Bolus infusion scheme for the adjustment of steady state [11C]Flumazenil levels in the grey matter and in the blood plasma for neuroreceptor imaging.

The use of hybrid PET/MR imaging facilitates the simultaneous investigation of challenge-related changes in ligand binding to neuroreceptors using PET, while concurrently measuring neuroactivation or blood flow with MRI. Having attained a steady state of the PET radiotracer using a bolus-infusion protocol, it is possible to observe alterations in ligand neuroreceptor binding through changes in distribution volumes. Here, we present an iterative procedure for establishing an administration scheme to obtain steady state [11C]flumazenil concentrations in grey matter in the human brain. In order to achieve a steady state in the shortest possible time, the bolus infusion ratio from a previous examination was adapted to fit the subsequent examination. 17 male volunteers were included in the study. Boli and infusions with different weightings were given to the subjects and were characterised by kbol values from 74 â€‹min down to 42 â€‹min. Metabolite analysis was used to ascertain the value of unmetabolised flumazenil in the plasma, and PET imaging was used to assess its binding in the grey matter. The flumazenil time-activity curves (TACs) in the brain were decomposed into activity contributions from pure grey and white matter and analysed for 12 â€‹vol of interest (VOIs). The curves highlighted a large variability in metabolic rates between the subjects, with kbol â€‹= â€‹54.3 â€‹min being a reliable value to provide flumazenil equilibrium conditions in the majority of the VOIs and cases. The distribution volume of flumazenil in all 12 VOIs was determined.

Serum Adipokines, Growth Factors, and Cytokines Are Independently Associated with Stunting in Bangladeshi Children.

Growth in young children is controlled through the release of several hormonal signals, which are affected by diet, infection, and other exposures. Stunting is clearly a growth disorder, yet limited evidence exists documenting the association of different growth biomarkers with child stunting. This study explored the association between different growth biomarkers and stunting in Bangladeshi children. A quasi-experimental study was conducted among 50 stunted (length-for-age Z-score (LAZ) < -2 SD) and 50 control (LAZ ≥ -2 SD) children, aged 12-18 months, residing in a Bangladeshi slum. The enrolled stunted children received an intervention package, which included food supplementation for three months, psychosocial stimulation for six months, and routine clinical care on community nutrition center at the study field site. The controls received routine clinical care only. All children were clinically screened over the study period. Length, weight, fasting blood and fecal biomarkers were measured. All biomarkers levels were similar in both groups except for oxyntomodulin at enrolment. Leptin (adjusted odds ratio, AOR: 4.0, p < 0.01), leptin-adiponectin ratio (AOR 5.07 × 108, p < 0.01), insulin-like growth factor-1 (IGF-1) (AOR 1.02, p < 0.05), and gamma interferon (IFN-γ) (AOR 0.92, p < 0.05) levels were independently associated with stunting at enrolment. Serum leptin, leptin-adiponectin ratio, interleukin-6 (IL-6), IL-10, tumor necrosis factor-alpha (TNF-α), and fecal alpha-1-antitrypsin (AAT) levels increased significantly (p < 0.001), while IFN-γ levels significantly decreased among stunted children after six months of intervention. Leptin, leptin-adiponectin ratio, IGF-1, and IFN-γ are independently associated with stunting in Bangladeshi children. This trial was registered at clinicaltrials.gov as NCT02839148.

Design of Infusion Schemes for Neuroreceptor Imaging: Application to [(11)C]Flumazenil-PET Steady-State Study.

This study aims at developing a simulation system that predicts the optimal study design for attaining tracer steady-state conditions in brain and blood rapidly. Tracer kinetics was determined from bolus studies and used to construct the system. Subsequently, the system was used to design inputs for bolus infusion (BI) or programmed infusion (PI) experiments. Steady-state quantitative measurements can be made with one short scan and venous blood samples. The GABAA receptor ligand [(11)C]Flumazenil (FMZ) was chosen for this purpose, as it lacks a suitable reference region. Methods. Five bolus [(11)C]FMZ-PET scans were conducted, based on which population-based PI and BI schemes were designed and tested in five additional healthy subjects. The design of a PI was assisted by an offline feedback controller. Results. The system could reproduce the measurements in blood and brain. With PI, [(11)C]FMZ steady state was attained within 40 min, which was 8 min earlier than the optimal BI (B/I ratio = 55 min). Conclusions. The system can design both BI and PI schemes to attain steady state rapidly. For example, subjects can be [(11)C]FMZ-PET scanned after 40 min of tracer infusion for 40 min with venous sampling and a straight-forward quantification. This simulation toolbox is available for other PET-tracers.

Determination of flumazenil in serum by liquid chromatography-mass spectrometry: Application to kinetics study in acute diazepam overdose.

BACKGOUND/AIM: Flumazenil is benzodiazepine receptor antagonist. It has been studied for a various indications, including reversal of sedation after surgery or diagnostic procedures, awakening of comatose patients in benzodiazepine overdose, or for symptomatic treatment of hepatic encephalopathy. Some drugs, like theophylline, may prolong its elimination half-life. Considering the long half-life of diazepam and its metabolites, concomitant use of theophylline may reduce the need for repeated dosing of flumazenil in patients with acute diazepam poisoning. The aim of this study was to introduce a reliable and accurate method for determining the concentration of flumazenil after therapeutic application in patients with acute poisoning, and using that method to assess whether the kinetics of flumazenil change in the presence of aminophylline (combination of theophylline and ethylenediamine in a 2:1 ratio) applied as concomitant therapy. METHODS: Blood samples from patients with acute diazepam poisoning that received flumazenil at the dose of 0.5 mg, or the same dose with 3 mg/kg of body weight of aminophylline, were collected 1, 3, 10, 30, 60, 120 and 240 min after its intravenous administration. Samples were prepared by solid-phase extraction on Oasis HLB cartridges with ethylacetate as extracting agens. Flumazenil was determined by liquid chromatography with mass spectrometry (LC-MS) in single ionmonitoring mode at m/z 304. Separation of flumazenil from matrix compound was performed on Lichrospher RP-8 column usingthe mixture of acidic acetonitrile and 20 mM of ammonium acetatein water (55 : 45) as a mobile phase. RESULTS: The applied analitycal method showed excellent recovery (94.65%). The obtained extracts were much cleaner than the extracts obtained by the sameextractant in the process of liquid-liquid extraction. The limit ofdetection of the LC-MS method described in this paper was 0.5 ng/mL and the limit of quantitation was 1 ng/mL. In the patientstreated with both flumazenil and aminophylline, the eliminationconstant for flumazenil was significantly lower and the elimination half-life was longer (p < 0.05) in comparison with the same parameters in.the patients who received flumazenil alone. CONCLUSION: The applied LC-MS method for the determination of flumazenil in serum samples of patients with acute diazepam poisoning is rapid, sensitive, precise and specific. Concomitant use with theophylline significantly prolonged elimination of flumazenil during the treatment of acute poisonings with diazepam.

In-vivo imaging characteristics of two fluorinated flumazenil radiotracers in the rat.

PURPOSE: [(11)C]Flumazenil shows promise as a clinical and research PET radiotracer to image changes in GABA(A) central benzodiazepine receptor (cBZR), but its widespread use has been limited by practical limitations of [(11)C]. This study evaluated the imaging characteristics of two fluorinated PET radiotracers in rats in vivo: [(18)F]fluoroflumazenil ([(18)F]FFMZ) and [(18)F]flumazenil ([(18)F]FMZ). METHODS: PET acquisitions were performed on a small-animal scanner following injection of [(18)F]FFMZ in nine rats and [(18)F]FMZ in eight rats. The following treatments were investigated: (1) injection of the tracer dose, (2) presaturation then injection of the tracer dose, and (3) injection of the tracer dose followed by a displacement injection. Unchanged tracer was measured in plasma and brain structures in four animals 10 and 30 min after injection, and ex-vivo autoradiography was also performed. RESULTS: For both [(18)F]FFMZ and [(18)F]FMZ maximal brain activity peaked rapidly, and was highest in the hippocampus (1.12+/-0.06 SUV, 1.24+/-0.10 SUV, respectively), and lowest in the pons (1.00+/-0.07 SUV, 1.03+/-0.09 SUV, respectively). By 50 min after injection, maximal uptake for [(18)F]FFMZ and [(18)F]FMZ had decreased in the hippocampus to 18+/-3% and 80+/-1% (p<0.01), respectively. The presaturation and displacement studies showed a higher nonspecific component for [(18)F]FFMZ than for [(18)F]FMZ. Metabolite studies showed that at 30 min only 10% of the signal was from [(18)F]FFMZ in the brain. This nonspecific binding was apparent on autoradiography. In contrast, [(18)F]FMZ accounted for >70% of the signal in the brain, which resulted in well-defined regional binding on autoradiography. CONCLUSION: These results demonstrate that [(18)F]FMZ is a superior radiotracer to [(18)F]FFMZ for in-vivo PET imaging of the GABA(A)/cBZR, having slower metabolism and leading to lower concentrations of metabolites in the brain that results in a substantially better signal-to-noise ratio.

Changes in GABAA receptor properties in amygdala kindled animals: in vivo studies using [11C]flumazenil and positron emission tomography.

PURPOSE: The purpose of the present investigation was to quantify alterations in GABA(A) receptor density in vivo in rats subjected to amygdala kindling. METHODS: The GABA(A) receptor density was quantified by conducting a [(11)C]flumazenil (FMZ) positron emission tomography (PET) study according to the full saturation method, in which each animal received a single injection of FMZ to fully saturate the GABA(A) receptors. Subsequently, the concentration-time curves of FMZ in blood [using high-pressure liquid chromatography with UV detector (HPLC-UV) or high-performance liquid chromatography coupled to tandem mass spectrometry (LC/MS/MS)] and brain (with PET-scanning) were analyzed by population modeling using a pharmacokinetic model, containing expressions to describe the time course of FMZ in blood and brain. RESULTS: The GABA(A) receptor density (B(max)) in kindled rats was decreased by 36% compared with controls. This is consistent with a reduction of 28% in electroencephalography (EEG) effect of midazolam in the same animal model, suggesting that a reduced number of GABA(A) receptors underlies the decreased efficacy of midazolam. Furthermore, receptor affinity (K(D)) was not changed, but the total volume of distribution in the brain (V(Br)), is increased to 178% of control after kindling, which might indicate an alteration in the transport of FMZ across the blood-brain barrier. CONCLUSIONS: Both the GABA(A) receptor density (B(max)), and possibly also the blood-brain barrier transport of FMZ (V(Br)) are altered after kindling. Furthermore, this study indicates the feasibility of conducting PET studies for quantifying moderate changes in GABA(A) receptor density in a rat model of epilepsy in vivo.

Tiagabine increases [11C]flumazenil binding in cortical brain regions in healthy control subjects.

Accumulating evidence indicates that synchronization of cortical neuronal activity at gamma-band frequencies is important for various types of perceptual and cognitive processes and that GABA-A receptor-mediated transmission is required for the induction of these network oscillations. In turn, the abnormalities in GABA transmission postulated to play a role in psychiatric conditions such as schizophrenia might contribute to the cognitive deficits seen in this illness. We measured the ability to increase GABA in eight healthy subjects by comparing the binding of [(11)C]flumazenil, a positron emission tomography (PET) radiotracer specific for the benzodiazepine (BDZ) site, at baseline and in the presence of an acute elevation in GABA levels through the blockade of the GABA membrane transporter (GAT1). Preclinical work suggests that increased GABA levels enhance the affinity of GABA-A receptors for BDZ ligands (termed 'GABA shift'). Theoretically, such an increase in the affinity of GABA-A receptors should be detected as an increase in the binding of a GABA-A BDZ-receptor site-specific PET radioligand. GAT1 blockade resulted in significant increases in mean (+/- SD) [(11)C]flumazenil-binding potential (BP(ND)) over baseline in brain regions representing the major functional domains of the cerebral cortex: association cortex +15.2+/-20.2% (p=0.05), sensory cortex +13.5+/-15.5% (p=0.03) and limbic (medial temporal lobe, MTL) +16.4+/-20.2% (p=0.03). The increase in [(11)C]flumazenil-BP(ND) was not accounted for by differences in the plasma-free fraction (f(P); paired t-test p=0.24) or changes in the nonspecific binding (pons V(T), p=0.73). Moreover, the ability to increase GABA strongly predicted (r=0.85, p=0.015) the ability to entrain cortical networks, measured through EEG gamma synchrony during a cognitive control task in these same subjects. Although additional studies are necessary to further validate this technique, these data provide preliminary evidence of the ability to measure in vivo, with PET, acute fluctuations in extracellular GABA levels and provide the first in vivo documentation of a relationship between GABA neurotransmission and EEG gamma-band power in humans.

Population pharmacokinetic analysis for simultaneous determination of B (max) and K (D) in vivo by positron emission tomography.

PURPOSE: Changes in GABA(A)-receptor density and affinity play an important role in many forms of epilepsy. A novel approach, using positron emission tomography (PET) and [C-11]flumazenil ([C-11]FMZ), was developed for simultaneous estimation of GABA(A)-receptor properties, characterized by B (max) and K (D). PROCEDURES: Following an injection of [C-11]FMZ (dose range: 1-2,000 mug) to 21 rats, concentration time curves of FMZ in brain (using PET) and blood (using HPLC-UV) were analyzed simultaneously using a population pharmacokinetic (PK) model, containing expressions to describe the time course of the plasma concentration (including distribution to the body), the brain distribution, and the specific binding within the brain. RESULTS: Application of this method in control rats resulted in estimates of B (max) and K (D) (14.5 +/- 3.7 ng/ml and 4.68 +/- 1.5 ng/ml, respectively). CONCLUSIONS: The proposed population PK model allowed for simultaneous estimation of B (max) and K (D) for a group of animals using single injection PET experiments per animal.

Evaluation of the use of a standard input function for compartment analysis of [123I]iomazenil data: factors influencing the quantitative results.

Adoption of standard input function (SIF) has been proposed for kinetic analysis of receptor binding potential (BP), instead of invasive frequent arterial samplings. The purpose of this study was to assess the SIF method in quantitative analysis of [123I]iomazenil (IMZ), a central benzodiazepine antagonist, for SPECT. SPECT studies were performed on 10 patients with cerebrovascular disease or Alzheimer disease. Intermittent dynamic SPECT scans were performed from 0 to 201 min after IMZ-injection. BPs calculated from SIFs obtained from normal volunteers (BPs) were compared with those of individual arterial samplings (BPo). Good correlations were shown between BP(o)s and BP(s)s in the 9 subjects, but maximum BP(s)s were four times larger than the corresponding BP(o)s in one case. There were no abnormal laboratory data in this patient, but the relative arterial input count in the late period was higher than the SIF. Simulation studies with modified input functions revealed that height in the late period can produce significant errors in estimated BPs. These results suggested that the simplified method with one-point arterial sampling and SIF can not be applied clinically. One additional arterial sampling in the late period may be useful.

Benzodiazepine receptor distribution in severe intractable tinnitus.

Tinnitus affects nearly 50 million people in the United States, with a minority demonstrating marked functional impairment. Alterations of gamma aminobutyric acid (GABA) neuronal function and benzodiazepine receptor (BZR) function in particular have been implicated in the pathophysiology of severe, chronic tinnitus. The purpose of our study was to evaluate the distribution of BZR in the brain using 123I-iomazenil single-photon emission computed tomography (SPECT) imaging in patients with severe, intractable central tinnitus. Six patients with severe intractable tinnitus received a bolus and constant infusion of 123I-iomazenil intravenously over 7 hours with SPECT and magnetic resonance imaging of the brain. After magnetic resonance imaging coregistration, standardized regions of interest were placed over the cerebellar, frontal (control), superior temporal, hippocampal, and thalamic regions bilaterally on (SPECT) images. Venous blood samples were drawn at specified intervals to determine equilibrium distribution volumes (V3') for each of the regions. Variation in V3' values in homotypic regions were calculated using a Wilcoxon signed rank test. Twelve normal control subjects were compared to the study subjects using statistical parametric mapping. Comparison of homotypic brain regions showed statistically significant asymmetry in the V3' data in the superior temporal cortex (p = .03 for both). No statistically significant difference was noted in any of the other regions studied. Comparison of the group of study subjects to healthy controls revealed an insignificant trend toward reduction in BZR density in the frontal lobes bilaterally (p = .000) and a reduction in the cerebellum (p = .045). Current understanding suggests GABA receptors and the temporal lobe system as the final common pathway. This pilot study suggests possible alterations on 123I-iomazenil SPECT imaging and the need for larger studies.

Determination of flumazenil in human plasma by liquid chromatography-electrospray ionisation tandem mass spectrometry.

A liquid chromatography-electrospray ionisation-tandem mass spectrometry (LC-ESI-MS/MS) method was developed to determine unlabelled flumazenil (Ro 15-1788) in human plasma in [11C]flumazenil positron emission tomography (PET) studies. N-Methyl tri-deuterated flumazenil was used as an internal standard. The analyte and internal standard were extracted from plasma samples using solid-phase extraction, with a recovery of 78%. This was determined through the convenience of radioactivity measurements of 11C-labelled flumazenil. The evaporated and reconstituted eluate was analysed by LC-ESI-MS/MS. The calibration curve was linear over the tested concentration range of 0.05-0.5 nM (15-150 pg/ml) with a correlation coefficient, R2, of 0.998+/-0.001. A high precision was achieved, with mean intra-assay and inter-assay relative standard deviations of at most 6 and 7%, respectively. The accuracy of the method ranged from 95 to 104%. As a proof of concept, the validated method was applied in the determination of flumazenil in plasma from two healthy volunteers participating in a PET study with three repeated investigations. A bolus-infusion protocol was used to achieve a constant concentration level of flumazenil. The average plasma concentrations ranged from 0.11 and 0.19 nM and all measurements were within the calibration standard range. The flumazenil concentrations were relatively constant within each scan and the average intra-scan precision was 15%.

Validation of a multiwell gamma-counter for measuring high-pressure liquid chromatography metabolite profiles.

OBJECTIVES: The purpose of this study was to verify the accuracy and reproducibility of a multiwell counter to assess its suitability for use within human PET studies in which metabolizing (11)C tracers are used. Such tracers often require metabolite analysis for deriving plasma metabolite-corrected input curves. High-pressure liquid chromatography (HPLC) with on-line activity measurement is often unreliable for later plasma samples due to the poor sensitivity of the on-line activity detector. Fraction collector obtained HPLC samples that are counted in a separate high-sensitivity well counter can be an alternative to overcome poor counting statistics. METHODS: Several experiments to evaluate background counting, reproducibility, and linearity were performed to validate the accuracy, precision, and detection limits of the well counter. In addition, measurements on a series of samples resembling activity profiles as seen within human (11)C-flumazenil studies were performed to evaluate the performance of the well counter for clinically relevant data. RESULTS: The tests proved that the well counter detection limit, linearity, and reproducibility were more than sufficient in circumstances as seen during patient studies for samples with both high and low activity. CONCLUSION: The use of a multiwell counter is a good alternative for the on-line activity detector of the HPLC, allowing derivation of plasma metabolite fractions with high accuracy and reproducibility.

Quantification of human brain benzodiazepine receptors using [18F]fluoroethylflumazenil: a first report in volunteers and epileptic patients.

Fluorine-18 fluoroethylflumazenil ([18F]FEF) is a tracer for central benzodiazepine (BZ) receptors which is proposed as an alternative to carbon-11 flumazenil for in vivo imaging using positron emission tomography (PET) in humans. In this study, [18F]FEF kinetic data were acquired using a 60-min two-injection protocol on three normal subjects and two patients suffering from mesiotemporal epilepsy as demonstrated by abnormal magnetic resonance imaging and [18F]fluorodeoxyglucose positron emission tomography. First, a tracer bolus injection was performed and [18F]FEF rapidly distributed in the brain according to the known BZ receptor distribution. Thirty minutes later a displacement injection of 0.01 mg/kg of unlabelled flumazenil was performed. Activity was rapidly displaced from all BZ receptor regions demonstrating the specific binding of [18F]FEF. No displacement was observed in the pons. Plasma input function was obtained from arterial blood sampling, and metabolite analysis was performed by high-performance liquid chromatography. Metabolite quantification revealed a fast decrease in tracer plasma concentration, such that at 5 min post injection about 70% of the total radioactivity in plasma corresponded to [18F]FEF, reaching 24% at 30 min post injection. The interactions between [18F]FEF and BZ receptors were described using linear compartmental models with plasma input and reference tissue approaches. Binding potential values were in agreement with the known distribution of BZ receptors in human brain. Finally, in two patients with mesiotemporal sclerosis, reduced uptake of [18F]FEF was clearly observed in the implicated left hippocampus.

Image-derived input function for [11C]flumazenil kinetic analysis in human brain.

PURPOSE: We describe a method for analysis of [11C]flumazenil data using an input curve directly derived from the positron emission tomography (PET) images. PROCEDURE: The shape of the tracer plasma curve was obtained from the product of the intact flumazenil fraction in plasma in six arterial samples and the internal carotid artery time-activity curve (TAC). The resulting curve was calibrated using the [11C]flumazenil concentration in three of the six samples. The curve peak was recovered by adding an exponential function to the scaled curve whose parameters were estimated from simultaneous fittings of several tissue TACs assuming that all regions share the same input. RESULTS: Good agreement was found between the image-derived and the experimental plasma curves in six subjects. Distribution volumes were highly correlated with linear regression slope and intercept values between [0.94, 1.03] and [-0.10, 0.16], respectively. CONCLUSION: The proposed method is suitable for benzodiazepine receptor quantification requiring only a few blood samples.

Simple analytic method of 11C-flumazenil metabolite in blood.

UNLABELLED: 11C-Flumazenil ((11)C-FMZ) is useful to estimate central benzodiazepine receptors by PET. The binding potential (BP) can be calculated with dynamic PET and continual blood sampling. Because conventional metabolite analysis of plasma samples is complicated and time consuming, a simple method is required to obtain an input function. In this article, a whole blood solvent extraction method was evaluated using data of 13 subjects. METHODS: The plasma solvent extraction method was estimated in comparison with the thin-layer chromatography (TLC) method. Then, the whole blood solvent extraction method was evaluated in comparison with the plasma solvent extraction method. RESULTS: Metabolite data analyzed by the plasma extraction method were well correlated with those by the TLC method (r = 0.99). The BP was calculated using both the whole blood extraction data and the plasma extraction data. No difference was observed in all brain regions. CONCLUSION: This simple whole blood solvent extraction method can be applied to clinical BP estimation using (11)C-FMZ.

The effects of flumazenil on sleepiness, task performance and nocturnal sleep after anesthesia with midazolam.

The purpose of the present study was to clarify the changes in psychophysiological functions after anesthesia with midazolam (intravenous (i.v.) benzodiazepine anesthetic) and to examine the ability of flumazenil (benzodiazepine antagonist) to prevent the adverse effects of anesthesia with midazolam. Clinical dose of midazolam (0.1 mg/kg i.v.) was administered to seven healthy volunteers and either flumazenil (0.3 mg i.v.) or saline was injected at the end of the anesthesia. After anesthesia with midazolam, subjective sleepiness and euphoria increased significantly, but these changes were not observed when flumazenil was administered. In addition, sleep latency was prolonged and sleep efficiency decreased significantly after midazolam anesthesia with and without flumazenil. Slow wave sleep decreased significantly only by co-administration of flumazenil.

Effects of diazepam and flumazenil on minimum alveolar concentrations for dogs anesthetized with isoflurane or a combination of isoflurane and fentanyl.

OBJECTIVE: To determine the effect of a constant-rate infusion of fentanyl on minimum alveolar concentration (MAC) of isoflurane and to determine the interaction between fentanyl and a benzodiazepine agonist (diazepam) and antagonist (flumazenil) in isoflurane-anesthetized dogs. ANIMALS: 8 mixed-breed adult dogs. PROCEDURE: Dogs were anesthetized with isoflurane 3 times during a 6-week period. After a 30-minute equilibration period, each MAC determination was performed in triplicate, using standard techniques. Fentanyl was administered as a bolus (10 microg/kg of body weight, IV) that was followed by a constant infusion (0.3 microg/kg per min, IV) throughout the remainder of the experiment. After determining isoflurane-fentanyl MAC in triplicate, each dog received saline (0.9% NaCl) solution, diazepam, or flumazenil. After 30 minutes, MAC was determined again. RESULTS: Fentanyl significantly decreased isoflurane MAC (corrected to a barometric pressure of 760 mm Hg) from 1.80+/-0.21 to 0.85+/-0.14%, a reduction of 53%. Isoflurane-fentanyl-diazepam MAC (0.48+/-0.29%) was significantly less than isoflurane-fentanyl-saline MAC (0.79+/-0.21%). Percentage reduction in isoflurane MAC was significantly greater for fentanyl-diazepam (74%), compared with fentanyl-saline (54%) or fentanyl-flumazenil (61%). Mean fentanyl concentrations for the entire experiment were increased over time and were higher in the diazepam group than the saline or flumazenil groups. CONCLUSIONS AND CLINICAL RELEVANCE: Fentanyl markedly decreased isoflurane MAC in dogs. Diazepam, but not flumazenil, further decreased isoflurane-fentanyl MAC. Our results indicate that diazepam enhances, whereas flumazenil does not affect, opioid-induced CNS depression and, possibly, analgesia in dogs.

A rapid high-pressure liquid chromatographic procedure for determination of flumazenil in plasma.

INTRODUCTION: Flumazenil antagonizes the effects of benzodiazepines at gamma-aminobutyric acid (GABA) type A receptors in the central nervous system. Flumazenil has been reported to provoke panic attacks in patients with panic disorder (PD) but not in healthy controls. A rapid high-pressure liquid chromatographic (HPLC) method was developed for determination of flumazenil in plasma samples from PD patients receiving flumazenil and the results obtained with that assay are reported here. METHODS: Samples from 37 PD subjects receiving 2 mg of flumazenil intravenously were analyzed. Extraction under basic conditions was followed by an HPLC assay with UV detection (250 nm). Lamotrigine was used as intermal standard and a standard curve was constructed for each assay run. Flumazenil concentrations were measured in all the subjects in samples collected at 2 and 4 min after the drug administration and in some subjects, measurements were also done in samples collected at 7.5, 15, 30, 45, and 60 min. RESULTS: The procedure was reproducible and linear (from 2.5 to 1000 ng/ml). At 2 and 4 min after flumazenil administration, the concentrations did not differ significantly between panicking and nonpanicking subjects, indicating that the pharmacokinetics of the drug is not the major determinant of the responses. There was a steep decline in the plasma concentration-time profile during the first 4 min, reflecting an extensive and rapid distribution after which the decline was slower. DISCUSSION: The method described here is rapid, replicable, and convenient for the determination of flumazenil in plasma.

Intrasubject correlation between static scan and distribution volume images for [11C]flumazenil PET.

Accumulation of [11C]flumazenil (FMZ) reflects central nervous system benzodiazepine receptor (BZR). We searched for the optimal time for a static PET scan with FMZ as semi-quantitative imaging of BZR distribution. In 10 normal subjects, a dynamic series of decay-corrected PET scans was performed for 60 minutes, and the arterial blood was sampled during the scan to measure radioactivity and labeled metabolites. We generated 13 kinds of "static scan" images from the dynamic scan in each subject, and analyzed the pixel correlation for these images versus distribution volume (DV) images. We also analyzed the time for the [11C]FMZ in plasma and tissue to reach the equilibrium. The intra-subject pixel correlation demonstrated that the "static scan" images for the period centering around 30 minutes post-injection had the strongest linear correlation with the DV image. The ratio of radioactivity in the cortex to that in the plasma reached a peak at 40 minutes after injection. Considering the physical decay and patient burden, we conclude that the decay corrected static scan for [11C]FMZ PET as semi-quantitative imaging of BZR distribution is to be optimally acquired from 20 to 40 minutes after injection.

Plasma concentration of flumazenil following intranasal administration in children.

PURPOSE: A pharmacokinetic study in children to determine plasma flumazenil concentrations after the intranasal administration of 40 microg x kg(-1). METHODS: Following institutional approval and informed written consent, 11 ASA physical status I-II patients, aged two to six years, undergoing general anesthesia for dental surgery were recruited. After induction, 40 microg x kg(-1) flumazenil Anexate, Roche, 0.1 mg x mL(-1) (0.4 mL x kg(-1))) were administered via a syringe as drops, prior to nasal intubation. Venous plasma samples were drawn prior to administration of flumazenil (t = 0), and then at 2, 4, 6, 8, 10, 15, 20, 30, 40, 60, and 120 min thereafter. The plasma samples were immediately processed by the on-site laboratory and then stored at -70 degrees C, before batch analysis via high performance liquid chromatography assay. Pharmacokinetic data calculations were performed using WinNonLin software (Scientific Consulting Inc.). RESULTS: Eleven patients were studied, but data for one patient were discarded due to insufficient sampling. The median age was 4.3 yr (range 3 to 6), with a median weight of 18.9 kg (range 14.9 to 22.2). There were seven boys and three girls. Mean Cmax was 67.8 ng x mL(-1) (SD 41.9), with Tmax at two minutes. The calculated half-life was 122 min (SD 99). CONCLUSION: The mean plasma concentrations of flumazenil attained were similar to those reported after intravenous administration, and may be sufficient to antagonize the side-effects of benzodiazepines. This route of administration may be useful when the intravenous route is not readily available.