Dose-response and time course of effect of rocuronium in male and female anesthetized patients

Unexpected delayed reversal of rocuronium-induced neuromuscular blockade by sugammadex: A case report and review of literature

BACKGROUND

Rocuronium, a nondepolarizing muscle relaxant, is usually administered during general anesthesia to facilitate endotracheal intubation and keep patients immobile during the surgery. Sugammadex, the selective reversal agent of rocuronium, fully reverses the neuromuscular blockade (NMB) at the end of surgery. Most reports show that sugammadex rapidly achieves a ratio of train-of-four (TOF), a quantitative method of neuromuscular monitoring, of 0.9 which ensures adequate recovery for safe extubation. However, very rare patients with neuromuscular diseases may respond poorly to sugammadex.

CASE SUMMARY

A 69-year-old female presented with abdominal fullness and nausea, and was diagnosed with gastroparesis. She underwent gastric peroral endoscopic myotomy under general anesthesia with rocuronium (0.7 mg/kg). At the end of surgery, sugammadex 3.6 mg/kg was administered when TOF showed 2 counts. Afterward, the TOF ratio recovered to 0.65 in 30 min. She was awake but could not fully open her eyelids. The tidal volume during spontaneous breathing was low. After additional doses of sugammadex (up to 7.3 mg/kg) in the following 3 h, the TOF ratio was 0.9, and the endotracheal tube was smoothly removed. After excluding possible mechanisms underlying the prolonged recovery course, we speculated our patient may have had an undiagnosed neuromuscular disease, hinted by her involuntary movement of the tongue and mouth. Furthermore, her poor renal function and history of delayed recovery from general anesthesia may be related to the long duration of rocuronium.

CONCLUSION

In our case, both prolonged rocuronium-induced NMB and poor response to sugammadex were noted. To optimize the dose of rocuronium, perioperative TOF combined with other neuromuscular monitoring is suggested.

The Association Between Intraoperative Objective Neuromuscular Monitoring and Rocuronium Consumption During Laparoscopic Abdominal Surgery: A Single-Center Retrospective Analysis

Background

Rocuronium consumption with or without intraoperative objective neuromuscular monitoring in clinical settings of unrestricted use of sugammadex and neuromuscular monitoring has not been reported earlier. The study aimed to investigate the association between the use of intraoperative objective neuromuscular monitoring and rocuronium consumption in patients undergoing laparoscopic abdominal surgery.

Methods

Data were collected by reviewing electronic medical records of patients who received laparoscopic abdominal surgery under general anesthesia with rocuronium and reversal with sugammadex at a university teaching hospital between May 2017 and April 2018. A multivariate linear regression model was developed to compare the amount of rocuronium consumption (mg) per weight (kg) per hour (mg/kg/h) between the group in which intraoperative objective neuromuscular monitoring was used (NMM+ group) and the group in which intraoperative neuromuscular monitoring was not used (NMM− group). Additionally, we performed an interaction test.

Results

A total of 429 patients were evaluated, with 371 patients (86%) included in the NMM+ group and 58 patients (14%) in the NMM− group. Log-transformed rocuronium consumption between the NMM+ group and NMM− group was not significantly different (back-transformed β coefficients [95% CI]: 1.080 [0.951-1.226]; P = 0.23). Male sex and body mass index (BMI) were independent factors associated with 15% (0.853 [0.788-0.924]; P < 0.001) and 3% (for every 1 kg/m² increase in BMI) (0.971 [0.963-0.979]; P < 0.001) decrease in intraoperative rocuronium consumption, respectively. A significant interaction was detected only between the use of neuromuscular monitoring and age ≥65 years (β: 0.803 [0.662-0.974]; P = 0.026).

Conclusions

Although the use of intraoperative objective neuromuscular monitoring was not an individual factor influencing intraoperative rocuronium consumption, this retrospective study demonstrated that the use of intraoperative neuromuscular monitoring reduced rocuronium consumption for approximately 20% of elderly patients (age ≥65 years) undergoing laparoscopic abdominal surgery.

The association between residual neuromuscular blockade (RNMB) and critical respiratory events: a prospective cohort study

Background

Inadequate neuromuscular recovery might impair pulmonary function among adult patients who undergo general anaesthesia and might thus contribute to critical respiratory events in the post-anaesthesia care unit (PACU). The pilot study aims to understand the baseline incidence of residual neuromuscular blockade (RNMB) and postoperative critical respiratory events (CREs), which are described in a modified Murphy’s criteria in the PACU.

Method

This is a prospective cohort study from January to March 2017 from a tertiary hospital in Saudi Arabia with thirty adult patients over 18 years old scheduled for elective surgery under general anaesthesia with neuromuscular blocking drugs (NMBDs) who were enrolled in the study. The Mann-Whitney U tests, chi-square tests and independent-samples T tests were used. The train-of-four (TOF) ratios were measured upon arrival in the PACU by using acceleromyography with TOF-Scan. Subjects’ demographics, perioperative data and the occurrence of postoperative CREs in the PACU were recorded.

Results

Twenty-six (86.7%) patients out of thirty in the study have received rocuronium as NMBDs whilst neostigmine as a reversal drug with only 23 (76.7%). The incidence of RNMB (TOF ratio < 0.9) was in 16 patients (53.3%). The incidence of RNMB was significantly higher in female patients (p = 0.033), in patients who had not undergone quantitative neuromuscular monitoring before extubation (p = 0.046) and in patients with a shorter duration of surgery (p = 0.001). Postoperative CREs occurred in twenty patients (66.7%), and there were significantly more of these CREs among patients with RNMB (p = 0.001). In addition, a statistically significant difference was observed in the occurrence of CREs according to body mass index (p = 0.047).

Conclusion

This research showed that RNMB is a significant contributing factor to the development of critical respiratory events during PACU stay. Therefore, routine quantitative neuromuscular monitoring is recommended to reduce the incidence of RNMB.

First genome-wide association study on rocuronium dose requirements shows association with SLCO1A2

Background

Rocuronium, a common neuromuscular blocking agent, is mainly excreted unchanged in urine (10–25%) and bile (>70%). Age, sex, liver blood flow, smoking, medical conditions, and ethnic background can affect its pharmacological actions. However, reasons for the wide variation in rocuronium requirements are mostly unknown. We hypothesised that pharmacogenetic factors might explain part of the variation.

Methods

One thousand women undergoing surgery for breast cancer were studied. Anaesthesia was maintained with propofol (50–100 μg kg⁻¹ min⁻¹) and remifentanil (0.05–0.25 μg kg⁻¹ min⁻¹). Neuromuscular block was maintained with rocuronium to keep the train-of-four ratio at 0–10%. DNA was extracted from peripheral blood and genotyped with a next-generation genotyping array. The genome-wide association study (GWAS) was conducted using an additive linear regression model with PLINK software. The FINEMAP tool and data from the Genotype-Tissue Expression project v8 were utilised to study the locus further.

Results

The final patient population comprised 918 individuals. Of the clinical variables tested, age, BMI, ASA physical status, and total dose of propofol correlated significantly (all P<0.001) with the rocuronium dose in a linear regression model. The GWAS highlighted one genome-wide significant locus in chromosome 12. The single-nucleotide polymorphisms (SNPs) with the most significant evidence of association were located in or near SLCO1A2. The two top SNPs, rs7967354 (P=5.3e⁻¹¹) and rs11045995 (P=1.4e⁻¹⁰), and the clinical variables accounted for 41% of the variability in rocuronium dosage.

Conclusions

Genetic variation in the gene SLCO1A2, encoding OATP1A2, an uptake transporter, accounted for 4% of the variability in rocuronium consumption. The underlying mechanism remains unknown.

Infusion dose requirement of rocuronium in patients on phenytoin therapy - A prospective comparative study

Background and Aims:

Patients with intracranial tumour are usually on anticonvulsants. Patients on phenytoin therapy demonstrate rapid metabolism of nondepolarising muscle relaxants secondary to enzyme induction. Infusion dose requirement of rocuronium in such patients has been sparingly studied. We studied the continuous infusion dose requirement of rocuronium bromide in patients on phenytoin therapy and its correlation with serum levels of phenytoin.

Methods:

Seventy-five patients scheduled for supratentorial tumour surgery were included in the study. Patients not on phenytoin were taken as control. The primary outcome variable studied was the infusion dose requirement of rocuronium in patients on phenytoin. Based on pre-operative serum phenytoin levels, study group patients were divided into two groups: sub-therapeutic level group (phenytoin level <10 μg/mL) and therapeutic level group (phenytoin level >10 μg/mL). Following anaesthesia induction, rocuronium bromide 0.6 mg/kg was administered to achieve tracheal intubation. Rocuronium infusion was titrated to maintain zero response on the train-of-four response.

Results:

Demographic data were comparable. Patients receiving phenytoin required higher infusion dose compared to the control group (0.429 ± 0.2 mg/kg/h vs. 0.265 ± 0.15 mg/kg/h, P < 0.001). The serum phenytoin level had no correlation to infusion dose requirement of rocuronium (0.429 ± 0.205 mg/kg/h vs. 0.429 ± 0.265 mg/kg/h (P = 0.815). The recovery was faster in the phenytoin group compared to the control group. Haowever, it was not clinically significant.

Conclusion:

The infusion dose requirement of rocuronium bromide in patients on phenytoin is higher and the serum levels of phenytoin does not influence the dose required.

Effective doses of cisatracurium in the adult and the elderly

Background

There are few information about the differences of the effective dose (ED) of cisatracurium between the adult and the elderly. We investigated the ED and the onset time of cisatracurium in the adults and the elderly.

Methods

We studied two hundred patients of the adults aged 20 through 64 years and the elderly aged ≥ 65 years, with American Society of Anesthesiologists physical status I or II. Each 100 patients with 20 patients of each dose group, randomly selected from 30, 40, 50, 60 or 70 µg/kg of cisatracurium, were randomly allocated to the adults and the elderly groups. We recorded the 0.1 Hz single twitch responses of the adductor pollicis and the onset times to maximal blockade. The magnitude of muscle relaxation was recorded by using an acceleromyography. The effect of cisatracurium on single twitch was calculated as percent reduction. After converting each drug dose into logarithm and percent reduction of the muscle reduction into probit, the EDs representing the muscle relaxation effects of 5%, 25%, 50%, 75% and 95% were estimated using the linear regression analysis.

Results

No significant differences were found in age, weight, height, or body mass index within or between the groups. The ED₅₀ and ED₉₅ of the adult group were 35.39 and 59.58 µg/kg. The ED₅₀ and ED₉₅ of the elderly group were 34.89 and 55.50 µg/kg, respectively. The onset times were 375.4 ± 76.9 seconds in the adult group and 369.1 ± 70.0 seconds in the elderly group.

Conclusions

The ED and the onset time were not significantly different between the adult and the elderly.

Qualitative Neuromuscular Monitoring: How to Optimize the Use of a Peripheral Nerve Stimulator to Reduce the Risk of Residual Neuromuscular Blockade

This review provides recommendations for anesthesia providers who may not yet have quantitative monitoring and sugammadex available and thus are providing care within the limitations of a conventional peripheral nerve stimulator (PNS) and neostigmine. In order to achieve best results, the provider needs to understand the limitations of the PNS. The PNS should be applied properly and early. All overdosing of neuromuscular blocking drugs should be avoided and the intraoperative neuromuscular blockade should be maintained only as deep as necessary. The adductor pollicis is the gold standard site and must be used for the pre-reversal assessment, also when the ulnar nerve and thumb were not accessible intraoperatively. Spontaneous recovery should be maximized and neostigmine should be administered after a TOF count of 4 has been confirmed at the adductor pollicis. Extubation should not occur within 10 min after administration of an appropriate dose of neostigmine.

Effective method of continuous rocuronium administration based on effect-site concentrations using a pharmacokinetic/pharmacodynamic model during propofol-remifentanil anesthesia

BACKGROUND

Rocuronium bromide (Rb) is a rapid onset, intermediate-acting neuromuscular blocking agent that is suitable for continuous administration. The appropriate rate of rocuronium administration is, however, difficult to determine due to large interindividual differences in sensitivity to rocuronium. The aim of this study was to clarify whether the simulated rocuronium concentration at the time of recovery to %T1 > 0 % after the initial administration of rocuronium is a good indicator of optimal effect-site concentrations during continuous rocuronium administration.

METHODS

Twenty-one patients were anesthetized with propofol. After induction, Rb 0.6 mg/kg was administered intravenously, and nerve stimulation using the single stimulation mode was conducted every 15 s. When %T1 recovered to >0 % after the initial administration of Rb, the effect-site concentration of rocuronium, calculated by pharmacokinetic simulation with Wierda's set of parameters, was recorded and defined as the recovery concentration (Rb r.c.). The administration rate of rocuronium was adjusted to maintain the Rb r.c. during surgery. Rb administration was discontinued just before the end of surgery, and the recovery time until %T1 > 25 % was recorded. Plasma Rb concentrations were measured at 1 and 3 h after the initiation of continuous Rb administration.

RESULT

The mean Rb r.c. was 1.56 ± 0.35 μg/ml, with minimum and maximum values of 1.09 and 2.08 μg/ml, respectively. The %T1 did not increase above 10 % in any of the patients during continuous administration of Rb, and the recovery period to %T1 > 25 % ranged from 9 to 29 min. The effect-site concentrations of Rb calculated with Wierda's parameters significantly correlated with plasma concentrations (P < 0.01) at both 1 and 3 h after the initial administration of Rb.

CONCLUSION

The results suggest that our method may be one of the most reliable protocols for the continuous administration of Rb described to date for maintaining suitable muscle relaxation during surgery without excessively prolonged effects.

Sex differences in remifentanil requirements for preventing cough during anesthetic emergence

PURPOSE

Target-controlled infusion (TCI) of remifentanil can suppress coughing during emergence from general anesthesia; nevertheless, previous studies under different clinical conditions recommend significantly different effective effect-site concentrations (effective Ce) of remifentanil for 50% of patients (EC₅₀). The differences among these studies include type of surgery and patient sex. In recent years, study of sex differences in regards to anesthetic pharmacology has drawn greater interest. Accordingly, we attempted to determine the effective Ce of remifentanil for preventing cough for each sex under the same clinical conditions.

MATERIALS AND METHODS

Twenty female and 25 male ASA physical status I-II grade patients between the ages of 20 and 46 years who were undergoing thyroidectomy were enrolled in this study. The effective Ce of remifentanil for preventing cough was determined for each sex using the isotonic regression method with a bootstrapping approach, following Dixon's up-and-down method.

RESULTS

Isotonic regression with a bootstrapping approach revealed that the estimated EC₅₀ of remifentanil for preventing coughing during emergence was significantly lower in females {1.30 ng/mL [83% confidence interval (CI), 1.20-1.47 ng/mL]} than in males [2.57 ng/mL (83% CI, 2.45-2.70 ng/mL)]. Mean EC₅₀ in females was also significantly lower than in males (1.23±0.21 ng/mL vs. 2.43±0.21 ng/mL, p<0.001). Mean arterial pressure, heart rate, and respiratory rate over time were not significantly different between the sexes.

CONCLUSION

When using remifentanil TCI for cough prevention during anesthetic emergence, patient sex should be a considered for appropriate dosing.

Gender-specific differences in the central nervous system's response to anesthesia

Males and females are physiologically distinct in their responses to various anesthetic agents. The brain and central nervous system (CNS), the main target of anesthesia, are sexually dimorphic from birth and continue to differentiate throughout life. Accordingly, gender has a substantial impact on the influence of various anesthetic agents in the brain and CNS. Given the vast differences in the male and female CNS, it is surprising to find that females are often excluded from basic and clinical research studies of anesthesia. In animal research, males are typically studied to avoid the complication of breeding, pregnancy, and hormonal changes in females. In clinical studies, females are also excluded for the variations that occur in the reproductive cycle. Being that approximately half of the surgical population is female, the exclusion of females in anesthesia-related research studies leaves a huge knowledge gap in the literature. In this review, we examine the reported sex-specific differences in the central nervous system's response to anesthesia. Furthermore, we suggest that anesthesia researchers perform experiments on both sexes to further evaluate such differences. We believe a key goal of research studying the interaction of the brain and anesthesia should include the search for knowledge of sex-specific mechanisms that will improve anesthetic care and management in both sexes.

Sex differences in drug disposition

Physiological, hormonal, and genetic differences between males and females affect the prevalence, incidence, and severity of diseases and responses to therapy. Understanding these differences is important for designing safe and effective treatments. This paper summarizes sex differences that impact drug disposition and includes a general comparison of clinical pharmacology as it applies to men and women.

A randomized trial to identify optimal precurarizing dose of rocuronium to avoid precurarization-induced neuromuscular block

PURPOSE

The aim of this study was to examine the safe precurarizing dose of rocuronium required to avoid neuromuscular block after precurarization.

METHODS

Twenty-four female patients were randomly allocated into two groups of 12 patients each. General anesthesia was induced and maintained with remifentanil and propofol, and a laryngeal mask was inserted without the aid of a neuromuscular blocking agent. Patients were randomized to receive either 0.03 or 0.06 mg/kg rocuronium as a precurarizing dose. Neuromuscular block was monitored using acceleromyographic train-of-four (TOF) of the adductor pollicis muscle. Three minutes after the precurarization, all patients received suxamethonium 1.5 mg/kg and were graded on severity of fasciculations.

RESULTS

The average TOF ratio was kept above 0.9 even 3 min after precurarization with 0.03 mg/kg rocuronium. In contrast, in patients who received 0.06 mg/kg rocuronium, the ratios significantly decreased to 0.72 (0.14) [mean (SD), P < 0.004] and 0.68 (0.18) (P < 0.006) 2 min and 3 min after the precurarization, respectively. No visible muscle movement was observed following suxamethonium injection, except that one patient who received 0.03 mg/kg rocuronium showed very fine muscle movements of the fingertips.

CONCLUSION

Rocuronium at 0.06 mg/kg is an overdose for precurarization. The results of the present study demonstrate that a safe and effective precurarizing dose of rocuronium is 0.03 mg/kg.

The effect of phenylephrine on the onset time of rocuronium

Background

Several studies have demonstrated that ephedrine shortens the onset time of muscle relaxants, and it does so probably by increasing the cardiac output. However, elevation of the systemic blood pressure through α adrenergic stimulation via ephedrine may affect the onset of muscle relaxants during the induction of anesthesia. We investigated the effect of phenylephrine, which is a selective α-1 agonist, on the onset time of rocuronium and the intubating conditions in adults after the administration of propofol.

Methods

Sixty-four patients were randomly assigned to two groups. Phenylephrine (0.9 µg/kg) (P group) or the same volume of saline (S group) was injected before rocuronium (0.6 mg/kg) administration. Anesthesia was induced with fentanyl 2 µg/kg and propofol 2 mg/kg. The onset time was defined as the time from the end of rocuronium injection to the time when a single twitch height gets to 0% or the minimum level. A well-trained anesthesiologist who was 'blinded' to the treatment groups evaluated the intubating conditions. The mean arterial pressure and heart rate were recorded before induction, before intubation, immediately after intubation and 1 minute and 2 minutes after intubation.

Results

The onset time was 84 ± 18 sec in the P-group and 72 ± 14 sec in the S-group. There was no difference of the intubating conditions, the mean arterial pressure and the heart rate between the two groups.

Conclusions

A small dose of phenylephrine, which has a limited effect on blood pressure, delayed the onset time of rocuronium after the administration of propofol, and the vasoconstriction effect of phenylephrine may affect the prolongation of the rocuronium onset time at the induction of anesthesia with using propofol.

Reversal of vecuronium with neostigmine: a comparison between male and female patients

We investigated the differences between males and females in the reversal effect of neostigmine on neuromuscular blockade. Thirty male and 30 female patients undergoing elective general anesthesia were studied. Vecuronium was given in all patients anesthetized with nitrous oxide, oxygen, and sevoflurane. After the surgical procedure, when T1 (1st response in train-of-four (TOF))/control returned to 0.25, neostigmine 40 microg/kg in combination with atropine 20 microg/kg was given to antagonize residual neuromuscular blockade. Three, six, nine, 12, and 15 minutes after neostigmine reversal, T1/control or TOF ratio (T4/T1) did not significantly differ between the sexes. Also, 15 minutes after neostigmine administration, the number of patients in whom recovery from neuromuscular blockade was sufficient to guarantee good respiratory function, i.e., TOF ratio > 0.74, did not significantly differ between the sexes. In contrast, 15 minutes after neostigmine, the number of patients in whom recovery from neuromuscular blockade was adequate to ensure satisfactory recovery from neuromuscular blockade including the return of the faculty of sight, i.e., TOF ratio > 0.9, was significantly less in the males than in females (6 vs. 14, P = 0.028). In conclusion, 15 min after neostigmine, TOF ratio less often returns to a value of more than 0.9 in males than in females.

Evaluation of a Sex-Based Difference in the Pharmacokinetics of Digoxin

STUDY OBJECTIVE

To determine whether a sex-based difference in digoxin pharmacokinetics exists in patients receiving long-term digoxin therapy for chronic heart failure or atrial fibrillation.

DESIGN

Single-center, retrospective review of medical records.

SETTING

University-based teaching hospital and outpatient clinic.

PATIENTS

Sixty-seven adults (32 men, 35 women) with chronic heart failure or atrial fibrillation who were receiving digoxin therapy.

MEASUREMENTS AND MAIN RESULTS

Serum digoxin concentrations and daily digoxin doses were obtained from patients' medical records. Daily doses were adjusted for patients' actual and ideal body weight and body mass index (BMI). The ratio between the serum digoxin concentration and each of the adjusted daily doses of digoxin was compared between men and women. The mean +/- SD serum digoxin concentration was 0.85 +/- 0.51 ng/ml for men compared with 1.02 +/- 0.51 ng/ml for women. Mean +/- SD unadjusted doses of digoxin were 0.180 +/- 0.063 and 0.164 +/- 0.059 mg/day for men and women, respectively; the difference was not statistically significant. Ratios of serum digoxin concentration to daily digoxin doses did not differ by sex when doses were estimated with actual or ideal weight. Only the ratio of the digoxin concentration to the BMI-adjusted dose was significantly different between men and women (0.14 +/- 0.09 and 0.19 +/- 0.11, respectively, p<0.05).

CONCLUSION

Sex-based differences in digoxin pharmacokinetics were absent when actual or ideal body weight was used. However, the ratio of serum digoxin concentration to daily digoxin dose adjusted for BMI differed by sex. Because digoxin is distributed to lean body mass, use of the BMI could have overadjusted body weight, leading to inaccurate pharmacokinetic assumptions and calculations. The pharmacokinetics of digoxin do not appear to differ by sex.

Sex differences in pharmacokinetics and pharmacodynamics

The importance of reviewing and studying sex-based differences in pharmacologic parameters is demonstrated by the increasing data on gender variation in drug efficacy and toxicity profiles. Sex-based differences in the four major factors that contribute to interindividual pharmacokinetic variability--bioavailability, distribution, metabolism, and elimination--are theorized to stem from variations between men and women in factors such as body weight, plasma volume, gastric emptying time, plasma protein levels, cytochrome P450 activity, drug transporter function, and excretion activity. Sex-determined variations in pharmacodynamics have traditionally been more difficult to study, but a number of recent studies have explored these differences. This review examines the biologic basis of differences in pharmacokinetics and pharmacodynamics between the sexes and summarizes studies that have addressed these differences. As an example, sex-based variation in the efficacy and toxicity of antiretroviral therapy in human immunodeficiency virus (HIV)-infected patients is explored more thoroughly to illustrate some of the factors underlying sex-based differences in drug therapy.

Newer neuromuscular blocking agents: how do they compare with established agents?

Rapacuronium bromide (rapacuronium; ORG-9487) is a nondepolarising muscle relaxant (NMBA) with a low potency [90% effective dose (ED90) 1 mg/kg], which to some extent is responsible for its rapid onset of action. Because of the high plasma clearance (5.3 to 11.1 mg/kg/min) of rapacuronium, its clinical duration of action following single bolus doses up to 2 mg/kg in adults is short (i.e. <20 minutes). Rapacuronium forms a pharmacologically active 3-desacetyl metabolite, ORG-9488, which may contribute to a delay in spontaneous recovery after repeat bolus doses or infusions. After rapacuronium 1.5 mg/kg clinically acceptable intubating conditions are achieved within 60 to 90 seconds in the majority of adult and elderly patients undergoing elective anaesthesia. However, in a rapid-sequence setting. intubating conditions are less favourable after rapacuronium 1.5 to 2.5 mg/kg than after succinylcholine. The most prominent adverse effects of rapacuronium (tachycardia, hypotension and bronchospasm) are dose-related, and in particular pulmonary adverse effects are observed more frequently under conditions of a rapid-sequence induction in adults. Therefore, it seems worthwhile to consider only doses of rapacuronium < or = 1.5 mg/kg to facilitate rapid tracheal intubation, and to use succinylcholine or rocuronium rather than rapacuronium in a rapid-sequence setting. Rapacuronium, however, is a suitable alternative to mivacurium chloride (mivacurium) and succinylcholine for short procedures (e.g. ambulatory anaesthesia). Rocuronium bromide (rocuronium) is a relatively low-potent, intermediateacting NMBA. Its main advantage is the rapid onset of neuromuscular block whereby good or excellent intubating conditions are achieved within 60 to 90 seconds after rocuronium 0.6 mg/kg (2 x ED95), and within 60 to 180 seconds after smaller doses (1 to 1.5 x ED95). Larger doses of rocuronium (> or = 1 mg/kg) seem to be suitable for rapid-sequence induction under relatively light anaesthesia. However, it is still a matter of controversy whether, in the case of an unanticipated difficult intubation, the long duration of rocuronium administered in such large doses outweighs the many adverse effects of succinylcholine. Rocuronium has mild vagolytic effects and does not release histamine, even when administered in large doses. Rocuronium is primarily eliminated via the liver and its pharmacokinetic profile is similar to that of vecuronium bromide (vecuronium). Unlike vecuronium, rocuronium has no metabolite. Cisatracurium besilate (cisatracurium), the IR-cis, 1'R-cis isomer of atracurium besilate (atracurium) is approximately 4 times more potent than atracurium. The onset time of cisatracurium is significantly slower than after equipotent doses of atracurium. The recommended intubating dose is 0.15 to 0.2 mg/kg (3 to 4 times ED95). Over a wide range of clinically relevant doses the recovery properties of cisatracurium are affected by neither the size of the bolus dose nor by the duration of infusion. Unlike atracurium, cisatracurium does not trigger histamine release. Like atracurium, cisatracurium undergoes Hofmann elimination. In contrast to atracurium, cisatracurium does not undergo hydrolysis by nonspecific plasma esterases. Moreover, about 77% of the drug is cleared by organ-dependent mechanisms.