Comparative ventricular electrophysiologic effect of racemic bupivacaine, levobupivacaine, and ropivacaine on the isolated rabbit heart

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.

Efficacy of Adding Dexmedetomidine to Intra-articular Levobupivacaine on Postoperative Pain after Knee Arthroscopy

Background and Aims:

Intrarticular ingection of local anesthetics in the knee joint decreases postoperative pain after knee arthrosopy. Dexmedetomidine an α₂ agonist has sedative and analgesic effects and decreases postoperative pain after knee arthroscopy when injected intraarticulary. Levobubivacaine is a long acting local anesthetic with less toxicity than bubivacaine. We compared the analgesic effects of dexmedetomidine when added to intraarticular levobupivacaine in patients posted for knee arthroscopy.

Methods:

Data were first tested for normality by Kolmogorov–Smirnov test. Study was done on 90 patients. Patients were divided into 3 groups 30 patients each. Group (C) received 50 ml saline only as a control group. Group (L) received 50 ml 0.25% levobupivacaine. Group (L/D) received 50 ml 0.25% levobupivacaine and dexmedetomidine 1μg.kg-1. (VAS) score was used to assess postoperative pain. Time of first pethidine demand and total dose of pethidine in the first 24 h were recorded, also postoperative complications such as pruritis, nausea and vomiting. SPSS version 16 was used for data analysis. P < 0.05 was considered significant.

Results:

Postoperative VAS sore at different intervals was less in Group LD than Group L than Group C, time to the first pethedine injection in (min) was longer (39 ± 6, 31 ± 7, 21 ± 6), and total pethedine dose given (mg) was lower (36 ± 9.8, 64 ± 19, 102 ± 24) in Group LD than Group L than Group C respectively.

Conclusion:

Adding dexmedetomidine to intraarticular levobupivacaine in patients undergoing knee arthroscopy provides more analgesic effect with lower pain scores than levobupivacaine alone with less use of postoperative analgesics during the first 24 h.

Effects on QTc Interval of 2 Different Doses of Spinal Anesthesia in Inguinal Hernia Operations

Background

Cardiac arrhythmia is a significant cause of morbidity and mortality. In this study, through examination of the effects on the QTc interval of different doses of hyperbaric bupivacaine, we investigated the relationship with arrhythmia.

Material/Methods

A total of 60 patients were separated into 2 groups: spinal block was applied with 10 mg bupivacaine to Group S1 and with 15 mg to Group S2. The mean arterial pressure (MAP) and heart rate (HR) values were recorded before the spinal block and at 5 and 30 min after the block and at 60 min postoperatively. By recording the time of the spinal sensory block to reach T10 dermatome (Anaesth T) and the duration of the surgical procedure (Surg T.), the QTc intervals were calculated.

Results

The demographic data were similar in both groups. A statistically significant difference was determined between the S1 and S2 groups between the baseline and the 30 mins after spinal block QTc intervals (p=0.001). No statistically significant difference in HR values was determined between the groups at baseline, 5 min after spinal block, and 1 h after surgery (all p>0.05), but at 30 min after spinal block value there was a statistically significant difference (p=0.010). No statistically significant difference was determined in MAP values between the groups at baseline and 1 h after surgery (p>0.05).

Conclusions

The QTc interval lengthened in a dose-dependent manner after spinal anesthesia was applied with different doses of bupivacaine, but the doses used did not cause any severe arrhythmia.

A Randomized Controlled Study of 0.5% Bupivacaine, 0.5% Ropivacaine and 0.75% Ropivacaine for Supraclavicular Brachial Plexus Block

INTRODUCTION

For any surgery in the upper extremity that does not involve the shoulder, a supraclavicular block is preferred, as it is a safe procedure associated with rapid onset and reliable anaesthesia. Although ropivacaine has been extensively studied for epidural anaesthesia, very few reports exist on its use in supraclavicular brachial plexus block.

AIM

This study was conducted to investigate and compare the effectiveness of supraclavicular brachial plexus anaesthesia with two different concentrations of ropivacaine (0.5% and 0.75%) and to compare them with the standard 0.5% bupivacaine.

MATERIALS AND METHODS

Ninety patients of age 18 to 60 years belonging to American Society of Anaesthesiologists (ASA) status 1 or 2, admitted to Pondicherry Institute of Medical Sciences were chosen for the study and were divided into three groups. Group A received 30 ml of 0.5% bupivacaine, group B received 30 ml of 0.5% ropivacaine and group C received 30 ml of 0.75% ropivacaine into the supraclavicular region, by a nerve-stimulator technique. Onset time of each of the drug was recorded both for the sensory and motor block. Duration of sensory and motor block was recorded along with peri-operative haemodynamic monitoring.

RESULTS

The onset of complete sensory and motor block observed with both ropivacaine groups and bupivacaine was similar (16.85±6.67 min in group A, 17.79±5.03 min in group B and 18.48±6.14 in group C, p>0.05); onset of motor block (21.45±4.45 min in group A, 22.23±4.05 min in group B and 22.33±5.17 in group C, p < 0.05). The duration of sensory block with 0.5% bupivacaine was 11.58 hours, with 0.5% ropivacaine was 9.02 hours with 0.75% ropivacaine was 8.87 hours (p<0.001). The duration of motor block with 0.5% bupivacaine was 12.94 hours, with 0.5% ropivacaine was 8.29 hours with 0.75% ropivacaine was 7.89 hours (p<0.001). Multiple comparison test with Bonferroni correction showed there was statistically significant difference in mean duration of sensory block between Group A (0.5% bupivacaine) and Group B (0.5% ropivacaine) and also between Group A (0.5% bupivacaine) and Group C (0.75% ropivacaine). However, there were no statistically significant difference in mean duration of sensory block between Group B (0.5% ropivacaine) and Group C (0.75% ropivacaine). The preoperative, intra operative and postoperative heart rate, systolic & diastolic blood pressure and oxygen saturation were comparable among the three study groups (p>0.05). No side effects were recorded in the study.

CONCLUSION

The onset of sensory and motor block was similar in all the three groups. However, when compared to bupivacaine group, recovery of motor functions was faster in both the ropivacaine groups. Patients in all the 3 groups did not experience any adverse effects.

The effect of intra-articular levobupivacaine on shoulder cartilage at different doses-experimental study

BACKGROUND AND OBJECTIVES

In this study it was aimed to examine the histological and morphometric effects on cartilage structure of intra-articular application of levobupivacaine to the shoulder joint.

METHODS

In twenty New Zealand adult male rabbits, 35 shoulders were used for the study and prepared in 5 groups of 7. These groups were defined as Groups L1, L2, L3 and L4 which were right shoulders administered with 0.25% and 0.5% levobupivacaine, Group C which were left shoulders as the control group and Groups S1 and S2 which were left shoulders administered with 0.9% saline. On the 2nd and 15th days the animals were killed, the glenohumeral joints were evaluated macroscopically then cartilage samples were taken. These samples were evaluated with Mankin score, and histomorphometrically by measuring the thickness of the cartilage between the superficial cartilage layer and the tidemark and the thickness of calcified cartilage between the tidemark and the subchondral bone.

RESULTS

Macroscopically, on the 15th day the joint fluid was seen to have reduced in all the groups. After microscopic evaluation, the highest Mankin score (mean: 3.14±2.1/14) was in the L4 group (15th day 0.5% levobupivacaine) and was found to be statistically significant (p<0.05). No statistically significant difference was determined between the other groups.

CONCLUSIONS

Histologically, as the highest Mankin score was in the L4 group, this indicates that in a single intra-articular injection of levobupivacaine a low concentration should be selected.

LEVEL OF EVIDENCE

Level 5, animal study.

[The effect of intra-articular levobupivacaine on shoulder cartilage at different doses-experimental study]

BACKGROUND AND OBJECTIVES

In this study it was aimed to examine the histological and morphometric effects on cartilage structure of intra-articular application of levobupivacaine to the shoulder joint.

METHODS

In twenty New Zealand adult male rabbits, 35 shoulders were used for the study and prepared in 5 groups of 7. These groups were defined as Groups L1, L2, L3 and L4 which were right shoulders administered with 0.25% and 0.5% levobupivacaine, Group C which were left shoulders as the control group and Groups S1 and S2 which were left shoulders administered with 0.9% saline. On the 2nd and 15th days the animals were killed, the glenohumeral joints were evaluated macroscopically then cartilage samples were taken. These samples were evaluated with Mankin score, and histomorphometrically by measuring the thickness of the cartilage between the superficial cartilage layer and the tidemark and the thickness of calcified cartilage between the tidemark and the subchondral bone.

RESULTS

Macroscopically, on the 15th day the joint fluid was seen to have reduced in all the groups. After microscopic evaluation, the highest Mankin score (mean: 3.14±2.1/14) was in the L4 group (15th day 0.5% levobupivacaine) and was found to be statistically significant (p<0.05). No statistically significant difference was determined between the other groups.

CONCLUSIONS

Histologically, as the highest Mankin score was in the L4 group, this indicates that in a single intra-articular injection of levobupivacaine a low concentration should be selected.

LEVEL OF EVIDENCE

Level 5, animal study.

Effect of Intralipid® on the Dose of Ropivacaine or Levobupivacaine Tolerated by Volunteers

Background

Rapid intravenous administration of lipid emulsion has become the standard treatment of severe local anesthetic systemic toxicity. This experiment in volunteers aimed at determining the effect of Intralipid® administration on the time to neurologic symptoms.

Methods

Ropivacaine or levobupivacaine was infused intravenously in 16 volunteers (8 mg/min up to 120 mg) with 120 ml Intralipid® 20% (Fresenius, Paris France) or placebo infused at T + 2 min). Each subject received all four treatments in a crossover manner. The infusion was stopped after the intended dose had been administered or on occurrence of incipient neurologic signs of toxicity. The primary outcome was time-to-event. In addition, blood ropivacaine and levobupivacaine concentrations were measured.

Results

The dose infused was not different whether volunteers received placebo (81.7 ± 22.3 vs. 80.8 ± 31.7 mg, ropivacaine vs. levobupivacaine) or Intralipid® (75.7 ± 29.1 vs. 69.4 ± 26.2 mg, ropivacaine vs. levobupivacaine), P = 0.755, Intralipid® versus placebo groups. Plasma concentrations were best modeled with an additional volume of distribution associated with Intralipid®. Simulations suggested that decreased peak concentrations would be seen if Intralipid® was given during a period of increasing concentrations after extravascular administration.

Conclusions

At modestly toxic doses of ropivacaine or levobupivacaine, we were unable to find any effect of the infusion of Intralipid® on the time to early signs of neurologic toxicity in volunteers. Peak concentration was decreased by 26 to 30% in the subjects receiving Intralipid®. Simulations showed that Intralipid® might prevent the rapid increase of local anesthetic concentration after extravascular administration.

Intrathecal bupivacaine or levobupivacaine: which should be used for elderly patients?

OBJECTIVES

To compare two intrathecal anaesthetics, bupivacaine and levobupivacaine, for their effects on motor and sensory blockade and haemodynamics in patients aged ≥ 65 years undergoing transurethral resection of the prostate (TUR-P) or transurethral resection of the urinary bladder (TUR-M).

METHODS

Patients scheduled to undergo TUR-P or TUR-M were randomized to receive either 3 ml (15 mg) 0.5% isobaric levobupivacaine (group L) or 3 ml (15 mg) of 0.5% hyperbaric bupivacaine (group B) for spinal anaesthesia. The onset time, maximum level and time to reach the maximum level of sensory and motor blockade were recorded. Changes to haemodynamic parameters were also recorded.

RESULTS

The study randomized 100 patients: 57 to group L and 43 to group B. Levobupivacaine did not cause any significant changes in haemodynamic parameters, including systolic blood pressure, and showed a similar sensory block onset time compared with bupivacaine, but it had a significantly longer motor block onset time compared with bupivacaine.

CONCLUSION

These current findings suggest that levobupivacaine can be used as a substitute for bupivacaine for spinal anaesthesia in elderly patients ≥ 65 years of age undergoing elective TUR-P or TUR-M operations.

Comparative study related to cardiovascular safety between bupivacaine (S75-R25) and ropivacaine in brachial plexus block

BACKGROUND AND OBJECTIVES

Bupivacaine is a first choice for regional anesthesia considering its effectiveness, long duration and less motor blockade. Bupivacaine (S75-R25) is a mixture of optical isomers containing 75% levobupivacaine (S-) and 25% dextrobupivacaine (R+) created by a Brazilian pharmaceutical company. This investigation compared cardiac safety and efficacy of bupivacaine S75-R25 with vasoconstrictor and ropivacaine for brachial plexus blockade.

METHODS

Patients were randomized to receive brachial plexus anesthesia with either bupivacaine S75-R25 with epinephrine 1:200,000 (bupi) or ropivacaine (ropi), both at 0.50%, in 30 mL solution. We registered a continuous Holter ECG throughout the procedure, as well as the Lovett scale of force in addition to monitoring (heart rate, pulse oximetry and non-invasive blood pressure). The incidence of adverse events was compared with the chi-square or Fisher test.

RESULTS

We allocated forty-four patients into two groups. They did not show any difference related to age, weight or height, gender, as well as for surgical duration. Supraventricular arrhythmias were not different before or after the plexus blockade, independent of the local anesthetic chosen. Loss of sensitivity was faster for the bupivacaine group (23.1 ± 11.7 min) compared to the ropivacaine one (26.8 ± 11.5 min), though not significant (p = 0.205, Student t). There was a reduction in the cardiac rate, observed during the twenty-four-hour Holter monitoring.

CONCLUSIONS

This study showed similar efficacy between bupivacaine S75-R25 for brachial plexus blockade and ropivacaine, with similar incidences of supraventricular arrhythmias.

Comparative study related to cardiovascular safety between bupivacaine (S75-R25) and ropivacaine in brachial plexus block

BACKGROUND AND OBJECTIVES

Bupivacaine is a fi rst choice for regional anesthesia considering its effectiveness, long duration and less motor blockade. Bupivacaine (S75-R25) is a mixture of optical isomers containing 75% levobupivacaine (S-) and 25% dextrobupivacaine (R+) created by a Brazilian pharmaceutical company. This investigation compared cardiac safety and efficacy of bupivacaine S75-R25 with vasoconstrictor and ropivacaine for brachial plexus blockade.

METHODS

Patients were randomized to receive brachial plexus anesthesia with either bupivacaine S75-R25 with epinephrine 1:200,000 (bupi) or ropivacaine (ropi), both at 0.50%, in 30 mL solution.We registered a continuous Holter ECG throughout the procedure, as well as the Lovett scale of force in addition to monitoring (heart rate, pulse oximetry and non-invasive blood pressure). The incidence of adverse events was compared with the chi-square or Fisher test.

RESULTS

We allocated forty-four patients into two groups. They did not show any difference related to age, weight or height, gender, as well as for surgical duration. Supraventricular arrhythmias were not different before or after the plexus blockade, independent of the local anestheticchosen. Loss of sensitivity was faster for the bupivacaine group (23.1 ± 11.7 min) compared to the ropivacaine one (26.8 ± 11.5 min), though not significant (p = 0.205, Student t). There was a reduction in the cardiac rate, observed during the twenty-four-hour Holter monitoring.

CONCLUSIONS

This study showed similar efficacy between bupivacaine S75-R25 for brachial plexus blockade and ropivacaine, with similar incidences of supraventricular arrhythmias.

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.

Reversal of bupivacaine-induced cardiac electrophysiologic changes by two lipid emulsions in anesthetized and mechanically ventilated piglets

BACKGROUND

Accidental IV administration of bupivacaine can compromise cardiovascular function by inducing lethal arrhythmias whose hemodynamic consequences may be alleviated by lipid emulsions. However, little is known about the electrophysiologic effects of lipid emulsions. In this study, we assessed whether 2 different lipid emulsions can reverse cardiac electrophysiologic impairment induced by the IV administration of bupivacaine in anesthetized and mechanically ventilated piglets.

METHODS

Bupivacaine (4 mg . kg(-1)) was injected over a 30-second period in 26 piglets. Thirty seconds after the end of bupivacaine injection, 1.5 mL . kg(-1) saline solution for the control group, and long-chain triglyceride emulsion (LCT group) or a mixture of long-chain and medium-chain triglyceride emulsion (LCT/MCT group) were infused over 1 minute. Cardiac conduction variables and hemodynamic variables were monitored for 30 minutes after injection.

RESULTS

Bupivacaine induced similar electrophysiologic and hemodynamic changes. After 3 minutes, His ventricle intervals (median and interquartiles) were 100 (85-105), 45 (35-55), and 53 (48-73) milliseconds in the control, LCT, and LCT/MCT groups, respectively (P < 0.001 between control and both lipid emulsion groups). Lipid emulsions also reversed the effects on QRS duration, atrial-His, and PQ (the onset of the P wave to the Q wave of the QRS complex) intervals. LCT/MCT emulsion restored the decrease in maximal first derivative of left ventricular pressure (P < 0.01 after 3 minutes versus control group).

CONCLUSIONS

LCT and LCT/MCT emulsions reversed the lengthening of His ventricle, QRS, atrial-His, and PQ intervals induced by the IV injection of 4 mg . kg(-1) bupivacaine.

Preclinical cardiac safety assessment of drugs

The heart is a frequent site of toxicity of pharmaceutical compounds in humans, and when developing a new drug it is critical to conduct a thorough preclinical evaluation of its possible adverse effects on cardiac structure and function. Changes in cardiac morphology such as myocardial necrosis, hypertrophy or valvulopathy are assessed in regulatory toxicity studies in laboratory animals, although specific models may be needed for a more accurate detection of the risk. The potential proarrhythmic risk of new drugs is a major subject of concern and needs to be fully addressed before treatment of volunteers or patients takes place. In vitro assays are conducted to determine the effects on cardiac ion channels, in particular I(Kr) potassium channel antagonism. Prolongation of the QT interval is assessed in vivo, generally in telemetered dogs. Together, these two tests are considered to detect most arrhythmic drugs. The results of this core battery can be refined by additional studies, in particular assays on isolated cardiac tissues determining changes in cardiac action potential duration, shape and variability over time. Triggering of arrhythmia is assessed in hypokalaemic dogs with artificially created bradycardia, or in vitro in isolated whole hearts. The proarrhythmic risk of the new compound is then evaluated by integrating the results of these different tests. Drug adverse effects on cardiac electrophysiological function, in particular impulse formation and conduction, are evaluated through changes in ECG, generally recorded in dogs, pigs or monkeys. Changes in cardiac contractility occurring either as a primary effect of the drug on cardiac function or as a consequence of cardiac lesions should also be carefully assessed. In telemetered or anaesthetised animals, cardiac contractility is evaluated by measurement of left ventricular pressure and its first derivative over time. Echocardiography allows non-invasive measurement of drug-induced changes in ventricular wall movements and cardiac haemodynamics indicative of effects on contractility. In conclusion, a reliable and accurate evaluation of the cardiac safety of a new pharmaceutical agent is based on the results of in vitro tests, with overall moderate to high throughput, and in vivo experiments assessing the effects of the drug on the heart in its physiological environment. The specific sensitivities of the animals used in these assays to cardiac adverse effects should also be considered. The final evaluation of the cardiac risk is therefore based on an integrated analysis of the results from a battery of tests.

Effect of sufentanil on minimum local analgesic concentrations of epidural bupivacaine, ropivacaine and levobupivacaine in nullipara in early labour

BACKGROUND

The aim was to assess the effect of epidural sufentanil on relative analgesic potencies of epidural bupivacaine, ropivacaine and levobupivacaine by determining the minimum local analgesic concentrations during labour.

METHODS

In a randomised, double-blind study, 171 parturients were allocated to one of six groups receiving a 10-mL bolus of bupivacaine, ropivacaine or levobupivacaine alone or with sufentanil 0.75 microg/mL. The concentration of local anaesthetic was determined by the response of the previous parturient using up-down sequential allocation starting at a concentration of 0.13% wt/vol with a testing interval of 0.01%. Effective analgesia was defined as a visual analogue pain score < or = 15/100 mm within 30 min and lasting for 30 min. Median effective concentrations were estimated and two-sided P < 0.05 was significant.

RESULTS

Local anaesthetic concentration, use of sufentanil and local anaesthetic drug were independent significant predictors of effective and ineffective analgesia. Bupivacaine was significantly more potent than levobupivacaine and ropivacaine. The relative potency ratios without sufentanil of 0.77:0.83:1.00 were reduced to 0.36:0.38:1.00 by the addition of sufentanil. The major factor influencing local anaesthetic requirements was the addition of sufentanil, which reduced overall requirements by a factor of 4.2 (95% CI 3.6-4.8); this effect was proportionately more enhanced for bupivacaine.

CONCLUSIONS

Local anaesthetic requirements for bupivacaine, levobupivacaine and ropivacaine follow an analgesic potency hierarchy. Any potency differences are small when compared to the effect of sufentanil, which resulted in a four-fold reduction in local anaesthetic requirements. Sufentanil may also enhance the potency differences between bupivacaine and the two S-enantiomer agents.

The effects of ropivacaine at clinically relevant doses on myocardial ischemia in pigs

A major risk associated with bupivacaine during myocardial ischemia is ventricular fibrillation. We investigated the influence of ropivacaine on cardiac contractility and the propensity to ventricular fibrillation before and after myocardial ischemia in a placebo-controlled pig study. Anesthetized domestic pigs were administered 1 mg.kg(-1) of ropivacaine intravenously over 1 min and then 0.03 mg.kg(-1).min(-1) as a 30-min infusion, or saline. The following endpoints were measured before and after ropivacaine administration: (1) the ventricular fibrillation threshold (VFT) before and during myocardial ischemia induced by total transient ligation of the anterior interventricular artery and (2) electrophysiological (sinus heart rate, duration of QRS and QT intervals) and hemodynamic (blood pressure, the time derivative of left ventricular pressure [peak LV dP/dt]) parameters. Ropivacaine induced no changes in sinus heart rate, QRS, and or QT before or during ischemia. In contrast, there was a mild increase in the VFT before ischemia, which was drastically and significantly reduced during ischemia. The reduction of peak LV dP/dt during ischemia was further increased by ropivacaine. We also found that the effect of ropivacaine on the VFT was coronary blood flow-dependent, with a markedly decreased threshold in the presence of ischemia. Similar effects have been observed in humans with several other local anesthetics, as well as with class I antiarrhythmic drugs. The results of this study should be taken into account by anesthesiologists when administering ropivacaine to coronary patients.

Anesthésiques locaux : qu'apportent les formes lévogyres ?

The use of levobupivacaine and of ropivacaine may increase the safety of regional anaesthesia. These pure enantiomers have similar pharmacokinetic properties as those of the racemic mixtures. However, they are less cardiotoxic than the racemic mixtures, especially at the high heart rate usually encountered in infants. We may then recommend the use of these agents in the paediatric patients.

[Levobupivacaine for regional anesthesia. A systematic review]

Levobupivacaine [S(-)bupivacaine], the levorotatory S-enantiomer of racemic bupivacaine, is commercially available in the U.S. and in most European countries. We performed a systematic review (MEDLINE database) and identified 88 articles on the clinical application of levobupivacaine in more than 3,000 patients. The use of levobupivacaine is described for epidural, caudal, and spinal anesthesia, for peripheral nerve blocks, for ophthalmic and dental anesthesia, for different pediatric indications and for intravenous regional anesthesia. In these regional techniques, levobupivacaine was used for all common indications in a wide range of clinical settings. Epidural levobupivacaine was combined with fentanyl, morphine, sufentanil, epinephrine, and clonidine, spinal levobupivacaine was combined with sufentanil, fentanyl, and epinephrine. In most studies, levobupivacaine was compared to bupivacaine and/or ropivacaine.

Paravertebral Block With Ropivacaine 0.5% Versus Systemic Analgesia for Pain Relief After Thoracotomy

PURPOSE

Paravertebral block in combination to intravenous analgesics could be an alternative to epidural analgesia for postoperative pain control after thoracotomy, but it has been scarcely evaluated so far. We thus assessed the efficacy of paravertebral block using a continuous infusion of ropivacaine in a multimodal analgesic approach.

DESCRIPTION

Forty patients were randomized to receive ketoprofen, paracetamol, and patient-controlled-analgesia (PCA) with intravenous morphine (control group) or the same treatment with a continuous 48-hour infusion of ropivacaine 0.5% (0.1 mL/kg(-1)/h(-1)) in a thoracic paravertebral catheter (thoracic paravertebral block [TPVB] group). Visual analog scale (VAS) at rest and when coughing, morphine consumption, and side effects were recorded during the first 48 hours after surgery. Venous blood was sampled at 24 and 48 hours for ropivacaine plasma concentration measurements.

EVALUATION

Mean VAS scores at rest and when coughing were significantly decreased in the TPBV group (p < 0.005). Despite a decrease in the morphine-titrated dose given in the postanesthesia care unit, cumulated morphine consumption was not significantly different between the two groups (51 +/- 29 mg and 57 +/- 24 mg in the TPVB and control groups, respectively). Side effects (nausea, vomiting, urinary retention) were less frequent in the TPBV group (30% vs 75%; p < 0.005). Plasma ropivacaine concentrations remained below the toxic threshold.

CONCLUSIONS

Continuous paravertebral ropivacaine 0.5% infusion improves pain control after thoracic surgery using a multimodal analgesic approach.

Randomized, double-blind, phase III, controlled trial comparing levobupivacaine 0.25%, ropivacaine 0.25% and bupivacaine 0.25% by the caudal route in children

BACKGROUND

The rationale for replacing racemic bupivacaine with the s-enantiomers levobupivacaine and ropivacaine is to provide a wider margin of safety with the same analgesic efficacy and less postoperative motor block. In a randomized, double-blind, phase III, controlled trial we compared the caudal administration of levobupivacaine 0.25% and ropivacaine 0.25% with bupivacaine 0.25% in children.

METHODS

Ninety-nine ASA I-II children less than 10 yr old scheduled for elective sub-umbilical surgery were randomized to receive caudal block with bupivacaine 0.25%, ropivacaine 0.25% or levobupivacaine 0.25%. The primary outcome of the study was the clinical efficacy of the caudal block during the operation. Secondary outcome measures were analgesic onset time, pain relief after the operation and residual motor blockade.

RESULTS

The proportion of children with effective analgesia during the operation was similar among groups. There were no significant differences in the analgesic onset time of the caudal block. Bupivacaine produced a significant incidence of residual motor block compared with levobupivacaine or ropivacaine at wake-up (P<0.01). There were no significant differences in the number of patients receiving rescue analgesia after surgery. However, analgesic block lasted significantly longer in patients receiving bupivacaine (P=0.03).

CONCLUSION

During sub-umbilical surgery, caudal levobupivacaine, ropivacaine and bupivacaine provided comparable analgesic efficacy. Bupivacaine produced a higher incidence of residual motor blockade and a longer analgesic block than ropivacaine and levobupivacaine.

Pharmacokinetics of Local Anaesthetics in Infants and Children

Amide local anaesthetics used for regional anaesthesia in paediatric patients are potent sodium channel blockers with marked stereospecificity, which consistently influences their action, especially their toxic action on the heart. At toxic concentrations, they induce severe arrhythmias with the potential for cardiac arrest. These agents are all bound to serum proteins, mainly to alpha(1)-acid glycoprotein (AAG), but also to human serum albumin. Protein binding ranges from 65% (lidocaine) to more than 95% (bupivacaine, ropivacaine). Because AAG is a major acute phase protein, its concentration rapidly increases when inflammatory processes develop, particularly during the postoperative period. Neonates and infants have a lower AAG concentration in serum as compared with adults; therefore, their free fraction of local anaesthetics is increased accordingly. This has important clinical implications since, at least at steady state, the toxic effects of local anaesthetics are directly related to the free (unbound) drug concentration. After injection into the epidural space, absorption into the bloodstream follows a biphasic process. The buffering properties of the epidural space are important and prevent a rapid rise in concentration. In infants and children, the epidural space seems to protect patients in a similar manner. Moreover, it has been observed that the peak plasma concentration (C(max)) of ropivacaine is delayed in infants and children when compared with adults. The time to C(max) decreases from 90-120 minutes in infants aged less than 6 months to 30 minutes in children aged more than 8 years. This delay in C(max) may also be related to the lower clearance observed in younger patients. Local anaesthetics are metabolised by cytochrome P450 (CYP). The main CYP isoforms involved are CYP3A4 for lidocaine and bupivacaine and CYP1A2 for ropivacaine. CYP3A4 is not mature at birth but is partly replaced by CYP3A7. The intrinsic clearance of bupivacaine is only one-third of that in adults at 1 month of age, and two-thirds at 6 months. CYP1A2 is not fully mature before the age of 3 years. Indeed, the clearance of ropivacaine does not reach its maximum before the age of 5 years. However, at birth this clearance is not as low as expected, and ropivacaine may be used even in younger patients.

Complications and local anaesthetic toxicity in regional anaesthesia

PURPOSE OF REVIEW

Local anaesthetic agents are administered every day in clinical practice. These agents are relatively safe when administered in proper dosages at appropiate anatomical sites. However, when excessive dosages are administered or the incorrect site of administration is used there is a potential for toxic reactions. Ropivacaine, a pure S-enantiomer, and levobupivacaine, a single isomer of bupivacaine, have been introduced as new long-acting local anaesthetic agents with a potentially reduced toxicity compared with bupivacaine. The present review deals with recent knowledge about systemically induced local anaesthetic toxicity and localized toxicity.

RECENT FINDINGS

Studies have compared cardiotoxicity directly between ropivacaine and levobupivacaine in intracoronary injection in sheep and pigs, in small mammals, and arrhythmias and resuscitation in dogs. Direct left coronary arterial infusions of local anaesthetics in a conscious sheep model precludes central nervous system actions. Intracoronary studies showed similar toxicity for levobupivacaine and ropivacaine. When comparing and interpreting in-vivo animal studies of local anaesthetic toxicity, species variations, differences in the mode and site of local anaesthetic administration, and whether the animal is under the influence of anaesthesia must all be considered. Stereoselectivity may play a role in the lengthening of the atrioventricular conduction time for bupivacaine. In-vitro studies have revealed that intracellular calcium concentrations may contribute to myotoxicity.

SUMMARY

Current evidence suggests that ropivacaine is slightly less toxic than levobupivacaine; however, the difference in potency between the two agents is greater. The new local anaesthetic agents can be regarded as 'safer', but must not be regarded as safe.

The number of injections does not influence local anesthetic absorption after paravertebral blockade

PURPOSE

The aims of this study are to determine if the injection of a single large dose of local anesthetics into the paravertebral space increases the risks of inducing toxicity compared with multiple small injections and to describe ropivacaine plasma concentrations resulting from paravertebral blockade.

METHODS

Paravertebral blockade was performed using a solution of 10 mL ropivacaine 0.75%, 10 mL lidocaine CO2 2% plus 0.1 mL epinephrine 1:1000 either by a single injection at T3 or T4 (Group S, n = 6) or by five injections of 4 mL each at T2 to T6 (Group M, n = 8). Blood samples were taken at zero, five, ten, 15, 20, 30, 45, 60 and 90 min and at two, three, four, five, six and eight hours. Ropivacaine and lidocaine plasma concentrations were measured by high performance liquid chromatography.

RESULTS

Maximal plasma concentrations were comparable for lidocaine: 2.6 +/- 1.3 (S) vs 2.6 +/- 0.8 microg x mL(-1) (M) and for ropivacaine: 1.3 +/- 0.2 (S) vs 1.3 +/- 0.1 microg x mL(-1) (M). Area under the plasma concentration-time curve was higher in Group M for lidocaine: 577.6 +/- 146.1 vs 401.7 +/- 53.2 mg x min(-1) x mL(-1) (P = 0.04) but similar for ropivacaine: 381.1 +/- 95.4 (M) vs 363.1 +/- 85.3 mg x min(-1) x L(-1) (S).

CONCLUSIONS

The injection of a single large bolus of local anesthetics into the paravertebral space does not increase its absorption. Maximal ropivacaine plasma concentrations resulting from paravertebral blockade are similar to those reported with equivalent doses of bupivacaine.

Cardiac and CNS toxicity of levobupivacaine: strengths of evidence for advantage over bupivacaine

Bupivacaine is currently the most widely used long-acting local anaesthetic. Its uses include surgery and obstetrics; however, it has been associated with potentially fatal cardiotoxicity, particularly when given intravascularly by accident. Levobupivacaine, a single enantiomer of bupivacaine, has recently been introduced as a new long-acting local anaesthetic with a potentially reduced toxicity compared with bupivacaine. Numerous preclinical and clinical studies have compared levobupivacaine with bupivacaine and in most but not all studies there is evidence that levobupivacaine is less toxic. Advantages for levobupivacaine are seen on cardiac sodium and potassium channels, on isolated animal hearts and in whole animals, anaesthetised or awake. In particular the intravascular dose of levobupivacaine required to cause lethality in animals is consistently higher compared with bupivacaine. In awake sheep, for example, almost 78% more levobupivacaine was required to cause death. In contrast, in anaesthetised dogs no differences were seen in the incidence of spontaneous or electrical stimulation- induced ventricular tachycardia and fibrillations among animals exposed to levobupivacaine or bupivacaine. The reversibility of levobupivacaine-induced cardiotoxicity has also been assessed. Some data point to an advantage of levobupivacaine over bupivacaine but this potential advantage was not confirmed in a recent study in anaesthetised dogs. Three clinical studies have been conducted using surrogate markers of both cardiac and CNS toxicity. In these studies levobupivacaine or bupivacaine were given by intravascular injection to healthy volunteers. Levobupivacaine was found to cause smaller changes in indices of cardiac contractility and the QTc interval of the electrocardiogram and also to have less depressant effect on the electroencephalogram. Assuming that levobupivacaine has the same local anaesthetic potency as bupivacaine, then, all things being equal, it is difficult to argue that levobupivacaine should not displace bupivacaine as the long-acting local anaesthetic of choice. It would appear, however, that levobupivacaine has not yet significantly displaced bupivacaine from the markets in which it is sold. This may be due to a lack of perceived safety benefit and/or consideration of the additional costs that are associated with switching to levobupivacaine, which is approximately 57% more expensive than bupivacaine. If the price of levobupivacaine were closer to bupivacaine then the argument to switch to levobupivacaine would undoubtedly be much stronger. With the continued clinical use of levobupivacaine the database available to make comparisons will increase and this may allow cost-benefit arguments to be made more forcefully for levobupivacaine in the future.

Bupivacaine-induced QRS prolongation is enhanced by lidocaine and by phenytoin in rabbit hearts

Lidocaine, phenytoin, and bupivacaine are sodium channel blockers. Lidocaine displaces bupivacaine from its receptor on the sodium channel. However, lidocaine does not seem to decrease bupivacaine toxicity. Phenytoin also has been used to treat bupivacaine cardiotoxicity. To test the hypothesis that lidocaine or phenytoin might be used for the treatment of bupivacaine overdose, we compared the effects of bupivacaine on intraventricular conduction in the isolated heart of rabbits with bupivacaine and with either phenytoin or lidocaine added to bupivacaine. Twenty-four rabbit hearts were retrogradely perfused in a nonrecirculating Langendorff apparatus. The duration of QRS was measured without any drug and 10 min after infusion of 3 microM bupivacaine. Saline (control group) or increasing concentrations of either lidocaine or phenytoin was then added by 10-min-step increments. QRS duration was measured for each concentration at the end of a 10-min step. It was also determined 10 min after discontinuation of bupivacaine and after a period of washout for all drugs. QRS duration was significantly increased by adding phenytoin or lidocaine to bupivacaine. These drugs should not be used to treat the manifestations of bupivacaine toxicity.

IMPLICATIONS

The effects of lidocaine and phenytoin on bupivacaine-related increases in cardiac conduction time have been studied in an isolated heart preparation. Both drugs increased the QRS widening induced by bupivacaine. We conclude that none of these drugs should be used for treating bupivacaine intoxication.

Update on ropivacaine

Long-acting local anaesthetics are primarily used in the practice of anaesthesia, particularly in regional anaesthesia and analgesia. Ropivacaine is a new long-acting local anaesthetic that has been the focus of interest because of its increased cardiovascular safety compared with bupivacaine. Other advantages of ropivacaine over bupivacaine include a greater sensorimotor differential block and shorter elimination half-life (t(1/2)), with a lower potential for accumulation. The most important attribute of ropivacaine, however, is its increased margin of safety compared with bupivacaine when given in equal doses. Many post-marketing studies have focused on the comparisons of efficacy in blocks and toxicity profiles of bupivacaine versus ropivacaine. Recent animal toxicity studies confirm the results of original studies showing that ropivacaine has less cardiovascular toxicity than bupivacaine with respect to direct myocardial depression, success of resuscitation and arrhythmogenic potential when given in equal doses. Reduced cardiotoxicity may be a distinct characteristic of ropivacaine. A review of current literature suggests that, at clinically relevant doses, ropivacaine provides the lowest potential risk of cardiotoxicity for inadvertent intravascular injection. Studies are currently under way comparing ropivacaine with levobupivacaine, the latest addition to the group of long-acting local anaesthetics.

Systemic toxicity and resuscitation in bupivacaine-, levobupivacaine-, or ropivacaine-infused rats

We compared the systemic toxicity of bupivacaine, levobupivacaine, and ropivacaine in anesthetized rats. We also compared the ability to resuscitate rats after lethal doses of these local anesthetics. Bupivacaine, levobupivacaine, or ropivacaine was infused at a rate of 2 mg. kg(-1). min(-1) while electrocardiogram, electroencephalogram, and arterial pressure were continuously monitored. When asystole was recorded, drug infusion was stopped and a resuscitation sequence was begun. Epinephrine 0.01 mg/kg was administered at 1-min intervals while external cardiac compressions were applied. Resuscitation was considered successful when a systolic arterial pressure > or =100 mm Hg was achieved within 5 min. The cumulative doses of levobupivacaine and ropivacaine that produced seizures were similar and were larger than those of bupivacaine. The cumulative doses of levobupivacaine that produced dysrhythmias and asystole were smaller than the corresponding doses of ropivacaine, but they were larger than those of bupivacaine. The number of successful resuscitations did not differ among groups. However, a smaller dose of epinephrine was required in the Ropivacaine group than in the other groups. We conclude that the systemic toxicity of levobupivacaine is intermediate between that of ropivacaine and bupivacaine when administered at the same rate and that ropivacaine-induced cardiac arrest appears to be more susceptible to treatment than that induced by bupivacaine or levobupivacaine.

Direct cardiac effects of intracoronary bupivacaine, levobupivacaine and ropivacaine in the sheep

1. The racemic local anaesthetic agent bupivacaine is widely used clinically for its long duration of action. Levobupivacaine and ropivacaine are bupivacaine enantiopure congeners, developed to improve upon the clinical safety of bupivacaine, especially the risk of fatal arrhythmogenesis. 2. In previous preclinical studies of the safety of these drugs with intravenous administration in conscious ewes over a wide dose range, we found that central nervous system (CNS) excito-toxicity reversed the cardiac depressant effects when doses approached the convulsant threshold and thus precluded accurate comparison of their cardiovascular system (CVS) effects. 3. To study CVS effects over a wide range of doses with minimal CNS and other influences, brief (3 min) infusions of bupivacaine, levobupivacaine or ropivacaine were administered into the left main coronary arteries of previously instrumented conscious ewes (approximately 50 Kg body weight). After dose-ranging studies, the drugs were compared in a randomized, blinded, parallel group design. Equimolar doses were increased from 8 micromol (approximately 2.5 mg) in 8 micromol increments, to either a fatal outcome or a 40 micromol (approximately 12.5 mg) maximum. 4. All three drugs produced tachycardia, decreased myocardial contractility and stroke volume and widening of electrocardiographic QRS complexes. Thirteen of 19 animals died of ventricular fibrillation: four of six with bupivacaine (mean+/-s.e.mean actual fatal dose: 21.8+/-6.4 micromol), five of seven with levobupivacaine (22.9+/-3.5 micromol), four of six with ropivacaine (22.9+/-5.9 micromol). No significant differences in survival or in fatal doses between these drugs were found. 5. The findings suggest that ropivacaine, levobupivacaine and bupivacaine have similar intrinsic ability to cause direct fatal cardiac toxicity when administered by left intracoronary arterial infusion in conscious sheep and do not explain the differences between the drugs found with intravenous dosage.