Do the pharmacokinetics of vecuronium change during prolonged administration in critically ill patients?

Neuromuscular blocking drugs may be administered over several days to patients in the intensive care unit (ICU), but their pharmacokinetics have been studied at only one point in time, or assumed to be constant throughout the period of administration. We sought to determine if, in individual patients, the pharmacokinetics of vecuronium changed over the course of its administration in the ICU. In six critically ill patients, we measured plasma vecuronium concentrations during two periods: first, during initial administration of vecuronium and second, after its administration continuously for 3-6 days. A pharmacokinetic model was fitted to these plasma concentration data, and its parameters permitted to vary between the periods to determine if they had altered. Individual clearance values during the study ranged from 1.4 to 4.4 ml kg-1 min-1. During prolonged administration, vecuronium clearance increased in three and decreased in two patients. This change ranged from a 61% decrease to a 58% increase, and was not linked to any clinical factor. The steady-state volume of distribution (range 368-1765 ml kg-1; median 494 ml kg-1) did not change in any patient during the study. The change in clearance of vecuronium during its prolonged administration in critically ill patients suggests that future studies of neuromuscular blocking drugs in the ICU should take account of their changing pharmacokinetics over the course of administration.

Solution structure of the thermostable sweet-tasting protein brazzein

The fruit of Pentadiplandra brazzeana Baillon contains a small, sweet-tasting protein named brazzein. The structure of brazzein in solution was determined by proton nuclear magnetic resonance spectroscopy at pH 5.2 and 22 degrees C. The brazzein fold, which contains one alpha-helix and three strands of antiparallel beta-sheet, does not resemble that of either of the other two sweet-tasting proteins with known structures, monellin and thaumatin. Instead, the structure of brazzein resembles those of plant gamma-thionins and defensins and arthropod toxins. Sequence comparisons predict that members of a newly-identified family of serine proteinase inhibitors share the brazzein fold.

The effect of clonidine on cerebral blood flow velocity, carbon dioxide cerebral vasoreactivity, and response to increased arterial pressure in human volunteers

BACKGROUND

Because patients may be taking clonidine chronically or may be receiving it as a premedication before surgery, the authors investigated its effect on cerebral hemodynamics.

METHODS

In nine volunteers, middle cerebral artery mean blood flow velocity (Vm) was measured using transcranial Doppler ultrasonography (TCD). CO2 vasoreactivity was measured before clonidine administration (preclonidine), 90 min after clonidine, 5 microg/kg orally, then following restoration of mean arterial pressure (MAP) to the preclonidine level. In addition, Vm was measured after a phenylephrine-induced 30-mmHg increase in MAP.

RESULTS

After clonidine administration, Vm decreased from 62 +/- 9 to 48 +/- 8 cm/s (P < 0.01), and MAP decreased from 86 +/- 10 to 63 +/- 5 mmHg (P < 0.01; mean +/- SD). Clonidine decreased the CO2 vasoreactivity slope from 2.2 +/- 0.4 to 1.2 +/- 0.5 cm x s(-1) x mmHg(-1) (P < 0.05); restoring MAP to the preclonidine level increased the slope to 1.60 +/- 0.5 cm x s(-1) x mmHg(-1), still less than the preclonidine slope (P < 0.05). CO2 vasoreactivity expressed as a percentage change in Vm, decreased after clonidine, 3.5 +/- 0.8 versus 2.4 +/- 0.8 %/mmHg (P < 0.05); this difference disappeared after restoration of MAP, 3.1 +/- 1.2 %/mmHg. With a 30-mmHg increase in MAP, Vm increased by 13% before and after clonidine (P < 0.05).

CONCLUSIONS

Clonidine, 5 microg/kg orally, decreases Vm and slightly attenuates cerebral CO2 vasoreactivity, therefore decreased cerebral blood flow and mildly attenuated CO2 vasoreactivity should be anticipated.

Venous bleeding during transsphenoidal surgery: its association with pre- and intraoperative factors and with cavernous sinus and central venous pressures

Venous bleeding during transsphenoidal surgery for resection of pituitary tumors is a common problem that interferes with the performance of the surgical procedure. In this study, data were collected prospectively from 50 patients to determine whether there were pre- or intraoperative factors (e.g., patient demographics, type and grade of pituitary tumor, intraoperative hemodynamics) associated with venous bleeding which might be used to predict its occurrence. In addition, central venous pressure (CVP), and cavernous sinus pressure (CSP) were measured in 13 patients to evaluate the relationship of these pressures to each other and to the severity of venous bleeding. During resection of the pituitary tumor, the severity of venous bleeding was graded as minimal, moderate, or severe, the latter two grades requiring therapeutic intervention. Moderate bleeding requiring intervention occurred in 15 of the 50 patients, and resolved in all cases. Moderate bleeding was not related to CSP or CVP, and no specific associated factor was observed. CSP was not correlated with CVP, and was higher than that predicted from the CVP and the position of the patient or the hydrostatic gravitational pressure gradient. These results suggest that it is not possible to predict in advance which patients will have problems with venous bleeding, but that simple therapeutic maneuvers are effective.

Improving the design of muscle relaxant studies. Stabilization period and tetanic recruitment

BACKGROUND

The results from studies of muscle relaxants show wide variations among institutions. The authors hypothesized that some of this variability could be explained by differences in duration of nerve stimulation before drug administration (stabilization period).

METHODS

Train-of-four stimulation was applied every 12 s to both ulnar nerves and adductor pollicis twitch tension was measured in anesthetized participants given 30 micrograms/kg vecuronium. In phase 1, the stabilization period was > 30 min for both extremities. In phase 2-4, stabilization period was 20 min for one extremity and 2 min for the other. In addition, in phase 3, a 2-s 50-Hz tetanus initiated the 2-min stimulation period; in phase 4, duration of tetanus was 5 s. Twitch recovery was recorded until stable for more than 15 min. Time to 25% recovery (clinical duration) was calculated based on two indices: predrug and final (recovery) twitch tension. Values for onset and clinical duration were compared by paired parametric and nonparametric tests.

RESULTS

In phase 1, predrug and recovery twitch tension were similar in each extremity, and onset and clinical duration did not differ between extremities, permitting paired comparisons in remaining studies. In phase 2, onset was more rapid with 20-min of prestimulation. With 20-min prestimulation, predrug and recovery twitch tension were similar; with 2-min prestimulation, recovery twitch tension exceeded predrug values. When referenced to predrug twitch tension, clinical duration was shorter with 2-min, that with 20-min prestimulation. Initiating stimulation with 2-s or 5-s 50-Hz tetani (phases 3, 4) abolished differences between extremities in onset and recovery.

CONCLUSIONS

With only train-of-four stimulation (no tetani), onset and clinical duration vary with duration of prestimulation, suggesting that a brief period of predrug stimulation is inadequate. However, lengthy prestimulation may be impractical in clinical studies. Tetanic stimulation for 2 or 5 s obviates the need for prolonged stabilization during studies of muscle relaxants.

Atracurium versus vecuronium in asthmatic patients. A blinded, randomized comparison of adverse events

BACKGROUND

To determine which of atracurium or vecuronium is associated with fewer adverse cardiovascular and pulmonary events in high-risk patients, the authors administered these drugs to patients with known asthma.

METHODS

Sixty patients aged 18-75 yr taking bronchodilators chronically for asthma were anesthetized with midazolam, fentanyl, nitrous oxide, and isoflurane; the trachea was intubated without paralysis. When anesthetic conditions and mechanical ventilation were stable, patients were randomly given 0.5 mg/kg atracurium or 0.1 mg/kg vecuronium over 5-10 s, and a blinded observer recorded cardiovascular, pulmonary, and cutaneous signs of adverse reactions for 6 min.

RESULTS

Arterial pressures and heart rate decreased after atracurium, and systolic pressure and heart rate decreased with vecuronium; these changes were small in magnitude. Cardiovascular effects (decrease in blood pressure or change in heart rate) > 10% were common with both atracurium (60% of patients) and vecuronium (57%). Cardiovascular effects > 20% were more frequent with atracurium (37%) than with vecuronium (13%, P < 0.05). The incidence of noncardiovascular adverse events (increase in peak airway pressure > 5 cmH2O, tidal volume decrease > 10%, rashes, and wheezing) did not differ between atracurium (17%) and vecuronium (7%). The largest increase in peak airway pressure was 5.1 cmH2O in a patient whose tidal volume decreased 16% with vecuronium; in the remaining patients, tidal volume decreased < 10%. No patients experienced inspiratory wheezing, marked decreases in arterial oxygen saturation, or marked increases in end-tidal carbon dioxide tension.

CONCLUSIONS

The authors conclude that, in patients with asthma, adverse cardiovascular events are more common with atracurium than with vecuronium.

Reversal of residual neuromuscular block with neostigmine at one to four hours after a single intubating dose of vecuronium

The purpose of this study was to measure the degree of residual neuromuscular block at different times after a single dose of vecuronium, and to evaluate the effectiveness of two different doses of neostigmine in antagonizing this residual block. Train-of-four (TOF) ratios were examined for up to 4 h after a single dose of vecuronium, 0.1 mg/kg, in 60 patients during nitrous oxide/isoflurane/fentanyl anesthesia. The effect of neostigmine, 40 micrograms/kg, was studied at 1,2,3, or 4 h. The effect of neostigmine, 20 micrograms/kg, was studied at 2 or 4 h after the vecuronium. Before neostigmine administration, the TOF ratio was less than 0.75 in 17 patients (including one patient at 4 h). Neostigmine produced an increase in TOF ratio in 52 patients and a decrease in 8. The TOF ratio decreased after neostigmine only, at 2,3, or 4 h after vecuronium, when the TOF ratio was > or = 0.9 and when neostigmine 40 micrograms/kg was administered. One patient, at 1 h, had a TOF ratio of 0.00 and this did not reach 0.75 until 57 min after neostigmine, 40 micrograms/kg. There was a high incidence (50%) of adverse cardiovascular effects after both doses of neostigmine. In making the decision as to whether neostigmine should be administered, the risk to the patient of residual neuromuscular block must be balanced against the adverse cardiovascular effects of the neostigmine.

New muscle relaxants

The Council on Scientific Affairs of the California Medical Association presents the following epitomes of progress in anesthesiology. Each item, in the judgment of a panel of knowledgeable physicians, has recently become reasonably firmly established, both as to scientific fact and clinical importance. The items are presented in simple epitome, and an authoritative reference, both to the item itself and to the subject as a whole, is generally given for those who may be unfamiliar with a particular item. The purpose is to assist busy practitioners, students, researchers, and scholars to stay abreast of progress in medicine, whether in their own field of special interest or another. The epitomes included here were selected by the Advisory Panel to the Section on Anesthesiology of the California Medical Association, and the summaries were prepared under the direction of Dr Jackson and the panel.

Onset and duration of rocuronium and succinylcholine at the adductor pollicis and laryngeal adductor muscles in anesthetized humans

BACKGROUND

Rocuronium, a new nondepolarizing muscle relaxant, has a rapid onset of activity and may be suitable as a component of a rapid-sequence induction of anesthesia. We evaluated a range of doses on onset and duration of effect at the larynx and the adductor pollicis and compared these characteristics with those of succinylcholine.

METHODS

Forty-eight patients aged 18-70 yr, of ASA physical status 1-3, were randomly allocated to receive succinylcholine (1 mg/kg) or one of three doses of rocuronium (0.4, 0.8, or 1.2 mg/kg) during surgery. Anesthesia was induced and maintained with propofol and fentanyl. The trachea was intubated without the use of muscle relaxants, and the cuff of the endotracheal tube placed between the vocal cords. Neuromuscular transmission was monitored by mechanomyography at the laryngeal adductor and adductor pollicis muscles. Muscular activity was evoked with supramaximal stimuli in a train-of-four sequence every 12 s to the anterior branch of the recurrent laryngeal nerve and the ulner nerve.

RESULTS

At the laryngeal adductors, peak effect exceeded 99% in all patients given succinylcholine and in none (0%), five (42%), and ten (83%) of those given rocuronium 0.4, 0.8, and 1.2 mg/kg, respectively. At the adductor pollicis, peak effect exceeded 99% in all study patients except two who received rocuronium 0.4 mg/kg (peak effects 91% and 97%). Onset of effect with succinylcholine was significantly more rapid at the laryngeal adductors (34 +/- 12 s, mean +/- SD) than at the adductor pollicis (56 +/- 15 s); this was true also for rocuronium 0.4 mg/kg (92 +/- 29 s and 155 +/- 40 s for the laryngeal adductors and adductor pollicis, respectively). Onset times were similar at the two muscle groups with rocuronium 0.8 and 1.2 mg.kg-1: 96 +/- 29 and 74 +/- 36 s with 0.8 mg/kg and 54 +/- 30 and 65 +/- 21 s with 1.2 mg/kg at the laryngeal adductors and the adductor pollicis, respectively.

CONCLUSIONS

The laryngeal adductors are more resistant to the action of rocuronium than is the adductor pollicis. Consequently, the onset of effect of rocuronium, in doses greater than 0.8 mg/kg, is similar to that of succinylcholine at the adductor pollicis but is significantly delayed compared with that of succinylcholine at the laryngeal adductors.

The pharmacodynamics and pharmacokinetics of the metabolite 3-desacetylvecuronium (ORG 7268) and its parent compound, vecuronium, in human volunteers

The pharmacology of 3-desacetylvecuronium, the principal metabolite of vecuronium, was investigated. We studied 12 healthy volunteers, each on two occasions. First they received 3-desacetylvecuronium alone and then, on a later occasion, vecuronium. Six subjects received a large dose of each drug (pharmacokinetic study), the remaining six received a small dose (pharmacodynamic study). Drug concentrations in plasma and urine were measured using capillary gas chromatography. Neuromuscular block was assessed by measuring force of contraction of the adductor pollicis. Drug plasma concentration vs. time and neuromuscular effect data were analyzed by nonlinear mixed-effects modeling. 3-Desacetylvecuronium, compared with vecuronium (median, range in parentheses), had a smaller plasma clearance, 3.51 (2.11-6.57) vs. 5.39 (5.04-7.19) ml.kg-1.min-1; a larger steady-state distribution volume, 254 (215-410) vs. 152 (111-170) ml.kg-1; a longer terminal elimination half-life 116 (44-672) vs. 34 (25-61) min and a longer mean residence time, 67 (42-145) vs. 26 (18-32) min (P < .05). Renal clearances of 3-desacetylvecuronium and vecuronium were 0.85 (0.15-1.24) and 0.58 (0.16-0.66) ml.kg-1.min-1, respectively (P < .05). Conversion to 3-desacetylvecuronium accounted for 12% of vecuronium's clearance. Concentrations of 3-desacetylvecuronium and vecuronium that produced 50% neuromuscular block were 123 (109-154) and 102 (71-123) ng.ml-1, respectively (P < .05). 3-Desacetylvecuronium is a potent neuromuscular blocking drug and may be responsible for episodes of prolonged paralysis after long-term administration of vecuronium to patients in intensive care units.

Influence of dose on suxamethonium-induced muscle damage

We have examined postoperative muscle pain and early increases in serum concentrations of myoglobin after administration of suxamethonium to see if these changes were dependent on the dose of drug. Thirty ASA I and II adult patients undergoing day-case surgery received a standard anaesthetic technique, including one of three doses of suxamethonium: 0.5, 1.5 or 3.0 mg kg-1. The incidence of postoperative myalgia and the severity of fasciculations were greater after suxamethonium 1.5 mg kg-1 than after a dose of 0.5 or 3.0 mg kg-1. Serum concentrations of myoglobin increased in a dose-dependent manner. Intubating conditions were significantly better with suxamethonium 1.5 or 3.0 mg kg-1 than with 0.5 mg kg-1. Changes in serum concentrations of calcium and potassium were small and similar in the three groups. We conclude that a dose of 3.0 mg kg-1 of suxamethonium provided a better combination of intubating conditions and minimal postoperative myalgia than the two lower doses.

Desflurane clinical pharmacokinetics and pharmacodynamics

Desflurane is a new volatile anaesthetic agent, with qualitative physiological and pharmacological effects similar to those of previously available drugs of this type. The feature that sets desflurane apart from other halogenated, volatile anaesthetics is its low solubility in blood and body tissues. Therefore, its uptake, distribution and elimination are more rapid than those for similar drugs. Desflurane undergoes negligible metabolism, and should have a low potential for producing toxic effects. Because it has a high vapour pressure desflurane needs a special delivery system, a heated, pressurised vaporizer. Its low solubility gives it the ability to produce rapid alterations in depth of anaesthesia and rapid emergence and recovery from anaesthesia.

Mild intraoperative hypothermia does not change the pharmacodynamics (concentration-effect relationship) of vecuronium in humans

To investigate the effect of mild hypothermia on the neuromuscular junction sensitivity to vecuronium, we determined the pharmacodynamics (concentration-effect relationship) of vecuronium in 10 patients (ASA physical class I or II; age range, 21-46 yr; weight range, 54-104 kg), during isoflurane-nitrous oxide-fentanyl anesthesia. Five were cooled to a mean temperature of 34.4 degrees C and five were maintained normothermic at a mean temperature of 36.8 degrees C. Neuromuscular function was monitored by measuring the evoked mechanical response of the adductor pollicis muscle after supramaximal train-of-four stimulation of the ulnar nerve at the wrist. Vecuronium, 3 micrograms.kg-1.min-1, was infused for 10 min, venous blood sampled for 60 min, and twitch tension and plasma concentration data were used to determine pharmacodynamic variables in each patient. Results for the hypothermic and normothermic groups were compared by Mann-Whitney U-test. There were no differences in any pharmacodynamic variable between the hypothermic and normothermic patients. For the hypothermic and normothermic patients, respectively, steady-state plasma concentrations of vecuronium producing 50% neuromuscular block (Css50) were 73 +/- 13 ng/mL (mean +/- SD) and 79 +/- 31 ng/mL; the rate constants for equilibration of vecuronium between the plasma and the neuromuscular junction (Keo) were 0.27 +/- 0.14 per min-1 and 0.26 +/- 0.11 per min, and the power functions representing the slope of the concentration-effect relationship (gamma) were 5.7 +/- 1.9 and 4.4 +/- 1.8.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional brain activity of free radical defense enzymes in autopsy samples from patients with Alzheimer's disease and from nondemented controls

Several lines of evidence support the hypothesis that oxygen free radicals are involved in the destruction of neurons in various degenerative disorders of the central nervous system. The activities of superoxide dismutase, catalase and glutathione peroxidase, three enzymes that contribute to the cellular defenses against free radical damage, were measured in different areas of autopsy brains from patients with Alzheimer's disease and from age matched controls. All brains were removed within 24 hours of the time of death and were cut in half sagitally. One half was stored frozen at -86 degrees C and the other half was examined histologically to confirm the presence or absence of Alzheimer's disease. Samples were taken from the frozen half for the enzyme assays. In control brains, the activity of superoxide dismutase is significantly higher in the cerebellum, frontal cortex and hippocampus than it is in the temporal cortex, parietal cortex and entorhinal cortex. The activity of catalase is significantly higher in cerebellum and frontal cortex than in hippocampus, parietal cortex and entorhinal cortex. Glutathione peroxidase activity is uniform across all brain areas studied. In Alzheimer's brains, superoxide dismutase activity is not statistically different among the various brain regions studied, but it is significantly lower than control in the cerebellum (-27%), frontal cortex (-27%) and hippocampus (-35%). Catalase is significantly higher in Alzheimer's cerebellum, frontal cortex and temporal cortex than in Alzheimer's hippocampus, parietal cortex and entorhinal cortex. However, there are no significant differences in catalase activity between Alzheimer's and control samples.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of hypothermia on adductor pollicis twitch tension during continuous infusion of vecuronium in isoflurane-anesthetized humans

The effect of total body cooling on force of contraction of the adductor pollicis was determined during a constant rate infusion of vecuronium. Anesthesia was induced with thiopental and maintained with isoflurane/nitrous oxide in eight volunteers (study group) and seven surgical patients (control group). After train-of-four (TOF) stimulation of the ulnar nerve, we measured the amplitude of the first response (T1) in the train and the ratio of the fourth-to-first response (TOF ratio). Vecuronium was then administered as an intravenous (i.v.) bolus, 25 micrograms/kg, followed by continuous i.v. infusion, 25 micrograms.kg-1 x h-1; central body (core) temperature was maintained stable for 60 min, at the end of which T1 and TOF responses were constant. In the study group, core temperature was then reduced (using circulating-water blankets) by a mean of 2.6 degrees C, decreasing the T1 and TOF ratio, respectively, by 19% and 18% per degrees C reduction in adductor pollicis temperature. Normothermia was maintained in the control group for a mean of 111 min, with no significant change in T1 and TOF responses. We conclude that, during a constant-rate infusion of vecuronium, the magnitude of neuromuscular block increases significantly when adductor pollicis temperature decreases secondary to core cooling.

Central nervous system effects of intrathecal muscle relaxants in rats

When given for a sufficient time and dose intravenously, neuromuscular blocking drugs eventually can enter the cerebrospinal fluid (CSF). To study the potential pharmacologic consequences of neuromuscular blocking drugs in the CSF, a model was developed in the rat by using an intrathecal infusion of these drugs. A cannula was stereotaxically implanted in a lateral cerebral ventricle of anesthetized male Sprague-Dawley rats (250-300 g). Several days later, the effects of an intraventricular infusion (5 microL/min) of atracurium (0.804 mumol/mL), pancuronium (0.172 mumol/mL), and vecuronium (21.978 mumol/mL) were studied in unanesthetized rats. These rats (n = 6 in each group) exhibited dose-dependent hyperexcitability, during drug infusion, with seizures occurring at threshold doses of (mean), 0.12, 0.26, and 0.065 +/- 0.010 and 3.32 mumol/kg of atracurium, pancuronium, and vecuronium, respectively. The neuromuscular ED50 (intravenous dose required to produce a 50% depression of twitch tension) in rats determined by other investigators are 0.408, 0.115, and 0.352 mumol/kg for atracurium, pancuronium, and vecuronium, respectively. Therefore, seizure threshold doses were not related to the potencies of these drugs as neuromuscular blocking drugs. Based on these data, central nervous system effects were studied over the subseizure dose range approximating 1/100, 1/10, and 1/5 of the cumulative dose causing seizures for each drug (n = 5 for each dose). At 1/100 of seizure dose, decreased locomotor activity and piloerection occurred. At 1/10 to 1/5 of seizure dose, agitation, shivering, splayed limbs, and whole body shaking resulted.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of rocuronium bromide (ORG 9426) in patients with normal renal function or patients undergoing cadaver renal transplantation

To determine the effect of end-stage renal disease on the pharmacokinetics of reocuronium bromide (ORG 9426), a new nondepolarizing monoquaternary steroidal neuromuscular blocking drug, the authors administered 600 micrograms/kg rocuronium (2 x ED95) intravenously to ten patients undergoing cadaver renal transplantation and ten healthy patients undergoing elective minor surgery (controls). All patients were anesthetized with nitrous oxide (50-70% in oxygen) and isoflurane (end-tidal concentrations of 1.2 +/- 0.5% and 0.8 +/- 0.2%, mean +/- SD, for control and transplant groups, respectively). Plasma concentrations of rocuronium were determined by capillary gas chromatography. A population-based pharmacokinetic analysis (NONMEM) was used to determine typical values, standard errors, and interindividual variability for the pharmacokinetic parameters and to determine whether these values differed between control and renal transplant patients. Total plasma clearance (2.89 +/- 0.25 ml.kg-1.min-1, mean +/- SE) and volume of the central compartment (76.9 +/- 10.6 ml/kg) did not differ between control and renal transplant patients, whereas volume of distribution at steady state was greater in renal transplant patients (264 +/- 19 ml/kg) than in control patients (207 +/- 14 ml/kg). This resulted in a longer elimination half life in renal transplant patients (97.2 +/- 17.3 min) compared to controls (70.9 +/- 4.7 min). The authors conclude that renal failure and renal transplantation alter the distribution but not the clearance of rocuronium.

4-oxatetradecanoic acid is fungicidal for Cryptococcus neoformans and inhibits replication of human immunodeficiency virus I

Candida albicans and Cryptococcus neoformans are major causes of systemic fungal infections, particularly in patients with acquired immunodeficiency syndrome. Metabolic labeling studies revealed that these organisms synthesize a small number of N-myristoylproteins, the most prominent being 20-kDa ADP-ribosylation factors (Arfs). C. albicans Arf has approximately 80% identity with the essential Arf1 and Arf2 proteins of Saccharomyces cerevisiae. [3H]Myristic acid analogs with oxygen for -CH2- substitutions at C4, C6, C11, and C13 are incorporated into cellular N-myristoylproteins, phospholipids, and neutral lipids produced by these three yeasts during exponential growth at 30 degrees C in complex media. Analog- and organism-specific differences in the efficiency of labeling of proteins and lipid classes were observed. The effects of oxatetradecanoic acids with oxygen for -CH2- substitutions at C3-C13 on C. neoformans, C. albicans, and S. cerevisiae were assessed during mid-log phase growth at 30 degrees C. A single dose of 3-oxa-, 4-oxa-, 5-oxa- or 6-oxatetradecanoic acid (O3-O6, final concentration = 300 microM) was able to inhibit growth of C. neoformans in the order O4 greater than O5 greater than O3 approximately O6. The other compounds were inactive. 4-Oxatetradecanoic acid was fungicidal, producing a 10,000-fold reduction in viable cell number 1 h after administration and continued suppression of cell growth for 7 h. A clear dose response was observed over a concentration range of 100-300 microM. 4-Oxatridecanoic acid was 100-fold less potent in reducing cell viability than 4-oxatetradecanoic acid but more potent than 5-oxatridecanoic acid. O4 produced approximately 10-100-fold reductions in the viability of C. albicans and S. cerevisiae at 300-500 microM, respectively, whereas O5 and O6 were less active. Since N-myristoylation of the Pr55gag polyprotein precursor produced by human immunodeficiency virus I (HIV-I) is essential for its assembly, we also assessed the antiviral effects of 4-oxatetradecanoic acid. O4 is able to produce a 50% reduction in the replication of HIV-I in acutely infected human T-lymphocyte cell lines at a concentration of 18 microM. Together, these data suggest that (i) the position of the oxygen for methylene substitution is a critical determinant of the fungicidal activity of O4 and (ii) NMT may be an attractive therapeutic target for treating opportunistic fungal infections in patients infected with HIV-I.

Persistent paralysis in critically ill patients after long-term administration of vecuronium

BACKGROUND

The muscle relaxant vecuronium is sometimes administered to facilitate mechanical ventilation. Neuromuscular paralysis lasting up to seven days may occur after the termination of long-term administration (i.e., more than two days) of vecuronium in critically ill patients. We investigated the role of clinical factors and plasma concentrations of vecuronium and its metabolite in causing this prolonged neuromuscular blockade.

METHODS

We studied 16 critically ill adult patients (8 women and 8 men) who had received vecuronium to facilitate mechanical ventilation for at least two consecutive days. Clinical factors and plasma concentrations of vecuronium and 3-desacetylvecuronium, the active metabolite of vecuronium, were compared in patients with and without prolonged neuromuscular blockade. In addition, we performed detailed pharmacokinetic studies in the patients without prolonged neuromuscular blockade.

RESULTS

Seven of the 16 patients had prolonged neuromuscular blockade, lasting from six hours to more than seven days, after the termination of vecuronium therapy. These seven patients, six of whom were women, had higher plasma magnesium concentrations and lower arterial blood pH values than the nine patients without prolonged neuromuscular blockade. They also had higher plasma concentrations of 3-desacetylvecuronium and a higher frequency of renal failure (seven of seven patients vs. four of nine patients, P less than 0.03). In the patients without prolonged neuromuscular blockade, the mean (+/- SD) plasma clearance, elimination half-life, and volume of distribution of vecuronium were 2.5 +/- 1.0 ml per kilogram of body weight per minute, 299 +/- 154 minutes, and 1.1 +/- 0.6 liters per kilogram, respectively.

CONCLUSIONS

Prolonged neuromuscular blockade after the termination of long-term treatment with vecuronium is associated with metabolic acidosis, elevated plasma magnesium concentrations, female sex, and probably more important, the presence of renal failure and high plasma concentrations of 3-desacetylvecuronium.