Five non-depolarizing muscle relaxants in precurarization

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.

Comparison of atracurium and "mini-dose" succinylcholine for preventing succinylcholine-induced muscle fasciculations: a randomized, double-blind, placebo-controlled study

Several drugs have been used to prevent or attenuate succinylcholine- induced muscle fasciculations. There are possible advantages to succinylcholine pretreatment. We designed the present study to compare the effectiveness of atracurium versus "mini-dose" (5 mg) succinylcholine pretreatment for the prevention of muscle fasciculations.

METHODS

Under standard monitoring, 79 patients were randomly assigned to three groups after premedication: Group 1 (n = 26) received normal saline as a placebo, Group 2 (n = 27) received 0.03 mg/kg atracurium, and Group 3 (n = 26) received 5 mg succinylcholine. Thiopental (4 mg/kg) was administered intravenously 90 seconds after pretreatment, followed by intravenous administration of 1.5 mg/kg succinylcholine. An anesthesiologist graded fasciculations based on a four-point scale, from 0 (none) to 3 (severe). All patients were evaluated on the first postoperative day for the presence of postoperative myalgia (POM), the severity of which was graded on a four-point scale, from 0 = no myalgia to 3 = generalized, severe discomfort.

RESULTS

There were no statistical differences among the three groups with respect to sex, weight or age. In Group 1, 3.8% of the patients showed no fasciculations, while 30.8% had mild, 53.8% had moderate and 11.5% had vigorous fasciculations. In Group 2, fasciculations were absent in 74.1% of the patients, while 25.9% of the patients had mild fasciculations. In Group 3, 23.1% patients had no fasciculations, while 42.3%, 30.8% and 3.8% of the patients showed mild, moderate and vigorous fasciculations, respectively, with succinylcholine pretreatment. There was no difference in the presence or severity of myalgia between Groups 1 and 3. Furthermore, the presence of fasciculations was not correlated with POM in Groups 1 and 3, but a significant correlation was found in Group 2.

CONCLUSION

Our results showed that the incidence and severity of fasciculations were significantly decreased by atracurium pretreatment but not by pretreatment with succinylcholine or placebo (p<0.0001 and p=0.0003 respectively). However, atracurium did not exert significant effects on POM.

Hyperkalemia and cardiac arrest following succinylcholine administration in a 16-year-old boy with acute nonlymphoblastic leukemia and sepsis

OBJECTIVES

To report a case of potentially lethal hyperkalemia related to succinylcholine administration.

DESIGN

Case report.

SETTING

A 13-bed pediatric intensive care unit in a tertiary level, university-based children's hospital.

PATIENT

A 16-yr-old boy treated in the intensive care unit due to Klebsiella pneumoniae sepsis, which developed after chemotherapy for nonlymphoblastic leukemia.

INTERVENTIONS

After admission to the intensive care unit, the patient required intubation (uneventful under ketamine and succinylcholine) and mechanical ventilation. On the 15th day of therapy, when his respiratory variables improved significantly, he was extubated. His cardiac rhythm, respiratory rate, arterial blood pressure, and hemoglobin oxygen saturation were continuously monitored. Several hours later, however, he required reintubation due to respiratory insufficiency. For intubation, precurarization with pancuronium, ketamine, propofol, and succinylcholine was used.

MEASUREMENTS AND MAIN RESULTS

Before and immediately after reintubation, serum potassium levels were measured. Two minutes after intubation, premature ventricular contractions, ventricular fibrillation, bradycardia, and finally cardiac arrest were recognized. An increase of serum potassium from 3.19 to 8.64 mmol/L was observed in arterial blood. The patient was immediately resuscitated with chest compressions, intravenous adrenaline, atropine, lidocaine, and sodium bicarbonate. Potassium values normalized within 30 mins. Further treatment in the intensive care unit was uneventful, and the patient was weaned from mechanical ventilation and discharged to a hematology clinic. At present his mental and physical state is satisfactory.

CONCLUSIONS

Succinylcholine may cause dangerous arrhythmias in septic and immobilized children. The alternative nondepolarizing agents should be used in such cases.

Succinylcholine-associated postoperative myalgia

The subject of postoperative myalgia associated with the use of succinylcholine is reviewed. We discuss the mechanisms of succinylcholine-induced myalgia and the techniques available to prevent and treat the myalgia. In situations where patients are at risk of developing myalgia and succinylcholine is the neuromuscular blocker of choice, the use of a combination of techniques may prove to be a useful strategy.

Continuous propofol administration for suxamethonium-induced postoperative myalgia

The effect of continuous propofol administration on creatine kinase and suxamethonium-induced postoperative myalgia was evaluated in 50 patients randomised into two groups of 25 patients each. Induction of anaesthesia was identical in all patients. Anaesthesia was maintained with 66% nitrous oxide in oxygen supplemented by either isoflurane 1% or continuous propofol. Creatine kinase was measured before and after operation. Myalgia was evaluated postoperatively by a blinded observer. The median level of myalgia was reduced significantly in the continuous propofol group (p = 0.011). The median creatine kinase value increased significantly in the isoflurane group (from 90 to 160 IU, p = 0.001).

A comparison of the effect of propofol or thiopentone on the incidence and severity of suxamethonium-induced myalgia

We conducted a prospective, randomised single-blind study in 48 adult women undergoing laparoscopic gynaecological surgery to assess the incidence of suxamethonium-induced myalgia. Anaesthesia was induced with either thiopentone or propofol. All other aspects of clinical care were standardised between the groups. The propofol group had a significantly lower incidence of suxamethonium myalgia (19%) compared with the thiopentone group (63%) (P < 0.05). The mechanism of this effect is not understood.

Waiting time after non-depolarizing relaxants alter muscle fasciculation response to succinylcholine

The purpose of the study was to determine the effect of nondepolarizing muscle relaxants and waiting time on muscle fasciculations after succinylcholine in anaesthetized patients. Adult men and women, 60-80 kg, received pretreatment doses of atracurium 5 mg (n = 160), pancuronium 1 mg (n = 123), d-tubocurarine 3 mg (n = 97), or vecuronium 1 mg (n = 62). Waiting times between pretreatment and succinylcholine, 100 mg, ranged between 0.6 and 5 min. Data points (presence or absence of fasciculations and waiting time) were entered for each patient. Waiting time response curves were obtained between the logit transformation of the probability of no fasciculations and the log waiting time for each drug. Statistical differences between wait time response curves were determined by non-overlapping of the associated 95% confidence intervals. The frequency of muscle fasciculations was reduced with increased waiting time for all nondepolarizers tested. Following wait times of three, four and five minutes, the probability of not fasciculating was greatest with d-tubocurarine (90, 97 and 99%, respectively) and atracurium (89, 93 and 96%). Corresponding values for pancuronium were 70, 82 and 88% and for vecuronium were 74, 82 and 86%. Waiting times to prevent fasciculations in 80% and 90% of patients were shorter with d-tubocurarine (2.46 and 3.02 min, respectively) or atracurium (2.16 and 3.24 min) than pancuronium (3.77 and 5.35 min) or vecuronium (3.73 and 6.36 min).(ABSTRACT TRUNCATED AT 250 WORDS)

Myalgia and biochemical changes following suxamethonium after induction of anaesthesia with thiopentone or propofol

The incidence and severity of muscle pains and changes in creatine kinase were assessed following administration of 1 mg.kg-1 suxamethonium either immediately or 2 min after induction of anaesthesia with propofol or thiopentone in patients undergoing elective dental and ophthalmic surgery. The incidence of muscle pains was 35 and 60% respectively in the groups given suxamethonium immediately and 2 min after propofol, and 35 and 55% when given immediately and 2 min after thiopentone, with no statistically significant differences among the groups. Creatine kinase levels increased in all the groups after operation with the least average increase in the group receiving suxamethonium immediately after propofol and the highest increase in the group receiving suxamethonium 2 min after thiopentone. There was no correlation between the incidence and severity of fasciculations, muscle pains and changes in creatine kinase within or between the groups. It is concluded that neither the induction agent nor the time between the induction agent and suxamethonium administration has any significant influence on the incidence of muscle pains or creatine kinase elevation following suxamethonium.

Neuromuscular effects of succinylcholine following different pretreatments

STUDY OBJECTIVE

To study the neuromuscular effects (onset, intensity, and duration of block) of succinylcholine following different pretreatments.

DESIGN

Randomized open study.

SETTING

University-affiliated hospital.

PATIENTS

Fifty ASA physical status I and II adult inpatients undergoing elective ophthalmic surgery.

INTERVENTIONS

Succinylcholine 0.5 mg/kg was administered after no pretreatment or after pretreatment with d-tubocurarine 0.05 mg/kg intravenously (IV) 3 minutes before, chlorpromazine 0.1 mg/kg i.v. 3 minutes before, alpha-tocopherol (vitamin E) 600 mg in three divided doses orally at 6-hour intervals, or aspirin 600 mg orally 1 hour before in groups of ten patients each.

MEASUREMENTS AND MAIN RESULTS

Neuromuscular block by stimulation of the ulnar nerve at the wrist by application of train-of-four stimuli at 2 Hz every 12 seconds and recording the force of contraction of the adductor pollicis muscle. There was no significant difference in the time to occurrence of maximum block (49 to 53 seconds), reappearance of the twitch response (254 to 307 seconds), or complete recovery of twitch response (532 to 607 seconds) between the groups receiving no pretreatment and those pretreated with chlorpromazine, alpha-tocopherol, or aspirin. However, the time to maximum block (71 seconds) was significantly longer and the time to reappearance of the response (172 seconds) was significantly shorter (both p < 0.05) in the d-tubocurarine pretreated group in comparison with the control group. The time to complete recovery (420 seconds) also was shorter but not significantly different.

CONCLUSIONS

Of the pretreatments used, only d-tubocurarine interferes with the neuromuscular blocking effects of succinylcholine. Chlorpromazine, which attenuates the muscle pains as well as the increase in creatine kinase and can be administered with the same convenience, may be a better pretreatment in the prevention of side effects of succinylcholine.

Alfentanil inhibits muscle fasciculations caused by suxamethonium in children and in young adults

The effect of alfentanil on suxamethonium-induced muscle fasciculations was studied in a double-blind study in 34 children (mean age 6.8 years) and in 30 adults (mean age 20 years). After pretreatment with either alfentanil 50 micrograms kg-1 or saline, each patient was anaesthetized with a sleep dose of thiopental followed by suxamethonium 1.5 mg kg-1 for endotracheal intubation. Compared to the control groups, alfentanil significantly decreased the intensity of visible muscle fasciculations caused by suxamethonium. In children, the duration of muscle fasciculations was shorter in the alfentanil than in the control group. In adults, the intensity rather than the duration of fasciculations was attenuated by alfentanil. The inhibition of fasciculations caused by alfentanil was also demonstrated in children in the surface electromyogram recorded on the biceps. There was no circulatory response to endotracheal intubation in the groups pretreated with alfentanil.

Muscle pains and biochemical changes following suxamethonium administration after six pretreatment regimens

The incidence of muscle pains and changes in serum concentrations of potassium, calcium and creatine kinase following suxamethonium were investigated after no pretreatment or pretreatment with intravenous tubocurarine 0.05 mg.kg-1, intravenous chlorpromazine 0.1 mg.kg-1, alphatocopherol (vitamin E) 600 mg in three divided doses orally, aspirin 600 mg orally or intravenous calcium chloride 5 mg.kg-1 in groups of 20 patients each. The incidence of myalgia was reduced significantly by tubocurarine, chlorpromazine and alphatocopherol. However, the increase in creatine kinase was attenuated only in the groups of patients who received tubocurarine and chlorpromazine. The changes in serum potassium and calcium concentrations were within acceptable limits. The intubating conditions were not as good in the patients who received tubocurarine as in the other groups. Effectiveness of chlorpromazine in preventing both the myalgia and the biochemical changes suggests the involvement of phospholipases in the pathogenesis of suxamethonium-induced muscle damage.

Pretreatment with pancuronium before suxamethonium administration in patients heterozygous for the usual and the atypical plasma cholinesterase gene

The object of this study was to investigate whether pretreatment with pancuronium before i.v. injection of suxamethonium could cause prolonged neuromuscular blockade in patients heterozygous for the usual and the atypical plasma cholinesterase gene (E1uE1a). Forty-three patients, 23 with genotype E1uE1a and 20 with normal genotype (E1uE1u), were pretreated with pancuronium 0.01 mg.kg-1 followed by suxamethonium 1.5 mg.kg-1, and received either neurolept anaesthesia or halothane anaesthesia. Seven patients (E1uE1a) were given suxamethonium 1.5 mg.kg-1 without pretreatment. The duration and type of neuromuscular block were evaluated using train-of-four (TOF) nerve stimulation. Type of anaesthesia did not significantly influence the results. The duration of block following pretreatment was significantly longer in heterozygous patients than in normal patients. Time to 90% twitch height recovery was 10.7 +/- 1.2 min (mean +/- s.d.) in genotypically normal patients, and 18.0 +/- 4.2 min in patients with genotype E1uE1a. Pretreatment with pancuronium caused a significantly slower recovery of the TOF ratio (phase II block). Thus, a TOF ratio of 0.7 was always reached within 13 min in genotypically normal patients. In genotypically abnormal patients, the same TOF ratio was reached within 20 min in all but three patients. In these three patients time to 90% twitch height recovery was prolonged (18-31 min), and TOF ratio did not return to normal, but stabilized at about 0.35, 0.50, and 0.65, respectively. Injection of edrophonium restored normal neuromuscular function in 10 min. It is concluded that in patients heterozygous for the usual and the atypical gene, pretreatment with pancuronium in combination with an increased dose of suxamethonium may cause a phase II block and thus a prolonged neuromuscular block.

Attenuation of suxamethonium myalgias. Effect of midazolam and vecuronium

We studied the incidence of fasciculations and postoperative myalgias in 100 female outpatients who had laparoscopy under thiopentone, N2O, isoflurane anaesthesia. Four groups of 20 patients each were pretreated with saline (group 1), tubocurarine 0.05 mg/kg (group 2), vecuronium 0.006 mg/kg (group 3), or midazolam 0.025 mg/kg (group 4), followed by suxamethonium 1.5 mg/kg. Group 5 received only vecuronium 0.1 mg/kg as relaxant (no suxamethonium). Fasciculations were graded, and postoperative myalgias rated on the first and third postoperative days. In groups 1-5 the incidence of fasciculations was 95, 15, 25, 95 and 0%; the incidence of myalgias on the first day after operation was 70, 45, 65, 75 and 60%, and on the third day after operation 20, 5, 20, 20, and 5%, respectively. We conclude that pretreatment with vecuronium, but not midazolam, decreases the incidence of fasciculations after suxamethonium (p less than 0.05) and that in this patient population, postoperative myalgias appear to be unrelated to the use of suxamethonium.

Effects of precurarisation on suxamethonium-induced postoperative myalgia during the first trimester of pregnancy

Two hundred and fifty women undergoing termination of pregnancy during the first trimester under general anaesthesia were studied to determine the effects of precurarisation on suxamethonium-induced postoperative myalgia and on the need for postoperative analgesics after suxamethonium. Either alcuronium (0.03 mg/kg), atracurium (0.04 mg/kg), tubocurarine (0.05 mg/kg), vecuronium (0.01 mg/kg) or saline was administered in a double-blind manner 4 min before giving suxamethonium. An additional 50 patients were studied who received isoflurane rather than precurarisation and suxamethonium. Every pretreatment prevented fasciculations better than did saline (P less than 0.001). In the saline group, 92% of patients had fasciculations and in the other groups this ranged from 8 to 32%, respectively. On the first postoperative day, 76% of the patients in the saline group had myalgia while myalgia was manifested in 28, 54 and 34% of patients given alcuronium, tubocurarine or vecuronium, respectively (P less than 0.05). Atracurium failed in this effect with 62% having myalgia. In the isoflurane group, none of the patients complained of myalgia on the first postoperative morning. The need for analgesics was less (P less than 0.005) in the isoflurane group (8%) and in the pretreatment groups (18-27%) than in the saline group (42%). It is concluded that precurarisation with tubocurarine, vecuronium or, most effectively, with alcuronium but not with atracurium decreases suxamethonium-induced postoperative myalgia and seems to be necessary also during the first trimester of pregnancy.

Suxamethonium induced myalgia and the effect of pre-operative administration of oral aspirin. A comparison with a standard treatment and an untreated group

Eighty-four fit, unpremedicated patients who presented for routine surgery and received a standard anaesthetic technique were allocated randomly to three equal groups. Group 1 received tubocurarine 0.05 mg/kg before induction of anaesthesia. Group 2 received soluble aspirin 600 mg orally one hour before surgery, while Group 3 received no pretreatment. Aspirin prophylaxis produced a significant reduction in the incidence of subsequent suxamethonium-induced myalgia and the improvement was similar to that achieved with tubocurarine pretreatment. Pre-operative oral administration of aspirin effectively reduces muscle pains and avoids many of the complications associated with pretreatment with non-depolarising agents.

Optimal time interval between pretreatment with alcuronium and suxamethonium during anaesthetic induction

Alcuronium 0.03 mg/kg was studied in a double-blind randomized fashion as a pretreatment before suxamethonium using different time intervals between the administration of the drugs in 78 patients (ASA I-II) undergoing otolaryngological surgery. Alcuronium was given 1, 2 or 3 min before suxamethonium 1.5 mg/kg. The control group received saline as a pretreatment and suxamethonium 1 mg/kg. Anaesthesia was induced with thiopental 5.5 mg/kg over 60 s. Muscle fasciculations, intubating conditions, cardiovascular responses to endotracheal intubation and duration of neuromuscular block were assessed. Muscle fasciculations were statistically and similarly inhibited (P less than 0.01) at all time intervals between alcuronium and suxamethonium. Intubating conditions were worse (P less than 0.05) in the 3-min group than in the other groups. Cardiovascular responses to endotracheal intubation were similar in all groups. The neuromuscular block after suxamethonium was significantly shorter (P less than 0.05) in the 2- and 3-min groups than in the other groups. In conclusion, from the clinical point of view the 1-min time interval between alcuronium and suxamethonium is optimal since muscle fasciculations are inhibited and intubating conditions are satisfactory.

Train-of-four fade of non depolarizing muscle relaxants: an insight into the mechanism of precurarization

This study was carried out to assess the prejunctional effect of non depolarizing muscle relaxants during the onset of neuromuscular blockade using the train-of-four ratio (TR). The prejunctional effect was compared with previous results concerning the ability of the relaxants to prevent suxamethonium-induced fasciculations. Fifty-three adult patients were relaxed with small incremental doses of either alcuronium (0.03 mg.kg-1), atracurium (0.04 mg.kg-1), pancuronium (0.01 mg.kg-1), d-tubocurarine (0.05 mg.kg-1) or vecuronium (0.01 mg.kg-1) during anaesthesia with thiopentone, fentanyl and nitrous oxide in oxygen. The muscle relaxant was given after recovery from an initial suxamethonium blockade needed for tracheal intubation. The evoked integrated EMG response to supramaximal train-of-four (2 Hz) stimulation was recorded every 20 s. TR % was calculated at different first twitch (T1) levels during the onset of neuromuscular blockade. Significant changes occurred at the 100% and 90% T1 levels, alcuronium having the lowest mean TR values. Atracurium, pancuronium and vecuronium gave similar TR values. Results with d-tubocurarine placed it between alcuronium and the others. These train-of-four ratio results were compared with the ability of non depolarizing muscle relaxants to prevent fasciculations. In conclusion, the stronger the train-of-four fade, the greater was the ability of the relaxant to prevent suxamethonium-induced fasciculations. This supports the theory that the blockade of prejunctional cholinergic receptors is the mechanism of action of precurarization.

The 'new' relaxants. A review of the clinical pharmacology of atracurium and vecuronium

Atracurium and vecuronium are reviewed with reference to the following aspects: Development and chemistry

Pharmacology

Potency and dosage

Onset and duration of action

Non-neuromuscular effects

Cardiovascular

Central nervous system

Histamine release and allergic responses

Fate in the body

Pharmacokinetics

Factors which affect response to atracurium and vecuronium

Anaesthetic agents

Suxamethonium

Age

Clinical aspects

Intubation

Cardiac disease and cardiac surgery

Renal disease

Liver disease

Obstetric anaesthesia

Anaesthesia for ophthalmic and neurosurgery

Intercurrent disease states

Outpatient surgery

Reversal of neuromuscular block

Conclusion

Alfentanil as an adjuvant of balanced anaesthesia for tonsillectomy in adults

In a double-blind study, 80 adult patients, undergoing tonsillectomy, were randomly allocated to one of the four groups: d-tubocurarine (d-Tc) 50 micrograms/kg+alfentanil (Alf) 20 micrograms/kg, d-Tc 50 micrograms/kg+Alf 50 micrograms/kg, Alf 10 micrograms/kg+Alf 20 micrograms/kg, Alf 10 micrograms/kg+Alf 50 micrograms/kg. The first drug was given 2 min before thiopental and the second drug 1 min before inserting the mouth gag. Intubation was facilitated with suxamethonium. Anaesthesia was maintained with 70% nitrous oxide in oxygen and peripheral muscle relaxation during operation with vecuronium. For analysis of the induction characteristics, both d-Tc-pretreatment groups were treated together and compared with the results of the Alf-pretreatment groups. Muscle fasciculations occurred in 20% in the d-Tc group and in 70% in the Alf group. Neither d-tubocurarine nor alfentanil prevented the cardiovascular intubation response. Cardiovascular responses to the placement of the mouth gag occurred only in the lower-dose alfentanil groups. ECG changes during operation occurred in 25-45% of the patients. The most common ECG change was junctional rhythm. The operating conditions were good in 65-80% of the patients. The mean recovery score (0-10) ranged from 9.3 to 9.7 between the groups. The incidence of nausea ranged from 20-30% and that of vomiting from 10-25% between the groups. Bleeding from the operation site occurred in 20-30% of the patients. None of the patients needed sutures to stop the bleeding.

Enflurane inhibits muscle fasciculations caused by suxamethonium in children

Eighty-three children with a mean age of 2.7 years were anaesthetized with either thiopental 5 mg/kg followed by suxamethonium 1.5 mg/kg i.v. or with enflurane 5 vol% in 70% nitrous oxide in oxygen via a face mask. In the enflurane group, venepuncture was performed when the children were unconscious, 1.8 +/- 0.05 (s.e.) min after the start of anaesthesia. After enflurane, suxamethonium 1, 1.5 or 2 mg/kg was administered i.v. for endotracheal intubation. The incidence and duration of muscle fasciculations after suxamethonium were significantly lower (P less than 0.01) in the enflurane groups than in the thiopental group. The fasciculation index was significantly lower (P less than 0.01) in the enflurane groups than in the thiopental group. In the enflurane groups, intubating conditions were better (P less than 0.05) in the children treated with suxamethonium 2 mg/kg than in those treated with suxamethonium 1 mg/kg.

Failure of two benzodiazepines to prevent suxamethonium-induced muscle pain

In a randomised double-blind trial carried out on fit, unpremedicated patients undergoing standard minor operations with early postoperative mobility, using a standard form of anaesthesia, pretreatment with diazepam 0.15 mg/kg or midazolam 0.1 mg/kg failed to reduce significantly the incidence of postoperative muscle pains following suxamethonium 1 mg/kg. By contrast, tubocurarine 0.05 mg/kg proved to be effective as a pretreatment. Neither benzodiazepine influenced the incidence or severity of fasciculations seen with suxamethonium or the duration of neuromuscular block. Tubocurarine virtually abolished visible fasciculation and, in the dose used, reduced the intensity and duration of the neuromuscular block. There were no clinically significant changes in serum potassium, creatinine phosphokinase or aldolase after suxamethonium, although 5 out of 47 showed an atypical rise in creatinine phosphokinase.