Development and Validation of a Sonication-Assisted Dispersive Liquid-Liquid Microextraction Procedure and an HPLC-PDA Method for Quantitative Determination of Zolpidem in Human Plasma and Its Application to Forensic Samples.

The use of z-drugs has increased worldwide since its introduction. Although the prescribing patterns of hypnotics differ among countries, zolpidem is the most widely used z-drug in the world. Zolpidem may be involved in poisoning and deaths. A simple and fast HPLC-PDA method was developed and validated. Zolpidem and the internal standard chloramphenicol were extracted from plasma using a sonication-assisted dispersive liquid-liquid microextraction procedure. The method was validated including selectivity, linearity, precision, accuracy, and recovery. The calibration range (0.15-0.6 µg/mL) covers therapeutic and toxic levels of zolpidem in plasma. The limit of quantification was set at 0.15 µg/mL. Intra- and interday accuracy and precision values were lower than 15% at the concentration levels studied. Excellent recovery results were obtained for all concentrations. The proposed method was successfully applied to ten real postmortem plasma samples. In our series, multiple substances (alcohol and/or other drugs) were detected in most cases of death involving zolpidem. Our analytical method is suitable for routine toxicological analysis.

Identification of post-mortem product of zolpidem degradation by hemoglobin via the Fenton reaction.

Zolpidem, N,N-dimethyl-2-[6-methyl-2-(4-methylphenyl)imidazo[1,2-a]pyridin-3-yl]acetamide, is a hypnotic agent widely used in clinical practice but is detected in many clinical cases of fatal intoxication and suicide. In forensic toxicology, the precise determination of zolpidem concentration in blood is a must to provide concrete evidence of death by zolpidem poisoning. However, the concentrations of zolpidem in blood at autopsy often differ from those at the estimated time of death. In the present study, we found that zolpidem was degraded by hemoglobin (Hb) via the Fenton reaction at various temperatures. The mechanism underlying zolpidem degradation involved the oxidation of its linker moiety. The MS and MS/MS spectra obtained by liquid chromatography quadrupole-Orbitrap mass spectrometry (LC-Q-Orbitrap-MS) showed the formation of 2-hydroxy-N,N-dimethyl-2-(6-methyl-2-(p-tolyl)imidazo[1,2-a]pyridin-3-yl)acetamide (2-OH ZOL) in Hb/H2O2 solution incubated with zolpidem and in the blood of several individuals who died from ingestion of zolpidem. These results suggest that 2-OH ZOL is the post-mortem product of zolpidem degradation by Hb via the Fenton reaction.

Recommended dosages of analgesic and sedative drugs in intensive care result in a low incidence of potentially toxic blood concentrations.

Background: Standard dosages of analgesic and sedative drugs are given to intensive care patients. The resulting range of blood concentrations and corresponding clinical responses need to be better examined. The purpose of this study was to describe daily dosages, measured blood concentrations, and clinical responses in critically ill patients. The purpose was also to contribute to establishing whole blood concentration reference values of the drugs investigated. Methods: A descriptive study of prospectively collected data from 302 admissions to a general intensive care unit (ICU) at a university hospital. Ten drugs (clonidine, fentanyl, morphine, dexmedetomidine, ketamine, ketobemidone, midazolam, paracetamol, propofol, and thiopental) were investigated, and daily dosages recorded. Blood samples were collected twice daily, and drug concentrations were measured. Clinical responses were registered using Richmond agitation-sedation scale (RASS) and Numeric rating scale (NRS). Results: Drug dosages were within recommended dose ranges. Blood concentrations for all 10 drugs showed a wide variation within the cohort, but only 3% were above therapeutic interval where clonidine (57 of 122) and midazolam (38 of 122) dominated. RASS and NRS were not correlated to drug concentrations. Conclusion: Using recommended dose intervals for analgesic and sedative drugs in the ICU setting combined with regular monitoring of clinical responses such as RASS and NRS leads to 97% of concentrations being below the upper limit in the therapeutic interval. This study contributes to whole blood drug concentration reference values regarding these 10 drugs.

Fast and reliable analysis of veterinary metomidate and etomidate in human blood samples by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in a postmortem case.

Metomidate and etomidate belong to the non-barbiturate imidazole family of sedative-hypnotics and elicit little analgesic action when used alone. Metomidate, in particular, has little analgesic activity in humans and is, therefore, used for veterinary purposes. In 2019, a Korean woman in her twenties was found unconscious in a motel bath and eventually died. Etomidate, alprazolam, escitalopram, and metomidate were detected in the postmortem specimens. To our knowledge, this is the first case of human metomidate abuse reported in the Republic of Korea. In this research, a simple and reliable method was developed for the analysis of metomidate and etomidate in human blood samples using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Blood samples were deproteinized with acetonitrile, filtered, and analyzed by LC-MS/MS. Linear calibration curves were obtained with six concentrations ranging from 1 to 50 ng/ml for metomidate and 10 to 500 ng/ml for etomidate. The method was validated by assessing the selectivity, linearity, limit of detection (LOD), limit of quantitation (LOQ), intra- and inter-day precision and accuracy, matrix effect, and stability and successfully applied to the analysis of metomidate and etomidate in human blood samples. In a postmortem case, the concentrations of metomidate and etomidate were found to be 8 and 110 ng/ml in femoral blood and 6 and 210 ng/ml in cardiac blood, respectively.

Pharmacokinetic properties of remimazolam in subjects with hepatic or renal impairment.

BACKGROUND: Remimazolam is a new benzodiazepine for procedural sedation and general anaesthesia. The aim of this study was to characterise its pharmacokinetic properties and safety in renally and hepatically impaired subjects. METHODS: Two separate trials were conducted in patients with hepatic (n=11) or renal impairment (n=11) compared with matched healthy subjects (n=9 and n=12, respectively). The hepatic impairment trial was an open-label adaptive 'Reduced Design' trial, using a single bolus of remimazolam 0.1 mg kg-1 i.v., whereas the renal impairment trial was an open-label trial of a single bolus dose of remimazolam 1.5 mg i.v. Remimazolam plasma concentrations over time were analysed by population pharmacokinetic modelling. RESULTS: Remimazolam pharmacokinetic properties were adequately described by a three-compartment, recirculatory model. Exposure in subjects with severe hepatic impairment was 38.1% higher (i.e. clearance was 38.1% lower) compared with healthy volunteers. This increase caused a slightly delayed recovery (8.0 min for healthy, 12.1 min for moderate, and 16.7 min for severe hepatic impairment). With renal impairment, plasma clearance was comparable with that measured in healthy subjects. Simulations of Cmax after a bolus dose of 10 mg showed no relevant impact of hepatic or renal impairment. The overall incidence of adverse events was low, and all adverse events were mild. CONCLUSIONS: As Cmax after a remimazolam bolus i.v. was not affected by hepatic or renal impairment, no dose adjustments are required. No unexpected adverse events related to remimazolam were seen in subjects with renal or hepatic impairment. CLINICAL TRIAL REGISTRATION: Hepatic impairment trial: ClinicalTrials.gov, NCT01790607 (https://clinicaltrials.gov/ct2/show/NCT01790607). Renal impairment trial: EudraCT Number: 2014-004575-23.

Midazolam and hydroxymidazolam plasma concentrations can be monitored with selected biochemical and physiological parameters of palliative care patients.

RATIONALE & OBJECTIVE: Midazolam is one of top three drugs used in palliative care. Its use increases in the last days of hospice patients' lives while safe dosage can be challenging. Equations currently used to estimate glomerular filtration rate, e.g: the Cockroft-Gault (eGFRCR) and the Modification of Diet in Renal Disease (eGFRMDRD) ones, do not generate precise calculations, especially in palliative patients exhibiting variations in body parameters. Our aim was to seek new relationships between mean midazolam (Mavg) and alfahydroxymidazolam (OH-Mavg) concentrations in plasma, and selected biochemical and physiological parameters of palliative patients, to enable optimal midazolam pharmacotherapy. STUDY DESIGN, PARTICIPANTS AND INTERVENTIONS: The pilot study included 11 Caucasians, aged 42-95, with advanced cancer disease, receiving midazolam in a hospice in-patient unit. We tested correlations among Mavg, BMI, eGFRMDRD, midazolam clearance (CL), OH-Mavg, bilirubin (Bil) and blood creatinine concentration (Cr). F test and leave-one out (LOO) validation was applied to verify the correlations' significance and predictive ability. RESULTS: We found ten statistically significant (p < 0.05) correlations related to midazolam pharmacokinetics and physiological factors. We formulated two equations with high degree of predictive ability, based on the eGFRMDRD→CL and the (Bil + BMI × Ln(Cr))→Mavg-(OH-Mavg) correlations. The limitations of the study mainly revolve around its pilot nature and the need to continue testing the results on a bigger population. No funding to disclose. CONCLUSIONS: The significance of correlations corresponding to the arithmetic expressions confirms that Bil, BMI, Ln(Cr) analyzed simultaneously report a series of processes on which midazolam metabolism depends. Two of ten correlations proposed came close to meet all LOO validation criteria. Current findings can help optimize midazolam treatment in palliative therapy.

Metabolic diversity as a reason for unsuccessful detoxification from benzodiazepines: the rationale for serum BZD concentration monitoring.

PURPOSE: Many harms secondary to benzodiazepine (BZD) dependence force users towards detoxification treatment. However, even strongly motivated patients tolerate the process badly or experience early relapse. The detoxification procedure has not yet been standardized. The objective of this paper is to examine the hypothesis that faulty detoxification routines may have caused some failures. METHODS: The detoxification approaches found in the literature were compared stage by stage. The review was used to identify possible common, across-the-board systematic errors. RESULTS: The presented literature review confirms that the widespread divergence in the BZD metabolism rate is effectively neglected during detoxification routines. Without laboratory measurements, these differences, additionally interfered with by auxiliary drugs, undermine not only the scheduled but even the symptom-driven procedures. An initial substitution with a long-acting BZD, although recommended, may lead to over-accumulation. This excess, varying between patients and incompatible with the current tapering stage, may lead to repeated overestimation of the patient's adjustments to reduced doses. Consequently, the patient's good clinical presentation at withdrawal, resulting in a conclusion of detoxification, may actually reflect a persistently high serum BZD concentration. The low-concentration stage, if shifted past the end of treatment, exposes patients to unexpected, unassisted withdrawal crises. With laboratory feedback, these crises, unlike the symptoms related to deficient re-adaptation mechanisms, could be prevented. Moreover, by minimizing the high-concentration phase, time can be saved for properly assisted low-concentration challenges. CONCLUSION: A customized detoxification procedure driven not only by the intensity of withdrawal symptoms but also by serum BZD monitoring may prevent some failures. As the standard regimen, it would make detoxification from BZDs more reliable and effective.

Effects of Vitamin D Receptor, Cytochrome P450 3A, and Cytochrome P450 Oxidoreductase Genetic Polymorphisms on the Pharmacokinetics of Remimazolam in Healthy Chinese Volunteers.

Remimazolam is a new ultra-short-acting benzodiazepine used to induce and maintain anesthesia and procedural sedation. Its compound structure is similar to midazolam's. Midazolam metabolism might be affected by vitamin D receptor (VDR), cytochrome P450 3A, and cytochrome P450 oxidoreductase genetic polymorphisms. This study investigated the effects of VDR, cytochrome P450 3A, and cytochrome P450 oxidoreductase genetic polymorphisms on the pharmacokinetics of remimazolam in healthy Chinese volunteers after a single intravenous injection of remimazolam besylate. Blood samples were collected from subjects (n = 62) at scheduled time intervals before and after injection. High-performance liquid chromatography-tandem mass spectrometry was used to quantify plasma remimazolam and RF7054 (its inactive carboxylic acid metabolite) concentrations. The relationship between plasma remimazolam concentration, pharmacokinetic parameters, and polymorphic alleles was assessed for each subject. The rs4516035 allele affected the elimination half-life of RF7054 (P = .043), while the rs1544410 allele affected the dose-normalized maximum observed plasma concentration (Cmax /D) of remimazolam (P = .025) in 46 volunteers. Results showed that VDR genetic polymorphisms might affect the pharmacokinetics of remimazolam in the Chinese population.

Pharmacokinetics and Pharmacodynamics of 3 Doses of Oral-Mucosal Dexmedetomidine Gel for Sedative Premedication in Women Undergoing Modified Radical Mastectomy for Breast Cancer.

BACKGROUND: Buccal dexmedetomidine (DEX) produces adequate preoperative sedation and anxiolysis when used as a premedication. Formulating the drug as a gel decreases oral losses and improves the absorption of buccal DEX. We compared pharmacokinetic and pharmacodynamic properties of 3 doses of buccal DEX gel formulated in our pharmaceutical laboratory for sedative premedication in women undergoing modified radical mastectomy for breast cancer. METHODS: Thirty-six patients enrolled in 3 groups (n = 12) to receive buccal DEX gel 30 minutes before surgery at 0.5 µg/kg (DEX 0.5 group), 0.75 µg/kg (DEX 0.75 group), or 1 µg/kg (DEX 1 group). Assessments included plasma concentrations of DEX, and pharmacokinetic variables calculated with noncompartmental methods, sedative, hemodynamic and analgesic effects, and adverse effects. RESULTS: The median time to reach peak serum concentration of DEX (Tmax) was significantly shorter in patients who received 1 µg/kg (60 minutes) compared with those who received 0.5 µg/kg (120 minutes; P = .003) and 0.75 µg/kg (120 minutes; P = .004). The median (first quartile-third quartile) peak concentration of DEX (maximum plasma concentration [Cmax]) in plasma was 0.35 ng/mL (0.31-0.49), 0.37 ng/mL (0.34-0.40), and 0.54 ng/mL (0.45-0.61) in DEX 0.5, DEX 0.75, and DEX 1 groups (P = .082). The 3 doses did not produce preoperative sedation. The 1 µg/kg buccal DEX gel produced early postoperative sedation and lower intraoperative and postoperative heart rate values. Postoperative analgesia was evident in the 3 doses in a dose-dependent manner with no adverse effects. CONCLUSIONS: Provided that it is administered 60-120 minutes before surgery, sublingual administration of DEX formulated as an oral-mucosal gel may provide a safe and practical means of sedative premedication in adults.

Xylazine, a Veterinary Tranquilizer, Detected in 42 Accidental Fentanyl Intoxication Deaths.

ABSTRACT: Xylazine is an emerging adulterant with fentanyl in fatal drug intoxications, which has public health, safety, and criminal investigative implications. Xylazine is a nonnarcotic sedative used for analgesia and muscle relaxation exclusively in veterinary medicine. Its chemical structure is similar to clonidine and acts as a central α-2 agonist which may cause bradycardia and transient hypertension followed by hypotension. We report the detection of xylazine in 42 deaths in Connecticut from March to August 2019. Xylazine combined with an opioid or stimulant may affect the toxicity of these drugs. Detection of xylazine may help the forensic pathologist distinguish illicit from prescribed fentanyl, and law enforcement agents track the illicit drugs to a specific drug supplier. Because of its lack of response to naloxone, emergency medicine physicians need to be aware of its potential presence as it may affect therapy.

Development of a new method for drug detection based on a combination of the dried blood spot method and capillary electrophoresis.

The aim of this study was to develop a new approach to sample preparation of biological material based on a combination of the Dried Blood Spot (DBS) method and capillary electrophoresis coupled with mass spectrometry (CE-MS) for the analysis of blood samples collected in vivo or post-mortem. The proposed approach allowed the identification of typical drugs from different groups, such as tricyclic antidepressants (amitriptyline, imipramine), selective serotonin reuptake inhibitors (citalopram), benzodiazepines (tetrazepam) and hypnotics (zolpidem). In this study, a blood sample was spotted on FTA DMPK C cards, then dried, and 6-mm discs were cut out. The sample preparation procedure involved microwave-assisted extraction (MAE). Various extraction agents, temperatures and durations of extraction were examined in order to achieve the highest efficiency of the process. The method was subjected to a validation procedure. Limits of detection (LOD = 1.76 - 14.7 ng/mL) and quantification (LOQ = 5.25 - 49.0 ng/mL), inter- (CV = 1.31 - 9.43%) and intra- (CV = 3.26 - 18.52%) day precision of the determinations, recovery (RE = 85.0-105.4%) and matrix effect on ionization of analytes (ME = 98.6-105.5%) were determined. Furthermore, the developed DBS/MAE/CM-MS method was selective and analytes present in the blood applied on DBS cards were found to be stable after 7 and after 14 days. Moreover, the developed method was successfully applied to the analysis of both post-mortem samples and blood samples taken from patients treated with the analyzed drugs.

Development and Validation of an LC-MS-MS Method for the Detection of 40 Benzodiazepines and Three Z-Drugs in Blood and Urine by Solid-Phase Extraction.

An analytical method for the detection of 40 benzodiazepines, (±)-zopiclone, zaleplon and zolpidem in blood and urine by solid-phase extraction liquid chromatography-tandem mass spectrometry was developed and validated. Twenty-nine of 43 analytes were quantified in 0.5 mL whole blood for investigating postmortem, drug-facilitated sexual assault (DFSA) and driving under the influence of drugs cases (DUID). The four different dynamic ranges of the seven-point, linear, 1/x weighted calibration curves with lower limits of quantification of 2, 5, 10 and 20 µg/L across the analytes encompassed the majority of our casework encountered in postmortem, DFSA and DUID samples. Reference materials were available for all analytes except α-hydroxyflualprazolam, a hydroxylated metabolite of flualprazolam. The fragmentation of α-hydroxyflualprazolam was predicted from the fragmentation pattern of α-hydroxyalprazolam, and the appropriate transitions were added to the method to enable monitoring for this analyte. Urine samples were hydrolyzed at 55°C for 30 min with a genetically modified ß-glucuronidase enzyme, which resulted in >95% efficiency measured by oxazepam glucuronide. Extensive sample preparation included combining osmotic lysing and protein precipitation with methanol/acetonitrile mixture followed by freezing and centrifugation resulted in exceptionally high signal-to-noise ratios. Bias and between-and within-day imprecision for quality controls (QCs) were all within ±15%, except for clonazolam and etizolam that were within ±20%. All 29 of the 43 analytes tested for QC performance met quantitative reporting criteria within the dynamic ranges of the calibration curves, and 14 analytes, present only in the calibrator solution, were qualitatively reported. Twenty-five analytes met all quantitative reporting criteria including dilution integrity. The ability to analyze quantitative blood and qualitative urine samples in the same batch is one of the most useful elements of this procedure. This sensitive, specific and robust analytical method was routinely employed in the analysis of >300 samples in our laboratory over the last 6 months.

Midazolam Intoxication in a Premature Neonate.

PURPOSE: We report the case of a male neonate with a respiratory disorder who developed adverse cardiorespiratory symptoms after the continuous infusion of midazolam. METHODS: To clarify the cause of cardiogenic shock, we performed whole exome sequencing and screened relative single-nucleotide variants of 2 cytochrome P450 (CYP) isoforms, CYP3A4 and CYP3A5, which play a dominant role in the metabolic elimination of midazolam. We measured endogenous cortisol 6ß-hydroxylation clearance to phenotypically assess CYP3A activity. FINDINGS: The CYP3A activity level in the patient was significantly lower than the mean CYP3A activity level in healthy adults. Three intronic mutations in the CYP3A4 and CYP3A5 isoforms were detected in the patient. IMPLICATIONS: Our findings suggest that the midazolam concentration in plasma was achieved at above the steady-state concentration during continuous infusion used to sedate neonates receiving mechanical ventilatory support. Evaluation of the drug-metabolizing ability based on CYP3A might be useful if adverse electrophysiologic variables or the induction of tachycardia occur because of delayed elimination.

Pharmacokinetics of xylazine after 2-, 4-, and 6-hr durations of continuous rate infusions in horses.

Intravenous (i.v.) bolus administration of xylazine (XYL) (0.5 mg/kg) immediately followed by a continuous rate infusion (CRI) of 1 mg kg-1  hr-1 for 2, 4, and 6 hr produced immediate sedation, which lasted throughout the duration of the CRI. Heart rate decreased and blood pressure increased significantly (p > .05) in all horses during the first 15 min of infusion, both returned to and then remained at baseline during the duration of the infusion. Compartmental models were used to investigate the pharmacokinetics of XYL administration. Plasma concentration-time curves following bolus and CRI were best described by a one-compartment model. No differences were found between pharmacokinetic estimates of the CRIs for the fractional elimination rate constant (Ke ), half-life (t1/2e ), volume of distribution (Vd ), and clearance (Cl). Median and range were 0.42 (0.15-0.97)/hr, 1.68 (0.87-4.52) hr, 5.85 (2.10-19.34) L/kg, and 28.7 (19.6-39.5) ml min-1  kg-1 , respectively. Significant differences were seen for area under the curve ( AUC 0 ∞ ) (p < .0002) and maximum concentration (Cmax ) (p < .04). This indicates that with increasing duration of infusion, XYL may not accumulate in a clinically relevant way and hence no adjustments are required in a longer XYL CRI to maintain a constant level of sedation and a rapid recovery.

Proof of Concept: First Pediatric [14 C]microtracer Study to Create Metabolite Profiles of Midazolam.

Growth and development affect drug-metabolizing enzyme activity thus could alter the metabolic profile of a drug. Traditional studies to create metabolite profiles and study the routes of excretion are unethical in children due to the high radioactive burden. To overcome this challenge, we aimed to show the feasibility of an absorption, distribution, metabolism, and excretion (ADME) study using a [14 C]midazolam microtracer as proof of concept in children. Twelve stable, critically ill children received an oral [14 C]midazolam microtracer (20 ng/kg; 60 Bq/kg) while receiving intravenous therapeutic midazolam. Blood was sampled up to 24 hours after dosing. A time-averaged plasma pool per patient was prepared reflecting the mean area under the curve plasma level, and subsequently one pool for each age group (0-1 month, 1-6 months, 0.5-2 years, and 2-6 years). For each pool [14 C]levels were quantified by accelerator mass spectrometry, and metabolites identified by high resolution mass spectrometry. Urine and feces (n = 4) were collected up to 72 hours. The approach resulted in sufficient sensitivity to quantify individual metabolites in chromatograms. [14 C]1-OH-midazolam-glucuronide was most abundant in all but one age group, followed by unchanged [14 C]midazolam and [14 C]1-OH-midazolam. The small proportion of unspecified metabolites most probably includes [14 C]midazolam-glucuronide and [14 C]4-OH-midazolam. Excretion was mainly in urine; the total recovery in urine and feces was 77-94%. This first pediatric pilot study makes clear that using a [14 C]midazolam microtracer is feasible and safe to generate metabolite profiles and study recovery in children. This approach is promising for first-in-child studies to delineate age-related variation in drug metabolite profiles.

Clonazolam a new designer benzodiazepine intoxication confirmed by blood concentration.

BACKGROUND: Recently the number of new psychoactive substances have significantly increased, becoming popular among experienced users of designer drugs. A significant group includes benzodiazepine derivatives, which have not been introduced as medications but are abused by people experimenting with new and classical psychoactive substances. CASE PRESENTATION: The aim of this paper was to present the case of a clonazolam ingestion by a person who was not habituated to benzodiazepines. The intake caused only prolonged coma, decreased muscle tone, and deep tendon reflexes without any other concomitant toxicity and cardio-respiratory failure. CONCLUSIONS: Clonazolam concentrations in patient's blood, measured three times were 0.077 mg/L, 0.015 mg/L, 0.009 mg/L after 4, 8 and 12 h, respectively. Clonazolam's human toxicity has not been well established, so any case of poisoning should be closely monitored.

Study on the Pharmacokinetics of Diazepam and Its Metabolites in Blood of Chinese People.

BACKGROUND AND OBJECTIVES: Driving under the influence of diazepam is increasing in China. The pharmacokinetics of diazepam and its metabolites, especially the glucuronide metabolites, are helpful in the identification of diazepam use by drivers. This study aimed to investigate the pharmacokinetics of diazepam and its metabolites (nordazepam, oxazepam, oxazepam glucuronide and temazepam glucuronide) in the blood of Chinese people, and to provide basic data for identifying diazepam use and estimating the time of last diazepam ingestion. METHODS: A total of 28 participants (14 men, 14 women) were recruited and each person received 5 mg diazepam orally. Whole blood was collected at 0 h (pre-dose), and 1 h, 2 h, 4 h, 8 h, 12 h, and 24 h, and at 2 days, 3 days, 6 days, 12 days, and 15 days post-dose. Analytes of interest were extracted via solid-phase extraction and analyzed by a liquid chromatography tandem mass spectrometry method operated in a positive multiple response monitoring mode. Pharmacokinetic parameters were analyzed by a pharmacokinetic software DAS according to the non-compartment model. The time of last diazepam use was estimated using the concentration ratios of diazepam to metabolites and metabolites to metabolites from controlled drug administration studies. RESULTS: The respective time of maximum concentration, the maximum concentration and the elimination half-life of diazepam were 1.04 ± 1.00 h, 87.37 ± 31.92 ng/mL and 129.07 ± 75.00 h; of nordazepam were 133.14 ± 109.63 h, 3.80 ± 1.75 ng/mL, and 229.73 ± 236.83 h; of oxazepam were 100.29 ± 87.16 h, 1.62 ± 2.64 ng/mL, and 382.86 ± 324.58 h; of temazepam glucuronide were 44.43 ± 55.41 h, 2.08 ± 0.88 ng/mL, and 130.53 ± 72.11 h; and of oxazepam glucuronide were 66.86 ± 56.33 h, 1.10 ± 0.41 ng/mL, and 240.66 ± 170.12 h. A good correlation model was obtained from the concentration ratio of diazepam to nordazepam and the time of diazepam use, and the prediction errors were less than 20%. CONCLUSIONS: This study provides a sensitive method to identify diazepam ingestion by monitoring diazepam and its metabolites including glucuronides, as well as to infer the time following oral consumption.

Treatment of phenobarbital intoxication using hemodialysis in two dogs.

OBJECTIVE: To describe the use of hemodialysis in 2 dogs with severe clinical signs from phenobarbital intoxication. SERIES SUMMARY: Two dogs ingested a toxic dose of phenobarbital, leading to severe neurological dysfunction and a comatose state. Both dogs received a 3-hour session of hemodialysis with complete resolution of clinical signs and returned to normal mentation by the end of the therapy. No negative side effects occurred and phenobarbital concentrations returned to therapeutic range during treatment. NEW INFORMATION PROVIDED: This is the first report on the utility and safety of using hemodialysis for phenobarbital intoxication in dogs.

Pharmacokinetics and Pharmacodynamics of Remimazolam (CNS 7056) after Continuous Infusion in Healthy Male Volunteers: Part I. Pharmacokinetics and Clinical Pharmacodynamics.

BACKGROUND: Remimazolam (CNS 7056) is a new ultra-short-acting benzodiazepine for intravenous sedation and anesthesia. Its pharmacokinetics and pharmacodynamics have been reported for bolus administration. This study aimed to investigate the pharmacokinetics and pharmacodynamics of remimazolam after continuous infusion. METHODS: Twenty healthy male volunteers (20 to 38 yr, 64 to 99 kg) received remimazolam as continuous intravenous infusion of 5 mg/min for 5 min, 3 mg/min for the next 15 min, and 1 mg/min for further 15 min. Pharmacokinetics of remimazolam and its metabolite were determined from arterial plasma concentrations. Sedation was assessed using the Modified Observer's Assessment of Alertness and Sedation scale. Pharmacokinetic-pharmacodynamic modeling was performed by population analysis. Hemodynamics and the electrocardiogram were also investigated. RESULTS: Pharmacokinetics was best described by a three-compartment model for remimazolam and a two-compartment model with transit compartment for the metabolite. Remimazolam showed a high clearance (1.15 ± 0.12 l/min, mean ± SD), a small steady-state volume of distribution (35.4 ± 4.2 l) and a short terminal half-life (70 ± 10 min). The simulated context-sensitive halftime after an infusion of 4 h was 6.8 ± 2.4 min. Loss of consciousness was observed 5 ± 1 min after start, and full alertness was regained 19 ± 7 min after stop of infusion. Pharmacodynamics of Modified Observer's Assessment of Alertness and Sedation score was best described by a sigmoid probability model with effect site compartment. The half-maximum effect site concentration for a Modified Observer's Assessment of Alertness and Sedation score less than or equal to 1 was 695 ± 239 ng/ml. The equilibration half-time between central and effect compartment was 2.7 ± 0.6 min. Mean arterial blood pressure decreased by 24 ± 6%, and heart rate increased by 28 ± 15%. Spontaneous breathing was maintained throughout the study. There was no significant prolongation of the QT interval of the electrocardiogram observed. CONCLUSIONS: Remimazolam was characterized by a pharmacokinetic-pharmacodynamic profile with fast onset, fast recovery, and moderate hemodynamic side effects.

Pharmacokinetics and Pharmacodynamics of Remimazolam (CNS 7056) after Continuous Infusion in Healthy Male Volunteers: Part II. Pharmacodynamics of Electroencephalogram Effects.

BACKGROUND: Remimazolam (CNS 7056) is a new ultra-short acting benzodiazepine for IV sedation. This study aimed to investigate the electroencephalogram (EEG) pharmacodynamics of remimazolam infusion. METHODS: Twenty healthy male volunteers received remimazolam as continuous IV infusion of 5 mg/min for 5 min, 3 mg/min for the next 15 min, and 1 mg/min for further 15 min. Continuous EEG monitoring was performed by a neurophysiologic system with electrodes placed at F3, F4, C3, C4, O1, O2, Cz, and Fp1 (10/20 system) and using the Narcotrend Index. Sedation was assessed clinically by using the Modified Observer's Assessment of Alertness and Sedation scale. Pharmacodynamic models were developed for selected EEG variables and Narcotrend Index. RESULTS: EEG changes during remimazolam infusion were characterized by an initial increase in beta frequency band and a late increase in delta frequency band. The EEG beta ratio showed a prediction probability of Modified Observer's Assessment of Alertness and Sedation score of 0.79, and could be modeled successfully using a standard sigmoid Emax model. Narcotrend Index showed a prediction probability of Modified Observer's Assessment of Alertness and Sedation score of 0.74. The time course of Narcotrend Index was described by an extended sigmoid Emax model with two sigmoid terms and different plasma-effect equilibration times. CONCLUSIONS: Beta ratio was identified as a suitable EEG variable for monitoring remimazolam sedation. Narcotrend Index appeared less suitable than the beta ratio for monitoring the sedative effect if remimazolam is administered alone.