Pharmacokinetics of Diazepam and Its Metabolites in Urine of Chinese Participants

BACKGROUND

Urine is conventionally used as a specimen to document diazepam-related crimes; however, few reports have described the pharmacokinetics of diazepam and its metabolites in urine.

OBJECTIVE

This study aimed to investigate the pharmacokinetics of diazepam and its metabolites, including glucuronide compounds, in the urine of Chinese participants.

METHODS

A total of 28 volunteers were recruited and each participant ingested 5 mg of diazepam orally. Ten milliliters of urine were collected from each participant at post-consumption timepoints of prior (zero), 1, 2, 4, 8, 12, and 24 h and 2, 3, 6, 12, and 15 days. All samples were extracted by solid-phase extraction and analyzed using high-performance liquid chromatography-tandem mass spectrometry. Diazepam and its main metabolites, except for temazepam, were detected in the urine of volunteers. Pharmacokinetic parameters were analyzed using the pharmacokinetic software DAS according to the non-compartment model.

RESULTS

Urinary diazepam peaked at 2.38 ng/mL (C_max) and 1.93 h (T_max). The urinary metabolite nordiazepam peaked at 1.17 ng/mL and 100.21 h; temazepam glucuronide (TG) peaked at 145.61 ng/mL and 41.14 h; and oxazepam glucuronide (OG) peaked at 101.57 ng/mL and 165.86 h. The elimination half-life (t_½z) and clearance (CLz/F) for diazepam were 119.58 h and 65.77 L/h, respectively. The t_½z of the metabolites nordiazepam, TG, and OG was 310.58 h, 200.17 h, and 536.44 h, respectively. Finally, this study found that both diazepam and its main metabolites in urine were detectable for at least 15 days, although there were individual differences.

CONCLUSION

The results regarding diazepam pharmacokinetics in urine would be of great help in forensic science and drug screening.

Voriconazole and fluconazole increase the exposure to oral diazepam

OBJECTIVE

We assessed the effect of voriconazole and fluconazole on the pharmacokinetics and pharmacodynamics of diazepam.

METHODS

Twelve healthy volunteers took 5 mg of oral diazepam in a randomised order on three study sessions: without pretreatment, after oral voriconazole 400 mg twice daily on the first day and 200 mg twice daily on the second day, or after oral fluconazole 400 mg on the first day and 200 mg on the second day. Plasma concentrations of diazepam and N-desmethyldiazepam were determined for up to 48 h. Pharmacodynamic variables were measured for 12 h.

RESULTS

In the voriconazole phase, the area under the plasma concentration time curve (AUC 0-infinity) of diazepam was increased (geometric mean ratio) 2.2-fold (p < 0.05; 90% confidence interval [CI] 1.56 to 2.82). This was associated with the prolongation of the mean elimination half-life (t(1/2)) from 31 h to 61 h (p < 0.01) after voriconazole. In the fluconazole phase, the AUC 0-infinity of diazepam was increased 2.5-fold (p < 0.01; 90% CI 1.94 to 3.40), and the t(1/2) was prolonged from 31 h to 73 h (p < 0.001). The peak plasma concentration of diazepam was practically unchanged by voriconazole and fluconazole. The pharmacodynamics of diazepam were changed only modestly.

CONCLUSION

Both voriconazole and fluconazole considerably increase the exposure to diazepam. Recurrent administration of diazepam increases the risk of clinically significant interactions during voriconazole or fluconazole treatment, because the elimination of diazepam is impaired significantly.

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.

Effect of the gene dosage of CgammaP2C19 on diazepam metabolism in Chinese subjects

OBJECTIVE

To determine whether the gene dosage of CYP2C19 affects the metabolism of diazepam and desmethyldiazepam in healthy Chinese subjects.

SUBJECTS AND METHODS

Eighteen unrelated adult men were recruited for the study from a total of 101 healthy Chinese volunteers who had been screened for CYP2C19 phenotype and genotype. All subjects received a single oral dose (5 mg) of diazepam, and the pharmacokinetics of diazepam and desmethyldiazepam were compared in six ml homozygotes (ml/ml), six ml heterozygotes (wt/ml), and six wild-type homozygotes (wt/wt).

RESULTS

The plasma elimination half-life values of diazepam (84.0 +/- 13.7 hours) and desmethyldiazepam (176.0 +/- 28.9 hours) in subjects of ml/ml were significantly longer than those (62.9 +/- 9.8 hours for diazepam; 132.1 +/- 24.9 hours for desmethyldiazepam; both P < .01) in subjects of wt/ml or those (20.0 +/- 10.8 hours for diazepam; 99.2.+/- 21.7 hours for desmethyldiazepam; both P < .01) in subjects of wt/wt. A significant difference in the corresponding half-life values existed between the wt/ml and wt/wt subjects (P < .01). As expected, the slowest mean clearance of diazepam was observed in the ml/ml subjects (2.8 +/- 0.9 mL/min) and the fastest in the wt/wt subjects (19.5 +/- 9.8 mL/min), with the wt/ml heterozygotes having an intermediate value (7.2 +/- 2.6 mL/min).

CONCLUSION

The presence of a single-nucleotide polymorphism (G681A) of the CYP2C19 gene cosegregates with the impaired metabolism of diazepam and desmethyldiazepam among Chinese subjects in a gene-dosage effect manner.

Effect of sertraline on the pharmacokinetics and protein binding of diazepam in healthy volunteers

A double-blind randomised placebo-controlled study was conducted in healthy male volunteers to determine the effects of sertraline on the pharmacokinetics of diazepam and its primary metabolite, N-demethyldiazepam. The effect of sertraline on the plasma protein binding of diazepam was also studied. Sertraline 50 mg/day titrated over a 10-day period to 200 mg/day or placebo was administered for 32 days. A single intravenous dose of diazepam 10 mg was given before the start, and after 21 days of sertraline or placebo treatment. The pharmacokinetic analyses were based on data from 20 individuals. The systemic clearance of diazepam decreased by 32% (-0.100 ml/min/kg) in the sertraline group compared with a 19% decrease (-0.054 ml/min/kg) in the placebo group (p = 0.0266). However, this small difference (13%) between the 2 groups was not considered meaningful. Other than a prolonged time to maximum plasma concentration for N-demethyldiazepam, no other pharmacokinetic parameters were significantly altered by sertraline. The plasma protein binding of diazepam was unchanged by concomitant administration of sertraline. These results suggest that sertraline at the maximum recommended dosage under steady-state conditions, and demethylsertraline, the principal metabolite of sertraline, are unlikely to exert significant inhibitory effects on the CYP2C19 and CYP3A3/4 hepatic isoenzymes responsible for the metabolism of diazepam. Therefore, it would be expected that sertraline would, similarly, have a minimal effect on the pharmacokinetic profile of other drugs metabolised by these hepatic isoenzymes.

Assessment of diazepam loading dose therapy of delirium tremens

The efficacy of the diazepam loading dose method of treatment of delirium tremens was assessed in comparison with the traditional therapy. The experimental group and the control group comprised 51 and 45 patients respectively. The clinical institute withdrawal assessment for alcohol (CIWA-A) scale was applied to assess the intensity of the symptoms. Diazepam doses in the experimental group oscillated from 40 to 210 mg (mean 86.9 +/- 47.2 mg). The control group was receiving diazepam and other psychotropic drugs in divided doses. In the experimental group deliric symptoms were present from 2 to 24 h (mean 6.9 +/- 4.8 h), and in the control group from 2 to 123 h (mean 33.8 +/- 25.7 h). The results show a large efficacy of the loading dose method corresponding to substantial reduction of the psychosis duration (fivefold in comparison to the control group). The method proved to be safe, with no significant complications.

[Benzodiazepines in geriatrics--a case report on prolonged action]

Due to the age-dependent changes of pharmacodynamic and pharmcokinetic, the frequency of undesirable side-effects of benzodiazepines is higher in geriatric patients. An increased sensitivity to benzodiazepines and their metabolites can induce extremely prolonged duration of action leading to unconsciousness and respiratory insufficiency. Because of an assumed postoperative "psychosyndrome", a 72-year-old patient was treated with high doses of diazepam combined with single doses of tramal, clonidin and ranitidin. This treatment was followed by the development of respiratory insufficiency requiring intensive care with intubation for 8 days including assisted ventilation for 2 days. The serum concentrations of diazepam and its metabolites lay within the therapeutic range until the 7th day after the end of application. Therefore, the authors conclude that when using benzodiazepines in geriatric patients, the physiological peculiarities of this age group and possible interactions with other drugs leading to an increase in potency must be carefully considered.

Flumazenil, diazepam, nordiazepam and oxazepam interactions on plasma protein binding

The effect of flumazenil (FLU) on plasma protein binding of diazepam (DZ), nordiazepam (ND) and oxazepam (OX) was determined in plasma from drug-naive dogs to which graded concentrations of tested drugs alone and in combination were added. The results revealed that as the concentration of FLU added to plasma alone was increased its binding with plasma proteins decreased and that there were no significant binding interactions between FLU and OX, ND and DZ.

Interethnic difference in omeprazole's inhibition of diazepam metabolism

OBJECTIVES

To compare the effect of omeprazole, a substrate and inhibitor of CYP2C19, on diazepam metabolism in white and Chinese subjects.

SUBJECTS AND METHODS

The study, which took place at a clinical research center in a University Hospital, was designed as a double blind, crossover, two-stage study; each stage lasted 21 days and was separated by 4 weeks. Subjects were eight white and seven Chinese men who were extensive metabolizers of debrisoquin and mephenytoin. The subjects received, in a randomized order, omeprazole, 40 mg/day, and placebo for 21 days, followed by a 10 mg oral dose of diazepam. Diazepam and desmethyldiazepam plasma concentrations were determined by HPLC during a 26-day period after diazepam administration.

RESULTS

In white subjects omeprazole treatment decreased diazepam clearance by 38% +/- 4.4% and increased desmethyldiazepam area under the plasma concentration-time curve (AUC) by 42.4% +/- 7.0%. In contrast, diazepam oral clearance decreased by only 20.7% +/- 7.3% and desmethyldiazepam AUC decreased by 25.4% +/- 4.6% in the Chinese group. The decrease in diazepam clearance and the prolongation in diazepam and desmethyldiazepam elimination half-lives after administration of omeprazole were significantly greater in the white group than in the Chinese group (p < 0.03, p < 0.001, and p < 0.004, respectively). In the absence of omeprazole, diazepam oral clearance was marginally greater (mean +/- SEM) (34.4 +/- 2.8 ml/min versus 25.2 +/- 3.5 ml/min, p = 0.057, respectively) and the AUC of desmethyldiazepam was significantly lower (8794 +/- 538 micrograms/L.hr versus 16,358 +/- 2985 mg/L.hr, p = 0.04, respectively) in the white subjects compared with the Chinese subjects.

CONCLUSION

The extent of the inhibitory effect of omeprazole on diazepam metabolism is dependent on ethnicity. Further studies are needed to determine the mechanism responsible for this phenomenon.

Flunitrazepam and nordiazepam slowly released from silastic capsules induce physical dependence in rat

The rates of in vitro release of flunitrazepam (FN), nordiazepam (ND) and diazepam (DZ) from silastic capsules were compared and found to be in the following order: DZ > FN > ND. Rats that were implanted subcutaneously with capsules filled with FN or ND for 5 to 7 weeks before administering flumazenil (FLU) (40 mg/kg, i.v.) showed precipitated abstinence as measured by the Precipitated Abstinence Score (PAS) which included a rapid onset of clonic and tonic-clonic convulsions. Rats implanted with DZ also demonstrated significant PAS and seizures. Implantation of similar doses of DZ, FN and ND resulted in different plasma levels of parent benzodiazepines and their metabolites that corresponded with their in vitro release: DZ > FN > ND. These data indicate that, as for DZ, the capsule implantation is an effective method of producing physical dependence on FN and ND in the rat.

Effects of liver disease on the pharmacokinetics of intravenous and oral chlordesmethyldiazepam

We studied the pharmacokinetics of a single 0.5-mg i.v. dose of chlordesmethyldiazepam in 8 patients with liver disease and in 12 age-matched healthy controls. The kinetics were also studied of a single 1-mg oral dose in the patients with liver disease. After i.v. administration the kinetics of total chlordesmethyldiazepam in patients with liver disease differed from those in controls: elimination half-life was almost twice that in controls (395 and 204 h), as a consequence of a marked reduction in total clearance (0.13 and 0.25 ng.ml-1.h-1), whereas the apparent volume of distribution was similar in patients and controls (4.7 and 3.9 l/kg-1). The free fraction of the drug in patients was higher (5.5%) than in controls (2.9%). Correction for differences in protein binding revealed clearance in the patients was one-fifth (1.8 and 10.5 ng ml-1.kg-1) and volume of distribution one-half (65.0 and 118.4 l.kg-1) that in controls. The systemic availability of oral chlordesmethyldiazepam was high (110%) in spite of a relatively slow absorption rate. These results indicate a need for caution in the administration of chlordesmethyldiazepam to patients with liver disease.

Diazepam metabolism by human liver microsomes is mediated by both S-mephenytoin hydroxylase and CYP3A isoforms

1. The primary metabolism of diazepam was studied in human liver microsomes in order to investigate the kinetics and to identify the cytochrome P450 (CYP) isoforms responsible for the formation of the main diazepam metabolites, temazepam and N-desmethyldiazepam. 2. The formation kinetics of both metabolites were atypical and consistent with the occurrence of substrate activation. A sigmoid Vmax model equivalent to the Hill equation was used to fit the data. The degree of sigmoidicity was greater for temazepam formation than for N-desmethyldiazepam formation, so that the ratio of desmethyldiazepam:temazepam formation increased as the substrate (diazepam) concentration decreased. 3. alpha-Naphthoflavone activated both reactions but with a greater effect on temazepam formation than on N-desmethyldiazepam formation. In the presence of 25 microM alpha-naphthoflavone the kinetics for both pathways were approximated by Michaelis-Menten kinetics. 4. Studies with a series of CYP isoform selective inhibitors and with an inhibitory anti-CYP2C antibody indicated that temazepam formation was carried out mainly by CYP3A isoforms, whereas the formation of N-desmethyldiazepam was mediated by both CYP3A isoforms and S-mephenytoin hydroxylase.

Radioiodinated nordiazepam analog for in vivo assessment of benzodiazepine receptors by single photon emission tomography

2'-Iodo-nordiazepam (2'-IND), a nordiazepam analog iodinated at the 2'-position of the C-5 phenyl ring, was synthesized and evaluated as a potential radiopharmaceutical for investigating brain benzodiazepine receptors by SPECT. [125I]2'-IND was synthesized by the halogen exchange reaction and purified by HPLC. In an in vitro competitive binding study using [3H]diazepam and rat cortical synaptosomol membranes, 2'-IND showed an almost equal affinity for benzodiazepine receptors as diazepam. In a saturation binding study using rat cortical synaptosomal membranes, 2'-IND displayed a Kd of 1.10 nM and a Bmax of 1.87 pmol/mg protein. Biodistribution and metabolism studies in mice showed that [125I]2'-IND exhibited rapid and high accumulation in the brain, and that the cerebral uptake and distribution of this compound occurred in the intact form. Furthermore, the administration of diazepam and flumazenil reduced cortical uptake by approx. 20%, suggesting that the uptake of 2'-IND occurred at least partly in association with benzodiazepine receptors.

Pharmacokinetic differences of desmethyldiazepam in three outbred Wistar strains related to differences in liver enzyme activities

Various strains of rats differ in their sensitivities towards benzodiazepines suggesting that variations in biological features are responsible for these differences. All reports concern inbred strains. We have studied male rats of three outbred Wistar strains with regard to the pharmacokinetics of desmethyldiazepam given as a single intravenous dose. The elimination half-life of desmethyldiazepam was longer in the Riv:TOX(M) (from the National Institute of Public Health and Environmental Protection) and in the Cpb:WU strain than in the Crl:(WI)BR strain. This strain difference in elimination of desmethyldiazepam may be related to differences in liver enzyme activities.

Pharmacokinetics of nordiazepam in physical dependence and precipitated abstinence in dogs

Previous studies suggested that the extensive accumulation of benzodiazepines is an important factor in the induction of physical dependence. The mechanistic basis for accumulation of nordiazepam (ND) and its metabolite, oxazepam (OX), have been examined in crossover studies in drug-naive and in ND-dependent dogs that exhibited a flumazenil-precipitated abstinence syndrome. ND and parent OX have similar pharmacokinetic profiles. Steady-state plasma levels of ND and OX cannot be predicted from single-dose pharmacokinetics. Reduced plasma clearance of ND and altered plasma protein binding were observed in dogs physically dependent upon ND. The benzodiazepine antagonist, flumazenil, significantly reduces steady-state plasma levels of total and free ND.

Studies on the excretion of diazepam and nordazepam into milk for the prediction of milk-to-plasma drug concentration ratios

The influence of varying protein and fat content in milk of New Zealand White rabbits on the milk-to-plasma drug concentration (M/P) ratio of diazepam was studied. At various time points after littering, a bolus dose (1.5 mg/kg) followed by a 26-hr infusion (1.8 mg/h) of diazepam was administered to freely moving rabbits via a jugular vein catheter. Milk and blood samples were collected to allow characterization of milk composition and quantitative determination of diazepam and nordazepam in milk and plasma. At steady state diazepam showed M/P ratios between 3.7 and 9.5, whereas nordazepam showed ratios between 2.1 and 4.3, respectively. The relative importance of milk protein binding and milk-fat partitioning for the excretion of a drug into milk depended on the drug's affinity to milk fat. A stepwise multiple regression analysis suggested that observed M/P ratios of diazepam could be explained by considering the fat content of milk alone. Nordazepam with a lower solubility in milk fat showed M/P ratios which could be best explained by considering protein and fat concentrations together. Using the data from the infusion studies, two recently published diffusional models to predict M/P ratios were evaluated. Neither model could accurately predict the M/P ratios of diazepam and nordazepam observed in rabbits. However, after extending the model described by Atkinson and Begg to take the actually measured partitioning between skim milk and milk fat into account, a great improvement in the predictive power for observed M/P ratios occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Diazepam metabolism by rat and human liver in vitro: inhibition by mephenytoin

1. Diazepam metabolism and its association with mephenytoin hydroxylase were studied in vitro using human and rat livers. 2. Enzyme kinetic parameters were obtained for the formation of p-hydroxydiazepam (p-hydroxy-DZP), N-desmethyldiazepam (NDZ), and temazepam (TMZ) from diazepam (DZP) in rat liver fractions. The Km values for formation in rat of p-hydroxy-DZP, NDZ and TMZ were 14 +/- 3 (SEM) microM, 44 +/- 4 and 63 +/- 8, respectively; clearance values calculated from Vmax/Km were 5.7, 3.2 and 4.9 ml/g per min, respectively. 3. Mephenytoin (MP) competitively inhibited, in rat liver, the formation of NDZ, but not the formation of p-hydroxy-DZP or TMZ; in human liver neither NDZ nor TMZ formation was inhibited by MP. 4. In seven different human livers the formation of p-hydroxy-DZP represented a minor pathway compared to the formation of NDZ and TMZ.

Pharmacokinetics of diazepam intramuscularly administered to rhesus monkeys

The purpose of this study was to define the pharmacokinetics of diazepam in monkeys following an im injection of 100 micrograms/kg (the minimum effective dose that prevents nerve agent-induced convulsions in pyridostigmine-pretreated, atropine- and 2-PAM-treated monkeys) in order to predict what im dose in humans is needed to prevent nerve agent-induced convulsions. Six rhesus monkeys were administered diazepam in the hind limb. Blood (3 mL) was collected via an indwelling saphenous catheter immediately prior to and 5, 10, 15, 25, 40, 60, 90, 120, 180, and 240 min after diazepam dosing. A contract laboratory, blind to the labeling code, analyzed diazepam serum concentrations by electron-capture gas chromatography and the percentage of unbound diazepam by equilibrium dialysis. The concentration-time data for total (unbound and bound) diazepam individually determined for each animal was best described by a one-compartment open model with first-order absorption and elimination. The average maximum serum concentration (50 ng/mL) was reached in 29 min. The volume of distribution and systemic clearance, assuming 100% bioavailability, were 1.5 L/kg and 19.4 mL/min/kg, respectively. The percentage of diazepam unbound to serum proteins was 4.6% and, therefore, the maximum concentration of free diazepam was 2.3 ng/mL. These results, when compared with human pharmacokinetic studies, allow a means of extrapolating effective monkey anticonvulsant doses to humans on a pharmacokinetic basis.

Chronic administration of and dependence on halazepam, diazepam, and nordiazepam in the dog

Halazepam administered chronically to dogs in oral doses of 180 and 450 mg/kg/day produced physical dependence which was revealed by a flumazenil precipitated abstinence syndrome and measured by the Nordiazepam Precipitated Abstinence Scale score (NPAS) (McNicholas et al., 1988; Sloan et al., 1990). This abstinence as measured by the NPAS score was more severe in diazepam- and halazepam-dependent than in nordiazepam-dependent dogs whereas the incidence of precipitated clonic seizures was greater in the diazepam- and nordiazepam-dependent than in the halazepam-dependent dogs. Pharmacokinetic studies showed that in the dog the major conversion of halazepam, like diazepam, was to nordiazepam and an oxazepam conjugate. Appreciable quantities of oxazepam, 3-OH halazepam and its conjugated metabolite were also identified in plasma. The NPAS score obtained in the halazepam-dependent dogs, however, was greater than the NPAS score obtained in nordiazepam-dependent dogs who had nordiazepam plasma levels over three times higher than those obtained in the halazepam-dependent dogs. Further, the precipitated abstinence observed in the halazepam-, diazepam- and nordiazepam-dependent dogs differed in qualitative as well as in quantitative aspects including marked differences in the time course of abstinence signs. These data argue that the different dependencies produced by halazepam, diazepam and nordiazepam are not due solely to either the parent compound or to a single metabolite but most likely to their combined effects.

Effect of orally administered misoprostol and cimetidine on the steady state pharmacokinetics of diazepam and nordiazepam in human volunteers

The effects of misoprostol and cimetidine on diazepam pharmacokinetics were evaluated in order to determine whether the kinetic variables for diazepam and nordiazepam alone differ with the repeated oral administration of misoprostol and cimetidine to healthy adult volunteers. The trial was conducted as an open crossover study in 12 normal subjects, divided into two groups with all subjects receiving both regimens. Total study duration was 5 weeks. An initial clinical assessment, including blood biochemistry and assessment of subject oxidation status was carried out on study day 1. On this day, subjects began taking diazepam (10 mg) orally for one week, with pharmacokinetic studies performed at day 8, when steady state levels of diazepam were reached. This was followed by one week with active drug, misoprostol to Group I and cimetidine to Group II, with pharmacokinetic studies performed at the end of a 1-week treatment. After a 2-week wash-out period, both groups took for one week, the alternate drug, i.e. cimetidine plus diazepam to Group I and misoprostol plus diazepam to Group II. On days 8, 15 and 36, subjects were admitted to the hospital for 12 h, during which time a clinical examination was carried out and blood samples were taken at time zero and at 4, 8, 12, 24, and 36 h post-dosing for the measurement of serum diazepam and nordiazepam. The main parameters measured and evaluated were diazepam and nordiazepam pharmacokinetics at steady state (days 8, 15 and 36). These were areas under the curve in the dose intervals (AUC0-24h), maximum plasma concentrations (Cmax), time to peak concentrations (Tmax), elimination half-life (t1/2), elimination constant (Kel), distribution volume (Vd), total body clearance (ClB) and clearance after oral administration (Cloral). The results demonstrated that plasma diazepam and nordiazepam concentrations had a significant increase after steady states have been reached with the simultaneous administration of 800 mg of cimetidine daily for one week. The simultaneous administration of 800 micrograms of misoprostol did not cause any significant change in diazepam and nordiazepam plasma levels after steady states had been reached. Comparing the pharmacokinetic parameters of Groups A and B as well as within groups on days 8, 15 and 36, a significant increase in plasma diazepam and nordiazepam levels was detected. This was due to a cimetidine-induced impairment in microsomal oxidation of diazepam and nordiazepam, which caused a decrease in total metabolic clearance and increased mean steady state plasma concentrations. A more prolonged half-life was observed for both groups taking cimetidine as well as an increase of mean maximum plasma concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacokinetics of intravenous and oral chlordesmethyldiazepam in patients on regular haemodialysis

The pharmacokinetics of a single 2 mg IV dose of chlordesmethyldiazepam has been studied in 11 patients with renal failure on regular haemodialysis and in 11 age-matched healthy controls. The kinetics was also examined after a single 2 mg oral dose in 6 of the 11 renal failure patients. After intravenous administration the kinetics of total chlordesmethyldiazepam in renal patients and controls were the same. The unbound fraction of the drug in renal patients was higher (5.5%) than in controls (2.9%). Correction for differences in protein binding revealed a reduced apparent volume of distribution (47 vs. 140 l.kg-1) and a reduced clearance (5.0 vs. 10.5 ml.min-1.kg-1) in the patients. The systemic availability of oral chlordesmethyldiazepam was good (82%) despite a relatively slow absorption rate.

Amnestic effects of intravenous diazepam in healthy young men

Changes in a test of memory performance were evaluated in 103 healthy young men after challenges with placebo and two different doses of intravenous diazepam (0.12 and 0.20 mg/kg). Both diazepam doses significantly impaired free recall in a dose-dependent manner. Within each dose challenge there was no significant correlation between the average serum diazepam or desmethyldiazepam levels and the average number of words recalled across the time points. The data expand our current understanding of the amnestic effects of benzodiazepines and suggest that patients abusing these drugs in large doses may develop profound degrees of memory impairment.

Distribution of diazepam, nordiazepam, and oxazepam between brain extraneuronal space, brain tissue, plasma, and cerebrospinal fluid in diazepam and nordiazepam dependent dogs

The compartmental distribution of diazepam (DZ) and nordiazepam (ND) and their metabolites was studied in DZ and ND dependent dogs. The levels of DZ, and ND and their metabolites were determined during the last week of stabilization in the extraneuronal brain space, in brain tissue, in plasma and in CSF. In these studies dependent dogs were anesthetized with pentobarbital and microdialysis probes were inserted bilaterally into the parietal cortex and perfused with artificial cerebrospinal fluid. Microdialysis probes were also used to determine the unbound parent drugs and their metabolites in plasma. The brain-plasma distribution of total ND and oxazepam (OX) is about equal in ND dependent dogs but in DZ dependent dogs total ND and OX are about 2-fold higher in brain than in plasma. The levels of DZ, ND, and OX in the extraneuronal brain space are similar to their unbound levels in plasma. These data suggest that the concentration of free benzodiazepines in plasma is a good approximation of the concentration in the vicinity of the membrane receptors in the dependent dogs.

Determination of pharmacodynamics of diazepam by quantitative pharmaco-EEG

The relationship between the quantitative EEG variables and plasma levels after the administration of diazepam (DZ) or N-desmethyldiazepam (synthesized NDDZ) was evaluated by simultaneously measuring the power spectra for EEG with two biological markers and plasma concentrations. After a single DZ administration, the EEG change corresponding to sedation appeared rapidly and showed a short duration. A close relationship was found between these effects and changes in the DZ plasma concentrations. DZ and synthesized NDDZ had the same pharmacodynamic characteristics, but the main metabolic product of DZ (metabolite NDDZ) showed a different pharmacokinetic profile. A multiple administration of DZ or synthesized NDDZ caused some reduction in sedation at the steady-state. These results led to the conclusions that a single administration of DZ causes sedation of a short duration, and the main metabolic product of DZ (metabolite NDDZ) does not seem to contribute to sedation. In addition, the reduction in the pharmacological effect after continuous treatment with DZ depends not on autoinduction or interference, but on acute tolerance or adaptation.

Placental transfer and distribution of pinazepam and its metabolite N-desmethyldiazepam in the maternal and fetal rabbit: effect of the stage of gestation

The distribution of pinazepam and its metabolite N-desmethyldiazepam was studied in fetuses of New Zealand rabbits on the 20th and 27th day of pregnancy. The concentrations of both compounds were also measured in the maternal brain, liver and uterus. Pregnant rabbits were sacrificed at 0.5, 2, 4 and 12 h after intravenous administration of pinazepam (5 mg/kg). The concentrations of pinazepam and N-desmethyldiazepam in various biological specimens were measured by a specific gas-chromatographic procedure. Pinazepam and N-desmethyldiazepam rapidly crossed the placenta. In 20 day old fetuses, comparable concentrations of pinazepam were found in the liver, brain, heart, lungs and kidneys. In contrast, the liver of 27 day old fetuses accumulated pinazepam at concentrations higher than the other tissues. The hepatic extraction of pinazepam, already described in adult rabbits (1), develops prenatally. A preferential accumulation of pinazepam rather than N-desmethyldiazepam was also observed in the maternal uterus. In this tissue the concentrations of pinazepam were 5-10 times higher on the 27th rather than the 20th day of pregnancy. The stage of pregnancy influences the distribution pattern of pinazepam in rabbit fetuses and their mothers.

Desmethyldiazepam pharmacokinetics: studies following intravenous and oral desmethyldiazepam, oral clorazepate, and intravenous diazepam

After single 10-mg intravenous (IV) doses of desmethyldiazepam (DMDZ) to 12 healthy human volunteers, (mean age, 62 years) blood samples were obtained over the next 14 or more days. Mean kinetic variables were volume of distribution (Vd), 90 liters; elimination half-life (t1/2), 93 hours; and clearance, 12.3 mL/min. Vd was significantly correlated with body weight (r = .73, P less than .01) and with percent ideal body weight (r = .91, P less than .001). Eleven of the same subjects also received 5- to 15-mg doses of IV diazepam (DZ). Mean kinetic variables were Vd, 180 liters; t1/2, 83 hours; and clearance, 28 mL/min. Clearances of DZ and DMDZ were significantly correlated (r = .73, P less than .02). Based on area analysis, the extent of conversion of DZ to systemic DMDZ averaged 53%. After oral administration of DMDZ in tablet form (10 mg), or of clorazepate dipotassium in capsule form (15 mg), systemic availability of DMDZ from each of the oral dosage forms was not significantly different from 100%.

Kinetics of drug action in disease states. XXV. Effect of experimental hypovolemia on the pharmacodynamics and pharmacokinetics of desmethyldiazepam

It has been reported that hypovolemia secondary to extensive blood loss alters the functionality of the central nervous system and is associated with changes in the dose requirements or intensity of action of various central nervous system depressants, including a benzodiazepine. To investigate the mechanism(s) of this effect, the influence of experimental hypovolemia on the pharmacodynamics, receptor binding and pharmacokinetics of a benzodiazepine drug was determined. Adult male Sprague-Dawley rats were made hypovolemic by removal of about 30% of their blood over 30 min. An i.v. infusion of desmethyldiazepam (DDZP) was started 30 min later and continued until the animals lost their righting reflex. Compared to results obtained with normal controls, the hypovolemic rats required about one-half the dose of DDZP to produce loss of righting reflex and had significantly lower DDZP concentrations in serum and cerebrospinal fluid at that time. This effect of substantial blood removal could not be reversed by prompt return of the removed blood to the animals. Experimental hypovolemia had no apparent effect on the in vitro binding of tritiated diazepam to benzodiazepine receptor sites in the cerebral cortex of rats. The plasma clearance of DDZP was decreased significantly and the biological half-life was increased in hypovolemic rats compared to normal animals when both received a 30-mg/kg dose by i.v. infusion over 10 min. It is concluded that acute hemorrhagic hypovolemia increases the sensitivity of the central nervous system to the depressant effect of DDZP and decreases the body clearance of that drug in rats. Thus, the pharmacodynamics as well as the pharmacokinetics of a benzodiazepine are altered by hypovolemia.

Effect of food on absorption of chlordemethyldiazepam

The kinetics of a single 1-mg oral dose of chlordemethyldiazepam (CDDZ, En) was determined on two occasions in 8 healthy volunteers. CDDZ was given in the fasting state on one occasion and following a standard meal on another. Compared with the fasting state, administration of CDDZ with food prolonged the time to reach peak concentration (1.5 vs. 6.8 h after dosage, p less than 0.01) and the absorption half-life (28 vs. 231 min, p less than 0.01). Total area under the curve was not influenced, nor was CDDZ elimination half-life (84.2 vs. 88.7 h). Thus administration of CDDZ with food slows the rate of its absorption but does not alter the completeness of absorption.

Comparison of sublingual and oral prazepam in normal subjects. II. Pharmacokinetic and pharmacodynamic data

The pharmacokinetic profiles of oral and sublingual administrations of prazepam 20 mg to 5 normal volunteers were compared in order to explain the clinical observation that sublingual prazepam appears to exhibit sedative properties when compared to the same dose of oral prazepam. Blood samples for pharmacokinetic evaluation were collected just before drug intake and 7.5, 15, 22.5, 30, 45, 60, 90 min, 2, 3, 5, 6, 7, 8, 9, 10 and 24 h after drug intake. The study was performed in double-blind and crossover conditions. Serum levels of prazepam and its major metabolite N-desmethyl-diazepam were measured by HPLC. No prazepam was detected at a concentration higher than 20 ng/ml (limit of detection) whereas N-desmethyl-diazepam reached concentrations around 140 ng/ml. To correlate this observation with the clinical data, the affinity of prazepam and N-desmethyl-diazepam was compared measuring their ability to displace 50% of 3H-flunitrazepam bound to benzodiazepine receptors contained in synaptosomal preparation obtained from rat brain. N-desmethyl-diazepam was 17-fold more potent than prazepam. This data suggests that prazepam is a pro-drug which is transformed to the active compound N-desmethyl-diazepam and that the difference in clinical observation with both administrations could be correlated to N-desmethyl-diazepam concentration-time curves. Nevertheless, the comparison of the area under the N-desmethyl-diazepam serum concentration-time curves, the maximum concentrations, the times when the maximum concentrations were observed and the times needed to detect a significant level after oral and sublingual administration did not show statistical difference.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and bioavailability of intravenous and oral chlordesmethyldiazepam in humans

Six healthy, fasting volunteers were given single doses of chlordesmethyldiazepam by 1 mg i.v., or as drops or tablets. Chlordesmethyldiazepam and its metabolite, lorazepam, in multiple plasma samples and in urine collected for 120 h after each dose were determined by electron-capture GLC. Mean kinetic variables for intravenous chlordesmethyldiazepam were: volume of distribution, 1.71 l.kg-1; elimination half-life, 113 h; total clearance, 0.21 ml.min-1.kg-1; cumulative excretion of lorazepam glucuronide 24.2% of the dose. Following a lag time of 15.5 min (tablets) and 4.2 min (drops), which were significantly different, the absorption of oral chlordesmethyldiazepam was a first order process, with apparent absorption half-life values averaging 1.5 h (tablets) and 1.1 h (drops). Bioavailability was 77% for tablets and 79% for drops.