Effect of cardiopulmonary bypass on the plasma concentrations of fentanyl and alcuronium.

This study was conducted to examine the effect of cardiopulmonary bypass surgery on the total and unbound plasma concentrations of fentanyl and the total plasma concentrations of alcuronium. Total fentanyl concentrations were measured by gas chromatography, the plasma protein binding of fentanyl by ultrafiltration, and alcuronium concentrations by high-performance liquid chromatography. Sixteen patients were studied. On initiation of cardiopulmonary bypass (CPB), there were mean decreases of 58.8 +/- 7.1% and 47 +/- 3.2% for total concentrations of fentanyl in plasma and haemoglobin in blood, respectively. The magnitude of these reductions in individual patients was significantly related (Spearman p = 0.65, P < 0.05). The unbound fraction of fentanyl rose from 0.23 to 0.34 after the start of CPB. The total fentanyl concentration remained relatively stable during bypass until near the end of CPB when the mean total concentration increased, coinciding with rewarming. The size of the increase was related to the body mass index (BMI) of the patient (Spearman p = 0.85, P < 0.01). The estimated elimination half-life of fentanyl using the grouped data was 4.7 h. The total alcuronium concentration in plasma fell by 29% on initiation of CPB and there was no increase on rewarming. The estimated elimination half-life of alcuronium using the grouped data was 234 min. Despite marked declines in the plasma concentrations of both drugs on initiation of CPB, suitable levels of anaesthesia were maintained throughout the procedure.

Uso de bloqueantes neuromusculares y su monitoreo en pediatría / Use of neuromuscular blocking agents and its monitoring in pediatrics

El actual arsenal farmacológico, en cuanto a relajantes musculares ha hecho necesario la constante actualización y desarrollo de técnicas para las indicaciones adecuadas y el correcto control de los mismos. El aumento de la utilización de estos fármacos en pediatría, sobre todo los relajantes musculares no despolarizantes ha facilitado la tarea médica del anestesiólogo, obligándolo a una constante actualización en el conocimiento sobre el desarrollo de estos fármacos y el monitoreo clínico e instrumental sobre el paciente. (AU)

Uso de bloqueantes neuromusculares y su monitoreo en pediatría / Use of neuromuscular blocking agents and its monitoring in pediatrics

El actual arsenal farmacológico, en cuanto a relajantes musculares ha hecho necesario la constante actualización y desarrollo de técnicas para las indicaciones adecuadas y el correcto control de los mismos. El aumento de la utilización de estos fármacos en pediatría, sobre todo los relajantes musculares no despolarizantes ha facilitado la tarea médica del anestesiólogo, obligándolo a una constante actualización en el conocimiento sobre el desarrollo de estos fármacos y el monitoreo clínico e instrumental sobre el paciente.

Alcuronium: a pharmacodynamic and pharmacokinetic update.

Alcuronium may be considered a muscle relaxant of historical rather than clinical significance. However, recent information from the manufacturer revealed its persisting clinical use in 26 countries worldwide. Thus, a pharmacodynamic-pharmacokinetic update appears mandatory. An intravenous (IV) single-bolus injection of alcuronium (0.25 mg/kg = ED95) was administered to 10 patients undergoing maxillofacial surgery during nitrous-oxide opioid anesthesia. Alcuronium neuromuscular block (evoked twitch tension), plasma concentration, and renal elimination (high-performance liquid chromatography [HPLC] assay) were measured during the 12-h after its administration. The time of onset, the time from end of injection to recovery to 25% of control twitch tension (DUR25%), and the recovery index were 2.2 +/- 1.2, 54 +/- 14, and 37 +/- 11 min, respectively (mean +/- SD). Two hours after the injection of alcuronium, partial recovery from the neuromuscular block had occurred from 100% to 26% +/- 24% depression of twitch tension, although less than 25% of the injected dose was recovered from the urine. The 12-h plasma concentration and urinary recovery were 0.1 +/- 0.08 mg/L (one-sixth of the 50% inhibitory concentration) and 61% +/- 20%, respectively. Recovery from neuromuscular block was dominated by intercompartmental distribution rather than by renal elimination. Since alcuronium does not undergo biodegradation, our data may serv as a reference for the complex pharmacokinetics of readily metabolized modern muscle relaxants. The long plasma half-life with slow excretion merits attention with respect to the erroneous original perception that alcuronium was an intermediate-acting muscle relaxant.

Pharmacokinetics of alcuronium in children with acyanotic and cyanotic cardiac disease undergoing cardiopulmonary bypass surgery.

The aim of this study was to determine the pharmacokinetic parameters for alcuronium in children with cyanotic or acyanotic congenital cardiac disease undergoing cardiopulmonary bypass surgery and to compare these parameters with previously reported values in children and adults with normal cardiac function. Seven children with acyanotic disease and seven with cyanotic disease were studied. Alcuronium (base) was administered in an initial dosage of 0.25 mg.kg-1 with additional doses as needed to maintain paralysis. Using time averaged data, cyanotic children had lower mean clearance, elimination half-life and volume of distribution at steady state than the acyanotic children; none of these differences was, however, statistically significant. In this study, children with acyanotic and cyanotic cardiac disease undergoing bypass, had a diminished clearance (P < 0.05) and a smaller volume of distribution (P < 0.05) than normal children and a shorter elimination half-life (P < 0.05) than adults. Onset of cardiopulmonary bypass caused an immediate marked decrease in alcuronium plasma concentrations which remained low in the acyanotic children at the completion of bypass.

Two populations of muscarinic binding sites in the chick heart distinguished by affinities for ligands and selective inactivation.

1. By measuring the binding of N-[3H-methyl]-scopolamine ([3H]-NMS) and of unlabelled subtype-specific muscarinic antagonists, two populations of muscarinic binding sites can be distinguished in the membranes of cardiac ventricles taken from 1-day-old chicks. One of them, corresponding to approximately 80% of [3H]-NMS binding sites, has higher affinities for AF-DX116 (pKi = 6.42) and methoctramine (pKi = 7.33); the rate of [3H]NMS dissociation from these sites is fast. The other population, corresponding to approximately 20% of [3H]-NMS binding sites, has lower affinities for AF-DX116 (pKi = 5.00) and methoctramine (pKi = 6.19); the rate of [3H]-NMS dissociation from these sites is slow. Both populations have high affinities for pirenzepine, but the affinity of the former (major) population is lower (pKi = 7.99) than that of the latter (minor) population (pKi = 10.14). 2. Since it has been shown earlier that two mRNAs for muscarinic receptors are expressed in the chick heart, one of them close to the genetically defined m2 and the other to the m4 subtype, we propose that the major population of binding sites with high affinities for AF-DX116 and methoctramine and the lower affinity for pirenzepine represents the M2-like receptors, while the minor population represents the M4-like receptors. 3. It proved possible to obtain isolated samples of either population by selectively protecting the M2-like sites with AF-DX116 and the M4-like sites with pirenzepine, and by inactivating the unprotected sites with benzilylcholine mustard. The properties of the isolated populations corresponded to those derived from the analysis of [3H]-NMS binding to the original mixed population.4 Alcuronium exerted positive allosteric action on the binding of [3H]-NMS both to the M2-like and the M4-like population and severely slowed down [3H]-NMS dissociation from them; its affinity for the M2-like sites was 3-10 times higher.

Simple and rapid high-performance liquid chromatography method for the determination of alcuronium in human plasma and urine.

A simple and quick HPLC assay for alcuronium is presented. Its characteristics are: precipitation of plasma proteins by acetonitrile; Spherisorb 5-CN column; acetonitrile-water (46:54, v/v) as mobile phase; flow-rate 1 ml/min; laudanosine 0.06 mg/l as internal standard with plasma; external standard with urine; UV detection at 294 nm; retention time 5.4 min; detection limit 0.025 mg/l; documented linearity: 0.025-2.0 mg/l for plasma and 1.0-80 mg/l for urine; intra- and inter-assay variability below 4%. None of nine drugs used in perioperative pharmacotherapy interfered with the assay. Satisfactory performance was exemplified in a 12-h pharmacokinetic evaluation of two patients.

The pharmacodynamics of alcuronium in the elderly.

Alcuronium (0.2 mg/kg) was given to 12 elderly patients, mean age 77 years (range 70-88 years) and 12 young patients, mean age 24 years (range 18-32 years) undergoing general anaesthesia. A compound muscle action potential was monitored continuously throughout anaesthesia, using an electromyograph and the train-of-four twitch technique. The rate of onset and maximum block achieved were similar in both the young and elderly patients, as were the times to 20% recovery of the first twitch compared with control (T1 : T0) and fourth twitch compared with the first, (T4 : T1). In contrast, the time to 70% recovery of T1 : T0 was significantly prolonged in the elderly (138 as compared with 89 minutes: p less than 0.01) as was the recovery index (25-75%) for T1 : T0 (95 as compared with 46 minutes: p less than 0.01) and the time to 70% recovery of T4 : T1 (181 as compared with 131 minutes: p less than 0.05). The recovery curves for T1 : T0 and T4 : T1 were also significantly different in the elderly from the young group (p less than 0.01 in both instances). These results show that the duration of action of alcuronium is significantly prolonged in the elderly.

Farmacocinética dos bloqueadores neuromusculares / Pharmacokinetics of neuromuscular relaxants

Os autores tecem comentários sobre a farmacocinética dos bloqueadores neuromusculares adespolarizantes e despolarizantes, enfatizando principalmente os aspectos da fisiopatologia que podem alterá-la, como a gravidez, hipotermia, idade avançada e insuficiência renal e hepática

[Comparison of the action kinetics of alcuronium and vecuronium by electromyographic monitoring]. / Comparaison de la cinétique d'action de l'alcuronium et du vécuronium par monitorage électromyographique.

Twenty-eight ASA I or ASA II adults undergoing microsurgery were anaesthetized according to a standard protocol using droperidol, phenoperidine and thiopentone followed by enflurane. The patients were randomly assigned to two homogeneous groups: the first group (n = 14) received 0.2 mg.kg-1 alcuronium, whereas the second group (n = 14) received 0.08 mg.kg-1 vecuronium. There was no reinjection of either drug and curarization tapered off spontaneously. Neuromuscular monitoring was begun once anaesthesia was stable and after intentional isovolaemic haemodilution. The type of stimulus used was the train-of-four, delivered by a Relaxograph monitor to the ulnar nerve. Muscle response was measured at the hypothenar eminence. The kinetic study considered the time interval required between the injection of the muscle relaxant and the appearance of the minimal value of the twitch (first response of the train-of-four = T1min). The times to recovery of the twitch height to 25, 75 and 100% of the reference value (T1/T0) and of the fourth response of the train-of-four to 25 and 75% of the ratio (T4/T1) were also recorded. Finally, the recovery indexes represented by the times required for T1/T0 and T4/T1 to rise from 25% to 75% respectively were studied. The maximal twitch height inhibition was significantly greater (p less than 0.001) in the vecuronium group (T1min = 0.36 +/- 1.33%) than in the alcuronium group (T1min = 4.36 +/- 5.08%); it occurred significantly more quickly (p less than 0.001) with vecuronium (139 +/- 48 s) than with alcuronium (316 +/- 133 s).(ABSTRACT TRUNCATED AT 250 WORDS)