Binding of long-lasting local anesthetics to lipid emulsions

Multi-modal contributions to detoxification of acute pharmacotoxicity by a triglyceride micro-emulsion

Triglyceride micro-emulsions such as Intralipid® have been used to reverse cardiac toxicity induced by a number of drugs but reservations about their broad-spectrum applicability remain because of the poorly understood mechanism of action. Herein we report an integrated mechanism of reversal of bupivacaine toxicity that includes both transient drug scavenging and a cardiotonic effect that couple to accelerate movement of the toxin away from sites of toxicity. We thus propose a multi-modal therapeutic paradigm for colloidal bio-detoxification whereby a micro-emulsion both improves cardiac output and rapidly ferries the drug away from organs subject to toxicity. In vivo and in silico models of toxicity were combined to test the contribution of individual mechanisms and reveal the multi-modal role played by the cardiotonic and scavenging actions of the triglyceride suspension. These results suggest a method to predict which drug toxicities are most amenable to treatment and inform the design of next-generation therapeutics for drug overdose.

An in vitro analysis of the effects of intravenous lipid emulsion on free and total local anaesthetic concentrations in human blood and plasma

Background. Intravenous lipid emulsion (ILE) is recommended as a “rescue” treatment for local anaesthetic (LA) toxicity. A purported mechanism of action suggests that lipophilic LAs are sequestered into an intravascular “lipid-sink,” thus reducing free drug concentration. There is limited data available correlating the effects of ILE on LAs. Aims. To compare the in vitro effect of ILE on LA concentrations in human blood/plasma and to correlate this reduction to LA lipophilicity. Method. One of four LAs (bupivacaine-most lipophilic-4 mg/L, ropivacaine-6 mg/L, lignocaine-14 mg/L, and prilocaine-least lipophilic-7 mg/L) was spiked into plasma or whole blood. ILE or control-buffer was added. Plasma was centrifuged to separate ILE and total-LA concentration assayed from the lipid-free fraction. Whole blood underwent equilibrium dialysis and free-LA concentration was measured. Percent reduction in LA concentration from control was compared between the LAs and correlated with lipophilicity. Results. ILE caused a significant reduction in total and free bupivacaine concentration compared with the other LAs. Ropivacaine had the least reduction in concentration, despite a lipophilicity similar to bupivacaine. The reduction in LA concentration correlated to increasing lipophilicity when ropivacaine was excluded from analysis. Conclusion. In this first in vitro model assessing both free- and total-LA concentrations exposed to ILE in human blood/plasma, ILE effect was linearly correlated with increasing lipophilicity for all but ropivacaine.

Effect of two lipid emulsions on reversing high-dose levobupivacaine-induced reduced vasoconstriction in the rat aortas

The goals of this study were to determine which lipid emulsion (Intralipid(®) and Lipofundin MCT/LCT(®)) is more effective in reversing high-dose levobupivacaine-induced reduced vasoconstriction in isolated rat aortas and to examine the associated cellular mechanisms with a particular focus on the endothelium. Two lipid emulsion concentration-response curves were generated using high-dose levobupivacaine-induced reduced vasoconstriction and vasodilation of isolated aortas pretreated with or without 60 mM KCl. Endothelial nitric oxide synthase (eNOS) and caveolin-1 phosphorylation were measured in rat aortic tissue treated with levobupivacaine in the presence or absence of lipid emulsion. Dichlorofluorescein oxidation, a measure of reactive oxygen species production, was measured in lipid emulsion-treated human umbilical vein endothelial cells. In levobupivacaine (0.3 mM)-induced reduced vasoconstriction of isolated aorta, the magnitude of the Intralipid(®)- and Lipofundin MCT/LCT(®)-mediated reversal was not significantly different. Lipid emulsion reversal of levobupivacaine-induced reduced vasoconstriction was greater in endothelium-intact aortas than in endothelium-denuded aortas. The two lipid emulsions similarly inhibited levobupivacaine-induced eNOS phosphorylation in aortic tissue. Pretreatment with both lipid emulsions increased dichlorofluorescein oxidation. Both Intralipid(®) and Lipofundin MCT/LCT(®) are equally effective for vascular tone recovery from high-dose levobupivacaine-induced reduced vasoconstriction. This reversal is mediated partially by decreasing nitric oxide bioavailability.

Review of the use of lipid emulsion in nonlocal anesthetic poisoning

Intravenous lipid emulsion (ILE) has been used widely for the treatment of poisoning due to local anesthetic agent and is increasingly reported as a therapy for other forms of poisoning. This article will review the proposed mechanisms of action for ILE in poisoning and the evidence from animal studies and human experience supporting the use of ILE for poisoning due to nonlocal anesthetic agents.

Intravenous lipid emulsion alters the hemodynamic response to epinephrine in a rat model

Intravenous lipid emulsion (ILE) is an adjunctive antidote used in selected critically ill poisoned patients. These patients may also require administration of advanced cardiac life support (ACLS) drugs. Limited data is available to describe interactions of ILE with standard ACLS drugs, specifically epinephrine. Twenty rats with intra-arterial and intravenous access were sedated with isoflurane and split into ILE or normal saline (NS) pretreatment groups. All received epinephrine 15 μm/kg intravenously (IV). Continuous mean arterial pressure (MAP) and heart rate (HR) were monitored until both indices returned to baseline. Standardized t tests were used to compare peak MAP, time to peak MAP, maximum change in HR, time to maximum change in HR, and time to return to baseline MAP/HR. There was a significant difference (p = 0.023) in time to peak MAP in the ILE group (54 s, 95 % CI 44-64) versus the NS group (40 s, 95 % CI 32-48) and a significant difference (p = 0.004) in time to return to baseline MAP in ILE group (171 s, 95 % CI 148-194) versus NS group (130 s, 95 % CI 113-147). There were no significant differences in the peak change in MAP, peak change in HR, time to minimum HR, or time to return to baseline HR between groups. ILE-pretreated rats had a significant difference in MAP response to epinephrine; ILE delayed the peak effect and prolonged the duration of effect of epinephrine on MAP, but did not alter the peak increase in MAP or the HR response.

Pre-treatment of bupivacaine-induced cardiovascular depression using different lipid formulations of propofol

BACKGROUND

Pre-treatment with lipid emulsions has been shown to increase lethal doses of bupivacaine, and the lipid content of propofol may alleviate bupivacaine-induced cardiotoxicity. The aim of this study is to investigate the effects of propofol in intralipid or medialipid emulsions on bupivacaine-induced cardiotoxicity.

METHODS

Rats were anaesthetised with ketamine and were given 0.5 mg/kg/min propofol in intralipid (Group P), propofol in medialipid (Group L), or saline (Group C) over 20 min. Thereafter, 2 mg/kg/min bupivacaine 0.5% was infused. We recorded time to first dysrhythmia occurrence, respective times to 25% and 50% reduction of the heart rate (HR) and mean arterial pressure, and time to asystole and total amount of bupivacaine consumption. Blood and tissue samples were collected following asystole.

RESULTS

The time to first dysrhythmia occurrence, time to 25% and 50% reductions in HR, and time to asystole were longer in Group P than the other groups. The cumulative bupivacaine dose given at those time points was higher in Group P. Plasma bupivacaine levels were significantly lower in Group P than in Group C. Bupivacaine levels in the brain and heart were significantly lower in Group P and Group L than in Group C.

CONCLUSION

We conclude that pre-treatment with propofol in intralipid, compared with propofol in medialipid or saline, delayed the onset of bupivacaine-induced cardiotoxic effects as well as reduced plasma bupivacaine levels. Further studies are needed to explore tissue bupivacaine levels of propofol in medialipid and adapt these results to clinical practice.

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

Background:

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

Methods:

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

Results:

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

Conclusion:

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

Intravenous lipid emulsion does not reverse dabigatran-induced anticoagulation in a rat model

OBJECTIVES

The anticoagulant dabigatran has no reversal agent and may cause life-threatening bleeding in patients with trauma or closed-space hemorrhage. Intravenous lipid emulsion (ILE) is thought to create a lipid compartment in serum that sequesters lipophilic drugs. Dabigatran is lipophilic, and its anticoagulant effects are concentration dependent. The study objective was to determine if ILE therapy reverses dabigatran's anticoagulant effects.

METHODS

Twenty rats were selected at random, 10 in the ILE group and 10 in a normal saline (NS) control group. Animals had a baseline tail bleeding time (T0), followed by oral dabigatran administration (15 mg/kg). At 45 minutes (T45), a second tail bleed time measurement was performed, followed by a 7-minute infusion of 15 mL/kg ILE or NS. A final 60-minute (T60) bleed time measurement was obtained. An ILE-only group of five animals had bleeding times assessed prior to (T0) and 15 minutes after (T15) ILE therapy. A mixed-effect repeated-measures analysis of variance modeling the effect of time, group, and the interaction of group and time on bleed times was conducted.

RESULTS

There was a significant within-subject change in bleeding time across the assessment points (F(2,36) = 33; p < 0.001), but there were no effect of group (F(1,18) = 1.42, p = 0.25) or an interaction between group and assessment point on mean bleeding time (F(2,36) = 0.59, p = 56). Between T0 and T45, average bleeding times increased from 109.5 seconds (95% confidence interval [CI] = 94 to 125 seconds) to 231.8 seconds (95% CI = 193 to 271 seconds; p < 0.0001) for both the ILE group and the NS control group. Between T45 and T60, bleeding times in the ILE group decreased by 31.5 seconds (95% CI = -77 to 14 seconds) and by 6 seconds (95% CI = -67 to 55 seconds) in the NS group (p = 0.46). In the five ILE-only animals, the average bleeding time at T0 was 114 seconds (95% CI = 62 to 166 seconds), which increased significantly at T15 to 237 seconds (95% CI = 161 to 313 seconds; p = 0.02).

CONCLUSIONS

The anticoagulant effects of dabigatran are not reversed with ILE therapy. Although ILE itself significantly prolonged bleeding times, when administered to dabigatran-anticoagulated rats, bleeding times did not change significantly. There may be a complex interaction of ILE with dabigatran that this study was not able to elucidate.

Binding of local anaesthetics to the lipid emulsion Clinoleic™ 20%

Lipid emulsions have been used to treat cardiovascular collapse due to local anaesthetic toxicity. However, there are few data available on the comparative efficiency of the partitioning properties of available lipid emulsions in clinical use. This in vitro study compared the buffering properties of the lipid emulsions Clinoleic™ 20% (Baxter, Old Toongabbie, NSW) and Intralipid® 20% (Fresenius Kabi, Pymble, NSW) using both bupivacaine (Marcain® 0.5%, AstraZeneca, North Ryde, NSW) and ropivacaine (Naropin® 1%, AstraZeneca, North Ryde, NSW). The concentration of anaesthetic in buffer before and after mixing with lipid was quantified using chromatographic analysis. Bupivacaine was more effectively bound by the lipid agents, with a 40% reduction in initial concentration. Ropivacaine demonstrated a 20% reduction in concentration with the addition of lipid agents. Importantly, there was no significant difference between Intralipid and Clinoleic in terms of their buffering behaviour, suggesting equivalent binding efficacy.

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

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

Validity of the lipid sink as a mechanism for the reversal of local anesthetic systemic toxicity: a physiologically based pharmacokinetic model study

BACKGROUND

In vitro observations support the lipid sink theory of therapeutic action by confirming the capacity of lipid emulsions to successfully uptake bupivacaine from aqueous media. However, competing hypotheses and some in/ex vivo small animal studies suggest that a metabolic or positive inotropic effect underlies the dramatic effects of lipid therapy. Controlled clinical tests to establish causality and mechanism of action are an impossibility. In an effort to quantitatively probe the merits of a "sink" mechanism, a physiologically based pharmacokinetic model has been developed that considers the binding action of plasma lipid.

METHODS

The model includes no fitting parameters and accounts for concentration dependence of plasma protein and lipid:anesthetic binding as well as the metabolism of the lipid scavenger. Predicted pharmacokinetics were validated by comparison with data from healthy volunteers administered a nontoxic dose of bupivacaine. The model was augmented to simulate lipid therapy and extended to the case of accidental IV infusion of bupivacaine at levels known to cause systemic toxicity.

RESULTS

The model yielded quantitative agreement with available pharmacokinetic data. Simulated lipid infusion following an IV overdose was predicted to yield (1) an increase in total plasma concentration, (2) a decrease in unbound concentration, and (3) a decrease in tissue content of bupivacaine.

CONCLUSIONS

Results suggest that the timescale on which tissue content is reduced varies from organ to organ, with the concentration in the heart falling by 11% within 3 min. This initial study suggests that, in isolation, the lipid sink is insufficient to guarantee a reversal of systemic toxicity.

Intravenous lipid emulsion to reverse acute drug toxicity in pediatric patients

OBJECTIVE

To identify and summarize published cases in which intravenous lipid emulsion was used to treat pediatric patients with acute drug toxicities.

DATA SOURCES

PubMed, SCOPUS, and EMBASE were searched up to December 2012 for relevant publications using the terms fat emulsion, lipid emulsion, Intralipid, Liposyn, Medialipide, Medialipid, lipid rescue, ILE, IVLE, IFE, IVFE, or lipid and intoxication, overdose, poisoning, toxicity, resuscitation, antidote, and rescue that were limited to reports in humans aged 18 years or younger.

STUDY SELECTION AND DATA EXTRACTION

A publication was included if an intravenous lipid emulsion was used to treat acute-onset drug toxicity as reported in prospective or retrospective observational studies, case reports, and abstracts for patients aged 18 years or younger.

DATA SYNTHESIS

Fourteen case reports were identified in which intravenous lipid emulsion was used to treat toxicities due to local anesthetics and other medications (amitriptyline, diltiazem, bupropion, dosulepin, lamotrigine, quetiapine, and verapamil). Thirteen cases demonstrated a beneficial response in reversing systemic toxicity; 1 of these patients developed hypertriglyceridemia and pancreatitis. The dosage regimens used in this series were dissimilar.

CONCLUSIONS

There is an increasing interest in use of intravenous lipid emulsions to treat life-threatening toxicity from several lipophilic drugs in adults and children. Although most of the literature describes adult cases, intravenous lipid emulsion has been used in neonates and adolescents, with generally positive outcomes. Given the life-threatening, sometimes near-death situations in which an intravenous lipid emulsion is typically used after conventional resuscitation is unsuccessful and the dramatic positive response to this therapy in most published cases, its use likely will continue. Continued reporting of pediatric cases will guide the optimal use and safety profile of intravenous lipid emulsion for the emergent reversal of drug toxicity.

Lipid emulsion-mediated reversal of toxic-dose aminoamide local anesthetic-induced vasodilation in isolated rat aorta

Background

Intravenous lipid emulsion has been used to treat systemic toxicity of local anesthetics. The goals of this in vitro study were to determine the ability of two lipid emulsions (Intralipid® and Lipofundin® MCT/LCT) to reverse toxic dose local anesthetic-induced vasodilation in isolated rat aortas.

Methods

Isolated endothelium-denuded aortas were suspended for isometric tension recording. Vasodilation was induced by bupivacaine (3 × 10^-4 M), ropivacaine (10^-3 M), lidocaine (3 × 10^-3 M), or mepivacaine (7 × 10^-3 M) after precontraction with 60 mM KCl. Intralipid® and Lipofundin® MCT/LCT were then added to generate concentration-response curves. We also assessed vasoconstriction induced by 60 mM KCl, 60 mM KCl with 3 × 10^-4 M bupivacaine, and 60 mM KCl with 3 × 10^-4 M bupivacaine plus 1.39% lipid emulsion (Intralipid® or Lipofundin® MCT/LCT).

Results

The two lipid emulsions reversed vasodilation induced by bupivacaine, ropivacaine, and lidocaine but had no effect on vasodilation induced by mepivacaine. Lipofundin® MCT/LCT was more effective than Intralipid® in reversing bupivacaine-induced vasodilation. The magnitude of lipid emulsion-mediated reversal of vasodilation induced by high-dose local anesthetics was as follows (from highest to lowest): 3 × 10^-4 M bupivacaine-induced vasodilation, 10^-3 M ropivacaine-induced vasodilation, and 3 × 10^-3 M lidocaine-induced vasodilation.

Conclusions

Lipofundin® MCT/LCT-mediated reversal of bupivacaine-induced vasodilation was greater than that of Intralipid®; however, the two lipid emulsions equally reversed vasodilation induced by ropivacaine and lidocaine. The magnitude of lipid emulsion-mediated reversal of vasodilation appears to be correlated with the lipid solubility of the local anesthetic.

Effect of lipid emulsion on the central nervous system and cardiac toxicity of bupivacaine and levobupivacaine in awake rats

PURPOSE

Despite numerous studies examining the effect of lipid emulsion on bupivacaine-induced cardiac toxicity, few studies have examined its effect on central nervous system (CNS) toxicity of local anesthetics. We investigated the effect of lipid emulsion on the CNS and cardiac toxicity of bupivacaine and levobupivacaine in awake, spontaneously breathing rats.

METHODS

Male Sprague-Dawley rats were randomly allocated to control-bupivacaine (CB), control-levobupivacaine (CL), lipid-bupivacaine (LB), and lipid-levobupivacaine (LL) groups (n = 8 in each group). After infusion of saline (CB and CL groups) or 20 % lipid emulsion (LB and LL groups) for 5 min, bupivacaine (CB and LB groups) or levobupivacaine (CL and LL groups) was administered IV at 1 mg/kg/min. Cumulative dose of anesthetics and their plasma concentrations at the onset of convulsions and cardiac arrest were measured.

RESULTS

The doses of bupivacaine for inducing convulsions and cardiac arrest in the LB group (8.8 ± 1.7 and 10.2 ± 1.5 mg/kg, respectively) were significantly larger than those in the CB group (5.9 ± 1.1 and 7.1 ± 1.3 mg/kg, respectively, p < 0.001 for both). The doses of levobupivacaine for inducing convulsions and cardiac arrest in the LL group (10.0 ± 2.0 and 13.7 ± 3.6 mg/kg, respectively) were significantly larger than those in the CL group (7.7 ± 1.6 and 9.4 ± 2.4 mg/kg, p = 0.03 and p = 0.02, respectively). Plasma concentrations of bupivacaine at the onset of convulsions and cardiac arrest in the LB group (12.9 ± 2.9 and 41.4 ± 5.2 μg/ml, respectively) were significantly higher than those in the CB group (7.9 ± 1.2 and 21.6 ± 3.3 μg/ml, respectively, p < 0.001 for both). Plasma concentrations of levobupivacaine at the onset of convulsions and cardiac arrest in the LL group (17.5 ± 1.5 and 47.6 ± 6.1 μg/ml, respectively) were significantly higher than in the CL group (10.9 ± 2.2 and 29.2 ± 3.5 μg/ml, respectively, p < 0.001 for both).

CONCLUSIONS

Lipid emulsion decreased CNS and cardiac toxicity of both bupivacaine and levobupivacaine.

The effect of lipid emulsion on pharmacokinetics and tissue distribution of bupivacaine in rats

BACKGROUND

While lipid emulsion may reverse the systemic toxicity of bupivacaine, the pharmacokinetics and tissue distribution of bupivacaine after lipid emulsion infusion are not clear. In this study, we assessed the influence of lipid emulsion administration on the pharmacokinetics and tissue distribution of bupivacaine.

METHODS

Rats in the lipid group were administered IV bupivacaine at the rate of 2 mg·kg(-1)·min(-1) for 4 minutes, and then were treated with an infusion of 30% lipid emulsion at the rate of 3 mL·kg(-1)·min(-1) for 5 minutes; saline was substituted in the control group (n = 6 for pharmacokinetics). We then randomly assigned 100 rats into the lipid group and control group (n = 50 for distribution). The toxicity model and treatment were the same as the pharmacokinetic portion. Plasma and tissues including brain, heart, liver, spleen, lung, kidney, omentum, and muscle were collected. The plasma concentration and tissue content of bupivacaine were measured by a liquid chromatography-tandem mass spectrometric method. A 2-compartmental analysis was performed to calculate the pharmacokinetics of bupivacaine.

RESULTS

All data are shown as mean ± SD. After treatment with the lipid emulsion, t1/2β of bupivacaine in the lipid group was significantly shorter (110 ± 25 minutes vs 199 ± 38 minutes, P = 0.001), the clearance was higher (14 ± 4 mL·mg(-1)·kg(-1) vs 9 ± 4 mL·mg(-1)·kg(-1), P = 0.038), and the t1/2α was longer than that of the control group (4 ± 1 minutes vs 2 ± 1 minutes, P = 0.014); the K12 in the lipid group was less than that of the control group (0.13 ± 0.04 vs 0.32 ± 0.13, P = 0.011). In the lipid group, the bupivacaine content in heart, brain, lung, kidney, and spleen was lower than that in the control group, but higher in the liver at 20, 30, and 45 minutes.

CONCLUSION

The lipid sink phenomenon was observed in this study. The use of a lipid emulsion accelerated the elimination of bupivacaine.

Lipídeos nas intoxicações por anestésicos locais

INTRODUÇÃO: Com o advento dos anestésicos locais de longa duração, a anestesia locorregional ganhou grande impulso sendo cada vez mais utilizada. Novas técnicas de bloqueios foram descritas e a técnica é frequentemente associada à anestesia geral com o objetivo de proporcionar analgesia pós-operatória. A contra-partida é a necessidade da utilização de grandes doses com risco de acidentes por injeção intravascular inadvertida; trata-se de complicação grave sem tratamento específico até há alguns anos. Em 1998 foi proposta a utilização de emulsões lipídicas em animais e a partir de 2006 vários trabalhos demonstraram o interesse dessas soluções nos casos de intoxicações por anestésicos locais com diminuição da morbi-mortalidade. O objetivo desta revisão foi fazer um levantamento da metodologia, revisando os mecanismos, interesses, limites e as condutas preconizadas atualmente. MÉTODO: Foram revistas algumas referências históricas sobre anestésicos locais, artigos publicados nos últimos 30 anos em revistas indexadas no Medline e em dois livros-texto. Foram selecionados os artigos que tratavam da intoxicação por anestésicos locais, da terapia com emulsões lipídicas, os de revisão sobre o assunto e as condutas adotadas em diversos serviços e países, sendo realizada uma síntese. CONCLUSÕES: A eficiência e interesse da terapia com emulsões lipídicas nas intoxicações por anestésicos locais não é mais a demonstrar; várias sociedades da especialidade já publicaram suas diretrizes e aconselham que se disponha desses produtos nos locais onde se pratica a anestesia locorregional.

The Use of IV Lipid Emulsion for Lipophilic Drug Toxicities

IV lipid emulsion (ILE) therapy is emerging as a potential antidote for lipophilic drug toxicities in both human and veterinary medicine. ILE has already gained acceptance in human medicine as a treatment of local anesthetic systemic toxicity, but its mechanism of action, safety margins, and standardized dosing information remains undetermined at this time. Experimental and anecdotal use of ILE in the human and veterinary literature, theorized mechanisms of action, current dosing recommendations, potential adverse effects, and indications for use in human and veterinary emergency medicine are reviewed herein.

Intravenous Lipid Emulsion for the Treatment of Drug Toxicity

Intravenous lipid emulsion (ILE) has emerged as a powerful antidote for the treatment of drug toxicity in the past decade. Initial efficacy of ILE was shown in the setting of local anesthetic systemic toxicity (LAST), but recent case reports suggest its consideration in a variety of other drug toxicities. In this review, we will summarize the experimental evidence as well as the clinical experience in using ILE as an antidote. Specifically, we will look at the evidence for using ILE in LAST as well as toxicity due to beta-blockers, calcium-channel blockers, and tricyclic antidepressants. We will also review the current dosing recommendations as well as potential side effects of ILE as an antidote.

Hemodynamic changes in lipid emulsion therapy (SMOFlipid) for bupivacaine toxicity in swines

PURPOSE: To evaluate the hemodynamic changes following SMOFlipid emulsion therapy with after bupivacaine intoxication in swines. METHODS: Large White pigs were anesthetized with thiopental, tracheal intubation was performed and mechanical ventilation was instituted. Hemodynamic variables were recorded with invasive pressure monitoring and pulmonary artery catheterization (Swan-Ganz catheter). After a 30-minute resting period, 5 mg.kg-1 of bupivacaine by intravenous injection was administered and new hemodynamic measures were performed 1 minute later; the animals were than randomly divided into two groups and received 4 ml.kg-1 of saline solution or 4 ml.kg-1 of SMOFlipid emulsion 20%. Hemodynamic changes were then re-evaluated at 5, 10, 15, 20 and 30 minutes. RESULTS: Bupivacaine intoxication caused fall in arterial blood pressure, cardiac index, ventricular systolic work index mainly and no important changes in vascular resistances. SMOFlipid emulsion therapy was able to improve blood pressure mainly by increasing vascular resistance since the cardiac index had no significant improvement in our study. Hemodynamic results of the use of lipid emulsion in bupivacaine intoxication were better than the control group. CONCLUSION: The SMOFlipid emulsion is a option for reversing hypotension in cases of intoxication by bupivacaine.

Case report: successful lipid resuscitation in multi-drug overdose with predominant tricyclic antidepressant toxidrome

We report a case of profound neurologic and cardiovascular manifestations of tricyclic antidepressant intoxication following self-poisoning with multiple pharmaceuticals including amitriptyline in excess of 43 mg/kg, in a 51-year-old male. Institution of mechanical ventilation, volume expansion, systemic alkalinisation (pH 7.51), and intermittent bolus metaraminol resulted in QRS narrowing but failed to resolve the developed shock. One 100-ml bolus of 20% lipid emulsion followed by a further 400 ml over 30 min was administered with restoration of haemodynamic stability, thereby curtailing the need for ongoing vasopressor medications. Assayed blood levels were consistent with the 'lipid sink' being a major effecter in the observed improvement.

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.

In vitro suppression of drug-induced methaemoglobin formation by Intralipid(®) in whole human blood: observations relevant to the 'lipid sink theory'

To provide further evidence for the lipid sink theory, we have developed an in vitro model to assess the effect of Intralipid® 20% on methaemoglobin formation by drugs of varying lipid solubility. Progressively increasing Intralipid concentrations from 4 to 24 mg.ml⁻¹ suppressed methaemoglobin formation by the lipid soluble drug glyceryl trinitrate in a dose-dependent manner (p < 0.001). Both dose and timing of administration of Intralipid to blood previously incubated with glyceryl trinitrate for 10 and 40 min resulted in significant suppression of methaemoglobin formation (p < 0.0001 and p < 0.05, respectively). Mathematical modelling demonstrated that the entire process of methaemoglobin formation by glyceryl trinitrate was slowed down in the presence of Intralipid. Intralipid did not significantly suppress methaemoglobin formation induced by 2-amino-5-hydroxytoluene (partially lipid soluble) or sodium nitrite (lipid insoluble; both p > 0.5). This work may assist determination of the suitability of drugs taken in overdose for which Intralipid might be deployed.

Local anesthetic systemic toxicity: prevention and treatment

Anesthesia is a sine qua non for most surgeries. Like any medical advance, progress in regional anesthesia has not come without its share of complications, including a spectrum extending from localized nerve injury to systemic cardiovascular toxicity and death. This article discusses the mechanisms and clinical presentation, prevention, treatment, and future trends of local anesthetic systemic toxicity. The adverse effects of lipid emulsion therapy are also included.

Serum verapamil concentrations before and after Intralipid® therapy during treatment of an overdose

CONTEXT. Intralipid® infusion is useful in reversing cardiac and central nervous system toxicity of local anesthetic drugs, and recent reports suggest utility in other drug overdoses. CASE DETAILS. A 47-year-old man presented to the emergency department with hypotension and complete heart block 3 h after a sustained-release verapamil overdose. He was given supportive care including calcium and hyperinsulinemia/euglycemia therapy. Nineteen and 29 h post-ingestion, Intralipid® was administered as a bolus, followed by an infusion. OBJECTIVE. The objective of this study was to determine the serum verapamil concentrations before and after Intralipid® administration and to ascertain its clinical effects. DISCUSSION. It was found that administration of Intralipid® was followed by a decrease in verapamil concentration once the lipid had been removed from the sample, demonstrating that Intralipid® was effective in sequestering verapamil, effectively removing it from the serum, and supporting its use in the treatment of verapamil overdose. Intralipid® administration was associated with an increase in the patient's blood pressure, but because other vasoactive drugs were given at the same time, it was difficult to determine its relative contribution to clinical improvement.

[Bupivacaine toxicity and propofol anesthesia : animal study on intravascular bupivacaine injection]

BACKGROUND

Several reports have confirmed the efficacy of Intralipid® (containing soya bean oil, egg phospholipids, glycerin and water) in the therapy of systemic local anesthetic intoxication. Pretreatment with Intralipid® shifted the dose-response to bupivacaine-induced asystole in rats. Whether intravenous anesthesia with propofol in the widely used medium chain triglyceride lipid emulsion increases the therapeutic range of systemically administered bupivacaine or not is unknown and was investigated in this study.

METHODS

A total of 30 piglets aged 2-6 weeks and weighing 4.5-6.5 kg were randomized into 2 groups and anesthetized with sevoflurane (group S) alone or with propofol 10 mg/kg body weight (BW)/h plus sevoflurane (group PS). After 60 min of steady state anesthesia arterial blood was sampled for assessment of blood gases, acid-base state and triglyceride plasma concentrations. Thereafter bupivacaine 0.125% was continuously infused by an infusion syringe pump through a central venous line at a rate of 4 mg/kg BW/min until invasively measured mean arterial pressure (MAP) was reduced by 50% of initial value. The bupivacaine infusion was stopped, blood for assessment of bupivacaine plasma concentration was drawn and the spontaneous hemodynamic course was observed. Resuscitation was not attempted. Results are presented as median and range. The Mann-Whitney U-test was used to assess differences between the two groups for triglyceride as well as for bupivacaine plasma concentrations measured at MAP 50%. A p-value≤0.05 was considered to be significant.

RESULTS

Baseline conditions (arterial blood pH, plasma protein and triglyceride plasma concentrations) did not differ significantly between the two groups. After 1 h of anesthesia, triglyceride plasma concentrations were significantly increased in group PS (median 0.69 mmol/l) compared to the corresponding baseline values (median 0.14 mmol/l; p<0.001) and to the 1 h values of group S (median 0.16 mmol/l; p<0.001). The total amount of bupivacaine administered was 9 mg/kg BW in both groups (6-13 mg/kg BW in group S, 5-13 mg/kg BW in group PS). Resulting bupivacaine plasma concentrations were 180 μmol/l (83-686 μmol/l) in group S and 185 μmol/l (130-465 μmol/l) in group PS. However, the total amount of bupivacaine administered and bupivacaine plasma concentrations at MAP 50% did not reveal statistically significant differences between the two groups but a huge variability of both parameters within each group was observed. None of the 30 piglets spontaneously recovered and they died from pulseless electrical activity or from asystolic cardiac arrest. The time from MAP 50% until cardiac arrest demonstrated a large variability but did not reveal significant differences between the two groups. The time to cardiac arrest was similar in both groups.

CONCLUSION

Medium/long chain triglyceride lipid emulsion (50:50) as widely used in propofol solutions did not increase therapeutic safety in cases of intravascular bupivacaine administration in this piglet model.