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Rationale: Succinylcholine has been increasingly used in the theft of animals. Because of the presence of residual levels of succinylcholine in poisoned animals, it is harmful for people to eat foods derived from these animals. Therefore, a method should be immediately established to determine succinylcholine and its metabolite in animal-derived foods., Methods: A fast, highly sensitive method, combining solid-phase extraction (SPE) with ultra-performance liquid chromatography/electrospray ionization tandem mass spectrometry (UPLC/ESI-MS/MS), was developed for the determination of succinylcholine and its metabolite in animal-derived foods. The sample was initially extracted with heptafluorobutyric acid and then further cleaned up using an SPE cartridge. Succinylcholine and its metabolite were separated using acetonitrile: 0.1% formic acid in 5 mmol L -1 ammonium acetate as the mobile phase. Quantitative results were based on positive ion ESI multiple reaction monitoring mode., Results: The results show good linearity over a wide range with correlation coefficients of determination of more than 0.998. Both the limits of detection of succinylcholine and succinylmonocholine are 0.2 μg kg -1 . The intra- and inter-day accuracies of the method are in the range 91.4%-104.6%, and the intra- and inter-day precisions are in the range 2.5%-6.6%., Conclusions: This method can be used for the determination of succinylcholine as an illicit drug in animal-derived foods. It was successfully applied to the identification and quantification of succinylcholine and succinylmonocholine in animal-derived foods collected from a local farmers market in Jilin Province of China., (© 2020 John Wiley & Sons, Ltd.)

Objectives: Butyrylcholinesterase (BChE), commonly known as pseudocholinesterase or non-neural cholinesterase, hydrolyzes neuromuscular blocker agents containing choline esters such as succinylcholine that is widely used in rapid sequence induction (RSI) for general anesthesia. The aim of this study is to compare plasma BChE levels and investigate the affects and relationship of succinylcholine on BChE levels in preeclamptic, gestational diabetic and healthy pregnants., Study Design: We designed a prospective, controlled, pilot single-center study. Thirty (n=30) pregnant women who were scheduled for cesarean section under general anesthesia (refusal of regional anesthesia) with RSI involved. Group 1 included ten (n=10) preeclamptic pregnancies, Group 2 included ten (n=10) gestational diabetic (GD) pregnancies and Group 3 included ten (n=10) healthy pregnancies., Main Outcome Measures: BChE levels of all patients were measured prior to the initiation of cesarean section. Train-of-four recovery of 90% (TOF T1) was used to monitor the degree of neuromuscular block beginning from the administration of succinylcholine., Results: No statistically significant difference was found between the groups comparing BChE levels and the duration between tracheal intubation and formation of TOF T1 (p>0.05)., Conclusions: As similar results were gathered from normal and high-risk pregnancies (preeclamptic pregnancy or gestational diabetic pregnancy) who underwent cesarean section under general anesthesia, we believe that succinylcholine is still neuromuscular agent of choice in cesarean section., (Copyright © 2016. Published by Elsevier B.V.)

A nurse administered the neuromuscular blocking agent succinylcholine (SUX) to at least one patient and gave first aid in the therapy of unexpected respiratory depression. SUX is regarded as an undetectable and thus perfect poison due to its short half-life and degradation to the endogenous compounds choline and succinic acid. However, SUX and especially its metabolite succinylmonocholine (SMC) were found in plasma and urine a few hours after administration by means of high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Compared to clinical studies, the window of detection was sufficient to gain definite proof; in other cases no samples were collected. The nurse enjoyed high reputation with the doctors. According to the court she wanted to present herself spectacularly as the first and decisive rescuer to demonstrate her special abilities and capacities, perhaps to receive a better job in the hospital. Considering the actual case, the hero syndrome is not limited to fire-fighters., (Copyright © 2013 John Wiley & Sons, Ltd.)

Background: Concerns about the safety of paralytics such as succinylcholine to facilitate endotracheal intubation limit their use in prehospital and emergency department settings. The ability to rapidly reverse paralysis and restore respiratory drive would increase the safety margin of an agent, thus permitting the pursuit of alternative intubation strategies. In particular, patients who carry genetic or acquired deficiency of butyrylcholinesterase, the serum enzyme responsible for succinylcholine hydrolysis, are susceptible to succinylcholine-induced apnea, which manifests as paralysis, lasting hours beyond the normally brief half-life of succinylcholine. We hypothesized that intravenous administration of plant-derived recombinant BChE, which also prevents mortality in nerve agent poisoning, would rapidly reverse the effects of succinylcholine., Methods: Recombinant butyrylcholinesterase was produced in transgenic plants and purified. Further analysis involved murine and guinea pig models of succinylcholine toxicity. Animals were treated with lethal and sublethal doses of succinylcholine followed by administration of butyrylcholinesterase or vehicle. In both animal models vital signs and overall survival at specified intervals post succinylcholine administration were assessed., Results: Purified plant-derived recombinant human butyrylcholinesterase can hydrolyze succinylcholine in vitro. Challenge of mice with an LD100 of succinylcholine followed by BChE administration resulted in complete prevention of respiratory inhibition and concomitant mortality. Furthermore, experiments in symptomatic guinea pigs demonstrated extremely rapid succinylcholine detoxification with complete amelioration of symptoms and no apparent complications., Conclusions: Recombinant plant-derived butyrylcholinesterase was capable of counteracting and reversing apnea in two complementary models of lethal succinylcholine toxicity, completely preventing mortality. This study of a protein antidote validates the feasibility of protection and treatment of overdose from succinylcholine as well as other biologically active butyrylcholinesterase substrates.

Background: Individuals who are unable to metabolize the short-acting muscle relaxant succinylcholine due to abnormal cholinesterase activity are currently investigated via spectrophotometry using artificial substrates and enzyme inhibitors. Methods have been described using succinylcholine as substrate but with measurement of the product choline. However, choline may be released from other endogenous substrates within the serum. Direct measurement of the in vitro metabolism of succinylcholine as substrate may provide a better indication of the in vivo situation with regard to cholinesterase status., Methods: The rate of in vitro metabolism of succinylcholine by cholinesterase was measured using liquid chromatography linked to tandem mass spectrometry (LC-MS/MS). A comparison was made using serum samples in which cholinesterase activity had been measured using propionylthiocholine as substrate and phenotyped by enzyme inhibitor studies., Results: A good correlation (r = 0.9, P < 0.0001) was found between cholinesterase activity measured by LC-MS/MS using succinylcholine as substrate compared with propionylthiocholine as substrate measured spectrophotometrically. All serum samples with a cholinesterase activity of <1 IU/L, as measured using succinylcholine as substrate, were considered to be at increased risk of succinylcholine sensitivity. These latter results correlated well to the atypical phenotypes., Conclusions: A simple and fast LC-MS/MS technique for the measurement of cholinesterase activity using succinylcholine as substrate has been described. This method clearly identifies patients at risk of prolonged apnoea following succinylcholine administration and compares favourably with existing spectrophotometric methods using artificial substrates.

Background and Objective: Succinylcholine administration, laryngoscopy and tracheal intubation are followed by increased intraocular pressure. Various premedications have been advocated for preventing increases in intraocular pressure, especially in patients undergoing surgical repair of open globe due to penetrating eye trauma. Results of studies in this area have been controversial., Methods: In this double-blind study, three groups of 70 patients receiving sufentanil, lidocaine and placebo 90 s prior to intubation were evaluated and compared for intraocular pressure changes following succinylcholine administration, laryngoscopy and tracheal intubation., Results: Mean intraocular pressure measured 2 and 3 min after succinylcholine administration in groups receiving sufentanil and lidocaine was significantly lower than in the placebo group. Mean intraocular pressure changes in the three groups were -1.84, -2.03 and +2.82 mmHg, respectively in minute 2; -4.78, -4.73 and +1.35 mmHg, respectively in minute 5. There was a significant intraocular pressure decrease in the sufentanil and lidocaine groups, compared to the placebo group. The eye surgeons' satisfaction was also significantly higher with the sufentanil and lidocaine groups., Conclusion: Previous studies have yielded controversial results as to the effect of sufentanil and lidocaine in preventing intraocular pressure following succinylcholine administration, laryngoscopy and tracheal intubation. The present study affirms the preventive effect of these drugs on intraocular pressure increase.

Background: Succinylcholine is one of the most widely used muscle relaxants in clinical anesthesia and emergency medicine. Although the clinical advantages and cardiovascular side effects are well known, its mechanism of action within the human nicotinic cholinergic receptor system remains to be understood. The aim of this study was to investigate the effect of succinylcholine on human muscle and neuronal nicotinic acetylcholine receptor (nAChR) subtypes., Methods: Xenopus laevis oocytes were injected with human messenger RNA for muscle and neuronal nAChR subunits. Receptor activation, desensitization, and inhibition induced by the natural ligand acetylcholine or by succinylcholine was studied using a multichannel two-electrode voltage clamp setup. Responses were measured as peak current and net charge., Results: Succinylcholine concentration-dependently activated the muscle-type nAChR with an EC50 value of 10.8 microm (95% confidence interval, 9.8-11.9 microm), and after the initial activation, succinylcholine desensitized the muscle-type nAChR. Succinylcholine did not activate the neuronal nAChR subtypes alpha3beta2, alpha3beta4, alpha4beta2, or alpha7 at concentrations up to 1 mm and was a poor inhibitor at these receptor subtypes, with IC50 values above 100 microm., Conclusion: Succinylcholine activates the muscle-type nAChR followed by desensitization. The observation that succinylcholine does not inhibit the presynaptic alpha3beta2 autoreceptor at clinically relevant concentrations provides a possible mechanistic explanation for the typical lack of tetanic fade in succinylcholine-induced neuromuscular blockade. Finally, cardiovascular side effects (e.g., tachyarrhythmias) of succinylcholine are not mediated via direct activation of the autonomic ganglionic alpha3beta4 subtype because succinylcholine does not activate the neuronal nAChRs.

No comparative information is available concerning the ability of various cholinesterase (ChE) methods to identify succinyldicholine-sensitive patients, purely on the basis of the enzyme activity recorded in serum. Here, we evaluated six different methods for the measurement of ChE activity; 131 subjects were subdivided according to ChE phenotype and, therefore, to succinyldicholine sensitivity. ChE phenotype was determined by measuring dibucaine and fluoride numbers. DNA analysis was also performed to confirm correlation between the phenotype classification used in the study and the ChE genotype. The tested methods were significantly different in their ability to discriminate between the subjects with and without succinyldicholine-sensitive phenotypes. The succinyldithiocholine/5,5'-dithio-bis(2-nitrobenzoate) (DTNB) method showed the highest accuracy (area under the receiver operating characteristic (ROC) curve 0.97) followed by the propionylthiocholine/DTNB method (area under the ROC curve 0.94). On the other hand, the two methods using butyrylthiocholine as substrate and that employing benzoylcholine showed limited clinical utility in discriminating subjects at risk of prolonged apnea (area under the ROC curve < or = 0.9). Using the succinyldithiocholine method, a value < or = 23 U/l was approximately five times as likely to occur in a sensitive individual as in a normal one.

In elephants the time lapsed from i.m. injection of an overdose of the muscle relaxant succinylcholine (SuCh) until death, is significantly longer than in impala. To determine a difference in the rate of SuCh hydrolysis, once the drug enters the circulation, contributes to this phenomenon we have measured the rate of hydrolysis of SuCh in elephant and impala plasma, and by elephant erythrocytes. Rate of hydrolysis was determined by incubating SuCh in plasma or erythrocyte lysate at 37 degrees C and quantifying the choline produced. Plasma SuCh hydrolytic activity in elephant plasma (12.1+/-1.7 Ul(-1) mean+/-S.D.; n=9) was significantly higher than it was in impala plasma (6.6+/-0.6 Ul(-1); n=5), but were approximately 12 and 21 times lower, respectively, than in human plasma. Elephant erythrocyte lysate had no SuCh hydrolytic activity. Applying this data to previous studies, we can show that the ratio of SuCh absorption to SuCh hydrolysis is expected to be 1.25:1 and 1.41:1 for elephants and impala respectively. It will thus take at least 1.7 times longer for elephant to achieve a plasma SuCh concentration similar to that in impala. We conclude that a more rapid hydrolysis of SuCh in elephant plasma is one factor that contributes to the longer time to death compared to impala.

The first use of neuromuscular blocking agents (muscle relaxants) in clinical practice (1942) revolutionised the practice of anaesthesia and started the modern era of surgery. Since 1942 introduction of tubocurarine (18) neuromuscular blocking agents have been used routinely to provide skeletal muscle relaxation during surgical procedures allowing access to body cavities without hindrance from voluntary or reflex muscle movement. After the introduction of tubocurarine and the depolarizing suxamethonium chloride (4) (1949) several nondepolarizing steroidal and nonsteroidal neuromuscular blocking agents with different onset time and duration of effect were introduced e.g. gallamine triethiodide (1) (1949), methocurine (2) (1949), alcuronium chloride (3) (1963), pancuronium bromide (9) (1968), vecuronium bromide (11) (1982), pipecuronium bromide (10) (1982), atracurium besylate (5) (1982), doxacurium chloride (6) (1991), mivacurium chloride (8) (1992), rocuronium bromide (12) (1994) cisatracurium besylate (7) (1996), and rapacuronium bromide (13) (2000). SZ 1677 (14) a steroid type nondepolarizing neuromuscular blocking agent under development (preclinical phase). This review article deals with a comprehensive survey of the progress in chemical, pharmacological and, in some respects, of clinical studies of neuromuscular blocking agents used in the clinical practice and under development, including the synthesis, structure elucidation, pharmacological actions, structure activity relationships studies of steroidal and nonsteroidal derivatives.

The historical development, pharmacology, pharmacodynamics, pharmacokinetics, clinical applications, pharmacologic basis for selection, adverse effects, and cost of neuromuscular blockers (NMBs) are discussed. The first NMB to be used was tubocurarine. During neurotransmission, acetylcholine is synthesized, stored in vesicles at the neuromuscular junction, released into the synapse, and bound to nicotinic receptors in the muscle end plate. For muscle contraction to occur, the impulse generated in a neuron's cell body must create an action potential that is chemically transmitted across the synapse. The postsynaptic nicotinic receptor at the neuromuscular junction is the major site of action of depolarizing and nondepolarizing NMBs. All NMBs have the potential for cross-reactivity at other nicotinic and muscarinic sites. Drug interactions most commonly occur between NMBs and inhalation anesthetics, certain antimicrobials, calcium-channel blockers, and anticholinesterases. When selecting an NMB, an agent's onset and duration of action must be considered. NMBs can be used on a short-term or long-term basis. Apart from cost, the choice of an NMB is made on the basis of its adverse-reaction profile, pharmacokinetics, and indications for use. Monitoring tools, their use, the rationale for their use, and the interpretation of the results they provide are unique. The patterns of peripheral nerve stimulation vary and elicit different characteristics of nondepolarizing neuromuscular blockade. The effectiveness of reversal agents is proportional to the degree of blockade. The mechanism of action of anticholinesterases involves inhibition of acetylcholinesterase. The expensive NMBs should be conserved for use in surgery, while the cheaper, long-acting [corrected] agents should be used in the intensive care unit. An understanding of the pharmacology, pharmacodynamics, and pharmacokinetics of NMBs will help health care providers gain expertise in the selection and use of these agents.

Succinylcholine, a depolarizing neuromuscular blocking agent used in anesthesia is hydrolyzed in the plasma by the enzyme pseudocholinesterase (PSC). Conditions associated with reduced PSC activity lead to sustained action of succinylcholine and result in prolonged apnea. Cyclophosphamide is an inhibitor of PSC and its suppressive effect may be dose-dependent. We report a case of severe PSC deficiency after high-dose cyclophosphamide at 7 g/m2. The patient received succinylcholine during anesthesia 9 h after chemotherapy and developed prolonged apnea. This case highlights the potential risk of drug-induced PSC deficiency and cautions the use of depolarizing muscular relaxants soon after high-dose cyclophosphamide.

Background: The factors that influence the onset time of submaximal (<100%) neuromuscular block are not fully known. The authors hypothesized that differences in the rate of decrease in the plasma concentration result in differences in the rate of equilibration between plasma and biophase and thus in different onset times. If this hypothesis is valid, inhibition of the enzymic degradation of muscle relaxants should increase the onset time of neuromuscular block., Methods: Twenty pigs received either suxamethonium or mivacurium. Dose finding (70% block) was done for each pig. The enzymic degradation of the muscle relaxant was randomly inhibited by selective inhibition of plasma cholinesterase activity by tetraisopropyl pyrophosphoramide (10 pigs) or was not inhibited (10 pigs). Plasma cholinesterase activities and the mechanomyographic muscle response after peroneal nerve stimulation (0.1 Hz) were measured., Results: Inhibition of plasma cholinesterase activity (by 93% and 89%, respectively) increased the onset time of suxamethonium from a median of 40 s (range, 20-45 s) to 131 s (range, 114-166 s; P = 0.009) and of mivacurium from a median of 52 s (range, 40-59 s) to 105 s (range, 90-125 s; P = 0.009). Inhibition of degradation decreased the effective dose of suxamethonium that resulted in 70% depression of the initial twitch height from 900 microg/kg (range, 400-1,000 microg/kg) to 150 microg/kg (range, 135-150 microg/kg) and of mivacurium from 100 microg/kg (range, 80-150 microg/kg) to 35 microg/kg (range, 20-50 microg/kg)., Conclusions: Inhibition of the enzymic degradation of suxamethonium and mivacurium increases the onset time of submaximal neuromuscular block. Therefore, pharmacokinetics influence the onset time of submaximal neuromuscular block. These results imply that to obtain an ultrashort onset time, muscle relaxants should be developed that not only have a low affinity for the receptor but also rapidly disappear from plasma.

Objective: To review current data on butyrylcholinesterase., Data Sources: Search through Medline data bases of articles in French or English., Study Selection: Original articles and case reports were selected. Letters to editor were excluded., Data Extraction: The articles were analyzed in order to obtain current data on biochemical structure, action, major pathological variations, especially with regard to the recent informations obtained by molecular biology concerning the identification of genetic variants., Data Synthesis: Butyrylcholinesterase must be differentiated from acetylcholinesterase, which cannot hydrolyse succinylcholine. The physiological action of butyrylcholinesterase remains unknown, although it can hydrolyse many drugs. Excluding genetical mutations, several physiopathological situations alter butyryl-cholinesterase activity. Butyrylcholinesterase activity assessment does not allow the diagnosis of genetic variants. Whatever the origin, only deficits of more than 50% modify significantly the metabolism of succinylcholine or mivacurium. The diagnosis of a prolonged neuromuscular blockade is obtained with systematic monitoring of the neuromuscular function in case of administration of mivacurium or succinylcholine. Mivacurium should only be re-injected when one response at train of four is obtained. In case of prolonged neuromuscular blockade, the anticholinesterasic agent should not be administered when no response at train of four is obtained. The biochemical methods using inhibitors (dibucaine, fluoride) of the butyrylcholinesterase and a familial study lead to the diagnosis in most cases because the atypical and fluoride variants are the most frequent. When results are doubtful, genetic molecular methods with the use of PCR and restriction enzymes allow a rapid diagnosis.

Plasma cholinesterase is an enzyme which has importance to the anaesthetist primarily for its role in the metabolism of suxamethonium, although other anaesthetic related drugs that this enzyme metabolises are also increasingly important. In this article we review current thoughts on the function, profile and chemistry of plasma cholinesterase. Causes of variations in the activity of the enzyme are described and the basis of genetic variations is explained.

The atypical variant of human butyrylcholinesterase has Gly in place of Asp 70. Patients with this D70G mutation respond abnormally to the muscle relaxant succinyldicholine, experiencing hours of apnea rather than the intended 3 min. Asp 70 is at the rim of the active site gorge 12 A from the active site Ser 198. An unanswered question in the literature is why the atypical variant has a 10-fold increase in Km for compounds with a single positive charge but a 100-fold increase in Km for compounds with two positive charges. We mutated residues Asp 70, Trp 82, Trp 231, Glu 197, and Tyr 332 and expressed mutant enzymes in mammalian cells. Steady-state kinetic parameters for hydrolysis of butyrylthiocholine, benzoylcholine, succinyldithiocholine, and o-nitrophenyl butyrate were determined. The wild type and the D70G mutant had identical k(cat) values for all substrates. Molecular modeling and molecular dynamics suggested that succinyldicholine could bind in two consecutive orientations in the active site gorge; formation of one complex caused a conformational change in the omega loop involving Asp 70 and Trp 82. We propose the formation of three enzyme-substrate intermediates preceding the acyl-enzyme intermediate; kinetic data support this contention. Substrates with a single positive charge interact with Asp 70 just once, whereas substrates with two positive charges, for example succinyldithiocholine, interact with Asp 70 in two complexes, thus explaining the 10- and 100-fold increases in Km in the D70G mutant.

Background: The metabolic hydrolysis of mivacurium (and succinylcholine) is markedly impaired in the presence of hereditary or acquired defects of pseudocholinesterase. Clinical reports are conflicting as to the utility of anticholinesterases, in the reversal of mivacurium paralysis. In the current study, the role of exogenous cholinesterases and/or of anticholinesterase, neostigmine, in the reversal of deep mivacurium-induced paralysis, was studied. The rat phrenic-diaphragm preparation, in a fixed volume of Krebs solution, was chosen to eliminate the confounding effects on the dissipation of neuromuscular effects caused by hydrolysis, elimination, and redistribution of the drug., Methods: In the phrenic-diaphragm preparation, mivacurium was administered to obtain >90% single twitch inhibition. Single twitch responses (0.1 Hz) were monitored for 60 min, after which the response to train-of-four stimulation was tested. The reversal of mivacurium by 0.5, 1.0, or 2.0 units/ml of (true) acetylcholinesterase, bovine pseudocholinesterase, or human plasma cholinesterase and by neostigmine, 0.1, 1.0, or 10.0 micrograms/ml tested. The efficacy of human plasma cholinesterase, 1 unit/ml in combination with each of the above neostigmine concentrations, also was examined. The reversal of succinylcholine-induced paralysis by the acetylcholinesterase, bovine pseudocholinesterase, or human plasma cholinesterase (1 unit/ml) alone and in the presence of neostigmine (10.0 micrograms/ml) was additionally tested as a positive control. A train-of-four ratio > 0.75 was considered adequate reversal., Results: Acetylcholinesterase was a poor hydrolyzer of mivacurium, as bioassayed by reversal of paralysis. Bovine pseudocholinesterase in concentrations of 0.5 and 1.0 units/ml did not effectively reverse single twitch and train-of-four responses by 60 min, but bovine pseudocholinesterase (2 units/ml) and all concentrations of human plasma cholinesterase did. Neostigmine alone, tested at all concentrations, was an incomplete reversal drug. Clinical or therapeutic concentrations (0.1 and 1.0 micrograms/ml) of neostigmine did not, but pharmacologic concentrations (10 micrograms/ml) interfere with the efficacy of human plasma cholinesterase (1 unit/ml). Bovine pseudocholinesterase and human plasma cholinesterase equally reversed the effects of succinylcholine but acetylcholinesterase did not, whereas the addition of 10 micrograms/ml neostigmine to the enzymes inhibited the reversal of succinylcholine., Conclusions: Human plasma cholinesterase will reverse mivacurium more effectively than bovine pseudocholinesterase, but both will effectively reverse succinylcholine. Acetylcholinesterase has no effects on either relaxant. The anticholinesterase neostigmine was an incomplete reversal drug. Pharmacologic concentrations of anticholinesterases do, while clinical or therapeutic concentrations do not, completely inhibit the metabolic activity of pseudocholinesterases.

We report a case of prolonged neuromuscular block after administration of mivacurium 0.2 mg kg-1 to a 16-yr-old patient where the duration of block was 2.5 h. The interesting points in this case were that the patient had homozygous atypical plasma cholinesterase deficiency (both parents had a normal phenotype) following liver transplantation. Investigations showed low plasma cholinesterase activity (343 iu litre-1; normal 600-1400) and dibucaine number was 25 (normal 76-83). Despite possessing atypical enzyme normally associated with markedly prolonged duration of suxamethonium, on two occasions the patient received suxamethonium and responded normally. This had not previously been reported. The patient demonstrated prolonged block with mivacurium as a result of atypical enzyme (despite normal metabolism of suxamethonium).

Plasma cholinesterase is a glycoprotein synthesized in the liver and is found in plasma, liver, intestinal mucosa and other tissues. Six percent to 7% of patients in most surgical populations have an abnormal plasma cholinesterase activity and about 65% of all cases of prolonged neuromuscular blockade following succinylcholine are due to genetic factors. This review focuses on the causes and clinical significance of plasma cholinesterase for the hydrolyses of succinylcholine. Diagnosis and treatment of prolonged response to succinylcholine in phenotypically normal patients, heterozygous abnormal patients and patients homozygous for the atypical gene is mentioned. Also presented is the relationship between plasma cholinesterase and the new relaxant mivacurium, and bambuterol, a prodrug to terbutaline. Additionally, the recent developments in the identification of the plasma cholinesterase genotypes are presented.

Pseudocholinesterase (ChE) (acylcholineacylhydrolase, EC 3.1.1.8) has been partially purified (about 270-fold) from sheep brain. The procedure included ammonium sulfate fractionation (20-80%), DEAE-Trisacryl M chromatography and procainamide-Sepharose 4B affinity chromatography. The molecular weight of purified ChE was found to be 290,000 by gel filtration. Kinetic properties of the enzyme have been studied using the substrate analogues choline, succinylcholine and benzoylcholine. It was shown that the inhibition was partially competitive.

The rare H-variant of human butyrylcholinesterase is a quantitative variant that reduces serum butyrylcholinesterase activity by about 90%. Individuals who are heterozygous for both the H-variant and the atypical variant are abnormally sensitive to the muscle relaxant succinylcholine. By using standard phenotypic serum assays, the Danish Cholinesterase Research Unit identified four individuals from two unrelated pedigrees who were heterozygous for both the H-variant (H) and the atypical (A) variant. DNA of these A/H individuals was extracted from white blood cells. Using the polymerase chain reaction and subsequent DNA sequencing, a point mutation was found at nucleotide 424 which changed amino acid 142 from valine to methionine. The previously identified atypical mutation, Asp 70 to Gly, was also seen, which segregated apart from the H-variant mutation in family studies. These two mutations were found in all four A/H individuals.

Nicotinic acetylcholine receptor was synthesized in Xenopus oocytes after injection of the mRNA purified from Electrophorus electricus electroplax. Nicotine, succinylcholine, and decamethonium (agonist)-elicited membrane currents in the injected oocytes were measured electrophysiologically by the voltage-clamping method. The following four different measurements were made to establish the relationship between the agonist concentration and the membrane current: 1) the agonist-induced membrane current before desensitization, 2) the agonist-induced membrane current after desensitization equilibrium, 3) the fraction of the active form of the receptors after desensitization equilibrium, 4) the rate of recovery of desensitized receptors upon removal of the agonist. These results were analyzed on the basis of the minimal model proposed from receptor-mediated ion translocation measurements. The equilibrium and rate constants of the model were evaluated for nicotine, succinylcholine, and decamethonium, and could explain the observed electrical responses in the injected oocyte, i.e. the characteristics of the receptor response caused by these agonists.

Succinylcholine is frequently employed in surgical procedures as a pre-anaesthetic. However, the lack of existing metabolic activity for this compound in some individuals entails a substantial risk. Normally, the risk is assessed indirectly through the measurement of pseudocholinesterase activity using other substrates, such as acetylcholine, rather than the agent itself. Thus, a method was devised to assess directly the hydrolysis of succinylcholine in human plasma samples. This method was applied to plasma samples derived from healthy men, healthy women, pregnant women and patients with silent pseudocholinesterasaemia.

In obstetric patients undergoing postpartum tubal ligation, we found that metoclopramide produced dose-dependent prolongation of suxamethonium-induced neuromuscular block. Mean block times after suxamethonium 1 mg kg-1 were 8.0 min, 9.83 min and 12.45 min for control and metoclopramide 10 mg and metoclopramide 20 mg groups, respectively. A laboratory study was therefore conducted on the inhibition of human plasma cholinesterase (PCHE) and erythrocyte acetylcholinesterase (ACHE) activity by varying concentrations of metoclopramide using acetylthiocholine as substrate. PCHE showed a greater sensitivity to inhibition by metoclopramide; the concentration of metoclopramide producing 50% inhibition of activity (I50) was 3.16 x 10(-7) mol litre-1, which is within the therapeutic range. ACHE was less sensitive to inhibition by metoclopramide (I50 2.24 x 10(-5) mol litre-1). Analysis of enzyme kinetics at varying substrate concentrations revealed that metoclopramide produced a potent non-competitive, dose-dependent inhibition of both ACHE and PCHE. The inhibition constant, Ki, was 1.88 x 10(-7) mol litre-1 for PCHE and 9.5 x 10(-8) mol litre-1 for ACHE. As metoclopramide is a potent inhibitor of PCHE, interactions might be expected to occur between metoclopramide and drugs that require PCHE for biotransformation, such as suxamethonium and ester local anaesthetics.

Alpha Bungarotoxin binding protein belongs to the group of nicotinic receptors regarding their pharmacologic characteristics. Presence of alpha Bungarotoxin binding sites was confirmed on six cell lines of human microcellular lung carcinomas. The binding sites are saturable, specific and show high affinity for alpha Bungarotoxin. The presence of the binding sites was found on human microcellular lung carcinoma cultured in the mice of "Nude" clones. Using pharmacologically active substances like succinilcholine, decamethonium, atropine and propranolol, the nicotinic characteristics of alpha Bungarotoxin binding sites were confirmed. The presence of alpha 5 subunits in the alpha Bungarotoxin binding protein of human microcellular lung cells was established by Northern blot experiments classifying alpha Bungarotoxin binding protein on microcellular cells as a neuronal nicotinic receptor regarding its structure.

People with genetic variants of cholinesterase respond abnormally to succinylcholine, experiencing substantial prolongation of muscle paralysis with apnea rather than the usual 2-6 min. The structure of usual cholinesterase has been determined including the complete amino acid and nucleotide sequence. This has allowed identification of altered amino acids and nucleotides. The variant most frequently found in patients who respond abnormally to succinylcholine is atypical cholinesterase, which occurs in homozygous form in 1 out of 3500 Caucasians. Atypical cholinesterase has a single substitution at nucleotide 209 which changes aspartic acid 70 to glycine. This suggests that Asp 70 is part of the anionic site, and that the absence of this negatively charged amino acid explains the reduced affinity of atypical cholinesterase for positively charged substrates and inhibitors. The clinical consequence of reduced affinity for succinylcholine is that none of the succinylcholine is hydrolyzed in blood and a large overdose reaches the nerve-muscle junction where it causes prolonged muscle paralysis. Silent cholinesterase has a frame shift mutation at glycine 117 which prematurely terminates protein synthesis and yields no active enzyme. The K variant, named in honor of W. Kalow, has threonine in place of alanine 539. The K variant is associated with 33% lower activity. All variants arise from a single locus as there is only one gene for human cholinesterase (EC 3.1.1.8). Comparison of amino acid sequences of esterases and proteases shows that cholinesterase belongs to a new family of serine esterases which is different from the serine proteases.

The neuromuscular blocking effects and recovery times following two doses of succinylcholine on a weight basis were evaluated in 16 infants and 16 children. Infants had less profound neuromuscular blockade than children at both 0.5 and 1.0 mg/kg doses. Succinylcholine, 1 mg/kg, in infants produced blockade equal to that produced by 0.5 mg/kg in children; at these equipotent doses there was no statistically significant difference between the times to recover to 10 and 90 per cent neuromuscular transmission in the two groups. However, the rate of recovery from 50 per cent neuromuscular transmission to 90 per cent neuromuscular transmission was 69.1 per cent/min in children, as opposed to 46.4 per cent/min in infants. When dosage was calculated on a surface area basis, there was a linear relationship for infants and children as a single group between the log dose and the times to recover to 50 and 90 per cent neuromuscular transmission. Similarly, there was a linear relationship between the log dose (mg/m2) and the maximum intensity of neuromuscular blockade.

Etomidate (Hypnomidate), a safe and effective short-acting hypnotic drug of special value for induction of anesthesia, seems to be a noncompetitive activator, as well as a competitive inhibitor, of pseudocholinesterase E.C. 3.1.1.8). This is analogous to the effects of morphine and its derivatives with which etomidate has a structural similarity. The analysis of enzyme kinetics in vitro gave a Km of 10.4 (+/- 1.1) microM and a Vmax of 2.4 (+/- 0.3) mmoles/1 min for the hydrolysis of S-butyrylthiocholine by human pseudocholinesterase. Etomidate does not show any influence on the reaction rate of pseudocholinesterase on S-butyrylthiocholine in the standard test. From the experimental results it is derived that even under in vivo conditions of induction of anesthesia by etomidate, no influence is to be expected on the turnover of succinylcholine by the normal pseudocholinesterase. There is no explanation for the occasionally prolonged postnarcotic apnea following administration of etomidate as far as competition of etomidate with succinylcholine for the pseudocholinesterase is concerned and as long as enzyme variants of higher affinity for etomidate can be excluded.

The elimination of succinylcholine appears to follow first-order kinetics with a linear relationship between intensity of effect and logarithm of the dose. Determination of the time-course of neuromuscular blockade following succinylcholine in infants and children allowed us to compare the rate of recovery and elimination rate constant with those determined by others in adults. The rate of recovery was independent of dose for each age group. The rate of recovery was faster in children than in infants; the rate of recovery of infants was faster than that of adults. The elimination rate constant for infants was similar to that of children; for both the infants and children the rate constants appeared dissimilar from those of adults.

We have developed a succinyldicholine-based assay for serum cholinesterase (EC 3.1.1.8) to help establish whether patients with suspected sensitivity to drugs of this type have enzyme abnormalities that cannot be detected by conventional laboratory techniques. Although the method discriminates between cholinesterase activities of drug-sensitive and nonsensitive people as well as an assay involving propionylthiocholine does, it has not revealed cholinesterase abnormalities in patients who experienced prolonged apnea after succinyldicholine, in whom no enzyme defect could be demonstrated by other procedures. Of 50 individuals who were apneic for between 20 and 180 min, only one had a cholinesterase activity less than the mean for E1u homozygotes by more than 2.5 SD. We conclude that the number of patients who experience clinical problems due to enzyme abnormalities that at present go unrecognized is small. Consequently, although succinyldicholine might eventually become the substrate of choice for cholinesterase, its advantages over propionylthiocholine are not yet sufficient to encourage its use.

This retrospective study examines the indications and the effects of 119 doses of succinylcholine or pancuronium given in the emergency department during a 24-month period to patients considered to have immediately life-threatening emergencies. The most common indication for succinylcholine was to accomplish tracheal intubation (20 of 25 patients). Indications for pancuronium included computerized tomography of the head (60 of 94), control of agitation (40 of 94), facilitation of tracheal intubation (20 of 94), control of ventilation (12 of 94), and control of seizure unresponsive to anticonvulsants (4 of 94). Deterioration following succinylcholine occurred in three cases. These included two involving bradycardia and one involving ventricular tachycardia. Major complications following pancuronium included four incidences of ventricular arrhythmias. Intubation failure requiring surgical airway occurred in one patient given succinylcholine, two patients given pancuronium, and one patient who received both succinylcholine and pancuronium. Inadequate documentation of neurological examination prior to blockade was noted in six of 25 succinylcholine and nine of 94 pancuronium cases. Failure to sedate patients who might be aware of paralysis occurred in three of 25 succinylcholine and eight of 94 pancuronium uses. Neuromuscular blocking agents facilitate expeditious management of selected critical patients in the ED. Their prudent use requires anticipation of potential complications, preparation for surgical airway should intubation fail, documentation of physical examination before paralysis, and prior sedation when the patient responds to pain.

Over a 10-year period 12,643 gynecologic surgical procedures were performed with the patients under general anesthesia. Succinylcholine was the muscle relaxant used in the majority of cases. Four of these patients developed prolonged postoperative apnea; the longest period of apnea was 6 hours. In one patient atypical cholinesterase was documented, and two of the patients were subsequently diagnosed as having myasthenia gravis. In the fourth case an etiology for the apnea was not demonstrated. A compilation of drugs in common clinical usage which interfere with neuromuscular transmission is included.

Four methods for measuring serum cholinesterase activity have been applied to sera of normal individuals and of patients shown to be sensitive to short-acting muscle relaxants of the succinyldicholine type. They have been assessed according to their ability to differentiate between sensitive and insensitive individuals on the basis of enzyme activity measurements alone. The method described, based upon that of Dietz et al. [Clin. Chem. 19, 1309 (1973)], in which propionylthiocholine is used as substrate, is best for this purpose, being capable of identifying over 90% of affected individuals with no false positives. Acetylcholine and butyrylthiocholine are slightly inferior substrates in this respect, and benzoylcholine gives little useful information.

In the first 2 years of life there is physical and biochemical maturation of the neuromuscular junction of man. With this maturation there is an increase in the neuromuscular reserve (margin of safety) of the infant and a change in the contractile properties of skeletal muscle. On a weight basis neonates and young infants are resistant to both depolarizing and non-depolarizing muscle relaxants; when dosage is calculated on the basis of surface area neonates and young infants are not resistant to succinylcholine, but appear sensitive to non-depolarizing relaxants. Variation in extracellular fluid volume probably explains these differences in apparent resistance. Data relating recovery of neuromuscular transmission to plasma or tissue bath concentrations of dTc are conflicting. Awareness of the clinical response of neonates and infants to muscle relaxants and awareness of the non-neuromuscular blocking properties of relaxants in infants and children permits the use of these anesthetic adjuncts in patients of any age.