[Systemic toxicity of local anesthetics. Pharmacokinetic and pharmacodynamic factors]

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.

Lack of local anesthetic properties of lidocaine gel in an experimental model

INTRODUCTION

Many reports negate the anesthetic properties of lidocaine gel placed in the urethra during catheterization. The anesthetic action of lidocaine is inseparably associated with the toxic action of this compound on cells.

MATERIALS AND METHODS

A primary rabbit urothelial cell culture (PRUCC) was previously established as a monolayer. The effect of 2% lidocaine gel on the viability of the PRUCC was assessed and compared with the cytotoxic effect of decreasing concentrations of lidocaine solution. Cell viability was evaluated after 1-hour exposure using the trypan blue exclusion test.

RESULTS

The 2% lidocaine gel did not show cytotoxic properties after 1 h of incubation on a PRUCC. The 2 and 1% lidocaine solutions induced statistically significant decreases in the viability of the PRUCC after 1 h of incubation.

CONCLUSIONS

Experimental tests evaluating the cytotoxicity of local anesthetics may prove to be an objective measure of the accessibility of these substances to cells and their anesthetic action.

Lidocaine inhibits potassium efflux and hemolysis in erythrocytes during oxidative stress in vitro

Lidocaine is a widely used local anesthetic agent. The aim of this work was to study the action of lidocaine on human red blood cells exposed to an oxidative stress in vitro. Blood was obtained from healthy volunteers. After separation from plasma, the erythrocytes were suspended in phosphate buffer. Oxidative stress was induced by incubation with a free radical generator, the 2,2' azobis (2-amidinopropane) hydrochloride (AAPH). Erythrocytes were incubated with or without lidocaine at two concentrations (36.93 and 73.85 microM) and with or without AAPH (20 mM). Electron paramagnetic resonance (EPR) spectroscopy was performed to identify the free radical species generated by AAPH using the spin trap 5-5'-dimethyl-L-pyroline-N-oxide (DMPO). Different sets of experiments were run. Potassium efflux was measured by flame photometry in each group at time 0 min and every 30 min of the experiment for 2 h. Hemolysis was studied by the Drabkin method at increasing concentrations of AAPH (20, 50, and 100 mM) and with or without lidocaine (36.93 microM). The oxygen radical absorbance capacity (ORAC) was measured by using allophycocyanin (APC) as a fluorescent indicator protein, and the antioxidant capacity of lidocaine (36.93 microM) was studied by the analysis of fluorescence of the APC. AAPH was shown to produce alkoxyl free radicals. Oxidative stress induced a marked increase in the potassium efflux and the hemolysis that was AAPH dose-dependent. Lidocaine inhibited the potassium efflux and delayed the occurrence of hemolysis. Lidocaine did not show any antioxidant properties for the free radical species generated by AAPH. In this model, lidocaine protects erythrocytes against oxidative stress. This effect is not explained by a free radical scavenging property. The results may be of great interest in clinical practice such as intravenous regional anesthesia or the prevention of ischemia-reperfusion injury.

Effects of bupivacaine on human erythrocytes submitted to stress and evidence for an interaction between bupivacaine and flumazenil

AIMS

To examine the effects of bupivacaine on erythrocytes submitted to an oxidative stress (AAPH) and to provide evidence for an in vitro interaction between bupivacaine and flumazenil.

METHODS

Human erythrocytes were studied with or without AAPH in the presence of different concentrations of bupivacaine (0.15, 0.3, 0.9 and 1.8 mmol l-1 ), or flumazenil (0.16 mmol l-1 ) and with the association of flumazenil and two doses of bupivacaine (0.15 and 0.3 mmol l-1 ). Potassium efflux was measured by flame photometry at T0, and every 30 min for 2 h.

RESULTS

In the absence of AAPH, extracellular potassium remained unchanged. Oxidative stress induced a significant increase in extracellular potassium, which was not modified by incubation with flumazenil. Bupivacaine significantly lowered the increase in extracellular potassium in a dose-related fashion. The association with flumazenil blunted the effects of bupivacaine. Discussion In this model, bupivacaine proved effective in protecting erythrocytes against oxidative stress. Flumazenil interacted with bupivacaine and blunted its protective effects.

[Does flumazenil correct disorders of intracardiac conduction induced by accidental intravenous injection of bupivacaine?]

The authors report the case of a patient who experienced intracardiac conduction disturbances from accidental intravenous injection of bupivacaine, which were reversed by an intravenous injection of flumazenil. Flumazenil could act either in displacing bupivacaine from its binding site, or by an interaction involving the GABAergic system, unless a specific interaction between flumazenil and bupivacaine does exist. In case of experimental confirmation of this feature, flumazenil could be proposed as a new therapeutic tool for bupivacaine-induced cardiotoxicity.