Tolerability of Large-Dose Intravenous Levobupivacaine in Sheep

The pharmacokinetics of levobupivacaine 0.5% after infraorbital or inferior alveolar block in anesthetized dogs

Introduction

Data are lacking on the pharmacokinetic profile and safety of levobupivacaine (LB) used for regional anesthesia of the maxilla and mandibles in dogs.

Methods

Infraorbital block (n = 10), inferior alveolar block (n = 10) or both infraorbital and inferior alveolar blocks (n = 10) were administered to dogs undergoing dental surgery under isoflurane anesthesia. The dose of LB was calculated as 0.11 ml/kg^2/3 for the infraorbital block and 0.18 ml/kg^2/3 for the inferior alveolar block. Blood samples were collected before and immediately after administration of the oral blocks, and 3, 4, 7, 12, 17, 32, 47, 62, 92, and 122 min thereafter. Quantification of LB in plasma was performed by LC-MS/MS.

Results and discussion

The results are presented as median and interquartile range. In dogs in which all four quadrants of the oral cavity were desensitized with LB, the C _max was 1,335 (1,030-1,929) ng/ml, the T _max was 7 (4-9.5) min, and the AUC_{(0 → 120)} was 57,976 (44,954-96,224) ng min/ml. Plasma concentrations of LB were several times lower than the reported toxic concentrations, and no signs of cardiovascular depression or neurotoxicity were observed in any of the dogs, suggesting that the occurrence of severe adverse effects after administration of LB at the doses used in this study is unlikely.

Prolonged anesthesia and decreased toxicity of enantiomeric-excess bupivacaine loaded in ionic gradient liposomes

Bupivacaine is the most employed local anesthetic in surgical procedures, worldwide. Its systemic toxicity has directed the synthesis of the less toxic, S(-) enantiomer. This work describes a formulation of ionic gradient liposomes (IGL) containing _S75BVC, an enantiomeric excess mixture of 75% S(-) and 25% R(+) bupivacaine. IGL prepared with 250 mM (NH₄)₂SO₄ in the inner aqueous core of phosphatidylcholine and cholesterol (3:2 mol%) vesicles plus 0.5% _S75BVC showed average sizes of 312.5 ± 4.5 nm, low polydispersity (PDI < 0.18), negative zeta potentials (-14.2 ± 0.2 mV) and were stable for 360 days. The encapsulation efficiency achieved with IGL_S75BVC (%EE = 38.6%) was higher than with IGL prepared with racemic bupivacaine (IGL_RBVC, %EE = 28.3%). TEM images revealed spherical vesicles and µDSC analysis provided evidence on the interaction of the anesthetic with the lipid bilayer. Then, in vitro - release kinetics and cytotoxicity- and in vivo - toxic effects in Zebrafish and biochemical/histopathological analysis plus analgesia in Wistar rats - tests were performed. IGL_S75BVC exhibited negligible toxicity against Schwann cells and Zebrafish larvae, and it did not affect biochemical markers or the morphology of rat tissues (heart, brain, cerebellum, sciatic nerve). The in vitro release of _S75BVC from IGL was extended from 4 to 24 h, justifying the prolonged anesthetic effect measured in rats (~9 h). The advantages of IGL_S75BVC formulation over IGL_RBVC and plain bupivacaine formulations (prolonged anesthesia, preferential sensorial blockade, and no toxicity) confirm its potential for clinical use in surgical anesthesia.

Comparação da latência anestésica de Articaína, Lidocaína, Levobupivacaína e Ropivacaína através de 'Pulp Tester'

INTRODUÇÃO: Um conhecimento profundo dos anestésicos odontológicos, como o tempo de latência da droga, pode assegurar o êxito do controle da dor no trans e no pós-operatório. OBJETIVO: Comparar a latência entre quatro soluções anestésicas, ou seja, o tempo entre o início da deposição do anestésico local e o momento em que seus efeitos tornam-se perceptíveis. Entretanto, isso não está relacionado com o êxito do controle da dor no trans e no pós-operatório (profundidade da anestesia). MATERIAL E MÉTODO: Foi realizado um estudo duplo cego, cruzado e randomizado, com 30 pacientes voluntários submetidos a quatro procedimentos em intervalos de uma semana, a partir de bloqueio do alveolar superior posterior. No segundo molar a ser tratado, foi utilizado o 'pulp tester' em intervalos de 2 minutos, considerando a insensibilidade da polpa quando da ausência de resposta após dois testes consecutivos de 80muV, chegando ao máximo de 10 minutos e determinando, assim, o período de latência do anestésico. Os dados foram submetidos aos testes T-student, de Friedman e de Kruskal-Wallis (p<0,05). RESULTADO: Não houve diferenças estatisticamente significativas (p=0,8327) entre as soluções anestésicas. Para todas estas, a mediana foi 2 minutos. Não houve, ainda, diferenças significantes entre os gêneros em relação à idade (p=0,4545), bem como entre os valores, quando se tentou observar a influência do gênero nos valores de latência (p=0,6754). CONCLUSÃO: Sendo os tempos médios de latência idênticos, a escolha da droga dependerá da duração do procedimento cirúrgico-odontológico a se realizar, além da necessidade ou não de analgesia pós-operatória.

Safety Evaluation of EXPAREL (DepoFoam Bupivacaine) Administered by Repeated Subcutaneous Injection in Rabbits and Dogs: Species Comparison

EXPAREL (bupivacaine extended-release liposome injection), DepoFoam bupivacaine, is in development for prolonged postsurgical analgesia. Repeat-dose toxicity studies were conducted in rabbits and dogs to compare the potential local and systemic toxicities of EXPAREL and bupivacaine HCl (Bsol), and the reversibility of any effects. Dogs tolerated much larger doses than rabbits. EXPAREL-related minimal-to-moderate granulomatous inflammation was noted at the injection sites. In recovery animals, the granulomatous inflammation was observed less frequently and was characterized by an increased number of multinucleated giant cells. These effects were considered a normal response to liposomes and nonadverse. Rabbits are more sensitive than dogs. In rabbits, convulsions were noted with EXPAREL and more frequently with Bsol; a NOAEL was not identified. In dogs, EXPAREL was well tolerated (NOAEL > 30 mg/kg/dose). The cumulative exposure of EXPAREL in these studies is well in excess of the proposed maximum single-dose exposure that is intended in humans.

Vasomotor effect after acute intoxication with bupivacaine and levobupivacaine in rats via intraperitoneal route analyzed via digital infrared imaging

BACKGROUND AND OBJECTIVES

The study of the vasomotor effect of local anesthetics (LA) is of paramount importance for the analysis of the occurrence of cardiotoxic and neurotoxic effects, and drug interactions. In order to find a safer drug than racemic bupivacaine, this study aimed to analyze digital infrared imaging of acute vasomotor effect of bupivacaine and levobupivacaine in rats intraperitoneally.

METHOD

We used 30 male Wistar rats distributed into three groups (n=10) and subjected to an intraperitoneal injection of LA. In Group C (control) 1 mL 0.9% saline was injected intraperitoneally. In Group B (bupivacaine), intraperitoneal injection of 0.5% of racemic bupivacaine (S50-R50), dose of 20 mg.kg⁻¹ of body weight. In Group L (levobupivacaine), intraperitoneal injection of levobupivacaine 0.5% enantiomeric excess (S75-R25) in dose of 20 mg.kg⁻¹ of body weight. The procedure was thermographicly continuously filmed from the time of pre-injection until 30 minutes after injection. The results of the recordings were analyzed in graphical form, verifying the maximum temperature of each rat and the average temperature of the system that housed the animal.

RESULTS

The results of graphic analysis showed no difference between Group L and Group C, and the average temperature remained stable throughout the experiment in both groups. In Group B, there was a phenomenon of temperature increase after intraperitoneal injection of bupivacaine.

CONCLUSIONS

The results demonstrated that the vasomotor effect of the acute toxicity of levobupivacaine was similar to Group C with saline, through macroscopic studies by infrared digital filmmaking, and that there were vasomotor changes (vasoconstriction), with bupivacaine intoxication in relation to both Group C and Group L.

The effects of Different Concentrations and Equivalent Volumes of Levobupivacaine in Epidural Anesthesia

BACKGROUND

Levobupivacaine, the S(-) isomer of bupivacaine, is less cardiotoxic than racemic bupivacaine. Previous studies have examined different concentrations of levobupivacaine in similar ways.

OBJECTIVES

This prospective, randomized, double-blind study was designed to determine the clinical efficacy and hemodynamic effects of different concentrations and equivalent volumes of levobupivacaine in epidural anesthesia. To our knowledge, this is the first study to evaluate the effects of concentration lower than 0.5% levobupivacaine.

METHODS

Forty adult patients with an American Society of Anesthesiology (ASA) I-III physical status undergoing transurethral endoscopic surgery were randomly divided into 2 groups to receive either 10 mL of isobaric levobupivacaine (0.5% + 5 mL 0.9% saline [group 1; n = 20]) or 10 mL of isobaric levobupivacaine (0.75% + 5 mL saline 0.9% saline [group 2; n = 20]) for epidural anesthesia. An observer blinded to group division evaluated the time of onset, maximum level, and time to 2-segment regression of sensory block.

RESULTS

There were no differences between the 2 groups in terms of hemodynamic parameters and time of onset of the sensory block. There were significant differences, however, between the 2 groups in the maximum level of the sensory block (group 1, T9; group 2, T8; P = 0.010) and the time to 2-segment regression of sensory block (group 1, 46.35 minutes; group 2, 62.94 minutes; P = 0.013).

CONCLUSION

This study indicated that 10 mL of 0.5% levobupivacaine plus 5 mL of 0.9% saline is a suitable solution for use in epidural anesthesia because it produces a block clinically comparable to that of 10 mL of 0.75% levobupivacaine plus 5 mL of 0.9% saline for transurethral resection of prostate surgery.

Chemical analgesia for velvet antler removal in deer

There is a legal requirement to provide analgesia for velvet antler removal in New Zealand. Currently, this is achieved using local anaesthetic blockade, with or without systemically administered sedative/analgesic agents, or by compression in 1-year-old stags. Lignocaine hydrochloride 2% is most commonly used and is most effective when administered as a high-dose ring block. Combinations of various amino-amide local anaesthetic agents can achieve rapid onset and prolonged duration of analgesia, though concerns about drug residues and carcinogenic potential of a lignocaine metabolite have led to consideration of the amino-ester family of local anaesthetics as alternatives. Systemically administered analgesics, including opioids, alpha-2-adrenergic agents and ketamine provide dose-dependent sedation and analgesia. However, none are sufficient, alone or in combination, to produce surgical analgesia at currently recommended dose rates and when reversal agents are given, analgesic effects are usually reversed as well as sedation. Thus, local anaesthetic blockade is still indicated, though the potential for drug or drug-metabolite residues in velvet antler remains a concern. The need for and effectiveness of non-steroidal anti-inflammatory drugs (NSAIDs) for post-operative analgesia requires investigation. Amitriptyline, locally administered opioid agonists, tramadol and other systemically administered agents may warrant future investigation for surgical and post-operative analgesia for velvet antler removal.

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.

Safety of amide local anesthetics: new trends

IMPORTANCE OF THE FIELD

Local anesthetics have become one of the most common drugs used in daily practice worldwide. Neurologic and cardiovascular events are the most frequent adverse reactions related to local anesthetics use. Recently, new trends have been developed on this topic.

AREAS COVERED IN THIS REVIEW

We performed an overview of the data available so far on local anesthetics adverse reactions. Relevant literature was identified using PubMed search of articles published up to November 2009, including experimental studies, case reports or clinical studies when available. Search terms included: 'local anaesthetics', 'adverse drug reaction', 'pharmacovigilance' and 'complication'.

WHAT THE READER WILL GAIN

Neurologic, cardiovascular and allergic reactions remain the most frequent adverse drug reactions related to local anesthetics in the literature. Studies based on pharmacovigilance systems have highlighted the frequency of adverse reactions little known until now, such as failure of block. Lipid emulsions are included into algorithm for cardiac resuscitation. Recent studies have demonstrated the myotoxicity and chondrotoxic effects of long-acting local anesthetics.

TAKE HOME MESSAGE

Physicians must keep in mind all these adverse reactions to better prevent their occurrence and give the most appropriate treatment.

Pharmacokinetics of levobupivacaine 0.5% after superficial or combined (deep and superficial) cervical plexus block in patients undergoing minimally invasive parathyroidectomy

STUDY OBJECTIVE

To evaluate the pharmacokinetic profile of 0.35 mL/kg of 0.5% levobupivacaine during superficial and combined (deep and superficial) cervical plexus block (CPB) in patients undergoing minimally invasive parathyroidectomy.

DESIGN

Prospective randomized study.

SETTING

Operating theater of a university hospital.

PATIENTS

12 ASA physical status II and III patients (11 women and 1 man), scheduled for minimally invasive parathyroidectomy.

INTERVENTIONS

Seven and 5 patients were randomly assigned to receive either superficial or combined CPB, respectively. The superficial CPB was performed with an injection of 0.35 mL/kg of 0.5% levobupivacaine subcutaneously along the posterior border of the sternocleidomastoid muscle and deeper on its medial surface. The combined CPB was initiated by the deep block at the C3 level vertebra by injecting 0.2 mL/kg of 0.5% levobupivacaine, followed by the superficial block with an injection of the remaining 0.15 mL/kg. After completion of the block, venous blood was sampled at the intervals of 5, 10, 15, 20, 30, 45, and 60 minutes.

MEASUREMENTS AND MAIN RESULTS

Venous plasma concentrations were measured using gas chromatography-mass spectroscopy. Mean +/- SD of maximal concentrations of levobupivacaine was 0.58 +/- 0.41 mg/L in group superficial and 0.52 +/- 0.28 mg/L in group combined (P = 0.71). The median (range) time required to reach the maximal concentrations was 30 minutes (20-30 min) in group superficial and 20 minutes (15-30 min) in group combined (P = 0.45). The areas under the drug concentration/time curve (AUC(10-60)) were also similar in both groups. No signs of central nervous system or cardiovascular toxicity or other untoward events were observed in any patient.

CONCLUSION

With the given dose regimen, levobupivacaine plasma concentrations were within safe ranges.

The effects of general anesthesia on the central nervous and cardiovascular system toxicity of local anesthetics

BACKGROUND

Local anesthetic toxicity is often studied experimentally in acutely prepared, anesthetized laboratory animals. We determined the influence of halothane/O(2) anesthesia on cardiovascular and central nervous system (CNS) toxic responses to six amide-type local anesthetics administered i.v..

METHODS

Behavioral, cardiovascular, and pharmacokinetic responses were determined in previously instrumented ewes (approximately 45-50 kg, n = 18), on separate occasions when conscious and anesthetized, to bupivacaine (100 mg), levobupivacaine (125 mg), ropivacaine (150 mg), lidocaine (350 mg), mepivacaine (350 mg), prilocaine (350 mg), and saline (control) infused i.v. over 3 min.

RESULTS

The local anesthetics caused convulsions in conscious sheep, but no overt CNS effects in anesthetized sheep. Negative inotropy and slight bradycardia without changes in arterial blood pressure occurred initially in conscious sheep, followed by positive inotropy, tachycardia, and hypertension at the abrupt onset of CNS excitotoxicity, along with widening of QRS complexes. Fatal cardiac arrhythmias occurred in, respectively, 3 of 11, 2 of 12, and 2 of 13 conscious sheep infused with bupivacaine, levobupivacaine, and ropivacaine; in 1 of 9 with prilocaine, electromechanical dissociation (followed by polymorphic ventricular tachycardia) caused death. In anesthetized sheep, cardiovascular depression, preexisting from the general anesthesia, was exacerbated by all local anesthetics, and increased QRS width was prolonged; concurrent blood local anesthetic concentrations were doubled. Nevertheless, all anesthetized animals survived.

CONCLUSIONS

General anesthesia produced physiological perturbations, exacerbated local anesthetic-induced cardiovascular depression, and changed the pharmacokinetics of toxic doses of local anesthetics. However, cardiovascular fatalities from local anesthetics occurred only in conscious animals.

Effects of bupivacaine, levobupivacaine and ropivacaine on myocardial relaxation

PURPOSE

Ropivacaine and levobupivacaine were developed to reduce the risk of occasional toxicity reported with bupivacaine. While the effects of long-acting local anesthetics (LAAs) on myocardial contractility (inotropy) are well described, their effects on relaxation (lusitropy) remain largely unknown. The present study aimed to compare the effects of LAAs on rat myocardium.

METHODS

Left ventricular papillary muscles of male Wistar rats were used to compare the inotropic and lusitropic responses of increasing concentrations of LAAs (10(-8) to 10(-3) M) under isometric and isotonic conditions. Data are mean % (SD) of baseline value.

RESULTS

Long-acting local anesthetics induced a significant impairment of relaxation in isotonic and isometric conditions. As compared to ropivacaine, bupivacaine and levobupivacaine induced greater negative lusitropic effects in isotony [at 10(-3) M, maximum unloaded shortening velocity ((max)Vr) = 27 +/- 11 vs 13 +/- 6 and 8 +/- 5%] and isometry (at 10(-3) M, time-to-half-relaxation: 106 +/- 10 vs 127 +/- 17 and 133 +/- 17%). When the comparison was made with equipotent concentrations, the negative lusitropic effects induced with levobupivacaine were significantly greater than those of bupivacaine and ropivacaine in isometric and isotonic conditions (at 10(-3) M, (max)Vr = 7 +/- 4 vs 13 +/- 6 and 17 +/- 4 %). As previously described, LAAs also induced concentration-dependent negative inotropic effects that were greater for levobupivacaine compared to equivalent or equipotent concentrations of bupivacaine and ropivacaine.

CONCLUSIONS

Long-acting local anesthetics induce marked negative inotropic and lusitropic effects. Among LAAs, levobupivacaine exerts the greater depressant effects. Impairment of calcium handling and sarcoplasmic reticulum could explain the differential responses to local anesthetics.

[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.

Enantioselective Actions of Bupivacaine and Ropivacaine on Coronary Vascular Resistance at Cardiotoxic Concentrations

The main concern with the use of the long-acting local anesthetics bupivacaine and ropivacaine is inadvertent IV injection, which exposes the heart to toxic drug concentrations. We tested the hypothesis that these chiral anesthetics exert enantioselective actions on coronary vascular tone, the regulation of which does not involve voltage-gated Na(+) channels. Coronary perfusion pressure (CPP) was continuously measured in isolated hearts perfused via the aorta at a constant flow rate. This method provides a sensitive assay of coronary vascular resistance in the intact heart. In parallel experiments, we examined the effects of bupivacaine and ropivacaine on intracellular [Ca(2+)] in coronary endothelial cells. In addition, the effect of bupivacaine on mitochondrial membrane potential was assessed using isolated ventricular myocytes. Racemic bupivacaine and R(+)-bupivacaine produced similar dose-dependent decreases in CPP. However, S(-)-bupivacaine, S(-)-ropivacaine and R(+)-ropivacaine increased CPP. In contrast to adenosine triphosphate, neither racemic bupivacaine nor S(-)-ropivacaine changed endothelial intracellular [Ca(2+)], suggesting that these clinically used drugs do not modulate endothelial nitric oxide synthase. We also showed that the putative uncoupler bupivacaine did not depolarize mitochondria in intact ventricular myocytes. In conclusion, the long-acting local anesthetics have enantioselective actions on coronary resistance vessels. Racemic bupivacaine and R(+)-bupivacaine are coronary vasodilators, whereas S(-)-bupivacaine, S(-)-ropivacaine and, to a lesser extent, R(+)-ropivacaine all induce coronary vasoconstriction.

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.

Onset time, quality of blockade, and duration of three-in-one blocks with levobupivacaine and bupivacaine

Levobupivacaine is the isolated S(-)-stereoisomer of racemic bupivacaine. Important pharmacodynamic properties of levobupivacaine have not been determined for the femoral three-in-one block. In this randomized, controlled, double-blinded trial, we studied 60 ASA physical status I-III patients scheduled for surgery of the lower limb. A nerve-stimulator-guided three-in-one block was performed as supplemental analgesic therapy with 20 mL of bupivacaine 0.5% (n = 20), levobupivacaine 0.5% (n = 20), or levobupivacaine 0.25% (n = 20). Sensory onset time, quality of blockade, and duration of blockade were assessed by pinprick test in the central sensory innervation region of the femoral nerve (distribution of the anterior femoral cutaneous nerve). A rating scale from 100% (normal sensation) to 0% (no sensation at all) as compared with the contralateral leg was used. No significant difference in sensory onset time among the three local anesthetic solutions was observed (mean [95% confidence interval]): bupivacaine 0.5%, 27 min (20-33 min); levobupivacaine 0.5%, 24 min (18-30 min); and levobupivacaine 0.25%, 30 min (23-36 min) (P = 0.49). The analgesic quality of the blockade was also not significantly different among the three groups, whereas a complete sensory block was achieved in significantly fewer patients in the levobupivacaine 0.25% group (P = 0.02). The duration of blockade was significantly shorter with levobupivacaine 0.25% compared with the other groups: bupivacaine 0.5%, 1053 min (802-1304 min); levobupivacaine 0.5%, 1001 min (844-1158 min); and levobupivacaine 0.25%, 707 min (551-863 min) (P = 0.01). Levobupivacaine 0.5% is recommended instead of bupivacaine 0.5% for the three-in-one block.

Pulmonary uptake of ropivacaine and levobupivacaine in rabbits

Local anesthetic toxicity produced by an inadvertent IV injection is attenuated by the pulmonary uptake of local anesthetics. We compared the pulmonary uptake of ropivacaine and levobupivacaine after a bolus injection in rabbits. Sixteen anesthetized rabbits were randomly assigned to either a ropivacaine group or a levobupivacaine group. A bolus containing ropivacaine or levobupivacaine 0.5 mg/kg and indocyanine green (an intravascular indicator) 0.25 mg/kg was injected rapidly into the vena cava. Arterial blood samples were collected serially at 1.2-s intervals for 30 s. Concentrations of local anesthetic and indocyanine green in each sample were determined for the calculation of first-pass uptake of a local anesthetic in the lung. The first-pass uptake of levobupivacaine (31.4% +/- 8.3%; mean +/- SD) was larger than that of ropivacaine (22.9% +/- 5.6%), and the maximum arterial concentration of ropivacaine (21.2 +/- 2.8 micro g/mL) was larger than that of levobupivacaine (18.6 +/- 1.9 micro g/mL). We conclude that the pulmonary uptake of levobupivacaine is larger than that of ropivacaine after a bolus injection. Therefore, the advantages of ropivacaine over levobupivacaine in terms of less cardiovascular toxicity may be offset by the smaller pulmonary uptake after an inadvertent IV injection.

Toxicity of local anaesthetics

The complications of failure, neural injury and local anaesthetic toxicity are common to all regional anaesthetic techniques, and individual techniques are associated with specific complications. All potential candidates for regional anaesthesia should be thoroughly evaluated and informed of potential complications. Central neural blockades still account for more than 70% of regional anaesthesia procedures. Permanent neurological injury is 0.02-0.07%. Pain on injection and paraesthesias while performing regional anaesthesia are danger signals of potential injury and must not be ignored. The incidence of systemic toxicity to local anaesthetics has significantly decreased in the past 30 years, from 0.2 to 0.01%. Peripheral nerve blocks are associated with the highest incidence of systemic toxicity (7.5 per 10,000) and the lowest incidence of serious neural injury (1.9 per 10,000).

Convulsions following axillary brachial plexus blockade with levobupivacaine

Neurotoxicity manifesting as convulsions is a recognised complication of the administration of local anaesthetic drugs as part of a regional anaesthetic technique. We describe a case of self-limiting convulsions following the institution of an axillary brachial plexus block with levobupivacaine. Although the occurrence of convulsions following the administration of racemic bupivacaine is a well-recognised complication, there have been no clinical case reports published describing convulsions following the use of levobupivacaine in regional anaesthesia.

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.

Chirality: a blueprint for the future

The chirality that is inherent in the enzyme systems of living organisms results in an abundance of enantiopure organic molecules in the living world. In addition to the optical properties first noticed by Pasteur, stereospecific interactions at recognition sites result in differences in both biological and toxicological effects. This fact underlies the continuing growth in chiral chemistry, rooted as it is in fundamental biochemistry. The pharmaceutical industry has undergone a strategic shift and embraced the wide spectrum of asymmetrical synthetic methods now available. The use of these processes in developmental synthesis and large-scale manufacturing has provided new challenges in drug discovery, motivated by a desire to improve industrial efficacy and decrease the time from the conception of a new drug to the market. The economic impact of the industrial production of chiral drugs is now huge--more than 50% of the 500 top-selling drugs were single-enantiomers in 1997. Sales have continued to increase by more than 20% for the past 6 yr and worldwide annual sales of enantiomeric drugs exceeded US$100 billion for the first time in the year 2000, chiral drugs representing close to one-third of all sales worldwide. While some 'chiral switches' may be of less apparent benefit, or indeed detrimental in some cases, encouragement by the regulatory agencies and the ability to extend the life cycle of a drug coming off patent promotes the trend. However, it may turn out to be the ability to provide chiral templates, and thereby attack the key targets of selectivity and specificity, that will lead to the greatest benefits. Research into new chemical entities that can interact specifically with enzyme families may potentially lead to new therapies for complex disease processes. As Richards has stated, the approach is designed to create a made to measure product, rather than one off the peg.

Anatomical-physiological approaches in pharmacokinetics and pharmacodynamics

Use of an anatomical-physiological approach allows an investigator an alternative to regarding the whole body as a 'black box' producing biofluid specimens for drug assay, and then blindly applying a formula-driven mathematical approach to determine the pharmacokinetics and pharmacodynamics of the drug of interest. Instead, it means the investigator can consider that the body is the sum of interacting parts or regions connected anatomically by blood flow carrying the drug of interest, that the regions as well as the carrier blood are not homogeneous because each has a physiological role, and that the parts or regions are connected neurally and humorally so that the response in any region or part of the system may be modified by and/or modulate effects at another region or part. Such an approach is difficult to institute experimentally because a complicated (and often expensive) preparation is usually required in animal studies, and is rarely possible in research with humans because of ethical constraints. Despite these restrictions, there are many examples of the use of an anatomical-physiological approach allowing greater insight into pharmacological problems than would have been possible with a conventional 'whole body' approach alone. This paper takes a number of examples from the discipline of anaesthesia and pain management and groups them to illustrate the principles of the approach regarding drug arterio-venous equality and tissue distribution, multiple sites of clearance and multiple sites of action.

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.

A comparison of epidural levobupivacaine 0.5% with or without epinephrine for lumbar spine surgery

Levobupivacaine, the S(-) isomer of bupivacaine, is less cardiotoxic than racemic bupivacaine. In this prospective, randomized, double-blinded study of epidural anesthesia, we compared the onset, extent, and duration of sensory and motor blockade produced by plain 0.5% levobupivacaine (15 mL, 75 mg) with that of 0.5% levobupivacaine with the addition of 1:400,000 or 1:200,000 epinephrine in 117 patients undergoing elective spine surgery. The time to onset of adequate sensory block (T10 dermatome) was similar in all groups (12.4 +/- 6.6 min for plain levobupivacaine, 13.9 +/- 7.9 min for levobupivacaine with 1:400,000 epinephrine, and 12.7 +/- 4.9 min for levobupivacaine with 1:200,000 epinephrine), with an average peak block height of T5. Time to complete regression of sensory blockade was also similar between groups (357 +/- 119 min for plain levobupivacaine, 378 +/- 98 min for levobupivacaine with 1:400,000 epinephrine, and 348 +/- 80 min for levobupivacaine with 1:200,000 epinephrine). Peak serum levobupivacaine levels were reduced in each of the epinephrine-containing groups. We conclude that 0.5% levobupivacaine with or without 1:200,000 or 1:400,000 epinephrine produced effective epidural anesthesia in patients having lumbar spine surgery. Epinephrine 1:400,000 is as effective as 1:200,000 in reducing the resultant serum levobupivacaine levels after epidural anesthesia.

Cardiotoxicity with modern local anaesthetics: is there a safer choice?

The recognition that long-acting local anaesthetics, particularly bupivacaine the de facto standard long-acting local anaesthetic, were disproportionately more cardiotoxic than their shorter-acting counterparts stimulated the development of the bupivacaine congeners, ropivacaine and levobupivacaine. These agents, like all local anaesthetics, can produce cardiotoxic sequelae by direct and indirect mechanisms that derive from their mode of local anaesthetic actions, i.e. inhibition of voltage-gated ion channels. While all local anaesthetics can cause direct negative inotropic effects, ropivacaine and levobupivacaine are less cardiotoxic than bupivacaine judging by the larger doses tolerated in laboratory animal preparations before the onset of serious cardiotoxicity (particularly electro-mechanical dissociation or malignant ventricular arrhythmias). Additionally, they are less toxic to the CNS than bupivacaine judging by the larger doses tolerated before the onset of seizures. This may be clinically important because CNS effects may be involved in the production of serious cardiotoxicity. Preclinical studies in humans are a 'blunt instrument' in their ability to distinguish significant differences between these drugs because of the relatively small doses that can be used. Nevertheless, available evidence from human studies corroborates the preclinical laboratory animal studies. Because clinically significant differences between these drugs are more quantitative than qualitative, i.e. toleration of a larger dose before manifestation of toxicity, we have concluded that these newer agents have a lower risk of causing serious cardiotoxicity than bupivacaine. Thus, compared with bupivacaine, the newer agents may be seen as 'safer', but they must not be regarded as 'safe'.

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.

Central Effects Index--a semiquantitative method for the assessment of CNS toxicity of local anaesthetic agents in sheep

Local anaesthetic agents can cause central nervous system (CNS) and cardiovascular system toxicity. Whereas most previous work has described their behavioural CNS effects qualitatively (i.e., absence or presence of convulsions), we wished to describe their CNS effects more quantitatively. We hypothesised that early CNS excitatory or disinhibitory effects leading to convulsions represent a prodrome to the onset of chaotic dynamics in the form of a bifurcation in the chaotic map. We therefore used a chaotic map with a continuous scale to model their CNS effects. A Central Effects Index (CEI) was developed from our observation of behaviours before and after intravenous (iv) administration of local anaesthetic agents in graded doses to conscious sheep. These behaviours were ranked in severity, and modelled according to a logistic population growth equation using the onset of convulsive behaviour and death as point attractors. The behaviours, scaled to the maximum and area under the curve (AUC) CEI units, were then compared for intravenous doses of (+/-)-RS-bupivacaine and (-)-(S)-bupivacaine (or levobupivacaine), which is being evaluated as a substitute for (+/-)-RS-bupivacaine. (-)-(S)-bupivacaine produced smaller maximum and AUC CEI values at 75 and 100 mg doses, but equivalent values at 150 and 200 mg when the doses exceeded the convulsant threshold. It was concluded that the CEI provides a useful quantitative tool for evaluating these agents in subconvulsant doses, and that the CNS stimulatory potency of (-)-(S)-bupivacaine is less than that of (+/-)-RS-bupivacaine.