Anesthesiologist Suicide with Atracurium

Atracurium is a nondepolarizing skeletal muscle relaxant used to facilitate endotracheal intubation and to induce skeletal muscle relaxation during surgery or mechanical ventilation. The drug undergoes a spontaneous non-enzymatic biotransformation, yielding laudanosine and an acrylate moiety. This report documents the case of a 45-year-old anesthesiologist who was found dead at the hospital where he worked. The victim was known to be depressed and undergoing treatment with venlafaxine. An empty syringe was found near the body. Toxicological analysis revealed the presence of laudanosine in the syringe, 0.6 mg/L of laudanosine in heart blood, 0.3 mg/L in urine, and 0.02 mg/L in vitreous humor. Meanwhile, concentrations of venlafaxine and O-desmethyl-venlafaxine, its active metabolite, were 0.7 and 1.1 mg/L in heart blood, 1.7 and 5.2 mg/L in urine, 0.5 and 0.7 mg/L in vitreous humor, and 400 and 20 mg in gastric content, respectively. All drugs and metabolites involved in the case were detected using gas chromatography with nitrogen-phosphorus detection (GC-NPD) and confirmed using GC-mass spectrometry in full scan mode after solid-phase extraction using Bond-Elut Certify columns. Additional high-performance liquid chromatography coupled to diode-array detection screening also obtained the same results. Quantitation of laudanosine and venlafaxine together with its metabolite was carried out using GC-NPD. No other drugs, including ethanol, were detected. Recoveries for laudanosine and venlafaxine were 89% and 86%, respectively, at 0.5 mg/L; intraday and interday precisions were 2% and 6%, and 3% and 7%, respectively; and limits of detection and quantitation were 6 and 20 ng/mL and 18 and 59 ng/mL, respectively. The linearity of the blood calibration curves was excellent for both drugs with r(2) values of > 0.999 (range 0.1-2.0 mg/L). Based on the autopsy findings, case history, and toxicology results, the forensic pathologists ruled that the cause of death was an overdose of atracurium, and the manner of death was suicide.

cis-Atracurium in dogs with and without porto-systemic shunts

OBJECTIVE

To evaluate the non-depolarizing neuromuscular blocking drug cis-atracurium in dogs with porto-systemic shunts, and to compare it in clinically normal animals.

ANIMALS

Thirteen dogs of mixed breed and sex, aged between 3 and 31 months old, weighing 2.2-25.5 kg, with ASA physical status II-IV, and undergoing surgical attenuation of porto-systemic shunt. A control group of 11 bitches of mixed breed, between 8 and 60 months old, and weighing 4.5-41.0 kg, all ASA physical status I, undergoing routine ovarohysterectomy were also studied.

MATERIALS AND METHODS

Pre-anaesthetic medication was an opioid analgesic, given either alone or in combination with acepromazine. Following induction of general anaesthesia with intravenous (IV) propofol and oro-tracheal intubation, anaesthesia was maintained using isoflurane in either oxygen or oxygen and nitrous oxide. Ventilation was controlled. The train of four (TOF) technique was used to monitor neuromuscular blockade. An initial dose of 0.1 mg kg(-1)cis-atracurium was given IV and additional doses of 0.03 mg kg(-1)cis-atracurium were administered when at least one twitch of the TOF was present.

RESULTS

Except for one dog that was killed during surgery because its anomaly was inoperable, all animals recovered satisfactorily from anaesthesia and surgery. In dogs with porto-systemic shunt, onset of neuromuscular blockade was 3.1 +/- 1.1 minutes (mean +/- SD) and in control dogs was 3.4 +/- 0.7 minutes (not significantly different). Neuromuscular blockade lasted 34 +/- 13 minutes in dogs with porto-systemic shunt and 29 +/- 17 minutes in control dogs (not significantly different).

CONCLUSIONS

The presence of porto-systemic shunt did not affect the rate of onset or duration of action of cis-atracurium.

CLINICAL RELEVANCE

cis-Atracurium may have a use in veterinary anaesthesia for producing neuromuscular blockade in dogs with hepatic insufficiency, including those with porto-systemic shunt.

The human heart as a shock organ in anaphylaxis

Human mast cells, by elaborating vasoactive mediators and cytokines, are the primary effector cells of anaphylaxis. A body of evidence implicates human heart mast cells (HHMCs) in anaphylaxis. These cells have been identified perivascularly, in dose proximity to myocytes and in the arterial intima in human heart tissue. The membrane surface of mast cells from human heart tissue of patients undergoing cardiac transplantation expresses the high affinity receptors for IgE (FcepsilonRI) and C5a receptors. Activation of HHMCs in vitro with anti-IgE or anti-FcepsilonRI induced the release of preformed mediators (histamine, tryptase and chymase) and the de novo synthesis of LTC4 (approximately equal to 18 ng/10(6) cells) and PGD2 (approximately equal to 18 ng/10(6) cells). Complement activation and anaphylatoxin formation occur during anaphylaxis in human. C5a caused rapid release of histamine and tryptase from HHMCs. These cells are activated in vitro by therapeutic (general anaesthetics, protamine, etc.) and diagnostic agents (radio contrast media, etc.) that may cause non-IgE-mediated anaphylactic reactions. Administration of low concentrations of histamine and cysteinyl leukotrienes in subjects undergoing diagnostic catheterization caused significant systemic and coronary haemodynamic effects. Taken together, these results indicate that the human heart can be both the site and the target of anaphylactic reactions.

[Carboxyperitoneum and clinical efficacy of nondepolarizing relaxants with different types of metabolism]

A total of 108 patients operated on the abdominal cavity were examined with laparoscopic equipment or via laparotomic assess. The recovery time of neuromuscular conduction was defined for a myorelaxant with organ-depended metabolism (pipecuronium) and, predominantly, nonorgan-depended metabolism (athracurium and cisathracurium) in relation to the type of surgical technique (laparoscopy and laparotomy). It is concluded that carboxyperitoneum prolongs the recovery of neuromuscular conduction for pipecuronium without affecting this parameter in athracurium and cisathracurium. It is more expedient to use these myorelaxants during laparoscopic operations than pipecuronium, a myorelaxant having organ-dependent metabolism.

Laudanosine, an atracurium and cisatracurium metabolite

Laudanosine is a metabolite of the neuromuscular-blocking drugs atracurium and cisatracurium with potentially toxic systemic effects. It crosses the blood-brain barrier and may cause excitement and seizure activity. Its interest in recent years has increased because of the recognized interaction with gamma-aminobutyric acid, opioid and nicotinic acetylcholine receptors. It has been shown to produce analgesia in animals. In the cardiovascular system, high plasma concentrations produce hypotension and bradycardia. In hepatic failure, its elimination half-life is prolonged but only moderate accumulation occurs in adults, whereas in infants and children plasma concentration are greater. In patients undergoing liver transplantation, laudanosine concentrations are increased during preanhepatic, anhepatic and postanhepatic stages. Patients with renal failure have higher plasma concentrations and a longer mean elimination half-life. In pregnancy, laudanosine crosses the placental barrier. The mean transplacental transfer is 14% of maternal blood concentrations. Except for prolonged administration of atracurium in intensive care units, laudanosine accumulation and related toxicity seem unlikely to be achieved in clinical practice. When cisatracurium is used, plasma concentrations of laudanosine are lower. Further studies are needed, especially around the interactions with gamma-aminobutyric acid, opioid and nicotinic acetylcholine receptors.

Blockade and activation of the human neuronal nicotinic acetylcholine receptors by atracurium and laudanosine

BACKGROUND

Curaremimetic nondepolarizing muscle relaxants are widely used in clinical practice to prevent muscle contraction either during surgery or during intensive care. Although primarily acting at the neuromuscular junction, these compounds can cause adverse effects, including modification of cardiac rhythm, arterial blood pressure, and in the worst cases, triggering of seizures. In this study, we assessed the interaction of atracurium and its metabolite, laudanosine, with neuronal nicotinic receptors.

METHODS

The human neuronal nicotinic receptors alpha4beta2, alpha3beta4, alpha3alpha5beta4, and alpha7 are heterologously expressed in Xenopus laevis oocytes, and the effect of atracurium and its degradation product, laudanosine, were studied on these receptors.

RESULTS

Atracurium and laudanosine inhibited in the micromolar range the major brain alpha4beta2 receptor and the ganglionic alpha3beta4 or alpha3beta4alpha5 and the homomeric alpha7 receptors. For all four receptors, inhibition was rapid and readily reversible within less than 1 min. Atracurium blockade was competitive at alpha4beta2 and alpha7 receptors but displayed a noncompetitive blockade at the alpha3beta4 receptors. Inhibition at this receptor subtype was not modified by alpha5. Laudanosine was found to have a dual mode of action; first, it competes with acetylcholine and, second, it blocks the ionic pore by steric hindrance. At low concentrations, these two drugs are able to activate both the alpha4beta2 and the alpha3beta4 receptors.

CONCLUSION

Adverse effects observed during atracurium administration may be attributed, at least partly, to an interaction with neuronal nicotinic receptors.

Clinical pharmacokinetics of cisatracurium besilate

Cisatracurium besilate, one of the 10 stereoisomers that comprise atracurium besilate, is a nondepolarising neuromuscular blocking agent with an intermediate duration of action. Following a 5- to 10-sec intravenous bolus dose of cisatracurium besilate to healthy young adult surgical patients, elderly patients and patients with renal or hepatic failure, the concentration versus time profile of cisatracurium besilate is best characterised by a 2-compartment model. The volume of distribution (Vd) of cisatracurium besilate is small because of its relatively large molecular weight and high polarity. Cisatracurium besilate undergoes Hofmann elimination, a process dependent on pH and temperature. Unlike atracurium besilate, cisatracurium besilate does not appear to be degraded directly by ester hydrolysis. Hofmann elimination, an organ independent elimination pathway, occurs in plasma and tissue, and is responsible for approximately 77% of the overall elimination of cisatracurium besilate. The total body clearance (CL), steady-state Vd and elimination half-life of cisatracurium besilate in patients with normal organ function are approximately 0.28 L/h/kg (4.7 ml/min/kg), 0.145 L/kg and 25 minutes, respectively. The magnitude of interpatient variability in the CL of cisatracurium besilate is low (16%), a finding consistent with the strict physiological control of the factors that effect the Hofmann elimination of cisatracurium besilate (i.e. temperature and pH). There is a unique relationship between plasma clearance and Vd because the primary elimination pathway for cisatracurium besilate is not dependent on organ function. There are minor differences in the pharmacokinetics of cisatracurium besilate in various patient populations. These differences are not associated with clinically significant differences in the recovery profile of cisatracurium besilate, but may be associated with differences in the time to onset of neuromuscular block.

Effects of neuromuscular blocking agents on excitatory transmission and gamma-aminobutyric acidA-mediated inhibition in the rat hippocampal slice

BACKGROUND

Although neuromuscular blocking agents do not cross the blood-brain barrier, they may penetrate the central nervous system under particular circumstances and eventually cause neurotoxic consequences.

METHODS

The effects of neuromuscular blocking agents on excitatory and inhibitory transmission in area CA1 of rat hippocampal slices were investigated using extracellular and intracellular recording techniques.

RESULTS

Application of atracurium in the perfusion medium resulted in a dose-dependent enhancement of excitatory synaptic responses averaging 48.7 +/- 4.3% at a concentration of 10 nM. This effect was correlated with an increase in the size of the presynaptic fiber volley. Laudanosine, but not pancuronium bromide or vecuronium bromide, produced similar changes. In addition, atracurium and laudanosine blocked inhibitory transmission and reduced intracellularly recorded gamma-aminobutyric acidA receptor-mediated potentials. These effects were observed only at concentrations >1 microM and were not reproduced by pancuronium bromide and vecuronium bromide.

CONCLUSIONS

Atracurium and its metabolite, laudanosine, contrary to pancuronium bromide and vecuronium bromide, produce two distinct effects on hippocampal slices. They enhance excitatory transmission and neuronal excitability and they block inhibitory gamma-aminobutyric acidA-mediated synaptic responses.

Resistance to atracurium in rats with experimental inflammation: role of protein binding

The influence of altered protein binding on the neuromuscular effect of atracurium has been studied in rats with experimental inflammation induced by subcutaneous injection of turpentine oil. Doses of atracurium ranging from 0.45 to 1.5 mg.kg-1 were administered to control (n = 30) and to experimental inflammation induced rats (n = 30). Neuromuscular transmission was monitored by recording the twitch tension of the tibialis-anterior muscle elicited by stimulation of the sciatic nerve. Three effect parameters were recorded: (i) intensity of the effect, measured as percentage depression of baseline twitch tension, (ii) duration of drug action (min) and (iii) recovery time (min). The dose-intensity of the effect relationship was modelled using a sigmoid Emax model. The ED50 (effective dose eliciting 50% of the maximum effect) was significantly increased (P < 0.01) in the inflammation group as compared to the control group (0.94 vs. 0.68 mg.kg-1). This change was reflected in a shift of the dose-response curve to the right in the pretreated rats. For equipotent doses ED95 (defined as the effective dose eliciting 95% of maximum effect), no differences were found in recovery time and duration of action between the two groups of rats. Mucoproteins levels (index of alpha 1-acid glycoprotein (AAG) and protein binding were significantly increased in rats with experimental inflammation as compared to control rats. Based on these results, altered serum protein binding of atracurium appears to be responsible, at least in part, for the resistance to atracurium.

Pharmacokinetics and pharmacodynamics of the benzylisoquinolinium muscle relaxants

The benzylisoquinolinium class of drugs comprises atracurium, 51W89, doxacurium, and mivacurium. Atracurium can be used as a pharmacokinetic benchmark; it has at least two distinct metabolic pathways, of which Hofmann elimination and ester hydrolysis are the most significant. The relative importance of each of these two routes is still a matter of speculation, and this, coupled with the fact that atracurium is a mixture of 10 isomers, has led to the development of many innovative pharmacokinetic modelling concepts. 51W89 is a cis-cis-isomer of atracurium and probably has a pharmacokinetic profile very similar to that of atracurium. Doxacurium, a long-acting benzylisoquinolinium, has a small apparent volume of distribution and an elimination half-time similar to that of pancuronium, and is excreted by the kidneys. Mivacurium is a short-acting benzylisoquinolinium that is rapidly hydrolysed by plasma cholinesterases. Two isomers of mivacurium are very similar, whereas the third isomer differs greatly in both pharmacological activity and elimination half-time, so that analysis requires complex pharmacokinetic methods.

Spontaneous recovery or evoked reversal of neuromuscular block

Recovery from the effects of muscle relaxants can occur either spontaneously by their metabolism in the body or by elimination via the normal excretion pathways, or by the administration of pharmacologic antagonists. The decision as to whether spontaneous recovery should be allowed to take place or pharmacologic reversal should be induced depends upon several factors, principal among them being the duration of action of the muscle relaxant used, its dose, and the time that is available. The recovery times of most relaxants, including atracurium and vecuronium, are such as to require antagonism if adequate recovery is to be attained quickly. An agent such as mivacurium may, however, allow complete spontaneous recovery to take place without the use of antagonists.

Interaction of gentamycin and atracurium in anaesthetised horses

Evoked hind limb digital extensor tension (hoof twitch) was maintained at 40% of baseline for 1 h by atracurium infusion in 7 horses anaesthetised with halothane. After 1 h, atracurium was discontinued and hoof twitch allowed to recover to 75%. Atracurium was again given by infusion to maintain 40% twitch for a second hour, then 2 mg gentamycin/kg bwt were given i.v. Atracurium infusion was continued for a third hour, and then hoof twitch was again allowed to recover spontaneously to 75%. Gentamycin reduced twitch strength from 40 +/- 1% (mean +/- sem) to 29 +/- 4% within 7.0 +/- 1.5 min (P = 0.02). Twitch gradually returned to pre-gentamycin strength over the course of the next hour. Recovery of hoof twitch from 50% to 75% took 7.7 +/- 0.7 min for atracurium alone and 11.5 +/- 2.7 min for atracurium plus gentamycin (P = 0.03). Recovery from 50% twitch to 75% fade recovery took 13.8 +/- 0.8 min for atracurium alone and 13.7 +/- 1.2 min for atracurium plus gentamycin. At 75% recovery of fade, hoof twitch was 87 +/- 3% for atracurium alone and 82 +/- 4% for atracurium plus gentamycin. Reversal of the block with edrophonium and subsequent recovery of the horses from anaesthesia were uneventful. It was concluded that, although gentamycin did augment the neuromuscular blockade of atracurium, the effect was minimal.

Influence of incubated atracurium on rat liver function

Degradation of atracurium by Hofmann elimination and ester hydrolysis depends mainly on pH and temperature and is said to be independent of liver and kidney function. Consequently atracurium is used widely in patients with liver failure. However, there is evidence that incubation of atracurium at 37 degrees C and pH 8 leads to leakage of LDH from hepatocyte cell cultures. We have tested the hepatotoxic effects of incubated atracurium in an isolated perfused rat liver model. After equilibration, atracurium 2010 mumol ml-1 (preincubated at pH 8 and 37 degrees C for 120 min) was administered over a period of 10 min followed by perfusion of Krebs-Henseleit bicarbonate buffer for 60 min. We found that incubation resulted in considerable degradation of atracurium and formation of laudanosine. Administration of incubated atracurium did not produce either biochemical or morphological damage to liver cells, but caused considerable increase in bile flow. We conclude that administration of preincubated atracurium did not produce impairment of liver cell function. The increase in bile flow could be beneficial if it occurs clinically.

Atracurium infusions in patients with fulminant hepatic failure awaiting liver transplantation

OBJECTIVE

To determine the pharmacokinetics and pharmacodynamics of the neuromuscular blocking agent atracurium besylate in patients with fulminant hepatic failure (FHF).

DESIGN

Open study of patients receiving atracurium infusions to facilitate mechanical ventilation.

SETTING

Intensive care unit in a tertiary referral university teaching hospital.

PATIENTS

Ten encephalopathic patients with FHF requiring mechanical ventilation while awaiting orthotopic liver transplantation. Three patients died before transplantation could be performed, three died after transplantation, and four survived following successful transplantation.

METHODS

Plasma, urine and dialysate fluid were analysed for atracurium and its metabolites using HPLC. Neuromuscular blockade was measured using transcutaneous ulnar nerve stimulation and an accelerometer. Electroencephalography and liver function tests were performed daily.

RESULTS

Patients received atracurium infusions for a period ranging from 38 to 217 h. Six patients required continuous arteriovenous haemodiafiltration (CAVHD) to replace renal function. Atracurium mean steady state clearance was 8.6 ml/min/kg, and train-of-four recovery ratio to 75% took 63 min (range 32-108). Laudanosine clearance was markedly reduced in the non-survivors; the half-life was 38.5 hrs compared with 5.3 h in the 4 patients who underwent successful transplantation. Laudanosine accumulation could be observed in all patients before transplantation, but kinetics returned to normal after successful transplantation. The highest laudanosine level recorded was 6,860 ng/ml. There was no evidence of adverse central neurological effects attributable to laudanosine. CAVHD did not contribute significantly to clearance of atracurium or its metabolites.

CONCLUSIONS

Atracurium kinetics and dynamics are near-normal even in patients with fulminant hepatic failure and renal failure; laudanosine accumulation will occur, but this is not associated with measurable central neurological effects. Implantation of a functioning liver graft results in clearance of laudanosine, which seems to be independent of renal function. Atracurium is an appropriate choice for producing neuromuscular blockade for periods of several days in patients with fulminant hepatic failure and renal impairment.

Hepatotoxicity testing of atracurium and laudanosine in the isolated, perfused rat liver

The pharmacokinetics of atracurium, which is degraded by Hofmann decomposition and ester hydrolysis, is not altered by impaired liver function. Atracurium should, therefore, be ideal for patients with heptic failure, and is now widely used in clinical practice. However, some studies reported considerable hepatotoxicity after atracurium, especially from its breakdown products--for example, leakage of lactate dehydrogenase (LDH) from isolated rat hepatocytes. Therefore, we have studied, in an isolated perfused rat liver model, biochemical and morphological changes after administration of either atracurium or its main metabolite, laudanosine. Despite using extremely high concentrations of these substances, we could not detect, biochemically (release of LDH or aspartate amino-transferase (AST)) or histologically, any signs of liver cell damage.

Pharmacokinetic modelling of a parent drug and its metabolite. Atracurium and laudanosine

A pharmacokinetic model was designed to describe simultaneously the plasma concentrations of atracurium and its metabolite laudanosine. The proposed model satisfactorily fits the observations and is based on the assumptions that the parent drug spontaneously degrades to laudanosine at the rate comparable with that observed in vitro at pH 7.4 and 37 degrees C; that 2 molecules of laudanosine are formed from 1 molecule of atracurium; that an initial very rapid decay of a fraction of the atracurium dose is responsible for the initially high plasma laudanosine concentrations; that the rapid disappearance of atracurium from plasma is accounted for by its spontaneous degradation and by the sequestration of atracurium in a deep compartment; and that laudanosine formed from atracurium is added to its central compartment, with its disposition described by a simple 2-compartment model with elimination from the central compartment. The model projects that about 43% of the atracurium dose is rapidly converted to laudanosine and that nearly the whole injected amount of atracurium is degraded to laudanosine.

Resistance to atracurium in a patient with an increase in plasma alpha 1 globulins

We observed that a female patient with a poorly differentiated adenocarcinoma of the stomach undergoing gastrectomy was markedly resistant to the action of the neuromuscular blocking drug atracurium. There was no evidence of tumour metastasis and her liver function tests were normal. Electrophoresis of plasma proteins revealed a marked increase in alpha 1 globulin. Alpha 1 acid glycoprotein is an acute phase reactant that is increased in patients with cancer and is present in the alpha 1 globulin electrophoresis pattern. It is likely that the mechanism for the resistance to neuromuscular block in the patient was an increase in drug binding to alpha 1 acid glycoprotein.

Transplacental distribution of atracurium, laudanosine and monoquaternary alcohol during elective caesarean section

Maternal venous (MV), umbilical venous (UV) and umbilical arterial (UA) blood samples were obtained for assay of atracurium, laudanosine and monoquaternary alcohol concentrations in 22 healthy patients undergoing elective Caesarean section under general anaesthesia. At delivery (at a mean time of 8.2 min after atracurium 0.3 mg kg-1), the mean UV concentrations were 103 ng ml-1 (range 44-189 ng ml-1) for atracurium, 26 ng ml-1 (range 6-60 ng ml-1) for laudanosine and 59 ng ml-1 (range 21-148 ng ml-1) for monoquaternary alcohol. The ratios of UV:MV, UA:MV and UA:UV blood concentrations were related positively to time since injection of atracurium for all three substances (P less than 0.01 in each instance). The UV:MV ratio at delivery was greatest for laudanosine: mean 19.4% (range 1-35%), compared with 7% (range 2-21%) for atracurium and 10% (range 0-15%) for monoquaternary alcohol. These low values confirm that, although atracurium crosses the placental barrier and its metabolites may be found in the fetus, the drug is safe to use during Caesarean section.

Plasma concentrations of laudanosine, but not of atracurium, are increased during the anhepatic phase of orthotopic liver transplantation in pigs

To quantify the changes in plasma concentrations of atracurium and laudanosine induced by the lack of hepatic function and circulation, the authors studied nine domestic pigs (22-25 kg) undergoing an orthotopic liver transplantation, and three control animals without surgery, using atracurium as the muscle relaxant. After intubation facilitated by isoflurane 2-3%, anesthesia was maintained with isoflurane (0.5% in oxygen) and fentanyl (4 micrograms.kg-1.hr-1). Ventilation was controlled to keep end-tidal CO2 at 35-40 mmHg, body temperature maintained at 35.5-37.5 degrees C, and arterial pH at 7.35-7.50. The right sciatic nerve was stimulated with a nerve stimulator delivering a single twitch at 0.1 Hz with 0.2-ms duration, at supramaximal stimulation. The force of the corresponding evoked isometric muscle contraction was continuously measured by a force-displacement transducer. A single iv bolus of atracurium (2 mg/kg) was given to obtain a 90-95% twitch depression, followed 5 min later by a constant-rate iv infusion of atracurium at 120 micrograms.kg-1.min-1 maintained during the entire investigation. Blood samples for plasma atracurium and laudanosine concentrations were drawn every 15 min. In the control group, plasma concentrations of atracurium remained stable between 6.5-8.0 micrograms/ml following initial bolus injection; plasma concentrations of laudanosine increased during the first 60 min, then remained stable between 0.69-0.74 micrograms/ml up to the end of the study. In animals undergoing transplantation, plasma concentrations of atracurium remained stable between 10-12 micrograms/ml, despite a 90-min duration of liver exclusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Reactivity and toxicity of atracurium and its metabolites in vitro

Cytotoxicity of atracurium and of its metabolites was tested in vitro. Exposure of isolated rat hepatocytes to atracurium produced cellular damage evidenced by extrusion of an intracellular enzyme, lactate dehydrogenase (LDH), into the incubation medium. Leakage of LDH was directly related to the concentration of atracurium in the medium (250 to 800 microM). If the spontaneous degradation of atracurium (presumably via Hofmann elimination) was first carried out in vitro and the degradation products subsequently added to the isolated hepatocytes, the leakage of LDH was also dose-dependent but larger than that observed after the addition of the parent drug. When l-cysteine was admixed to the products of the spontaneous degradation of atracurium prior to their addition to the liver cells, no leakage of LDH was observed. The results are compatible with the working hypothesis that atracurium itself and, even more so, acrylates formed in Hofmann elimination of atracurium, are reactive toward nucleophiles and damage the cells by alkylating nucleophiles present in cellular membranes. Antecedent covalent binding of acrylates to the nucleophile cysteine, i.e., the formation of acrylate-cysteine adducts, saturated the reactive capacity of acrylates for nucleophiles and thus prevented the reactive metabolites from alkylating the endogenous nucleophiles. Possible clinical consequences resulting from in vivo generation of reactive metabolites are not clear at the present time but are projected to be related to (a) the dose of atracurium administered, (b) the amount of acrylates generated, (c) the functional importance of the endogenous nucleophiles alkylated, and (d) the pathway and the speed of detoxification of atracurium and its metabolites.

The pharmacokinetics of atracurium isomers in vitro and in humans

Atracurium is a mixture of ten isomers. By high-performance liquid chromatography, using acidified methanol as the mobile phase and silica support, it was separated into its three geometrical isomer groups, cis-cis, cis-trans, and trans-trans, which contain three, four, and three isomers, respectively. The clinically available form of atracurium was made up of 58% cis-cis, 36% cis-trans, and 6% trans-trans isomers. In buffered saline, pH 7.4, at 37 degrees C, the half-lives of the three isomer groups were 57.1 +/- 0.9, 59.7 +/- 0.9, and 66.4 +/- 2.7 min, respectively, for the cis-cis, cis-trans, and trans-trans groups. In whole blood, under similar conditions, the three groups showed different behavior. The cis-cis group broke down in a monoexponential manner with a half-life of 23.3 +/- 2.8 min. The cis-trans group showed bi-exponential breakdown with a rapid phase of 2.3 +/- 0.4 min and a slow phase of 22.1 +/- 2.9 min. The trans-trans group decayed rapidly, but, because of the low concentration of this group in the mixture, kinetic parameters could not be obtained. In eight patients, the mean elimination half-life and apparent clearance of the cis-cis group were 20.6 +/- 1.5 min and 5.3 +/- 0.4 ml.kg-1.min-1, respectively. For the cis-trans group, the apparent elimination half-life and clearance were 17.7 +/- 1.8 min and 9.0 +/- 1.0 ml.kg-1.min-1, but these figures require care in interpretation, as this isomer group contains isomers of widely varying rates of decomposition.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of atracurium and its metabolites in patients with normal renal function, and in patients in renal failure

The plasma pharmacokinetic profiles of atracurium and its derivatives, laudanosine and monoquaternary alcohol, were studied in six patients with renal failure after a bolus dose of atracurium 0.3-0.4 mg kg-1. The pharmacokinetics of the derivatives only were studied in a group of four normal patients receiving atracurium 0.3 mg kg-1. Measurements of plasma and urine concentrations were performed by high pressure liquid chromatography. Pharmacokinetics of atracurium were not significantly different in the renal failure group when compared with those obtained in a previous study on six normal patients. Although 2-10% of the dose was recovered in the urine of normal patients as unchanged atracurium, and 3-4% as laudanosine, renal failure produced no significant differences in plasma pharmacokinetics, with mean plasma elimination half-lives of 20 min for atracurium, 234 min for laudanosine and 39 min for quaternary alcohol.

Potentiation of atracurium toxicity in isolated rat hepatocytes by inhibition of its hydrolytic degradation pathway

This study tested the hypothesis that the esters of acrylic acid might be responsible for the previously observed cytotoxic effect of atracurium. Rats were pretreated with triorthotolyl phosphate (TOTP), an inhibitor of the hydrolytic degradation of atracurium. Because hydrolysis of acrylates is also inhibited by TOTP and because the hydrolysis represents a detoxification pathway for these esters, we postulated that the leak of lactic dehydrogenase (LDH) induced by atracurium would be enhanced in hepatocytes harvested from rats pretreated with TOTP. Hepatocytes isolated from rats previously treated with TOTP (25 or 50 mg/kg intraperitoneally, 20 hr before induced death) were incubated for 4 hr in the absence of muscle relaxants or in the presence of either atracurium (0.008-0.8 mM) or metocurine (0.015-0.85 mM). Atracurium produced a concentration-dependent leakage of LDH. The leakage out of cells obtained from TOTP-pretreated rats was greater than was the leakage out of hepatocytes harvested from animals pretreated only with corn oil (a vehicle for TOTP). Metocurine did not produce a leak of LDH. It is concluded that the LDH leakage was produced by ester-type products of atracurium degradation. Acrylates appear to be the toxic agent.

Involvement of nucleophiles in the inactivation of atracurium

Atracurium was incubated in 0.9% sodium chloride solution at pH 7.4 and 37 degrees C. The following compounds were added to the incubation solution: propionic acid, alanine and cysteine (0.1 mol litre-1 final concentration). Metocurine was also incubated with cysteine under identical conditions. Aliquots of the incubation solutions were injected i.v. to anaesthetized rats at the start (0 min) and at the end of incubation (45 min), and the indirectly elicited, single twitches of the gastrocnemius muscle were observed. Whereas inactivation of atracurium proceeded slowly in the control solution and in the presence of sodium propionate, the presence of alanine and, especially, of cysteine markedly enhanced the inactivation. Incubation of metocurine with cysteine did not alter the pharmacological responses. The concentration of cysteine decreased progressively during its incubation with atracurium (37 degrees C, pH 7.4). We conclude that the data are compatible with the postulate that a nucleophile may enhance the degradation of atracurium by a reaction with the parent compound (nucleophilic substitution reaction), by reaction with acrylates (Michael addition) or both.

Use of atracurium in a patient with plasma cholinesterase deficiency

The use of atracurium during anaesthesia for abdominal hysterectomy in a 37-year-old patient with homozygous plasma cholinesterase [EsEs] deficiency is described. Intubation was achieved utilizing 0.47 mg X kg-1 of atracurium. Subsequent doses of 0.08 mg X kg-1, 0.12 mg X kg-1 and 0.12 mg X kg-1 were given 34, 57 and 78 minutes respectively after the initial dose. At the time of reversal of the residual effects of neuromuscular blockade, 26 minutes after the last dose, spontaneous respiration had resumed. The duration of action of the drug was not different from that described in normal patients. Atracurium would appear to be a safe drug to provide neuromuscular relaxation in patients with plasma cholinesterase deficiency, where surgical procedures of intermediate duration are being undertaken.

Pharmacokinetics of atracurium in anaesthetized infants and children

The pharmacokinetics of atracurium were studied in infants and children anaesthetized with isoflurane and nitrous oxide in oxygen. There were no significant differences in volume of distribution (area) (139 v. 152 ml kg-1), clearance (5.1 v. 5.3 ml kg-1 min-1), T1/2 alpha (2.1 v. 2.0 min), or T1/2 beta (19.1 v. 20.3 min) between children with normal hepatic and renal function and those with moderately impaired hepatic function presenting for hepatic transplantation. There were significant differences in volume of distribution (area) (176 v. 139 ml kg-1) and in clearance of atracurium (9.1 v. 5.1 ml kg-1 min-1) between infants and children with normal excretory function. In infants the clearance of atracurium in ml m-2 min-1 (153 v. 133) tended to be greater and the T1/2 alpha and T1/2 beta tended to be shorter (1.0 v. 2.0 and 13.6 v. 19.1) than in children with normal excretory function; however, these trends did not reach statistical significance. Plasma laudanosine concentration was around 100 ng ml-1 greater in patients with liver disease than in normal children from 15-45 min following a bolus of atracurium 0.5 mg kg-1.