Perioperative Pharmacologic Considerations in Obesity

Obesity has increased in incidence worldwide. Along with the increased number of obese patients, comorbid conditions are also more prevalent in this population. Obesity leads to changes in the physiology of patients along with an altered response to pharmacologic therapy. Vigilant perioperative physicians must be aware of the unique characteristics of administered agents in order to appropriately provide anesthetic care for obese patients. Because of the variability in tissue content in obese patients and changes in pharmacokinetic modeling, a one-size-fits-all approach is not justified and a more sophisticated and prudent approach is indicated.

Pharmacologic Considerations of Anesthetic Agents in Pediatric Patients: A Comprehensive Review

Acute pain in the pediatric population has important differences in terms of biology, intrapopulation variation, and epidemiology. Discussion as to the pharmacologic considerations of anesthetic agents, such as induction agents, neuromuscular blockers, opioids, local anesthetics, and adjuvant agents, is presented in this article. Special considerations and concerns, such as risk for propofol infusion syndrome and adverse potential side effects of anesthesia agents, are discussed. Anesthesiologists managing pediatric patients need to have a firm understanding of physiologic and pharmacologic differences compared with the adult population. Future studies to improve the understanding of pharmacokinetics in the pediatric population are needed.

[When muscle relaxants have unexpected prolonged duration during anaesthesia]

Muscle relaxation facilitates tracheal intubation and improves surgical conditions during anaesthesia. However, unexpected prolonged muscle relaxation may occur. This article describes important causes of prolonged muscle relaxation and gives suggestions for its prevention. Drug interactions, incomplete reversal, co-morbidity, inaccurate neuromuscular monitoring and critical illness may prolong the effect of muscle relaxants. The anaesthetist must titrate the muscle relaxants using objective neuromuscular monitoring and proper reversal of the blockade when needed.

[Reversion of sedation and general anaesthesia--agonist-antagonist technique]

OBJECTIVE

To study an expediency and efficacy of application of different reverses drugs (naloxone, flumazenil, neostigmine, galantamine, sugammadex) either their separate or combined using.

METHODS

We studied 119 patients underwent endoluminal endoscopic procedures and surgeries on trachea-bronchial tree and intestines under sedation or general anaesthesia.

RESULTS

The article deals with conceptual approaches to the reversal of residual effects of opioids, benzodiazepine sedation and neuromuscular block (the so-called agonist-antagonist technique).

CONCLUSIONS

A reversion of neuromuscular block without using of antagonists' combination does not provide complete recovery of psychomotor and cognitive functions for rapid socialization of patients after anaesthesia.

Comparative pharmacodynamics of pancuronium, cisatracurium, and CW002 in rabbits

Pancuronium is a long-duration neuromuscular blocking drug (NMBD) that has been used in anesthetized rabbits at 0.1 mg/kg. However, there are limited data regarding the time course for recovery from this dose either spontaneously or with pharmacologic reversal. Here we defined the potency, onset, and recovery characteristics for the intermediate-duration NMBD cisatracurium and CW002 (a novel cysteine-inactivated molecule) in the rabbit, and test the hypothesis that these drugs may be alternatives to 0.1 mg/kg pancuronium for survival procedures. New Zealand white rabbits anesthetized with isoflurane were studied in a cross-over design. Potencies of cisatracurium and CW002 were defined as the effective dose for 95% depression of evoked muscle twitch (ED95). Responses to 3×ED95 were used to define onset (time to maximal effect), recovery index (RI; time from 25% to 75% recovery of twitch), and duration (time to complete recovery). Responses to all drugs were determined with and without reversal by neostigmine-glycopyrrolate or L-cysteine. CW002 was 4-fold more potent than was cisatracurium, but their onset, RI, and duration were similar. Pancuronium had similar onset and RI but longer duration, compared with cisatracurium and CW002. Reversal shortened the recovery index and duration for all 3 drugs. At 3×ED95, cisatracurium and CW002 had the same onset as did standard-dose pancuronium, but durations were shorter and more predictable. In addition, CW002 can be reversed without the potential side effects of cholinergic manipulation. We conclude that cisatracurium and CW002 are viable alternatives to pancuronium for survival studies in rabbits.

Influence of acute normovolemic hemodilution on the pharmacokinetics of Cisatracurium Besylate

BACKGROUND

Acute normovolemic hemodilution (ANH) is an efficacious blood conservation strategy for avoiding or reducing allogeneic blood transfusion. In a previous publication, on a different cohort of patients, we demonstrated that cisatracurium's potency and duration of action were not influenced by ANH, but we could not establish which role, if any, pharmacokinetics played.

METHODS

Forty patients were randomly allocated to the ANH or control groups. Patients received cisatracurium single 100 µg kg-1 bolus dose, serial arterial blood samples were collected and assayed for pharmacokinetic analysis.

RESULTS

Central and steady state apparent volumes of distribution (V1, Vdss) and slope factor (γ) were larger, effect-compartment concentration at 50% neuromuscular block was lower in the ANH (90.8±41.6 mL kg-1, 159.1±39.2 mL kg-1, 6.0±0.9 and 136.4±29.1 ng·mL-1) compared with the control group (65.5±26.1 mL kg-1, 134.8±31.8 mL kg-1, 5.5±0.8 and 158.5±26.0 ng·mL-1) respectively. Elimination half-life (t1/2 β) and mean residence time (MRT) were longer in the ANH (37.2±20.9, 23.5±13.2 min) than the control group (26.8±9.8, 16.9±6.2 min), albeit not statistically significant (P=0.051, P=0.051). There were no significant differences in distribution half-life (t1/2 α), effect-compartment equilibration rate-constant (keo), central and total clearances (Clc, Cl) between the ANH (2.4±1.2 min, 0.070±0.013 min-1, 6.1±1.9 mL kg-1 min-1 and 7.7±2.3 mL kg-1 min-1) and control group (1.9±1.2 min, 0.063±0.008 min-1, 7.0±1.8 mL kg-1 min-1 and 8.5±2.1 mL kg-1 min-1) respectively.

CONCLUSION

ANH altered some pharmacokinetic parameters such as significantly larger volumes of distribution. Other parameters such as elimination half-life were considerably longer albeit not statistically significant.

Myths and facts in neuromuscular pharmacology. New developments in reversing neuromuscular blockade

Pharmacologic reversal of neuromuscular blockade is a topic not very well acknowledged and controversially discussed. Reasons for this are numerous and include missing perception of the potential complications of residual neuromuscular paralysis including an increased morbidity and mortality, as well as low efficacy and numerous unwanted side effects of the available antagonists. Duration of action of muscle relaxants cannot be pharmacologically predicted. Objective neuromuscular monitoring is the only way to detect residual paralysis. This review article would like to discuss in its first part some of the myths which revolve around the use of muscle relaxants, then highlight the problems regarding the use of acetylcholine esterase inhibitors and, in the third part, discuss the steroidal muscle relaxant encapsulator sugammadex.

[New developments in neuromuscular blocking agents]

Curare was clinically used in a patient with acute appendicitis by Griffith and Johnson in January 1942. From the day on, the development of new muscle relaxants went on in the world. Since pancuronium was synthesized by Savage in 1964, it was widely used in clinical cases because it provided sufficient muscle relaxation during operation. At present, pancuronium, vecuronium and rocuronium are routinely used in the world. In the future, we expect development of new muscle relaxants with rapid onset, intermediate duration of action, rapid recovery and without side effects.

Functional recovery after neuromuscular blockade in mechanically ventilated critically ill patients

BACKGROUND

An estimated 24% to 70% of individuals have prolonged paralysis or severe weakness after receiving neuromuscular blocking agents (NMBAs) when therapy is terminated.

OBJECTIVES

The purposes of this study were to (1) evaluate the relationship between recovery of neuromuscular transmission (NMT) and functional muscle activity after NMBA administration; (2) evaluate the relationship between delayed recovery of NMT or muscle activity and functional performance; and (3) determine the predictors of delayed recovery of NMT, muscle activity, and functional performance.

METHODS

This was a multisite study using a prospective, nonexperimental, descriptive design with convenience sampling techniques. Instruments used included a five-point muscle score, Actigraph, and peripheral nerve stimulator.

RESULTS

Key findings were as follows: (1) NMT returned promptly, whereas muscle activity remained severely depressed; (2) only two subjects (5%) recovered functional performance within 24 hours; (3) degree of muscle weakness immediately after neuromuscular blockade was associated with prolonged time to extubation and mobility; and (4) predictors of delayed recovery included cumulative dose of aminosteroid NMBAs, age, and renal function.

CONCLUSION

Prolonged recovery of muscle activity and extreme weakness may occur despite brisk recovery of NMT after neuromuscular blockade.

Randomised controlled trial comparing cisatracurium and vecuronium infusions in a paediatric intensive care unit

OBJECTIVE

To evaluate and compare the efficacy, infusion rate and recovery profile of vecuronium and cisatracurium continuous infusion in critically ill children requiring mechanical ventilation.

DESIGN AND SETTING

Prospective, randomised, double-blind, single-centre study in critically ill children in a paediatric intensive care unit in a tertiary children's hospital.

METHODS

Thirty-seven children from 3 months to 16 years old (median 4.1 year) were randomised to receive either drug; those already receiving more than 6 h of neuromuscular blocking drugs were excluded. The Train-of-Four (TOF) Watch maintained neuromuscular blockade to at least one twitch in the TOF response. Recovery time was measured from cessation of infusion until spontaneous TOF ratio recovery of 70%.

RESULTS

The cisatracurium infusion rate in nineteen children averaged 3.9+/-1.3 microg kg(-1) min(-1) with a median duration of 63 h (IQR 23-88). The vecuronium infusion rate in 18 children averaged mean 2.6+/-1.3 microg kg(-1) min(-1) with a median duration of 40 h (IQR 27-72). Median time to recovery was significantly shorter with cisatracurium (52 min, 35-73) than with vecuronium (123 min, 80-480). Prolonged recovery of neuromuscular function (>24 h) occurred in one child (6%) on vecuronium.

CONCLUSIONS

Recovery of neuromuscular function after discontinuation of neuromuscular blocking drug infusion in children is significantly faster with cisatracurium than vecuronium. Neuromuscular monitoring was not sufficient to eliminate prolonged recovery in children on vecuronium infusions.

Development of ultra short-acting muscle relaxant agents: History, research strategies, and challenges

Author has reviewed the literature and his own work related to the chemistry, pharmacology, and clinical aspects of new muscle relaxants. Emphasis has been placed on the basic science concepts and technologies (e.g. structure-activity relationships, nicotinic receptor pharmacology, and investigation of side effects) behind the development of rapidly and short acting nondepolarizing muscle relaxants.

Physicochemical properties of neuromuscular blocking agents and their impact on the pharmacokinetic-pharmacodynamic relationship

BACKGROUND

Among the factors influencing the onset of action of neuromuscular blocking agents (NMBA), the potency (EC50) and the rate of equilibration between blood and the effect compartment (k(e0)) have been highlighted. Although these descriptors are intrinsically influenced by the physicochemical characteristics of the drug, the impact of lipid solubility, molecular weight and protein binding on pharmacokinetic-pharmacodynamic (PK-PD) descriptors has not been established for most NMBA.

METHODS

The octanol/phosphate buffer distribution coefficients (logD) of various NMBA (vecuronium, rocuronium, mivacurium isomers (cis-cis, cis-trans and trans-trans), doxacurium, cisatracurium, atracurium, succinylcholine) were determined. The free fraction for each drug was measured using an ultrafiltration technique. PK-PD descriptors were obtained from selected clinical studies. Correlations between physicochemical parameters (including molecular weight) and PK-PD descriptors were assessed by linear or multiple linear regression.

RESULTS

A wide range of log D (-4.15 for succinylcholine to 0.75 for vecuronium) and free fraction (from 31% for vecuronium to 80% for succinylcholine) is observed for NMBA. Molecular weight combined with either lipid solubility (r2=0.70; P=0.001) or free fraction (r2=0.84; P<0.001) were highly correlated with potency, while for k(e0) a greater degree of correlation was obtained when both lipid solubility and free fraction (r2=0.74; P=0.002) were included.

CONCLUSIONS

The basic characteristics of NMBAs, namely, molecular weight, lipid solubility and protein binding, are strongly associated with the kinetics of the drug response.

[Anesthesia with propofol, remifentanil and cisatracurium in renal transplantation]

A 41-year-old woman with end-stage renal insufficiency in peritoneal dialysis for 3 years received a kidney transplant under anesthesia with remifentanil, propofol, and cisatracurium. She had a history of hypertension and was being treated with enalapril, metoprolol and erythropoietin. After anesthetic induction, blood pressure fell significantly and surgery was performed in a context of hemodynamic stability. The postoperative course was good, with a functional graft and adequate diuresis from the start. Anesthetics with minimal residual effects and as little renal toxicity as possible are ideal for use in kidney transplantation. The drugs used in this case had pharmacokinetic and pharmacodynamic properties that make them particularly appropriate for such patients.

Selecting neuromuscular-blocking drugs for elderly patients

The physiological changes that occur with increasing age can have significant effects on the pharmacokinetics of neuromuscular-blocking drugs. Changes in cardiac output can affect drug distribution and therefore the speed of onset of neuromuscular block. A decrease in muscle mass and increase in body fat with age can also affect their distribution. The deterioration in renal and hepatic function associated with aging affects the clearance and elimination of many neuromuscular-blocking drugs. The effects of these physiological changes on the pharmacokinetics of neuromuscular-blocking agents may not become apparent clinically in healthy individuals until the age of at least 75 years. There is very little evidence to suggest any alteration in the sensitivity of the neuromuscular junction to neuromuscular-blocking drugs with increasing age. Neuromuscular-blocking drugs that undergo a significant degree of organ-dependent elimination, such as pancuronium bromide, vecuronium bromide, rocuronium bromide and doxacurium chloride, may have a significantly prolonged duration of action in elderly patients. These drugs can be used safely in elderly patients if the anaesthetist is aware of their altered pharmacokinetics in this patient group. Appropriate changes must be made to drug dosage and dose intervals. As the pharmacokinetic changes can be unpredictable, monitoring of neuromuscular block is strongly advised when using these drugs in such patients. The risk of residual block occurring postoperatively after the use of pancuronium bromide increases with age. The duration of action of mivacurium chloride may also be prolonged in the elderly; this change has not been demonstrated to be a result of an alteration in plasma cholinesterase activity. In contrast, there is no evidence of an alteration in the action of suxamethonium chloride (succinylcholine chloride) with increasing age. Atracurium besilate and cisatracurium besilate undergo predominantly organ-independent elimination. Onset of block with these two drugs may be prolonged in the elderly, but their clinical duration of action does not alter significantly with age, making them particularly suitable for use in this patient group. Although atracurium besilate may cause histamine release, there is little evidence of it producing haemodynamic changes in the elderly. Its (1R,1R')-isomer, cisatracurium besilate, has very little direct or indirect cardiovascular effect and is, therefore, the most suitable nondepolarising agent to use in elderly patients.

A pharmacokinetic-pharmacodynamic model for neuromuscular blocking agents to predict train-of-four twitches

The train-of-four (TOF) stimulation pattern consists of 4 stimuli (T1, T2, T3, and T4) at 2 Hz, and is used in daily anesthesiological practice to determine the degree of relaxation caused by muscle relaxants. At a surgical levels of relaxation the degree of relaxation can be estimated by counting the number of "measurable" or "visible" muscular reactions to the 4 stimuli in the TOF stimulation pattern (TOF count). During recovery relaxation can be estimated by calculating the TOF ratio (T4/T1). Bartkowski and Epstein described a pharmacokinetic-pharmacodynamic (PK-PD) model to predict TOF ratio by modifying and extending the PK-PD model as described by Sheiner to use a hypothetical distributed effect compartment described by a median equilibration rate constant and a dispersion parameter. We extended the Bartkowski and Epstein PK-PD model to simulate all four TOF twitches by including EC50 terms for T2 and T3. We fit this model to data from the pig and compared the results to fitted models using separate PD models for each TOF twitch (extended Sheiner model). The extended Bartkowski and Epstein model fit the twitch height data from all four TOF twitches better than the extended Sheiner model and has fewer parameters.

Synthesis and structure-activity relationships of neuromuscular blocking agents

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.

Interactions of neuromuscular blocking drugs

Many drugs interact with neuromuscular blocking drugs and often enhance the induced block; this is of clinical importance for volatile anaesthetics, antimicrobials, magnesium and some more specific drugs. Difficulty in reversing the block occurs with calcium-channel blockers and polymyxin. Phenytoin, carbamazepine and other anticonvulsants may cause resistance to neuromuscular blocking drugs. Moreover, clinically important interactions are found between individual neuromuscular blockers. Giving succinylcholine after a non-depolarizing neuromuscular blocking drug prolongs the onset of succinylcholine; when non-depolarizing drugs are administered after succinylcholine their effects are prolonged. The succinylcholine block is prolonged when the drug is administered during recovery from pancuronium or following neostigmine reversal. Drugs or diseases that decrease the activity of plasma cholinesterase may prolong a succinylcholine-induced block. Finally, liver dysfunction, renal failure, disturbances of acid-base balance, change in temperature and neurological diseases all have an effect on the profile of the neuromuscular blocking drugs; the response to an induced block may be altered in patients under intensive care and those with cancer. Although knowledge of the most important theoretical interactions of neuromuscular blocking drugs is favourable, the anaesthetist should be aware that pharmacological interactions can lead to an unpredictable induced neuromuscular block in many cases in daily clinical practice. Therefore anaesthetists should become familiar with the use of neuromuscular transmission monitoring in order to manage the block correctly.

An isolated, antegrade, perfused, peroneal nerve anterior tibialis muscle model in the rat: a novel model developed to study the factors governing the time course of action of neuromuscular blocking agents

BACKGROUND

A model of an antegrade, perfused, isolated rat peroneal nerve anterior tibial muscle was developed to study potentially important factors governing the time course of action of (nondepolarizing) neuromuscular blocking agents such as concentration, blood flow, and temperature. The model allows observation of the effects of selective changes in these factors.

METHODS

The authors isolated the anterior tibial muscle and cannulated the anterior tibial artery and vein, providing a way for single-pass perfusion with blood from a donor rat. A force transducer was connected to the tibialis anterior muscle and a stimulator was connected to the tibial nerve. The influence of intrinsic potency (EC90) and muscle blood flow rate on the time course of pancuronium and rocuronium was investigated.

RESULTS

The model remained stable for at least 4 h with respect to twitch height, muscle structure and function, and blood chemistry. Doubling the muscle-blood flow resulted in a significantly faster onset and offset for both pancuronium and rocuronium. Trebling the intrinsic potency (EC90) was not associated with significant changes in the time course of action of the relaxants.

CONCLUSION

The authors developed and validated a model that allows us to study biophase kinetics of neuromuscular blocking agents in the anterior tibial muscle of the rat. In this model, muscle-blood flow rather than EC90 appears to predominantly determine the onset and offset time of nondepolarizing muscle relaxants.

Muscle relaxants suitable for day case surgery

Neuromuscular blocking agents are used as adjuvants in day case anaesthesia to facilitate tracheal intubation and/or surgery. Although the majority of day case procedures are performed without the use of neuromuscular blocking agents, there are procedures, such as laparoscopic surgery, microsurgery, open eye surgery, some ear, nose and throat procedures and some paediatric procedures, which may require neuromuscular blockade. The characteristics of an ideal neuromuscular blocking agent for day case surgery are a short onset, a short clinical duration and a short recovery time, with or without reversal. It should also lack histamine release, provide haemodynamic stability, and be competitively priced. This paper reviews the neuromuscular blocking agents currently available and used, such as succinylcholine and mivacurium, low doses of an intermediate-acting neuromuscular block, such as rocuronium and the recently introduced rapacuronium. Their advantages and disadvantages are described and discussed, with special reference to the needs of day case surgery. Rapacuronium offers certain benefits compared with the currently available neuromuscular blocking agents for day care anaesthesia.

Muscle relaxants in paediatric day case surgery

It has been estimated that more than 60% of all paediatric surgery is performed on a day case basis. The benefits of this type of surgery in children include reduced costs, avoidance of the stress of hospitalization and less disruption to family life. The growth of day surgery in children has been facilitated by the development of non-depolarizing neuromuscular blocking agents characterized by short and intermediate duration of action and fewer side-effects. The more rapid onset and shorter duration of action of non-depolarizing neuromuscular blocking agents in children should facilitate the use of these agents in place of succinylcholine for day case procedures.

Neuromuscular blocking drugs in pediatric anesthesia

There are differences between pediatric patients and adults in the responses to neuromuscular blockers. The results of new studies of neuromuscular blockers in pediatric patients are generally consistent with earlier studies in the type of age-related differences documented. Surprising new results are the side effects, including anaphylaxis, that have been observed, and studied directly, in pediatric patients. Continued evaluation of these drugs in pediatric patients will provide better information regarding the variability of the effects of neuromuscular blockers in healthy and diseased infants and children.

Dose requirements and recovery profile of an infusion of cisatracurium during liver transplantation

STUDY OBJECTIVE

To examine the dose requirements and recovery profile of an infusion of cisatracurium during liver transplantation.

DESIGN

Open-label, descriptive study.

SETTING

University hospital.

PATIENTS

6 ASA physical status III and IV patients with end-stage liver disease, undergoing liver transplantation.

INTERVENTIONS

Neuromuscular transmission was monitored electromyographically. After recovery of T1/T0 to 10%, cisatracurium was infused at an initial rate of 1.5 microg/kg/min. The infusion rate was adjusted to maintain T1/T0 at 10%. At the end of surgery, spontaneous recovery from the neuromuscular block was awaited.

MEASUREMENTS AND MAIN RESULTS

The infusion rate of cisatracurium was 1.6 +/- 0.4 microg/kg/min. Before the anhepatic phase, this rate was 1.5 +/- 0.4 microg/kg/min; during the anhepatic phase it was 1.7 +/- 0.5 microg/kg/min; and after reperfusion it was 1.9 +/- 0.4 microg/kg/min. There was a significant difference between the cisatracurium infusion rates before and after the anhepatic phase (p < 0.05). Following termination of the infusion, the time to 25% recovery of T1/T0 was 19.2 +/- 6.1 minutes, the recovery index (25% to 75%) was 28.8 +/- 7.0 minutes, and the time for the train-of-four (TOF) ratio to reach 0.7 was 50.2 +/- 7.1 minutes. The time for the TOF ratio to reach 0.9 was 61.4 +/- 6.6 minutes. There was no difference in body temperature or pH during the consecutive stages of transplantation.

CONCLUSIONS

The infusion dose requirement for cisatracurium during liver transplantation tended to be higher than previously reported in healthy patients; recovery appeared prolonged. In continuous infusion of cisatracurium during liver transplantation, the tendency toward higher dose requirements, the protracted duration of infusion, the non-Hofmann elimination and/or other pharmacokinetic changes during transplantation might influence recovery from the neuromuscular block. Potential temperature or pH change during surgery seemed irrelevant in explaining the delayed recovery.

Liquid chromatography/mass spectrometric bioanalysis of a modified gamma-cyclodextrin (Org 25969) and Rocuronium bromide (Org 9426) in guinea pig plasma and urine: its application to determine the plasma pharmacokinetics of Org 25969

A sensitive and specific liquid chromatography/mass spectrometry (LC/MS) method has been developed and validated for the quantification of the modified gamma-cyclodextrin Org 25969 and Rocuronium bromide (Roc or Org 9426) in the plasma and urine of guinea pigs. The assay was linear and reproducible over the range 25-10000 ng/mL for both compounds. The lowest limit of quantification (LLOQ) for both compounds in urine was 25 ng/mL. In plasma, the LLOQ was 25 ng/mL for Org 9426 and 50 ng/mL for Org 25969. The inter- and intra-day variation was lower than 20%. The physicochemical properties of both compounds imposed different modes of extraction from plasma. The modified gamma-cyclodextrin was extracted by trifluoroacetic acid (TFA) precipitation while Rocuronium was extracted by acetonitrile precipitation. Both compounds were quantified in urine by direct injection onto the column. The LC/MS analyses of Org 25969 and Org 9426 were performed using two different assay conditions. It was not possible to quantify the complex of cyclodextrin and Roc as it dissociated on the LC column. The use of LC/MS conferred great advantage to the quantification of both Org 25969 and Org 9426, as they were not chromogenic enough to afford the sensitivity and specificity required for the assay.

Neuromuscular blockers in surgery and intensive care, Part 1

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.

Neuromuscular-blocking drugs. Use and misuse in the intensive care unit

The use of NMB agents for more than 24 to 48 hours in critically ill patients is associated with many potential complications. Neuromuscular-blocking drugs should be used only when their use is essential for optimal patient care. The indications for neuromuscular blockade must be defined clearly, and patients should be evaluated during treatment for the need for continued muscle relaxation. The smallest doses of NMB agents that will accomplish clinical goals should be used. This dosage can be determined through clinical evaluations and peripheral nerve monitoring. It is essential that all patients treated with NMB drugs receive appropriate sedation and analgesia. Myopathies, neuropathies, and alterations of the neuromuscular junction can occur in the ICU setting, and nondepolarizing muscle relaxants seem to be involved in the development of these disorders. Clinicians should be aware of risk factors that may predispose certain patients to neuromuscular complications, including sepsis and the use of high-dose steroids. Neuromuscular-blocking agents should be avoided in these patients if possible. Although not proved, early recognition and treatment of iatrogenic neuromuscular complications may improve patient outcome.

The pharmacokinetics of cisatracurium in patients with acute respiratory distress syndrome

Continuous neuromuscular blockade is often necessary in patients being treated for acute respiratory distress syndrome (ARDS) to optimize oxygenation. In this study, neuromuscular blockade (no response to two responses at the train-of-four stimulation at the orbicularis oculi muscle) was achieved in six patients with ARDS by a continuous infusion of cisatracurium. The plasma concentration of cisatracurium during the infusion averaged 1.00 (0.25-1.45) microg/mL, expressed as median (range). The clearance and half-life were 6.5 (3.3-7.6) mL. min(-1). kg(-1) and 25 (16-48) min, respectively. The laudanosine plasma concentrations were 0.70 (0.12-1.20) microg/mL. The pharmacokinetic variables of cisatracurium are similar to those of patients without organ failure undergoing elective surgery. Plasma laudanosine levels always remained well less that those associated with seizure activity in animal models. Long-term infusion of cisatracurium was not associated with any side effects. Cisatracurium is a suitable muscle relaxant when deep and continuous levels of muscle relaxation are required in patients treated for ARDS.

IMPLICATIONS

We studied the pharmacokinetics of cisatracurium in six patients treated for respiratory distress syndrome by continuous muscle relaxation. A deep degree of neuromuscular blockade corresponding to abolition of two responses at the orbicularis oculi to train-of-four stimulation was obtained in all patients. The pharmacokinetic variables observed in these severely ill patients were similar to those of anesthetized patients. No accumulation of laudanosine was seen. Cisatracurium appears to be suitable when continuous muscle relaxation is required in critically ill patients.

Gas chromatographic-mass spectrometric assay for rocuronium with potential for quantifying its metabolite, 17-desacetylrocuronium, in human plasma

A rapid, sensitive and selective method has been developed for the quantification of plasma concentrations of neuromuscular blocking drug, rocuronium, using gas chromatography with mass spectrometric detection. 3-Desacetylvecuronium served as the internal standard. The method involved iodide ion pair formation and a single-step liquid-liquid extraction with dicholoromethane. This method also permits simultaneous determination of its putative metabolite, 17-desacetylrocuronium, although the high detection limit for the metabolite limits the practical application of this method in pharmacokinetic study of the metabolite. The extraction efficiency was approximately 75% for rocuronium and approximately 50% for 17-desacetylrocuronium. The limit of quantification was 26 ng/ml for rocuronium and 870 ng/ml for its metabolite. The assay was used successfully in a patient undergoing liver transplantation and receiving rocuronium as a constant rate infusion and in a patient undergoing general elective surgery receiving the drug as an intravenous bolus. This assay is a time-saving alternative to published gas or liquid chromatographic methods for assaying rocuronium.

[Recovery of neuromuscular block after continuous infusion of cisatracurium in patients with renal dysfunction]

OBJECTIVE

Study of the recovery of neuromuscular block after continuous infusion of cisatracurium in patients with renal dysfunction.

STUDY DESIGN

Prospective case-control study.

PATIENTS

Forty adult patients scheduled for urological surgery were assigned to two groups according to the creatinine clearance (CC) as a measure of the renal function: group IR (CC < 60 mL.min-1) or group NR (CC > or = 60 mL.min-1).

METHODS

After premedication with hydroxyzine, anaesthesia was induced with propofol, sufentanil and cisatracurium (0.15 mg.kg-1), and maintained using isoflurane, sufentanil and a continuous infusion of cisatracurium (0.12 mg.kg-1.h-1) adjusted for maintained a post-tetanic count < or = 5. Neuromuscular transmission was monitored at the adductor pollicis using accelerography (TOF Gard). Onset and recovery times in both groups were compared using Student's t test.

RESULTS

Infusion time and total dose of cisatracurium were comparable in both groups. Onset times were 3.9 +/- 0.8 min and 3.5 +/- 0.6 min in groups IR and NR respectively. After the infusion, the time to train-of-four ratio of 0.8 were not different in both groups: 77 +/- 18 min (group IR) and 73 +/- 13 min (group NR). However, the spontaneous recovery intervals 25%-75% were delayed in group IR (20 +/- 9 min vs 14 +/- 5 min p < 0.05).

CONCLUSION

There are minor differences in the pharmacodynamics of cisatracurium between patients with normal or impaired renal function. Nevertheless, a marked interindividual variability in the recovery parameters was observed in patients with renal dysfunction.

[The effect of anesthetic technique on recovery from neuromuscular blockade with cisatracurium]

OBJECTIVES

To assess the effect of four anesthetic techniques on recovery after a single dose of 0.2 mg/kg of cisatracurium.

PATIENTS AND METHOD

After giving informed consent, 96 patients of both sexes, ASA I-III, were enrolled. Anesthesia was induced with fentanyl, propofol O2-N2O (FiO2 40%) after which the patients were randomly assigned to four groups according to maintenance technique: propofol by infusion, sevoflurane, desflurane or isoflurane at 1.3 MAC. Neuromuscular block was monitored (electromyographic recording of the pollicis adductor). Variables recorded were time of maximum block, duration of action of 1% and 25%, and recovery indices at T0-TR75 andT25%-T75%. ANOVA was performed ( = 0.05 and beta = 0.1).

RESULTS

The groups were homogeneous. Time until recovery of 25% of baseline amplitude of the first response to a train of four (TOF) (T1) was longer in the desflurane group (68.4 +/- 11.1 min) than in the propofol group (60.2 +/- 9.4 min; p < 0.05). Time until recovery of 75% of the TOF-ratio was longer in the sevoflurane (96.8 +/- 13.1 min), desflurane (101.5 +/- 14.4 min) and isoflurane (94.1 +/- 13.9 min) groups than in the propofol group (83.7 +/- 1.3 min) (p < 0.0001). Times until recovery of T1 up to 1% were not statistically different: 45.8 +/- 10.7 (propofol), 50.6 +/- 11.0 (sevoflurane), 51.3 +/- 11.5 (desflurane) and 46.5 +/- 11.2 min (isoflurane). The 25% - 75% recovery index was also similar at 19.0 +/- 9.3 (propofol), 20.0 +/- 5.1 (sevoflurane), 25.7 +/- 12.4 (desflurane) and 20.9 +/- 7.9 (isoflurane).

CONCLUSIONS

The inhaled anesthetics studied prolong the duration of clinical effect of cisatracurium more than does propofol.

Pharmacokinetic studies of neuromuscular blocking agents: good clinical research practice (GCRP)

In September 1997, an international consensus conference on standardization of studies of neuromuscular blocking agents was held in Copenhagen, Denmark. Based on the conference, a set of guidelines for good clinical research practice (GCRP) in pharmacokinetic studies of neuromuscular blocking agents is presented. Guidelines include: design of the study; relevant patient groups to investigate; test drug administration, sampling and analysis; pharmacokinetic analysis; pharmacokinetic/pharmacodynamic modeling; population pharmacokinetics; statistics; and presentation of pharmacokinetic data. The guidelines are intended to aid those working in this research area; it is hoped that they will assist researchers, editors of scientific papers, and pharmaceutical companies in improving the quality of pharmacokinetic studies.

Structure-pharmacokinetics relationship of series of aminosteroidal neuromuscular blocking agents in the cat

To obtain more insight in the relationship between physicochemical properties of neuromuscular blocking agents (NMBAs) and their pharmacokinetic characteristics, a series of 12 aminosteroidal NMBAs, supplemented with data on five related NMBAs from the literature, was investigated in anaesthetized cats. After i.v. bolus injection, plasma concentration decreased very rapidly, showing a biphasic pattern, with half-lives ranging from 0.4 to 1.4 min, and from 3 to 10 min, respectively. Clearance was in the range from 24 to 58 ml. min(-1). kg(-1). Compounds containing an acetyl-ester group at position 3 were partly metabolized to the 3-OH derivative. The urinary excretion of the parent drug and metabolites amounted to <10% for each of the compounds. The parent drugs were excreted in large amounts into bile, along with smaller amounts of 3-OH derivatives. The terminal half-life of the urinary and biliary excretion rate were markedly longer than the apparent terminal half-life in plasma, ranging from 11 to 40 min, and from 119 to 489 min in urine and bile, respectively. Lipophilicity of the NMBAs, expressed as the partition coefficient octanol/Krebs (log P), was found to be correlated positively with unbound plasma clearance and unbound initial plasma clearance, and negatively with plasma half-life, volume of distribution at steady state, and mean residence time. The increase of the unbound plasma clearance with increasing lipophilicity is counteracted by the concurrent increase in plasma protein binding.

Binding properties of (3)H-PbTx-3 and (3)H-saxitoxin to brain membranes and to skeletal muscle membranes of puffer fish Fugu pardalis and the primary structure of a voltage-gated Na(+) channel alpha-subunit (fMNa1) from skeletal muscle of F. pardalis

The dissociation constants for (3)H-saxitoxin to brain membranes and to skeletal muscle membranes of puffer fish Fugu pardalis have been estimated to be 190- and 460-fold, respectively, larger than those to corresponding membranes of rat, by a rapid filtration assay, while these values for (3)H-PbTx-3 have been estimated to be one-third and one-half of those to rat, respectively. We have obtained a cDNA, encoding an entire voltage-gated Na(+) channel alpha-subunit (fMNa1, 1880 residues) from skeletal muscle of F. pardalis by composition of the fragments obtained from cDNA library and RT-PCR products. In fMNa1 protein, the residues for ion-selective filter and voltage sensor and the charged residues in SS2 regions of domains I-IV were conserved, but the aromatic amino acid (Phe/Tyr), commonly located in the SS2 region of domain I of tetrodotoxin-sensitive Na(+) channels, was replaced by Asn. With this particular criterion, we propose that the fMNa1 protein is a tetrodotoxin-resistant Na(+) channel.

Controversies in anaesthesia--designer drugs

In the past, the discovery of new drugs often occurred by chance. Over recent years, an increasing knowledge of the mode of drug action and receptor sites has improved our ability to design new drugs. While the mode of action of volatile and intravenous anaesthetic agents remains unclear, neuromuscular blocking agents and opioids have undergone considerable development and design. Drugs are being tailored to produce fewer side effects and to improve desirable properties. As a result, the introduction of new drugs has helped to improve techniques in anaesthesia. The development of remifentanil is an example of this which is discussed. The application of modern technology with target controlled infusions (TCI) for the administration of remifentanil represents further advancement in techniques which may become available to anaesthetists in the future.

Do plasma concentrations obtained from early arterial blood sampling improve pharmacokinetic/pharmacodynamic modeling?

In pharmacokinetic/pharmacodynamic (PK/PD) modeling the first blood sample is usually taken 1 to 2 min after drug administration (late sampling). Therefore, investigators have to extrapolate the plasma concentration to Time 0. Extrapolation, however, erroneously assumes instantaneous and complete mixing of drug in the central volume of distribution. We investigated whether plasma concentrations obtained from early arterial blood sampling would improve PK/PD modeling. In 14 pigs, one of five neuromuscular blocking agents (NMBAs) was administered into the right ventricle within 1 sec and arterial sampling was performed every 1.2 sec (1st min). The response of the tibialis muscle was measured mechanomyographically. The influence of inclusion of data from early arterial sampling on PK/PD modeling was determined. Furthermore, the concentrations in the effect compartment at 50% block (EC50) derived from modeling were compared to the measured concentration in plasma during a steady state 50% block. A very high peak in arterial plasma concentration was seen within 20 sec after administration of the NMBA. Extensive modeling revealed that plasma concentrations obtained from early arterial blood sampling improve PK/PD modeling. Independent of the type of modeling, the EC50 and KeO based on data sets that include early arterial blood sampling were, for all five NMBAs, significantly higher and lower respectively, than those based on data sets obtained from late sampling. Early arterial sampling shows that the mixing of the NMBA in the central volume of distribution is incomplete. A parametric PD (sigmoid Emax) model could not describe the time course of effect of the NMBAs adequately.

Adjuncts to analgesia. Sedation and neuromuscular blockade

This article provides an overview of some of the current issues involved in sedation and anxiolysis in the intensive care unit. The problems involved in trying to monitor sedation levels are discussed, as are some of the newer options available for physiologic monitoring of the central nervous system. The problem of abnormal mental states in the intensive care unit and the range of antidepressant therapy now available are also covered. The importance of sleep deprivation and the properties of the neuromuscular blockers are also discussed.

Comparative clinical pharmacology of rocuronium, cisatracurium, and their combination

BACKGROUND

The comparative clinical pharmacology of cisatracurium and rocuronium and their combinations has not been reported. In this study, the authors compared the relative potency and the clinical profile and characterized the interaction of both drugs.

METHODS

Two hundred twenty adults classified as American Society of Anesthesiologists physical status I and anesthetized with propofol-fentanyl-nitrous oxide were studied. In part 1, the neuromuscular-blocking effects of cisatracurium and rocuronium were assessed after administration of bolus doses of 20-50 microg/kg and 100-300 microg/kg, respectively. In part 2, we compared the time course of 1xED50, 1, 1.5, and 2xED95 doses of both drugs (where ED50 and ED95 are, respectively, the doses producing 50% and 95% depression of the first twitch height [T1]). In part 3, equieffective combinations of both drugs were studied to characterize their interaction.

RESULTS

The calculated ED50 values and their 95% confidence intervals were 111 (107-115) and 26.2 (25.8-26.5) microg/kg [corrected] for rocuronium and cisatracurium, respectively. Compared with equipotent doses of cisatracurium, rocuronium had a faster onset, and a faster spontaneous T1 and train-of-four recovery times that were significant except at maximum recovery with the 2xED95 dose. The interaction between rocuronium and cisatracurium was synergistic, and the time profile of the combination group was different from that of the single-dose groups.

CONCLUSIONS

Cisatracurium is four to five times more potent than rocuronium. Rocuronium had a faster onset of action, a shorter clinical duration, and a faster spontaneous recovery rate compared with equipotent doses of cisatracurium.

Pharmacokinetics and pharmacodynamics of cisatracurium after a short infusion in patients under propofol anesthesia

Fourteen patients, ASA physical status I or II, were recruited to assess the pharmacokinetic-pharmacodynamic relationship of cisatracurium under nitrous oxide/sufentanil/propofol anesthesia. The electromyographic response of the abductor digiti minimi muscle was recorded on train-of-four stimulation of the ulnar nerve. A 0.1-mg/kg dose of cisatracurium was given as an infusion over 5 min. Arterial plasma concentrations of cisatracurium and its major metabolites were measured by using high-performance liquid chromatography. A nontraditional two-compartment pharmacokinetic model with elimination from central and peripheral compartments was used. The elimination rate constant from the peripheral compartment was fixed to the in vitro rate of degradation of cisatracurium in human plasma (0.0237 min(-1)). The mean terminal half-life of cisatracurium was 23.9+/-3.3 min, and its total clearance averaged 3.7+/-0.8 mL x min(-1) x kg(-1). Using this model, the volume of distribution at steady state was significantly increased compared with that obtained when central elimination only was assumed (0.118+/-0.027 vs 0.089+/-0.017 L/kg). The effect-plasma equilibration rate constant was 0.054+/-0.013 min(-1). The 50% effective concentration (153+/-33 ng/mL) was 56% higher than that reported in patients anesthetized with volatile anesthetics, which suggests that, compared with inhaled anesthetics, a cisatracurium neuromuscular block is less enhanced by propofol.

IMPLICATIONS

The drug concentration-effect relationship of the muscle relaxant cisatracurium has been characterized under balanced and isoflurane anesthesia. Because propofol is now widely used as an IV anesthetic, it is important to characterize the biological fate and the concentration-effect relationship of cisatracurium under propofol anesthesia as well.

The effects of aging on anesthetic pharmacology

Aging alters both the pharmacokinetic and the pharmacodynamic aspects of anesthetic requirement. Studies of the relationship between drug concentration and effect in older adults clearly demonstrate a decline in median effective dose requirement for agents that act within the central nervous system, but there appears to be little change in the dose required for peripheral effects such as neuromuscular blockade. Most drugs also undergo somewhat slower biotransformation and demonstrate prolonged clinical effects if they require hepatic or renal degradation, although many newer agents such as remifentanil and cisatracurium have organ-independent pathways that are not affected by age. In some cases, however, the appearance of increased sensitivity to a given dose of anesthetic or opiate may actually reflect higher-than expected plasma concentrations of drug following a rapid intravenous injection. Therefore, it is impossible to completely separate the interactions between pharmacodynamic and pharmacokinetic factors associated with aging. The use of pharmacological sympathectomy with intrathecal agents and with sympatholytic adrenergic agonists may further improve outcome in a patient population at high risk because of reduced functional reserve, increased incidence of polypharmacy, and the consequences of age-related disease.