Topical lidocaine gel relieves postherpetic neuralgia

Rapid dissolution microneedle based on polyvinyl alcohol/chitosan for local oral anesthesia

At present, the main clinical methods of oral local anesthesia are direct injection of anesthetic and surface ointment. However, the pain and fear caused by the injection, the discomfort of topical anesthetic creams, and the scour and moist oral environment during the procedure pose great challenges to oral anesthesia. Herein, we designed a Lido-PVP/PVA DMNP microneedle (MN) for oral local anesthesia. The microneedle tip was consisted of Polyvinylpyrrolidone/Polyvinyl alcohol (PVP/PVA), which can quickly dissolve and release the lidocaine hydrochloride (Lido) drug within 5 min to achieve rapid anesthesia. The backing was composed of polyvinyl alcohol/chitosan (PVA/CS), and its excellent adhesion can overcome saliva erosion and anchor firmly to the oral mucosa, significantly improving the utilization rate of drugs, as well as the patient compliance. MNs have good mechanical properties for tissue insertion while possessing high drug loading (3 mg/MNs). Von Frey tests proved that MNs showed a faster and more effective local anesthetic effect (anesthesia takes effect at 5 min) compared to cream (anesthesia takes effect at 30 min). In addition, the excellent biocompatibility and no skin irritation endowed Lido-PVP/PVA DMNP MNs a great potential for oral local anesthesia in the oral cavity.

Placebo analgesia and nocebo hyperalgesia in patients with Alzheimer disease and healthy participants

ABSTRACT

The role of placebo analgesia and nocebo hyperalgesia in patients with Alzheimer disease (AD) is largely unknown, with only few studies in the area. Therefore, this study aims to investigate to which extent placebo analgesia and nocebo hyperalgesia effects are present in patients experiencing mild-to-moderate AD. Twenty-one patients with AD (test population) and 26 healthy participants (HP; design validation) were exposed to thermal pain stimulation on 3 test days: Lidocaine condition (open/hidden lidocaine administration), capsaicin condition (open/hidden capsaicin administration), and natural history (no treatment), in a randomized, within-subject design. Open lidocaine and open capsaicin were accompanied by verbal suggestions for pain relief and pain increase, respectively. Expected pain and actual pain intensity were measured on a numerical rating scale (0-10). Placebo and nocebo effects were calculated as pain differences in open-hidden lidocaine and capsaicin, respectively, controlled for no treatment. Healthy participants obtained a placebo effect ( P = 0.01) and a trend for a nocebo effect ( P = 0.07). Patients with AD did not obtain a placebo effect ( P = 0.44) nor a significant nocebo effect ( P = 0.86). Healthy participants expected lower and higher pain with open vs hidden lidocaine and capsaicin, respectively ( P < 0.001). The same expectation effects were seen in patients with AD (open vs hidden lidocaine, P = 0.008; open vs hidden capsaicin, P < 0.001). With a well-controlled experimental setting, this study suggests that patients with AD may not experience placebo analgesia effects. Nocebo hyperalgesia effects in patients with AD needs further research. These findings may have implications for the conduction of clinical trials and the treatment of patients with AD in clinical practice.

Efficacy and Safety of Botulinum Toxin A and Pulsed Radiofrequency on Postherpetic Neuralgia: A Randomized Clinical Trial

This study evaluated the effectiveness and safety of botulinum toxin type A (BoNT-A) and pulsed radiofrequency (RF) in the clinical treatment of postherpetic neuralgia (PHN). A total of 100 patients with PHN were randomly divided into two groups (n = 50 per group): RF group and BoNT-A group. Based on conventional drug treatment, patients were treated with either a single nerve root pulsed radiofrequency therapy or a single local subcutaneous injection of BoNT-A in the lesion area. All the patients were followed up for 24 weeks on pain scores, sleep quality, anxiety, and depression scores, etc. In the last follow-up at the end of 24 weeks postoperation, the pain scores of patients in both groups were significantly lower than those before the operation (P < 0.05), indicating that both treatments were effective against PHN; however, there was no significant difference between these two groups (P > 0.05). It is noteworthy that the subcutaneous injection of BoNT-A is relatively easy to administer and less expensive compared to RF. Therefore, we believe that the subcutaneous injection of BoNT-A is an effective and safe method for the treatment of PHN.

Hard polymeric porous microneedles on stretchable substrate for transdermal drug delivery

Microneedles offer a convenient transdermal delivery route with potential for long term sustained release of drugs. However current microneedle technologies may not have the mechanical properties for reliable and stable penetration (e.g. hydrogel microneedles). Moreover, it is also challenging to realize microneedle arrays with large size and high flexibility. There is also an inherent upper limit to the amount and kind of drugs that can be loaded in the microneedles. In this paper, we present a new class of polymeric porous microneedles made from biocompatible and photo-curable resin that address these challenges. The microneedles are unique in their ability to load solid drug formulation in concentrated form. We demonstrate the loading and release of solid formulation of anesthetic and non-steroidal anti-inflammatory drugs, namely Lidocaine and Ibuprofen. Paper also demonstrates realization of large area (6 × 20 cm²) flexible and stretchable microneedle patches capable of drug delivery on any body part. Penetration studies were performed in an ex vivo porcine model supplemented through rigorous compression tests to ensure the robustness and rigidity of the microneedles. Detailed release profiles of the microneedle patches were shown in an in vitro skin model. Results show promise for large area transdermal delivery of solid drug formulations using these porous microneedles.

Topical Lidocaine for Chronic Pain Treatment

Topical lidocaine is widely used in current practice for a variety of pain conditions. This literature review shows that its limited absorption and relative lack of systemic adverse events are an attractive analgesic option for a number of vulnerable patients. Topical lidocaine has been approved by health authorities for the treatment of post-herpetic neuralgia in a number of countries, and studies present some degree of evidence of its efficacy and safety in postsurgical pain, diabetic peripheral neuropathy, carpal tunnel syndrome, chronic lower back pain and osteoarthritis. Topical lidocaine may be a great alternative alone or in addition to systemic drugs and non-pharmacological approaches for an optimized pain management and in multimodal analgesia.

Efficacy of Electroacupuncture Therapy in Patients With Postherpetic Neuralgia: Study Protocol for a Multicentre, Randomized, Controlled, Assessor-Blinded Trial

Introduction: The efficacy of conventional treatments for treating postherpetic neuralgia (PHN) remains unsatisfactory. Thus, this multicentre, randomized controlled, assessor-blinded trial aims to investigate the efficacy and safety of electroacupuncture (EA) therapy in patients with PHN. Methods and Analysis: This multicentre randomized controlled trial will enroll 132 patients with PHN from 3 hospitals. All patients will be randomly assigned to either the EA combined with medication group or medication group through a computerized central randomization system in a 1:1 ratio. Outcome measures will be assessed before intervention, at 2, 4, 6 weeks after intervention and at the end of 8-week follow-up. Primary outcomes will be sensory thresholds and pain intensity. Secondary outcomes will include dosage of analgetic, quality of life, anxiety, and depression severity and sleep quality. All adverse effects will be assessed during the trial. Conclusions: This study will provide evidence to ascertain whether EA is effective and safe for treating PHN. Ethics and Dissemination: Ethics approval (No.ZSLL-KY-2017-025) has been obtained from the Ethics Committee of The Third Affiliated Hospital of Zhejiang Chinese Medical University. Informed consent will be signed prior to subject enrolment. The results will be submitted to international peer-reviewed journals and presented at international conferences. Trial Registration Number: The study protocol has been registered in the clinicaltrials registry with the identification code NCT04594226.

Application of Nalbuphine in Trigeminal Ganglion Pulse Radiofrequency Surgery in Patients with Postherpetic Neuralgia

This study aimed to explore the application value of nalbuphine in pulsed radiofrequency operation of trigeminal ganglion in patients with postherpetic neuralgia (PHN). Thirty patients with PHN were randomly divided into the nalbuphine (Nalbu) group and ketorolac tromethamine (KT) group and received CT-guided pulsed radiofrequency surgery on trigeminal ganglion. The numeric rating scale (NRS) scores of patients were recorded at preoperative, intraoperative, and postoperative time points, before going to bed, and the next morning after the operation. In addition, the number of breakthrough pain before operation and within 24 hours after operation, the incidence of nausea and vomiting within 24 hours after surgery, and the patient's sleep quality before and on the day after surgery were evaluated. The outcome data demonstrated that patients treated with nalbuphine had lower NRS scores after the pulse radiofrequency operation during and after the pulse radiofrequency operation compared to those with KT. In addition, nalbuphine effectively decreased the number of breakthrough pain, reduced the occurrence of nausea and vomiting after surgery, and improved the sleep quality. In conclusion, intramuscular injection of nalbuphine 30 min before trigeminal ganglion pulse radiofrequency surgery can be conducive to pain relief and improve the postoperative comfort of patients, providing an effective alternative for the alleviation of PHN in clinic.

Neuronal delivery of nanoparticles via nerve fibres in the skin

Accessing the peripheral nervous system (PNS) by topically applied nanoparticles is a simple and novel approach with clinical applications in several PNS disorders. Skin is richly innervated by long peripheral axons that arise from cell bodies located distally within ganglia. In this study we attempt to target dorsal root ganglia (DRG) neurons, via their axons by topical application of lectin-functionalized gold nanoparticles (IB4-AuNP). In vitro, 140.2 ± 1.9 nm IB4-AuNP were found to bind both axons and cell bodies of DRG neurons, and AuNP applied at the axonal terminals were found to translocate to the cell bodies. Topical application of IB4-AuNP on rat hind-paw resulted in accumulation of three to fourfold higher AuNP in lumbar DRG than in contralateral control DRGs. Results from this study clearly suggest that topically applied nanoparticles with neurotropic targeting ligands can be utilized for delivering nanoparticles to neuronal cell bodies via axonal transport mechanisms.

Characteristics of Analgesic Patch Formulations

Topical and transdermal formulations are a common means of pharmaceutical drug delivery. If a drug is able to penetrate transcutaneously, the skin is an ideal site for the delivery of medications for both local (topical) and systemic (transdermal) effects. The administration of analgesics through the skin poses several potential advantages to those administered orally including compliance, the ability to deliver a drug to a peripheral target site and more stable and sustained plasma levels. One method of drug delivery is with the use of patch formulations - also known as patch systems. Typically, transdermal patches deliver medications intended to reach the systemic circulation, whereas topical patches are designed to keep medication localized for targeted delivery in proximity to the application site. There are a variety of technologies and materials utilized in patches, as well as penetration and formulation enhancers that ultimately affect the performance, efficacy and safety of the patch system. The degree of adherence to the skin is also of critical importance in drug delivery. Patches that lift up or fall off before the prescribed time period may represent a therapeutic failure and must be replaced, increasing patch utilization and cost to the healthcare system or to the patient. The added risk from accidental exposure makes poor patch adhesion a safety issue as well. A variety of analgesics are currently available as patch formulations including local anesthetics, capsaicin, nonsteroidal anti-inflammatory drugs and opioids. This review will highlight each of those patch delivery systems and introduce newer patch technologies that lend towards improved adhesion and compliance. Understanding the designs, limitations and benefits of patch systems will allow clinicians to select between these therapies when appropriate for their patients.

Inflammatory cytokine expression in the skin of patients with postherpetic neuralgia

Objective

To assess the expression of inflammatory cytokines in the affected and normal skin of postherpetic neuralgia (PHN) patients.

Methods

Affected skin and normal skin samples were collected from PHN patients. Inflammatory cell infiltration in the dermis were evaluated by hematoxylin-eosin (HE) staining. A human inflammatory protein array containing 40 cytokines was used to assess expression differences between PHN and control skin. Enzyme linked immunosorbent assay (ELISA) kits were used to confirm cytokine expression in 10 PHN patients.

Results

HE staining showed that the epidermis of PHN skin was thicker than that of contralateral normal skin. Compared with normal skin, there was more infiltration of inflammatory cells into the dermis of PHN skin. The cytokine array detected the presence of 21/40 cytokines; however, only interleukin (IL)-1α showed differential expression between PHN skin and normal skin. ELISA results for IL-1α, IL-16, intercellular adhesion molecule-1, and monocyte chemoattractant protein-1 were consistent with those of cytokine arrays.

Conclusions

Expression of inflammatory cytokines in PHN skin was not significantly altered compared with normal skin. Chronic refractory pain in PHN is not necessarily associated with increased inflammation in the affected skin.

Neuropathic Pain and Sickle Cell Disease: a Review of Pharmacologic Management

PURPOSE OF REVIEW

Sickle cell disease (SCD) remains among the most common and severe monogenic disorders present in the world today. Although sickle cell pain has been traditionally characterized as nociceptive, a significant portion of sickle cell patients has reported neuropathic pain symptoms. Our review article will discuss clinical aspects of SCD-related neuropathic pain, epidemiology of neuropathic pain among individuals with SCD, pain mechanisms, and current and future potential pharmacological interventions.

RECENT FINDINGS

Neuropathic pain in SCD is a complicated condition that often has a lifelong and significant negative impact on life; therefore, improved pain management is considered a significant and unmet need. Neuropathic pain mechanisms are heterogeneous, and the difficulty in determining their individual contribution to specific pain types may contribute to poor treatment outcomes in this population. Our review article outlines several pharmacological modalities which may be employed to treat neuropathic pain in SCD patients.

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.

Dissolving Microneedles for Rapid and Painless Local Anesthesia

Microneedles are emerging drug delivery methods for painless treatment. The current study tested dissolving microneedles containing lidocaine (Li-DMN) for use in local anesthesia. An Li-DMN patch was fabricated by centrifugal lithography with carboxymethyl cellulose as a structural polymer and assessed for physical properties by optical microscopy and a fracture force analyzer. The biocompatibility was evaluated by a histology section in vitro and by ear thickness in vivo. The efficacy of the Li-DMN patch was assessed by electrophysiological recordings in primary cultured sensory neurons in vitro and a von Frey test on rats’ hind paws in vivo. The physical properties of the microneedle showed enough rigidity for transdermal penetration. The maximal capacity of lidocaine-HCl in the Li-DMN patch was 331.20 ± 6.30 µg. The cytotoxicity of the dissolving microneedle to neuronal cells was negligible under an effective dose of lidocaine for 18 h. Electrophysiological recordings verified the inhibitory effect of the voltage-gated sodium channel current by the Li-DMN patch in vitro. A skin reaction to the edema test and histologic analysis of the rats’ ears after application of the Li-DMN patch were negligible. Also, the application of the Li-DMN patch reduced the nocifensive behavior of the rats almost immediately. In conclusion, the dissolving microneedle patch with carboxymethyl cellulose is a promising candidate method for the painless delivery of lidocaine-HCl.

MicroRNA And Circular RNA Expression In Affected Skin Of Patients With Postherpetic Neuralgia

Mechanisms of postherpetic neuralgia (PHN) are still not clear. Transcripts such as microRNA (miRNA) and circular RNA (circRNA) in the affected skin may take part in the initiation and development of this neuropathic pain; however, their expression profiles in skins of PHN patients have not been reported. The PHN affected skin and the mirror skin were collected and subjected to miRNA and circRNA microarray, and expression profiles were comparatively analyzed. There were 317 differently expressed miRNAs in PHN affected skin compared with mirror skin (fold change ≥2.0), and 13 of them showed fold change >10 in the PHN skin. Only one circRNA, hsa_circRNA_405463 showed fold change >2 in PHN skin, however, 31 circRNAs with fold change ≥1.5. To evaluate functions of differential miRNAs, their target mRNAs were predicted and bioinformatics analyses including gene ontology, Kyoto Encyclopedia of Genes and Genomes pathway were conducted. Target mRNAs significantly (P<0.05) enriched in 85 pathways, such as FoxO, AMPK, MAPK and pathway. These data reported for the first time that miRNA and circRNA differentially expressed in the PHN skin and these transcripts with abnormal expression could be potential targets to treat PHN.

Short-Term Effects of 10% Lidocaine Ointment on Allodynia in Cancer Pain: A Randomized, Double-Blind, Placebo-Controlled Crossover Study

Background: There is currently no established therapy for allodynia, which is a type of neuropathic pain. However, high concentrations of topical anesthetics can anesthetize the skin and increase the sensory threshold to tactile stimulation. Objective: We aimed to evaluate the short-term effects and safety of 10% lidocaine ointment for treating allodynia in cancer pain. Design: This was a randomized double-blind crossover study comparing the efficacies of 10% lidocaine ointment and placebo ointment for the treatment of static allodynia and spontaneous pain within 24 hours after ointment application, using a numerical rating scale (NRS). Setting/Subjects: The subjects were 25 cancer patients with current pain rating of ≥4 on NRS of static allodynia in cancer pain. Results: The NRS scores for static allodynia were significantly lower in the lidocaine group than in the placebo group at two to eight hours after initial ointment application. A total of 56% of patients (95% confidence interval 35%-77%) had NRS improvements of ≥50% at eight hours after lidocaine ointment application compared with 20% (3%-37%) after placebo ointment application. There was no interaction between time and group in terms of NRS values for spontaneous pain (p = 0.835), but a significant main effect of group was found, with NRS scores being significantly lower in the lidocaine group than in the placebo group (p = 0.027). There were no adverse events associated with lidocaine use. Conclusions: Lidocaine ointment 10% can alleviate allodynia for two to eight hours after application.

Opioid Adjuncts: Optimizing Opioid Therapy With Nonopioid Medications

In this article, we describe a variety of medications that physicians managing outpatient chronic pain should familiarize themselves with to better aid their approach to multimodal pain therapy. Physicians should always consider the use of an adjuvant or coanalgesic drug as first-line treatments. Although many of these medications are not primarily analgesics, in clinical practice they have independent analgesic effects or synergistic analgesic properties when used with opioids. The use of adjunct analgesics reduces opioid-related adverse effects and optimizes pain management. Although there may be some medication overlap with this section and the ERAS section, the purpose of this article is to understand prolonged use in the outpatient setting to reduce opioid use or limit opioid dose with adjuvant therapy.

Pharmacokinetics of intravenous, subcutaneous, and topical administration of lidocaine hydrochloride and metabolites 3-hydroxylidocaine, monoethylglycinexylidide, and 4-hydroxylidocaine in horse

Intravenous (iv), subcutaneous (sq), and topical (tp) lidocaine was administered to six horses in a cross-over, randomized design study. Samples were collected for up to 72 hr. Compartmental models were used to investigate the pharmacokinetics of (LD) and its metabolites 3-hydroxylidocaine (3-OH), 4-hydroxylidocaine (4-OH), and monoethylglycinexylidide (MEGX). Metabolites 3-OH and 4-OH were present in conjugated forms, whereas LD and metabolite MEXG were present primarily in the un-conjugated form. Plasma concentrations of LD after iv administration (100 mg) were described by three-compartment model with an additional three compartments to describe the elimination of metabolites. Median (range) elimination micro-constants (K_e ) for LD, 3-OH, 4-OH, and MEXG were 4.12 (2.62-6.23), 1.25 (1.10-2.15), 1.79 (1.22-2.39), and 1.69 (1.03-1.99)/hr, respectively. Median (range) values of alpha (t_½α ), beta (t_½β ), and gamma (t_½γ ) half-lives were 0.08 (0.07-0.13), 0.57 (0.15-1.25), and 4.11 (0.52-7.36) hr. Plasma concentrations of LD after sq (200 mg) administration were described by absorption and two-compartment elimination model. The median (range) of the LD absorption half-life (t_½ab ) was 0.47 (0.29-0.61) hr. The K_e for LD, 3-OH, 4-OH, and MEXG was 3.91 (1.48-9.25), 1.00 (0.78-1.08), 1.76 (0.96-2.11), and 1.13 (0.69-1.33)/hr. The median (range) of t_½α and t_½β was 0.15 (0.06-0.27) and 3.04 (2.53-6.39) hr. Plasma concentrations of LD after tp (400 mg) application were described by one-compartment model with a t_½ab of 8.49 (5.16-11.80) hr. The K_e for LD, 3-OH, and MEXG was 0.24 (0.10-0.81), 0.41 (0.08-0.93), and 0.38 (0.26-1.14)/hr.

A Review of Neuropathic Pain: From Diagnostic Tests to Mechanisms

Neuropathic pain develops when the somatosensory nervous system is affected by a lesion or disease. Diagnostic tests aimed at assessing somatosensory afferent pathway damage are therefore useful for diagnosing neuropathic pain. Neuropathic pain manifests with a range of different symptoms such as ongoing burning pain, squeezing or pressure pain, paroxysmal electric shock-like sensations, stabbing pain, or mechanical dynamic allodynia. The various types of neuropathic pain are associated with different underlying nerve fiber abnormalities. This article summarizes the available methods of somatosensory afferent pathway assessment and discusses the potential pathophysiology underlying the most representative neuropathic pain types, i.e., ongoing burning pain, paroxysmal pain, and mechanical dynamic allodynia.

FUNDING

Pfizer, Italy.

Management of Pain Associated with Selected Conditions in Dermatology

Dermatologists face a wide range of pain control challenges in daily practice, from the transient pain of dermatologic surgery to the persistent pain that plagues some chronic dermatologic conditions. Although the pathophysiology of pain is well described and the profound impact of dermatological pain on patients' quality of life is well appreciated, there is an identified need for clear therapeutic plans for providing symptomatic pain relief of common painful dermatoses. In this paper, we will review and clearly outline approaches to pain management of a number of common painful dermatoses such as herpes zoster and post-herpetic neuralgia, ulcers, oral dermatoses, dysesthesias, and many others.

Use of EMLA as an adjunct for burning pain associated with a liposarcoma

Objective. To report the successful use of EMLA cream (a topical anesthetic) for the relief of neuro pathic pain in a patient with a liposarcoma.

Case Summary. A 63-year-old male with a lipo sarcoma was admitted to the hospital to establish an effective pain control regimen. Despite the use of high-dose hydromorphone, dexamethasone, and in domethacin, he still complained of a burning sensa tion in the skin over the tumor site. EMLA—applied regularly every 8 hours, was started, and within 24 hours the patient reported relief from this pain.

Discussion. While there is some experience with the use of systemically administered anesthetics for the control of neuropathic pain in cancer patients, there is little reported experience of the use of topical anesthetics. EMLA has, however, been successfully used for postherpetic neuralgia. Adverse reactions from its use for reducing the pain of venipuncture are usually mild and transient, and repeated use does not appear to increase the risk of toxicity. In this case, the patient's pain was well-controlled without any observ able adverse reactions.

Summary. This patient experienced relief of burning pain when EMLA was added to his treatment regimen. EMLA cream could be considered as a treatment option for cancer patients experiencing neuropathic pain, but the patients most likely to benefit and the optimal treatment regimen have yet to be determined by a prospective study.

Allodynia and hyperalgesia in neuropathic pain: clinical manifestations and mechanisms

Allodynia (pain due to a stimulus that does not usually provoke pain) and hyperalgesia (increased pain from a stimulus that usually provokes pain) are prominent symptoms in patients with neuropathic pain. Both are seen in various peripheral neuropathies and central pain disorders, and affect 15-50% of patients with neuropathic pain. Allodynia and hyperalgesia are classified according to the sensory modality (touch, pressure, pinprick, cold, and heat) that is used to elicit the sensation. Peripheral sensitisation and maladaptive central changes contribute to the generation and maintenance of these reactions, with separate mechanisms in different subtypes of allodynia and hyperalgesia. Pain intensity and relief are important measures in clinical pain studies, but might be insufficient to capture the complexity of the pain experience. Better understanding of allodynia and hyperalgesia might provide clues to the underlying pathophysiology of neuropathic pain and, as such, they represent new or additional endpoints in pain trials.

Expectations and positive emotional feelings accompany reductions in ongoing and evoked neuropathic pain following placebo interventions

Research on placebo analgesia and nocebo hyperalgesia has primarily included healthy subjects or acute pain patients, and it is unknown whether these effects can be obtained in ongoing pain in patients with chronic pain caused by an identifiable nerve injury. Eighteen patients with postthoracotomy neuropathic pain were exposed to placebo and nocebo manipulations, in which they received open and hidden administrations of pain-relieving (lidocaine) or pain-inducing (capsaicin) treatment controlled for the natural history of pain. Immediately after the open administration, patients rated their expected pain levels on a mechanical visual analogue scale (M-VAS). They also reported their emotional feelings via a quantitative/qualitative experiential method. Subsequently, patients rated their ongoing pain levels on the M-VAS and underwent quantitative sensory testing of evoked pain (brush, pinprick, area of hyperalgesia, wind-up-like pain). There was a significant placebo effect on both ongoing (P=.009 to .019) and evoked neuropathic pain (P=.0005 to .053). Expected pain levels accounted for significant amounts of the variance in ongoing (53.4%) and evoked pain (up to 34.5%) after the open lidocaine administration. Furthermore, patients reported high levels of positive and low levels of negative emotional feelings in the placebo condition compared with the nocebo condition (P⩽.001). Pain increases during nocebo were nonsignificant (P=.394 to 1.000). To our knowledge, this is the first study to demonstrate placebo effects in ongoing neuropathic pain. It provides further evidence for placebo-induced reduction in hyperalgesia and suggests that patients' expectations coexist with emotional feelings about treatments.

Topical lidocaine for neuropathic pain in adults

BACKGROUND

Lidocaine is a local anaesthetic that is sometimes used on the skin to treat neuropathic pain.

OBJECTIVES

To assess the analgesic efficacy of topical lidocaine for chronic neuropathic pain in adults, and to assess the associated adverse events.

SEARCH METHODS

We searched CENTRAL, MEDLINE, and EMBASE from inception to 1 July 2014, together with the reference lists of retrieved papers and other reviews. We also searched ClinicalTrials.gov and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) search portal to identify additional published or unpublished data.

SELECTION CRITERIA

We included randomised, double-blind studies of at least two weeks' duration comparing any formulation of topical lidocaine with placebo or another active treatment in chronic neuropathic pain. Participants were adults aged 18 and over. We included only full journal publication articles.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted efficacy and adverse event data, and examined issues of study quality. We performed analysis using three tiers of evidence. First tier evidence derived from data meeting current best standards and subject to minimal risk of bias (outcome equivalent to substantial pain intensity reduction, intention-to-treat analysis without imputation for dropouts; at least 200 participants in the comparison, 8 to 12 weeks' duration, parallel design); second tier evidence from data that failed to meet one or more of these criteria and that we considered at some risk of bias but with adequate numbers in the comparison; and third tier evidence from data involving small numbers of participants that we considered very likely to be biased or used outcomes of limited clinical utility, or both.

MAIN RESULTS

We included 12 studies (508 participants) in comparisons with placebo or an active control. Six studies enrolled participants with moderate or severe postherpetic neuralgia, and the remaining studies enrolled different, or mixed, neuropathic pain conditions, including trigeminal neuralgia and postsurgical or post-traumatic neuralgia. Four different formulations were used: 5% medicated patch, 5% cream, 5% gel, and 8% spray. Most studies used a cross-over design, and two used a parallel-group design. Two studies used enriched enrolment with randomised withdrawal. Seven studies used multiple doses, with one to four-week treatment periods, and five used single applications. We judged all of the studies at high risk of bias because of small size or incomplete outcome assessment, or both.There was no first or second tier evidence, and no pooling of data was possible for efficacy outcomes. Only one multiple-dose study reported our primary outcome of participants with ≥ 50% or ≥ 30% pain intensity reduction. Three single-dose studies reported participants who were pain-free at a particular time point, or had a 2-point (of 10) reduction in pain intensity. The two enriched enrolment, randomised withdrawal studies reported time to loss of efficacy. In all but one study, third tier (very low quality) evidence indicated that lidocaine was better than placebo for some measure of pain relief. Pooling multiple-dose studies across conditions demonstrated no clear evidence of an effect of lidocaine on the incidence of adverse events or withdrawals, but there were few events and the withdrawal phase of enriched enrolment designs is not suitable to assess the true impact of adverse events (very low quality evidence).

AUTHORS' CONCLUSIONS

This review found no evidence from good quality randomised controlled studies to support the use of topical lidocaine to treat neuropathic pain, although individual studies indicated that it was effective for relief of pain. Clinical experience also supports efficacy in some patients. Several large ongoing studies, of adequate duration, with clinically useful outcomes should provide more robust conclusions about both efficacy and harm.

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.

WITHDRAWN: Topical lidocaine for the treatment of postherpetic neuralgia

BACKGROUND

This is an update of the original Cochrane review published in Issue 2, 2007. The cause of postherpetic neuralgia is damage to peripheral neurons, dorsal root ganglia, and the dorsal horn of the spinal cord, secondary to herpes zoster infection (shingles). In postherpetic neuralgia, peripheral neurons discharge spontaneously and have lowered activation thresholds, and exhibit an exaggerated response to stimuli. Topical lidocaine dampens peripheral nociceptor sensitisation and central nervous system hyperexcitability, and may benefit patients with postherpetic neuralgia.

OBJECTIVES

To examine efficacy and safety of topical lidocaine in the treatment of postherpetic neuralgia.

SEARCH METHODS

We searched the Cochrane Pain, Palliative and Supportive Care Group Trials Register, CENTRAL, MEDLINE, EMBASE, LILACS, SIGLE, Citation Index, the reference lists of all eligible trials, key textbooks, and previous systematic reviews. Last search conducted April 2011.

SELECTION CRITERIA

Randomised or quasi‐randomised trials comparing topical applications of lidocaine in patients of all ages with postherpetic neuralgia (pain persisting at the site of shingles at least one month after the onset of the acute rash).

DATA COLLECTION AND ANALYSIS

Two review authors extracted data, and a third checked them.

MAIN RESULTS

In the original review three studies involving 182 topical lidocaine treated participants and 132 control participants were included. Two studies gave data on pain relief, and the remaining study provided data on secondary outcome measures. The largest study published as an abstract compared topical lidocaine patch to a placebo patch and accounted for 150 of the 314 participants (48%). A meta‐analysis combining two studies identified a significant difference between topical lidocaine and control groups for the primary outcome measure: a mean improvement in pain relief according to a pain relief scale. Topical lidocaine relieved pain better than placebo (P = 0.003). There was a statistical difference between the groups for the secondary outcome measure of mean VAS score reduction (P = 0.03), but this was only for a single small study. There were a similar number of adverse skin reactions in both treatment and placebo groups. The highest recorded blood lidocaine concentration varied between 59 ng/ml and 431 ng/ml between studies. The latter figure is high and the authors of the study suggest that the sample had been contaminated during the assay procedure.

AUTHORS' CONCLUSIONS

Since the last version of this review in Issue 2, 2007 no new studies have been found and the results therefore remain the same. There is still insufficient evidence to recommend topical lidocaine as a first‐line agent in the treatment of postherpetic neuralgia with allodynia. Further research should be undertaken on the efficacy of topical lidocaine for other chronic neuropathic pain disorders, and also to compare different classes of drugs (e.g. topical anaesthetic applications versus anti‐epileptic drugs).

Reappraising neuropathic pain in humans--how symptoms help disclose mechanisms

Neuropathic pain--that is, pain arising directly from a lesion or disease that affects the somatosensory system--is a common clinical problem, and typically causes patients intense distress. Patients with neuropathic pain have sensory abnormalities on clinical examination and experience pain of diverse types, some spontaneous and others provoked. Spontaneous pain typically manifests as ongoing burning pain or paroxysmal electric shock-like sensations. Provoked pain includes pain induced by various stimuli or even gentle brushing (dynamic mechanical allodynia). Recent clinical and neurophysiological studies suggest that the various pain types arise through distinct pathophysiological mechanisms. Ongoing burning pain primarily reflects spontaneous hyperactivity in nociceptive-fibre pathways, originating from 'irritable' nociceptors, regenerating nerve sprouts or denervated central neurons. Paroxysmal sensations can be caused by several mechanisms; for example, electric shock-like sensations probably arise from high-frequency bursts generated in demyelinated non-nociceptive Aβ fibres. Most human and animal findings suggest that brush-evoked allodynia originates from Aβ fibres projecting onto previously sensitized nociceptive neurons in the dorsal horn, with additional contributions from plastic changes in the brainstem and thalamus. Here, we propose that the emerging mechanism-based approach to the study of neuropathic pain might aid the tailoring of therapy to the individual patient, and could be useful for drug development.

Targeting novel peripheral mediators for the treatment of chronic pain

Research efforts over the past two decades have helped us better understand the biological mechanisms that lead to chronic pain. Despite this, there has been limited progress in developing novel analgesics to treat sufferers of persistent pain conditions, who may account for as many as one-fifth of the population. A re-evaluation of the strategies used to discover pain-relieving drugs is needed to meet this widespread clinical need. Here, we discuss the merits of pursuing peripherally acting pain mediators. We review the significant clinical evidence that neuronal activity from the periphery is a major contributor to painful symptom production and that peripheral mediators play a substantial role in this aberrant nociceptor activity. We discuss the clinical benefits of blocking individual known mediators and describe our own approach to identify novel mediators.

Effects of dorsal root ganglion destruction by adriamycin in patients with postherpetic neuralgia

PURPOSE

To investigate the effects of dorsal root ganglion destruction in patients with postherpetic neuralgia (PHN).

METHODS

Seventy-two patients with PHN selected were randomly divided into two groups (n=36). Group A was the control group (treated by injection) and group B was the group of dorsal root ganglion destruction by adriamycin. Visual analog scale scores (VAS), SAS, SF-MPQ scores. Clinical effects and therapy safety were evaluated before therapy, one week, three and six months after therapy. Forty-four patients were available for intention-to-treat analysis.

RESULTS

The average pain scores on the Likert scale were significantly reduced at each point in group B. Patients in group B reported clinical effectiveness at six months as excellent response, good response, improved but unsatisfactory or unchanged 16, 12 and 8.VAS scores at each time point after the operation were lower than that before operation and in group A, there was significant difference. Patients showed significant improvement in sleep scores in group B. There was significant difference at T2 in group A than T1. There was no significant difference in group A at T3, T4 after the operation than that before operation. Between group comparison: there was significant difference between group A and group B at each time point after the operation.

CONCLUSIONS

Dorsal root ganglion destruction by adriamycin under guidance of C-arm perspective, the puncture operation was accurate without any adverse reaction or serious complications, which could effectively relieve pain of patients with postherpetic neuralgia, but the long-term effects needed further study.

Considerations for neuropathic pain conditions in life care planning

Significant progress has been made in assessing and managing neuropathic pain. Newer, more effective treatments with minimal side effects are available. Despite advances in treatments, neuropathic pain remains a multifaceted phenomenon that can be difficult to alleviate. Diagnosis, mechanisms of injury, and treatment recommendations are critical components of life care plans for patients with neuropathic pain. A clear understanding of the underlying issues and careful coordination with neurologists and other treatment providers are key to providing optimal life care plans. Understanding that pain treatments vary over time and by individual patient is integral to comprehensive life care planning.

Herpes virus infection of the peripheral nervous system

Among the human herpes viruses, three are neurotropic and capable of producing severe neurological abnormalities: herpes simplex virus type 1 and 2 (HSV-1 and HSV-2) and varicella-zoster virus (VZV). Both the acute, primary infection and the reactivation from the site of latent infection, the dorsal sensory ganglia, are associated with severe human morbidity and mortality. The peripheral nervous system is one of the major loci affected by these viruses. The present review details the virology and molecular biology underlying the human infection. This is followed by detailed description of the symtomatology, clinical presentation, diagnosis, course, therapy, and prognosis of disorders of the peripheral nervous system caused by these viruses.

Advances in targeting voltage-gated sodium channels with small molecules

Blockade of voltage-gated sodium channels (VGSCs) has been used successfully in the clinic to enable control of pathological firing patterns that occur in conditions as diverse as chronic pain, epilepsy, and arrhythmias. Herein we review the state of the art in marketed sodium channel inhibitors, including a brief compendium of their binding sites and of the cellular and molecular biology of sodium channels. Despite the preferential action of this drug class toward over-excited cells, which significantly limits potential undesired side effects on other cells, the need to develop a second generation of sodium channel inhibitors to overcome their critical clinical shortcomings is apparent. Current approaches in drug discovery to deliver novel and truly innovative sodium channel inhibitors is next presented by surveying the most recent medicinal chemistry breakthroughs in the field of small molecules and developments in automated patch-clamp platforms. Various strategies aimed at identifying small molecules that target either particular isoforms of sodium channels involved in specific diseases or anomalous sodium channel currents, irrespective of the isoform by which they have been generated, are critically discussed and revised.

Topical amitriptyline, ketamine, and lidocaine in neuropathic pain caused by radiation skin reaction: a pilot study

PURPOSE

The purpose of this study is to assess the effect of topical amitriptyline, ketamine, and lidocaine (AKL) on alleviation of neuropathic pain from radiation dermatitis and the feasibility of a randomized trial.

MATERIALS AND METHODS

Eligible subjects had radiation dermatitis with dry or moist desquamation with neuropathic pain and were intolerant or allergic to standard intervention. AKL was applied to painful sites three times a day daily until 2 weeks post-radiotherapy. Subjects were monitored every 2-5 days during radiotherapy and at 2 and 6 weeks after completion of radiotherapy. The University of Washington Neuropathic Pain Scale was used to grade the neuropathic pain before and after use of the interventional gel. Compliance was assessed by asking subjects at each visit how frequently they were using the interventional gel.

RESULTS

Over a 14-month period, 16 subjects met eligibility criteria. Eighty-two percent of subjects used the AKL as directed. Five subjects (32%) reported fatigue, and three subjects (19%) reported site irritation from the interventional gel. AKL was shown to significantly reduce (p < 0.05) pain intensity, sharpness, burning, sensitivity, itchiness, unpleasantness, deepness, and surfaceness levels on a short-term basis (i.e., between pre-treatment and 30 min post-treatment). AKL was shown to significantly reduce (p < 0.05) burning levels on a long-term basis (i.e., between pre-treatment and 2 weeks post-treatment).

CONCLUSIONS

AKL was a safe intervention to use with minimal toxicity and good compliance. It significantly reduced several measures of neuropathic pain associated with radiation dermatitis. A larger-scale study would require recruitment from multiple centers.

Cost-effectiveness analysis of a new 8% capsaicin patch compared to existing therapies for postherpetic neuralgia

OBJECTIVE

The purpose of this study was to compare the cost effectiveness of a new 8% capsaicin patch, compared to the current treatments for postherpetic neuralgia (PHN), including tricyclic antidepressants (TCAs), topical lidocaine patches, duloxetine, gabapentin, and pregabalin.

METHODS

A 1-year Markov model was constructed for PHN with monthly cycles, including dose titration and management of adverse events. The perspective of the analysis was from a payer perspective, managed-care organization. Clinical trials were used to determine the proportion of patients achieving at least a 30% improvement in PHN pain, the efficacy parameter. The outcome was cost per quality-adjusted life-year (QALY); second-order probabilistic sensitivity analyses were conducted.

RESULTS

The effectiveness results indicated that 8% capsaicin patch and topical lidocaine patch were significantly more effective than the oral PHN products. TCAs were least costly and significantly less costly than duloxetine, pregabalin, topical lidocaine patch, 8% capsaicin patch, but not gabapentin. The incremental cost-effectiveness ratio for the 8% capsaicin patch overlapped with the topical lidocaine patch and was within the accepted threshold of cost per QALY gained compared to TCAs, duloxetine, gabapentin, and pregablin. The frequency of the 8% capsaicin patch retreatment assumption significantly impacts its cost-effectiveness results. There are several limitations to this analysis. Since no head-to-head studies were identified, this model used inputs from multiple clinical trials. Also, a last observation carried forward process was assumed to have continued for the duration of the model. Additionally, the trials with duloxetine may have over-predicted its efficacy in PHN. Although a 30% improvement in pain is often an endpoint in clinical trials, some patients may require greater or less improvement in pain to be considered a clinical success.

CONCLUSIONS

The effectiveness results demonstrated that 8% capsaicin and topical lidocaine patches had significantly higher effectiveness rates than the oral agents used to treat PHN. In addition, this cost-effectiveness analysis found that the 8% capsaicin patch was similar to topical lidocaine patch and within an accepted cost per QALY gained threshold compared to the oral products.

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.

Lidocaine eye drops attenuate pain associated with ophthalmic postherpetic neuralgia

BACKGROUND

Topical lidocaine (LDC) treatment using a gel or patch preparation is effective in the treatment of postherpetic neuralgia (PHN), but neither is suited for the eye in patients with ophthalmic PHN. Herein, we examined the effect of LDC 4% eye drops on ophthalmic PHN pain.

METHODS

Twenty-four patients with ophthalmic PHN were randomized to receive 0.4 mL eye drops of either LDC 4% or saline placebo (PBO) in the painful eye. After a 7-day period, the patients were crossed over to receive the alternative eye drops. The pain in the eye and the forehead was assessed with a visual analog scale (VAS) before and 15 minutes after treatment. Patients used a descriptive scale to grade pain outcome and were asked to note whether the pain returned and how long after therapy it recurred.

RESULTS

LDC significantly decreased the VAS score of persistent pain in the eye (baseline: 5.9 +/- 2.2 cm; 15 minutes after eye drops: 0.9 +/- 1.8 cm, mean +/- SD [P < 0.01]) and in the forehead (baseline: 6.3 +/- 2.0 cm; 15 minutes after eye drops: 2.6 +/- 2.7 cm [P < 0.01]). The delta change in these VAS scores between LDC and PBO was significant (P < 0.01). Moreover, pain was described as moderate or better by 23 patients after they received LDC and 4 patients of the PBO group. The effect of LDC persisted for a median of 36 hours (range, 8-96 hours) after application.

CONCLUSIONS

This study suggests that LDC provides a significant improvement of ophthalmic PHN because of its prompt analgesia, lack of systemic side effects, and convenience of use.