Etomidate-Induced Myoclonus in Sprague-Dawley Rats Involves Neocortical Glutamate Accumulation and N -Methyl- d -Aspartate Receptor Activity.

BACKGROUND: Etomidate-induced myoclonus, a seizure-like movement, is of interest to anesthetists. However, its origin in the brain and its underlying mechanism remain unclear. METHODS: Adult male Sprague-Dawley rats were anesthetized with etomidate, propofol, or lidocaine plus etomidate. We assessed the incidence of myoclonus, behavioral scores, and levels of glutamate and γ-aminobutyric acid (GABA) in the neocortex and hippocampus. To determine the origin and how N -methyl- d -aspartate receptors (NMDARs) modulate etomidate-induced neuroexcitability, the local field potential and muscular tension were monitored. Calcium imaging in vitro and immunoblotting in vivo were conducted to investigate the mechanisms underlying myoclonus. RESULTS: The incidence of etomidate (1.5 mg/kg in vivo)-induced myoclonus was higher than that of propofol (90% vs 10%, P = .0010) and lidocaine plus etomidate (90% vs 20%, P = .0050). Etomidate at doses of 3.75 and 6 mg/kg decreased the mean behavioral score at 1 (mean difference [MD]: 1.80, 95% confidence interval [CI], 0.58-3.02; P = .0058 for both), 2 (MD: 1.60, 95% CI, 0.43-2.77; P = .0084 and MD: 1.70, 95% CI, 0.54-2.86; P = .0060), 3 (MD: 1.60, 95% CI, 0.35-2.85; P = .0127 and MD: 1.70, 95% CI, 0.46-2.94; P = .0091) minutes after administration compared to etomidate at a dose of 1.5 mg/kg. In addition, 0.5 and 1 µM etomidate in vitro increased neocortical intracellular calcium signaling; this signaling decreased when the concentration increased to 5 and 10 µM. Etomidate increased the glutamate level compared to propofol (mean rank difference: 18.20; P = .003), and lidocaine plus etomidate (mean rank difference: 21.70; P = .0002). Etomidate in vivo activated neocortical ripple waves and was positively correlated with muscular tension amplitude (Spearman's r = 0.785, P < .0001). Etomidate at 1.5 mg/kg decreased the K-Cl cotransporter isoform 2 (KCC2) level compared with propofol (MD: -1.15, 95% CI, -1.47 to -0.83; P < .0001) and lidocaine plus etomidate (MD: -0.64, 95% CI, -0.96 to -0.32; P = .0002), DL-2-amino-5-phosphopentanoic acid (AP5) suppressed these effects, while NMDA enhanced them. CONCLUSIONS: Etomidate-induced myoclonus or neuroexcitability is concentration dependent. Etomidate-induced myoclonus originates in the neocortex. The underlying mechanism involves neocortical glutamate accumulation and NMDAR modulation and myoclonus correlates with NMDAR-induced downregulation of KCC2 protein expression.

A weight of evidence assessment of the genotoxicity of 2,6-xylidine based on existing and new data, with relevance to safety of lidocaine exposure.

Lidocaine has not been associated with cancer in humans despite 8 decades of therapeutic use. Its metabolite, 2,6-xylidine, is a rat carcinogen, believed to induce genotoxicity via N-hydroxylation and DNA adduct formation, a non-threshold mechanism of action. To better understand this dichotomy, we review literature pertaining to metabolic activation and genotoxicity of 2,6-xylidine, identifying that it appears resistant to N-hydroxylation and instead metabolises almost exclusively to DMAP (an aminophenol). At high exposures (sufficient to saturate phase 2 metabolism), this may undergo metabolic threshold-dependent activation to a quinone-imine with potential to redox cycle producing ROS, inducing cytotoxicity and genotoxicity. A new rat study found no evidence of genotoxicity in vivo based on micronuclei in bone marrow, comets in nasal tissue or female liver, despite high level exposure to 2,6-xylidine (including metabolites). In male liver, weak dose-related comet increases, within the historical control range, were associated with metabolic overload and acute systemic toxicity. Benchmark dose analysis confirmed a non-linear dose response. The weight of evidence indicates 2,6-xylidine is a non-direct acting (metabolic threshold-dependent) genotoxin, and is not genotoxic in vivo in rats in the absence of acute systemic toxic effects, which occur at levels 35 × beyond lidocaine-related exposure in humans.

The 14-day repeated-dose toxicity study of a fixed-dose combination, QXOH/levobupivacaine, via subcutaneous injection in beagle dogs.

QXOH-Levobupivacaine (LB) is a fixed-dose combination of 35-mM QXOH and 10-mM LB. It was developed for perioperative analgesia because of its long-acting analgesic effect. The purpose of this study was to evaluate the potential toxicity of QXOH-LB in beagle dogs in accordance with the Guidance on the repeated-dose toxicity published by the China Food and Drug Administration. Groups of five male and five female beagle dogs received normal saline, QXOH-LB (2, 4, and 8 mg/kg, calculated as QXOH), QXOH (2, 4, and 8 mg/kg), or LB (2 mg/kg, equals the concentration of LB in 8-mg/kg QXOH-LB group) at the volume of 1 mL/kg once per day for 14 days through subcutaneous injection. No mortality was observed. Dogs in the control group as well as animals treated with 2-mg/kg QXOH or QXOH-LB exhibited normal behaviors. Clinical signs of toxicity in dogs treated with 4 and 8 mg/kg of QXOH or QXOH-LB included decreased activity, unsteady gait, jerks, tremors, vocalization, emesis, ataxia, lateral/sternal recumbency, deep/rapid respiration, and gasping. Additionally, neurological function was found to be affected by QXOH and QXOH-LB at the doses of 4 and 8 mg/kg. All clinical signs were recovered within 24 h. The no-observed-adverse-effect level of QXOH and QXOH-LB was considered to be 2 mg/kg. Toxicokinetic data showed that exposure to QXOH and LB increased as QXOH-LB doses were increased from 4 to 8 mg/kg. There was no evidence of drug accumulation or any effect of gender.

Lidocaine-induced potentiation of thermal damage in skin and carcinoma cells.

OBJECTIVE: Lidocaine acts as a local anesthetic by blocking transmembrane sodium channel permeability, but also induces the synthesis of heat shock proteins and sensitizes cells to hyperthermia. A previous study reported two cases of deep focal skin ulceration at points corresponding to depot local lidocaine injection sites after treatment with non-ablative fractional resurfacing and it was hypothesized that lidocaine had focally sensitized keratinocytes to the thermal damage of laser treatment. The objective of this study was to investigate whether lidocaine potentiates hyperthermia damage to both normal and cancerous skin cells using an in vitro model. METHODS: Normal skin cell lines (fibroblasts, keratinocytes), skin cancer cell lines (melanoma, basal cell carcinoma), and a mucosal cancer cell line (cervical carcinoma) were exposed to various concentrations of lidocaine (0-0.3%) with or without hyperthermia (37°C, 42°C). RESULTS: Compared to normal skin cells, we demonstrate that cancer cell lines show significantly increased cell toxicity when a moderate temperature (42°C) and low lidocaine concentrations (0.1-0.2%) are combined. The toxicity directly correlates with a higher percentage of cells in S-phase (28-57%) in the cancer cell lines compared to normal skin cell lines (13-19%; R-square 0.6752). CONCLUSION: These results suggest that lidocaine potentiates thermal sensitivity of cell cycle active skin cells. The direct correlation between cell toxicity and S-phase cells could be harnessed to selectively treat skin and mucosal cancer cells while sparing the surrounding normal tissue. Additional research pre-clinically and clinically using several different heat sources (e.g., lasers, ultrasound, etc.) and lidocaine concentrations is needed to confirm and optimize these results. Lidocaine-enhanced hyperthermia may provide a non-invasive, alterative treatment option for highly proliferating, superficial skin, and mucosal lesions such as cancer or warts. Lasers Surg. Med. 51:88-94, 2019. © 2018 Wiley Periodicals, Inc.

Exposure to Tumescent Solution Significantly Increases Phosphorylation of Perilipin in Adipocytes.

BACKGROUND: Lidocaine and epinephrine could potentially decrease adipocyte viability, but these effects have not been substantiated. The phosphorylation status of perilipin in adipocytes may be predictive of cell viability. Perilipin coats lipid droplets and restricts access of lipases; phospho-perilipin lacks this protective function. OBJECTIVES: The authors investigated the effects of tumescent solution containing lidocaine and epinephrine on the phosphorylation status of perilipin in adipocytes. METHODS: In this in vitro study, lipoaspirates were collected before and after tumescence from 15 women who underwent abdominoplasty. Fat samples were fixed, sectioned, and stained for histologic and immunohistochemical analyses. Relative phosphorylation of perilipin was inferred from pixel intensities of immunostained adipocytes observed with confocal microscopy. RESULTS: For adipocytes collected before tumescent infiltration, 10.08% of total perilipin was phosphorylated. In contrast, 30.62% of total perilipin was phosphorylated for adipocytes collected from tumescent tissue (P < .01). CONCLUSIONS: The tumescent technique increases the relative phosphorylation of perilipin in adipocytes, making these cells more vulnerable to lipolysis. Tumescent solution applied for analgesia or hemostasis of the donor site should contain the lowest possible concentrations of lidocaine and epinephrine. LEVEL OF EVIDENCE 5.

Hyaluronan suppresses lidocaine-induced apoptosis of human chondrocytes in vitro by inhibiting the p53-dependent mitochondrial apoptotic pathway.

AIM: Intra-articular injection of local anesthetics (LAs) is a common procedure for therapeutic purposes. However, LAs have been found toxic to articular cartilage, and hyaluronan may attenuate this toxicity. In this study we investigated whether hyaluronan attenuated lidocaine-induced chondrotoxicity, and if so, to elucidate the underlying mechanisms. METHODS: Human chondrocyte cell line SW1353 and newly isolated murine chondrocytes were incubated in culture medium containing hyaluronan and/or lidocaine for 72 h. Cell viability was evaluated using MTT assay. Cell apoptosis was detected with DAPI staining, caspase 3/7 activity assay and flow cytometry. Cell cycle distributions, ROS levels and mitochondrial membrane potential (ΔΨm) were determined using flow cytometry. The expression of p53 and p53-regulated gene products was measured with Western blotting. RESULTS: Lidocaine (0.005%-0.03%) dose-dependently decreased the viability of SW1353 cells. This local anesthetic (0.015%, 0.025%) induced apoptosis, G2/M phase arrest and loss of ΔΨm, and markedly increased ROS production in SW1353 cells. Hyaluronan (50-800 µg/mL) alone did not affect the cell viability, but co-treatment with hyaluronan (200 µg/mL) significantly attenuated lidocaine-induced apoptosis and other abnormalities in SW1353 cells. Furthermore, co-treatment with lidocaine and hyaluronan significantly decreased the levels of p53 and its transcription targets Bax and p21 in SW1353 cells, although treatment with lidocaine alone did not significantly change these proteins. Similar results were obtained in ex vivo cultured murine chondrocytes. CONCLUSION: Hyaluronan suppresses lidocaine-induced apoptosis of human chondrocytes in vitro through inhibiting the p53-dependent mitochondrial apoptotic pathway.

Lidocaine Impairs Proliferative and Biosynthetic Functions of Aged Human Dermal Fibroblasts.

BACKGROUND: The aged are at increased risk of postoperative wound healing complications. Because local anesthetics are infiltrated commonly into the dermis of surgical wounds, we sought to determine whether local anesthetics adversely affect proliferative and biosynthetic functions of dermal fibroblasts. We also evaluated the effect of local anesthetics on insulin-like growth factor-1 (IGF-1) and transforming growth factor-ß1 (TGF-ß1), growth factors that are important regulators of wound healing. METHODS: Human dermal fibroblasts (HFB) from aged and young donors were exposed to local anesthetic agents at clinically relevant concentrations. We screened the effects of lidocaine, bupivacaine, mepivacaine, and ropivacaine on proliferation of HFB. Lidocaine was most detrimental to proliferation in HFB. We then evaluated the effect of lidocaine on expression and function of the growth factors, IGF-1 and TGF-ß1. Lastly, concurrent exposure to lidocaine and IGF-1 or TGF-ß1 was evaluated for their effects on proliferation and expression of dermal collagens, respectively. RESULTS: Lidocaine and mepivacaine inhibited proliferation in aged HFB (for lidocaine 88% of control, 95% confidence interval [CI], 80%-98%, P = .009 and for mepivacaine 90% of control, 95% CI, 81%-99%, P = .032) but not in young HFB. Ropivacaine and bupivacaine did not inhibit proliferation. Because of the clinical utility of lidocaine relative to mepivacaine, we focused on lidocaine. Lidocaine decreased proliferation in aged HFB, which was abrogated by IGF-1. Lidocaine inhibited transcripts for IGF-1 and insulin-like growth factor-1 receptor (IGF1R) in fibroblasts from aged donors (IGF-1, log2 fold-change -1.25 [42% of control, 95% CI, 19%-92%, P = .035] and IGF1R, log2 fold-change -1.00 [50% of control, 95% CI, 31%-81%, P = .014]). In contrast, lidocaine did not affect the expression of IGF-1 or IGF1R transcripts in the young HFB. Transcripts for collagen III were decreased after lidocaine exposure in aged and young HFB (log2 fold-change -1.28 [41% of control, 95% CI, 20%-83%, P = .022] in aged HFB and log2 fold-change -1.60 [33% of control, 95% CI, 15%-73%, P = .019] in young HFB). Transcripts for collagen I were decreased in aged HFB (log2 fold-change -1.82 [28% of control, 95% CI, 14%-58%, P = .006]) but not in the young HFB. Similar to the transcripts, lidocaine also inhibited the protein expression of collagen III in young and aged HFB (log2 fold-change -1.79 [29% of control, 95% CI, 18%-47%, P = .003] in young HFB and log2 fold-change -1.76 [30% of control, 95% CI, 9%-93%, P = .043] in aged HFB). The effect of lidocaine on the expression of collagen III protein was obviated by TGF-ß1 in both young and aged HFB. CONCLUSIONS: Our results show that lidocaine inhibits processes relevant to dermal repair in aged HFB. The detrimental responses to lidocaine are due, in part, to interactions with IGF-1 and TGF-ß1.

Central Nervous System-Toxic Lidocaine Concentrations Unmask L-Type Ca²âº Current-Mediated Action Potentials in Rat Thalamocortical Neurons: An In Vitro Mechanism of Action Study.

BACKGROUND: High systemic lidocaine concentrations exert well-known toxic effects on the central nervous system (CNS), including seizures, coma, and death. The underlying mechanisms are still largely obscure, and the actions of lidocaine on supraspinal neurons have received comparatively little study. We recently found that lidocaine at clinically neurotoxic concentrations increases excitability mediated by Na-independent, high-threshold (HT) action potential spikes in rat thalamocortical neurons. Our goal in this study was to characterize these spikes and test the hypothesis that they are generated by HT Ca currents, previously implicated in neurotoxicity. We also sought to identify and isolate the specific underlying subtype of Ca current. METHODS: We investigated the actions of lidocaine in the CNS-toxic concentration range (100 µM-1 mM) on ventrobasal thalamocortical neurons in rat brain slices in vitro, using whole-cell patch-clamp recordings aided by differential interference contrast infrared videomicroscopy. Drugs were bath applied; action potentials were generated using current clamp protocols, and underlying currents were identified and isolated with ion channel blockers and electrolyte substitution. RESULTS: Lidocaine (100 µM-1 mM) abolished Na-dependent tonic firing in all neurons tested (n = 46). However, in 39 of 46 (85%) neurons, lidocaine unmasked evoked HT action potentials with lower amplitudes and rates of de-/repolarization compared with control. These HT action potentials remained during the application of tetrodotoxin (600 nM), were blocked by Cd (50 µM), and disappeared after superfusion with an extracellular solution deprived of Ca. These features implied that the unmasked potentials were generated by high-voltage-activated Ca channels and not by Na channels. Application of the L-type Ca channel blocker, nifedipine (5 µM), completely blocked the HT potentials, whereas the N-type Ca channel blocker, ω-conotoxin GVIA (1 µM), had little effect. CONCLUSIONS: At clinically CNS-toxic concentrations, lidocaine unmasked in thalamocortical neurons evoked HT action potentials mediated by the L-type Ca current while substantially suppressing Na-dependent excitability. On the basis of the known role of an increase in intracellular Ca in the pathogenesis of local anesthetic neurotoxicity, this novel action represents a plausible contributing candidate mechanism for lidocaine's CNS toxicity in vivo.

Despite differences in cytosolic calcium regulation, lidocaine toxicity is similar in adult and neonatal rat dorsal root ganglia in vitro.

BACKGROUND: Neuraxial local anesthetics may have neurological complications thought to be due to neurotoxicity. A primary site of action of local anesthetics is the dorsal root ganglia (DRG) neuron. Physiologic differences have been noted between young and adult DRG neurons; hence, the authors examined whether there were any differences in lidocaine-induced changes in calcium and lidocaine toxicity in neonatal and adult rat DRG neurons. METHODS: DRG neurons were cultured from postnatal day 7 (P7) and adult rats. Lidocaine-induced changes in cytosolic calcium were examined with the calcium indicator Fluo-4. Cells were incubated with varying concentrations of lidocaine and examined for viability using calcein AM and ethidium homodimer-1 staining. Live imaging of caspase-3/7 activation was performed after incubation with lidocaine. RESULTS: The mean KCl-induced calcium transient was greater in P7 neurons (P < 0.05), and lidocaine significantly inhibited KCl-induced calcium responses in both ages (P < 0.05). Frequency distribution histograms of KCl-evoked calcium increases were more heterogeneous in P7 than in adult neurons. With lidocaine, KCl-induced calcium transients in both ages became more homogeneous but remained different between the groups. Interestingly, cell viability was decreased by lidocaine in a dose-dependent manner similarly in both ages. Lidocaine treatment also activated caspase-3/7 in a dose- and time-dependent manner similarly in both ages. CONCLUSIONS: Despite physiological differences in P7 and adult DRG neurons, lidocaine cytotoxicity is similar in P7 and adult DRG neurons in vitro. Differences in lidocaine- and KCl-evoked calcium responses suggest the similarity in lidocaine cytotoxicity involves other actions in addition to lidocaine-evoked effects on cytosolic calcium responses.

Lidocaine attenuates lipopolysaccharide-induced inflammatory responses in microglia.

BACKGROUND: Lidocaine has been used as a local anesthetic with anti-inflammatory properties, but its effects on neuroinflammation have not been well defined. In the present study, we investigated the prophylactic effects of lidocaine on lipopolysaccharide (LPS)-activated microglia and explored the underlying mechanisms. MATERIALS AND METHODS: Microglial cells were incubated with or without 1 µg/mL LPS in the presence or absence of lidocaine, a p38 mitogen-activated protein kinase (p38 MAPK) inhibitor (SB203580), a nuclear factor-kappa B (NF-κB) inhibitor (pyrrolidine dithiocarbamate), or small interfering RNA. The protein and expression levels of inflammatory mediators, such as monocyte chemotactic protein 1, nitric oxide, prostaglandin E2, interleukin 1ß, and tumor necrosis factor α were measured using enzyme-linked immunosorbent assays and real-time polymerase chain reaction. The effect of lidocaine on NF-κB and p38 MAPK activation was evaluated using enzyme-linked immunosorbent assays, Western blot analysis, and electrophoretic mobility shift assay. RESULTS: Lidocaine (≥2 µg/mL) significantly inhibited the release and expression of nitric oxide, monocyte chemotactic protein 1, prostaglandin E2, interleukin 1ß, and tumor necrosis factor α in LPS-activated microglia. Treatment with lidocaine also significantly inhibited the phosphorylation of p38 MAPK and the nuclear translocation of NF-κB p50/p65, increased the protein levels of inhibitor kappa B-α. Furthermore, our study shows that the LPS-induced release of inflammatory mediators was suppressed by SB203580, pyrrolidine dithiocarbamate, and small interfering RNA. CONCLUSIONS: Prophylactic treatment with lidocaine inhibits LPS-induced release of inflammatory mediators from microglia, and these effects may be mediated by blockade of p38 MAPK and NF-κB signaling pathways.

Lidocaine potentiates the deleterious effects of triamcinolone acetonide on tenocytes.

BACKGROUND: Local anesthetics are commonly used for the treatment of a variety of tendinopathies in combination with corticosteroids injection. The goal of this study was to evaluate the effects of lidocaine and triamcinolone acetonide (TA) on cultured rat tenocytes and to determine whether there is a synergistic effect. MATERIAL/METHODS: Rat patellar tendon-derived tenocytes were cultured with or without TA and lidocaine, and the culture without any additive served as the control. Cell morphology and cell viability were evaluated. Expressions of tenocyte-related genes were measured by qRT-PCR. RESULTS: TA, when exposed to tenocytes in vitro, significantly decreased cell viability. The cells cultured with TA had a flattened shape. Moreover, the expressions of tenocyte-related genes in tenocytes were markedly decreased in the TA-treated group. We found that 1% lidocaine synergistically increased the deleterious effects of TA. CONCLUSIONS: Our data provide evidence of the detrimental effects of these drugs on tendon tissues. Injection of TA in combination with 1% lidocaine should be used with caution.

More methemoglobin is produced by benzocaine treatment than lidocaine treatment in human in vitro systems.

The clinical use of local anesthetic products to anesthetize mucous membranes has been associated with methemoglobinemia (MetHba), a serious condition in which the blood has reduced capacity to carry oxygen. An evaluation of spontaneous adverse event reporting of MetHba submitted to FDA through 2013 identified 375 reports associated with benzocaine and 16 reports associated with lidocaine. The current study was performed to determine the relative ability of benzocaine and lidocaine to produce methemoglobin (MetHb) in vitro. Incubation of 500µM benzocaine with whole human blood and pooled human liver S9 over 5h resulted in MetHb levels equaling 39.8±1.2% of the total hemoglobin. No MetHb formation was detected for 500µM lidocaine under the same conditions. Because liver S9 does not readily form lidocaine hydrolytic metabolites based on xylidine, a primary metabolic pathway, 500µM xylidine was directly incubated with whole blood and S9. Under these conditions MetHb levels of 4.4±0.4% were reached by 5h. Studies with recombinant cytochrome P450 revealed benzocaine to be extensively metabolized by CYP 1A2, with 2B6, 2C19, 2D6, and 2E1 also having activity. We conclude that benzocaine produces much more MetHb in in vitro systems than lidocaine or xylidine and that benzocaine should be more likely to cause MetHba in vivo as well.

Inhibition of murine cardiomyocyte respiration by amine local anesthetics.

The hydrophobic amino acyl amide-linked local anesthetics (e.g., lidocaine and bupivacaine) impose potent cardiac toxicity and direct mitochondrial dysfunction. To investigate these adverse events, an in vitro system was employed to measure their effects on O2 consumption (cellular respiration) by murine myocardium. Specimens were collected from the ventricular myocardium and immediately immersed in ice-cold Krebs-Henseleit buffer saturated with 95 % O2:5 % CO2. O2 concentration was determined as a function of time from the phosphorescence decay rates of Pd(II)-meso-tetra-(4-sulfonatophenyl)-tetrabenzoporphyrin. Myocardial O2 consumption was linear with time (zero-order kinetics); its rate (k, in µM O2 min(-1)), thus, was the negative of the slope of [O2] vs. time. Cyanide inhibited O2 consumption, confirming the oxidation occurred in the respiratory chain. Lidocaine and bupivacaine produced immediate and sustained inhibition of cellular respiration at plasma concentrations of the drugs (low micromolar range). Bupivacaine was twice as potent as lidocaine. The inhibition was dose-dependent, saturating at concentrations ≥30 µM. At saturating doses, lidocaine produced ~20 % inhibition and bupivacaine ~40 % inhibition. Cellular ATP was also decreased in the presence of 30 µM lidocaine or bupivacaine. The studied amines inhibited myocardial cellular respiration. This effect is consistent with their known adverse events on mitochondrial function. The described approach allows accurate assessments and comparisons of the toxic effects of local anesthetics on heart tissue bioenergetics.

Spinal anesthesia revisited: toxicity of new and old drugs and compounds.

PURPOSE OF REVIEW: Neural toxicity of substances injected into the intrathecal space has been a matter of debate since the introduction of spinal anesthesia in clinical practice. In recent years, new local anesthetics and adjuvants have been proposed for intrathecal use, and new techniques such as the use of ultrasound have been propagated. The present review summarizes recent clinical and experimental data on the neurotoxic effects of drugs and substances used for or in conjunction with spinal anesthesia. RECENT FINDINGS: Chloroprocaine has been demonstrated to be associated with a lower risk of transient neurologic symptoms compared with lidocaine. However, despite extensive research, the issue of chloroprocaine or bisulfite neurotoxicity has not yet been resolved.Recent experimental data have identified a smaller neurotoxic potential for ropivacaine compared to levobupivacaine, procaine and bupivacaine. The addition of epinephrine has not been shown to increase lidocaine neurotoxicity. In-vivo experimental data suggest that lidocaine and bupivacaine neurotoxicity is not enhanced in diabetic patients.Furthermore, intrathecal introduction of aqueous ultrasound gel has been demonstrated to cause a distinct neuroinflammatory reaction. Finally, a large cohort study did not find the use of chlorhexidine gluconate for skin disinfection before neuraxial block to be associated with the risk of adhesive arachnoiditis. SUMMARY: Clinical data suggest a high safety profile for intrathecal drugs and substances used for or in conjunction with spinal anesthesia. Recent experimental models for toxicity have provided further insight into the mechanisms and demonstrated possible, albeit clinically small differences in the relative neurotoxic potential of intrathecal drugs. This may contribute to a further increase in the safe use of spinal anesthesia in the clinical setting.

Exploring the effects of eugenol, menthol, and lidocaine as anesthetics on zebrafish glucose homeostasis.

Zebrafish (Danio rerio) are widely employed as an experimental model in various scientific fields. The investigation of glucose metabolism dysfunctions has gained recent significant prominence. Considering that certain anesthetics may impact glycemic levels, it is imperative to carefully select an anesthetic that does not induce such side effects, thereby mitigating potential adverse influences on research outcomes. In this sense, this study aimed to evaluate potential glucose alterations and induction and recovery times resulting from the use of eugenol, menthol and lidocaine as anesthetics in zebrafish. A total of 150 adult male and female zebrafish were divided into ten groups, comprising a control group euthanized by rapid chilling, and three groups anesthetized with low (40 mg/L eugenol, 60 mg/L menthol, 100 mg/L lidocaine), intermediate (60 mg/L eugenol, 90 mg/L menthol, 225 mg/L lidocaine), and high (80 mg/L eugenol, 120 mg/L menthol, 350 mg/L lidocaine) anesthetic concentrations. Glucose levels and induction and recovery times were assessed. The findings reveal that eugenol and menthol did not cause glucose level alterations at any of the investigated concentrations, while lidocaine caused a non-concentration-dependent hyperglycemia. Eugenol and menthol also exhibited similar recovery times at different concentrations, while lidocaine recovery times were concentration-dependent. This study, therefore, concludes that eugenol and menthol are safe and satisfactory anesthetics for use in zebrafish research involving glucose analyses, while lidocaine use can cause biases due to altered glucose levels and safety concerns. Researchers should, therefore, carefully consider anesthetic selection to ensure reliable results in zebrafish assessments.

Exposure to lidocaine in early life does not cause negative long-term behavioural changes in mice.

BACKGROUND: The local anaesthetic lidocaine is widely used in the neonatal intensive unit to treat seizures in premature babies. However, other antiepileptics administered during early development in various animal models have shown negative long-term behavioural effects. Since no long-term behavioural data so far exist regarding lidocaine exposure at an early age, we decided to perform this extended follow-up study using a sensitive behavioural test. METHODS: Neonatal mice received a subcutaneous administration of saline or one dose of lidocaine (0.5, 4, or 12 mg kg-1) on postnatal day 10 (P10; peak of the Brain Growth Spurt). A well-established test to detect long-term behavioural alterations was conducted at 2 and 6 months of age, corresponding to early and late adulthood in humans. RESULTS: All animal survived to later testing. No signs of acute toxicity were observed. Lidocaine exposure did not result in any negative behavioural effects during habituation to a new home environment at any of the two studied time points, compared to saline placebo. CONCLUSIONS: Lidocaine does not by itself produce any negative long-term behavioural effects in mice exposed in early life (P10) despite long-term follow-up. This is reassuring regarding the current practice of treating seizures in premature babies with intravenous lidocaine.

Safety evaluation of adenosine, lidocaine and magnesium (ALM) intranasal therapy toward human nasal epithelial cells in vitro.

Adenosine, lidocaine and Mg2+ (ALM) solution is an emerging therapy that reduces secondary injury after intravenous administration in experimental models of traumatic brain injury (TBI). Intranasal delivery of ALM may offer an alternative route for rapid, point-of-care management of TBI. As a preliminary safety screen, we evaluated whether ALM exerts cytotoxic or inflammatory effects on primary human nasal epithelial cells (pHNEC) in vitro. Submerged monolayers and air-liquid interface cultures of pHNEC were exposed to media only, normal saline only, therapeutic ALM or supratherapeutic ALM for 15 or 60 min. Safety was measured through viability, cytotoxicity, apoptosis, cellular and mitochondrial stress, and inflammatory mediator secretion assays. No differences were found in viability or cytotoxicity in cultures exposed to saline or ALM for up to 60 min, with no evidence of apoptosis after exposure to supratherapeutic ALM concentrations. Despite comparable inflammatory cytokine secretion profiles and mitochondrial activity, cellular stress responses were significantly lower in cultures exposed to ALM than saline. In summary, data show ALM therapy has neither adverse toxic nor inflammatory effects on human nasal epithelial cells, setting the stage for in vivo toxicity studies and possible clinical translation of intranasal ALM therapy for TBI treatment.

Prilocaine- and lidocaine-induced methemoglobinemia is caused by human carboxylesterase-, CYP2E1-, and CYP3A4-mediated metabolic activation.

Prilocaine and lidocaine are classified as amide-type local anesthetics for which serious adverse effects include methemoglobinemia. Although the hydrolyzed metabolites of prilocaine (o-toluidine) and lidocaine (2,6-xylidine) have been suspected to induce methemoglobinemia, the metabolic enzymes that are involved remain uncharacterized. In the present study, we aimed to identify the human enzymes that are responsible for prilocaine- and lidocaine-induced methemoglobinemia. Our experiments revealed that prilocaine was hydrolyzed by recombinant human carboxylesterase (CES) 1A and CES2, whereas lidocaine was hydrolyzed by only human CES1A. When the parent compounds (prilocaine and lidocaine) were incubated with human liver microsomes (HLM), methemoglobin (Met-Hb) formation was lower than when the hydrolyzed metabolites were incubated with HLM. In addition, Met-Hb formation when prilocaine and o-toluidine were incubated with HLM was higher than that when lidocaine and 2,6-xylidine were incubated with HLM. Incubation with diisopropyl fluorophosphate and bis-(4-nitrophenyl) phosphate, which are general inhibitors of CES, significantly decreased Met-Hb formation when prilocaine and lidocaine were incubated with HLM. An anti-CYP3A4 antibody further decreased the residual formation of Met-Hb. Met-Hb formation after the incubation of o-toluidine and 2,6-xylidine with HLM was only markedly decreased by incubation with an anti-CYP2E1 antibody. o-Toluidine and 2,6-xylidine were further metabolized by CYP2E1 to 4- and 6-hydroxy-o-toluidine and 4-hydroxy-2,6-xylidine, respectively, and these metabolites were shown to more efficiently induce Met-Hb formation than the parent compounds. Collectively, we found that the metabolites produced by human CES-, CYP2E1-, and CYP3A4-mediated metabolism were involved in prilocaine- and lidocaine-induced methemoglobinemia.

Peripheral nerve injury after local anesthetic injection.

BACKGROUND: A well-known complication of peripheral nerve block is peripheral nerve injury, whether from the needle or toxicity of the medication used. In this study, we sought to determine the extent of damage that results from intrafascicular injection of various commonly used local anesthetics (LAs). METHODS: Sixteen Lewis rats received an intrafascicular injection of saline (control) or 1 of 3 LAs (bupivacaine, lidocaine, or ropivacaine) into the sciatic nerve (n = 4). At a 2-week end point, the sciatic nerves were harvested for histomorphometric and electron microscopic analysis. RESULTS: Animals that received intrafascicular LA injections showed increased severity of injury as compared with control. In particular, there was a significant loss of large-diameter fibers as indicated by decreased counts (P < 0.01 for all LAs) and area (P < 0.01 for all LAs) of remaining fibers in severely injured versus noninjured areas of the nerve. There was a layering of severity of injury with most severely injured areas closest to and noninjured areas furthest from the injection site. Bupivacaine caused more damage to large fibers than the other 2 LAs. In all groups, fascicular transection injury from the needle was observed. Electron microscopy confirmed nerve injury. CONCLUSIONS: Frequently used LAs at traditional concentrations are toxic to and can injure the peripheral nerve. Any combination of motor and/or sensory sequelae may result due to the varying fascicular topography of a nerve.

Local toxicity from local anesthetic polymeric microparticles.

BACKGROUND: Local tissue injury from sustained-release formulations for local anesthetics can be severe. There is considerable variability in reporting of that injury. We investigated the influence of the intrinsic myotoxicity of the encapsulated local anesthetic (lidocaine, low; bupivacaine, high) on tissue reaction in rats. METHODS: Cytotoxicity from a range of lidocaine and bupivacaine concentrations was measured in C2C12 myotubes over 6 days. Rats were given sciatic nerve blocks with 4 microparticulate formulations of lidocaine and bupivacaine: 10% (w/w) lidocaine poly(lactic-co-glycolic) acid (PLGA), 10% (w/w) bupivacaine PLGA, 50% (w/w) lidocaine PLGA, and 50% (w/w) bupivacaine PLGA. Effectiveness of nerve blockade was assessed by a modified hotplate test and weightbearing measurements. Myotoxicity was scored in histologic sections of injection sites. Bupivacaine and lidocaine release kinetics from the particles were measured. RESULTS: Median sensory blockade duration for 50% (w/w) lidocaine was 255 (90-540) minutes versus 840 (277-1215) minutes for 50% (w/w) bupivacaine (P = 0.056). All microparticulate formulations resulted in myotoxicity. The choice of local anesthetic did not influence the severity of myotoxicity. Median myotoxicity scores for 50% (w/w) lidocaine compared with 50% (w/w) bupivacaine at 4 days were 3.4 (2.1-4.2) vs 3.3 (2.9-3.5) (P = 0.44) and at 14 days 1.9 (1.8-2.4) vs 1.7 (1.3-1.9) (P = 0.23), respectively. CONCLUSIONS: Lidocaine and bupivacaine PLGA microspheres resulted in similar degrees of myotoxicity, irrespective of drug loading. Intrinsic myotoxicity did not predict tissue injury from sustained release of these anesthetics. Caution is warranted in the use of such devices near muscle and nerve.