Lignocaine selectively reduces C fibre-evoked neuronal activity in rat spinal cord in vitro by decreasing N-methyl-D-aspartate and neurokinin receptor-mediated post-synaptic depolarizations; implications for the development of novel centrally acting analgesics

Intravenous Lidocaine for Treatment of Chronic Pain: A Retrospective Cohort Study

Introduction

Neuropathic pain is a widespread problem with a big impact on quality of life. The currently used drug regimens are often insufficiently effective or cause - sometimes unacceptable - side effects. Intravenous lidocaine could be an alternative treatment, by blocking spontaneous depolarization and hyperexcitability in upregulated sodium channels in nociceptors. Research so far has shown varying results but the treatment protocols differed a lot and follow-up was usually short. In our hospital, lidocaine infusions have been applied for many years in a unique treatment protocol consisting of a relatively high dose of lidocaine (1000 mg) administered over 25 hours. Our aim is to share information on both the efficacy and safety of this treatment schedule.

Methods

We conducted a retrospective cohort study in all patients who received a lidocaine infusion between January 2014 and January 2018. The standard infusion protocol consists of a total of 1000 mg lidocaine administered intravenously during 25 hours (40 mg/hour). Pain diagnoses were stratified into 15 groups, in agreement with diagnoses used in daily practice. Effectiveness of the treatment was classified as effect or no effect based on the description found in the chart.

Results

We included 282 patients, with a median age of 58 years and 64% of whom were female. Patients with myofascial pain syndrome, peripheral (mono)neuropathy, small fiber neuropathy and vascular disease benefited most. Patients with cancer pain, postherpetic neuralgia, chemotherapy-induced neuropathy and radicular pain showed the least pain improvement. There were no serious adverse events.

Conclusion

In selected patients, lidocaine infusions may be a safe and efficacious treatment for chronic neuropathic pain. More prospective research is needed to further determine the optimal dosing, duration and interval of lidocaine infusion therapy, and to better understand in which specific patient categories this treatment is most beneficial.

Phase 1 study to access safety, tolerability, pharmacokinetics, and pharmacodynamics of kynurenine in healthy volunteers

The kynurenine pathway (KP) is the main path for tryptophan metabolism, and it represents a multitude of potential sites for drug discovery in neuroscience, including pain, stroke, and epilepsy. L‐kynurenine (LKYN), the first active metabolite in the pathway, emerges to be a prodrug targeting glutamate receptors. The safety, tolerability, pharmacokinetics, and pharmacodynamics of LKYN in humans have not been previously investigated. In an open‐label, single ascending dose study, six participants received an intravenous infusion of 50, 100, and 150 µg/kg LKYN and new six participants received an intravenous infusion of 0.3, 0.5, 1, and 5 mg/kg LKYN. To compare the pharmacological effects between species, we investigated in vivo the vascular effects of LKYN in rats. In humans, LKYN was safe and well‐tolerated at all dose levels examined. After infusion, LKYN plasma concentration increased significantly over time 3.23 ± 1.12 µg/mL (after 50 µg/kg), 4.04 ± 1.1 µg/mL (after 100 µg/kg), and 5.25 ± 1.01 µg/mL (after 150 µg/kg) (p ≤ 0.001). We observed no vascular changes after infusion compared with baseline. In rats, LKYN had no effect on HR and MAP and caused no dilation of dural and pial arteries. This first‐in‐human study of LKYN showed that LKYN was safe and well‐tolerated after intravenous infusion up to 5 mg/kg over 20 minutes. The lack of change in LKYN metabolites in plasma suggests a relatively slow metabolism of LKYN and no or little feed‐back effect of LKYN on its synthesis. The therapeutic potential of LKYN in stroke and epilepsy should be explored in future studies in humans.

Effects of fentanyl-lidocaine-ketamine versus sufentanil-lidocaine-ketamine on the isoflurane requirements in dogs undergoing total ear canal ablation and lateral bulla osteotomy

OBJECTIVE

To compare the isoflurane-sparing effects of sufentanil-lidocaine-ketamine (SLK) and fentanyl-lidocaine-ketamine (FLK) infusions in dogs undergoing total ear canal ablation and lateral bulla osteotomy (TECA-LBO).

STUDY DESIGN

Randomized blinded clinical study.

ANIMALS

A group of 20 client-owned dogs undergoing TECA-LBO.

METHODS

Intravenous (IV) administration of lidocaine (3 mg kg^-1) and ketamine (0.6 mg kg^-1) with fentanyl (5.4 μg kg^-1; n = 10; FLK group) or sufentanil (0.72 μg kg^-1; n = 10; SLK group) was immediately followed by the corresponding constant rate infusion (CRI) (lidocaine 3 mg kg^-1 hour^-1; ketamine 0.6 mg kg^-1 hour^-1; either fentanyl 5.4 μg kg^-1 hour^-1 or sufentanil 0.72 μg kg^-1 hour^-1). Anaesthesia was induced with propofol 3-5 mg kg^-1 IV and was maintained with isoflurane. End-tidal isoflurane concentration (Fe'Iso) was decreased in 0.2% steps every 15 minutes until spontaneous movements were observed (treated with propofol 1 mg kg^-1 IV) or an increase of > 30% in heart rate or mean arterial pressure from baseline occurred (treated with rescue fentanyl or sufentanil). Quality of recovery and pain were assessed at extubation using the short-form Glasgow Composite Pain Scale (SF-GCPS), Colorado State University Canine Acute Pain scale (CSU-CAP), and visual analogue scale (VAS). Data were analysed with analysis of variance, t tests, Fisher test and Spearman coefficient (p < 0.05).

RESULTS

Fe'Iso decreased significantly in SLK group (45%; p = 0.0006) but not in FLK (15%; p = 0.1135) (p = 0.0136). SLK group had lower scores for recovery quality (p = 0.0204), SF-GCPS (p = 0.0071) and CSU-CAP (p = 0.0273) than FLK at extubation. Intraoperative rescue analgesia and VAS were not significantly different between groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Compared with FLK infusion, CRI of SLK at these doses decreased isoflurane requirements, decreased pain scores and improved recovery quality at extubation in dogs undergoing TECA-LBO.

The Analgesic and Emotional Response to Intravenous Lidocaine Infusion in the Treatment of Postherpetic Neuralgia: A Randomized, Double-Blinded, Placebo-controlled Study

OBJECTIVES

This study evaluated the analgesic efficacy and emotional response to intravenous lidocaine infusion compared with placebo in patients with postherpetic neuralgia (PHN).

METHODS

In this randomized, double-blinded study, patients with PHN received 5 mg/kg intravenous lidocaine infusion or placebo. The primary outcome was pain measured by Visual Analogue Scale, Von Frey, and area of allodynia. Moreover, emotional status of anxiety and depression were evaluated by Self-rating Anxiety Scale (SAS) and Self-rating Depression Scale (SDS). Quality of life was assessed by Short Form Health Survey 36.

RESULTS

In total, 197 patients were enrolled and eligible data were collected from 183 of those patients. The Visual Analogue Scale scores were reduced to a minimum at 2 weeks (2.74, 2.99) after infusion, but no significant difference was found between the lidocaine and placebo groups. Similar changes were also found in mechanical pain threshold and area of allodynia. However, the lidocaine group was associated with a statistically significant reduction in consumption of analgesics with a relative risk of 6.2 (95% confidence interval [CI], 2.24-17.16). Lidocaine infusion also significantly improved the anxiety and depression status; the values of mean change in anxiety and depression were 3.89 (95% CI, 1.43-6.35) and 4.3 (95% CI, 0.63-7.98), respectively, at 2 weeks. Moreover, improvement was exhibited in Short Form Health Survey 36 health status, with the mean change of 49.81 (95% CI, 28.17-71.46) at 1 week, in particular scores on vitality, physical and emotional role functioning, and mental health.

CONCLUSIONS

The analgesic response of 5 mg/kg lidocaine intravenous infusion is comparable to placebo in patients with PHN, but intravenous lidocaine infusion significantly reduced total analgesic consumption, and improved the overall emotional and health status.

A systematic review of rescue analgesic strategies in acute exacerbations of primary trigeminal neuralgia

BACKGROUND

Trigeminal neuralgia (TN) can have a significant impact on wellbeing and quality of life. Limited data exist for treatments that improve TN pain acutely, within 24 h of administration. This systematic review aims to identify effective treatments that acutely relieve TN exacerbations.

METHODS

We searched Medline and Cochrane Central Register of Controlled Trials (CENTRAL) for relevant English language publications. The reference list for all articles was searched for other relevant publications. All studies that satisfied the following PICO criteria were included: (i) Population-adults with acute exacerbation of primary TN symptoms; (ii) Intervention-any medication or intervention with the primary goal of pain relief within 24 h; (iii) Comparator-usual medical care, placebo, sham or active treatment; (iv) Outcome-more than 50% reduction in pain intensity within 24 h of administration.

RESULTS

Of 431 studies, 17 studies were identified that reported immediate results of acute treatment in TN. The evidence suggests that the following interventions may be beneficial: local anaesthetic, mainly lidocaine (ophthalmic, nasal or oral mucosa, trigger point injection, i.v. infusion, nerve block); anticonvulsant, phenytoin or fosphenytoin (i.v. infusion); serotonin agonist, sumatriptan (s.c. injection, nasal). Other referenced interventions with very limited evidence include N-methyl-d-aspartate receptor antagonist (magnesium sulphate infusion) and botulinum toxin (trigger point injection).

CONCLUSIONS

Several treatment options exist that may provide fast and safe relief of TN. Future studies should report on outcomes within 24 h to improve knowledge of the acute analgesic TN treatments.

Evaluation of lignocaine infusion on recovery profile, quality of recovery, and postoperative analgesia in patients undergoing total abdominal hysterectomy

Background and Aims:

Multimodal analgesia entrains the use of drugs in perioperative period producing adequate pain relief without affecting the quality of recovery by decreasing drug-related adverse effects. Systemic lignocaine has effective analgesic, anti-inflammatory, and anti-hyperalgesic properties and improves the quality of recovery after surgery.

Material and Methods:

Ninety women scheduled for elective transabdominal hysterectomy under general anesthesia were randomized to receive infusion of lignocaine (1.5 mg/kg over 15 min followed by a 2 mg/kg/h infusion until the end of surgery) (Group 1) or normal saline (10 mL over 15 min followed by infusion 1 mL/kg/h till end of surgery) (Group 2). Standard anesthesia techniques were used in both the groups. The patients received inj. tramadol for postoperative analgesia. Perioperative hemodynamics, extubation variables, postoperative analgesic requirement, and quality of recovery score were evaluated.

Results:

Hemodynamics were maintained in both the groups. Time for extubation was also similar. Demand for first postoperative analgesic was after 70.8 ± 70.4 min (Group 1) and 40.7 ± 30.0 min (Group 2) (P = 0.006). Total tramadol usage was 477.0 ± 133.2 mg (Group 1) and 560.0 ± 115.0 mg (Group 2) (P < 0.001). Return of bowel function was faster in Group 2 compared with Group 1 (37.1 ± 5 vs 41.8 ± 7.4 h, P < 0.001). The median (interquartile range) recovery score (QoR-40) was 184 (178–191) in Group 1 and 178 (171–180) in Group 2 (P < 0.001).

Conclusion:

Perioperative use of intravenous infusion of lignocaine is associated with decreased analgesic requirement postoperatively, and improved quality of recovery score signifying greater patient satisfaction.

Lidocaine Infusion: A Promising Therapeutic Approach for Chronic Pain

Opioid abuse is a national epidemic in the United States, where it is estimated that a prescription drug overdose death occurs every 19 minutes. While opioids are highly effective in acute and subacute pain control, their use for treatment of chronic pain is controversial. Chronic opioids use is associated with tolerance, dependency, hyperalgesia. Although there are new strategies and practice guidelines to reduce opioid dependence and opioid prescription drug overdose, there has been little focus on development of opioid-sparing therapeutic approaches. Lidocaine infusion has been shown to be successful in controlling pain where other agents have failed. The opioid sparing properties of lidocaine infusion added to its analgesic and antihyperalgesic properties make lidocaine infusion a viable option for pain control in opioid dependent patients. In this review, we provide an overview of the opioid abuse epidemic, and we outline current evidence supporting the potential use of lidocaine infusion as an adjuvant therapeutic approach for management of chronic pain.

A comparison between intravenous lidocaine and ketamine on acute and chronic pain after open nephrectomy: A prospective, double-blind, randomized, placebo-controlled study

BACKGROUND

Recently, there has been increasing interest in the use of analgesic adjuncts such as intravenous (IV) ketamine and lidocaine.

OBJECTIVES

To compare the effects of perioperative IV lidocaine and ketamine on morphine requirements, pain scores, quality of recovery, and chronic pain after open nephrectomy.

STUDY DESIGN

A prospective, randomized, placebo-controlled, double-blind trial.

SETTINGS

The study was conducted in Charles Nicolle University Hospital of Tunis.

METHODS

Sixty patients were randomly allocated to receive IV lidocaine: bolus of 1.5 mg/kg at the induction of anesthesia followed by infusion of 1 mg/kg/h intraoperatively and for 24 h postoperatively or ketamine: bolus of 0.15 mg/kg followed by infusion of 0.1 mg/kg/h intraoperatively and for 24 h postoperatively or an equal volume of saline (control group [CG]).

MEASUREMENTS

Morphine consumption, visual analog scale pain scores, time to the first passage of flatus and feces, postoperative nausea and vomiting (PONV), 6-min walk distance (6MWD) at discharge, and the incidence of chronic neuropathic pain using the "Neuropathic Pain Questionnaire" at 3 months.

RESULTS

Ketamine and lidocaine reduced significantly morphine consumption (by about 33% and 42%, respectively) and pain scores compared with the CG (P < 0.001). Lidocaine and ketamine also significantly improved bowel function in comparison to the CG (P < 0.001). Ketamine failed to reduce the incidence of PONV. The 6 MWD increased significantly from a mean ± standard deviation of 27 ± 16.2 m in the CG to 82.3 ± 28 m in the lidocaine group (P < 0.001). Lidocaine, but not ketamine, reduced significantly the development of neuropathic pain at 3 months (P < 0.05).

CONCLUSION

Ketamine and lidocaine are safe and effective adjuvants to decrease opioid consumption and control early pain. We also suggest that lidocaine infusion serves as an interesting alternative to improve the functional walking capacity and prevent chronic neuropathic pain at 3 months after open nephrectomy.

Spinal Reflexes and Windup In Vitro: Effects of Analgesics and Anesthetics

The spinal cord is the first relay center for nociceptive information. Following peripheral injury, the spinal cord sensitizes. A sign of spinal sensitization is the hyper-reflexia which develops shortly after injury and can be detected in the isolated spinal cord as a "memory of pain." In this context, it is easy to understand that many analgesic compounds target spinally located sites of action to attain analgesia. In vitro isolated spinal cord preparations have been used for a number of years, and experience on the effects of compounds of diverse pharmacological families on spinal function has accumulated. Recently, we have proposed that the detailed study of spinal segmental reflexes in vitro may produce data relevant to the evaluation of the analgesic potential of novel compounds. In this review, we describe the main features of segmental reflexes obtained in vitro and discuss the effects of compounds of diverse chemical nature and pharmacological properties on such reflexes. Our aim was to compare the different profiles of action of the compounds on segmental reflexes in order to extract clues that may be helpful for pharmacological characterization of novel analgesics.

Durability of Benefit From Repeated Intravenous Lidocaine Infusions in Fibromyalgia Patients: A Case Series and Literature Review

Fibromyalgia is a painful disorder with no curative treatments, and available medications typically provide partial relief of pain. Reported here is the effective use of serial intravenous lidocaine infusions for the chronic management of 3 patients with fibromyalgia. The details of the infusion procedure are described, and relevant literature is reviewed. Lidocaine infusions should be considered in fibromyalgia patients who are refractory to other treatments, and a positive response to 1 infusion may justify repeated infusions for chronic management.

Pharmacokinetics and pharmacodynamics of lignocaine: A review

Lignocaine is an essential drug on World Health Organisation essential drug list, considered efficacious, safe and cost-effective for any health-care system. Despite its ubiquitous use in medicine and surgery, there are few detailed reviews of its pharmacokinetics and pharmacodynamics. Being an amide-type local anesthetic and Class 1b antiarrhythmic, lignocaine is most frequently used clinically for its anesthetic and antiarrhythmic benefits. However, lignocaine has important antinociceptive, immuno-modulating, and anti-inflammatory properties. Information pertaining to the pharmacokinetics and pharmacodynamics of lignocaine was examined by performing a literature search of PubMed, Embase and MEDLINE (via Ovid), pharmacology textbooks and online sources. We present a focused synopsis of lignocaine’s pharmacological composition, indications for use and mechanisms of action, focusing on its anti-inflammatory, immuno-modulating and analgesia effects. In addition we review the dosing regimes and infusion kinetics of lignocaine in the clinical setting. Finally, we review the evidence for ligocaine’s modulation of the inflammatory response during major surgery and its specific effects on cancer recurrence. These indirect effects of local anesthetics in tumor development may stem from the reduction of neuroendocrine responses to the stress response elicited by major surgery and tissue damage, enhanced preservation of immune-competence, in addition to opioid-sparing effects of modulating tumor growth.

Analgesic comparison of systemic lidocaine, morphine or lidocaine plus morphine infusion in dogs undergoing fracture repair

PURPOSE

To compare the postoperative analgesic effects of lidocaine, morphine and lidocaine plus morphine administered by constant rate infusion (CRI) and analyzing their effects on opioid requirements after orthopedic surgery in dogs.

METHODS

Twenty-four dogs underwent fracture repairs were premedicated with IM acepromazine (0.05 mg/kg) combined with morphine (0.3mg/kg). Anesthesia was induced with IV propofol (4 to 5 mg/ kg) and maintained with isoflurane. The dogs were randomly assigned to 3 groups and administered a CRI IV of lidocaine (T-L), morphine (T-M) or lidocaine plus morphine (T-LM) at the same doses. Postoperative analgesia was assessed for 24 hours using a Visual Analog Scale (VAS) and the Glasgow Composite Pain Scale (GCPS). Rescue analgesia was performed if the evaluation score exceeded 50% of the VAS and/or 33% of the GCPS.

RESULTS

The pain score and postoperative opioid requirements did not differ among the treatments. Rescue analgesia was administered to 1/8 dogs in the T-M and T-LM, and to 3/8 dogs in the T-L.

CONCLUSION

Lidocaine, morphine or lidocaine/morphine CRI may be efficacious techniques for pain management in the first 24 hours post-surgery. However, the two drugs administered together did not reduce the postoperative opioid requirement in dogs undergoing fracture repair. Key words: Anesthesia. Analgesics. Analgesics, Opioid. Lidocaine. Morphine. Dogs.

Benefits of intravenous lidocaine on post-operative pain and acute rehabilitation after laparoscopic nephrectomy

BACKGROUND AND AIMS

Intravenous (I.V.) lidocaine has analgesic, antihyperalgesic and anti-inflammatory properties and is known to accelerate the return of bowel function after surgery. We evaluated the effects of I.V. lidocaine on pain management and acute rehabilitation protocol after laparoscopic nephrectomy.

MATERIALS AND METHODS

A total of 47 patients scheduled to undergo laparoscopic nephrectomy were included in a two-phase observational study where I.V. lidocaine (1.5 mg/kg/h) was introduced, in the second phase, during surgery and for 24 h post-operatively. All patients underwent the same post-operative rehabilitation program. Post-operative pain scores, opioid consumption and extent of hyperalgesia were measured. Time to first flatus and 6 min walking test (6MWT) were recorded.

RESULTS

Patient demographics were similar in the two phases (n = 22 in each group). Lidocaine significantly reduced morphine consumption (median [25-75% interquartile range]; 8.5 mg[4567891011121314151617] vs. 25 mg[1920212223242526272829303132]; P < 0.0001), post-operative pain scores (P < 0.05) and hyperalgesia extent on post-operative day 1-day 2-day 4 (mean ± standard deviation (SD); 1.5 ± 0.9 vs. 4.3 ± 1.2 cm (P < 0.001), 0.6 ± 0.5 vs. 2.8 ± 1.2 cm (P < 0.001) and 0.13 ± 0.3 vs. 1.2 ± 1 cm (P < 0.001), respectively). Time to first flatus (mean ± SD; 29 ± 7 h vs. 48 ± 15 h; P < 0.001) and 6MWT at day 4 (189 ± 50 m vs. 151 ± 53 m; P < 0.001) were significantly enhanced in patients with i.v. lidocaine.

CONCLUSION

Intravenous (I.V.) lidocaine could reduce post-operative morphine consumption and improve post-operative pain management and post-operative recovery after laparoscopic nephrectomy. I.V. lidocaine could contribute to better post-operative rehabilitation.

Partial intravenous anaesthesia in the horse: a review of intravenous agents used to supplement equine inhalation anaesthesia. Part 1: lidocaine and ketamine

OBJECTIVE

To review the literature with regard to the use of different intravenous agents as supplements to inhalational anaesthesia in horses. These drugs include lidocaine, ketamine, opioids and α2 -agonists. The Part 1 of this review will focus in the use of lidocaine and ketamine.

DATABASES USED

Pubmed & Web of Science. Search terms: horse, inhalant anaesthesia, balanced anaesthesia, partial intravenous anaesthesia, lidocaine, ketamine.

CONCLUSIONS

Different drugs and their combinations can be administered systemically in anaesthetized horses, with the aim of reducing the amount of the volatile agent whilst improving the recovery qualities and providing a multimodal analgesic approach. However, full studies as to whether these techniques improve cardiopulmonary status are not always available and potential disadvantages should also be considered.

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.

Xenon reduces activation of transient receptor potential vanilloid type 1 (TRPV1) in rat dorsal root ganglion cells and in human TRPV1-expressing HEK293 cells

AIMS

Xenon provides effective analgesia in several pain states at sub-anaesthetic doses. Our aim was to examine whether xenon may mediate its analgesic effect, in part, through reducing the activity of transient receptor potential vanilloid type 1 (TRPV1), a receptor known to be involved in certain inflammatory pain conditions.

MAIN METHODS

We studied the effect of xenon on capsaicin-evoked cobalt uptake in rat cultured primary sensory neurons and in human TRPV1 (hTRPV1)-expressing human embryonic kidney 293 (HEK293) cells. We also examined xenon's effect on the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in the rat spinal dorsal horn evoked by hind-paw injection of capsaicin.

KEY FINDINGS

Xenon (75%) reduced the number of primary sensory neurons responding to the TRPV1 agonist, capsaicin (100 nM-1 μM) by ~25% to ~50%. Xenon reduced the number of heterologously-expressed hTRPV1 activated by 300 nM capsaicin by ~50%. Xenon (80%) reduced by ~40% the number of phosphorylated ERK1/2-expressing neurons in rat spinal dorsal horn resulting from hind-paw capsaicin injection.

SIGNIFICANCE

Xenon substantially reduces the activity of TRPV1 in response to noxious stimulation by the specific TRPV1 agonist, capsaicin, suggesting a possible role for xenon as an adjunct analgesic where hTRPV1 is an active contributor to the excitation of primary afferents which initiates the pain sensation.

Stimulation of dorsal root afferents increases the excitability of ascending sensory axons in the isolated spinal cord of mature mice

The phenomenon of windup has often been used to assess excitability increases of spinal neurons induced by repetitive stimulation of nociceptive afferents. Windup has been studied in individual spinal cord neurons and in spinal motor reflexes neither of which accurately reflect the forward transmission of nociceptive signals to the brain. In addition, most in vitro studies of spinal windup have been conducted on immature or juvenile animals and it is challenging to extrapolate these results to the adult spinal cord. In the present study, we have used an in vitro whole spinal cord preparation from functionally mature mice (up to 8 weeks old) to record windup activity in ascending axons in the mid-thoracic region evoked by electrical stimulation of a lumbar or sacral dorsal root. Windup responses were observed in axons in the ipsi- and contralateral dorsolateral funiculus (iDLF and cDLF) and in the contralateral ventrolateral funiculus (cVLF). No windup responses were evoked in postsynaptic axons of the ipsilateral dorsal columns (iDC) and no postsynaptic responses were elicited in the ipsilateral ventrolateral funiculus (iVLF) or contralateral dorsal columns (cDC). Between 40% and 45% of all axons in the DLF and cVLF that responded to a single dorsal root stimulus also showed windup. The NMDA receptor antagonist MK-801 reversibly blocked such windup responses. These results illustrate that windup can be consistently recorded from ascending pathways in the mature spinal cord in vitro but also show that windup can only be elicited in a proportion of sensory axons projecting through some, but not all, ascending spinal cord pathways.

Developmental changes in threshold, conduction velocity, and depressive action of lignocaine on dorsal root potentials from neonatal rats are associated with maturation of myelination

Conduction velocity of primary afferent fibres and blocking actions of local anaesthetics seem to be developmentally regulated. The current work investigated physiological (threshold, conduction velocity, and myelination) and pharmacological (lignocaine (0.0625 to 2 mmol/L) and capsaicin (2 micromol/L)) ontogenic changes on in vitro sciatic nerve-dorsal root preparations from 0- to 12-day-old rats. As rats aged, stimulus intensities necessary to evoke A-fibre thresholds significantly decreased and A-fibre conduction velocities significantly increased. For C-fibres, thresholds significantly increased and conduction velocities significantly varied with age. The blocking potency of lignocaine varied with age: A-fibres from 4-day-old rats and younger were significantly more resistant than those from older rats, and C-fibres were blocked more uniformly amongst ages. Capsaicin significantly depressed C-fibres irrespective of age, and A-fibres were significantly reduced during the first postnatal week only. Myelination significantly increased as rats aged. A-fibre physiological parameters were significantly correlated with both other A-fibre physiological and pharmacological parameters, but C-fibre parameters were not. Peripheral A-fibre transduction mechanisms seem to require time to acquire their full stimulus-response sensitivity, which coincides with development of myelination. In contrast, peripheral C-fibres seem to have mature transduction mechanisms from the first days of postnatal life.

Frequency-dependent ERK phosphorylation in spinal neurons by electric stimulation of the sciatic nerve and the role in electrophysiological activity

The phosphorylation of extracellular signal-regulated kinase (pERK) in DRG and dorsal horn neurons is induced by the C-fiber electrical stimulation to the peripheral nerve. The present study was designed to investigate the expression and modulation of pERK in the rat dorsal horn neurons produced by repetitive electrical stimulation, and its involvement in the electrophysiological activity of dorsal horn neurons. Electrical stimulation of C-fiber intensity at different frequencies was applied to the sciatic nerve; the stimuli-induced pERK expression and the activity in dorsal horn neurons were studied by immunohistochemistry and extracellular recording, respectively. Electrical stimulation of C-fibers (3 mA) induced pERK expression in dorsal horn neurons in a frequency-dependent manner, indicating that the frequency of electrical stimulation is an important factor which activates the intracellular signal pathway in the spinal cord. To demonstrate the underlying mechanism of this frequency-dependent pERK expression, an NMDA receptor antagonist, MK-801, and a voltage sensitive calcium channel antagonist, nifedipine, were administrated intrathecally before the stimulation. We found that high frequency (0.5 Hz and 10 Hz) but not low frequent (0.05 Hz) stimulus-evoked pERK was partially inhibited by MK-801. Both high and low frequency stimulus-evoked pERK were inhibited by the nifedipine treatment. The extracellular single unit activities were recorded from the laminae I-II and V of the L4-5 dorsal horn, and we found that blockage of the intracellular ERK signal suppressed the wind-up responses in a dose-dependent manner. In contrast, any change in the mechanically evoked responses was not observed following the administration of ERK inhibitor. These observations indicate that ERK activation plays an important role in the induction of the wind-up responses in dorsal horn nociceptive neurons.

A randomized, double-masked, placebo-controlled pilot trial of extended IV lidocaine infusion for relief of ongoing neuropathic pain

OBJECTIVES

To determine the dose-response effect and safety of IV lidocaine at different dose infusion rates on spontaneous ongoing neuropathic pain.

METHODS

In this double-masked, placebo-controlled, parallel study conducted in an outpatient clinical research center, patients with peripheral neuropathic pain received a 6-hour infusion of three doses (1, 3, and 5 mg/kg) of lidocaine or placebo. The main outcome measure was relief of pain intensity (percentage pain intensity difference [PID %]). Other measures were responder rate, adverse events, and correlation between lidocaine levels and PID %.

RESULTS

There was a significant difference in the median PID % between the group treated with lidocaine 5 mg/kg/h (-34.60) and the placebo group (-11.96, P=0.012). Such effect began 4 hours after the onset of treatment and lasted until the end of the study. Lidocaine at lower infusion rates was no better than placebo in relieving pain. A modest but significant correlation was found between methylethylglycinexylidide (MEGX) levels and pain relief (R=0.60). There were no serious adverse events, but in two patients lidocaine was stopped prematurely.

CONCLUSIONS

Lidocaine at 5 mg/kg/h was more effective than placebo at relieving neuropathic pain. The effect started 4 hours after the onset of treatment and continued for at least 4 hours after the end of the infusion. Additional research is needed using higher infusion rates with larger sample sizes to confirm these results and to explore the role of MEGX in the relief of neuropathic pain.

Translating basic research on sodium channels in human neuropathic pain

A number of experimental studies in animals have suggested that voltage-gated sodium channels may play a crucial role in neuropathic pain. However, it is still difficult to translate the pathophysiological mechanisms identified in animal studies to the clinic and several questions regarding the role of sodium channels in neuropathic pain must therefore be addressed primarily in the clinical setting. Despite providing indirect information, pharmacologic challenge using sodium channel blockers, such as some antiepileptics, local anesthetics and derivatives, is the best way to investigate the role of sodium channels in the various clinical symptoms of neuropathies (eg, spontaneous pain, mechanical or thermal allodynia, and hyperalgesia). Randomized controlled trials have demonstrated the efficacy of these compounds for various neuropathic pain conditions. Recent psychophysical studies in which symptoms and signs are more accurately assessed indicate that these compounds act as antihyperalgesic agents rather than as simple analgesics. They also show that the sensitivity to these drugs is not affected by the aetiology of pain and the peripheral or central location of the nerve lesion. These data emphasize the role of peripheral and central sodium channels in neuropathic pain. Studies using more selective sodium channel blockers are required to gain further insight into the role of the various subtypes of sodium channel in these pain conditions.

PERSPECTIVE

Pharmacological challenge using sodium channel blockers is the best way to translate basic research on sodium channels in human neuropathic pain. To date, the role of sodium channels in neuropathic pain symptoms/signs is mostly documented for mechanical static and dynamic allodynia, and either peripheral or central sodium channels may be involved.

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

We reviewed randomized controlled trials to determine the efficacy and safety of systemically administered local anesthetics compared with placebo or active drugs. Of 41 retrieved studies, 27 trials of diverse quality were included in the systematic review. Ten lidocaine and nine mexiletine trials had data suitable for meta-analysis (n = 706 patients total). Lidocaine (most commonly 5 mg/kg IV over 30-60 min) and mexiletine (median dose, 600 mg daily) were superior to placebo (weighted mean difference on a 0-100 mm pain intensity visual analog scale = -10.60; 95% confidence interval: -14.52 to -6.68; P < 0.00001) and equal to morphine, gabapentin, amitriptyline, and amantadine (weighted mean difference = -0.60; 95% confidence interval: -6.96 to 5.75) for neuropathic pain. The therapeutic benefit was more consistent for peripheral pain (trauma, diabetes) and central pain. The most common adverse effects of lidocaine and mexiletine were drowsiness, fatigue, nausea, and dizziness. The adverse event rate for systemically administered local anesthetics was more than for placebo but equivalent to morphine, amitriptyline, or gabapentin (odds ratio: 1.23; 95% confidence interval: 0.22 to 6.90). Lidocaine and mexiletine produced no major adverse events in controlled clinical trials, were superior to placebo to relieve neuropathic pain, and were as effective as other analgesics used for this condition.

Tolperisone-type drugs inhibit spinal reflexes via blockade of voltage-gated sodium and calcium channels

The spinal reflex depressant mechanism of tolperisone and some of its structural analogs with central muscle relaxant action was investigated. Tolperisone (50-400 microM), eperisone, lanperisone, inaperisone, and silperisone (25-200 microM) dose dependently depressed the ventral root potential of isolated hemisected spinal cord of 6-day-old rats. The local anesthetic lidocaine (100-800 microM) produced qualitatively similar depression of spinal functions in the hemicord preparation, whereas its blocking effect on afferent nerve conduction was clearly stronger. In vivo, tolperisone and silperisone as well as lidocaine (10 mg/kg intravenously) depressed ventral root reflexes and excitability of motoneurons. However, in contrast with lidocaine, the muscle relaxant drugs seemed to have a more pronounced action on the synaptic responses than on the excitability of motoneurons. Whole-cell measurements in dorsal root ganglion cells revealed that tolperisone and silperisone depressed voltage-gated sodium channel conductance at concentrations that inhibited spinal reflexes. Results obtained with tolperisone and its analogs in the [3H]batrachotoxinin A 20-alpha-benzoate binding in cortical neurons and in a fluorimetric membrane potential assay in cerebellar neurons further supported the view that blockade of sodium channels may be a major component of the action of tolperisone-type centrally acting muscle relaxant drugs. Furthermore, tolperisone, eperisone, and especially silperisone had a marked effect on voltage-gated calcium channels, whereas calcium currents were hardly influenced by lidocaine. These data suggest that tolperisone-type muscle relaxants exert their spinal reflex inhibitory action predominantly via a presynaptic inhibition of the transmitter release from the primary afferent endings via a combined action on voltage-gated sodium and calcium channels.

Systemic administration of local anesthetic agents to relieve neuropathic pain

BACKGROUND

Lidocaine, mexiletine, tocainide, and flecainide are local anesthetics which give an analgesic effect when administered orally or parenterally. Early reports described the use of intravenous lidocaine or procaine to relieve cancer and postoperative pain (Keats 1951; Gilbert 1951; De Clive-Lowe 1958; Bartlett 1961). Interest reappeared decades later when patient series and clinical trials reported that parenteral lidocaine and its oral analogs tocainide, mexiletine, and flecainide relieved neuropathic pain in some patients (Boas 1982; Lindblom 1984; Petersen 1986; Dunlop 1988; Bach 1990; Awerbuch 1990). With the recent publication of clinical trials with high quality standards, we have reviewed the use of systemic lidocaine and its oral analogs in neuropathic pain to update our knowledge, to measure their benefit and harm, and to better define their role in therapy.

OBJECTIVES

To evaluate pain relief and adverse effect rates between systemic local anesthetic-type drugs and other control interventions.

SEARCH STRATEGY

We searched MEDLINE (1966 through 15 May 2004), EMBASE (January 1980 to December 2002), Cancer Lit (through 15 December 2002), Cochrane Central Register of Controlled Trials (2nd Quarter, 2004), System for Information on Grey Literature in Europe (SIGLE), and LILACS, from January 1966 through March 2001. We also hand searched conference proceedings, textbooks, original articles and reviews.

SELECTION CRITERIA

We included trials with random allocation, that were double blinded, with a parallel or crossover design. The control intervention was a placebo or an analgesic drug for neuropathic pain from any cause.

DATA COLLECTION AND ANALYSIS

We collected efficacy and safety data from all published and unpublished trials. We calculated combined effect sizes using continuous and binary data for pain relief and adverse effects as primary and secondary outcome measurements, respectively.

MAIN RESULTS

Thirty-two controlled clinical trials met the selection criteria; two were duplicate articles. The treatment drugs were intravenous lidocaine (16 trials), mexiletine (12 trials), lidocaine plus mexiletine sequentially (one trial), and tocainide (one trial). Twenty-one trials were crossover studies, and nine were parallel. Lidocaine and mexiletine were superior to placebo [weighted mean difference (WMD) = -11; 95% CI: -15 to -7; P <0.00001], and limited data showed no difference in efficacy (WMD = -0.6; 95% CI: -7 to 6), or adverse effects versus carbamazepine, amantadine, gabapentin or morphine. In these trials, systemic local anesthetics were safe, with no deaths or life-threatening toxicities. Sensitivity analysis identified data distribution in three trials as a probable source of heterogeneity. There was no publication bias.

AUTHORS' CONCLUSIONS

Lidocaine and oral analogs were safe drugs in controlled clinical trials for neuropathic pain, were better than placebo, and were as effective as other analgesics. Future trials should enroll specific diseases and test novel lidocaine analogs with better toxicity profiles. More emphasis is necessary on outcomes measuring patient satisfaction to assess if statistically significant pain relief is clinically meaningful.

NOTES

Notes 2017 A restricted search in June 2017 did not identify any potentially relevant studies likely to change the conclusions. Therefore, this review has now been stabilised following discussion with the authors and editors. If appropriate, we will update the review if new evidence likely to change the conclusions is published, or if standards change substantially which necessitate major revisions. 2019 We performed another restricted search in September 2019 but did not identify any potentially relevant studies likely to change the conclusions. Therefore, this review has now been stabilised following discussion with the authors and editors, and we will reassess the review for updating in 2020. If appropriate, we will update the review sooner if new evidence likely to change the conclusions is published, or if standards change substantially which necessitate major revisions. 2020 We performed another restricted search in September 2020 but again did not identify any potentially relevant studies likely to change the conclusions. This area of research is not active and therefore this review has now been stabilised following discussion with the authors and editors; we will reassess the review for updating in 2025. If appropriate, we will update the review sooner if new evidence likely to change the conclusions is published, or if standards change substantially which necessitate major revisions.

Different basal levels of CaMKII phosphorylated at Thr286/287 at nociceptive and low-threshold primary afferent synapses

Postsynaptic autophosphorylation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) at Thr286/287 is crucial for the induction of long-term potentiation at many glutamatergic synapses, and has also been implicated in the persistence of synaptic potentiation. However, the availability of CaMKII phosphorylated at Thr286/287 at individual glutamatergic synapses in vivo is unclear. We used post-embedding immunogold labelling to quantitatively analyse the ultrastructural localization of CaMKII phosphorylated at Thr286/287 (pCaMKII) at synapses formed by presumed nociceptive and low-threshold mechanosensitive primary afferent nerve endings in laminae I-IV of rat spinal cord. Immunogold labelling was enriched in the postsynaptic densities of such synapses, consistent with observations in pre-embedding immunoperoxidase-stained dorsal horn. Presynaptic axoplasm also exhibited sparse immunogold labelling, in peptidergic terminals partly associated with dense core vesicles. Analysis of single or serial pCaMKII-immunolabelled sections indicated that the large majority of synapses formed either by presumed peptidergic or non-peptidergic nociceptive primary afferent terminals in laminae I-II of the spinal cord, or by presumed low-threshold mechanosensitive primary afferent terminals in laminae IIi-IV, contained pCaMKII in their postsynaptic density. However, the postsynaptic levels of pCaMKII immunolabelling at low-threshold primary afferent synapses were only approximately 50% of those at nociceptive synapses. These results suggest that constitutively autophosphorylated CaMKII in the postsynaptic density is a common characteristic of glutamatergic synapses, thus potentially contributing to maintenance of synaptic efficacy. Furthermore, pCaMKII appears to be differentially regulated between high- and low-threshold primary afferent synapses, possibly reflecting different susceptibility to synaptic plasticity between these afferent pathways.

Investigation of the EEG effects of intravenous lidocaine during halothane anaesthesia in ponies

OBJECTIVE

To record the electroencephalographic changes during castration in ponies anaesthetized with halothane and given intravenous (IV) lidocaine by infusion. The hypothesis tested was that in ponies, IV lidocaine is antinociceptive and would therefore obtund EEG changes during castration.

ANIMALS

Ten Welsh mountain ponies referred to the Department of Clinical Veterinary Medicine, Cambridge for castration under general anaesthesia.

MATERIALS AND METHODS

Following pre-anaesthetic medication with intramuscular acepromazine (0.02 mg kg(-1)) anaesthesia was induced with IV guaiphenesin (60 mg kg(-1)) and thiopental (9 mg kg(-1)) and maintained with halothane at an end-tidal concentration (FE'HAL) of 1.2%. A constant rate infusion of IV lidocaine (100 microg kg(-1) minute(-1)) was administered throughout anaesthesia. The electroencephalogram (EEG) was recorded continuously using subcutaneous needle electrodes. All animals were castrated using a closed technique. The raw EEG signal was analysed after completion of each investigation, and the mean values of EEG variables (median frequency, spectral edge frequency, total amplitude) recorded during a baseline period (before surgery began) and the removal of each testicle were compared using anova for repeated measures.

RESULTS

Spectral edge frequency (SEF) 95% decreased during removal of the second testicle compared with baseline recordings. No other significant EEG changes during castration were measured.

CONCLUSIONS

Lidocaine obtunded the EEG changes identified during castration in a previous control study, providing indirect evidence that lidocaine administered peri-operatively was antinociceptive and contributed to anaesthesia during castration.

CLINICAL RELEVANCE

The antinociceptive effect of lidocaine combined with its minimal cardiovascular effects indicate a potential use for systemic lidocaine in clinical anaesthetic techniques.

Preincisional Dextromethorphan Combined with Thoracic Epidural Anesthesia and Analgesia Improves Postoperative Pain and Bowel Function in Patients Undergoing Colonic Surgery

Colonic surgery is associated with severe postoperative pain and postoperative ileus, which contribute to delayed hospital discharge. In previous studies, we demonstrated that IM dextromethorphan (DM) provided preemptive analgesia and improved postoperative pain. The benefit of thoracic epidural anesthesia (TEA) and postoperative epidural analgesia on postoperative pain was well demonstrated. The goal of this study was to investigate the effect of preincisional IM DM combined with intraoperative TEA and postoperative patient-controlled epidural analgesia (PCEA) on pain and bowel function after colonic surgery. Patients were randomized into 3 equal groups to receive: 1) chlorpheniramine maleate (CPM) 20 mg and general anesthesia (CPM-GA); 2) CPM 20 mg and GA combined with TEA (CPM-TEA); or 3) DM 40 mg (containing 20 mg of CPM) and GA combined with TEA (DM-TEA). The CPM, DM, and TEA with lidocaine were administered after GA induction via an IM injection and 30 min before the skin incision. All patients received postoperative PCEA for pain control. Analgesic effects were evaluated for 72 h after surgery using visual analog scale pain scores at rest and moving, time to first PCEA request for pain relief, total PCEA consumption, and the time to first passage of flatus. Statistically significant improvement of postoperative pain and bowel function was observed in the following order: DM-TEA > CPM-TEA > CPM-GA. Compared with the CPM-TEA group, the DM-TEA group averaged 1.6 points lower on first-hour pain scores, 40 min longer to first PCEA request, 15.8 mL less PCEA drug over 72 h, and 14.7 h earlier bowel function (all P < 0.01). We conclude that the combination of preincisional DM (40 mg IM), intraoperative TEA, and postoperative PCEA enhances analgesia and facilitates recovery of bowel function, suggesting possible synergistic interaction with local anesthetics and opioids.