Stereoselective block of cardiac sodium channels by bupivacaine in guinea pig ventricular myocytes

Drugs exhibit diverse binding modes and access routes in the Nav1.5 cardiac sodium channel pore

Small molecule inhibitors of the sodium channel are common pharmacological agents used to treat a variety of cardiac and nervous system pathologies. They act on the channel via binding within the pore to directly block the sodium conduction pathway and/or modulate the channel to favor a non-conductive state. Despite their abundant clinical use, we lack specific knowledge of their protein-drug interactions and the subtle variations between different compound structures. This study investigates the binding and accessibility of nine different compounds in the pore cavity of the Nav1.5 sodium channel using enhanced sampling simulations. We find that most compounds share a common location of pore binding-near the mouth of the DII-III fenestration-associated with the high number of aromatic residues in this region. In contrast, some other compounds prefer binding within the lateral fenestrations where they compete with lipids, rather than binding in the central cavity. Overall, our simulation results suggest that the drug binding within the pore is highly promiscuous, with most drugs having multiple low-affinity binding sites. Access to the pore interior via two out of four of the hydrophobic fenestrations is favorable for the majority of compounds. Our results indicate that the polyspecific and diffuse binding of inhibitors in the pore contributes to the varied nature of their inhibitory effects and can be exploited for future drug discovery and optimization.

A Deep Learning Approach to Uncover Voltage-Gated Ion Channels' Intermediate States

Owing to recent advancements in cryo-electron microscopy, voltage-gated ion channels have gained a greater comprehension of their structural characteristics. However, a significant enigma remains unsolved for a large majority of these channels: their gating mechanism. This mechanism, which encompasses the conformational changes between open and closed states, is pivotal to their proper functioning. Beyond the binary states of open and closed, an ensemble of intermediate states defines the transition path in-between. Due to the lack of experimental data, one might resort to molecular dynamics simulations as an alternative to decipher these states and the transitions between them. However, the high-energy barriers and the colossal time scales involved hinder access to the latter. We present here an application of deep learning as a reliable pipeline for a comprehensive exploration of voltage-gated ion channel conformational rearrangements during gating. We showcase the pipeline performance specifically on the Kv1.2 voltage sensor domain and confront the results with existing data. We demonstrate how our physics-based deep learning approach contributes to the theoretical understanding of these channels and how it might provide further insights into the exploration of channelopathies.

Comparison Between the Effects of Bupivacaine and Levobupivacaine for Spinal Anesthesia on QT Dispersion

BACKGROUND

Bupivacaine and Levobupivacaine are frequently used local anesthetic drugs in spinal anesthesia practice. Both agents have arrhythmic effects on the heart. However, there is no clear information about which agent is more arrhythmogenic.

OBJECTIVE

The aim of this article is to investigate the effects of bupivacaine and its S (-)-enantiomer, levobupivacaine, on cardiac arrhythmias in patients.

METHODS

The study included 40 patients scheduled for inguinal hernia surgery. Patients were randomly divided into the following two groups using a sealed envelope method: Group I, the bupivacaine group (n = 20); and Group II, the levobupivacaine group (n = 20). The QT values were taken preoperatively and during the 10th of the spinal block, the 10th of the surgical incision, and the 10th postoperative minute. Additionally, systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), oxygen saturation (SO₂), and heart rate (HR) values, in addition to motor block (Bromage scale) levels and durations, were recorded for each patient.

RESULTS

HR values measured at 10 min after spinal block were significantly higher than the baseline values in the levobupivacaine group (p < 0.05). The corrected QT interval (QTc) values increased significantly at 10 minutes after spinal block and at 10 min postoperatively in the bupivacaine group (p < 0.05). QTd and QTcd measurements were taken at the 10th minute of spinal anesthesia, the 10th minute of the incision, and the 10th minute postoperatively. When compared to the levobupivacaine group, a statistically significant increase was found in the bupivacaine group (p < 0.05).

CONCLUSION

Levobupivacaine allows greater hemodynamic stability, while bupivacaine affects QTc and QTd measurement times more. As such, we believe that levobupivacaine may be a better alternative to bupivacaine during clinical practice, particularly in patients with cardiac problems.

Identification of a critical binding site for local anaesthetics in the side pockets of Kv 1 channels

BACKGROUND AND PURPOSE

Local anaesthetics block sodium and a variety of potassium channels. Although previous studies identified a residue in the pore signature sequence together with three residues in the S6 segment as a putative binding site, the precise molecular basis of inhibition of K_v channels by local anaesthetics remained unknown. Crystal structures of K_v channels predict that some of these residues point away from the central cavity and face into a drug binding site called side pockets. Thus, the question arises whether the binding site of local anaesthetics is exclusively located in the central cavity or also involves the side pockets.

EXPERIMENTAL APPROACH

A systematic functional alanine mutagenesis approach, scanning 58 mutants, together with in silico docking experiments and molecular dynamics simulations was utilized to elucidate the binding site of bupivacaine and ropivacaine.

KEY RESULTS

Inhibition of K_v 1.5 channels by local anaesthetics requires binding to the central cavity and the side pockets, and the latter requires interactions with residues of the S5 and the back of the S6 segments. Mutations in the side pockets remove stereoselectivity of inhibition of K_v 1.5 channels by bupivacaine. Although binding to the side pockets is conserved for different local anaesthetics, the binding mode in the central cavity and the side pockets shows considerable variations.

CONCLUSION AND IMPLICATIONS

Local anaesthetics bind to the central cavity and the side pockets, which provide a crucial key to the molecular understanding of their K_v channel affinity and stereoselectivity, as well as their spectrum of side effects.

Bupivacaine inhibits a small conductance calcium-activated potassium type 2 channel in human embryonic kidney 293 cells

Background

Bupivacaine blocks many ion channels in the heart muscle, causing severe cardiotoxicity. Small-conductance calcium-activated potassium type 2 channels (SK2 channels) are widely distributed in the heart cells and are involved in relevant physiological functions. However, whether bupivacaine can inhibit SK2 channels is still unclear. This study investigated the effect of bupivacaine on SK2 channels.

Methods

The SK2 channel gene was transfected into human embryonic kidney 293 cells (HEK-293 cells) with Lipofectamine 2000. The whole-cell patch-clamp technique was used to examine the effect of bupivacaine on SK2 channels. The concentration–response relationship of bupivacaine for inhibiting SK2 currents (0 mV) was fitted to a Hill equation, and the half-maximal inhibitory concentration (IC50) value was determined.

Results

Bupivacaine inhibited the SK2 channels reversibly in a dose-dependent manner. The IC50 value of bupivacaine, ropivacaine, and lidocaine on SK2 currents was 16.5, 46.5, and 77.8µM, respectively. The degree of SK2 current inhibition by bupivacaine depended on the intracellular concentration of free calcium.

Conclusions

The results of this study suggested the inhibitory effect of bupivacaine on SK2 channels. Future studies should explore the effects of SK2 on bupivacaine cardiotoxicity.

Ablation of small conductance calcium-activated potassium type-2 channel (SK2) delays occurrence of bupivacaine-induced cardiotoxicity in isolated mouse hearts

Bupivacaine is frequently used for conducting regional anesthesia. When accidentally injected or excessively absorbed into circulation, bupivacaine can induce severe arrhythmia and potentially lead to cardiac arrest. The specific mechanisms underlying this cardiotoxicity, however, remain to be clarified. We transfected HEK-293 cells to express the small conductance calcium-activated potassium type-2 channel (SK2), and used a whole-cell patch clamp method in order to explore how bupivacaine affected these channels. We subsequently used SK2 knockout mice to explore the relevance of SK2 channels in bupivacaine-induced cardiotoxicity in isolating mouse hearts, mounting them on a Langendorff apparatus, and perfusing them with bupivacaine. Using this system, arrhythmia, asystole, and cardiac functions were monitored. We observed dose-dependent inhibition of SK2 channels by bupivacaine: half-maximal inhibitory concentration (IC50) value = 18.6 μM (95% CI 10.8-32.1). When SK2 knockout (SK2 -/-) or wild-type (WT) mice were perfused with Krebs-Henseleit buffer (KHB), we did not observe any instances of arrhythmia. When SK2 -/- mice or WT were perfused with KHB containing bupivacaine (40 μM), the time to arrhythmia (Tarrhythmia) and time to asystole (Tasystole) were both significantly longer in SK2 -/- mice relative to WT mice (P < 0.001). Similarly, SK2 -/- mice exhibited a significantly longer time to 25%, 50%, and 75% reductions in heart rate (HR) and rate-pressure product (RPP) relative to WT mice following bupivacaine perfusion (P < 0.001). These results reveal that bupivacaine was able to mediate a dose-dependent inhibition of SK2 channels in HEK-293 cells, and deletion of SK2 channels can delay bupivacaine-induced cardiotoxicity in isolated mouse hearts.

Comparison of General Anesthesia (Sevoflurane) and Spinal Anesthesia (Levobupivacaine) Methods on QT Dispersion in Inguinal Hernia Operations

Introduction Arrhythmias are one of the most frequently seen issues during surgical operations. In this study, we investigated and compared the effects on the QT dispersion of patients when using a method of volatile inhalation mask anesthesia with sevoflurane (VIMA: Group I) and when spinal anesthesia was performed with levobupivacaine (Group II). Methods The study included 40 patients who had American Society of Anesthesiology scores of I-II (ASA I-II), were aged from 18 to 65 years, and were scheduled for inguinal hernia operations. Approval of the university ethics committee was obtained before the study began. All patients had measurements taken for non-invasive blood pressure, including systolic arterial pressure (SAP), diastolic arterial pressure (DAP), and mean arterial pressure (MAP), heart rate (HR), and oxygen saturation (SO2) values. The QT intervals were measured using the 12-derivation electrocardiogram (ECG) device (Cardiofax V). Our study was performed with randomization using the closed envelope method. Results When the percentage differences of the HR values from the initial period in both groups were compared, we observed significant differences between the groups, with increases in the VIMA group at the second period as well as increases in the VIMA group at the fourth, fifth, sixth, seventh, and ninth periods but decreases in the spinal anesthesia group for these periods. There were statistically significant differences between the two groups at the third and fifth periods when the percentage differences of the QTc values from the initial period were compared. We observed increases in the spinal anesthesia group. Conclusion In our study, we suggest that the tendency toward arrhythmia may be reduced by choosing general anesthesia with sevoflurane rather than levobupivacaine in patients with cardiac complaints who are undergoing regional anesthesia and/or taking medication that affects QT intervals.

Chiral Aspects of Local Anesthetics

Thanks to the progress made in chemical technology (particularly in the methodologies of stereoselective syntheses and analyses) along with regulatory measures, the number of new chiral drugs registered in the form of pure enantiomers has increased over the past decade. In addition, the pharmacological and pharmacokinetic properties of the individual enantiomers of already-introduced racemic drugs are being re-examined. The use of the pure enantiomer of a drug that has been used to date in the form of a racemate is called a "chiral switch". A re-examination of the properties of the pure enantiomers of racemates has taken place for local anesthetics, which represent a group of drugs which have long been used. Differences in (R) and (S)-enantiomers were found in terms of pharmacodynamic and pharmacokinetic activity as well as in toxicity. Levobupivacaine and robivacaine were introduced into practice as pure (S)-(-)-enantiomers, exhibiting more favorable properties than their (R)-(+)-stereoisomers or racemates. This overview focuses on the influence of chirality on the pharmacological and toxicological activity of local anesthetics as well as on individual HPLC and capillary electrophoresis (CE) methods used for enantioseparation and the pharmacokinetic study of individual local anesthetics with a chiral center.

Chirality of Central Nervous System (CNS) Acting Drugs: A Formidable Therapeutic Hurdle Against CNS Diseases

BACKGROUND

Over fifty percent of drugs being used clinically are chiral and 90% of them are racemates. Unfortunately, they have both adverse and beneficial effects on body systems.

METHODS

Because of the erratic effects of chiral compounds on body functional systems, literature search was carried out with a view to identify CNS chiral drugs, their clinical advantages and disadvantages, unique physicochemical properties and structural modifications into safer drugs.

RESULTS

Findings have shown that majority of CNS and non-CNS acting drugs have chiral functional groups that may occur as either dextrorotatory (clockwise) or levorotatory (anticlockwise) or racemates which are inert. Sometimes, the enantiomers (optical isomers) could undergo keto-enol tautomerism, appearing in either acidic or basic or inert form. Chiral CNS acting drugs have agonistic and antagonistic effects, clinical advantages, disadvantages, and special clinical applications, possible modifications for better therapeutic effects and possible synthesis of more potent drugs from racemates. Clockwise chirality may be more effective and safer than the drugs with anticlockwise chirality. When chiral drugs are in racemate state they become inert and may be safer than when they are single. Also, diastereoisomers may be more dangerous than stereoisomers.

CONCLUSION

Therefore, chiral compounds should be adequately studied in lab rodents and primates, and their mechanisms of actions should be comprehensively understood before being used in clinical setting. Since many of them are toxic, their use should be based on principle of individualized medicine. Their molecular weights, functional groups, metabolites, polymers and stereoisomers could be valuable tools for their modifications.

Closed and open state dependent block of potassium channels cause opposing effects on excitability - a computational approach

Block of voltage-gated potassium (Kv) channels has been demonstrated to affect neuronal activity described as increasing excitability. The effect has been associated with a closed-state dependent block. However, the block of Kv channels in e.g. local anesthetic and antiarrhythmics, is open state-dependent. Since the reduced excitability in this case mainly is due to sodium channel block, the role of the Kv channel block is concealed. The present investigation aims to analyse the specific role of state-dependent Kv channel block for excitability. Using a computational approach, with introduced blocked states in the Kv channel of the Frankenhaeuser-Huxley axon membrane model, we calculated the effects on threshold, firing and presynaptic Ca influx. The Ca influx was obtained from an N-type Cav channel model linked to the Frankenhaeuser-Huxley membrane. The results suggested that a selective block of open Kv channels decreased the rate of repetitive firing and the consequent Ca influx, thus challenging the traditional view. In contrast, presence of a closed-state block, increased the firing rate and the Ca influx. These findings propose that Kv channel block may either increase or decrease cellular excitability, thus highlighting the importance of further investigating the role of state-specific blocking mechanisms.

Levobupivacaine versus Racemic Bupivacaine in Spinal Anaesthesia for Urological Surgery

Racemic bupivacaine is the most common local anaesthetic used intrathecally. This prospective, randomized, double-blind study compared the clinical efficacy and motor block of 0.5% levobupivacaine with 0.5% racemic bupivacaine in spinal anaesthesia for urological surgery. The surgery required an upper level of sensory block of at least the tenth thoracic dermatome. Fifty patients were recruited (levobupivacaine group n=24; bupivacaine group n=26). Spinal anaesthesia was achieved with 2.6 ml of study solution injected in the subarachnoid space at the lumbar 3/4 interspace. One patient from the levobupivacaine group was excluded due to technical failure. There were no significant differences between the two groups in the quality of sensory and motor block or in haemodynamic change. Anaesthesia was adequate and patient satisfaction good in all cases.

We conclude that 0.5% levobupivacaine can be used as an alternative to 0.5% racemic bupivacaine in spinal anaesthesia for surgery when a sensory block to at least T10 is required.

Evaluation of the cardiotoxicity and resuscitation of rats of a newly developed mixture of a QX-314 analog and levobupivacaine

Objective

This study was designed to evaluate the cardiotoxicity of a QX-314 analog (QX-OH) and a mixture of QX-OH and levobupivacaine (LL-1) and to compare the ability to resuscitate rats after asystole induced by levobupivacaine (Levo-BUP), QX-314, QX-OH, and LL-1.

Methods

First, we used the “up-and-down” method to determine median dose resulting in appearance of cardiotoxicity (CD_50C) and asystole (CD_50A) of Levo-BUP, QX-314, QX-OH, and LL-1 in rats. Safety index (SI; ratio of CD_50C compared with 2-fold median effective dose needed to produce sensory blockade) of the 4 drugs was calculated. Isobolograms were used for drug interaction analysis. Second, rats received 1.2-fold CD_50A in the 4 groups. When asystole occurred, standard cardiopulmonary resuscitation was started and continued for 30 min or until return of spontaneous circulation (ROSC) with native rate–pressure product ≥30% baseline for 5 min.

Results

Ranking of CD_50C was Levo-BUP < QX-314 ≈ QX-OH. Ranking of CD_50A was Levo-BUP < QX-314 < QX-OH. However, the SI of Levo-BUP was significantly higher than that of QX-314 (10.60 vs. 1.20) or QX-OH (10.60 vs. 1.44). The SI of LL-1 was similar to that of Levo-BUP. Nonsynergistic interaction was observed for cardiac effects between QX-OH and Levo-BUP. ROSC was attained initially by 8 of 8 rats in the Levo-BUP group, 3 of 8 in the QX-314 group, 6 of 8 in the QX-OH group, and 8 of 8 in the LL-1 group. Sustained recovery was achieved in the Levo-BUP group but not in the other groups.

Conclusion

Levo-BUP and LL-1 are safer than QX-314 or QX-OH. Cardiac effects between QX-OH and Levo-BUP were nonsynergistic. Initial successful resuscitation could be achieved in the QX-OH- and LL-1-induced asystole, but advanced life support might be needed.

Myocardial contractility impairment with racemic bupivacaine, non-racemic bupivacaine and ropivacaine. A comparative study

PURPOSE

To study racemic bupivacaine, non-racemic bupivacaine and ropivacaine on myocardial contractility.

METHODS

Isolated Wistar papillary muscles were submitted to 50 and 100 mM racemic bupivacaine (B50 and B100), non-racemic bupivacaine (NR50 and NR100) and ropivacaine (R50 and R100) intoxication. Isometric contraction data were obtained in basal condition (0.2 Hz), after increasing the frequency of stimulation to 1.0 Hz and after 5, 10 and 15 min of local anesthetic intoxication. Data were analyzed as relative changes of variation.

RESULTS

Developed tension was higher with R100 than B100 at D1 (4.3 ± 41.1 vs -57.9 ± 48.1). Resting tension was altered with B50 (-10.6 ± 23.8 vs -4.7 ± 5.0) and R50 (-14.0 ± 20.5 vs -0.5 ± 7.1) between D1 and D3. Maximum rate of tension development was lower with B100 (-56.6 ± 38.0) than R50 (-6.3 ± 37.9) and R100 (-1.9 ± 37.2) in D1. B50, B100 and NR100 modified the maximum rate of tension decline from D1 through D2. Time to peak tension was changed with NR50 between D1 and D2.

CONCLUSIONS

Racemic bupivacaine depressed myocardial contractile force more than non-racemic bupivacaine and ropivacaine. Non-racemic and racemic bupivacaine caused myocardial relaxation impairment more than ropivacaine.

A Comparative Analysis of Bupivacaine and Ropivacaine Effects on Human Cardiac SCN5A Channels

BACKGROUND

Intoxication with local anesthetics may induce cardiac arrhythmias by interaction with ion channels. Ropivacaine has been introduced into clinical anesthesia as a safer alternative to bupivacaine, which is associated with a relatively high risk of cardiac arrhythmias. Diverging safety profiles may result from differences in the mode of interaction with cardiac Na(+) channels. We conducted this study to test this hypothesis and to provide experimental basis for the ongoing discussion regarding the cardiotoxic profiles of these local anesthetics.

METHODS

The influence of bupivacaine and ropivacaine on the electrophysiological properties of Na(+) channels was investigated in human embryonic kidney-293 cells stably transfected with SCN5A channels cloned from the human heart using the patch-clamp technique in the outside-out configuration.

RESULTS

Open-channel block of SCN5A channels was concentration dependent, with bupivacaine being approximately 4.5-fold more potent than ropivacaine (IC50 = 69.5 ± 8.2 μM vs IC50 = 322.2 ± 29.9 μM). Both drugs influenced the voltage dependency of channel activation and steady-state inactivation by shifting the membrane potential of half-maximal activation/inactivation toward somewhat more negative membrane potentials. In their inactivated state, SCN5A channels were slightly more sensitive toward bupivacaine than toward ropivacaine (IC50 = 2.18 ± 0.16 μM vs IC50 = 2.73 ± 0.27 μM). Blockade of inactivated channels developed in a concentration-dependent manner, with comparable time constants for both drugs, whereas recovery from block was approximately 2-fold faster for ropivacaine than for bupivacaine.

CONCLUSIONS

Human cardiac Na(+) channels show state-dependent inhibition by ropivacaine, and the mode of interaction is comparable to that of bupivacaine. Therefore, modest differences in cardiotoxicity between these local anesthetic drugs are compatible with subtle differences in their interaction with human cardiac Na(+) channels.

Structural Insights into GIRK Channel Function

G protein-gated inwardly rectifying potassium (GIRK; Kir3) channels, which are members of the large family of inwardly rectifying potassium channels (Kir1-Kir7), regulate excitability in the heart and brain. GIRK channels are activated following stimulation of G protein-coupled receptors that couple to the G(i/o) (pertussis toxin-sensitive) G proteins. GIRK channels, like all other Kir channels, possess an extrinsic mechanism of inward rectification involving intracellular Mg(2+) and polyamines that occlude the conduction pathway at membrane potentials positive to E(K). In the past 17 years, more than 20 high-resolution atomic structures containing GIRK channel cytoplasmic domains and transmembrane domains have been solved. These structures have provided valuable insights into the structural determinants of many of the properties common to all inward rectifiers, such as permeation and rectification, as well as revealing the structural bases for GIRK channel gating. In this chapter, we describe advances in our understanding of GIRK channel function based on recent high-resolution atomic structures of inwardly rectifying K(+) channels discussed in the context of classical structure-function experiments.

Epinephrine reversed high-concentration bupivacaine- induced inhibition of calcium channels and transient outward potassium current channels, but not on sodium channel in ventricular myocytes of rats

Background

Epinephrine is a first-line drug for cardiopulmonary resuscitation, but its efficacy in the treatment of bupivacaine-induced cardiac toxicity is still in question. We hypothesized that epinephrine can reverse cardiac inhibition of bupivacaine by modulating ion flows through the ventricular myocyte membrane channels of rats. The aim of this study was to observe and report the effects of epinephrine on high-concentration bupivacaine-induced inhibition of sodium (I_Na), L-type calcium (I_Ca-L), and transient outward potassium (I_to) currents in the ventricular myocytes of rats.

Methods

The ventricular myocytes were isolated from Sprague-Dawley rats (250-300 g) by acute enzymatic dissociation. The whole-cell patch clamp technique was used to record the ion channel currents in single ventricular myocytes both before and after administration of medications.

Result

Administration of bupivacaine 100 μmol/L significantly reduced I_Na, (P < 0.05). However, administration of bupivacaine 100 μmol/L in conjunction with epinephrine 0.15 μg/ml had no effect in restoring I_Na to its previous state. Similarly, a sharp decline of I_Ca-L and I_to was observed after administration of bupivacaine 100 μmol/L (P < 0.05). In contrast to I_Na, I_Ca-L and I_to were significantly improved after the administration of the aforementioned combination of bupivacaine and epinephrine (P < 0.05).

Conclusion

Epinephrine can reverse high-concentration bupivacaine induced inhibition of I_Ca-L and I_to, but not I_Na. Thus, epinephrine’s effectiveness in reversal of bupivacaine-induced cardiac toxicity secondary to sodium channel inhibition may be limited.

The Comparison of the Effects of Epidural Bupivacaine and Levobupivacaine on the Autonomic Nervous System and Cardiac Arrhythmia Parameters in Inguinal Hernia Surgeries

OBJECTIVE

The aim of this study is to investigate the effects of bupivacaine and levobupivacaine, used to create epidural anaesthesia in inguinal hernia operations, on heart rate variability and cardiac arrhythmia parameters.

METHODS

Sixty male patients of the American Society of Anesthesiology (ASA) I-II group, scheduled to be operated on for inguinal hernia surgery with epidural anaesthesia, were randomly divided into two groups. The patients, with a 12-channel Holter recorder (Rozinn RZ153+12-USA) attached 1 hour before the operation to record until the end of the surgery, were taken into the preparation room and anaesthetised. In group L (n=30), 17 mL of 0.5% levobupivacaine (Chirocain 0.5%-Abbot, El-verum, Norway) was given into the epidural space within 10 minutes, versus 17 mL of 0.5% bupivacaine in (Marcain 0.5%, Astra Zeneca, İstanbul, Turkey) group B (n=30). After 30 minutes, when there was enough block, the operation had been started. Holter recordings, starting 1 hour before the anaesthetic procedure and completed by the end of the operations, were transferred to the computer. The records were evaluated by the cardiologists.

RESULTS

When analysing the frequency effect measurement results of the heart rate variability, it was seen that neither of the medications created any statistically significant change in or among the groups in total, very-low-frequency (VLF), low-frequency (LF), high-frequency (HF) and LF/HF ratio levels. Only normalised low-frequency band was significantly lower in Group L (p=0.013).

CONCLUSION

In the volumes and concentrations that were used in our study, levobupivacaine and bupivacaine created sensory blockade at the same level on average and did not reduce heart rate variability at the levels of these blockages.

Pain relief in day care arthroscopic knee surgery: A comparison between intra-articular ropivacaine and levobupivacaine: A prospective, double-blinded, randomized controlled study

Background:

Post-operative pain frequently hampers implementation of day care arthroscopic knee surgery in spite of so many analgesic, local anesthetic drugs and routes of administration.

Aims:

The aim of the present study was carried out to compare the efficacy of ropivacaine and levobupivacaine when administered through intra-articular route in controlling pain after day care arthroscopic knee surgery.

Setting and Design:

It was a prospective, double-blinded and randomized controlled study.

Materials and Methods:

April 2008-December 2008, 60 patients of both sex, of American Society of Anesthesiologists physical status I and II, undergoing day care arthroscopic knee surgery were randomly assigned into two groups (R, L). Group R received 10 ml of 0.75% ropivacaine, whereas group L received 10 ml of 0.50% levobupivacaine through intra-articular route at the end of the procedure. Pain assessed using visual analog scale (VAS) and diclofenac sodium given as rescue analgesia when VAS >3. Time of first analgesic request and total rescue analgesic were calculated.

Statistical Analysis and Results:

based on comparable demographic profiles; time for the requirement of first post-operative rescue analgesia (242.16 ± 23.86 vs. 366.62 ± 24.42) min and total mean rescue analgesic requirement was (104.35 ± 18.96 vs. 76.82 ± 14.28) mg in group R and L respectively. Group R had higher mean VAS score throughout the study period. No side effects found among the groups. These two results were clinically and statistically significant (P < 0.05).

Conclusion:

Hence, it was evident that intra-articular levobupivacaine give better post-operative pain relief, with an increase in time of first analgesic request and decreased need of total post-operative analgesia compared with ropivacaine.

The opioid methadone induces a local anaesthetic-like inhibition of the cardiac Na⁺ channel, Na(v)1.5

BACKGROUND AND PURPOSE

Treatment with methadone is associated with severe cardiac arrhythmias, a side effect that seems to result from an inhibition of cardiac hERG K⁺ channels. However, several other opioids are inhibitors of voltage-gated Na⁺ channels. Considering the common assumption that an inhibition of the cardiac Na⁺ channel Na(v)1.5, is the primary mechanism for local anaesthetic (LA)-induced cardiotoxicity, we hypothesized that methadone has LA-like properties leading to a modulation of Na(v)1.5 channels.

EXPERIMENTAL APPROACH

The whole-cell patch clamp technique was applied to investigate the effects of methadone on wild-type and mutant human Na(v)1.5 channels expressed in HEK293 cells. A homology model of human Na(v)1.5 channels was used to perform automated ligand-docking studies.

KEY RESULTS

Methadone inhibited Na(v)1.5 channels in a state-dependent manner, that is, tonic block was stronger with inactivated channels than with resting channels and a use-dependent block at 10 Hz. Methadone induced a concentration-dependent shift of the voltage dependency of both fast and slow inactivation towards more hyperpolarized potentials, and impaired recovery from fast and slow inactivation. The LA-insensitive mutants N406K and F1760A exhibited reduced tonic and use-dependent block by methadone, and docking predictions positioned methadone in a cavity that was delimited by the residue F1760. Dextromethadone and levomethadone induced discrete stereo-selective effects on Na(v)1.5 channels.

CONCLUSIONS AND IMPLICATIONS

Methadone interacted with the LA-binding site to inhibit Na(v)1.5 channels. Our data suggest that these channels are a hitherto unrecognized molecular component contributing to cardiac arrhythmias induced by methadone.

Voltage-dependent blockade by bupivacaine of cardiac sodium channels expressed in Xenopus oocytes

Bupivacaine ranks as the most potent and efficient drug among class I local anesthetics, but its high potential for toxic reactions severely limits its clinical use. Although bupivacaine-induced toxicity is mainly caused by substantial blockade of voltage-gated sodium channels (VGSCs), how these hydrophobic molecules interact with the receptor sites to which they bind remains unclear. Nav1.5 is the dominant isoform of VGSCs expressed in cardiac myocytes, and its dysfunction may be the cause of bupivacaine-triggered arrhythmia. Here, we investigated the effect of bupivacaine on Nav1.5 within the clinical concentration range. The electrophysiological measurements on Nav1.5 expressed in Xenopus oocytes showed that bupivacaine induced a voltage- and concentration-dependent blockade on the peak of I Na and the half-maximal inhibitory dose was 4.51 μmol/L. Consistent with other local anesthetics, bupivacaine also induced a use-dependent blockade on Nav1.5 currents. The underlying mechanisms of this blockade may contribute to the fact that bupivacaine not only dose-dependently affected the gating kinetics of Nav1.5 but also accelerated the development of its open-state slow inactivation. These results extend our knowledge of the action of bupivacaine on cardiac sodium channels, and therefore contribute to the safer and more efficient clinical use of bupivacaine.

Spinal anesthesia for knee arthroscopy using isobaric bupivacaine and levobupivacaine: anesthetic and neuroophthalmological assessment

INTRODUCTION

The aim of the study was to compare the sensory, motor, and neuroophthalmological effects of isobaric levobupivacaine and bupivacaine when intrathecally administered.

MATERIALS AND METHODS

A prospective, double-blind, randomized study with 60 ASA grade I-II patients aged 18-65 years awaiting knee arthroscopy under spinal anesthesia. Patients received 12.5 mg of isobaric bupivacaine or levobupivacaine. Several features were recorded.

RESULTS

No significant intergroup differences were observed for ASA classification, time to micturate, demographic data, surgery duration, and patient/surgeon satisfaction. Similar hemodynamic parameters and sensory/motor blockade duration were found for both groups. There were no neuroophthalmological effects in either group. Sensory (P = 0.018) and motor blockade onset (P = 0.003) was faster in the bupivacaine group. T6 (T2-T12) and T3 (T2-T12) were the highest sensory block levels for the levobupivacaine and bupivacaine groups, respectively (P = 0.008). It took less time to regain maximum motor blockade in the bupivacaine group (P = 0.014), and the levobupivacaine group required use of analgesia earlier (P = 0.025).

CONCLUSIONS

Isobaric bupivacaine and levobupivacaine are analogous and well-tolerated anesthetics for knee arthroscopy. However, for bupivacaine, sensory and motor blockade onset was faster, and greater sensory blockade with a longer postoperative painless period was achieved.

Lipid Rescue Reverses the Bupivacaine-induced Block of the Fast Na+ Current (INa) in Cardiomyocytes of the Rat Left Ventricle

Background:

Cardiovascular resuscitation upon intoxication with lipophilic ion channel–blocking agents has proven most difficult. Recently, favorable results have been reported when lipid rescue therapy is performed, i.e., the infusion of a triglyceride-rich lipid emulsion during resuscitation. However, the mechanism of action is poorly understood.

Methods:

The authors investigate the effects of a clinically used lipid emulsion (Lipovenös® MCT 20%; Fresenius Kabi AG, Bad Homburg, Germany) on the block of the fast Na+ current (INa) induced by the lipophilic local anesthetic bupivacaine in adult rat left ventricular myocytes by using the whole cell patch clamp technique.

Results:

Bupivacaine at 10 µm decreased INa by 54% (−19.3 ± 1.9 pApF−1vs. −42.3 ± 4.3 pApF−1; n = 17; P &lt; 0.001; VPip = −40 mV, 1 Hz). Addition of 10% lipid emulsion in the presence of bupivacaine produced a 37% increase in INa (−26.4 ± 2.8 pApF−1; n = 17; P &lt; 0.001 vs. bupivacaine alone). To test whether these results could be explained by a reduction in the free bupivacaine concentration by the lipid (lipid-sink effect), the authors removed the lipid phase from the bupivacaine–lipid mixture by ultracentrifugation. Also, the resulting water phase led to an increase in INa (+19%; n = 17; P &lt; 0.001 vs. bupivacaine), demonstrating that part of the bupivacaine had been removed during ultracentrifugation. The substantially less lipophilic mepivacaine (40 µm) reduced INa by 27% (n = 24; P &lt; 0.001). The mepivacaine–lipid mixture caused a significant increase in INa (+17%; n = 24; P &lt; 0.001). For mepivacaine, only a small lipid-sink effect could be demonstrated (+8%; n = 23; P &lt; 0.01), reflecting its poor lipid solubility.

Conclusion:

The authors demonstrate lipid rescue on the single-cell level and provide evidence for a lipid-sink mechanism.

Interaction of local anesthetics with biomembranes consisting of phospholipids and cholesterol: mechanistic and clinical implications for anesthetic and cardiotoxic effects

Despite a long history in medical and dental application, the molecular mechanism and precise site of action are still arguable for local anesthetics. Their effects are considered to be induced by acting on functional proteins, on membrane lipids, or on both. Local anesthetics primarily interact with sodium channels embedded in cell membranes to reduce the excitability of nerve cells and cardiomyocytes or produce a malfunction of the cardiovascular system. However, the membrane protein-interacting theory cannot explain all of the pharmacological and toxicological features of local anesthetics. The administered drug molecules must diffuse through the lipid barriers of nerve sheaths and penetrate into or across the lipid bilayers of cell membranes to reach the acting site on transmembrane proteins. Amphiphilic local anesthetics interact hydrophobically and electrostatically with lipid bilayers and modify their physicochemical property, with the direct inhibition of membrane functions, and with the resultant alteration of the membrane lipid environments surrounding transmembrane proteins and the subsequent protein conformational change, leading to the inhibition of channel functions. We review recent studies on the interaction of local anesthetics with biomembranes consisting of phospholipids and cholesterol. Understanding the membrane interactivity of local anesthetics would provide novel insights into their anesthetic and cardiotoxic effects.

Chirality and anaesthetic drugs: A review and an update

Many molecules can exist as right-handed and left-handed forms that are non-superimposable mirror images of each other. They are known as enantiomers or substances of opposite shape. Such compounds are also said to be chiral (Greek chiros meaning ‘hand’). Such chiral molecules are of great relevance to anaesthetic theory and practice. This review summarizes the basic concepts, pharmacokinetic and pharmacodynamic aspects of chirality, and some specific examples of their application in anaesthesia, along with recent advances to elucidate the anaesthetic mechanisms. Chirality is relevant to anaesthesia, simply because more than half of the synthetic agents used in anaesthesia practice are chiral drugs. Almost all these synthetic chiral drugs are administered as racemic mixture, rather than as single pure enantiomers. These mixtures are not drug formulations containing two or more therapeutic substances, but combination of isomeric substances, with the therapeutic activity residing mainly in one of the enantiomer. The other enantiomer can have undesirable properties, have different therapeutic activities or be pharmacologically inert. Specific examples of application of chirality in anaesthetic drugs include inhalational general anaesthetics (e.g. isoflurane), intravenous anaesthetics (e.g. etomidate, thiopentone), neuromuscular blocking agents (e.g. cisatracurium), local anaesthetics (e.g. ropivacaine and levobupivacaine) and other agents (e.g. levosimendan, dexmedetomidine, L-cysteine). In the recent advances, chirality study has not only helped new drug development as mentioned above, but has also contributed in a more profound way to the understanding of the mechanism of anaesthesia and anaesthetic drugs.

Toxicity of local anesthetic drugs: a pediatric perspective

The main mechanism of action of local anesthetics (LA) is to block sodium channels, thereby interrupting the propagation of nerve impulses. However, this action not only is localized to the sodium channels of nerve tissues involved with pain transmission but will have its effect on any tissue containing sodium channels. Thus, if there is a rapid absorption into the systemic circulation of locally injected LA or if LA inadvertently is injected into a blood vessel, then significant blockade of sodium channels in other tissues may also be blocked and serious complications may ensue. The two most important tissues associated with systemic toxicity of LA are the central nervous and the cardiovascular systems, which may lead to seizures, tachyarrhythmias, and ultimately death from apnea and cardiovascular collapse. The aim of this communication is to elucidate some issues that are associated with toxicity of LA and its treatment in the pediatric population.

Local anesthetics and their adjuncts

Local anesthetics (LA) block propagation of impulses along nerve fibers by inactivation of voltage-gated sodium channels, which initiate action potentials (1). They act on the cytosolic side of phospholipid membranes. Two main chemical compounds are used, amino esters and amino amides. Amino esters are degraded by pseudocholinesterases in plasma. Amino amides are metabolized exclusively by the liver. Only amide LAs will be considered in this article.

Update on local anesthetics: focus on levobupivacaine

In recent years levobupivacaine, the pure S (−)-enantiomer of bupivacaine, emerged as a safer alternative for regional anesthesia than its racemic parent. It demonstrated less affinity and strength of depressant effects onto myocardial and central nervous vital centers in pharmacodynamic studies, and a superior pharmacokinetic profile. Clinically, levobupivacaine is well tolerated in a variety of regional anesthesia techniques both after bolus administration and continuous postoperative infusion. Reports of toxicity with levobupivacaine are scarce and occasional toxic symptoms are usually reversible with minimal treatment with no fatal outcome. Yet, levobupivacaine has not entirely replaced bupivacaine in clinical practice. In anesthesia and analgesia practice, levobupivacaine and bupivacaine produce comparable surgical sensory block with similar adverse side effects, and equal labor pain control with comparable maternal and fetal outcome. The equipotency of the two drugs has been recently questioned, prompting clinicians to increase the dose of levobupivacaine in an attempt to ensure adequate anesthesia and analgesia and offsetting, therefore, the advantages of less motor block with levobupivacaine. In this review we aim to discuss the pharmacological essentials of the safer profile of levobupivacaine, and analyze the evidence regarding the current clinical indications.

Stereostructure-based differences in the interactions of cardiotoxic local anesthetics with cholesterol-containing biomimetic membranes

Amide-type pipecoloxylidide local anesthetics, bupivacaine, and ropivacaine, show cardiotoxic effects with the potency depending on stereostructures. Cardiotoxic drugs not only bind to cardiomyocyte membrane channels to block them but also modify the physicochemical property of membrane lipid bilayers in which channels are embedded. The opposite configurations allow enantiomers to be discriminated by their enantiospecific interactions with another chiral molecule in membranes. We compared the interactions of local anesthetic stereoisomers with biomimetic membranes consisting of chiral lipid components, the differences of which might be indicative of the drug design for reducing cardiotoxicity. Fluorescent probe-labeled biomimetic membranes were prepared with cardiolipin and cholesterol of varying compositions and different phospholipids. Local anesthetics were reacted with the membrane preparations at a cardiotoxically relevant concentration of 200 μM. The potencies to interact with biomimetic membranes and change their fluidity were compared by measuring fluorescence polarization. All local anesthetics acted on lipid bilayers to increase membrane fluidity. Chiral cardiolipin was ineffective in discriminating S(-)-enantiomers from their antipodes. On the other hand, cholesterol produced the enantiospecific membrane interactions of bupivacaine and ropivacaine with increasing its composition in membranes. In 40 mol% and more cholesterol-containing membranes, the membrane-interacting potency was S(-)-bupivacaine<racemic bupivacaine<R(+)-bupivacaine, and S(-)-ropivacaine<R(+)-ropivacaine. Ropivacaine (S(-)-enantiomer), levobupivacaine (S(-)-enantiomeric), and bupivacaine (racemic) interacted with biomimetic membranes in increasing order of intensity. The rank order of membrane interactivity agreed with that of known cardiotoxicity. The stereoselective membrane interactions determined by cholesterol with higher chirality appears to be associated with the stereoselective cardiotoxic effects of local anesthetics. The stereostructure and membrane interactivity relationship supports the clinical use and development of S(-)-enantiomers to decrease the adverse effects of pipecoloxylidide local anesthetics on the cardiovascular system.

The influence of age on bupivacaine cardiotoxicity

BACKGROUND

The susceptibility of children and newborns to cardiotoxicity from racemic bupivacaine, RS(±)-bupivacaine, is controversial. Some studies indicate that newborns can sustain higher bupivacaine plasma levels than adults, without severe toxicity. In this study, we compared the influence of age on cardiotoxicity from RS(±)-bupivacaine and S(-)-bupivacaine in rats. The effects of these local anesthetics (LAs) on the regulation of intracellular Ca(2+) concentrations in cardiac fibers were also investigated.

METHODS

The lethal dose was determined in ventilated male Wistar rats at 2, 4, 8, and 16 weeks of age by monitoring when cardiac electrical activity stopped after infusion of RS(±)-bupivacaine and S(-)-bupivacaine (4 mg · kg(-1) · min(-1)). The effects on cardiac muscle contraction were investigated by in vitro measurement of papillary muscle twitches in the presence and absence of RS(±)-bupivacaine or S(-)-bupivacaine. Skinned ventricular fibers were used to investigate the intracellular effects on Ca(2+) regulation induced by both LAs.

RESULTS

The lethal dose for RS(±)-bupivacaine and S(-)-bupivacaine in 2-week-old animals (46.0 ± 5.2 and 91.3 ± 4.9 mg · kg(-1), respectively) was higher than in 16-week-old animals (22.7 ± 1.3 and 22.0 ± 2.7 mg · kg(-1), respectively). Papillary muscle twitches were reduced in a dose-dependent manner, with significant difference between young and adult hearts. In adults, the muscle twitches were reduced to 8.6% ± 0.8% of control by RS(±)-bupivacaine, and to 18.1% ± 2.7% of control by S(-)-bupivacaine (100 μM). S(-)-bupivacaine had a positive inotropic effect at <10 μM, but only in 2-week-old animals. In chemically skinned ventricular fibers, RS(±)-bupivacaine and S(-)-bupivacaine induced similar increases in Ca(2+) release from the sarcoplasmic reticulum (SR) preactivated with caffeine (1 mM), and this effect was greater in younger rats than adults. In 16-week-old rats, caffeine-induced tension was 53.9% ± 1.7% of the maximal fiber response with RS(±)-bupivacaine, and 54.1% ± 3.2% with S(-)-bupivacaine. The caffeine response in 2-week-old rats was 81.1% ± 3.7% of the maximal response with RS(±)-bupivacaine, and 78.1% ± 4.5% with S(-)-bupivacaine. The Ca(2+) sensitivity of contractile proteins was equally increased at both ages tested, with RS(±)-bupivacaine or S(-)-bupivacaine. Ca(2+) uptake from the SR was not altered by the LA or by age.

CONCLUSIONS

Differences in the mechanisms for regulating intracellular SR Ca(2+) may contribute to the decreased susceptibility of young animals to cardiodepression induced by RS(±)-bupivacaine and S(-)-bupivacaine.

Stereoselective Inhibition of the hERG1 Potassium Channel

A growing number of drugs have been shown to prolong cardiac repolarization, predisposing individuals to life-threatening ventricular arrhythmias known as Torsades de Pointes. Most of these drugs are known to interfere with the human ether à-gogo related gene 1 (hERG1) channel, whose current is one of the main determinants of action potential duration. Prolonged repolarization is reflected by lengthening of the QT interval of the electrocardiogram, as seen in the suitably named drug-induced long QT syndrome. Chirality (presence of an asymmetric atom) is a common feature of marketed drugs, which can therefore exist in at least two enantiomers with distinct three-dimensional structures and possibly distinct biological fates. Both the pharmacokinetic and pharmacodynamic properties can differ between enantiomers, as well as also between individuals who take the drug due to metabolic polymorphisms. Despite the large number of reports about drugs reducing the hERG1 current, potential stereoselective contributions have only been scarcely investigated. In this review, we present a non-exhaustive list of clinically important molecules which display chiral toxicity that may be related to hERG1-blocking properties. We particularly focus on methadone cardiotoxicity, which illustrates the importance of the stereoselective effect of drug chirality as well as individual variations resulting from pharmacogenetics. Furthermore, it seems likely that, during drug development, consideration of chirality in lead optimization and systematic assessment of the hERG1 current block with all enantiomers could contribute to the reduction of the risk of drug-induced LQTS.

The acute toxicity of local anesthetics

IMPORTANCE OF THE FIELD

Systemic toxicity, usually from overdose or intravascular dose, is feared because it mainly affects the heart and brain, and may be acutely life-threatening.

AREAS COVERED IN THIS REVIEW

Pharmacological studies of local anesthetic toxicity have largely been reviewed primarily relating to the evaluation of ropivacaine and levobupivacaine during the past decade. This review/opinion focuses more on the principles and concepts underlying the main models used, from chemical pharmacological and pharmacokinetic perspectives.

WHAT THE READER WILL GAIN

Research models required to produce pivotal toxicity data are discussed. The potencies for neural blockade and systemic toxicity are associated across virtually all models, with some deviations through molecular stereochemistry. These models show that all local anesthetics can produce direct cardiovascular system toxicity and CNS excitotoxicity that may further affect the cardiovascular system response. Whereas the longer-acting local anesthetics are more likely to cause cardiac death by malignant arrhythmias, the shorter-acting agents are more likely to cause cardiac contraction failure. In most models, equi-anesthetic doses of ropivacaine and levobupivacaine are less likely to produce serious toxicity than bupivacaine.

TAKE HOME MESSAGE

Of the various models, this reviewer favors a whole-body large animal preparation because of the comprehensive data collection possible. The conscious sheep preparation has contributed more than any other, and may be regarded as the de facto 'standard' experimental model for concurrent study of local anesthetic toxicity ± pharmacokinetics, using experimental designs that can reproduce the toxicity seen in clinical accidents.

Overlapping binding sites of structurally different antiarrhythmics flecainide and propafenone in the subunit interface of potassium channel Kv2.1

Kv2.1 channels, which are expressed in brain, heart, pancreas, and other organs and tissues, are important targets for drug design. Flecainide and propafenone are known to block Kv2.1 channels more potently than other Kv channels. Here, we sought to explore structural determinants of this selectivity. We demonstrated that flecainide reduced the K(+) currents through Kv2.1 channels expressed in Xenopus laevis oocytes in a voltage- and time-dependent manner. By systematically exchanging various segments of Kv2.1 with those from Kv1.2, we determined flecainide-sensing residues in the P-helix and inner helix S6. These residues are not exposed to the inner pore, a conventional binding region of open channel blockers. The flecainide-sensing residues also contribute to propafenone binding, suggesting overlapping receptors for the drugs. Indeed, propafenone and flecainide compete for binding in Kv2.1. We further used Monte Carlo-energy minimizations to map the receptors of the drugs. Flecainide docking in the Kv1.2-based homology model of Kv2.1 predicts the ligand ammonium group in the central cavity and the benzamide moiety in a niche between S6 and the P-helix. Propafenone also binds in the niche. Its carbonyl group accepts an H-bond from the P-helix, the amino group donates an H-bond to the P-loop turn, whereas the propyl group protrudes in the pore and blocks the access to the selectivity filter. Thus, besides the binding region in the central cavity, certain K(+) channel ligands can expand in the subunit interface whose residues are less conserved between K(+) channels and hence may be targets for design of highly desirable subtype-specific K(+) channel drugs.

Effect of Newly Synthesized Compounds 44Bu and 444 on QRS-Complex Width and Fast Sodium Current: Differences between Isomers

Two newly synthesized short-acting agents 44Bu and 444 were observed to suppress the aconitine-induced arrhythmias and block the fast sodium currentINain the rat heart. No data about their effect on the electrocardiographic parameters are available. In this study, we explored the effect of both racemates and particular isomers of 44Bu and 444 on the QRS-complex widthin vivoin rats and onINain isolated rat ventricular myocytes. All variants of 44Bu and 444 (1.5 mg/kg) caused a significant QRS-widening reaching the peak effect at the 1st or 2nd min after their intravenous administration. 44Bu racemate widened the QRS-complex from 16.8 ± 0.4 to 26.3 ± 0.5 ms (by 57%), significantly more than R- (33%-widening) and S-isomer (36%-widening). 444 racemate widened the QRS-complex from 20.8 ± 1.0 to 34.1 ± 0.9 ms (by 64%), which was comparable to S-isomer (63%-widening), however, substantially more than R-isomer (40%-widening). Regarding the effect onINa, 44Bu caused a significantly deeperINa- block compared to 444 when applied at the same concentration of 3 μmol/l (~0.1 mg/kg). 44Bu racemate and R-isomer blockedINasimilarly (91.7 ± 0.8 and 91.8 ± 1.6%-block, respectively) and significantly more than S-isomer (82.4 ± 2.3%-block). 444 R-isomer blockedINaless than racemate and S-isomer (by 31.7 ± 3.9% vs. 48.3 ± 4.7 and 50.2 ± 4.1%, respectively). We conclude that both racemates and particular isomers of 44Bu and 444 induce a QRS-widening and blockINain the rat heart, however, their effects notably differed. The relative widening of the QRS-complex after application of 44Bu did not conform to the level ofINa-block observed in isolated cardiomyocytes which stresses the importance ofin vivoexperiments in the pre-clinical testing of new drugs.

Hemodynamic effects of ropivacaine and levobupivacaine intravenous injection in swines

PURPOSE: To compare the hemodynamic effects following a toxic dose of either agent after intravenous injection in swines, as might accidentally occur during regional anesthesia in humans. METHODS: Large White pigs were anesthetized with thiopental, tracheal intubation was performed and mechanical ventilation was instituted. Hemodynamic variables were recorded with invasive pressure monitoring and pulmonary artery catheterization. After a 30-minute resting period, the animals were randomly divided into two groups in a double-blinded fashion and received a bolus intravenous injection of 4 mg.kg-1 of either agent. Hemodynamic results were evaluated at rest and 1, 5, 10, 15, 20 and 30 minutes after intoxication. RESULTS: Hemodynamic repressions of acute intoxication with levobupivacaine were more important and more prolonged than those of ropivacaína. CONCLUSION: In pigs, levobupivacaine was shown to be more toxic than ropivacaine when the same large doses are injected intravenously.

Hemodynamic effects of local anesthetics intoxication: experimental study in swine with levobupivacaine and bupivacaine

PURPOSE

To compare the hemodynamic repercussions following a toxic dose of levobupivacaine and bupivacaine intravascularly injected in swines.

METHODS

Large White pigs were anesthetized with thiopental, tracheal intubation was performed and mechanical ventilation was instituted. Hemodynamic variables were recorded with invasive pressure monitoring and pulmonary artery catheterization (Swan-Ganz catheter). After a 30-minute resting period, the animals were randomly divided into two groups in a double-blinded fashion and received a bolus injection of 4 mg/kg of either agent for intoxication. Hemodynamic results were then evaluated at 1, 5, 10, 15, 20 and 30 minutes.

RESULTS

Levobupivacaine had greater hemodynamic repercussions than racemic bupivacaine. These results disagree with those found when the levorotatory isomer of bupivacaine was used in humans, but are in agreement with recently reported findings in animals.

CONCLUSION

Levobupivacaine was shown to be more toxic in pigs than racemic bupivacaine when large doses are injected intravenously.