The right blood collection tube for therapeutic drug monitoring and toxicology screening procedures: Standard tubes, gel or mechanical separator?

Stability data of toxics or drugs in gel-based or mechanical separation blood collection tubes are lacking, especially for therapeutic drug monitoring and clinical toxicology procedures. According to ISO 15189 accreditation standard, laboratories need to master the entire preanalytical process including the stability of analytes in a specific tube. Here we explored the impact of BD PST™ II and Barricor™ separator tubes on the stability of 167 therapeutic compounds and common drugs of abuse in plasma samples using LC-MS/MS. Forty drugs were significantly affected by the use of PST™ II tubes, including antidepressants (11/26), neuroleptics (9/13), cardiovascular drugs (5/26), anxiolytics and hypnotics (4/25) and some drugs of abuse (5/26). Six compounds exhibited significant reduction by the mechanical Barricor™ tubes. Ten drugs exhibited low (<85%) but non-significant recoveries due to inter-assay variability. Besides, a logP > 3.3 was determined as a cut-off value to predict a potential lack of stability in PST™ II gel tubes with an 86.4% sensitivity and a 61.4% specificity. As a consequence, determination of drugs with a logP > 3.3 should be carried out with caution in plasma samples withdrawn on PST™ II. The study showed the Barricor™ and non-gel tubes cause less drug interference and are recommended for the drugs studied.

Spoken words are processed during dexmedetomidine-induced unresponsiveness.

BACKGROUND: Studying the effects of anaesthetic drugs on the processing of semantic stimuli could yield insights into how brain functions change in the transition from wakefulness to unresponsiveness. Here, we explored the N400 event-related potential during dexmedetomidine- and propofol-induced unresponsiveness. METHODS: Forty-seven healthy subjects were randomised to receive either dexmedetomidine (n=23) or propofol (n=24) in this open-label parallel-group study. Loss of responsiveness was achieved by stepwise increments of pseudo-steady-state plasma concentrations, and presumed loss of consciousness was induced using 1.5 times the concentration required for loss of responsiveness. Pre-recorded spoken sentences ending either with an expected (congruous) or an unexpected (incongruous) word were presented during unresponsiveness. The resulting electroencephalogram data were analysed for the presence of the N400 component, and for the N400 effect defined as the difference between the N400 components elicited by congruous and incongruous stimuli, in the time window 300-600 ms post-stimulus. Recognition of the presented stimuli was tested after recovery of responsiveness. RESULTS: The N400 effect was not observed during dexmedetomidine- or propofol-induced unresponsiveness. The N400 component, however, persisted during dexmedetomidine administration. The N400 component elicited by congruous stimuli during unresponsiveness in the dexmedetomidine group resembled the large component evoked by incongruous stimuli at the awake baseline. After recovery, no recognition of the stimuli heard during unresponsiveness occurred. CONCLUSIONS: Dexmedetomidine and propofol disrupt the discrimination of congruous and incongruous spoken sentences, and recognition memory at loss of responsiveness. However, the processing of words is partially preserved during dexmedetomidine-induced unresponsiveness. CLINICAL TRIAL REGISTRATION: NCT01889004.

Neural correlates of successful semantic processing during propofol sedation.

Sedation has a graded effect on brain responses to auditory stimuli: perceptual processing persists at sedation levels that attenuate more complex processing. We used fMRI in healthy volunteers sedated with propofol to assess changes in neural responses to spoken stimuli. Volunteers were scanned awake, sedated, and during recovery, while making perceptual or semantic decisions about nonspeech sounds or spoken words respectively. Sedation caused increased error rates and response times, and differentially affected responses to words in the left inferior frontal gyrus (LIFG) and the left inferior temporal gyrus (LITG). Activity in LIFG regions putatively associated with semantic processing, was significantly reduced by sedation despite sedated volunteers continuing to make accurate semantic decisions. Instead, LITG activity was preserved for words greater than nonspeech sounds and may therefore be associated with persistent semantic processing during the deepest levels of sedation. These results suggest functionally distinct contributions of frontal and temporal regions to semantic decision making. These results have implications for functional imaging studies of language, for understanding mechanisms of impaired speech comprehension in postoperative patients with residual levels of anesthetic, and may contribute to the development of frameworks against which EEG based monitors could be calibrated to detect awareness under anesthesia.

[BIS values were useful on the evaluation of consciousness recovery in acute Vegetamin-A poisoning: report of a case].

A 37-year-old man was admitted to our hospital with acute phenobarbital poisoning. On arrival, he was in deep coma with respiro-circulatory depressions. The serum concentration of the agent was elevated to 149.04 µg/mL which was consistent with a lethal concentration level. He underwent a gastric lavage, administration of activated charcoal, urinary alkalinazation and bowel irrigation. Respiro-circulatory status was recovered rapidly, while the serum concentration of phenobarbital did not decrease smoothly. Although the concentration of the agent decreased to 77.07 µg/mL that should be a comatose level, BIS values were gradually elevated, and then eventually the patient regained his consciousness. Because he was a chronic user of Vegetamin-A containing phenobarbital, the serum level might not have been correlated with symptoms. BIS values were highly reflective of the consciousness level, so it could be a useful indicator for predicting the consciousness levels of patients in deep coma with acute poisoning from hypnotic agents.

Pharmacokinetics of valerenic acid after administration of valerian in healthy subjects.

OBJECTIVES: To describe the pharmacokinetics of valerenic acid in a group of healthy adults after a single oral dose of valerian using a newly developed sensitive assay for serum concentrations of valerenic acid, a commonly used marker for qualitative and quantitative analysis of valerian root and valerian products. STUDY DESIGN: Six healthy adults (22-61 years, five men, one female) received a single 600 mg dose of valerian at 08:00. Blood samples were collected for 8 h after administration. Valerenic acid was extracted from serum and measured using a LC/MS/MS method developed in our laboratory. RESULTS: The maximum serum concentration of valerenic acid for five of the six subjects occurred between 1 and 2 h ranging from 0.9 to 2.3 ng/mL. Valerenic acid serum concentrations were measurable for at least 5 h after the valerian dose. One subject showed a peak plasma value at 1 h and a second peak at 5 h. The elimination half-life (T(1/2)) for valerenic acid was 1.1 +/- 0.6 h. The area under the concentration time curve (AUC) as a measure of valerenic acid exposure was variable (4.80 +/- 2.96 microg/mL. h) and not correlated with subject's age or weight. CONCLUSIONS: Assuming that valerenic acid serum concentrations correlate with the pharmacological activity of valerian, the timing of the valerenic acid peak concentration is consistent with the standard dosage recommendation to take valerian 30 min to 2 h before bedtime. Ongoing studies are evaluating the relationship between valerenic acid serum concentrations and objective measures of sleep in patients.

[Can treatment associated with ticlopidine and nifedipine increase serum levels of phenobarbital?]. / ¿Puede el tratamiento asociado con ticlopidina y nifedipina aumentar los niveles séricos de fenobarbital?

INTRODUCTION: We report a case in which the association between ticlopidine, nifedipine and phenobarbital was linked with a higher than expected phenobarbital concentration in serum, which suggested a possible interaction between these drugs. CASE REPORT: A 67 year old male who received treatment with phenobarbital, digoxin, nifedipine, ticlopidine, paroxetine and clorazepate dipotassium. The first control of the level of phenobarbital in serum was performed without any symptoms or signs of toxicity or ineffectiveness. A phenobarbital concentration in serum of 21.4 mg/L was obtained, with a serum level/dosage ratio of 16.7. DISCUSSION: The serum level/dosage ratio of phenobarbital that was found in this case is almost twice as high as expected. In the absence of other factors that can explain this finding, we believe that two drugs (ticlopidine and nifedipine) may be involved in an interaction with phenobarbital. CONCLUSIONS: The high value of the serum level/dosage ratio that was found makes it advisable to monitor the concentrations of phenobarbital in serum in treatment associated with ticlopidine or nifedipine, especially when adjusting the dosage, beginning or ending treatment with these drugs.

Effects of propofol on hemodynamic and inflammatory responses to endotoxemia in rats.

OBJECTIVE: To document the effects of propofol on the hemodynamic and inflammatory responses to endotoxemia in an animal model. DESIGN: Randomized, prospective laboratory study. SETTING: University experimental laboratory. SUBJECTS: Thirty-two male rats. INTERVENTIONS: The animals were randomly assigned to one of four groups: a) endotoxemia group (n = 8), which received intravenous Escherichia coli endotoxin (15 mg/kg over 2 mins); b) control group (n = 8), which was treated identically to the endotoxemia group except for the substitution of 0.9% saline for endotoxin; c) propofol group (n = 8), which was treated identically to the control group but also received propofol (10 mg/kg bolus, followed by infusion at 10 mg/kg/hr) immediately after the injection of 0.9% saline; and d) propofol-endotoxemia group (n = 8), which was treated identically to the endotoxemia group with the additional administration of propofol (10 mg/kg bolus, followed by infusion at 10 mg/kg/hr) immediately after endotoxin injection. MEASUREMENTS AND MAIN RESULTS: Hemodynamics, arterial blood gases, and acid-base status were recorded and the blood propofol concentrations and plasma cytokine concentrations were measured during the 5-hr observation. Microscopic findings of lung tissue for each group were obtained at necropsy. The systolic arterial pressure and heart rate of the propofol-endotoxemia group were similar to those of the endotoxemia group. The increases in the plasma cytokine (tumor necrosis factor, interleukin-6, and interleukin-10) concentrations, in the base deficit, and in the infiltration of neutrophils in the air space or vessel walls of the lungs were attenuated in the propofol-endotoxemia group compared with the endotoxemia group. CONCLUSIONS: Propofol attenuated cytokine responses, base deficit, and activation of neutrophils to endotoxemia. These findings suggest that propofol may inhibit inflammatory response and prevent the development of metabolic acidosis during endotoxemia.

Brain mechanisms of propofol-induced loss of consciousness in humans: a positron emission tomographic study.

In the present study, we used positron emission tomography to investigate changes in regional cerebral blood flow (rCBF) during a general anesthetic infusion set to produce a gradual transition from the awake state to unconsciousness. Five right-handed human volunteers participated in the study. They were given propofol with a computer-controlled infusion pump to achieve three stable levels of plasma concentrations corresponding to mild sedation, deep sedation, and unconsciousness, the latter defined as unresponsiveness to verbal commands. During awake baseline and each of the three levels of sedation, two scans were acquired after injection of an H215O bolus. Global as well as regional CBF were determined and correlated with propofol concentrations. In addition, blood flow changes in the thalamus were correlated with those of the entire scanned volume to determine areas of coordinated changes. In addition to a generalized decrease in global CBF, large regional decreases in CBF occurred bilaterally in the medial thalamus, the cuneus and precuneus, and the posterior cingulate, orbitofrontal, and right angular gyri. Furthermore, a significant covariation between the thalamic and midbrain blood flow changes was observed, suggesting a close functional relationship between the two structures. We suggest that, at the concentrations attained, propofol preferentially decreases rCBF in brain regions previously implicated in the regulation of arousal, performance of associative functions, and autonomic control. Our data support the hypothesis that anesthetics induce behavioral changes via a preferential, concentration-dependent effect on specific neuronal networks rather than through a nonspecific, generalized effect on the brain.

Simultaneous determination of zolpidem and zopiclone in human plasma by gas chromatography-nitrogen-phosphorus detection.

A simple, specific and selective method for the simultaneous determination of zolpidem and zopiclone in human plasma is described. After a liquid-liquid extraction, the extract is injected into a capillary gas chromatograph with an OV-1 fused-silica column coupled to a nitrogen-phosphorus detector. The detection limits are 1 and 2 ng/ml for zolpidem and zopiclone, respectively. The method described is reproducible and linear over a range of concentrations, rendering it suitable for use for pharmacokinetic studies or toxicological evaluations. Absolute identification of the chromatographed compounds is accomplished by gas chromatography--mass spectrometry in both electron-impact and positive-ion chemical ionisation modes.

Midazolam: the first water-soluble benzodiazepine. Pharmacology, pharmacokinetics and efficacy in insomnia and anesthesia.

Midazolam is a 1,4-benzodiazepine derivative with a unique chemical structure: depending on environmental pH, the drug can produce highly water-soluble salts (pH less than 4) or exist in lipophilic diazepine ring-closed form (pH greater than 4). This characteristic contributes to rapid onset of action and to good local tolerance after parenteral administration. After both oral and parenteral administration, midazolam has a fast absorption rate and is rapidly excreted, with a half-life of only about 2 hours. A reasonably good correlation has been found between plasma levels and clinical effects, indicating a fast but brief response. As a hypnotic, midazolam is mainly indicated in insomniac patients with difficulties in falling asleep or having a pathologic sleep pattern during the first half of the night. No marked hangover effects are present the next morning. In anesthesiology, midazolam appears to be a useful, short-acting, sedative-anxiolytic and amnesic premedicant after both oral and parenteral administration. In minor surgery, however, the slow, unpredictable onset and variable duration of action, as compared with thiopental, may inhibit its routine use as an induction agent, especially in young patients, without heavy premedication. In major surgery, midazolam is an alternative to thiopental for induction of anesthesia in spite of its slow, variable induction time. Its advantages include good cardiovascular stability, transient and mild respiratory depression, low frequency of venous irritation, production of anterograde amnesia and short duration of action in comparison with other benzodiazepines.