Lidocaine and seizures

A novel strategy to increase the therapeutic potency of GBM chemotherapy via altering parenchymal/cerebral spinal fluid clearance rate

Patients with glioblastoma (GBM) face a poor prognosis with a median survival of less than two years. Escalating the dose of chemotherapy is often impossible due to patient comorbidities; thus, we focused on modulating brain clearance as a mechanism to enhance drug accumulation. Given the recently identified interconnectivity between brain parenchymal fluid and cerebral spinal fluid (CSF), we reasoned enhancing drug concentration in the CSF also increases drug concentration in the parenchyma where a GBM resides. To improve drug accumulation in the CSF, we impair the motility of ependymal cell cilia. We identified FDA-approved therapeutics that interact with cilia as a "side effect." Therapeutics that inhibit airway cilia also inhibit ependymal cilia. Multiple cilia-inhibiting drugs, when administered in combination with GBM chemotherapy temozolomide (TMZ), significantly improved the overall survival of mice bearing orthotopic GBM. Combining TMZ with lidocaine results in 100% of animals surviving tumor-free to the study endpoint. This treatment results in a ~ 40-fold increase in brain TMZ levels and is well-tolerated. Mice bearing MGMT methylated, human PDX orthotopic GBM also responded with 100% of animals surviving tumor-free to the study endpoint. Finally, even mice bearing TMZ-resistant, orthotopic GBM responded to the combination treatment with 40% of animals surviving tumor-free to the study endpoint, implying this strategy can sensitize TMZ-resistant GBM. These studies offer a new concept for treating malignant brain tumors by improving the accumulation of TMZ in the CNS. In the future, this regimen may also improve the treatment of additional encephalopathies treated by brain-penetrating therapeutics. SIGNIFICANCE: We exploit the interconnectivity of parenchymal and cerebral spinal fluid to enhance the amount of temozolomide that accumulates in the central nervous system to improve the survival of mice bearing brain tumors.

Clinical effects and pharmacokinetics of nebulized lidocaine in healthy horses

Background

Nebulized lidocaine appears promising as a novel corticosteroid-sparing therapeutic for equine asthma, but its safety and pharmacokinetic behavior have yet to be confirmed.

Objective

To describe the effect of nebulized lidocaine on upper airway sensitivity, lung mechanics, and lower respiratory cellular response of healthy horses, as well as delivery of lidocaine to lower airways, and its subsequent absorption, clearance, and duration of detectability.

Animals

Six healthy university- and client-owned horses with normal physical examination and serum amyloid A, and no history of respiratory disease within 6 months.

Methods

Prospective, descriptive study evaluating the immediate effects of 1 mg/kg 4% preservative-free lidocaine following nebulization with the Flexineb^®. Prior to and following nebulization, horses were assessed using upper airway endoscopy, bronchoalveolar lavage, and pulmonary function testing with esophageal balloon/pneumotachography and histamine bronchoprovocation. Additionally, blood and urine were collected at predetermined times following single-dose intravenous and nebulized lidocaine administration for pharmacokinetic analysis.

Results

Upper airway sensitivity was unchanged following lidocaine nebulization, and no laryngospasm or excessive salivation was noted. Lidocaine nebulization (1 mg/kg) resulted in a mean epithelial lining fluid concentration of 9.63 ± 5.05 μg/mL, and a bioavailability of 29.7 ± 7.76%. Lidocaine concentrations were higher in epithelial lining fluid than in systemic circulation (C_max 149.23 ± 78.74 μg/L, C_ELF:C_maxplasma 64.4, range 26.5–136.8). Serum and urine lidocaine levels remained detectable for 24 and 48 h, respectively, following nebulization of a single dose. Baseline spirometry, lung resistance and dynamic compliance, remained normal following lidocaine nebulization, with resistance decreasing post-nebulization. Compared to the pre-nebulization group, two additional horses were hyperresponsive following lidocaine nebulization. There was a significant increase in mean airway responsiveness post-lidocaine nebulization, based on lung resistance, but not dynamic compliance. One horse had BAL cytology consistent with airway inflammation both before and after lidocaine treatment.

Conclusions

Nebulized lidocaine was not associated with adverse effects on upper airway sensitivity or BAL cytology. While baseline lung resistance was unchanged, increased airway reactivity to histamine bronchoprovocation in the absence of clinical signs was seen in some horses following nebulization. Further research is necessary to evaluate drug delivery, adverse events, and efficacy in asthmatic horses.

Drug-Induced Seizures: Considerations for Underlying Molecular Mechanisms

A broad spectrum of chemical entities have been associated with drug-induced seizure (DIS), emphasizing the importance of this potential liability across various drug classes (e.g., antidepressants, antipsychotics, antibiotics, and analgesics among others). Despite its importance within drug safety testing, an understanding of the molecular mechanisms associated with DIS is often lacking. The etiology of DIS is understood to be a result of either a deficit in inhibitory (e.g., gamma aminobutyric acid) or an elevated excitatory (e.g., glutamate) signaling, leading to synchronous neuronal depolarization affecting various brain regions and impairing normal neurological functions. How this altered neuronal signaling occurs and how these changes interact with other non-brain receptor driven DIS-associated changes such as metabolic disturbances, electrolyte imbalances, altered drug metabolism, and withdrawal effects are poorly understood. Herein, we discuss important molecular mechanisms identified in DIS for several drugs and/or drug classes. With a better understanding of the molecular mechanisms associated with DIS, in vivo or in vitro models may be applied to characterize and mitigate DIS risk during drug development. Susceptibility stratification for DIS presents species differences in the following order beagle dogs > rodents and cynomolgus monkeys > Göttingen minipigs with a more than 2-fold difference between canines and minipigs, which is important to consider during non-clinical species selection. While clinical signs such as myoclonus, severe muscle jerks, or convulsions are often associated with abnormal epileptiform EEG activity, tremors are most of the time physiological and rarely observed with concurrent epileptiform EEG activity which need to be considered during DIS risk evaluation.

Focused ultrasound enhances the anesthetic effects of topical lidocaine in rats

BACKGROUND

High-intensity ultrasound has been used to induce acoustic cavitation in the skin and subsequently enhances skin permeability to deliver hydrophobic topical medications including lidocaine. In contrast, instead of changing skin permeability, pulsed application of low-intensity focused ultrasound (FUS) has shown to non-invasively and temporarily disrupt drug-plasma protein binding, thus has potential to enhance the anesthetic effects of hydrophilic lidocaine hydrochloride through unbinding it from serum/interstitial α1-acid glycoprotein (AAG).

METHODS

FUS, operating at fundamental frequency of 500 kHz, was applied pulse-mode (55-ms pulse duration, 4-Hz pulse repetition frequency) at a spatial-peak pulse-average intensity of 5 W/cm2. In vitro equilibrium dialysis was performed to measure the unbound concentration of lidocaine (lidocaine hydrochloride) from dialysis cassettes, one located at the sonication focus and the other outside the sonication path, all immersed in phosphate-buffered saline solution containing both lidocaine (10 µg/mL) and human AAG (5 mg/mL). In subsequent animal experiments (Sprague-Dawley rats, n = 10), somatosensory evoked potential (SSEP), elicited by electrical stimulations to the unilateral hind leg, was measured under three experimental conditions-applications of FUS to the unilateral thigh area at the site of administered topical lidocaine, FUS only, and lidocaine only. Skin temperature was measured before and after sonication. Passive cavitation detection was also performed during sonication to evaluate the presence of FUS-induced cavitation.

RESULTS

Sonication increased the unbound lidocaine concentration (8.7 ± 3.3 %) from the dialysis cassette, compared to that measured outside the sonication path (P < 0.001). Application of FUS alone did not alter the SSEP while administration of lidocaine reduced its P23 component (i.e., a positive peak at 23 ms latency). The FUS combined with lidocaine resulted in a further reduction of the P23 component (in a range of 21.8 - 23.4 ms after the electrical stimulations; F(2,27) = 3.2 - 4.0, P < 0.05), indicative of the enhanced anesthetic effect of the lidocaine. Administration of FUS neither induced cavitation nor altered skin conductance or temperature, suggesting that skin permeability was unaffected.

CONCLUSIONS

Unbinding lidocaine from the plasma proteins by exposure to non-thermal low-intensity ultrasound is attributed as the main mechanism behind the observation.

Conjoint analysis of influence of LC-HCL and Mor-HCL on Vth and neurite length in hippocampal neuronal network

Lidocaine hydrochloride (LC-HCl) and morphine hydrochloride (Mor-HCl) are two kinds of most prevalently used anesthetics. However, their influences on electrical excitability of hippocampal neuronal networks and hippocampal brain slices were rarely studied. Previously, our group have assessed the influence of acetylcholine, alcohol and temperature change on the excitability of neural networks with the so-called Voltage Threshold Measurement Method (VTMM) based on microelectrode array (MEA). In this paper, we will study the influence of LC-HCl and Mor-HCl on the electrical excitability of neural networks and the morphological features of neurons, and discuss the relations between the changes of electrical excitability of neural networks and the morphological changes of neurons. The results of VTMM showed: The voltage threshold (V_Th) of hippocampal neuronal networks and hippocampal brain slices first increased and then decreased as the LC-HCl concentration increased. The V_Th of hippocampal neuronal networks and hippocampal brain slices increased as the Mor-HCl concentration increased. The results of HCS experiments showed: The neurite length change of cultured hippocampal neuronal networks increased first and then decreased with increased LC-HCl concentration, but decreased as the Mor-HCl concentration increased. The combined analysis of VTMM and HCS experiments showed that under effects of the two drugs, the V_Th and the hippocampal neurite length were strongly negatively correlated.

Status Epilepticus in the Neonate: Updates in Treatment Strategies

PURPOSE OF REVIEW

The purpose of this review is to report recent advances in treatment of neonatal seizures, with a specific focus on new literature since a 2013 systematic review performed by this author (Slaughter) and others. There is a paucity of data with regard to well-defined status epilepticus (SE) in neonates, so treatment of recurrent seizures was also included in this inquiry. We aimed to summarize the efficacy and safety profiles of current therapeutic options as well as describe trends in medication selection in the neonatal intensive care unit (NICU) setting.

RECENT FINDINGS

Phenobarbital remains first-line therapy in practice, though there is increasing evidence of its neurotoxicity and long-term sequelae. Bumetanide failed an open-label trial for efficacy, demonstrated an increased risk for hearing loss, and has since fallen out of favor for use in this population. New agents, such as levetiracetam and topiramate, still have very limited data but appear to be as efficacious as older medications, with more favorable side effect profiles. There are limited high-level evidence-based data to guide treatment of neonatal seizures. Emerging research focusing on drug mechanisms and safety profiles may provide additional information to guide decisions; however, further research is needed.

Seizure liability assessments using the hippocampal tissue slice: Comparison of non-clinical species

INTRODUCTION

Traditionally, rat hippocampal tissue slice models are used as an in vitro electrophysiology assay to assess seizurogenic potential in early drug development despite non-clinical species-specific differences noted during in vivo seizure studies.

METHODS

Hippocampal tissue slices were acutely isolated from rats, minipigs, dogs and nonhuman primates (NHP). Population spikes (PS) were evoked through stimulation of the CA3 Schaffer collateral pathway and recorded using in vitro electrophysiological techniques via an extracellular electrode placed within the CA1 stratum pyramidale cell body layer.

RESULTS

Hippocampal slices, across all species, displayed a concentration-dependent increase in PS area and number with the pro-convulsant pentylenetetrazol (PTZ; 0.1-10mM). Beagle dogs exhibited higher sensitivities to PTZ-induced changes in PS area and number compared to both rats and NHPs which presented nuanced differences in their responsiveness to PTZ modulation. Minipigs were comparatively resistant to PTZ-induced changes in both PS area and number. Rat and NHP hippocampal tissues were further characterized with the pro-convulsant agents 4-aminopyradine (4-AP; 1-100μM) and cefazolin (0.001-10mM). Rats possessed higher sensitivities to 4-AP- and cefazolin-induced changes to both PS area and number whereas NHP displayed greater modulation in PS duration. The anti-convulsant agents, diazepam (10-500μM) and lidocaine (1-500μM), were also tested on either rat and/or NHP tissue with both drugs repressing PS activation at high concentrations.

DISCUSSION

Hippocampal tissue slices, across all species, possessed distinct sensitivities to pro- and anti-convulsant agents which may benefit the design of non-clinical seizure liability studies and their associated data interpretation.

Chronic Pain in Neurosurgery

This review includes a summary of contemporary theories of pain processing and advocates a multimodal analgesia approach for providing perioperative care. A summary of various medication classes and anesthetic techniques is provided that highlights evidence emerging from neurosurgical literature. This summary covers opioid management, acetaminophen, nonsteroidal antiinflammatories, ketamine, lidocaine, dexmedetomidine, corticosteroids, gabapentin, and regional anesthesia for neurosurgery. At present, there is not enough investigation into these areas to describe best practices for treating or preventing chronic pain in neurosurgery; but providers can identify a wider range of options available to personalize perioperative care strategies.

Medical Disorders Related to Diving

Exposure to the underwater environment is associated with several unique disorders that may require recompression in a hyperbaric chamber. Increasing pressure during descent reduces the volume of the paranasal sinuses and middle ear, which, if not properly equalized, will sustain injury due to barotrauma. Barotrauma of the inner ear results in vertigo, tinnitus, and often permanent hearing loss. During ascent, expanding gas can produce lung injury accompanied by pneumothorax, mediastinal and subcutaneous emphysema, injection of air into the pulmonary veins, and arterial air embolism to the brain. Divers with pulmonary barotrauma often present with unconsciousness, seizures, or other evidence of cerebral dysfunction. Rapid treatment with recompression often reverses the cerebral deficits. Air embolism lesions are usually diffuse, in contradistinction to a stroke which usually follows the distribution of a single cerebral artery. Decompression sickness is a disorder caused by evolution of supersaturated dissolved gas in tissues and blood following exposure to increased pressure. Protocols for avoiding excess supersaturation during ascent from depth have been available for more than 100 years, and diving is considered safe when established decompression schedules are followed. Decompression sickness causes pain in the joints of the upper and lower extremities, and can injure the spinal cord. Paralysis, paresthesias, sensory loss, and bowel and bladder paralysis accompany spinal cord injury. Treatment involves recompression and oxygen. Platelet inhibitors and other anti-inflammatory drugs are also useful. A diving disorder must be considered in any patient with a neurologic syndrome, vertigo, hearing loss, or joint pain following diving.

Recurrent seizures after lidocaine ingestion

Lidocaine has a concentration-dependent effect on seizures. Concentrations above 15 μg/mL frequently result in seizures in laboratory animals and human. We report a case of central nervous system (CNS) lidocaine toxicity and recurrent seizure after erroneous ingestion of lidocaine solution. A 4-year-old boy presented to the Emergency Department of Imam Hospital of Sari in December 2013 due to tonic-clonic generalized seizures approximately 30 min ago. 3 h before seizure, his mother gave him 2 spoons (amount 20-25 cc) lidocaine hydrochloride 2% solution instead of pediatric gripe by mistake. Seizure with generalized tonic-clonic occurred 3 times in home. Neurological examination was essentially unremarkable except for the depressed level of consciousness. Personal and medical history was unremarkable. There was no evidence of intracranial ischemic or hemorrhagic lesions in computed tomography scan. There were no further seizures, the condition of the patient remained stable, and he was discharged 2 days after admission. The use of viscous lidocaine may result in cardiovascular and CNS toxicity, particularly in children. Conservative management is the best option for treatment of lidocaine induced seizure.

Optimal antiarrhythmic drug therapy for electrical storm

Electrical storm, defined as 3 or more separate episodes of ventricular tachycardia or ventricular fibrillation within 24 hours, carries significant morbidity and mortality. These unstable ventricular arrhythmias have been described with a variety of conditions including ischemic heart disease, structural heart disease, and genetic conditions. While implantable cardioverter defibrillator implantation and ablation may be indicated and required, antiarrhythmic medication remains an important adjunctive therapy for these persons.

Tranexamic Acid Impairs γ-Aminobutyric Acid Receptor Type A–mediated Synaptic Transmission in the Murine Amygdala

Background:

Tranexamic acid (TXA) is commonly used to reduce blood loss in cardiac surgery and in trauma patients. High-dose application of TXA is associated with an increased risk of postoperative seizures. The neuronal mechanisms underlying this proconvulsant action of TXA are not fully understood. In this study, the authors investigated the effects of TXA on neuronal excitability and synaptic transmission in the basolateral amygdala.

Methods:

Patch clamp recordings and voltage-sensitive dye imaging were performed in acute murine brain slices. Currents through N-methyl-d-aspartate, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, and γ-aminobutyric acid receptor type A (GABAA) receptors were recorded. GABAA receptor–mediated currents were evoked upon electrical stimulation or upon photolysis of caged GABA. TXA was applied at different concentrations.

Results:

Voltage-sensitive dye imaging demonstrates that TXA (1 mM) reversibly enhances propagation of neuronal excitation (mean ± SEM, 129 ± 6% of control; n = 5). TXA at concentrations of 0.1, 0.3, 1, 5, or 10 mM led to a dose-dependent reduction of GABAA receptor–mediated currents in patch clamp recordings. There was no difference in the half-maximal inhibitory concentration for electrically (0.76 mM) and photolytically (0.84 mM) evoked currents (n = 5 to 9 for each concentration), and TXA did not affect the paired-pulse ratio of GABAA receptor–mediated currents. TXA did not impact glutamatergic synaptic transmission.

Conclusions:

This study clearly demonstrates that TXA enhances neuronal excitation by antagonizing inhibitory GABAergic neurotransmission. The results provide evidence that this effect is mediated via postsynaptic mechanisms. Because GABAA receptor antagonists are known to promote epileptiform activity, this effect might explain the proconvulsant action of TXA.

Cardiorespiratory and antinociceptive effects of two different doses of lidocaine administered to horses during a constant intravenous infusion of xylazine and ketamine

BACKGROUND

This study investigated the antinociceptive effects of a constant rate infusion (CRI) of lidocaine during xylazine and ketamine anesthesia in horses and aimed to correlate these effects with cardiorespiratory variables, bispectral index (BIS) and plasma lidocaine concentrations. Six adult crossbred mares weighing 320-400 kg were anesthetized on three different occasions. Sedation was performed with xylazine (0.75 mg/kg IV) and anesthetic induction with guaifenesin (75 mg/kg IV) and ketamine (2 mg/kg IV). Anesthesia was maintained with 37.5 μg/kg/min of xylazine and 87.5 μg/kg/min of ketamine both administered intravenously for 75 min. The three treatments consisted of: lidocaine (loading dose: 5 mg/kg, CRI: 100 μg/kg/min; THL); lidocaine (loading dose: 2.5 mg/kg; CRI: 50 μg/kg/min: TLL); and saline (TS); all given 15 min after induction and maintained for 1 h. Antinociception was measured by response to electrical stimulation and bispectral index (BIS) was recorded during anesthesia. Parametric and non-parametric data were compared using ANOVA followed by Student-Newman-Keuls and Friedman tests, respectively.

RESULTS

Plasma lidocaine concentrations peaked at the end of lidocaine loading dose and was greater in THL (9.61 ± 2.75 μg/mL) vs TLL (4.50 ± 3.34 μg/mL). Electrical noxious stimulation caused purposeful movement in all horses from TS, but no response in THL. The BIS was decreased in THL only and was less when compared to the other treatments throughout anesthesia. Blood pressure, PaO2 and PaCO2 increased and heart rate (HR), respiratory rate (RR), pH, total plasma protein and temperature decreased during anesthesia in all treatments. PaCO2 and HR were greater and RR and pH less in THL compared to TLL and TS at 30 min during anesthesia. All recoveries were considered excellent. Time to standing was longer after THL (60 ± 20 min) than following TLL and TS (32 ± 17 and 30 ± 15 min, respectively).

CONCLUSIONS

At the highest dose administered (THL) lidocaine CRI during xylazine/ketamine anesthesia decreased BIS and motor response to noxious stimulation, and prolonged recovery time without significant added cardiorespiratory depression.

Antidepressant overdose-induced seizures

Treating patients with psychiatric problems can present numerous challenges for clinicians. The deliberate self-ingestion of antidepressants is one such challenge frequently encountered in hospitals throughout the United States. This review focuses on 1) the classes of antidepressants, their pharmacologic properties, and some of the proposed mechanism(s) for antidepressant overdose-induced seizures; 2) the evidence for seizures caused by antidepressants in overdose; 3) management strategies for patients who have intentionally or unintentionally overdosed on an antidepressant, or who have experienced an antidepressant overdose-induced seizure.

Antidepressant overdose-induced seizures

Antidepressants are the most commonly prescribed class of medications in the United States. The clinician should be mindful of the many antidepressants that can produce seizures following an accidental exposure or an overdose. A broader understanding of the seizure potential of antidepressants, combined with the ability to recognize individuals at risk for a seizure after an overdose, can aid clinicians in determining the need for inpatient monitoring, and help facilitate their treatment decisions.

Effect of PaCO2 and PaO2 on lidocaine and articaine toxicity

Alterations in arterial PaCO₂ can influence local anesthetic toxicity. The objective of this study was to evaluate the effect of stress-induced changes in PaCO₂ and PaO₂ on the seizure threshold of lidocaine and articaine. Lidocaine (2% with 1 : 100,000 epinephrine) or articaine (4% with 1 : 100,000 epinephrine) was administered intravenously under rest or stress conditions to 36 rats separated into 4 groups. Propranolol and prazosin were administered preoperatively to minimize cardiovascular effects of epinephrine. Mean arterial pressure (MAP), heart rate (HR), and arterial pH, PaCO₂, and PaO₂ were measured. Results showed no differences in MAP, HR, or pH. Stress significantly increased the latency period for the first tonic-clonic seizure induced by a toxic dose of both lidocaine and articaine (P < .05). Seizures were brought on more rapidly by articaine. No significant difference between toxic doses of lidocaine and articaine was noted. Stress raised the seizure threshold dose for both drugs and significantly (P < .01) increased arterial PaO₂ from 94.0 ± 1.90 mm Hg to 113.0 ± 2.20 mm Hg, and reduced PaCO₂ from 36.0 ± 0.77 mm Hg to 27.0 ± 0.98 mm Hg. In conclusion, reduction in PaCO₂ and/or increase in PaO₂ raised the seizure threshold of lidocaine and articaine. This study also confirmed that lidocaine and articaine have equipotent central nervous system toxicity.

Depolarizing shift in the GABA-induced current reversal potential by lidocaine hydrochloride

Lidocaine hydrochloride (LC-HCl) is widely used as a local anesthetic, while various adverse effects of LC-HCl, such as seizures have also been reported. Lidocaine is reported to inhibit various channels and receptors including GABA(A) receptors. Although the GABA(A) receptor-mediated response depends on Cl(-) equilibrium potential (E(Cl)), little is known about the effect of LC-HCl on E(Cl). In the present study, we investigated the effect of LC-HCl on GABA-induced currents in cultured rat hippocampal neurons with gramicidin-perforated patch-clamp recording which is known to keep the intracellular Cl(-) concentration intact. LC-HCl inhibited outward GABA-induced currents with depolarizing shift of the GABA reversal potential (E(GABA)). The LC-HCl-induced positive E(GABA) shift was not observed with conventional whole-cell patch-clamp method which cannot retain intact intracellular Cl(-) concentration. The LC-HCl action on E(GABA) was inhibited by either furosemide, a blocker of both Na(+)-K(+)-Cl(-) cotransporter (NKCC) and K(+)-Cl(-) cotransporter (KCC), or an increase in extracellular K(+) concentrations. Neither bumetanide, a specific inhibitor of NKCC, nor Na(+)-free external solution had any effect on the LC-HCl-induced E(GABA) shift. QX-314, a membrane impermeable lidocaine derivative, failed to shift E(GABA) to positive potential. Furthermore, LC-HCl caused a depolarizing shift of E(GABA) in cultured GT1-7 cells expressing KCC2 but failed to change E(GABA) in GT1-7 cells without expression of KCC2. These results suggest that the LC-HCl-induced positive E(GABA) shift is due to a blockade of KCC2. Together with the direct LC-HCl action to GABA(A) receptors, the positive E(GABA) shift induced by LC-HCl reduces the GABAergic inhibition in the central nervous system.

Systemic Levels of Local Anaesthetic after Intra-Peritoneal Application – a Systematic Review

There is a lack of cohesive reports on the systemic levels of local anaesthetic after intraperitoneal application. A comprehensive systematic review with no language restriction was conducted. Eighteen suitable articles were identified. Data were compiled and presented according to local anaesthetic agent. Intraperitoneal local anaesthetic has been studied in many different procedures, including open and laparoscopic surgery. A total of 415 patients were included for analysis. There were no cases of clinical toxicity. There were 11 (2.7%) cases with a systemic level above or close to a safe threshold (as determined by the report authors) in three trials utilising intraperitoneal local anaesthetic after laparoscopic cholecystectomy. Intraperitoneal lignocaine doses varied from 100 to 1000 mg, mean Cmax ranged from 1.01 to 4.32 μg/ml and mean Tmax ranged from 15 to 40 minutes. Intraperitoneal bupivacaine doses varied from 50 to 150 mg (weight based doses also reported), mean Cmax ranged from 0.29 to 1.14 μg/ml and mean Tmax ranged from 15 to 60 minutes. Intraperitoneal ropivacaine doses varied from 100 to 300 mg, mean Cmax ranged from 0.66 to 3.76 μg/ml and mean Tmax ranged from 15 to 35 minutes. The addition of adrenaline to intraperitoneal local anaesthetic almost halves systemic levels and prolongs Tmax. Intraperitoneal local anaesthetic results in detectable systemic levels in the perioperative setting. Despite a lack of clinical toxicity, careful attention to dose is still required to prevent potential systemic toxic levels. Clinicians should also consider the addition of adrenaline to intraperitoneal local anaesthetic solutions to further add to the systemic safety profile.

Seizures during medetomindine sedation and local anaesthesia in two dogs undergoing skin biopsy

Each of two dogs presented for multiple skin biopsies were sedated with intravenous medetomidine and lignocaine was injected subcutaneously to provide local anaesthesia for skin biopsy. One dog had a seizure during skin biopsy and again immediately following reversal of medetomidine with atipamezole. The other dog developed seizures 2 h following skin biopsy at which time the medetomidine was reversed with atipamezole. Both dogs were neurologically normal with no history of seizures prior to the procedure and remained neurologically normal for 14 weeks and 9 months, respectively, following the procedure. A drug interaction between the alpha(2)-adrenergic agonist medetomidine and lignocaine is suspected and highlights the potential for seizures following the subcutaneous administration of relatively large doses of lignocaine under medetomidine sedation.

Investigation of the effects of the novel anticonvulsant compound carisbamate (RWJ-333369) on rat piriform cortical neurones in vitro

BACKGROUND AND PURPOSE

Carisbamate is being developed for adjuvant treatment of partial onset epilepsy. Carisbamate produces anticonvulsant effects in primary generalized, complex partial and absence-type seizure models, and exhibits neuroprotective and antiepileptogenic properties in rodent epilepsy models. Phase IIb clinical trials of carisbamate demonstrated efficacy against partial onset seizures; however, its mechanisms of action remain unknown. Here, we report the effects of carisbamate on membrane properties, evoked and spontaneous synaptic transmission and induced epileptiform discharges in layer II-III neurones in piriform cortical brain slices.

EXPERIMENTAL APPROACH

Effects of carisbamate were investigated in rat piriform cortical neurones by using intracellular electrophysiological recordings.

KEY RESULTS

Carisbamate (50-400 micromol x L(-1)) reversibly decreased amplitude, duration and rise-time of evoked action potentials and inhibited repetitive firing, consistent with use-dependent Na+ channel block; 150-400 micromol x L(-1) carisbamate reduced neuronal input resistance, without altering membrane potential. After microelectrode intracellular Cl(-) loading, carisbamate depolarized cells, an effect reversed by picrotoxin. Carisbamate (100-400 micromol x L(-1)) also selectively depressed lateral olfactory tract-afferent evoked excitatory synaptic transmission (opposed by picrotoxin), consistent with activation of a presynaptic Cl(-) conductance. Lidocaine (40-320 micromol x L(-1)) mimicked carisbamate, implying similar modes of action. Carisbamate (300-600 micromol x L(-1)) had no effect on spontaneous GABA(A) miniature inhibitory postsynaptic currents and at lower concentrations (50-200 micromol x L(-1)) inhibited Mg2+-free or 4-aminopyridine-induced seizure-like discharges.

CONCLUSIONS AND IMPLICATIONS

Carisbamate blocked evoked action potentials use-dependently, consistent with a primary action on Na+ channels and increased Cl(-) conductances presynaptically and, under certain conditions, postsynaptically to selectively depress excitatory neurotransmission in piriform cortical layer Ia-afferent terminals.

The pharmacology of voltage-gated sodium channels in sensory neurones

Voltage-gated sodium channels (VGSCs) are vital for the normal functioning of most excitable cells. At least nine distinct functional subtypes of VGSCs are recognized, corresponding to nine genes for their pore-forming alpha-subunits. These have different developmental expression patterns, different tissue distributions in the adult and are differentially regulated at the cellular level by receptor-coupled cell signalling systems. Unsurprisingly, VGSC blockers are found to be useful as drugs in diverse clinical applications where excessive excitability of tissue leads to pathological dysfunction, e.g. epilepsy or cardiac tachyarrhythmias. The effects of most clinically useful VGSC blockers are use-dependent, i.e. their efficacy depends on channel activity. In addition, many natural toxins have been discovered that interact with VGSCs in complex ways and they have been used as experimental probes to study the structure and function of the channels and to better understand how drugs interact with the channels. Here we have attempted to summarize the properties of VGSCs in sensory neurones, discuss how they are regulated by cell signalling systems and we have considered briefly current concepts of their physiological function. We discuss in detail how drugs and toxins interact with archetypal VGSCs and where possible consider how they act on VGSCs in peripheral sensory neurones. Increasingly, drugs that block VGSCs are being used as systemic analgesic agents in chronic pain syndromes, but the full potential for VGSC blockers in this indication is yet to be realized and other applications in sensory dysfunction are also possible. Drugs targeting VGSC subtypes in sensory neurones are likely to provide novel systemic analgesics that are tissue-specific and perhaps even disease-specific, providing much-needed novel therapeutic approaches for the relief of chronic pain.

Lidocaine treatment in pediatric convulsive status epilepticus

BACKGROUND

Convulsive status epilepticus (CSE) may end fatally or leave serious sequelae. CSE treatment, invariably an emergency case, is based upon i.v. benzodiazepines as well as phenytoin, barbiturates or both. The present paper reports efficiency of lidocaine in CSE.

METHODS

The effects of lidocaine on patients with CSE due to infectious and non-infectious reasons were compared. Lidocaine was given in 29 episodes of CSE to 49 patients having failed to respond to first-line anticonvulsive drugs, such as diazepam, phenobarbital and phenytoin therapy. Lidocaine was given in doses of 2 mg/kg bolus i.v., and then in 4 mg/kg per h infusion.

RESULTS

Mean duration of lidocaine infusion was 14.6 +/- 7.8 h. Effectiveness of lidocaine in patients with CSE was found to be 44.4%. Also, 11 patients responded to a single dose of lidocaine (37.9%), while another two (6.9%) required another dose to suppress their seizures. Patients with seizures attributable to infections were observed to have responded favorably to lidocaine when compared to those with seizures due to epilepsy (37.9% vs 6.8%; P < 0.05). Subsequent epilepsy was found to occur more frequently in patients with a poor response to lidocaine than in patients with a good response (P < 0.05). Adverse reactions to lidocaine were observed in three patients (10.3%), two of them having ventricular arrhythmia. As for the other patient, the focal seizure developed into a generalized one.

CONCLUSIONS

Lidocaine seems to be useful for the management of CSE as a rapid-acting anticonvulsant, particularly in patients with CSE due to infections. But further studies with larger number of patients are needed.

Lidocaine-induced altered mental status and seizure after hematoma block

Hematoma blocks with lidocaine are routinely utilized in the Emergency Department to allow reduction of Colles' fractures. Lidocaine toxicity is a potential complication of this procedure. We present a case report of a patient who developed acute mental status changes and generalized seizure immediately following administration of lidocaine during a hematoma block. The rapid onset of seizure development following injection was most likely due to inadvertent intravascular administration.

Development of an optimal lidocaine infusion strategy for neonatal seizures

INTRODUCTION

Lidocaine is an effective drug for the treatment of neonatal convulsions not responding to traditional anticonvulsant therapy. However, one of the side-effects is a risk of cardiac arrhythmias. The aim of this study was to develop an optimal dosing strategy with minimal risk of cardiac arrhythmias.

MATERIALS AND METHODS

As a first step, we studied 20 neonates during routine treatment of neonatal seizures with lidocaine. All were given a loading dose of 2 mg/kg in 10 min, followed by the continuous infusion of 6 mg/kg per hour for 12 h, 4 mg/kg per hour for 12 h and finally 2 mg/kg per hour for 12 h. Effectiveness, cardiac toxicity and lidocaine plasma concentrations were then determined.

RESULTS

No cardiac arrhythmias were observed, and lidocaine was effective in 76% of the treatments. In most of the treatments (13 out of 20) maximal lidocaine plasma concentrations were >9 mg/L. Plasma levels >9 mg/L have been related to cardiac toxicity when used as an anti-arrhythmic drug in adults. It was of interest that all preterm infants showed high lidocaine plasma levels. Secondly, we developed the optimal dosing regimen, which was defined as an infusion regimen at which maximal lidocaine plasma concentrations are <9 mg/L. Simulations with the developed pharmacokinetic model indicated a reduction in the infusion duration of lidocaine at 6 mg/kg per hour from 12 to 6 h. Thirdly, the new lidocaine dosing regimen was evaluated. Fifteen neonates (16 treatments) were studied. No cardiac arrhythmias were observed, and lidocaine was effective in 78% of the treatments. In most of the treatments (11 out of 16) maximal lidocaine plasma concentrations were <9 mg/L. Again preterm infants showed relatively high lidocaine plasma levels.

CONCLUSION

A new lidocaine dosing schedule was developed. This new regimen should have a lower risk of cardiac arrhythmias and appears to be as effective in term infants. For preterm infants the optimal regimen needs to be determined.

Intermittent bolus dosing of lidocaine in emergency medical services-an alternative to bolus followed by a drip

OBJECTIVE

To determine the effectiveness and safety, in an emergency medical services setting, of intermittent bolus dosing of lidocaine versus a bolus followed by a drip.

METHODS

This was a prechange and postchange observational study, following a protocol change. Patients 18 years or older treated with lidocaine for cardiac dysrhythmia were included in the study. Patients were excluded for lidocaine for intubation, cardiac arrest without return of spontaneous circulation, trauma, interhospital transport, and incomplete charts. Patients were divided into two groups. The drip group (January 1, 2002, to January 14, 2003) was treated with lidocaine 1.0-1.5 mg/kg intravenous bolus up to 3 mg/kg until the dysrhythmia resolved and then a 2-4 mg/min drip. The bolus group (January 15, 2003 to December 31, 2003) was treated with lidocaine 1.5 mg/kg intravenous bolus, followed by 0.75 mg/kg bolus every five minutes up to 3 mg/kg until the dysrhythmia resolved; once the dysrhythmia resolved, intermittent boluses of 0.75 mg/kg every 10 minutes were adminstered. Outcome variables studied were maintenance of rhythm of nonventricular origin, occurrence of complications, and adherence to written protocols. Complications considered were seizures, respiratory depression, and cardiac arrest.

RESULTS

The study included 146 patients in the drip group and 113 patients in the bolus group. Overall, 119 of 146 patients (81.5%) in the drip group and 101 of 113 patients (89.3%) in the bolus group maintained a rhythm of nonventricular origin (p = 0.079). There was no statistical difference between the two groups in complications or protocol variance: one of 146 patients (0.7%) in the drip group and one of 113 patients (0.9%) in the bolus group had a serious complication; 64 of 146 patients (43.8%) in the drip group and 54 of 113 patients (47.8%) in the bolus group had a protocol variance.

CONCLUSIONS

Intermittent bolus dosing protocol was associated with an equivalent effectiveness in maintaining rhythms of nonventricular origin without an increase in complications.

Management of Seizures in the Critically Ill

Seizures in a critically ill patient are not infrequent phenomena. Physicians are perplexed by the wide range of possible cranial or extracranial etiologies, alerted by the risk for further crucial organ compromise if seizures recur, and confused about the treatment options in an environment rich in complex drug interactions and multiple organ dysfunction. The advent of an armamentarium containing multiple new antiepileptic medications complicates the situation further, since several of them have less known mechanisms of action, side effects, or interactions with other intensive care unit (ICU) medications. This review contains useful information regarding the most common etiologies and treatment options for intensivists, consulting neurologists, neurosurgeons, or other specialized physicians treating ICU patients with seizures.

Influence of general anesthesia on pharmacokinetics of intravenous lidocaine infusion in horses

OBJECTIVE

To compare the disposition of lidocaine administered IV in awake and anesthetized horses.

ANIMALS

16 horses.

PROCEDURE

After instrumentation and collection of baseline data, lidocaine (loading infusion, 1.3 mg/kg administered during 15 minutes (87 microg/kg/min); constant rate infusion, 50 microg/kg/min) was administered IV to awake or anesthetized horses for a total of 105 minutes. Blood samples were collected at fixed times during the loading and maintenance infusion periods and after the infusion period for analysis of serum lidocaine concentrations by use of liquid chromatography with mass spectral detection. Selected cardiopulmonary parameters including heart rate (HR), mean arterial pressure (MAP), arterial pH, PaCO2, and PaO2 were also recorded at fixed time points during lidocaine administration. Serum lidocaine concentrations were evaluated by use of standard noncompartmental analysis.

RESULTS

Serum lidocaine concentrations were higher in anesthetized than awake horses at all time points during lidocaine administration. Serum lidocaine concentrations reached peak values during the loading infusion in both groups (1,849 +/- 385 ng/mL and 3,348 +/- 602 ng/mL in awake and anesthetized horses, respectively). Most lidocaine pharmacokinetic variables also differed between groups. Differences in cardiopulmonary variables were predictable; for example, HR and MAP were lower and PaO2 was higher in anesthetized than awake horses but within reference ranges reported for horses under similar conditions.

CONCLUSIONS AND CLINICAL RELEVANCE

Anesthesia has an influence on the disposition of lidocaine in horses, and a change in dosing during anesthesia should be considered.

Seizures After a Bier Block with Clonidine and Lidocaine

A 47-yr-old man with history of complex regional pain syndrome type 1 underwent an IV Bier block with a mixture of lidocaine and clonidine. The tourniquet was deflated after 60 min, and approximately 10 min later he presented with complex partial seizures. The possible mechanisms for this are discussed, and the effects of clonidine, lidocaine, and the mixture of both are reviewed, as are four additional published cases reporting seizures after the administration of clonidine.

Excitatory and inhibitory effects of tricaine (MS-222) on fictive breathing in isolated bullfrog brain stem

This study examined the direct effects of tricaine methanesulfonate (MS-222), a sodium-channel blocking local anesthetic, on respiratory motor output using an in vitro brain stem preparation of adult North American bullfrogs (Rana catesbeiana). Bullfrogs were anesthetized with halothane, and the brain stem was removed and superfused with artificial cerebrospinal fluid containing MS-222 at concentrations ranging from 0.1 to 1,000 micro M. At the lowest concentration of MS-222, respiratory frequency (fR) increased significantly (P < 0.05), but at higher concentrations, fR progressively decreased and was abolished in all preparations at 1,000 micro M (P < 0.01). Respiratory burst amplitude and burst duration were not affected by MS-222. The frequency of nonrespiratory neural activity did not significantly change with the addition of MS-222 below 1,000 micro M. These data indicate that MS-222 has a significant, direct effect on respiratory motor output from the central nervous system, producing both excitation and inhibition of fictive breathing. The results are consistent with other studies demonstrating that low concentrations of anesthetics generally cause excitation followed by depression at higher concentrations. Although the mechanisms underlying the excitatory effects of MS-222 in this study are unclear, they may include increased excitatory neurotransmission and/or disinhibition of inputs to the respiratory central pattern generator.

Incidence of intravascular penetration in transforaminal cervical epidural steroid injections

STUDY DESIGN A prospective, observational, human, study was conducted. OBJECTIVES To evaluate the incidence of vascular penetration during fluoroscopically guided, contrast-enhanced transforaminal cervical epidural steroid injections, and to determine whether the observation of blood in the needle hub can be used to predict a vascular injection. SUMMARY OF BACKGROUND DATA Incorrectly placed intravascular cervical spinal injections result in medication flow systemically and not to the desired target. A recently published study demonstrates a high incidence of intravascular injections in transforaminal lumbosacral epidural injections. No studies so far have evaluated the incidence of vascular injections in transforaminal cervical epidural steroid injections, nor have they calculated the ability of observed blood in the needle hub to predict a vascular injection in the cervical spine.METHODS The incidence of fluoroscopically confirmed intravascular uptake of contrast was prospectively observed in 337 patients treated with cervical transforaminal epidural steroid injections. The ability of observed blood in the needle hub to predict intravascular injection was also investigated. For each subject, the injection level was chosen on the basis of the clinical scenario including history, physical examination, and review of imaging studies. Some patients had multilevel injections. Using fluoroscopic guidance, the authors placed a 25-gauge needle into the epidural space using a transforaminal approach according to accepted standard technique. Needle tip location was confirmed with biplanar imaging. The presence or absence of blood in the needle hub spontaneously ("flash") and after attempted aspiration by pulling back on the syringe's plunger was documented. Contrast then was injected under real-time fluoroscopy to determine whether the location of the needle tip was intravascular. The results were recorded in a prospective manner indicating the presence or absence of blood in the needle hub and whether a vascular pattern was noted with contrast injection, and these were correlated. Relevant epidemiologic data also were recorded. RESULTS The study included 504 transforaminal epidural steroid injections. The overall rate of fluoroscopically confirmed intravascular contrast injections was 19.4%. Use of observed blood in the needle hub to predict intravascular injections was 97% specific, but only 45.9% sensitive. There was no significant difference in intravascular rates related to age or gender. CONCLUSIONS As compared with a previous study of lumbosacral epidural steroid injections, there is an overall higher incidence of intravascular injections with cervical transforaminal epidural steroid injections. Use of observed blood in the needle hub to predict an intravascular injection is not sensitive, and therefore the absence of blood in the needle hub despite aspiration is not reliable. The reported sensitivity and specificity rates are similar to lumbar data. Fluoroscopically guided procedures without contrast confirmation instill medications intravascularly, and therefore not in the desired epidural location. This study confirms that there is a need not only for fluoroscopic guidance, but also for contrast instillation in cervical transforaminal epidural steroid injections.