Construction and Verification of Physiologically Based Pharmacokinetic Models for Four Drugs Majorly Cleared by Glucuronidation: Lorazepam, Oxazepam, Naloxone, and Zidovudine.

Physiologically based pharmacokinetic (PBPK) modeling is less well established for substrates of UDP-glucuronosyltransferases (UGT) than for cytochrome P450 (CYP) metabolized drugs and more verification of simulations is necessary to increase confidence. To address specific challenges of UGT substrates, we developed PBPK models for four drugs cleared majorly via glucuronidation (lorazepam, oxazepam, naloxone, and zidovudine). In vitro to in vivo scaling of intrinsic clearance generated with co-cultured human hepatocytes was applied for hepatic metabolism and extra-hepatic clearance was extrapolated based on relative expression of UGT isoforms in the liver, kidney, and intestine. Non-metabolic clearance and the contributions of individual UGT isoforms to glucuronidation were based on in vitro and in vivo studies taken from the literature and simulations were verified and evaluated with a broad set of clinical pharmacokinetic data. Model evaluation showed systemic clearance predictions within 1.5-fold for all drugs and all simulated parameters were within 2-fold of observed. However, during the verification step, top-down model fitting was necessary to adjust for under-prediction of zidovudine VSS and renal clearance and over estimation of intestinal first pass for lorazepam, oxazepam, and zidovudine. The impact of UGT2B15 polymorphisms on the pharmacokinetics of oxazepam and lorazepam was simulated and glucuronide metabolites were also simulated for all four drugs. To increase confidence in predicting extra-hepatic clearance, improvement of enzyme phenotyping for UGT substrates and more quantitative tissue expression levels of UGT enzymes are both needed. Prediction of glucuronide disposition is also challenging when active transport processes play a major role.

Metabolic profile of oxazepam and related benzodiazepines: clinical and forensic aspects.

Anxiolytic drugs, namely benzodiazepines, are the most commonly used psychoactive substances since anxiety disorders are prevalent mental disorders particularly in the Western world. Oxazepam is a short-acting benzodiazepine and one of the most frequently prescribed anxiolytic drugs. It is also the active metabolite of a wide range of other benzodiazepines, such as diazepam, ketazolam, temazepam, chlordiazepoxide, demoxazepam, halazepam, medazepam, prazepam, pinazepam, and chlorazepate. Therefore, relevant clinical and forensic outocomes may arise, namely those related to interference in driving performance. It is clinically available as a racemic formulation, with S-enantiomer being more active than R-enantiomer. In humans, it is mainly polimorphically metabolized by glucuronide conjugation at the 3-carbon hydroxyl group, yielding stable diastereomeric glucuronides (R- and S-oxazepam glucuronide). Relevant metabolic and stereoselective interspecies differences have been reported. In this work, the pharmacokinetics of oxazepam with particular focus on metabolic pathways is fully reviewed. Moreover, the metabolic profile of other prescribed benzodiazepines that produce oxazepam as a metabolite is also discussed. It is aimed that knowing the metabolism of oxazepam and related benzodiazepines may lead to the development of new analytical strategies for its early detection and help in further toxicological and clinical interpretations.

Toxicodynetics in nordiazepam and oxazepam overdoses.

OBJECTIVES: Toxicodynetics aims at defining the time-course of major clinical events in drug overdose. We report the toxicodynetics in mono-intoxications with oxazepam and nordiazepam. METHODS: Cases of oxazepam or nordiazepam overdoses collected at the Paris poison control centre from 1999 to 2014 on the basis of self-report. A particular attention was paid to eliminate the concomitant alcohol or psychotropic co-ingestions. The toxicodynetic parameters were assessed as previously described. Results are expressed using 10-90 percentiles. In adults, the dose was normalized (TI, toxic Index) by dividing the supposed ingested dose by the maximal recommended dose. RESULTS: Two hundred and fifty-one and 74 cases of oxazepam and nordiazepam poisonings were included, respectively. The Emax for oxazepam and nordiazepam were sleepiness or obtundation in 106 and 36 cases, respectively. Coma was used to qualify only one oxazepam overdose. The median delay in onset of the Emax was 1.5h (0.33-15) in nordiazepam and 4h (0.5-15) in oxazepam overdose. In both overdoses, the onset of Emax occurred on an "on-off" mode. In adults, the greatest TIs in nordiazepam and oxazepam overdoses were 45 and 26.7, respectively. The TI in the oxazepam-induced coma was 26.7, the largest dose. CONCLUSION: Data collected in PCC allow determining a number of toxicodynetic parameters. Toxicodynetics showed that nordiazepam is not a cause of coma even in large overdose while oxazepam causes coma only at a very high dose. Deep coma in nordiazepam overdose whatever the dose and deep coma in overdose with oxazepam involving TI less than 20 result from unrecognized drug-drug interaction.

Site-, Technique-, and Time-Related Aspects of the Postmortem Redistribution of Diazepam, Methadone, Morphine, and their Metabolites: Interest of Popliteal Vein Blood Sampling.

Sampling site, technique, and time influence postmortem drug concentrations. In 57 cases, we studied drug concentration differences as follows: subclavian vein-dissection/clamping versus blind stick, femoral vein-dissection/clamping versus blind stick, right cardiac chamber, and popliteal vein-dissection and clamping only. Cases were distributed in group #1 (all cases with both techniques), group #2 (dissection/clamping), and group #3 (blind stick). Sampled drugs were diazepam, methadone, morphine, and their metabolites. To assess PMR, mean concentrations and ratios were calculated for each group. Time-dependent variations of blood concentrations and ratios were also assessed. Results indicate that site, method, and time may influence postmortem distribution interpretation in different ways. Popliteal blood seems less subject to PMR. In conclusion, our study is the first to evaluate concurrently three main aspects of PMR and confirms that the popliteal vein may represent a site that is more resistant to the changes seen as a result of PMR.

Home alone-The effects of isolation on uptake of a pharmaceutical contaminant in a social fish.

A wide range of biologically active pharmaceutical residues is present in aquatic systems worldwide. As uptake potential and the risk of effects in aquatic wildlife are directly coupled, the aim of this study was to investigate the relationships between stress by isolation, uptake and effects of the psychiatric pharmaceutical oxazepam in fish. To do this, we measured cortisol levels, behavioral stress responses, and oxazepam uptake under different stress and social conditions, in juvenile perch (Perca fluviatilis) that were either exposed (1.03µgl-1) or not exposed to oxazepam. We found single exposed individuals to take up more oxazepam than individuals exposed in groups, likely as a result of stress caused by isolation. Furthermore, the bioconcentration factor (BCF) was significantly negatively correlated with fish weight in both social treatments. We found no effect of oxazepam exposure on body cortisol concentration or behavioral stress response. Most laboratory experiments, including standardized bioconcentration assays, are designed to minimize stress for the test organisms, however wild animals experience stress naturally. Hence, differences in stress levels between laboratory and natural environments can be one of the reasons why predictions from artificial laboratory experiments largely underestimate uptake of oxazepam, and other pharmaceuticals, in the wild.

Characterization of equine cytochrome P450: role of CYP3A in the metabolism of diazepam.

Research on drug metabolism and pharmacokinetics in large animal species including the horse is scarce because of the challenges in conducting in vivo studies. The metabolic reactions catalyzed by cytochrome P450s (CYPs) are central to drug pharmacokinetics. This study elucidated the characteristics of equine CYPs using diazepam (DZP) as a model compound as this drug is widely used as an anesthetic and sedative in horses, and is principally metabolized by CYPs. Diazepam metabolic activities were measured in vitro using horse and rat liver microsomes to clarify the species differences in enzyme kinetic parameters of each metabolite (temazepam [TMZ], nordiazepam [NDZ], p-hydroxydiazepam [p-OH-DZP], and oxazepam [OXZ]). In both species microsomes, TMZ was the major metabolite, but the formation rate of p-OH-DZP was significantly less in the horse. Inhibition assays with a CYP-specific inhibitors and antibody suggested that CYP3A was the main enzyme responsible for DZP metabolism in horse. Four recombinant equine CYP3A isoforms expressed in Cos-7 cells showed that CYP3A96, CYP3A94, and CYP3A89 were important for TMZ formation, whereas CYP3A97 exhibited more limited activity. Phylogenetic analysis suggested diversification of CYP3As in each mammalian order. Further study is needed to elucidate functional characteristics of each equine CYP3A isoform for effective use of diazepam in horses.

Population Pharmacokinetics of High-Dose Oxazepam in Alcohol-Dependent Patients: Is There a Risk of Accumulation?

BACKGROUND: According to the guidelines, benzodiazepines with a short half-life are the reference medication to treat alcohol withdrawal syndrome. The doses of oxazepam used in this population may reach up to 300 mg per day, significantly higher than usual doses. Its use in these patients deserves further information to confirm that the half-life remains constant and that no accumulation appears. The objective of this study was to investigate the pharmacokinetics of high doses of oxazepam in alcohol-dependent patients treated for alcohol withdrawal syndrome. METHODS: Overall, 63 outpatients [weight, 71.1 kg (45.0-118.0); age, 47.6 years (31-67)] followed in the addictology unit, were studied. Total mean dose of 96.0 mg per day (range, 20-300 mg/d) was administered by oral route. Therapeutic drug monitoring allowed the measurement of 96 plasma concentrations. The following covariates were evaluated: demographic data (age, body weight, height, gender) and biological data (creatinine, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, gamma-glutamyl transferase). Pharmacokinetic analysis was performed using a nonlinear mixed-effect population model. RESULTS: Data were modeled with a 1-compartment pharmacokinetic model. The population typical mean 90% confidence interval values for clearance, apparent volume of distribution (V), and duration of absorption (D1) were 6.8 L/h (range, 3.9-8.0 L/h), 159 L (range, 98.0-282 L), and 2 hours (fixed), respectively. The interindividual variability of clearance and V, and residual variability (90% confidence interval) were 74% (44%-96%), 69% (40%-89%), and 32% (20%-41%), respectively. The elimination half-life was 16 hours (range, 3-42 hours). CONCLUSIONS: Oxazepam exhibited a linear pharmacokinetics with a proportional relationship from 20 to 300 mg per day, the dose range currently used in alcohol-dependent patients treated for alcohol withdrawal syndrome. We did not find any evidence of drug accumulation with these doses.

Pharmacokinetics of the cytochrome P-450 substrates phenytoin, theophylline, and diazepam in healthy Greyhound dogs.

The purpose of this study was to determine the pharmacokinetics of phenytoin, theophylline, and diazepam in six healthy Greyhound dogs. Additionally, the pharmacokinetics of the diazepam metabolites, oxazepam and nordiazepam, after diazepam administration was determined. Phenytoin sodium (12 mg/kg), aminophylline (10 mg/kg), and diazepam (0.5 mg/kg) were administered IV on separate occasions, and blood was collected at predetermined time points for the quantification of plasma drug concentrations by fluorescence polarization immunoassay (phenytoin, theophylline) or mass spectrometry (diazepam, oxazepam, and nordiazepam). The terminal half-life was 4.9, 9.2, and 1.0 h, respectively, for phenytoin, theophylline, and diazepam, and 6.2 and 2.4 h for oxazepam and nordiazepam after IV diazepam. The clearance was of 2.37, 0.935, and 27.9 mL · min/kg, respectively, for phenytoin, theophylline, and diazepam. The C(MAX) was 44.7 and 305.2 ng/mL for oxazepam and nordiazepam, respectively, after diazepam administration. Temazepam was not detected above 5 ng/mL in any sample after IV diazepam.

An in vitro approach to estimate putative inhibition of buprenorphine and norbuprenorphine glucuronidation.

An in vitro inhibition study was performed to investigate potential drug-drug interactions on glucuronidation of buprenorphine (BUP) and norbuprenorphine (NBUP), which represents the major elimination pathway of the drug using cDNA-expressed uridine 5'-diphosphate glucuronosyltransferases (UGTs) and human liver microsomes (HLMs). Following identification of major UGT enzymes for BUP and NBUP glucuronidation, substrates were incubated with drugs (amitriptyline, nortriptyline, lamotrigine, oxazepam, and temazepam), which are extensively cleared by glucuronidation as well as are often used during maintenance treatment. To evaluate the inhibitory potential, the half maximal inhibitor concentration (IC(50)), the inhibition constant (K (i)), and the inhibitor concentration (K (I)) that yield half the maximum rate of inactivation and the enzyme inactivation rate constant (k (inact)) were determined, if appropriate. Amitriptyline and temazepam are inhibitors of NBUP glucuronidation (UGT1A3, HLMs), whereas BUP glucuronidation was affected by amitriptyline (HLMs), oxazepam, and temazepam (UGT2B7). Additionally, BUP inhibits NBUP glucuronidation (UGT1A1, 1A3, HLMs) and vice versa (UGT1A3). A decrease in the metabolic clearance of NBUP may increase the risk of adverse effects such as respiratory depression. Further investigations are needed to evaluate whether inhibition of BUP and NBUP glucuronidation contributes to adverse events.

Effects of the combination of metyrapone and oxazepam on cocaine and food self-administration in rats.

For several years, our laboratory has investigated the role for the HPA axis in cocaine reinforcement. Two classes of drugs that we have studied include corticosterone synthesis inhibitors (e.g., metyrapone) and benzodiazepine receptor agonists (e.g., oxazepam). In the experiments described in this manuscript, we tested the effects of various doses of metyrapone and oxazepam against several doses of self-administered cocaine. Behavioral, endocrine and pharmacokinetic measures of the effects of the combination of metyrapone and oxazepam on cocaine reward are presented. Combinations of metyrapone and oxazepam at doses that produced no observable effects when administered separately significantly reduced cocaine self-administration without affecting food-maintained responding during the same sessions. Changes in pharmacokinetics or endocrine function do not appear to mediate these effects, suggesting a central mechanism of action. Therefore, although these drugs produce their effects through distinct mechanisms, an additive effect on cocaine self-administration is obtained when these drugs are administered together, suggesting that combinations of low doses of metyrapone and oxazepam may be useful in reducing cocaine seeking with a reduced incidence of unwanted side effects and a decreased potential for abuse.

The concentration of oxazepam and oxazepam glucuronide in oral fluid, blood and serum after controlled administration of 15 and 30 mg oxazepam.

AIMS: To measure and compare the concentration-time profiles of oxazepam and oxazepam glucuronide in blood, serum and oral fluid within the scope of roadside testing. METHODS: Biological samples were collected from eight male subjects after ingestion of 15 or 30 mg oxazepam on separate dosing occasions with an interval of 7 days. The concentration-time profiles of oxazepam and oxazepam glucuronide were fitted by using a one-compartment model. RESULTS: For oxazepam and oxazepam glucuronide, the mean oral fluid/blood ratios were 0.05 (range 0.04-0.07) and 0.004 (range 0.002-0.006), respectively. The concentration-time profiles in oral fluid paralleled those in blood. CONCLUSION: After oral administration of therapeutic doses of oxazepam, concentrations in oral fluid are very much lower than those in blood, and those of oxazepam glucuronide are much lower than those of the parent compound. Nevertheless, assay of oral fluid for oxazepam can be used to detect recent ingestion of the drug in drivers suspected of impaired driving performance.

Quetiapine and drug interactions: evidence from a routine therapeutic drug monitoring service.

OBJECTIVE: The objective of the present study was to investigate the effect of age, gender, and various comedications on the pharmacokinetics of quetiapine in a naturalistic setting. METHOD: In total, 2111 serum samples analyzed for quetiapine during the period from June 2001 to December 2004 were included in the study. The samples had been collected for routine therapeutic drug monitoring purposes from 1179 patients treated with quetiapine. A log-linear mixed model was used to identify factors influencing the dose-corrected quetiapine serum concentration, expressed as the quetiapine concentration-to-dose (C/D) ratio. Variables included in the analysis were age, gender, and concomitant treatment with a total of 41 drugs most often used in combination with quetiapine. RESULTS: Age >or= 70 years (p = .001) and comedication with alimemazine (p = .002), fluvoxamine (p = .001), citalopram/escitalopram (p = .041), or clozapine (p < .001) significantly increased the serum concentrations of quetiapine, while age < 18 years (p = .044) and comedication with lamotrigine (p = .024), levomepromazine (p = .011), oxazepam (p < .001), or carbamazepine (p < .001) significantly decreased the serum concentrations. The effects were most pronounced for fluvoxamine (+159%), clozapine (+82%), age >or= 70 years (+67%), and carbamaze-pine (-86%). In 18% of the samples, the daily dose exceeded the currently recommended maximum of 800 mg/day. CONCLUSION: Due to the increased serum levels of quetiapine, a lower dose than usual should be considered when quetiapine is administered to elderly patients and to patients comedicated with clozapine or fluvoxamine. As the inducing effect of carbamazepine on quetiapine metabolism is very potent, cotreatment with carbamazepine cannot be recommended. On the basis of our data and pharmacokinetic considerations, the majority of drugs commonly used in psychiatry can safely be given in combination with quetiapine.

New high-performance liquid chromatographic method for serum analysis of oxazepam: application to bioequivalence and pharmacokinetic study.

A rapid and sensitive high-performance liquid chromatographic method was developed and validated for determination of oxazepam in serum. Oxazepam was isolated from biological fluid using a simple liquid-liquid extraction with dichloromethane. Nordazepam was used as the internal standard. The chromatographic separation was accomplished using a 125 x 4-mm (inner diameter) stainless-steel (5 microm) Perfectsil Target ODS-3 reversed phase column with a mobile phase consisting of ammonium dihydrogen phosphate buffer (0.05 mol x L(-1), pH 5.8) and methanol (50:50, v/v), running at a flow rate of 1.5 ml x min(-1). The absorbance of the fluent was monitored at 254 nm. The developed method resulted in totally symmetrical peaks. It has been applied to assess the pharmacokinetics of oxazepam. Also the bioequivalence of two different oxazepam preparations following oral administration in healthy volunteers was assessed by this method.

Fast in vivo microextraction: a new tool for clinical analysis.

BACKGROUND: We sought to develop a technique with the potential to partly replace current methods of analysis based on blood draws. To achieve this goal, we developed an in vivo microextraction technique that is faster than conventional methods, interferes minimally with the investigated system, minimizes errors associated with sample preparation, and limits exposure to hazardous biological samples. METHODS: Solid-phase microextraction devices based on hydrophilic polypyrrole and polyethylene glycol coatings were used for direct extraction of drugs from the flowing blood of beagle dogs, over a period of 8 h. The drugs extracted on the probes were subsequently quantified by liquid chromatography coupled to tandem mass spectrometry. Two calibration strategies--external and standard on the fiber--were used to correlate the amount extracted with the in vivo concentration. RESULTS: Diazepam and its metabolites were successfully monitored over the course of a pharmacokinetic study, repeated 3 times on 3 beagles. The fast microextraction technique was validated by comparison with conventional plasma analysis, and a correlation factor of 0.99 was obtained. In addition to total concentrations, the method was useful for determining free drug concentrations. CONCLUSIONS: The proposed technique has several advantages and is suitable for fast clinical analyses. This approach could be used not only for drugs, but for any other endogenous or exogenous compounds.

Toxicological data and growth characteristics of single post-feeding larvae and puparia of Calliphora vicina (Diptera: Calliphoridae) obtained from a controlled nordiazepam study.

Larvae of the Calliphora vicina (Diptera: Calliphoridae) were reared on artificial food spiked with different concentrations of nordiazepam. The dynamics of the accumulation and conversion of nordiazepam to its metabolite oxazepam in post-feeding larvae and empty puparia were studied. Analysis was performed using a previously developed liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. This method enabled the detection and quantitation of nordiazepam and oxazepam in single larvae and puparia. Both drugs could be detected in post-feeding larvae and empty puparia. In addition, the influence of nordiazepam on the development and growth of post-feeding larvae was studied. However, no major differences were observed for these parameters between the larvae fed on food containing nordiazepam and the control group. To our knowledge, this is the first report describing the presence of nordiazepam and its metabolite, oxazepam, in single Calliphora vicina larvae and puparia.

Comparison of the rates of hydrolysis of lorazepam-glucuronide, oxazepam-glucuronide and tamazepam-glucuronide catalyzed by E. coli beta-D-glucuronidase using the on-line benzodiazepine screening immunoassay on the Roche/Hitachi 917 analyzer.

The catalytic rates of hydrolysis of lorazepam-glucuronide, oxazepam-glucuronide, and temazepam-glucuronide when catalyzed by E. Coli. beta-glucuronidase both in phosphate buffer and buffered drug-free urine were compared as well as the pH dependence of enzyme activity. In 50 mM phosphate buffer pH 6.4, lorazepam-glucuronide has the highest turnover rate of 3.7 s(-1) with an associated Km of about 100 microM, followed by oxazepam-glucuronide, which has a turnover rate of 2.4 s(-1) with an associated Km of 60 microM. Temazepam-glucuronide has the lowest rate of 0.94 s(-1) with an associated Km of 34 microM. In buffered drug-free urine, a similar trend was observed. In addition, an optimal pH for beta-glucuronidase was determined to be between 6 and 7 when the enzyme hydrolyzes the benzodiazepine conjugates in buffered drug-free urine. Effects of temperature and incubation time were also examined. It can be concluded that the electron donating or withdrawing of the individual benzodiazepine structure may play an important role in the reactivity of the lorazepam-glucuronide, oxazepam-glucuronide and temazepam-glucuronide catalyzed by beta-glucuronidase. This is consistent with other observations made for monosubstituted phenyl-beta-glucuronides by Wang et al. (1).

Antipyrine, oxazepam, and indocyanine green clearance in patients with chronic pancreatitis and healthy subjects.

BACKGROUND: Hepatic drug metabolism was examined in patients with chronic pancreatitis and healthy controls by using a cocktail design with three different model compounds: antipyrine to express phase-I oxidation, oxazepam to express phase-II conjugation, and indocyanine green (ICG), a high-clearance compound. METHODS: Eight patients with chronic pancreatitis and seven healthy controls participated. Patients were diagnosed by the presence of typical morphologic changes of the pancreas on imaging and had a moderately but significantly reduced exocrine function and no or only slight impairment of the glucose tolerance. No one had a history or clinical signs of liver disease. Clearance of the three model compounds was estimated after the administration of 1 g antipyrine and 15 mg oxazepam orally and a bolus of indocyanine green, 0.5 mg/kg body weight, intravenously. RESULTS: The antipyrine clearance and ICG clearance were significantly decreased in the patients compared with the controls (mean, 27.2 ml/min; 95% confidence interval (CI), 19.4-35; versus 46.2 ml/min; 34.7-58.7, and 501 ml/min; 4014601, versus 771 mU/min; 677-865 (P < 0.05), respectively). The oxazepam clearance did not differ significantly between the two groups (181 ml/min (145-217) versus 178 ml/min (152-204)). The model drug clearance ratios between the patient and control clearances showed decreased values for antipyrine and ICG compared with the oxazepam data (0.59 and 0.65 versus 1.02, respectively). Patients and controls were characterized by a body weight of 58.2 kg (53.1-63.3) and 83.4 kg (72.7-94.1), respectively, and a body mass index (BMI) of 19.6 kg/m2 (17.9-21.3) versus 25.9 kg/m2 (23.4-28.4) (P < 0.05 for both). CONCLUSIONS: Patients with chronic pancreatitis characterized by a moderately reduced exocrine function and absence of diabetes mellitus and overt liver disease had a decreased antipyrine oxidation and ICG clearance, whereas no difference was seen in oxazepam conjugation when compared with healthy volunteers. In chronic pancreatitis the hepatic phase-I oxidation is reduced compared with the phase-II conjugation, as shown by the model drug clearance ratios. The clearance of ICG was also affected, pointing at a reduced hepatic plasma flow, provided that the hepatic extraction fraction is normal for these patients.

Single dose pharmacokinetics and pharmacodynamics of oxazepam in normal and renal dysfunction rats.

The purpose of this work was to investigate the disposition characteristics and pharmacodynamics of a benzodiazepine, oxazepam, in renal dysfunction rats. For the in vivo experiment, normal and renal dysfunction rats were given 40 mg/kg of oxazepam as the bolus dose. A quantitative electroencephalographic (EEG) method was used as the surrogate measure of the pharmacological response. The oxazepam concentration in plasma and cerebrospinal fluid (CSF) was assayed by the HPLC method. The steady-state volume of distribution and clearance based on total and unbound plasma did not change in renal dysfunction rats. Amplitude changes in the EEG induced by oxazepam in normal and renal dysfunction rats were characterized by a log-concentration response model or sigmoidal Emax model. The pharmacodynamic parameters from these models were not altered in renal dysfunction. In in vitro binding studies for gamma-aminobutyric acid (GABA)-benzodiazepine receptor complex, the oxazepam-induced effect was not potentiated by the plasma dialysate from renal dysfunction rats. Thus, it was suggested that the brain sensitivity to benzodiazepines was not altered in renal insufficiency.

Glucuronidation of drugs by hepatic microsomes derived from healthy and cirrhotic human livers.

Pharmacokinetic studies demonstrated that the decrease in drug biotransformation in hepatic failure depends on the metabolic pathways involved. To test whether glucuronidation reactions supported by UDP-glucuronosyltransferases are differentially affected in such conditions, we investigated the in vitro glucuronidation of four selected drugs and xenobiotics (zidovudine, oxazepam, lamotrigine, and umbelliferone) by using microsomes from human healthy and unhealthy (cirrhosis, hepatitis) livers as enzyme sources. Theses substances are glucuronidated by several UDP-glucuronosyltransferase isoforms. Lidocaine N-deethylation activity measured concomitantly was used as a positive control, because the inhibition of this reaction in patients with hepatic diseases is well documented. The metabolic clearances of zidovudine and lidocaine were decreased significantly in liver cirrhosis (0.17 versus 0.37 microliter/min/mg protein and 0.40 versus 2.73 microliter/min/mg protein, respectively) as a consequence of a decrease of their corresponding Vmax of metabolism. By contrast, the metabolic clearances of oxazepam, umbelliferone, and lamotrigine glucuronidation remained unchanged. Previous studies reported that the in vivo oral clearances of zidovudine and lidocaine were decreased by 70% and 60%, respectively, in cirrhotic livers, whereas those of lamotrigine and oxazepam were not affected. Consequently, it is likely that the in vitro metabolic data, which support the in vivo results, therefore could contribute to reasonably predict the level of impairment of hepatic clearance in patients with liver cirrhosis.

Pharmacodynamic responses of F344 rats to the mouse hepatocarcinogen oxazepam in a 90-day feed study.

Oxazepam (Serax) is a widely used benzodiazepine anxiolytic agent and a metabolite of other benzodiazepines such as Valium and Librium. Chronic feeding studies indicated that oxazepam is an hepatocarcinogen in B6C3F1 mice but did not increase hepatic tumors in F344 rats. The present study was performed to compare the hepatic responses of rats with our previous findings in mice to explore the reason(s) for the dramatic differences in tumor response between the two species. Male F344 rats (10 per dose-time group) received diets containing oxazepam at 0, 25, 125, 2500, and 5000 ppm. Hepatocyte labeling indices were measured immunohistochemically by PCNA and BrDU during the last 7 days before sacrifices after 15, 30, 45, and 90 days of dosing. Serum oxazepam was determined by reverse phase HPLC. Results indicated that oxazepam induced significant liver weight increases in a dose-related fashion by 15 days, which remained elevated for the entire study. No important clinical chemistry or pathology changes were noted except those related to hypertrophy. Cell proliferation was significantly increased in a dose-related manner by the 15- and 30-day timepoint in the 2500 and 5000 ppm groups. The most significant finding in the present study of oxazepam was plasma levels of the parent compound. Plasma levels in rats were dramatically lower than in B6C3F1 mice exposed to oxazepam in studies conducted earlier at the same dose levels. These results suggest that the early responses of rats and mice to oxazepam, such as cell proliferation and clinical chemistry parameters, are similar. Our previous studies demonstrated that oxazepam metabolites are excreted in the urine of rats, similar to humans, whereas mice excrete oxazepam metabolites in bile allowing enterohepatic recirculation, which results in high plasma levels of oxazepam. These data indicate that the rat excretes oxazepam kinetically (rate and route) similar to humans, but the mouse produces metabolites similar to humans.