Systemic administration of local anesthetics to relieve neuropathic pain: a systematic review and meta-analysis

Ultraviolet Radiation on the Skin: A Painful Experience?

Excessive exposure of skin to ultraviolet radiation (UVR) has dramatic clinical effects in humans, and it is a significant public health concern. Discomfort and sensory changes caused by skin sunburn are the main common features experienced by many of us, a phenomena triggered by the combination of long and short wavelengths radiation (UVA and UVB, respectively). Although the biological processes underlying UVR exposure are not fully understood, in the last few years many studies have made significant progress in characterizing sunburn at the cellular and molecular levels, making use of both humans and laboratory animal models. Here we review and reason that UVR can be used as an excellent model of sensitization and inflammation for pain research. UVR, particularly UVB, produces a controllable and sterile inflammation that causes a robust dose‐dependent hypersensitivity with minimal confounding effects. Importantly, we show that UVR animal models precisely recapitulate the sensory, cellular, and molecular changes observed in human skin, giving it great confidence as a translational model. Furthermore, in this article, we give an overview of the pharmacology underlying UVB inflammation, the latest advances in the field, and potential new targets for inflammatory pain.

Outcome measures in randomized-controlled trials of neuropathic pain conditions: a systematic review of systematic reviews and recommendations for practice

OBJECTIVES

Neuropathic pain (NeP) is a prevalent, disabling, multidimensional condition with significant morbidity; however, there appears to be a variable approach in the use of outcome measures in NeP trials. A search of systematic reviews of interventional randomized-controlled trials for NeP was undertaken to investigate the range and types of outcome measures used to determine treatment effects.

METHODS

Keywords and MESH searches were conducted in 5 electronic databases from inception to January 31, 2012. Full-text English-language reviews based on various acute and chronic NeP conditions were included. Two independent reviewers screened papers for inclusion, extracted data, and assessed the quality of reviews. Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines were used to critically appraise the reviews.

RESULTS

A total of 46 studies were identified: the majority of reviews (n=28/46, 61%) scored well on the PRISMA (PRISMA scores of 20-27/27). Change in levels or intensity of pain were used by the majority of studies as the primary outcome measure in intervention studies (n=40/46 studies, 87%). Few studies used a functional outcome measure as either a primary or secondary outcome measure (n=7/46, 15% of studies).

DISCUSSION

These results demonstrate that measures of pain are predominantly used in trials of NeP conditions and highlight the scant usage of functional outcome measures. The lack of standardization for the diagnostic criteria in NeP trials is also an issue that needs to be considered for future research and guideline development.

5% Lidocaine Medicated Plaster for the Treatment of Postherpetic Neuralgia: A Review of the Clinical Safety and Tolerability

Postherpetic neuralgia (PHN) is a common, very painful, and often long-lasting complication of herpes zoster which is frequently underdiagnosed and undertreated. It mainly affects the elderly, many of whom are already treated for comorbidities with a variety of systemic medications and are thus at high risk of drug-drug interactions. An efficacious and safe treatment with a low interaction potential is therefore of high importance. This review focuses on the safety and tolerability of the 5% lidocaine medicated plaster, a topical analgesic indicated for the treatment of PHN. The available literature (up to June 2014) was searched for publications containing safety data regarding the use of the 5% lidocaine medicated plaster in PHN treatment; unpublished clinical safety data were also included in this review. The 5% lidocaine medicated plaster demonstrated good short- and long-term tolerability with low systemic uptake (3 ± 2%) and minimal risk for systemic adverse drug reactions (ADRs). ADRs related to topical lidocaine treatment were mainly application site reactions of mild to moderate intensity. The treatment discontinuation rate was generally below 5% of patients. In one trial, the 5% lidocaine medicated plaster was better tolerated than systemic treatment with pregabalin. The 5% lidocaine medicated plaster provides a safe alternative to systemic medications for PHN treatment, including long-term pain treatment.

Paravertebral block is a proper alternative anesthesia for outpatient lithotripsy

Context:

This study evaluated the effectiveness of paravertebral block as an alternative anesthetic technique for extracorporeal shock wave lithotripsy (ESWL) procedure. A total of 50 patients with renal stones, aged 20-60 years, were randomly allocated into two groups; 25 patients in group P; received unilateral paravertebral block from T8 through L1 with injection of 5 mL 0.5% bupivacaine and 25 patients in group L; received local infiltration by bupivacaine 0.25% (2 mg/kg) into the 30 cm² area after localizing the stones site, 10 min before the session. A total of 10 mm visual analogue scale (VAS) was used to evaluate pain every 10 min during the session. At the end of the procedure, total doses of rescue analgesia, the number of shockwaves, their power, and the total duration of shockwave treatment were recorded. After completion of the procedure, the patient was assessed for pain and nausea in the postanesthesia care unit (PACU) using the VAS. Patient's satisfaction and time needed to discharge patients to home also were recorded. Time to do the anesthetic technique was significantly higher (P < 0.001) in group-P than group-L, it was 12.7 ± 2.3 min versus 6.9 ± 1.9 min, respectively; intraoperative rescue analgesia by fentanyl was lesser (P < 0.001) in group-P than group-L, 26.7 ± 6.32 mcg versus 78.6 ± 5.41 mcg, respectively, also time interval between ends of the procedure till discharge to home was significantly higher (P < 0.001) in group-P than group-L, it was 99 ± 17 min versus 133 ± 31 min, respectively. VAS was not significant difference between both groups either intraoperative or postoperative in first hour. Patient's satisfaction was significantly higher (P < 0.05) in group-P than group-L, it was 8.8 ± 1.1 versus 6.1 ± 0.6, respectively. Adverse events were lesser, but not significant in group-P than in group-L. Two patients (8%) in group-L and one patient (4%) in the group-P experienced episodes of postoperative nausea and vomiting (PONV).

Paravertebral block is an effective alternative anesthesia for outpatient lithotripsy; multiple level paravertebral blocks provide an optimal anesthetic condition, with acceptable adverse events for ESWL. And, providing proper analgesia during the procedure and in first hour after finishing of the procedure, early discharge to home and providing better patient's satisfactions.

Aims:

This study evaluated the effectiveness of paravertebral block as an alternative anesthetic technique for ESWL procedure.

Settings and Design:

Prospective open label study.

Subject and Methods:

A total of 50 patients with renal stones, aged 20-60 years, were randomly allocated into two groups; 25 patients in group P; received unilateral paravertebral block from T8 through L1 with injection of 5mL 0.5% bupivacaine and 25 patients in group L; received local infiltration by bupivacaine 0.25% (2 mg/kg) into the 30 cm² area after localizing the stones site, 10 min before the session. A total of 10 mm VAS was used to evaluate pain every 10 min during the session. At the end of the procedure, total doses of rescue analgesia, the number of shockwaves, their power, and the total duration of shockwave treatment were recorded. After completion of the procedure, the patient was assessed for pain and nausea in the PACU using the VAS. Patient's satisfaction and time needed to discharge patients to home also were recorded.

Statistical Analysis:

The findings of the two groups were statistically compared using SPSS version 12 (SPSS Inc., Chicago, IL). Data were expressed as mean ± standard deviation, number, and percentage. Nominal nonparametric data were analyzed using Chi-square test. Parametric data were compared using unpaired t-test. Ordinal nonparametric data were analyzed using Mann-Whitney U-test.

Results:

Time to do the anesthetic technique was significantly higher (P < 0.001) in group-P than group-L, it was 12.7 ± 2.3 min versus 6.9 ± 1.9 min, respectively; intraoperative rescue analgesia by fentanyl was lesser (P < 0.001) in group-P than group-L, 26.7 ± 6.32 mcg versus 78.6 ± 5.41 mcg, respectively, also time interval between ends of the procedure till discharge to home was significantly higher (P < 0.001) in group-P than group-L, it was 99 ± 17 min versus 133 ± 31 min, respectively. VAS was not significant difference between both groups either intraoperative or postoperative in first hour. Patient's satisfaction was significantly higher (P < 0.05) in group-P than group-L, it was 8.8 ± 1.1 versus 6.1 ± 0.6, respectively. Adverse events were lesser, but not significant in group-P than in group-L. Two patients (8%) in group-L and one patient (4%) in the group-P experienced episodes of PONV.

Conclusions:

Paravertebral block is an effective alternative anesthesia for outpatient lithotripsy; multiple level paravertebral blocks provide an optimal anesthetic condition, with acceptable adverse events for ESWL. And providing proper analgesia during the procedure and in first hour after finishing of the procedure, early discharge to home and providing better patient's satisfactions.

Management of chronic neuropathic pain: a protocol for a multiple treatment comparison meta-analysis of randomised controlled trials

INTRODUCTION

Chronic neuropathic pain is associated with reduced health-related quality of life and substantial socioeconomic costs. Current research addressing management of chronic neuropathic pain is limited. No review has evaluated all interventional studies for chronic neuropathic pain, which limits attempts to make inferences regarding the relative effectiveness of treatments.

METHODS AND ANALYSIS

We will conduct a systematic review of all randomised controlled trials evaluating therapies for chronic neuropathic pain. We will identify eligible trials, in any language, by a systematic search of CINAHL, EMBASE, MEDLINE, AMED, HealthSTAR, DARE, PsychINFO and the Cochrane Central Registry of Controlled Trials. Eligible trials will be: (1) enrol patients presenting with chronic neuropathic pain, and (2) randomise patients to alternative interventions (pharmacological or non-pharmacological) or an intervention and a control arm. Pairs of reviewers will, independently and in duplicate, screen titles and abstracts of identified citations, review the full texts of potentially eligible trials and extract information from eligible trials. We will use a modified Cochrane instrument to evaluate risk of bias of eligible studies, recommendations from the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) to inform the outcomes we will collect, and the Grading of Recommendations Assessment, Development and Evaluation (GRADE) system to evaluate our confidence in treatment effects. When possible, we will conduct: (1) in direct comparisons, a random-effects meta-analysis to establish the effect of reported therapies on patient-important outcomes; and (2) a multiple treatment comparison meta-analysis within a Bayesian framework to assess the relative effects of treatments. We will define a priori hypotheses to explain heterogeneity between studies, and conduct meta-regression and subgroup analyses consistent with the current best practices.

ETHICS AND DISSEMINATION

We do not require ethics approval for our proposed review. We will disseminate our findings through peer-reviewed publications and conference presentations.

TRIAL REGISTRATION NUMBER

PROSPERO (CRD42014009212).

Pharmacological management of chronic neuropathic pain: revised consensus statement from the Canadian Pain Society

BACKGROUND

Neuropathic pain (NeP), redefined as pain caused by a lesion or a disease of the somatosensory system, is a disabling condition that affects approximately two million Canadians.

OBJECTIVE

To review the randomized controlled trials (RCTs) and systematic reviews related to the pharmacological management of NeP to develop a revised evidence-based consensus statement on its management.

METHODS

RCTs, systematic reviews and existing guidelines on the pharmacological management of NeP were evaluated at a consensus meeting in May 2012 and updated until September 2013. Medications were recommended in the consensus statement if their analgesic efficacy was supported by at least one methodologically sound RCT (class I or class II) showing significant benefit relative to placebo or another relevant control group. Recommendations for treatment were based on the degree of evidence of analgesic efficacy, safety and ease of use.

RESULTS

Analgesic agents recommended for first-line treatments are gabapentinoids (gabapentin and pregabalin), tricyclic antidepressants and serotonin noradrenaline reuptake inhibitors. Tramadol and controlled-release opioid analgesics are recommended as second-line treatments for moderate to severe pain. Cannabinoids are now recommended as third-line treatments. Recommended fourth-line treatments include methadone, anticonvulsants with lesser evidence of efficacy (eg, lamotrigine, lacosamide), tapentadol and botulinum toxin. There is support for some analgesic combinations in selected NeP conditions.

CONCLUSIONS

These guidelines provide an updated, stepwise approach to the pharmacological management of NeP. Treatment should be individualized for each patient based on efficacy, side-effect profile and drug accessibility, including cost. Additional studies are required to examine head-to-head comparisons among analgesics, combinations of analgesics, long-term outcomes and treatment of pediatric, geriatric and central NeP.

Mexiletine as a treatment for primary erythromelalgia: normalization of biophysical properties of mutant L858F NaV 1.7 sodium channels

BACKGROUND AND PURPOSE

The non-selective sodium channel inhibitor mexiletine has been found to be effective in several animal models of chronic pain and has become popular in the clinical setting as an orally available alternative to lidocaine. It remains unclear why patients with monogenic pain disorders secondary to gain-of-function SCN9a mutations benefit from a low systemic concentration of mexiletine, which does not usually induce adverse neurological side effects. The aim of this study was, therefore, to investigate the biophysical effects of mexiletine on the L858F primary erythromelalgia NaV 1.7 mutation in vitro.

EXPERIMENTAL APPROACH

Human wild-type and L858F-mutated NaV 1.7 channels were expressed in HEK293A cells. Whole-cell currents were recorded by voltage-clamp techniques to characterize the effect of mexiletine on channel gating properties.

KEY RESULTS

While the concentration-dependent tonic block of peak currents by mexiletine was similar in wild-type and L858F channels, phasic block was more pronounced in cells transfected with the L858F mutation. Moreover, mexiletine substantially shifted the pathologically-hyperpolarized voltage-dependence of steady-state activation in L858F-mutated channels towards wild-type values and the voltage-dependence of steady-state fast inactivation was shifted to more hyperpolarized potentials, leading to an overall reduction in window currents.

CONCLUSION AND IMPLICATIONS

Mexiletine has a normalizing effect on the pathological gating properties of the L858F gain-of-function mutation in NaV 1.7, which, in part, might explain the beneficial effects of systemic treatment with mexiletine in patients with gain-of-function sodium channel disorders.

Emulsified isoflurane increases convulsive thresholds of lidocaine and produces neural protection after convulsion in rats

BACKGROUND

Local anesthetic-induced convulsions remain a concern of anesthesiologists when performing regional anesthesia. Our previous study found that the lidocaine requirement for IV regional anesthesia was reduced with coadministration of emulsified isoflurane. We designed this study to examine whether emulsified isoflurane could increase the convulsive threshold of lidocaine and produce protection after a lidocaine-induced convulsion.

METHODS

In experiment 1, the median convulsive dose of lidocaine with or without the addition of emulsified isoflurane was determined using the up-and-down method. In experiment 2, emulsified isoflurane (0.032 mL/kg for isoflurane), midazolam (1.6 mg/kg), 30% Intralipid (solvent of emulsified isoflurane) or saline was infused to treat lidocaine-induced convulsions, respectively. Convulsive behavior was scored by the modified Racine scale. Cognitive function and the pathology of hippocampus cornu ammonis 3 pyramid neurons of rats were evaluated on days 1, 3, 5, and 7 after convulsions.

RESULTS

In experiment 1, the median convulsive dose of lidocaine alone producing convulsions was 18.7 ± 2.6 mg/kg, and it was increased to 22.7 ± 2.6 (P = 0.010) and 26.7 ± 2.6 mg/kg (P < 0.001) with coadministration of emulsified isoflurane at doses of 0.016 and 0.032 mL/kg isoflurane, respectively. In experiment 2, both emulsified isoflurane and midazolam significantly suppressed lidocaine-induced tonic-clonic seizures. Rats treated with emulsified isoflurane regained full consciousness (convulsive score = 0) significantly earlier than rats treated with midazolam (8.7 ± 2.4 vs 19.5 ± 3.9 minutes, P < 0.001). Cognitive impairment and hippocampus cornu ammonis 3 pyramid neuron abnormalities were found after convulsions and improved with the administration of both emulsified isoflurane and midazolam.

CONCLUSION

Emulsified isoflurane increased the convulsive threshold of lidocaine and preserved neurological function in rats experiencing lidocaine-induced convulsions.

The Effect of Intravenous Lidocaine on Trigeminal Neuralgia: A Randomized Double Blind Placebo Controlled Trial

Trigeminal neuralgia is the most common neuralgia. Its therapeutic approach is challenging as the first line treatment often does not help, or even causes intolerable side effects. The aim of our randomized double blind, placebo controlled, crossover study was to investigate in a prospective way the effect of lidocaine in patients with trigeminal neuralgia. Twenty patients met our inclusion criteria and completed the study. Each patient underwent four weekly sessions, two of which were with lidocaine (5 mgs/kg) and two with placebo infusions administered over 60 minutes. Intravenous lidocaine was superior regarding the reduction of the intensity of pain, the allodynia, and the hyperalgesia compared to placebo. Moreover, contrary to placebo, lidocaine managed to maintain its therapeutic results for the first 24 hours after intravenous infusion. Although, intravenous lidocaine is not a first line treatment, when first line medications fail to help, pain specialists may try it as an add-on treatment. This trial is registered with NCT01955967.

Effects of various antiepileptics used to alleviate neuropathic pain on compound action potential in frog sciatic nerves: comparison with those of local anesthetics

Antiepileptics used for treating neuropathic pain have various actions including voltage-gated Na(+) and Ca(2+) channels, glutamate-receptor inhibition, and GABA(A)-receptor activation, while local anesthetics are also used to alleviate the pain. It has not been fully examined yet how nerve conduction inhibitions by local anesthetics differ in extent from those by antiepileptics. Fast-conducting compound action potentials (CAPs) were recorded from frog sciatic nerve fibers by using the air-gap method. Antiepileptics (lamotrigine and carbamazepine) concentration dependently reduced the peak amplitude of the CAP (IC50 = 0.44 and 0.50 mM, resp.). Carbamazepine analog oxcarbazepine exhibited an inhibition smaller than that of carbamazepine. Antiepileptic phenytoin (0.1 mM) reduced CAP amplitude by 15%. On the other hand, other antiepileptics (gabapentin, sodium valproate, and topiramate) at 10 mM had no effect on CAPs. The CAPs were inhibited by local anesthetic levobupivacaine (IC50 = 0.23 mM). These results indicate that there is a difference in the extent of nerve conduction inhibition among antiepileptics and that some antiepileptics inhibit nerve conduction with an efficacy similar to that of levobupivacaine or to those of other local anesthetics (lidocaine, ropivacaine, and cocaine) as reported previously. This may serve to know a contribution of nerve conduction inhibition in the antinociception by antiepileptics.

Lidocaine and pain management in the emergency department: a review article

Context:

In the present review, the analgesic effects of lidocaine in acute or chronic painful conditions in the emergency department are discussed. Lidocaine, as a medium-acting local anesthetic with short onset time, is well-recognized, not only as a valuable medication for numerous neuropathic pain conditions, but also for the management of both acute and chronic pain.

Evidence Acquisition:

Research studies related to the different applications of lidocaine in the emergency department were collected from different databases including Cochrane library, Medline (Ovid) and PubMed. The pooled data were categorized, summarized and finally compared.

Results:

Our study revealed that lidocaine is broadly used in various therapeutic approaches for different types of pain, such as visceral/central pain, renal colic etc., in the emergency department.

Conclusions:

The antinociceptive properties of lidocaine are derived from multifaceted mechanisms, turning it into a medication that is safe to administer via different routes which makes it available for use in a variety of medical conditions.

Drug repositioning: playing dirty to kill pain

The number of approved new molecular entity drugs has been decreasing as the pharmaceutical company investment in research and development is increasing. As we face this painful crisis, called an innovation gap, there is increasing awareness that development of new uses of existing drugs may be a powerful tool to help overcome this obstacle because it takes too long, costs too much and can be risky to release drugs developed de novo. Consequently, drug repositioning is emerging in different therapeutic areas, including the pain research area. Worldwide, pain is the main reason for seeking healthcare, and pain relief represents an unmet global clinical need. Therefore, development of analgesics with better efficacy, safety and cost effectiveness is of paramount importance. Despite the remarkable advancement in research on cellular and molecular mechanisms underlying pain pathophysiology over the past three decades, target-based therapeutic opportunities have not been pursued to the same extent. Phenotypic screening remains a more powerful tool for drug development than target-based screening so far. It sounds somewhat heretical, but some multi-action drugs, rather than very selective ones, have been developed intentionally. In the present review, we first critically discuss the utility of drug repositioning for analgesic drug development and then show examples of 'old' drugs that have been successfully repositioned or that are under investigation for their analgesic actions. We conclude that drug repositioning should be more strongly encouraged to help build a bridge between basic research and pain relief worldwide.

Subunit and frequency-dependent inhibition of acid sensing ion channels by local anesthetic tetracaine

BACKGROUND

Extracellular acidosis is a prominent feature of multiple pathological conditions, correlating with pain sensation. Acid-sensing ion channels (ASICs), a family of proton-gated cation channels, are distributed throughout the central and peripheral nervous systems. Activation of ASICs, particularly ASIC3 and ASIC1a channels, by acidic pH and the resultant depolarization of nociceptive primary sensory neurons, participates in nociception. Agents that inhibit the activation of ASICs are thus expected to be analgesic. Here, we studied the effect of local anesthetic tetracaine on ASIC currents.

RESULTS

Tetracaine inhibited the peak ASIC3 current in a concentration-dependent manner with an IC50 of 9.96 ± 1.88 mM. The degree of inhibition by tetracaine was dependent on the extracellular pH but independent of the membrane potential. Furthermore, 3 mM tetracaine also inhibited 29.83% of the sustained ASIC3 current. In addition to ASIC3, tetracaine inhibited the ASIC1a and ASIC1β currents. The inhibition of the ASIC1a current was influenced by the frequency of channel activation. In contrast to ASIC3, ASIC1a, and ASIC1β currents, ASIC2a current was not inhibited by tetracaine. In cultured mouse dorsal root ganglion neurons, 1-3 mM tetracaine inhibited both the transient and sustained ASIC currents. At pH4.5, 3 mM tetracaine reduced the peak ASIC current to 60.06 ± 4.51%, and the sustained current to 48.24 ± 7.02% of the control values in dorsal root ganglion neurons. In contrast to ASICs, voltage-gated sodium channels were inhibited by acid, with 55.15% inhibition at pH6.0 and complete inhibition at pH5.0.

CONCLUSIONS

These findings disclose a potential new mechanism underlying the analgesic effects of local anesthetics, particularly in acidic conditions where their primary target (i.e. voltage-gated Na+ channel) has been suppressed by protons.

Predictive value of lidocaine for treatment success of oxcarbazepine in patients with neuropathic pain syndrome

Introduction

Pharmacotherapy in patients with neuropathic pain syndromes (NPS) can be associated with long periods of trial and error before reaching satisfactory analgesia. The aim of this study was to investigate whether a short intravenous (i.v.) infusion of lidocaine may have a predictive value for the efficacy of oxcarbazepine.

Methods

In total, 16 consecutive patients with NPS were studied in a prospective, uncontrolled, open-label study design. Each patient received i.v. lidocaine (5 mg/kg) within 30 min followed by a long-term oral oxcarbazepine treatment (900–1,500 mg/day). During an observation period of 28 days, treatment response was documented by a questionnaire including the average daily pain score documented on a numeric rating scale (NRS).

Results

A total of 6 out of 16 patients (38%) were lidocaine responders (defined as pain reduction >50% during the infusion), and 4 of 16 (25%) were oxcarbazepine responders. In total, 6 out of 16 participants (38%) discontinued oxcarbazepine treatment due to side effects. In an interim analysis predictive value of the lidocaine infusion was low with a Kendall’s tau correlation coefficient of 0.29 and coefficient of determination R² of 0.119 (95% confidence interval –0.29 to 0.72). As a consequence of this low correlation, the study was discontinued for ethical reasons.

Conclusion

In conclusion, lidocaine infusion has a low predictive value for effectiveness of oxcarbazepine—if at all.

Lidocaine patch (5%) is no more potent than placebo in treating chronic back pain when tested in a randomised double blind placebo controlled brain imaging study

Background

The 5% Lidocaine patch is used for treating chronic neuropathic pain conditions such as chronic back pain (CBP), diabetic neuropathy and complex regional pain syndrome, but is effective in a variable proportion of patients. Our lab has reported that this treatment reduces CBP intensity and associated brain activations when tested in an open labelled preliminary study. Notably, effectiveness of the 5% Lidocaine patch has not been tested against placebo for treating CBP. In this study, effectiveness of the 5% Lidocaine patch was compared with placebo in 30 CBP patients in a randomised double-blind study where 15 patients received 5% Lidocaine patches and the remaining patients received placebo patches. Functional MRI was used to identify brain activity for fluctuations of spontaneous pain, at baseline and at two time points after start of treatment (6 hours and 2 weeks).

Results

There was no significant difference between the treatment groups in either pain intensity, sensory and affective qualities of pain or in pain related brain activation at any time point. However, 50% patients in both the Lidocaine and placebo arms reported a greater than 50% decrease in pain suggesting a marked placebo effect. When tested against an untreated CBP group at similar time points, the patch treated subjects showed significantly greater decrease in pain compared to the untreated group (n = 15).

Conclusions

These findings suggest that although the 5% Lidocaine is not better than placebo in its effectiveness for treating pain, the patch itself induces a potent placebo effect in a significant proportion of CBP patients.

Effect of intravenous lidocaine on the neuropathic pain of failed back surgery syndrome

BACKGROUND

An intravenous infusion of lidocaine has been used on numerous occasions to produce analgesia in neuropathic pain. In the cases of failed back surgery syndrom, the pain generated as result of abnormal impulse from the dorsal root ganglion and spinal cord, for instance as a result of nerve injury may be particularly sensitive to lidocaine. The aim of the present study was to identify the effects of IV lidocaine on neuropathic pain items of FBSS.

METHODS

The study was a randomized, prospective, double-blinded, crossover study involving eighteen patients with failed back surgery syndrome. The treatments were: 0.9% normal saline, lidocaine 1 mg/kg in 500 ml normal saline, and lidocaine 5 mg/kg in 500 ml normal saline over 60 minutes. The patients underwent infusions on three different appointments, at least two weeks apart. Thus all patients received all 3 treatments. Pain measurement was taken by visual analogue scale (VAS), and neuropathic pain questionnaire.

RESULTS

Both lidocaine (1 mg/kg, 5 mg/kg) and placebo significantly reduced the intense, sharp, hot, dull, cold, sensitivity, itchy, unpleasant, deep and superficial of pain. The amount of change was not significantly different among either of the lidocaine and placebo, or among the lidocaine treatments themselves, for any of the pain responses, except sharp, dull, cold, unpleasant, and deep pain. And VAS was decreased during infusion in all 3 group and there were no difference among groups.

CONCLUSIONS

This study shows that 1 mg/kg, or 5 mg/kg of IV lidocaine, and palcebo was effective in patients with neuropathic pain attributable to FBSS, but effect of licoaine did not differ from placebo saline.

Combination Drug Therapy for Pain following Chronic Spinal Cord Injury

A number of mechanisms have been elucidated that maintain neuropathic pain due to spinal cord injury (SCI). While target-based therapeutics are being developed based on elucidation of these mechanisms, treatment for neuropathic SCI pain has not been entirely satisfactory due in part to the significant convergence of neurological and inflammatory processes that maintain the neuropathic pain state. Thus, a combination drug treatment strategy, wherein several pain-related mechanism are simultaneously engaged, could be more efficacious than treatment against individual mechanisms alone. Also, by engaging several targets at once, it may be possible to reduce the doses of the individual drugs, thereby minimizing the potential for adverse side effects. Positive preclinical and clinical studies have demonstrated improved efficacy of combination drug treatment over single drug treatment in neuropathic pain of peripheral origin, and perhaps such combinations could be utilized for neuropathic SCI pain. At the same time, there are mechanisms that distinguish SCI from peripheral neuropathic pain, so novel combination therapies will be needed.

Continuous intravenous infusion of ketamine and lidocaine as adjuvant analgesics in a 5-year-old patient with neuropathic cancer pain

For difficult to treat neuropathic pain from cancer, adjuvant analgesics are often used with opioids. We present the case of a 5-year-old girl who was diagnosed with meningitis caused by malignant T-cell lymphoma. She had severe neuropathic pain not relieved by increasing doses of a fentanyl infusion. Intravenous administration of ketamine and lidocaine in combination with fentanyl provided excellent analgesia without significant side effects. Ketamine and lidocaine can be safely infused together with concomitant opioids for the treatment of refractory neuropathic pain caused by cancer.

Mechanisms of neuropathic pain

Neuropathic pain is a disease of global burden. Its symptoms include spontaneous and stimulus-evoked painful sensations. Several maladaptive mechanisms underlying these symptoms have been elucidated in recent years: peripheral sensitization of nociception, abnormal excitability of afferent neurons, central sensitization comprising pronociceptive facilitation, disinhibition of nociception and central reorganization processes, and sympathetically maintained pain. This review aims to illustrate these pathophysiological principles, focussing on molecular and neurophysiological findings. Finally therapeutic options based on these findings are discussed.

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

OBJECTIVE

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

DATA SOURCES

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

STUDY SELECTION AND DATA EXTRACTION

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

DATA SYNTHESIS

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

CONCLUSIONS

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

Different pathophysiology underlying animal models of fibromyalgia and neuropathic pain: comparison of reserpine-induced myalgia and chronic constriction injury rats

The reserpine-induced myalgia (RIM) rat manifests fibromyalgia-like chronic pain symptoms. The present study explored the pathophysiology underlying the pain symptoms in the RIM rat and the chronic constriction injury (CCI) rat, an animal model of neuropathic pain as a reference. Nerve tissue samples were collected from the nociception-tested animals for pathological examinations. Additionally, the therapeutic efficacy of a sodium channel blocker mexiletine was assessed in both rats. A slight vacuolization in the substantia nigra (SN) occurred in some of the RIM rats without any other histopathological changes in the brain or peripheral neurons. All the RIM rats, with or without vacuolization, showed hypersensitivity to tactile, muscle pressure, and cold stimuli. In the CCI rat, neurodegenerative changes were apparent in the sciatic nerve and the spinal cord only. CCI rats displayed muscle hyperalgesia in addition to tactile and cold allodynia. Pharmacotherapy with mexiletine did not attenuate the pain in the RIM rat, although it was effective in the CCI rat. Taken together, it is not likely that pain symptoms in RIM rats are caused by degenerative changes at the level of primary afferents and spinal cord, as is the case for CCI rats. The significance of the vacuolization in the SN is less clear at present because of the minor extent of the change and the lack of correlation with nociceptive sensitivity. The pain symptoms in RIM rats could be associated with dysfunction of biogenic amines-mediated CNS pain control even without apparent pathologies in the nervous system.

Lidocaine attenuates the development of diabetic-induced tactile allodynia by inhibiting microglial activation

BACKGROUND

Lidocaine is used clinically for tactile allodynia associated with diabetes-induced neuropathy. Although the analgesic effect of lidocaine through suppression of microglial activation has been implicated in the development of injury-induced neuropathic pain, its mechanism of action in diabetes-induced tactile allodynia has not yet been completely elucidated.

METHODS

To evaluate the effects of lidocaine on microglial response in diabetic neuropathy, streptozotocin (STZ)-injected mice received a continuous infusion of lidocaine (vehicle, 2, or 10%) from day 14 to day 21 after STZ injection. On day 21, microglial accumulation and p38 mitogen-activated protein kinase activation in the dorsal horn were evaluated. In vitro, the effects of lidocaine on cell viability, chemotactic response to monocyte chemotactic protein-1, and induction of proinflammatory mediators were examined in interferon (IFN)-γ-stimulated primary microglial cells.

RESULTS

Continuous systemic administration of lidocaine in the early progression of tactile allodynia produced long-lasting analgesic effects in STZ-treated mice. Lidocaine significantly reduced accumulation and p38 phosphorylation of microglial cells in the dorsal horn. In vitro, lidocaine down-regulated IFN-γ-induced gene induction of inducible oxide synthase and interleukin-1β. Pretreatment with lidocaine significantly reduced chemotactic response to monocyte chemotactic protein-1 of IFN-γ-activated microglial cells.

CONCLUSION

Lidocaine alleviates STZ-induced tactile allodynia, possibly by modulating the p38 pathway in spinal microglial cells. Inhibiting microglial activation by lidocaine treatment early in the course of diabetes-induced neuropathy represents a potential therapeutic strategy for tactile allodynia.

Intravenous lidocaine and mexiletine in the management of trigeminal autonomic cephalalgias

Lidocaine and mexiletine are class 1B antiarrhythmic drugs that act on sodium channels. Lidocaine is also an important anesthetic and topical agent that is useful in the treatment of multiple pain disorders, and mexiletine is commonly used for neuropathic pain and myotonia. Both intravenous lidocaine and mexiletine are increasingly used to treat pain syndromes and appear to be particularly effective in neuropathic pain. This suggests a role for these agents in patients with headache disorders. This article describes the role of intravenous lidocaine and mexiletine in the management of headache and trigeminal autonomic cephalalgias based on the published literature to date and provides practical guidelines for their use.

A role for intravenous lidocaine in severe cancer-related neuropathic pain at the end-of-life

BACKGROUND

Systemic administration of lidocaine has been widely reported to provide effective analgesia in both cancer and non-malignant pain.

CASE REPORT

We report the use of intravenous lidocaine in the management of cancer-related neuropathic pain and its pivotal role in restoring function and facilitating end-of-life care at home.

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

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

The development of new analgesics over the past 50 years: a lack of real breakthrough drugs

Fifty-nine drugs identified as analgesics were introduced from 1960 to 2009 and remain in use. Seven can be regarded as having novel molecular targets; however, only one, sumatriptan, was sufficiently effective to motivate the introduction of many similar drugs acting at the same target (triptans). Publication productivity in the area of pain grew exponentially during this period. Pain-related publications on morphine were dominant among other analgesics. Very intensive research efforts directed at diverse molecular targets related to pain mechanisms produced thousands of publications, but those efforts have not yet yielded new analgesics with sufficient effectiveness to change the share of publications on opioids or nonsteroidal antiinflammatory drugs. Morphine and aspirin, introduced for the treatment of pain more than a century ago, continue to dominate biomedical publications despite their limited effectiveness in many areas (e.g., neuropathic pain) and multiple serious adverse effects. The present assessment reveals the lack of real breakthroughs in analgesic drug development despite intense research efforts. Possible factors contributing to the apparent drought of novel analgesics are discussed.

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.

Efficacy of a metered-dose 8% lidocaine pump spray for patients with post-herpetic neuralgia

OBJECTIVE

Topical lidocaine patch is effective in the treatment of post-herpetic neuralgia (PHN), but not suited for paroxysmal pain because of the long latency of analgesia. Here, we examined the efficacy of 8% lidocaine pump spray (Xylocaine pump spray, XPS) for PHN.

DESIGN

Twenty-four patients with PHN were recruited into a randomized, double-blind, placebo-controlled, crossover study (study 1), and 100 patients with PHN were recruited into an open-labeled study (study 2). In study 1, patients were randomized to receive either XPS or saline placebo pump spray (PPS) applied to the painful skin areas. Following a 7-day period, patients were crossed over to receive the alternative treatment. In study 2, XPS was prescribed for patients who were advised to use the spray anytime, with a 2-hour gap between applications, for 2 weeks. The pain was assessed with a visual analogue scale (VAS). Details of use were noted in the diary.

RESULTS

In study 1, greater decreases in VAS of persistent pain followed application of XPS (baseline: 6.1 +/- 1.7 cm, 15-minute post-spray: 2.3 +/- 2.5 cm, mean +/- SD) than with PPS (6.1 +/- 1.7 cm, 5.7 +/- 1.6 cm, [P < 0.01]). The effect persisted for a median of 4.5 hours (range, 2 to 24 hours) after application. In study 2, 13 of 100 patients discontinued the treatment because of mild local side effects or insufficient effect. In the remaining 87 patients, XPS maintained significant pain relief relative to baseline throughout the 2-week period. Satisfaction with the therapy was reported by 79% of patients.

CONCLUSIONS

In both studies, XPS provided a significant improvement in PHN due to its prompt analgesia, lack of systemic side effects, and convenience of use.

Axonal ion channels from bench to bedside: a translational neuroscience perspective

Over recent decades, the development of specialised techniques such as patch clamping and site-directed mutagenesis have established the contribution of neuronal ion channel dysfunction to the pathophysiology of common neurological conditions including epilepsy, multiple sclerosis, spinal cord injury, peripheral neuropathy, episodic ataxia, amyotrophic lateral sclerosis and neuropathic pain. Recently, these insights from in vitro studies have been translated into the clinical realm. In keeping with this progress, novel clinical axonal excitability techniques have been developed to provide information related to the activity of a variety of ion channels, energy-dependent pumps and ion exchange processes activated during impulse conduction in peripheral axons. These non-invasive techniques have been extensively applied to the study of the biophysical properties of human peripheral nerves in vivo and have provided important insights into axonal ion channel function in health and disease. This review will provide a translational perspective, focusing on an overview of the investigational method, the clinical utility in assessing the biophysical basis of ectopic symptom generation in peripheral nerve disease and a review of the major findings of excitability studies in acquired and inherited neurological disease states.

Effects of amitriptyline, a tricyclic antidepressant, on smooth muscle reactivity in isolated rat trachea

PURPOSE

This study was designed to investigate the action of amitriptyline, a tricyclic antidepressant, on airway smooth muscle reactivity and its underlying mechanisms.

METHODS

In isolated rat trachea, isometric force was recorded to examine the effects of amitriptyline on the contractile response to acetylcholine (ACh), electrical field stimulation (EFS), calyculin A (a myosin light chain phosphatase inhibitor), and sphingosylphosphorylcholine (SPC; a Rhokinase activator). In addition, inositol monophosphate (IP1) accumulation was measured to examine its effects on inositol 1, 4, 5-trisphosphate (IP(3)) production during stimulation with ACh.

RESULTS

Amitriptyline inhibited the contractile responses to ACh, EFS, calyculin A, and SPC, with the concentrations of amitriptyline (mean +/- SD) required to exert 50% inhibition (IC(50)) being 4.3 +/- 1.3 microM, 3.2 +/- 1.6 microM, 256.4 +/- 106.4 microM, and 98.2 +/- 21.8 microM, respectively. In addition, amitriptyline (10 microM) eliminated the ACh (10 microM)-induced IP(1) accumulation.

CONCLUSION

The results suggest that amitriptyline does not influence tracheal smooth muscle reactivity at clinical concentrations (<1 microM), but attenuates the reactivity at supraclinical concentrations (> or =1 microM). The attenuated response to ACh brought about by amitriptyline is presumably due, at least in part, to the inhibition of phosphatidylinositol (PI) metabolism. The ability of amitriptyline to inhibit the calyculin Ainduced contraction suggests that amitriptyline also inhibits the Ca(2+)-calmodulin-myosin light chain pathway independently of the inhibition of PI metabolism. Finally, the difference between the IC(50) values for SPC-induced contraction and those for calyculin A-induced contraction suggests that amitriptyline may also inhibit the Rho-kinase pathway.