgesic may be needed for optimal pain management in some patients. This review summarizes how comorbidities and concomitant medications should be taken into account when selecting among available pharmacotherapies for PHN and provides recommendations for the selection of therapies that will provide analgesia while minimizing the risk of adverse events.

Management of chronic pain following nerve injuries/CRPS type II

Chronic pain affects quality of life and adversely affects functional outcomes. Chronic postoperative pain is a frustrating problem for the surgeon because it ruins a technically perfect procedure, and the surgeon may be unsure of treatment strategies. There is much information on chronic pain and its treatment, but it is often published outside of surgery and diffusion of this information across disciplines is slow. This article synthesizes some of this literature and provides a systematic presentation of the evidence on pain associated with peripheral nerve injury. It highlights the use of perioperative and early intervention to decrease this debilitating problem.

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.

Clinical pharmacology of analgesics assessed with human experimental pain models: bridging basic and clinical research

The medical impact of pain is such that much effort is being applied to develop novel analgesic drugs directed towards new targets and to investigate the analgesic efficacy of known drugs. Ongoing research requires cost-saving tools to translate basic science knowledge into clinically effective analgesic compounds. In this review we have re-examined the prediction of clinical analgesia by human experimental pain models as a basis for model selection in phase I studies. The overall prediction of analgesic efficacy or failure of a drug correlated well between experimental and clinical settings. However, correct model selection requires more detailed information about which model predicts a particular clinical pain condition. We hypothesized that if an analgesic drug was effective in an experimental pain model and also a specific clinical pain condition, then that model might be predictive for that particular condition and should be selected for development as an analgesic for that condition. The validity of the prediction increases with an increase in the numbers of analgesic drug classes for which this agreement was shown. From available evidence, only five clinical pain conditions were correctly predicted by seven different pain models for at least three different drugs. Most of these models combine a sensitization method. The analysis also identified several models with low impact with respect to their clinical translation. Thus, the presently identified agreements and non-agreements between analgesic effects on experimental and on clinical pain may serve as a solid basis to identify complex sets of human pain models that bridge basic science with clinical pain research.

Skin matters: identifying pain mechanisms and predicting treatment outcomes

The skin acts as a complex sensory organ. The emerging new data on peripheral pain mechanisms from within the skin is presented. This data has led to new insights into the potential pain mechanisms for various pain conditions including neuropathic pain (from small fiber neuropathies) and Complex Regional Pain Syndrome. The somatosensory neurons that innervate our skin constantly update our brains on the objects and environmental factors that surround us. Cutaneous sensory neurons expressing nociceptive receptors such as transient receptor potential vanilloid 1 channels and voltage-gated sodium channels are critical for pain transmission. Epidermal cells (such as keratinocytes, Langerhans cells, and Merkel cells) express sensor proteins and neuropeptides; these regulate the neuroimmunocutaneous system and participate in nociception and neurogenic inflammation. In the past two decades, there has been widespread use of modalities such as punch skin biopsies, quantitative sensory testing, and laser-evoked potentials to evaluate small caliber nerve fibers. This paper explores these laboratory techniques as well as the phenomenon of small fiber neuropathy. Treatment using transdermal drug delivery is discussed. There is potential for these findings to predict treatment outcomes in clinical practice and to develop new therapies for different pain conditions. These findings should enhance the physician's ability to evaluate and treat diverse types of pain.

Interventions for treating pain and disability in adults with complex regional pain syndrome

BACKGROUND

There is currently no strong consensus regarding the optimal management of complex regional pain syndrome although a multitude of interventions have been described and are commonly used.

OBJECTIVES

To summarise the evidence from Cochrane and non-Cochrane systematic reviews of the effectiveness of any therapeutic intervention used to reduce pain, disability or both in adults with complex regional pain syndrome (CRPS).

METHODS

We identified Cochrane reviews and non-Cochrane reviews through a systematic search of the following databases: Cochrane Database of Systematic Reviews, Database of Abstracts of Reviews of Effects (DARE), Ovid MEDLINE, Ovid EMBASE, CINAHL, LILACS and PEDro. We included non-Cochrane systematic reviews where they contained evidence not covered by identified Cochrane reviews. The methodological quality of reviews was assessed using the AMSTAR tool.We extracted data for the primary outcomes pain, disability and adverse events, and the secondary outcomes of quality of life, emotional well being and participants' ratings of satisfaction or improvement. Only evidence arising from randomised controlled trials was considered. We used the GRADE system to assess the quality of evidence.

MAIN RESULTS

We included six Cochrane reviews and 13 non-Cochrane systematic reviews. Cochrane reviews demonstrated better methodological quality than non-Cochrane reviews. Trials were typically small and the quality variable.There is moderate quality evidence that intravenous regional blockade with guanethidine is not effective in CRPS and that the procedure appears to be associated with the risk of significant adverse events.There is low quality evidence that bisphosphonates, calcitonin or a daily course of intravenous ketamine may be effective for pain when compared with placebo; graded motor imagery may be effective for pain and function when compared with usual care; and that mirror therapy may be effective for pain in post-stroke CRPS compared with a 'covered mirror' control. This evidence should be interpreted with caution. There is low quality evidence that local anaesthetic sympathetic blockade is not effective. Low quality evidence suggests that physiotherapy or occupational therapy are associated with small positive effects that are unlikely to be clinically important at one year follow up when compared with a social work passive attention control.For a wide range of other interventions, there is either no evidence or very low quality evidence available from which no conclusions should be drawn.

AUTHORS' CONCLUSIONS

There is a critical lack of high quality evidence for the effectiveness of most therapies for CRPS. Until further larger trials are undertaken, formulating an evidence-based approach to managing CRPS will remain difficult.

Interventions for treating pain and disability in adults with complex regional pain syndrome

BACKGROUND

There is currently no strong consensus regarding the optimal management of complex regional pain syndrome although a multitude of interventions have been described and are commonly used.

OBJECTIVES

To summarise the evidence from Cochrane and non-Cochrane systematic reviews of the effectiveness of any therapeutic intervention used to reduce pain, disability or both in adults with complex regional pain syndrome (CRPS).

METHODS

We identified Cochrane reviews and non-Cochrane reviews through a systematic search of the following databases: Cochrane Database of Systematic Reviews, Database of Abstracts of Reviews of Effects (DARE), Ovid MEDLINE, Ovid EMBASE, CINAHL, LILACS and PEDro. We included non-Cochrane systematic reviews where they contained evidence not covered by identified Cochrane reviews. The methodological quality of reviews was assessed using the AMSTAR tool.We extracted data for the primary outcomes pain, disability and adverse events, and the secondary outcomes of quality of life, emotional well being and participants' ratings of satisfaction or improvement. Only evidence arising from randomised controlled trials was considered. We used the GRADE system to assess the quality of evidence.

MAIN RESULTS

We included six Cochrane reviews and 13 non-Cochrane systematic reviews. Cochrane reviews demonstrated better methodological quality than non-Cochrane reviews. Trials were typically small and the quality variable.There is moderate quality evidence that intravenous regional blockade with guanethidine is not effective in CRPS and that the procedure appears to be associated with the risk of significant adverse events.There is low quality evidence that bisphosphonates, calcitonin or a daily course of intravenous ketamine may be effective for pain when compared with placebo; graded motor imagery may be effective for pain and function when compared with usual care; and that mirror therapy may be effective for pain in post-stroke CRPS compared with a 'covered mirror' control. This evidence should be interpreted with caution. There is low quality evidence that local anaesthetic sympathetic blockade is not effective. Low quality evidence suggests that physiotherapy or occupational therapy are associated with small positive effects that are unlikely to be clinically important at one year follow up when compared with a social work passive attention control.For a wide range of other interventions, there is either no evidence or very low quality evidence available from which no conclusions should be drawn.

AUTHORS' CONCLUSIONS

There is a critical lack of high quality evidence for the effectiveness of most therapies for CRPS. Until further larger trials are undertaken, formulating an evidence-based approach to managing CRPS will remain difficult.

Management of herpes zoster and post-herpetic neuralgia

Herpes zoster and its sequela post-herpetic neuralgia (PHN) are conditions with significant morbidity. PHN is a chronic, debilitating neuropathic pain that can persist long beyond resolution of visible cutaneous manifestations. This paper provides practical guidelines for management of herpes zoster and PHN. For herpes zoster, antivirals should be started, preferably within 72 h of onset, to reduce the severity and duration of the eruptive phase and to reduce the intensity of acute pain. PHN can be treated with either topical or systemic agents. Topical lidocaine and capsaicin are effective. For patients with more severe pain, the following systemic agents can be considered (in decreasing order of recommendation): the anticonvulsants gabapentin and pregabalin, the tricyclic antidepressants amitriptyline, nortriptyline, and desipramine, and, lastly, the opioid analgesics tramadol, morphine, oxycodone, and methadone. For patients at high risk of developing PHN, early initiation of gabapentin or amitriptyline after the onset of herpes zoster is suggested. The new zoster vaccine has been shown to be effective in reducing the incidence of herpes zoster and PHN.

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

BACKGROUND

Topical creams with capsaicin are used to treat peripheral neuropathic pain. Following application to the skin capsaicin causes enhanced sensitivity, followed by a period with reduced sensitivity and, after repeated applications, persistent desensitisation. High-concentration (8%) capsaicin patches were developed to increase the amount of capsaicin delivered; rapid delivery was thought to improve tolerability because cutaneous nociceptors are 'defunctionalised' quickly. The single application avoids noncompliance. Only the 8% patch formulation of capsaicin is available, with a capsaicin concentration about 100 times greater than conventional creams.High-concentration topical capsaicin is given as a single patch application to the affected part. It must be applied under highly controlled conditions, normally under local anaesthetic, due to the initial intense burning sensation it causes. The benefits are expected to last for about 12 weeks, when another application might be made.

OBJECTIVES

To review the evidence from controlled trials on the efficacy and tolerability of topically applied, high-concentration (8%) capsaicin in chronic neuropathic pain in adults.

SEARCH METHODS

We searched CENTRAL, MEDLINE, EMBASE and clinicaltrials.gov to December 2012.

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 on numbers of participants with pain relief (clinical improvement) after at least six weeks, and with local skin reactions. We calculated risk ratio and numbers needed to treat to benefit (NNT) and harm (NNH). We sought details of definition of pain relief and specific adverse events.Efficacy outcomes reflecting long-duration pain relief after a single drug application were from the patient global impression of change (PGIC) at specific points, usually eight and 12 weeks. We regarded these outcomes as first-tier evidence. We regarded average pain scores over weeks 2 to 8 and 2 to 12 and the number and/or percentage of participants with pain intensity reduction of at least 30% or at least 50% over baseline as second-tier evidence.

MAIN RESULTS

We included six studies, involving 2073 participants; they were of generally good reporting quality; the control was 0.04% topical capsaicin to help maintain blinding. Efficacy outcomes were inconsistently reported between studies, however, resulting in analyses for most outcomes being based on less than complete data.Four studies involved 1272 participants with postherpetic neuralgia. All efficacy outcomes were significantly better than control. At both eight and 12 weeks there was a significant benefit for high-concentration over low-concentration topical capsaicin for participants reporting themselves to be much or very much better, with point estimates of the NNTs of 8.8 (95% confidence interval (CI) 5.3 to 26) and 7.0 (95% CI 4.6 to 15) respectively. More participants had average 2 to 8-week and 2 to 12-week pain intensity reductions over baseline of at least 30% and at least 50% with active treatment than control, with NNT values between 10 and 12.Two studies involved 801 participants with painful HIV-neuropathy. In a single study the NNT at 12 weeks for participants to be much or very much better was 5.8 (95% CI 3.8 to 12). Over both studies more participants had average 2 to 12-week pain intensity reductions over baseline of at least 30% with active treatment than control, with an NNT of 11.Local adverse events were common, but not consistently reported. Serious adverse events were no more common with active treatment (4.1%) than control (3.2%). Adverse event withdrawals did not differ between groups, but lack of efficacy withdrawals were somewhat more common with control than active treatment, based on small numbers of events. No deaths were judged to be related to study medication.

AUTHORS' CONCLUSIONS

High-concentration topical capsaicin used to treat postherpetic neuralgia and HIV-neuropathy generates more participants with high levels of pain relief than does control treatment using a much lower concentration of capsaicin. The additional proportion who benefit over control is not large, but for those who do obtain high levels of pain relief there are additional improvements in sleep, fatigue, depression and an improved quality of life. High-concentration topical capsaicin is therefore similar to other therapies for chronic pain. In this case, the high cost of single and repeated applications suggest that high-concentration topical capsaicin is likely to be used when other available therapies have failed, and that it should probably not be used repeatedly without substantial documented pain relief. Even when efficacy is established, there are unknown risks, especially on epidermal innervation, of repeated application of long periods.

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

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

Guidelines in the management of diabetic nerve pain: clinical utility of pregabalin

Diabetic peripheral neuropathy is a common complication of diabetes. It presents as a variety of syndromes for which there is no universally accepted unique classification. Sensorimotor polyneuropathy is the most common type, affecting about 30% of diabetic patients in hospital care and 25% of those in the community. Pain is the reason for 40% of patient visits in a primary care setting, and about 20% of these have had pain for greater than 6 months. Chronic pain may be nociceptive, which occurs as a result of disease or damage to tissue with no abnormality in the nervous system. In contrast, neuropathic pain is defined as "pain arising as a direct consequence of a lesion or disease affecting the somatosensory system." Persistent neuropathic pain interferes significantly with quality of life, impairing sleep and recreation; it also significantly impacts emotional well-being, and is associated with depression, anxiety, and noncompliance with treatment. Painful diabetic peripheral neuropathy is a difficult-to-manage clinical problem, and patients with this condition are more apt to seek medical attention than those with other types of diabetic neuropathy. Early recognition of psychological problems is critical to the management of pain, and physicians need to go beyond the management of pain per se if they are to achieve success. This evidence-based review of the assessment of the patient with pain in diabetes addresses the state-of-the-art management of pain, recognizing all the conditions that produce pain in diabetes and the evidence in support of a variety of treatments currently available. A search of the full Medline database for the last 10 years was conducted in August 2012 using the terms painful diabetic peripheral neuropathy, painful diabetic peripheral polyneuropathy, painful diabetic neuropathy and pain in diabetes. In addition, recent reviews addressing this issue were adopted as necessary. In particular, reports from the American Academy of Neurology and the Toronto Consensus Panel on Diabetic Neuropathy were included. Unfortunately, the results of evidence-based studies do not necessarily take into account the presence of comorbidities, the cost of treatment, or the role of third-party payers in decision-making. Thus, this review attempts to give a more balanced view of the management of pain in the diabetic patient with neuropathy and in particular the role of pregabalin.