Radiofrequency ablation versus surgical resection for the treatment of oligometastatic lung disease

PURPOSE

The purpose of this study was to compare efficacy and tolerance between radiofrequency ablation (RFA) and surgery for the treatment of oligometastatic lung disease.

MATERIALS AND METHODS

This retrospective study reviewed patients treated in two institutions for up to 5 pulmonary metastases with a maximal diameter of 4cm and without associated pleural involvement or thoracic lymphadenopathy. Patient demographics, tumor characteristics, treatment outcome, and length of hospital stay were compared between the two groups. Efficacy endpoints were overall survival (OS), progression-free survival (PFS) and pulmonary or local tumor progression rates.

RESULTS

Among 204 patients identified, 78 patients (42 men, 36 women; mean age, 53.3±14.9 [SD]; age range: 15-81 years) were treated surgically, while 126 patients (59 men, 67 women; mean age, 62.2±10.8 [SD]; age range: 33-80 years) were treated by RFA. In the RFA cohort, patients were significantly older (P<0.0001), with more extra-thoracic localisation (P=0.015) and bilateral tumour burden (P=0.0014). In comparison between surgery and RFA cohorts, respectively, the 1- and 3-year OS were 94.8 and 67.2% vs. 94 and 72.1% (P=0.46), the 1- and 3-year PFS were 49.4% and 26.1% vs. 38.9% and 14.8% (P=0.12), the pulmonary progression rates were 39.1% and 56% vs. 41.2% and 65.3% (P>0.99), and the local tumour progression rates were 5.4% and 10.6% vs. 4.8% and 18.6% (P=0.07). Tumour size>2cm was associated with a significantly higher local tumor progression in the RFA group (P=0.010). Hospitalisation stay was significantly shorter in the RFA group (median of 3 days; IQR=2 days; range: 2-12 days) than in the surgery group (median of 9 days; IQR=2 days; range: 6-21 days) (P<0.01).

CONCLUSION

RFA should be considered a minimally-invasive alternative with similar OS and PFS to surgery in the treatment of solitary or multiple lung metastases measuring less than 4cm in diameter without associated pleural involvement or thoracic lymphadenopathy.

Impact of peripheral elimination on the concentration-effect relationship of remifentanil in anaesthetized dogs

BACKGROUND

This study elucidates the impact of sampling site when estimating pharmacokinetic-pharmacodynamic (PK-PD) parameters of drugs such as remifentanil that undergo tissue extraction in the biophase. The interrelationship between the concentrations of remifentanil predicted for the effect compartment and those measured in arterial, venous, and cerebrospinal fluid were investigated under steady-state conditions.

METHODS

Following induction of anaesthesia with pentobarbital, an arterial cannula (femoral) and two venous catheters (jugular and femoral) were inserted. Electrodes were placed for EEG recording of theta wave activity. Each dog received two consecutive 5-min infusions for the PK-PD study and a bolus followed by a 60-min infusion was started for the steady-state study. Cerebrospinal fluid, arterial and venous blood samples were drawn simultaneously after 30, 40, and 50 min. At the end of the infusion, arterial blood samples were collected for pharmacokinetic analysis.

RESULTS

Remifentanil PK-PD parameters based on theta wave activity were as follows: apparent volume of distribution at steady-state (V(ss)) (231+/-37 ml kg(-1)), total body clearance (Cl) (63+/-16 ml min(-1) kg(-1)), terminal elimination half-life (t(1/2 beta)) (7.71 min), effect compartment concentration at 50% of maximal observed effect (EC(50)) (21+/-13 ng ml(-1)), and equilibration rate constant between plasma and effect compartment (k(e0)) (0.48+/-0.24 min). The mean steady-state cerebrospinal fluid concentration of 236 ng ml(-1) represented 52 and 74% of that in arterial and venous blood, respectively.

CONCLUSIONS

Our study re-emphasizes the importance of a sampling site when performing PK-PD modelling for drugs undergoing elimination from the effect compartment. For a drug undergoing tissue elimination such as remifentanil, venous rather than arterial concentrations will reflect more exactly the effect compartment concentrations, under steady-state conditions.

Interstitial muscle concentrations of rocuronium under steady-state conditions in anaesthetized dogs: actual versus predicted values

INTRODUCTION

The objective of this study was to compare rocuronium effect (C(e)) and peripheral (C(2)) compartment concentrations predicted by pharmacokinetic-pharmacodynamic (PK-PD) modelling with those measured in plasma (C(p)) and in the interstitial fluid of muscle tissue (C(ISF,u)) by microdialysis in anaesthetized dogs.

METHODS

After approval by the Animal Care Committee, eight adult male dogs with a body weight ranging from 7 to 18 kg were anaesthetized with pentobarbital. Each dog received a 2-min rocuronium infusion of 0.15 mg kg(-1) min(-1) followed by a 118-min infusion of 60 microg kg(-1) min(-1) via the right jugular vein. Arteriovenous gradient across the hindlimb was measured at 40, 60, 100 and 120 min. Three microdialysis samples were collected at 40-min intervals. Once the infusion stopped, arterial samples were collected every 2 min for the first 10 min and every 20 min for the next 120 min. Neuromuscular function was monitored using train-of-four stimulation until full recovery. Dogs were then killed and a biopsy of muscle tissue was performed (C(m)).

RESULTS

At steady state, the mean C(ISF,u) value was 1353 ng ml(-1). After correction for the unbound fraction in plasma, the mean C(e,corr) and C(2,corr) were 1681 and 1481 ng ml(-1), respectively. At the terminal sampling point, C(m) was 10-fold higher than C(p).

CONCLUSION

Unbound concentration of rocuronium measured in the muscle interstitial fluid under steady-state conditions confirms that parametric PK-PD modelling gives reliable estimates of effect site concentrations. Rocuronium accumulates in muscle tissue, probably by non-specific protein binding in the interstitial space.

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.

Simultaneous solid-phase extraction combined with liquid chromatography with ultraviolet absorbance detection for the determination of remifentanil and its metabolite in dog plasma

To establish pharmacokinetic/pharmacodynamic relationships, a selective and specific high-performance liquid chromatographic method was developed for the quantitation of remifentanil and its metabolite in dog plasma. The assay involves a solid-phase extraction and a reversed-phase chromatographic separation with ultraviolet detection (lambda=210 nm). The calibration curves are linear in the range of 7.89-1500 ng ml(-1). Intra-day assay variability is less than 7% for all standards evaluated. Good recovery, linearity, accuracy, and precision were achieved with the assay that proved readily applicable to pharmacokinetic studies in dogs.

Stereoselective in vitro degradation pattern of mivacurium in human plasma

BACKGROUND

Mivacurium is a mixture of three isomers, two of which are rapidly broken down in vivo by plasma cholinesterases. This study investigates the stereospecificity of mivacurium in vitro degradation to determine if it accounts for its in vivo behaviour.

METHODS

The in vitro rate of degradation of each isomer of mivacurium and the in vitro rate of formation of their primary (monoesters and alcohols) and secondary (alcohols) metabolites were examined using human plasma from six healthy volunteers. The in vitro rate of degradation of the monoester metabolites was also assessed. All these determinations were made using a stereospecific high-performance liquid chromatography assay.

RESULTS

The in vitro rate of disappearance of the two active isomers of mivacurium was very rapid, with mean values for the trans trans and cis trans isomers of 0.803 and 0.921 min(-1) respectively. These values are twofold faster than published in vivo data. The in vitro rate of disappearance was much slower for the cis cis isomer, with a mean value of 0.0106 min(-1). The cis trans isomer was converted exclusively to cis monoester and trans alcohol, while only metabolites in the trans and cis configuration were found for the trans trans and cis cis isomers respectively. Mean in vitro rates of disappearance for the trans and cis monoester were 0.00750 and 0.000633 min(-1) respectively.

CONCLUSIONS

The in vitro rates of hydrolysis of the active isomers of mivacurium confirm that plasma cholinesterases play a major role in their in vivo degradation, but that in vivo elimination is slowed by extravascular distribution. Mivacurium hydrolysis is stereoselective, the ester group in the trans configuration being more accessible to enzymatic attack. This stereoselective pattern, along with the relatively slow breakdown of the cis cis isomer, sheds light on the in vivo disposition of the cis alcohol metabolite.

Response to mivacurium in a patient compound heterozygous for a novel and a known silent mutation in the butyrylcholinesterase gene: genotyping by sequencing

BACKGROUND

Patients who are homozygous for the atypical mutation, compound heterozygous for atypical and silent mutations, or homozygous for silent mutations (SS) respond to mivacurium with extensively prolonged neuromuscular block. Although important, exact phenotyping of these patients is difficult. This article presents the pharmacodynamics and pharmacokinetics of a normal dose of mivacurium in a patient with phenotype SS, including a pedigree analysis and delineation of the molecular genetic method used to identify the genotype.

METHODS

The neuromuscular block following administration of mivacurium, at a dose of 0.14 mg/kg, was monitored in a 30-yr-old healthy man with use of a mechanosensor and mechanomyography, and times to different levels of recovery were measured. Venous samples for determination of the mivacurium isomers were collected during the interval 134-494 min after administration of mivacurium, and the terminal half-lives were calculated. Butyrylcholinesterase activity, phenotype, and genotype were determined for both the patient and the family. Complete nucleotide sequencing was used to identify the genotype.

RESULTS

A train-of-four ratio of 0.75 was reached 469 min after the injection of mivacurium. The terminal elimination half-lives of the mivacurium isomers, cis-trans and trans-trans, were 90 min. Complete nucleotide sequencing revealed two point mutations, the known silent variant S7 and a previously undescribed mutation of amino acid residue 170 introducing a stop codon.

CONCLUSIONS

The patient was compound heterozygous for silent mutations in the butyrylcholinesterase gene. The response to mivacurium was an extensively prolonged duration of action. Identification of the rare silent mutations presupposes access to modern molecular genetic methods such as complete nucleotide sequencing.

Concentration-effect relationship of cisatracurium at three different dose levels in the anesthetized patient

BACKGROUND

The linearity of cisatracurium elimination and its concentration-effect relation were determined as part of a traditional rich data study with three dose levels in patients receiving balanced anesthesia.

METHODS

Forty-eight adults with American Society of Anesthesiologists status I-II were randomized to receive an intravenous bolus dose of 0.075, 0.15, or 0.30 mg/kg cisatracurium. Anesthesia was induced and maintained with nitrous oxide-oxygen, propofol, and fentanyl. The mechanical response of the adductor pollicis muscle was recorded. Arterial blood samples were collected over 8 h. Cisatracurium, laudanosine, and the monoquaternary alcohol concentrations were measured by high-performance liquid chromatography. To assess the relative contribution of the input function, a parametric (assuming elimination from both the central and peripheral compartments) and a nonparametric pharmacokinetic-pharmacodynamic model were both applied to data.

RESULTS

Dose proportionality of the body disposition of cisatracurium and its two major metabolites at doses up to 0.30 mg/kg was confirmed. With the parametric approach, the effect compartment concentration at 50% block (EC50) significantly increased with the dose (136 vs. 157 vs. 209 ng/ml), whereas the effect compartment equilibration rate constant decreased (0.0675 vs. 0.0568 vs. 0.0478 min(-1)). A similar dose-dependent effect of the pharmacokinetic-pharmacodynamic relation was observed with the nonparametric approach, but the trend was 50% less pronounced.

CONCLUSION

A dose-related change in pharmacokinetic-pharmacodynamic parameters was identified with both modeling approaches. A pharmacokinetic origin was ruled out, although no definite explanation of the underlying mechanism could be provided. These findings suggest that doses relevant to the anesthetic practice be used for estimation of EC50.

Measurement of succinylcholine concentration in human plasma by electrospray tandem mass spectrometry

An electrospray mass spectrometric method for the quantification of the depolarizing neuromuscular blocking agent succinylcholine (SUX) is described. An extraction method compatible with direct infusion inlet was developed and leads to an analysis cycle time of 7--8 min instead of 25 min that would be required for HPLC inlet. SUX was extracted from human plasma on C1 solid-phase cartridges and was analyzed using positive ion electrospray tandem mass spectrometry (ESI-MS/MS). SUX plasma concentrations were determined by a stable isotope dilution assay using hexadeuterosuccinylcholine diiodide (SUXd6) as the internal standard. The calibration curve was prepared using the ratio of intensities of the major product ions in the collision-induced dissociation spectrum for known concentration ratios of SUX and SUXd6 in plasma. Calibration curves for the quantification were linear from 25 to 4000 ng/ml. For intraday precision, CV were < or =6% and accuracy ranged from 98 to 103%. For the interday precision, CV were < or =10% and accuracy ranged from 90 to 102%. This method is specific, sensitive, reproducible, and practical in a clinical setting.

Peripheral link model as an alternative for pharmacokinetic-pharmacodynamic modeling of drugs having a very short elimination half-life

Attempts to obtain estimates of pharmacokinetic-pharmacodynamic (PK-PD) parameters for mivacurium with traditional central link models were unsuccessful in many patients. We hypothesized that a link model with the peripheral compartment would be more appropriate for mivacurium in view of its extremely rapid plasma clearance and its potential elimination by tissue pseudocholinesterases. For validation purposes, the peripheral link model was applied to other neuromuscular blocking agents (NMBA), i.e., atracurium and doxacurium which have respectively an intermediate and a long elimination half-life. Assuming peripheral elimination in PK-PD modeling was investigated but found to have no impact on the estimation of PK-PD parameters. Our results indicate that, for drugs having intermediate and long elimination half-lives, EC50 values are similar with either the central or peripheral link model. For mivacurium, a peripheral link model enables PK-PD modeling in all subjects, with more precision in the PK-PD parameter estimates and a better fitting of the effect data when compared to the central link model. For these reasons, a peripheral link model should be preferred for mivacurium.

Vecuronium pharmacokinetics and pharmacodynamics during hypothermic cardiopulmonary bypass in infants and children

PURPOSE

To determine the effect of moderate and deep hypothermic cardiopulmonary bypass (CPB) on the pharmacokinetic and pharmacodynamic behaviour of vecuronium in infants and children.

METHODS

We studied 12 patients undergoing surgery for congenital heart disease under narcotic-nitrous oxide anesthesia. Neuromuscular blockade was maintained constant (TI 4-10% by Datex electromyograph) by adjusting a vecuronium infusion. Plasma vecuronium concentrations (Cpss) were analysed by HPLC to describe a pseudosteady-state during each of the pre-CPB, CPB and post-CPB phases. Paired arterial blood samples were taken 20 min apart after at least 20 min of constant infusion.

RESULTS

Nine cases were analysed, mean age 20 mo, mean weight 9 kg. Three patients had deep and six moderate hypothermia. In the pre-CPB phase Cpss fell into two groups (mean +/- SD: 330 +/- 42 ng x ml(-1); 127 +/- 27 ng x ml(-1); P < 0.001); similarly the clearances showed a bimodal distribution (mean +/- SD: 5.08 +/- 0.94; 11.51 +/- 0.2 ml x min(-1) x kg(-1) P < 0.001), although in different patients. During CPB this bimodal distribution disappeared. Vecuronium infusion rate (VIR) decreased by 84% and 92% from pre-CPB to CPB phase in deep and moderate hypothermia groups respectively (P < 0.05), paralleled by decreases in Cpss of 36% (P > 0.05) and 52% (P < 0.05).

CONCLUSION

Changes in vecuronium requirements and plasma concentrations during CPB demonstrate that vecuronium pharmacokinetics and pharmacodynamics are both affected by hypothermic CPB in infants. The finding of bimodal distributions for plasma vecuronium and vecuronium clearance highlights the need for individual monitoring of neuromuscular blockade in this age group.

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.

Oral absorption of clarithromycin in acute illness and during convalescence in patients with community-acquired pneumonia

STUDY OBJECTIVE

To compare the extent of oral clarithromycin absorption in patients during an illness and in health.

DESIGN

Sequential two-phase prospective study including an acutely ill pneumonia phase (PP) and a subsequent convalescent phase (CP).

STUDY POPULATION

Patients >/= 18 years old with radiographically confirmed community-acquired pneumonia (CAP) who were admitted to the hospital.

METHODS

During both study phases, patients received one single 500-mg dose of oral clarithromycin. Serial blood samples were drawn over a 24-h period in order to characterize the plasma concentration-time curves. Area under the curve from zero to 24 h (AUC(0-24)), maximum plasma concentration (Cmax), and time to maximum concentration (Tmax) were determined for both clarithromycin and its metabolite, 14-hydroxyclarithromycin, and compared between the two phases.

RESULTS

Twelve patients completed both phases of the study. For clarithromycin, there was a significant increase AUC(0-24) (47.37 +/- 8.51 microg/h/mL vs 36.22 +/- 6.09 microg/h/mL) in favor of the PP. There were no significant differences detected with respect to Cmax (4.32 +/- 0.63 microg/mL vs 3.57 +/- 0.46 microg/mL), or Tmax (3.50 +/- 0.50 h vs 2.83 +/- 0.59 h) between PP and CP. For 14-hydroxyclarithromycin, the AUC(0-24) and Cmax were significantly higher (5.84 +/- 1.08 microg/h/mL vs 8.84 +/- 1.92 microg/h/mL; 0.42 +/- 0.08 microg/mL vs 0.76 +/- 0.23 microg/mL) in the CP as compared to the PP. Tmax remained unchanged.

CONCLUSION

The extent of absorption of oral clarithromycin was not diminished during an acute illness with CAP.

Assuming peripheral elimination: its impact on the estimation of pharmacokinetic parameters of muscle relaxants

For anesthetic drugs undergoing nonorgan-based elimination, there is a definite trend towards using pharmacokinetic (PK) models in which elimination can occur from both central (k10) and peripheral compartments (k20). As the latter cannot be assessed directly, assumptions have to be made regarding its value. The primary purpose of this paper is to evaluate the impact of assuming various degrees of peripheral elimination on the estimation of PK parameters. For doing so, an explanatory model is presented where previously published data from our laboratory on three muscle relaxants, i.e., atracurium, doxacurium, and mivacurium, are used for simulations. The mathematical aspects for this explanatory model as well as for two specific applications are detailed. Our simulations show that muscle relaxants having a short elimination half-life are more affected by the presence of peripheral elimination as their distribution phase occupies the major proportion of their total area under the curve. Changes in the exit site dependent PK parameters (Vdss) are also mostly significant when k20 is smaller than k10. Although the physiological processes that determine drug distribution and those affecting peripheral elimination are independent, the two are mathematically tied together in the two-compartment model with both central and peripheral elimination. It follows that, as greater importance is given to k20, the rate of transfer from the central compartment (k12) increases. However, as a result of a proportional increase in the volume of the peripheral compartment, peripheral concentrations remain unchanged whether or not peripheral elimination is assumed. These findings point out the limitations of compartmental analysis when peripheral elimination cannot be measured directly.

Determination of neostigmine in human plasma and cerebrospinal fluid by high-performance liquid chromatography with ultraviolet detection

A high-performance liquid chromatographic assay coupled with ultraviolet detection has been developed for the determination of neostigmine in human plasma and cerebrospinal fluid. A novel solid-phase extraction procedure was first used for this analyte and allowed good recovery (89+/-4.5%) together with ease and speed of execution. The method was sensitive, reproducible (C.V.<4.5%) and accurate (100+/-6.6%) over the range 2.6-167.0 ng/ml neostigmine concentrations in plasma or cerebrospinal fluid, and was applied successfully to study the pharmacokinetics of neostigmine in patients suffering from chronic postoperative abdominal pain.

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.

Determination of succinylcholine in human plasma by high-performance liquid chromatography with electrochemical detection

An alternative HPLC method for the quantification of the depolarizing neuromuscular blocking agent succinylcholine in human plasma is described. Drug spiked plasma and patient plasma samples were extracted using a C1 solid-phase cartridge. Succinylcholine was separated on a Cyano column and quantitated using electrochemical detection at a potential of 450 mV and 750 mV. Mobile phase consisted of a mixture of phosphoric acid-acetonitrile-methanol (45:35:25) adjusted to an apparent pH of 5. Standard curves for the quantitation were linear in the range of 250-8000 ng/ml. Between-day and within-day relative standard deviations were 5.1% and 1.7%, respectively. Mean drug recovery and accuracy was 68% and 104%, respectively.

Pharmacokinetics of doxacurium during normothermic and hypothermic cardiopulmonary bypass surgery

PURPOSE

To compare the pharmacokinetic behaviour of doxacurium in patients undergoing normothermic or hypothermic cardiopulmonary bypass (CPB) for coronary artery bypass graft surgery.

METHODS

Twenty patients in two equal groups were studied. Anaesthesia was induced with sufentanil and midazolam after a standard premedication. Doxacurium was administered at 3 x ED95 (80 micrograms.kg-1), and anaesthesia was maintained with 0.5 microgram.kg-1 hr-1 sufentanil, 0.05 mg.kg-1 midazolam and isoflurane 0.5-1%. Systemic temperature for patients in the normothermic and hypothermic groups was maintained at 33-36 C and 26-30 C respectively. Timed blood and urine samples were collected and pharmacokinetic parameters were estimated using a non-compartmental approach.

RESULTS

For the normothermic and hypothermic groups, terminal elimination half-life (t1/2 beta) was 100.1 +/- 28 and 183.8 +/- 60 min (P < 0.05) respectively, elimination half-life during the CPB phase (T1/2 CPB) 114.5 +/- 10 and 183.8 +/- 60 min (P < 0.05), mean residence time 108.8 +/- 25 and 164.8 +/- 34 min (P < 0.05) and apparent volume of distribution at steady state 0.20 +/- 0.03 and 0.26 +/- 0.04 L.kg-1 (P < 0.05). Compared with the hypothermic group, the normothermic group had a higher rate of renal clearance (1.40 +/- 0.4 vs 0.93 +/- 0.3 ml.min-1.kg-1; P < 0.05) and a higher value for renal clearance as a percentage of the total clearance (76.2 +/- 10 vs 58.3 +/- 20%).

CONCLUSION

The elimination rate of doxacurium during normothermic CPB is faster than that in hypothermic CPB.

Clinical pharmacokinetics of neuromuscular relaxants in pregnancy

Despite an increased in bodyweight, plasma volume by 45% and blood volume by 35% that might influence the volume of distribution of polar drugs, the apparent volume of distribution at steady state (Vss), volume of distribution (Vd) and the apparent volume of the central compartment (Vc) of atracurium, vecuronium and pancuronium are unchanged during pregnancy. With an elimination that is independent of renal, hepatic and enzymatic functions, the clearance of atracurium is also unchanged. This is corroborated by an unchanged clinical duration of atracurium during pregnancy. The clearance of pancuronium is increased by 27% during caesarean section. This may be explained by the increased glomerular filtration rate reported in pregnant women. The clinical duration of vecuronium in term and postpartum women is twice that reported in nonpregnant women. On the other hand, an increase in the clearance clearance of vecuronium during cesarean sections has been reported. The umbilical/maternal vein concentration ratio (UV/MV) of nondepolarising neuromuscular relaxants varies from 7 to 26% and clinical doses of these drugs may induce partial residual curarisation in neonates. Fetal concentrations of non-depolarising neuromuscular relaxants are proportional to the maternal dose injected as demonstrated for pancuronium and vecuronium. Increasing UV/MV with longer drug injection to delivery intervals have been demonstrated for drugs with a high molecular weight, such as atracurium, but not for those with a low molecular weight, such as vecuronium, while conflicting results have been reported for pancuronium. Despite decreased plasma pseudocholinesterases, the clinical duration of succinylcholine 1 mg/kg is unchanged in pregnant women, and only is slightly increased in postpartum women. On the other hand, larger doses of succinylcholine have induced prolonged apnoea and phase II block. The use of a pretreatment dose of a nondepolarising neuromuscular relaxant to decrease fasciculations and subsequent postoperative muscle pain is not only unnecessary in pregnant women but may be hazardous, since it may produce unexpected significant curarisation with respiratory distress. At clinical doses, transplacental passage of succinylcholine is insufficient to produce curarisation of neonates except in those born to mothers with abnormal plasma pseudocholinesterases. Magnesium sulfate, used in the treatment of pre-eclampsia, will enhance the blocking effects of nondepolarising neuromuscular relaxants but will have no effects on the characteristics of paralysis of succinylcholine. Histamine type 2 antagonists used to decrease the risk of aspiration during induction of anaesthesia do not influence the blocking properties of neuromuscular relaxants, while metoclopramide prolongs the block of succinylcholine.

Determination of ubiquinone-9 and 10 levels in rat tissues and blood by high-performance liquid chromatography with ultraviolet detection

A high-performance liquid chromatographic (HPLC) method is presented for the simultaneous detection of ubiquinone-9 and 10 in rat tissues such as blood, myocardium, and muscle. After liquid-liquid extraction, the ubiquinones are subsequently analyzed by HPLC with ultraviolet (UV) detection at their maximum absorbance (275 nm). Reference calibration curves in ethanol are used to determine tissular levels of ubiquinones. Because a treatment with HMG-CoA reductase inhibitors is expected to decrease the ubiquinone levels, reference calibration curves are performed to ensure that the ratios (ubiquinone/internal standard) observed in such an experiment could be evaluated directly on a calibration curve. The assay is sensitive (0.0625 microgram/mL), reproducible (4% coefficient of variation for ubiquinone-9 and 6% for ubiquinone-10), and linear up to 20 micrograms/mL (or 100 mg of tissue) for ubiquinone-9 and up to 10 micrograms/mL (or 100 mg of tissue) for ubiquinone-10. The ubiquinone levels in control tissues or blood are within the ranges of those previously reported.

40 Hz auditory steady-state response and EEG spectral edge frequency during sufentanil anaesthesia

PURPOSE

The auditory steady-state evoked response (ASSR) is an evoked potential which provides a sensitive measure of the effects of general anaesthetics on the brain. We used pharmacokinetic-pharmacodynamic (PK-PD) modelling to compare the effects of sufentanil on the amplitude of the ASSR with its effect on spectral edge frequency (SEF) of the electroencephalogram.

METHODS

Nine patients scheduled for elective cardiac surgery participated. Midazolam (70 micrograms.kg-1 i.m.) was given 60 min before entering the operating room. Anaesthesia was induced with 5 micrograms.kg-1 sufentanil at a rate of 0.83 microgram.kg-1.min-1. The ASSR, SEF and plasma sufentanil concentrations were measured for 30 min after induction of anaesthesia before surgery. The half-life between the central and effect site compartments (t1/2Keo), the 50% inhibitory concentration (IC50) and the slope factor (gamma) were computed.

RESULTS

The amplitude of the ASSR increased during the first three minutes of infusion of sufentanil by up to 40%. This was followed by a rapid decrease between the fourth and fifth minutes to 16% of baseline. The SEF decreased progressively during the first five minutes of infusion to 18% of baseline. Both measures subsequently showed modest recovery. The parameters gamma, IC50 and t1/2Keo for ASSR were (mean +/- SD) 6.0 +/- 3.7, 2.1 +/- 1.2 ng.ml-1 and 7.3 +/- 2.4 min. For SEF the values were 5.9 +/- 5.2, 1.4 +/- 0.7 ng.ml-1 (P < 0.05 compared with ASSR) and 6.8 +/- 2.4 min.

CONCLUSION

The sensitivity of ASSR to sufentanil is less than that of the SEF.

Pharmacokinetics of mivacurium isomers and their metabolites in healthy volunteers after intravenous bolus administration

BACKGROUND

Previous studies report the pharmacokinetics of mivacurium isomers after an infusion using venous blood sampling. Although the extent of the mivacurium arterial-venous gradient is not known, the sampling site is likely to influence mivacurium pharmacokinetic parameters because the drug is rapidly metabolized as it traverses the circulation. The objectives of this study were (1) to determine the pharmacokinetics of mivacurium isomers in healthy persons after intravenous bolus administration using intensive arterial blood sampling, and (2) to characterize the formation and elimination of mivacurium metabolites in human plasma.

METHODS

Eight persons classified as American Society of Anesthesiologists physical status 1 or 2 who were scheduled to undergo elective surgery under balanced anesthesia received 0.15 mg/kg mivacurium chloride as an intravenous bolus. Arterial blood samples were collected every 10 s during the first 2 min and at frequent intervals for 4 h thereafter. Plasma concentrations of mivacurium isomers and their metabolites were determined by two stereoselective high-performance liquid chromatographic methods coupled with fluorometric detection and noncompartmental pharmacokinetic parameters.

RESULTS

Mean elimination half-lives of the trans-trans, cis-trans, and cis-cis isomers were 2.4, 2, and 28.5 min, respectively, with corresponding mean plasma clearances of 29.2, 45.7, and 6.7 ml.min 1.kg-1. The volumes of distribution at steady state of the trans-trans, cis-trans, and cis-cis isomers were 0.047, 0.054, and 0.189 l/kg, respectively. Plasma concentrations of monoester and alcohol metabolites peaked 25 s (median) after mivacurium injection, with half-lives in the range of 90 min, except for the cis alcohol metabolite, which was only negligibly and transiently formed.

CONCLUSIONS

Substantial hydrolysis of mivacurium isomers by cholinesterases was confirmed by the rapid appearance of mivacurium metabolites in plasma. The intensive arterial sampling proved to be critical for the trans-trans and cis-trans isomers because the area under the curve between 0 and 2 min accounted for 75% and 86% of the total, respectively.

Pharmacokinetic-pharmacodynamic modeling of doxacurium: effect of input rate

One of the basic assumptions in pharmacokinetic-pharmacodynamic modeling (PK-PD) is that drug equilibration rate constant between plasma concentration and effect (Ke0) is not changed by input rate. To test this assumption in a clinical setting, a 25 micrograms/kg i.v. dose of doxacurium was administered either by bolus injection or 10-min infusion to 15 anesthetized patients. Neuro-muscular function was monitored using train-of-four stimulation of the ulnar nerve. For the short infusion dose, arterial concentrations were measured at I-min intervals during infusion and at frequent intervals thereafter. Following the iv bolus dose, the early PK profile of doxacurium was investigated by measuring doxacurium arterial concentrations every 10 sec during the first 2 min and at frequent intervals thereafter. PK-PD modeling was performed using nonparametric approach with and without including a finite receptor concentration (Rtot) in the effect compartment. Kinetic parameters were unchanged. For the bolus and the infusion, Ke0 values were 0.053 +/- 0.006 and 0.056 +/- 0.009 min-1, respectively. Using the Rtot model, corresponding Ke0 values were 0.148 +/- 0.016 and 0.150 +/- 0.024, respectively. The relatively faster Ke0 obtained with the Rtot model is compatible with the high potency of doxacurium. Our results show that PK-PD parameters derived with either a bolus or an infusion mode of administration are equally reliable.

Anticonvulsant pharmacodynamics and disposition of triazolam in rats

Triazolam (TZ) is a triazolobenzodiazepine used in the treatment of insomnia that possesses significant anticonvulsant properties. Despite the widespread use of this drug, detailed pharmacokinetic-pharmacodynamic information is lacking, especially with respect to inhibition of seizure activity. TZ disposition has been described previously by methods with limited specificity, and the concentration-anticonvulsant effect relationship has not been characterized. The current studies were undertaken to examine TZ disposition with a specific HPLC method, and to evaluate the relationship between anticonvulsant effect and concentration in Sprague-Dawley rats. TZ pharmacokinetics were characterized after bolus or infusion administration; in a separate experiment, TZ pharmacodynamics were assessed with pentylenetetrazol-induced seizures. The systemic disposition of TZ could be described with a two-compartment model; systemic clearance ranged from 2.45 to 5.30 L/h/ kg, steady-state volume of distribution ranged from 2.10 to 4.02 L/kg, and mean residence time ranged from 47 to 65 min. The concentration-effect relationship was well described by a simple Emax model: Emax, expressed as the ratio of post-TZ to pre-TZ threshold convulsant doses of pentylenetetrazol, was 9.9 +/- 0.7, and the EC50 values were 10.0 +/- 4.6 ng/mL and 34.8 +/- 9.0 ng/g in serum and whole brain tissue, respectively. Under single-dose conditions, TZ is a very potent anticonvulsant in the rat pentylenetetrazol seizure model.

Pharmacokinetic origin of carbamazepine-induced resistance to vecuronium neuromuscular blockade in anesthetized patients

BACKGROUND

Patients receiving chronic carbamazepine therapy have shortened recovery times from a neuromuscular block induced by vecuronium. The current study investigates the pharmacokinetic or pharmacodynamic mechanisms responsible for this observation.

METHODS

Pharmacokinetics and pharmacodynamics of 0.1 mg/kg intravenous bolus vecuronium in ten epileptic patients receiving chronic carbamazepine therapy were compared to that of ten control subjects. All patients were scheduled for neurosurgery while anesthetized with isoflurane and sufentanil. Arterial blood samples were collected for 6 h. Plasma vecuronium concentrations were measured by high-performance liquid chromatography coupled to electrochemical detection. The adductor pollicis force of contraction was recorded after supramaximal ulnar nerve stimulation. Plasma vecuronium concentrations were fitted to a two-compartment pharmacokinetic model, and the effect compartment equilibration rate constant was derived with a nonparametric link model. The effect compartment concentrations were fitted to a sigmoid Emax model. Results were compared using Student's t-test for independent samples.

RESULTS

In the carbamazepine group, the mean recovery times to T(1) 25% were shorter (28.1 +/- 3.4 vs. 47.3 +/- 5.1 min in control subjects; P=0.007), and the T(1) 25% to T(1) 75% recovery index was decreased (7.6 +/- 1.2 vs. 21.9 +/- 6.8 min in control subjects; P=0.025). No changes in onset times were observed. Clearance was 9.0 +/- 1.2 ml x kg-1 x min-1 versus 3.8 +/- 0.3 in the control group (P=0.003), whereas no changes in volumes of distribution at steady-state were observed. Therefore, the mean residence time was halved (17.8 +/- 2.5 vs. 31.9 +/- 2.5 min in control subjects; P=0.001). No differences in the effect compartment equilibration rate constant, vecuronium effect compartment concentration present at a 50% block (EC50), or slope of the sigmoid between the two groups were found.

CONCLUSIONS

The twofold increase in clearance provides evidence of a pharmacokinetic origin to the carbamazepine-vecuronium interaction; however, the possibility of a concurrent pharmacodynamic alteration cannot be assessed. Greater knowledge of protein drug binding needs to be acquired to give a meaningful interpretation to the similar EC50 values observed in the two groups.

Pharmacokinetics and anticonvulsant effect of a new hypnotic, CL 284,846, in rats

PURPOSE

CL 284,846 (CL846) is an investigational non-benzodiazepine agent with hypnotic, anxiolytic, myorelaxant and anticonvulsant properties. This study assessed the pharmacokinetics and anticonvulsant action of CL846 in female Sprague-Dawley rats.

METHODS

CL846 pharmacokinetics were examined after either an iv bolus dose (2.5 mg/kg) or a 6-hr infusion (0.4 mg/kg/hr). CL846 pharmacodynamics were evaluated with a pentylenetetrazol (PTZ) infusion 5 min after a CL846 in bolus dose (0 to 10 mg/kg). CL846 and the derived metabolite CL 284,859 (CL859) concentrations in serum and brain tissue were determined by HPLC with fluorescence detection.

RESULTS

Both the steady-state volume of distribution (1636 +/- 162 and 1804 +/- 293 ml/kg, after bolus and infusion administration, respectively) and systemic clearance (19.1 +/- 7.1 and 22.2 +/- 4.3 ml/min/kg for bolus and infusion administration, respectively) were high. No differences in pharmacokinetic parameters were noted between the two modes of administration. The relationship between anticonvulsant effect and brain/serum concentrations was well described by an Emax model. CL846 was as effective as triazolam in antagonizing PTZ-induced seizures.

CONCLUSIONS

Under the conditions of the present study, CL846 pharmacokinetics were linear and stationary. Further evaluation of the anticonvulsant properties of CL846 is warranted, including the potential development of tolerance, which is well known for benzodiazepines.

In vitro plasma protein binding of neuromuscular blocking agents in different subpopulations of patients

In vitro protein binding of several neuromuscular blocking agents (NMBAs) was measured by ultrafiltration in plasma from patients susceptible to demonstrate changes in their protein constituents. First, the relationship between the free fraction of atracurium and plasma lipoproteins levels in young volunteers (22-32 yr old, n = 6) and hyperlipidemic patients (44-68 yr old, n = 13) was studied, and second, the free fraction of atracurium, mivacurium, doxacurium, and vecuronium was determined in plasma of healthy young (27-47 yr old, n = 10), elderly (72-89 yr old, n = 11) and obese (21-57 yr old, n = 9, 200%-360% ideal body weight) patients scheduled for elective surgery. In hyperlipidemic patients, atracurium free fraction was significantly less than in young volunteers (40% +/- 5% vs 50% +/- 5%, mean +/- SD), and decreased as total cholesterol, low-density lipoprotein cholesterol and triglycerides increased (P < 0.05). In young individuals, NMBA free fraction was 25% +/- 5% for vecuronium, 58% +/- 8% for doxacurium, 52% +/- 6% for atracurium, and 72% +/- 3%, 70% +/- 3%, 70% +/- 4% for mivacurium trans-trans, cis-trans, and cis-cis isomers, respectively. Higher triglyceride concentrations in obese patients and lower high-density-lipoprotein cholesterol concentrations in both obese and elderly patients were observed when compared with young subjects. However, there was no significant difference in protein binding of NMBAs among these three groups. We conclude that, in otherwise healthy patients, age and weight are not likely to alter the free fraction of NMBAs.

High-performance liquid chromatographic assays with fluorometric detection for mivacurium isomers and their metabolites in human plasma

Two high-performance liquid chromatographic assays coupled with fluorometric detection have been developed for the determination of mivacurium isomers (trans-trans, cis-trans and cis-cis) and their monoester and alcohol metabolites in human plasma. A novel solid-phase extraction procedure allowed good recovery of the mivacurium isomers (mean 98%) and their monoester metabolites (mean 83%), whereas the alcohol metabolites were analyzed after direct precipitation of plasma proteins. For all analytes, these assays proved to be sensitive (LOQ 3.9-15.6 ng/ml), reproducible (C.V. < 15%) and accurate (> 94%) over the therapeutic range of concentrations of mivacurium and its metabolites. These two methods were applied successfully to a pharmacokinetic study of mivacurium after a bolus dose of 0.15 mg/kg in anesthetized patients.

Bretylium decreases and verapamil increases defibrillation threshold in pigs

BACKGROUND

Patients with ischemic heart disease may require antianginal and/or antiarrhythmic regimes. These patients may also be candidates for implantable defibrillators. The effects of antiarrhythmics, such as bretylium, or calcium antagonists, such as verapamil, nifedipine, or diltiazem on internal defibrillation efficacy have been inconsistent or are unknown.

METHODS AND RESULTS

The effects of bretylium and verapamil on the energy requirements for ventricular defibrillation threshold (DFT) were determined in 92 open-chest anesthetized pigs. Triplicate DFTs were determined before and after intravenous administration of saline or one of four doses of verapamil, or saline or one of three doses of bretylium, in a balanced random order. Bretylium elicited a dose dependent reduction of DFT (F = 2.72 at 3 degrees and 36 degrees of freedom). DFT was significantly reduced with the highest dose of bretylium, (from 5.9 +/- 0.6 J to 4.7 +/- 0.6 J, mean +/- S.E.M.; P < 0.01). However, cardiac massage was sometimes needed at this dose due to low blood pressure immediately after defibrillation. In contrast, there was a positive correlation between DFT and serum verapamil concentration (r = 0.54, P < 0.001). The highest dose of verapamil significantly increased DFT (from 6.3 +/- 0.6 J to 8.2 +/- 1.1 J; P < 0.05), at a serum verapamil concentration of 86.6 +/- 6.8 ng/mL.

CONCLUSIONS

These data indicate that bretylium decreases while verapamil increases the minimum energy requirement for internal defibrillation. Caution is warranted in patients who may be hemodynamically comprised and may be candidates for bretylium therapy or in patients who have marginal DFT value who might be candidates for verapamil therapy.

Determination of midazolam and two of its metabolites in human plasma by high-performance liquid chromatography

A high-performance liquid chromatographic assay coupled with UV detection (254 nm) has been developed for the determination of midazolam and two of its hydroxylated metabolites, 1-hydroxymidazolam (1-OH) and 4-hydroxymidazolam (4-OH), in human plasma. Following a novel solid-phase extraction procedure, midazolam and its metabolites are well recovered from plasma. The analytes were extracted with C1 cartridges and the extracts were evaporated to dryness. The dry residues were dissolved in 200 microliters of mobile phase [0.02 M ammonium phosphate monobasic buffer-methanol-acetonitrile (60:35:5, v/v) (300 ml), 600 microliters of 0.2 M tetrabutylammonium bromide solution, adjusted to a pH* (apparent pH) of 4.10]. The separation of the analytes was performed on a Spherisorb C8 column (10 cm x 4.6 mm I.D.) maintained at 30 degrees C. The mobile phase was pumped at a flow-rate of 1.5 ml/min. The method has a lower limit of quantitation of 15 ng/ml of plasma for midazolam and proved to be reproducible (inter-assay precision 5.4%) and accurate (94 +/- 5%) over the therapeutic range of concentrations.

Importance of early blood sampling on vecuronium pharmacokinetic and pharmacodynamic parameters

The effect of early blood sampling on the description of the vecuronium pharmacokinetic-pharmacodynamic relationship was studied following a bolus injection. Sample collection every 10 sec during the first 2 min showed a high concentration peak at 30 to 40 sec, accounting for an important proportion of the total area under the plasma concentration-time curve (AUC). Neglecting it, using only blood samples drawn at 1 and 2 min (limited sampling), led to a significant overestimation of noncompartmentally derived values of mean residence time, clearance, volume of distribution at steady-state and rate of transfer of vecuronium into the effect compartment. Compartmental pharmacokinetics could not be applied to concentration-time curves constructed with early samples, but limited sampling data were fitted to a 2-compartment model. Derived compartmental pharmacokinetic and pharmacokinetic-pharmacodynamic parameters were similar to those obtained noncompartmentally with complete sampling every 10 sec, because back-extrapolation to time zero contributed to the increase in the AUC. However, compartmental analysis does not provide an accurate description of concentration changes following injection.

Influence of aging on the pharmacokinetics and pharmacodynamics of doxacurium

Doxacurium (30 micrograms/kg) pharmacokinetics and pharmacodynamics were evaluated in nine elderly (age range, 70 to 83 years) and nine young (age range, 19 to 39 years) patients under nitrous oxide-isoflurane anesthesia. The force of contraction of the adductor pollicis was monitored and plasma samples were collected for an 8-hour period. In the elderly group, doxacurium elimination half-life was prolonged (119.7 versus 75.9 minutes) and plasma clearance was significantly reduced (1.75 versus 2.54 ml/min/kg) without any change in volume of distribution. Onset (12.9 versus 8.9 minutes) and recovery times (113.4 versus 48.1 minutes) were longer in the elderly group. The equilibrium rate constant to the effect compartment (kco) was decreased in the elderly (0.039 versus 0.051 min-1), whereas the effect compartment concentration at 50% block was similar in both groups (44.7 versus 54.1 ng/ml). An age-related reduction in muscle blood flow may be responsible for the decrease in kco. The pharmacokinetic changes observed in the elderly are consistent with a decreased function in the organs of elimination.

Simple, rapid and selective method using high-performance liquid chromatography for the determination of bretylium in plasma

A high-performance liquid chromatographic method with ultraviolet detection has been developed for the determination of bretylium in plasma. Following a single-step solid-phase extraction procedure, bretylium is selectively isolated and well recovered from plasma. The assay sensitivity is 0.156 micrograms/ml from 250-microliters plasma samples and its linearity was assessed up to 40 micrograms/ml. The method is accurate (101.0 +/- 5.4%) and precise (maximum coefficient of variation of 8%). It provides a simple and time-saving alternative to existing methods and is particularly suitable for pharmacokinetic studies.

High-performance liquid chromatographic determination of spironolactone and its metabolites in human biological fluids after solid-phase extraction

A simple and sensitive high-performance liquid chromatographic procedure to determine spironolactone and its three major metabolites in biological specimens is described. The assay involves sequential extraction on C18 and CN solid phases, and subsequent separation on a reversed-phase column. In plasma samples, spironolactone and its metabolites were completely separated within 8 min using an isocratic mobile phase, while in urine samples a methanol gradient was necessary to achieve a good separation within 14 min. Recoveries for all analytes were greater than 80% in plasma and 72% in urine. Linear responses were observed for all compounds in the range 6.25-400 ng/ml for plasma and 31.25-2000 ng/ml for urine. The plasma and urine methods were precise (coefficient of variation from 0.8 to 12.5%) and accurate (-12.1% to 7.4% of the nominal values) for all compounds. The assay proved to be suitable for the pharmacokinetic study of spironolactone in healthy human subjects.

High-performance liquid chromatography—electrochemical detection of vecuronium and its metabolites in human plasma

A high-performance liquid chromatographic assay coupled with electrochemical detection has been developed for the determination of vecuronium and its three putative deacetylated metabolites in human plasma. A novel solid-phase extraction procedure allowed good recovery of both vecuronium and its metabolites, together with ease and speed of execution. This method was sensitive, reproducible and accurate over the therapeutic range of concentrations of vecuronium and its metabolites, and was applied successfully to a study of the pharmacokinetics of vecuronium in anaesthetized patients.

Pharmacokinetics of sufentanil in normal children

The pharmacokinetic variables of sufentanil were studied in 20 healthy children between two and eight years of age. The plasma concentrations of sufentanil were measured for up to 480 min after administration of a bolus of sufentanil, 1-3 micrograms.kg-1. The distribution half-life (t1/2 alpha) was 5.2 +/- 2.2 (mean +/- SD) min and the elimination half life (t1/2 beta) was 97.0 +/- 42.0 min. The volume of distribution at steady state (Vdss) was 2.9 +/- 0.6 L.kg-1 and the clearance was 30.5 +/- 8.8 ml.kg-1.min-1. The Vdss was one and a half times greater than that reported in adults when expressed as a function of body weight but similar to that of adults when expressed as a function of body surface area. According to our results, the clearance of sufentanil in normal children between two and eight years of age is twice as rapid as that described in adults and adolescents. A greater clearance of sufentanil in children suggests that they would require relatively greater maintenance doses than adults.

Residual curarization in the neonate after caesarean section

The transplacental transfer and the neonatal effects of atracurium 0.3 mg.kg-1 (ED95) were compared with those of d-tubocurarine at the usual clinical dose of 0.3 mg.kg-1 (ED90) in 46 patients undergoing elective Caesarean section. The atracurium group (25 patients) was similar to the d-tubocurarine group (21 patients) as far as age, parity and time intervals between precurarization, induction, skin incision, muscle relaxant administration, hysterotomy and birth. The transplacental transfer of atracurium was lower than that of d-tubocurarine, with a feto-maternal ratio of 9 +/- 3% for atracurium and 12 +/- 5% for d-tubocurarine (P less than 0.05). The transplacental transfer of laudanosine was low at 14 +/- 5%, with blood levels of 0.101 +/- 0.032 microM.L-1 in the umbilical vein. Newborns in the two groups were comparable in terms of Apgar scores at one, five and ten minutes, as well as for NACS scores (neurological and adaptive capacity scoring test) at two and 24 hours after birth. However, at 15 min after birth, only 55% of newborns in whom the mothers received atracurium had a normal NACS score (greater than or equal to 35/40) compared with 83% of newborns in whom the mothers received d-tubocurarine (P less than 0.05). Further analysis of the five variables related to active muscle tone revealed that the modal score for active extension of the neck of newborns from the atracurium group was lower than for newborns from the d-tubocurarine group (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and pharmacodynamics of atracurium obtained with arterial and venous blood samples

To determine the influence of sampling site on atracurium pharmacokinetic-pharmacodynamic relationships, blood was drawn simultaneously from the radial artery and peripheral vein during a 20-minute period after injection of atracurium, 0.2 mg/kg, in eight patients. Atracurium and laudanosine concentrations were measured by HPLC. Neuromuscular blockade was measured at the adductor pollicis, after stimulation of the ulnar nerve. Venous levels were lower than corresponding arterial values for up to 20 minutes, and this difference was marked for the early samples. Neuromuscular blockade was maximum after 5 to 7 minutes, much later than the peak venous concentration (1 to 3 minutes). Nonparametric analysis yielded (mean +/- SEM) a rate constant, concentration for 50% blockade, and slope of the effect-concentration relationship of 0.092 +/- 0.01 min-1, 379 +/- 27 ng/ml, and 7.3 +/- 1.67, respectively, when based on arterial samples. The values were statistically different (0.135 +/- 0.011 min-1, 235 +/- 42 ng/ml, and 3.41 +/- 0.37, respectively) when venous levels were used (p less than 0.05). It is concluded that forearm venous levels do not correspond to adductor pollicis neuromuscular blockade and the kinetics and kinetic-dynamic relationship for atracurium are heavily dependent on sampling site.

Pharmacokinetics and pharmacodynamics of atracurium with and without previous suxamethonium administration

Suxamethonium increases neuromuscular block produced by non-depolarizing agents administered subsequently. To determine if this effect has a pharmacokinetic or pharmacodynamic origin, 18 ASA physical status I or II adults received atracurium 0.2 mg kg-1, with (n = 10) or without (n = 8) previous injection of suxamethonium 1 mg kg-1, during a thiopentone-nitrous oxide-isoflurane (0.5% end-tidal) anaesthetic. Arterial blood samples were obtained and plasma atracurium concentration measured by HPLC. Train-of-four stimulation was applied to the ulnar nerve and the force of contraction of the adductor pollicis muscle was recorded. Mean (SEM) volume of distribution was slightly greater with previous suxamethonium (143 (13) ml kg-1) than without (109 (5) ml kg-1) (P less than 0.04). Mean elimination half-life was unaffected (20.3 (0.8) min and 20.4 (1.6) min, respectively). Neuromuscular block was more intense and recovery was slower with previous administration of suxamethonium. Atracurium concentration at 50% block (Cpss50) was 305 (30) ng ml-1 with and 454 (25) ng ml-1 without previous suxamethonium (P less than 0.01). It is concluded that suxamethonium may be associated with a slight increase in the volume of distribution of atracurium, but this effect is more than compensated by a decrease in atracurium concentration required for a given effect.

Potentiation of atracurium neuromuscular blockade by enflurane: time-course of effect

This study was designed to determine the time required for potentiation of atracurium neuromuscular blockade after the introduction of enflurane. Ten ASA physical status I and II adults anesthetized with thiopental, nitrous oxide, and alfentanil were given 0.4 mg/kg atracurium besylate. The force of contraction of the adductor pollicis muscle in response to train-of-four stimulation of the ulnar nerve was recorded. When the first twitch (T1) of the train-of-four recovered to 10% of control, an atracurium infusion was started and adjusted to keep the level of blockade constant. After 15 min of stable blockade, 1.6%-1.7% end-tidal enflurane was started and maintained for up to 2 h. Venous blood samples were drawn and plasma atracurium concentrations were measured 15 min before and 0, 5, 10, 15, 30, 45, 60, 90, and 120 min after the introduction of enflurane. Atracurium plasma concentrations were 730 +/- 127 (SEM) ng/mL at time 0. During the first 30 min, no significant decrease in plasma levels occurred; but at 45 min, concentrations were only 67% +/- 8% of their initial value (P less than 0.01) and 48% +/- 2% at 120 min (P less than 0.01). This suggests that the interaction between enflurane and atracurium is time-dependent. Clinically, the interaction between atracurium and enflurane is negligible during procedures of less than 45 min.

Isolation of 6-mercaptopurine in human plasma by aluminum ion complexation for high-performance liquid chromatographic analysis

A sample preparation technique and a high-performance liquid chromatographic method for 6-mercaptopurine (6-MP) that is simple, sensitive and without interference from its metabolites is described. 6-Thioguanine (6-TG) is added as an internal standard to the plasma sample, which is then treated with an aqueous solution of aluminum perchlorate to denature the plasma proteins and form complexes with 6-TG, 6-MP and its major metabolite, 6-thiouric acid (6-TUA). These complexes coprecipitate with proteins on centrifugation. 6-MP and its analogues are then extracted from the precipitate with perchloric acid containing sodium hydrosulfite and the extract is chromatographed on an Ultrasphere ODS column eluted with 0.1 M phosphoric acid and 0.001 M dithiothreitol in deionized water. The eluate is monitored at 340 nm. No interfering peak was encountered in over 300 clinical plasma samples. 6-TUA was separated from 6-MP and was found to be present in much higher concentration than 6-MP itself throughout the sampling time (6 h) following oral administration of the drug.

Determination of atracurium and laudanosine in human plasma by high-performance liquid chromatography

A high-performance liquid chromatographic method coupled with fluorometric detection has been developed for the determination of atracurium and its major end-product laudanosine in human plasma. The method enables good separation of atracurium from its metabolites after direct precipitation of plasma proteins. The assay is sensitive, reproducible and linear for atracurium concentrations ranging from 31.25 to 8000 ng/ml. In a clinical setting, drugs commonly administered during anesthesia did not interfere with the assay. This method provides a simple and time-saving alternative to existing methods.

Influence of extreme obesity on the body disposition and neuromuscular blocking effect of atracurium

The pharmacokinetics and pharmacodynamics of atracurium, a nondepolarizing neuromuscular blocking agent, were compared between morbidly obese patients and nonobese patients. Atracurium besylate (0.2 mg/kg) was administered intravenously as a bolus to patients who had received anesthesia. The force of contraction of the adductor pollicis was measured and plasma samples were collected for a 2-hour period. The concentrations of atracurium and its major end product, laudanosine, were determined by use of a chromatographic method. The pharmacokinetic-pharmacodynamic relationship was characterized by use of several models. No difference was observed between obese patients and nonobese patients in atracurium elimination half-life (19.8 +/- 0.7 versus 19.7 +/- 0.7 minutes), volume of distribution at steady state (8.6 +/- 0.7 versus 8.5 +/- 0.7 L), and total clearance (444 +/- 29 versus 404 +/- 25 ml/min). However, if values were expressed on a total body weight basis, there was a difference between obese and nonobese patients in the volume of distribution at steady state (0.067 versus 0.141 L/kg) and total clearance (3.5 +/- 0.2 versus 6.6 +/- 0.5 ml/min/kg). Although atracurium concentrations were consistently higher in obese patients than in nonobese patients, there was no difference in the time of recovery from neuromuscular blockade between the two groups. Consequently, the median effective concentration was higher in obese than in nonobese patients (470 +/- 46 versus 312 +/- 33 ng/ml).

Influence of food on the bioavailability of diltiazem and two of its metabolites following the administration of conventional tablets and slow-release capsules

The influence of food on the bioavailability of a conventional tablet and of a slow-release capsule of diltiazem was investigated in two separate groups of 24 healthy volunteers in two open crossover studies. Diltiazem, as a conventional tablet (2 x 30 mg, first group) or as a slow-release capsule (120 mg SR, second group), was administered in a fasting condition and 30 min after a breakfast of 784 kcal (23 per cent proteins, 55 per cent lipids, and 22 per cent of carbohydrates). Multiple blood samples were withdrawn during the next 24 h and diltiazem, desmethyldiltiazem, and deacetyldiltiazem were assayed by HPLC. Neither the rate of absorption, assessed by the rate constant of absorption, the peak plasma concentration, and the time required to reach the peak, nor the amount of drug reaching the systemic circulation, assessed by the area under the plasma concentration time curve (AUC infinity) were influenced by food, and that independently of the formulation. Compared to the fasting experiment, food did not affect either the rate of formation or the AUC infinity of desmethyldiltiazem or deacetyldiltiazem. The results of the present study show that the relative bioavailability of the single dose of diltiazem administered as a slow-release capsule is significantly higher (69 per cent) than that estimated after the administration of diltiazem in a conventional tablet. It was concluded that food does not influence the bioavailability of diltiazem administered as a conventional tablet or as a slow-release formulation.