Exposure via biotransformation: Oxazepam reaches predicted pharmacological effect levels in European perch after exposure to temazepam

It is generally expected that biotransformation and excretion of pharmaceuticals occurs similarly in fish and mammals, despite significant physiological differences. Here, we exposed European perch (Perca fluviatilis) to the benzodiazepine drug temazepam at a nominal concentration of 2 µg L^-1 for 10 days. We collected samples of blood plasma, muscle, and brain in a time-dependent manner to assess its bioconcentration, biotransformation, and elimination over another 10 days of depuration in clean water. We observed rapid pharmacokinetics of temazepam during both the exposure and depuration periods. The steady state was reached within 24 h of exposure in most individuals, as was complete elimination of temazepam from tissues during depuration. Further, the biologically active metabolite oxazepam was produced via fish biotransformation, and accumulated significantly throughout the exposure period. In contrast to human patients, where a negligible amount of oxazepam is created by temazepam biotransformation, we observed a continuous increase of oxazepam concentrations in all fish tissues throughout exposure. Indeed, oxazepam accumulated more than its parent compound, did not reach a steady state during the exposure period, and was not completely eliminated even after 10 days of depuration, highlighting the importance of considering environmental hazards posed by pharmaceutical metabolites.

In vitro diazepam metabolism in horses

There is little information about drug metabolism and pharmacokinetics in horses. Therefore, it is necessary to characterize the profiles of drug metabolites for the safe use of drugs. In this study, we focused on cytochrome P450 enzymes (CYPs), which represent an important enzyme group to determine pharmacological effects of drugs. We chose diazepam as the drug of choice for this study. The aim of this study was to elucidate the metabolic pathway of diazepam in horses in comparison with rats, and to clarify CYP subfamilies responsible for diazepam metabolism in horses. Our results showed temazepam was the major diazepam metabolite produced from microsomal reactions in horse liver, but horses produced drastically less p-hydroxydiazepam as compared with rats. Furthermore, CYP3A was a major contributor from the CYP subfamily of temazepam production.

Strain differences in diazepam metabolism at its three metabolic sites in sprague-dawley, brown norway, dark agouti, and wistar strain rats

Knowledge of strain differences in drug metabolism is important for the selection of animals for pharmacokinetic, pharmacodynamic, and toxicological studies. Hepatic microsomes from Sprague-Dawley (SD) and Brown Norway (BN) rats had 300-fold higher diazepam p-hydroxylation activity than Dark Agouti (DA) and Wistar (W) rats at a low diazepam concentration (3 microM). Kinetic studies indicated that diazepam p-hydroxylation in SD and BN rats proceeded with lower K(m) and higher V(max) values than it did in DA and W rats. However, the expression levels of cytochrome P450 CYP2D1, the reported enzyme for diazepam p-hydroxylation, did not cosegregate with the activity. These results suggest the presence of a new high-affinity diazepam p-hydroxylation enzyme other than CYP2D1 in SD and BN rats. DA rats showed 3- and 2-fold higher diazepam 3-hydroxylation and N-desmethylation activities, respectively, than the other rat strains. In agreement with this, DA rat liver microsomes had a higher expression of CYP3A2, which is responsible for diazepam 3-hydroxylation and partly responsible for N-desmethylation. Values of CL(int) (V(max)/K(m)) indicated that p-hydroxy-diazepam is the major metabolite in SD and BN rats, whereas 3-hydroxy-diazepam is the major metabolite in DA and W rats. The sum of the CL(int) in each strain was in the order of DA > SD = BN >> W. Strain differences in the pharmacodynamics of diazepam between SD and DA rats may be due to these differences in diazepam metabolism. We found that both the rate of elimination of diazepam and the major metabolic pathways in diazepam metabolism differed among the different rat strains due to polymorphic expression of the two enzymes involved in diazepam metabolism.

The simultaneous determination of diazepam and its three metabolites in dog plasma by high-performance liquid chromatography with mass spectroscopy detection

A fast, sensitive and specific LC/MS/MS method for the simultaneous determination of diazepam and its three metabolites, oxazepam, temazepam and desmethyldiazepam, in dog plasma is described. The method consists of an automated 96-well solid phase extraction procedure and electrospray LC/MS/MS analysis. D(5)-Diazepam is used as the internal standard for all the compounds. Intra-day and inter-day assay coefficients of variations are less than 12.7%. The lower limit of quantitation (LLOQ) is 1 nM for each analyte, based on 0.1 ml aliquots of dog plasma. The analytical run time was 5 min. Linearity is observed over the range of 1--500 nM. This method has been used to support the discovery of pharmacokinetic studies.

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).

Identification of benzodiazepines in Artemisia dracunculus and Solanum tuberosum rationalizing their endogenous formation in plant tissue

Sterile cultivated plant cell tissues and cell regenerates of several species were tested for their binding affinity to the central human benzodiazepine receptor. Binding activity was found in extracts of Artemisia dracunculus cell tissue (IC(50) = 7 microg/ml) and, to a lesser extent, in plant regenerates of potato herb (Solanum tuberosum). Preparative HPLC led to the isolation of fractions with a significant displacing potency in the benzodiazepine receptor binding assay. Using on-line HPLC-electrospray-tandem mass spectrometry (HPLC-ESI-MS/MS) in the "selected reaction monitoring" (SRM) mode, delorazepam and temazepam were found in amounts of about 100 to 200 ng/g cell tissue of Artemisia dracunculus, whereas sterile potato herb contained temazepam and diazepam ranging approximately from 70 to 450 ng/g cell tissue. It is the first report on the endogenous formation of benzodiazepines by plant cells, as any interaction of microorganisms and environmental factors was excluded.

Sigmoidal kinetic model for two co-operative substrate-binding sites in a cytochrome P450 3A4 active site: an example of the metabolism of diazepam and its derivatives

Cytochrome P450 3A4 (CYP3A4) plays a prominent role in the metabolism of a vast array of drugs and xenobiotics and exhibits broad substrate specificities. Most cytochrome P450-mediated reactions follow simple Michaelis-Menten kinetics. These parameters are widely accepted to predict pharmacokinetic and pharmacodynamic consequences in vivo caused by exposure to one or multiple drugs. However, CYP3A4 in many cases exhibits allosteric (sigmoidal) characteristics that make the Michaelis constants difficult to estimate. In the present study, diazepam, temazepam and nordiazepam were employed as substrates of CYP3A4 to propose a kinetic model. The model hypothesized that CYP3A4 contains two substrate-binding sites in a single active site that are both distinct and co-operative, and the resulting velocity equation had a good fit with the sigmoidal kinetic observations. Therefore, four pairs of the kinetic estimates (KS1, kalpha, KS2, kbeta, KS3, kdelta, KS4 and kgamma) were resolved to interpret the features of binding affinity and catalytic ability of CYP3A4. Dissociation constants KS1 and KS2 for two single-substrate-bound enzyme molecules (SE and ES) were 3-50-fold greater than KS3 and KS4 for a two-substrate-bound enzyme (SES), while respective rate constants kdelta and kgamma were 3-218-fold greater than kalpha and kbeta, implying that access and binding of the first molecule to either site in an active pocket of CYP3A4 can enhance the binding affinity and reaction rate of the vacant site for the second substrate. Thus our results provide some new insights into the co-operative binding of two substrates in the inner portions of an allosteric CYP3A4 active site.

Role of cDNA-expressed human cytochromes P450 in the metabolism of diazepam

The metabolic conversion of diazepam (DZ) to temazepam (TMZ, a C3-hydroxylation product of DZ) and N-desmethyldiazepam (NDZ, an N1-demethylation product of DZ) was studied using cDNA-expressed human cytochrome P450 (CYP) isozymes 1A2, 2B6, 2C8, 2C9, 2C9R144C, 2E1, 3A4, and 3A5 and human liver microsomes from five organ donors. Of the CYPs examined, 3A5, 3A4, and 2B6 exhibited the highest enzymatic activities with turnovers ranging from 7.5 to 12.5 nmol of product formed/min/nmol for the total metabolism of DZ, while 2C8, 2C9, and 2C9R144C showed lesser and moderate activities. 1A2 and 2E1 produced insignificant amounts of metabolites of DZ. The regioselectivity of CYPs was determined, and 2B6 was found to catalyze exclusively and 2C8, 2C9, and 2C9R144C preferentially the N1-demethylation of DZ to form NDZ. 3A4 and 3A5 catalyzed primarily the C3-hydroxylation of DZ, which was more extensive than the N1-demethylation. The ratios of TMZ to NDZ formed in the metabolism of DZ by 3A4 and 3A5 were approximately 4:1. Enzyme kinetic studies indicated that 2B6- and 2C9-catalyzed DZ metabolism followed Michaelis-Menten kinetics, whereas 3A4 and 3A5 displayed atypical and non-linear curves in Lineweaver-Burk plots. Human liver microsomes converted DZ to both TMZ and NDZ at a ratio of 2:1. Our results suggest that hepatic CYP3A, 2C, and 2B6 enzymes have an important role in the metabolism of DZ by human liver.

Development of tolerance in mice to the sedative effects of the neuroactive steroid minaxolone following chronic exposure

Minaxolone is a potent ligand for the neurosteroid binding site of the GABAA, receptor. In radioligand binding studies to rat brain membranes, minaxolone caused a 69% increase in [3H]muscimol binding and a 25% increase in [3H]flunitrazepam binding and inhibited the binding of [3H]TBOB with an IC50 of 1 microM. In mice, minaxolone (100 mg/kg, orally) had marked sedative effects as indicated by a reduction in locomotor activity. Chronic dosing with minaxolone (100 mg/kg, orally, once daily for 7 days) resulted in a loss of sedative response to an acute dose of the drug, indicating development of tolerance. Chronic dosing with temazepam (10 mg/kg, orally, once daily for 7 days) resulted in the development of tolerance to an acute dose of temazepam; however, the two drugs did not appear to be cross-tolerant, indicating that they may have a different mechanism of action at the level of the GABAA receptor.

Physical stability of solid dispersions containing triamterene or temazepam in polyethylene glycols

The effect of storage on the physical stability of solid dispersions of triamterene or temazepam in polyethylene glycols was studied using differential scanning calorimetry (DSC), particle-size analysis and dissolution methods. The enthalpies of fusion of the carriers, without included drug and previously fused and crystallized, increased on storage. Analysis of similarly treated solid dispersions, containing either 10% temazepam or 10% triamterene, showed that each drug influenced the morphology of the polyethylene glycol (PEG). The enthalpies and melting points of the solidus components of the dispersions' carriers were initially reduced after preparation, but on storage these increased. The particle sizes of the drugs dispersed in the PEGs increased on storage. The changes in dissolution after storage of triamterene or temazepam dispersions were smaller for dispersions in PEG 1500 than for dispersions in PEGs of higher molecular weight (PEG 2000, PEG 4000 or PEG 6000) in which the reduction in dissolution was particularly marked during the first month of storage. The rank order of changes in dissolution were PEG 1500 < < PEG 2000 < PEG 4000 approximately PEG 6000.

Progesterone: does it affect response to drug?

This article presents an overview of the gamma-aminobutyric acid (GABA)-benzodiazepine receptor complex (GBRC) and its in vitro modulation by THP, a metabolite of progesterone, as well as the results of a single-dose study of progesterone and triazolam in 16 post-menopausal women. The study results indicate that a 300 mg oral dose of progesterone administered 2.5 hours prior to a challenge dose of triazolam significantly increases sensitivity to triazolam: concentration values required for 50 percent of maximum effect (EC50) decreased by 20 to 32 percent after pre-treatment with progesterone. These data support the In vitro findings that THP enhances binding of benzodiazepines to the GBRC. The full clinical implications of these data, including extensions to other steroids, need to be explored.

Effects of food deprivation and adrenalectomy on CYP3A induction by RU486 in female rats

We have studied the effects of food deprivation and adrenalectomy on the induction by RU486 of female rat liver microsomal CYP3A apoprotein, erythromycin N-demethylase and diazepam C3-hydroxylase activities. RU486 was a potent inducer of CYP3A apoprotein in intact animals and food deprivation enhanced this response. Food deprivation alone caused only weak CYP3A apoprotein induction suggesting a synergistic interaction in the regulation of protein expression. These results were reflected in the measurements of diazepam C3-hydroxylase activity. This confirms diazepam C3-hydroxylase as a useful and easily measured index of CYP3A monooxygenase content in female rat liver microsomes. Erythromycin N-demethylase did not show concordance with this pattern; this monooxygenase was much more strongly induced by food deprivation alone than by RU486 administration and, in addition, adrenalectomy abolished the induction response to food deprivation. The lack of correspondence between the apoprotein and erythromycin N-demethylase results suggests that non-CYP3A or novel, hitherto uncharacterized CYP3A isoforms may contribute to erythromycin N-demethylation in female rats. The close agreement between the results for CYP3A apoprotein and diazepam C3-hydroxylase indicates that although RU486 possesses a terminal acetylenic moeity it does not, at the dosages used here, cause mechanism-based inactivation of the CYP3A monooxygenase protein it induces. Current studies are directed to characterizing the particular CYP3A isoform(s) whose production is stimulated by RU486.

Concentration-dependent metabolism of diazepam in mouse liver

Previous mouse liver studies with diazepam (DZ), N-desmethyldiazepam (NZ), and temazepam (TZ) confirmed that under first-order conditions, DZ formed NZ and TZ in parallel. Oxazepam (OZ) was generated via NZ and not TZ despite that preformed NZ and TZ were both capable of forming OZ. In the present studies, the concentration-dependent sequential metabolism of DZ was studied in perfused mouse livers and microsomes, with the aim of distinguishing the relative importance of NZ and TZ as precursors of OZ. In microsomal studies, the Kms and Vmaxs, corrected for binding to microsomal proteins, were 34 microM and 3.6 nmole/min per mg and 239 microM and 18 nmole/min per mg, respectively, for N-demethylation and C3-hydroxylation of DZ. The Kms and Vmaxs for N-demethylation and C3-hydroxylation of TZ and NZ, respectively, to form OZ, were 58 microM and 2.5 nmole/min per mg and 311 microM and 2 nmole/min per mg, respectively. The constants suggest that at low DZ concentrations, NZ formation predominates and is a major source of OZ, whereas at higher DZ concentrations, TZ is the important source of OZ. In livers perfused with DZ at input concentrations of 13 to 35 microM, the extraction ratio of DZ (E[DZ]) decreased from 0.83 to 0.60. NZ was the major metabolite formed although its appearance was less than proportionate with increasing DZ input concentration. By contrast, the formation of TZ increased disproportionately with increasing DZ concentration, whereas that for OZ decreased and paralleled the behavior of NZ. Computer simulations based on a tubular flow model and the in vitro enzymatic parameters provided a poor in vitro-organ correlation. The E[DZ], appearance rates of the metabolites, and the extraction ratio of formed NZ (E[NZ, DZ]) were poorly predicted; TZ was incorrectly identified as the major precursor of OZ. Simulations with optimized parameters improved the correlations and identified NZ as the major contributor of OZ. Saturation of DZ N-demethylation at higher DZ concentrations increased the role of TZ in the formation of OZ. The poor aqueous solubility (limiting the concentration range of substrates used in vitro), avid tissue binding and the coupling of enzymatic reactions in liver, favoring sequential metabolism, are possible explanations for the poor in vitro-organ correlation. This work emphasizes the complexity of the hepatic intracellular milieu for drug metabolism and the need for additional modeling efforts to adequately describe metabolite kinetics.

Achiral and chiral analysis of camazepam and metabolites by packed-column supercritical fluid chromatography

Supercritical fluid chromatography, using carbon dioxide as the mobile phase and ethanol as a modifier, has been applied to the analysis of products formed in rat liver microsomal metabolism of racemic camazepam, a hypnotic/anxiolytic drug in clinical use. An achiral (amino) column and a chiral (Chiralcel OD-H) column were used. The results suggest that achiral and chiral packed-column supercritical fluid chromatography gives a shorter analysis time and higher selectivity and efficiency than achiral and chiral stationary-phase high-performance liquid chromatography in the analysis of camazepam and its derivatives.

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.

Acid-catalyzed ethanolysis of temazepam in anhydrous and aqueous ethanol solutions

The benzodiazepines are a family of anxiolytic and hypnotic drugs. When taken concurrently with ethanol, a pharmacological interaction may occur, potentiating the central nervous system depression produced by either drug. In addition to this pharmacological interaction, this report describes a novel chemical reaction between temazepam (a 3-hydroxy-1,4-benzodiazepine) and ethanol under acidic conditions similar to those found in vivo, resulting in a 3-ethoxylated product. Optimal conditions, kinetics, equilibrium, and the mechanism of this acid-catalyzed ethanolysis are reported. The results raise the possibility that the ethanolysis reaction may occur in the stomach of people who consume alcohol and 3-hydroxy-1,4-benzodiazepine on a regular basis. The acid-catalyzed ethanol-drug reaction is a relatively unexplored area and may alter the pharmacological action of some drugs.

Enantiomer resolution of camazepam and its derivatives and enantioselective metabolism of camazepam by human liver microsomes

Camazepam [3-(N,N-dimethyl)carbamoyloxy-7-chloro-1-methyl-1,3-dihydro- 5-phenyl-2H-1,4-benzodiazepin-2-one, CMZ] possesses anxiolytic, anticonvulsant, muscle relaxant, and hypnotic properties. CMZ is clinically used as a racemate. Enantiomer resolution of CMZ and 11 of its derivatives was studied by high-performance liquid chromatography (HPLC) using 5 different chiral stationary phase (CSP) columns. Enantiomers of 10 compounds were resolved by at least one of the 5 CSP's tested. Enantiomers of two other compounds, which have either one or two hydroxymethyl groups at the carbamoyl nitrogen, were either not resolved or resolved with very low efficiency. However, enantiomers of the hydroxymethyl derivatives were resolved via base-catalyzed dehydroxymethylation. In vitro metabolism of racemic CMZ by human liver microsomes was found to be enantioselective. Major metabolites were isolated by normal-phase and reversed-phase HPLC and further characterized by ultraviolet absorption and circular dichroism spectral analyses, and by chiral stationary phase HPLC analysis. Following an in vitro incubation of rac-CMZ, the unmetabolized CMZ was found to be enriched in (S)-CMZ, indicating that the R-enantiomer was enantioselectively metabolized. Metabolites were formed primarily by hydroxylation and demethylation of the methyl groups at the C3 side chain. All metabolites were found to be optically active, enriched in either the S-enantiomer or the R-enantiomer.

Enantioselective metabolism of camazepam by rat liver microsomes

Camazepam [3-(N,N-dimethyl)carbamoyloxy-7-chloro-1-methyl-1, 3-dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one, CMZ] possesses anxiolytic, anticonvulsant, muscle relaxant and hypnotic properties. CMZ is clinically used as a racemate. The enantioselective metabolism of racemic CMZ by rat liver microsomes was studied. Major metabolites were isolated by normal-phase and reversed-phase liquid chromatography (LC) and further characterized by UV absorption, mass, and circular dichroism spectral analyses, and by chiral stationary phase LC analysis. Following an in vitro incubation of rac-CMZ, the unmetabolized CMZ was found to be enriched (S)-CMZ, indicating that the R-enantiomer was enantioselectively metabolized. Two of the most abundant metabolites, formed by hydroxylation and demethylation of a methyl group of the N,N-dimethylcarbamyloxy side chain, were found to be enriched in the R-enantiomer. The results indicated that the (R)-CMZ was metabolized at a faster rate than (S)-CMZ by rat liver microsomes.

Kinetics of sequential metabolism. I. Formation and metabolism of oxazepam from nordiazepam and temazepam in the perfused murine liver

In murine liver, temazepam (TZ) and nordiazepam (NZ) are mainly metabolized via N-demethylation and C3-hydroxylation, respectively, to form a common metabolite, oxazepam (OZ), which is then glucuronidated. With these precursors, we tested the hypotheses that the sequential metabolism of a primary metabolite (OZ) is less than that of the preformed metabolite and is dependent on the effective intrinsic clearance (unbound fraction x intrinsic clearance) of its precursor, as predicted by the parallel tube and dispersion models of hepatic drug clearances. Mouse livers were perfused with tracer concentrations of [14C]-NZ, [14C]-TZ and [3H]NZ in a single-pass fashion (2.5 ml/min). The steady-state extraction ratio (E) of [3H]NZ, [14C]NZ and [14C]TZ were 0.29, 0.40 and 0.49, respectively (P < .01), whereas the fractional metabolism (formation rate/total elimination rate of drug) of [3H]-NZ, [14C]NZ and [14C]TZ to form OZ was 0.39, 0.79 and 0.68, respectively. Values of E of [3H]NZ and [14C]NZ and fractional metabolism for OZ formation had differed because of a kinetic isotope effect (around 3.5) that affected the C3-hydroxylation of [3H]NZ. The extraction ratios of OZ (E[OZ,P]) arising from [14C]-NZ and [14C]TZ were both 0.056, and were less than that for preformed OZ (E[OZ]), previously found to be 0.125. The parameter E[OZ,P] was poorly correlated with the extraction ratio of the precursor, was overestimated by the parallel tube and dispersion models, but was highly correlated with the effective intrinsic clearance of the precursor (unbound fraction x intrinsic clearance).(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.

Benzodiazepine metabolism in ethanol-treated male rats: use of pair-fed and age-matched controls

The effects of chronic moderate (15%) ethanol consumption and ageing on rat hepatic cytochrome P450 monooxygenase activities were examined using diazepam, nordazepam, d-benzphetamine, erythromycin, ethylmorphine and nitrosodimethylamine (NDMA) as substrates. In addition, the effects of moderate ethanol alone on the oxidation of metoprolol, morphine and temazepam were examined. Cytochrome P450 specific content increased significantly only in the 6-week ethanol-treated rats, and no changes in percentage liver to body weights were apparent in any of the ethanol-treated animals compared with pair-fed controls. Only cytochrome P450IIIA enzyme activities displayed age-related decreases, these being identified in the pair-fed animals. C3-hydroxylation of diazepam and nordazepam (36% of controls) and N-demethylation of erythromycin and ethylmorphine (58% and 64% of controls) were decreased in 6-week ethanol-treated animals, these effects being less pronounced in the 12, 24 and 48-week ethanol-treated groups. The decrease seen for diazepam and d-benzphetamine N-demethylation caused by ethanol consumption was approximately 80% of control groups for the duration of the treatment. NDMA and morphine N-demethylations were increased to 120% of control activities and metoprolol alpha-hydroxylase was increased to 140% of control activities at 6 weeks, whilst metoprolol O-demethylase activity remained unaltered. NDMA N-demethylase activity showed a two-fold induction at 24 and 48 weeks of ethanol treatment, compared with corresponding pair-fed control groups. These results support previous findings from this laboratory showing that the same or similar P450IIIA family isozymes are involved in the C3-hydroxylation of diazepam and nordazepam.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of temazepam and temazepam glucuronide by reversed-phase high-performance liquid chromatography

A rapid and sensitive method for extracting temazepam from human serum and urine is presented. Free temazepam is extracted from plasma and urine samples using n-butyl chloride with nitrazepam as the internal standard. Temazepam glucuronide is analyzed as free temazepam after incubating extracts with beta-glucuronidase. Separation is achieved using a C8 reversed-phase column with a methanol-water-phosphate buffer mobile phase. An ultraviolet detector operated at 230 nm is used and a linear response is observed from 20 ng/ml to 10 micrograms/ml. The limit of detection is 15.5 ng/ml and the limit of quantitation is 46.5 ng/ml. Coefficients of variation are less than 10% for concentrations greater than 50 ng/ml. Application of the methodology is demonstrated in a pharmacokinetic study using eight healthy male subjects.

Oxidative versus conjugative biotransformation of temazepam

Twenty-four healthy volunteers, aged 21-59 years, received single 30 mg oral doses of the benzodiazepine hypnotic temazepam. Levels of intact temazepam were determined in multiple plasma samples drawn during 48 h after dosage. Intact temazepam, its direct glucuronide conjugate, and the conjugate of its demethylated (oxidized) metabolite oxazepam were measured in two consecutive 24-h urine collections. Mean kinetic variables for temazepam in plasma were: peak plasma level (Cmax), 873 ng ml-1; time of peak, 1.36 h after dosage; volume of distribution, 0.961 kg-1; elimination half-life 9.9 h; clearance, 1.16 ml min-1 kg-1. Volume of distribution increased significantly with body weight (r = 0.67, p less than 0.001), and Cmax decreased with weight (r = -0.58, p less than 0.01). Only 0.2 per cent of the dose was excreted as intact temazepam, and negligible amounts as intact oxazepam. However, 39 per cent of the dose was recovered as temazepam glucuronide, and oxazepam glucuronide accounted for another 4.7 per cent of the dose. The remainder was not accounted for. Thus, a significant fraction of temazepam clearance occurs by direct glucuronide conjugation, with the conjugate temazepam glucuronide excreted in urine. A much smaller fraction undergoes parallel oxidation to form oxazepam, which is subsequently conjugated to oxazepam glucuronide and excreted in urine.

Cytochrome P450IIIA enzymes in rat liver microsomes: involvement in C3-hydroxylation of diazepam and nordazepam but not N-dealkylation of diazepam and temazepam

Microsomes prepared from livers of male and female rats of nine inbred and outbred strains and of male Sprague-Dawley rats pretreated with monooxygenase-inducing agents were used to study N-dealkylation of diazepam and temazepam and C3-hydroxylation of diazepam and nordazepam. Both C3-hydroxylation reactions were more rapid in male than in female liver preparations, but this gender-dependent pattern was not seen with the N-dealkylation reactions. These results indicate the lack of identity of the monooxygenases responsible for the two kinds of reaction and suggest that male-specific enzyme(s) are responsible for the C3-hydroxylations. Induction studies were undertaken to further define these enzymes. To do this, liver microsomes prepared from male Sprague-Dawley rats pretreated with a variety of agents known to have different monooxygenase induction effects were used. With triacetyloleandomycin, dexamethasone, and phenobarbital pretreatment, the specific activities of the C3-hydroxylation reactions were selectively elevated over corresponding control values. These particular xenobiotics are known to enhance the abundance of cytochrome P450IIIA family enzymes, and our results strongly suggest the involvement of these enzymes in the benzodiazepine B ring monooxygenations. Formation of temazepam was also shown to be inhibited by triacetyloleandomycin. This effect was demonstrated to be equal in both saline-treated and dexamethasone-treated male Sprague-Dawley rat liver microsomes, with the antibiotic present either with diazepam throughout the entire incubation period or initially with NADPH in a preincubation mix for 15 min, following which C3-hydroxylation was initiated by the addition of diazepam. These results confirm the uniformity of the involvement of cytochrome P450IIIA family enzymes in diazepam C3-hydroxylation in untreated and inducer-treated rat liver microsomes. Recent studies with human and rabbit liver microsomal preparations have shown that orthologues of these enzymes also catalyze an equivalent hydroxylation in the B ring of midazolam. These findings, considered with the present results showing that the adjacent methyl N-substituent (absent in nordazepam but present in diazepam) did not affect the selectivity of these enzymes for the C3-hydroxylation reaction, suggest that neither steric nor electronic factors markedly influence catalysis of this monooxygenation by these enzymes.

In vitro drug metabolism and pharmacokinetics of diazepam in cynomolgus monkey hepatocytes during culture for six days

Diazepam (DZ), N-desmethyl diazepam (NOR) and temazepam (TEM) were used as substrates in drug metabolism studies to characterize the changes in cytochrome P-450 mono-oxygenase pathways in hepatocytes isolated from cynomolgus monkeys, during culture for 6 days. Hepatocytes were incubated with DZ (20 microM), NOR (6 microM) or TEM (20 microM) for 3 hr at 3, 24, 48, 96 and 144 hr post-isolation in culture, and the profiles of disappearance of DZ, as substrate, and appearance of its metabolites determined. Major metabolites were NOR, TEM and oxazepam (OX). The kinetic profiles for the disappearance of DZ and the accumulation of metabolite were analysed using a four-compartment model and constants for the rates of formation of the metabolites were derived. There were significant changes during the period in culture for the rate constants of DZ demethylation, but no alteration in the 3-hydroxylation activities. Rates of DZ metabolism were unchanged during the initial 2 days in culture and well maintained for the subsequent 4 days, despite a fall in total cytochrome P-450 to 23% of initial values after 6 days. Cynomolgus monkey hepatocytes produce similar metabolite profiles for DZ to those found in man, both in vitro and in vivo, indicating that cynomolgus monkey hepatocytes may represent a relatively stable and valuable model of human drug metabolism.

Metabolism of diazepam in vitro by human liver. Independent variability of N-demethylation and C3-hydroxylation

The interindividual variability of diazepam metabolism was studied using human livers. The formation of N-desmethyldiazepam (NDZ) and 3-hydroxydiazepam (temazepam, TMZ), was monitored by gas chromatography. In 10 livers, Km values for NDZ and TMZ formation varied independently from each other, each by a factor of 4, from 100 to 400 microM. This variability is consistent with the presence of at least two different cytochrome P-450 species controlling formation of these metabolites. In the same livers, Vmax for NDZ and TMZ production varied 6-fold and 15-fold, respectively.

I.v. temazepam: theoretical and clinical considerations

Two injectable forms of temazepam, in 90% propylene glycol or 40% salicylic acid, were studied in volunteers, and before surgery in healthy patients. The volunteers also received two forms (capsule and elixir) by mouth. The salicylate preparation was painful on injection and both i.v. formulations caused an unacceptably high incidence of venous thrombosis. Temazepam was detected in plasma earlier following the elixir preparation than the capsule. Plasma concentrations were similar following both injectable preparations. The potency of i.v. temazepam in inducing drowsiness in patients was much less than expected and doses greater than 0.6 mg kg-1 were required to produce adequate sedation. There was a significant reduction in thiopentone induction dose in patients receiving temazepam i.v.

The metabolic fate of camazepam in rats

The metabolites of camazepam in rat plasma were characterized by t.l.c., mass spectroscopy and n.m.r. spectroscopy as the mono- or di-desmethylated metabolites and the mono- or di-hydroxymethylated metabolites. The postulated metabolic pathways of camazepam involved stepwise series of desmethylations. The mono- and di-hydroxymethylated metabolites were found to be intermediates in desmethylation. Temazepam and oxazepam, metabolites of camazepam, were formed from the mono- or di-hydroxymethylated metabolites.

[Racemation of the benzodiazepines camazepam and ketazolam and receptor binding of enantiomers]

The chiral benzodiazepines camazepam (1) and ketazolam (2) were resolved into the enantiomers by chromatography on the optically active adsorbent poly[(S)-N-(1-cyclohexylethyl)-methacrylamide] and fractional crystallisation or repeated chromatography, respectively. The IC50 values of the isomers and of the racemates of both compounds were determined by displacement of radioactively labelled 3H-flunitrazepam and 3H-propyl-beta-carboline-carboxylate from their specific binding sites. (+)-Camazepam exhibits 14fold higher affinity compared to the (-)-enantiomer. In contrast only slight differences in the receptor affinity are observed with the ketazolam enantiomers.

Receptor-mediated model relating anticonvulsant effect to brain levels of camazepam in the presence of its active metabolites

In a displacement test using 3H-diazepam as a radioligand, the in vitro affinities of metabolites of camazepam (CZ) for the benzodiazepine receptors were 1-50 times more potent than that of CZ. In contrast, only three metabolites (temazepam, oxazepam, and hydroxy CZ), as well as CZ itself, exhibited an in vivo affinity parallel to their ability to protect against pentylenetetrazole--induced clonic convulsion in rats. In addition, CZ and these active metabolites displaced the radioligand from their receptor sites in a concentration-dependent saturable manner, indicating the competitive bimolecular interaction of these molecules with their receptors. The percent anticonvulsant effect was a nonlinear, single-valued function of the in vivo percent displacement of specific 3H-diazepam binding, independent of these displacers after i.v. dosing; this relationship could be approximated by the Hill equation. On the basis of these findings, a receptor-mediated model, including the Langmuir equation to describe the receptor binding-brain concentration relationship and the Hill equation to accommodate the anticonvulsant effect-receptor binding relationship, was constructed. This model was found to adequately relate the time course values of anticonvulsant effect and of brain levels of CZ and its active metabolites after oral administration. These results demonstrate that CZ and its active metabolites exert anticonvulsant effect by competitive binding to the benzodiazepine receptors.

Aging: changes in distribution of diazepam and metabolites in the rat

The brain levels of diazepam and its metabolites after a single iv injection of diazepam were measured over a 2-hr time period in young (3-4-month-old), mature (12-15-month-old), and senescent (29-31-month-old) male Fischer 344 rats. The areas under the brain level time curves were used as an index of exposure. Senescent rats were exposed to significantly more diazepam, N-desmethyldiazepam, and oxydiazepam between 0 and 120 min after an injection of 180 micrograms/kg of diazepam than the young or mature animals. The unbound plasma level failed to adequately account for the age-related increase in brain exposure to diazepam. Mechanisms other than the unbound diazepam in plasma are probably involved in eliciting the age-associated increase in brain levels of diazepam and its metabolites.

Quazepam and temazepam: effects of short- and intermediate-term use and withdrawal

Two benzodiazepine hypnotics, one with an intermediate elimination t1/2 (temazepam, 15 mg) and the other with a long t1/2 (quazepam, 15 mg), were evaluated in 22- night sleep laboratory studies. The effectiveness and side effects of these benzodiazepines were assessed during short- and intermediate term use. Subjects were also assessed for the presence of rebound insomnia after abrupt withdrawal. Quazepam, 15 mg, was significantly effective in improving sleep both with short- and intermediate-term use, but the effectiveness of temazepam was considerably less. Although temazepam was effective for maintaining sleep with short-term use, there was rapid development of tolerance for this effect with intermediate-term use. Temazepam did not produce any behavioral side effects during either drug condition. The only side effect associated with quazepam was a significant degree of daytime sleepiness. After its withdrawal, temazepam was associated with some sleep and mood disturbance on the first withdrawal night, whereas quazepam had carryover effectiveness.

Temazepam clearance unaltered in cirrhosis

The kinetics of a single oral dose of the benzodiazepine hypnotic temazepam was evaluated in nine patients with biopsy-proven cirrhosis and in seven healthy controls matched for age and sex. Peak serum temazepam concentrations were reached later in cirrhotics than in controls (2.9 versus 0.6 h after dosage; p less than 0.05), indicating slower temazepam absorption in patients with cirrhosis. Temazepam volume of distribution was smaller in cirrhotics compared to controls, and elimination half-life shorter (10.6 versus 14.6 h). However, these differences were not significant. There were no significant differences between cirrhotics and controls in clearance of total temazepam (1.03 versus 1.03 ml/min/kg), clearance of unbound temazepam (27 versus 31 ml/min/kg), or free fraction in serum (3.9 versus 3.5% unbound). In two cirrhotic patients who received 20 mg of temazepam daily for 8 days, the extent of accumulation was consistent with the dosage interval relative to the elimination half-life, and was similar to the accumulation profile in healthy volunteers. Thus the onset of temazepam hypnotic activity may be delayed in cirrhotic patients, but the rate of elimination and the extent of accumulation are not altered compared to healthy persons of similar age and sex.

A comparison of the soft gelatin capsule and the tablet form of temazepam

Pharmacokinetics and pharmacodynamics of the soft gelatin capsule and tablet form of temazepam were compared. In a single blind study, six healthy volunteers, in the supine position, took either a tablet of temazepam 20 mg or a soft gelatin capsule of temazepam 20 mg. Sixty gynaecological in-patients received either a tablet or a soft gelatin capsule of temazepam 20 mg the night before surgery as premedication. Subjective parameters were assessed in the morning. The soft gelatin capsule yielded clearly higher serum concentrations during the first hour after administration. In the pharmacodynamic parameters there were slight but insignificant differences in favour of the capsule form. As a premedicant the capsule resulted in a significantly (P less than 0.01) shorter delay in the onset of sedative action and to an almost significant (P less than 0.05) delay in falling asleep; also an almost significantly (P less than 0.05) longer action of sleep in comparison with the tablet.

The effects of age and chronic liver disease on the elimination of temazepam

The pharmacokinetics of the newer 1, 4 benzodiazepine temazepam were evaluated in 16 healthy subjects aged 18-92 years and in 15 cirrhotic patients, to ascertain the effect of ageing and liver disease. The data were analysed both by classic two compartment and by non-compartmental methods. The mean elimination half-life in the control subjects was 15.5 h, considerably longer than previous estimates. No correlation was found between age and pharmacokinetic parameters. The cirrhotic group showed no statistically significant difference in the pharmacokinetic parameters nor in the urinary recovery of the dose from the control group. Temazepam plasma protein binding was assessed in a second group of 9 cirrhotics of similar severity to the main group and in matched controls. When these binding data were applied to the mean clearance data, a modest although not statistically significant, reduction in free drug clearance was observed in the cirrhotic group. This study adds further support to the observation that drugs which undergo ether glucuronidation have normal elimination patterns in patients with liver disease. Temazepam may prove to be a useful hypnotic sedative in patients with liver disease.

Pharmacokinetics of temazepam in geriatric patients

A single dose of temazepam 10 mg, as a solution in soft gelatin capsules, was given to 10 fasting geriatric in-patients (mean age 83 years) in a stable clinical condition. The mean peak plasma concentration was 306 ng/ml, with a median time of 0.75 h to peak concentration. Temazepam was eliminated from plasma in a biexponential manner, with a distribution phase (mean t1/2 alpha = 0.7 h) predominating for 3 h. The drug had a mean elimination half-life of 8.7 h. In a chronic study, in which temazepam 10 mg p.o. was given nightly to 13 patients, the plasma concentrations on Days 3, 5, 8, 12 and 15 were not significantly different from each other, showing rapid attainment of steady state levels and the lack of drug accumulation.

Species differences in the disposition and metabolism of camazepam

After i.v. injection of camazepam, plasma camazepan concn. declined biexponentially. The half-life of the elimination phase (t1/2, beta) increased in the order: mice (0.73 h), rats (1.3 h), dogs (5.3 h). After oral dosing of camazepam, absorption was almost complete whereas systemic availability varied eight-fold, i.e., rats and mice (10-15%) less than dogs and monkeys (about 60%) less than humans (greater than 90%), indicating species difference in the first-pass effect. Camazepam was metabolized extensively in all species investigated to more than 10 metabolites, which were desmethyl, descarbamoyl and/or hydroxy products. In comparison with camazepam, plasma concn. of pharmacologically active metabolites, temazepam, oxazepan and hydroxy camazepam, were much higher in rats and mice than in dogs and monkeys.

Relation between time courses of pharmacological effects and of plasma levels of camazepam and its active metabolites in rats

Camazepam (CZ), a benzodiazepine, was biotransformed to more than ten metabolites. After intravenous and oral administration of these metabolites to rats, CZ, tempazepam (TZ), oxazepam (OZ), and hydroxy CZ (M5) were found to possess pharmacological activities. The brain-to-plasma concentration ratios of CZ and these active metabolites were essentially constant with time after oral administration of CZ. Thus the brain, target organ, was kinetically included in the plasma compartment. The extent of binding of these compounds to plasma protein was independent of concentration tested. Plasma levels of an unchanged drug and its active metabolite(s), and muscle relaxation effect (the impairment of rota rod performance) were measured at 0.5 to 8 h after oral administration of 2 to 3 doses of CZ, TZ, and OZ to rats. When the effect and plasma level data were computer-fitted to a simple Hill equation or a modified Hill equation including competitive factors, the modified Hill equation was found to be adequately applicable to the concentration-effect relation. The parameter values thus obtained could predict the contribution of the administered drug and its active metabolite(s) to the observed pharmacological effect after administration.

Active drug metabolites. An overview of their relevance in clinical pharmacokinetics

This review underlines the importance of considering in the overall evaluation of drug effect and efficacy not only the kinetics and activities of the administered drug, but also those of the chemical species (metabolites) which are formed in the body. The circumstances in which a role for active drug metabolites may be suspected are described, and a number of specific examples are given. Four different categories are described: drugs which are inactive precursors of active metabolites (e.g. DOPA and cyclophosphamide); active metabolites which contribute to the duration of action of the parent compound (e.g. hexamethylmelamine and clobazam); active metabolites showing a mechanism of action different from that of the parent compound (e.g. buspirone and 1-pyrimidinyl piperazine; fenfluramine and norfenfluramine); and active metabolites showing an antagonistic effect on the activity of the parent drug (e.g. trazodone and m-chlorophenyl-piperazine; aspirin and salicylate).

Effects of end-stage renal disease and aluminum hydroxide on temazepam kinetics

The kinetics of temazepam, 30 mg, were evaluated in 11 patients with end-stage renal disease. Age ranged from 18 to 65 years. On two occasions separated by 1 week, single oral 30 mg doses of temazepam were given once with water (TM) and once with 3600 mg aluminum hydroxide gel (TM + AHG). There were no significant differences in the maximum plasma concentration, the time to reach maximum concentration, or elimination rates between TM and TM + AHG dosing. In approximately half the subjects there were secondary temazepam peak concentrations. In the remaining subjects, temazepam elimination was biphasic, with the terminal t1/2 ranging from 11 to 77 hours. There was a lag time before absorption in all subjects. The percent free temazepam in plasma from dialysis subjects ranged from 4.4% to 8.8% (mean = 5.9%). Compared with literature reports of subjects with normal renal function, the maximum plasma concentration was lower and the percent free temazepam was higher in dialysis subjects. When sedation score was plotted against plasma temazepam concentration, there was clockwise hysteresis consistent with tolerance or adaptation to effects of the drug. Thus aluminum hydroxide gel does not affect temazepam absorption. The clinical significance of the low plasma concentrations and high free temazepam fraction in dialysis subjects is uncertain.

Effect of oral contraceptives on triazolam, temazepam, alprazolam, and lorazepam kinetics

The effects of low-dose estrogen oral contraceptives (OC) on the elimination of the oxidized benzodiazepines triazolam (TRZ) and alprazolam (ALP) and the conjugated benzodiazepines temazepam (TMZ) and lorazepam (LOR) were studied in two parallel crossover studies of 20 women each. Women taking OC steroids containing low doses of estrogen and women matched for age, weight, and cigarette smoking received single oral doses of TRZ (0.5 mg) and TMZ (30 mg) or ALP (1 mg) and LOR (2 mg). Kinetics were determined as plasma concentrations during 48 hr after dosing. OCs inhibited the metabolism of ALP: The AUC increased and the elimination rate constant was greater in users of OCs. For TRZ, which has an intermediate extraction ratio, the AUC was increased by OCs but not significantly so. In contrast, OCs decreased the AUC for TMZ and the elimination rate constants for LOR and TMZ. The AUC of LOR was not affected by OCs. Low-dose estrogen OCs may therefore inhibit the metabolism of some oxidized benzodiazepines and accelerate the metabolism of some conjugated benzodiazepines.

Is temazepam an accumulating hypnotic?

Ten healthy volunteers aged 22 to 30 years received a single 20-mg oral dose of temazepam. Serum temazepam concentrations were measured by gas chromatography at multiple times during the next 48 hours. Mean kinetic variables were: volume of distribution, 1.45 liter/kg; elimination half-life, 8.6 hours; total clearance, 2.33 ml/min/kg. The subjects then received 20 mg temazepam once daily for seven consecutive days. Serum concentrations were measured just prior to each dose and at multiple time points after the last dose. Predose serum levels increased during the first three days of dosage, then increased no further. Mean values measured 24 hours after doses 1 through 6, respectively, were 33, 43, 55, 47, 53, and 51 ng/ml. Based on the area under the serum concentration curve after the last dose compared with that after the first dose, the mean accumulation ratio was 1.32, which was significantly greater than unity. The extent of accumulation was consistent with that predicted from the single-dose study. Postdosage washout half-life averaged 10.2 hours. Thus, temazepam has a pharmacokinetic profile of an intermediate half-life benzodiazepine that produces an intermediate degree of accumulation with multiple dosage.

A study of the effects of zimelidine on the pharmacokinetics and pharmacodynamics of temazepam in healthy volunteers

In this double-blind two-period crossover study, ten healthy volunteers received either 200 mg zimelidine each morning for 5 days, or placebo on the same schedule. On day 5 they received 20 mg temazepam 2 h after zimelidine or placebo. A battery of psychometric tests and subjective measurements was carried out on days 4 and 5. Blood samples were collected on day 5 for pharmacokinetic analysis of temazepam. All the measures of psychomotor performance showed the effects of temazepam, as did two of the subjective measures, the "alert/drowsy" and "steady/dizzy" visual analogue scales. No effect of zimelidine alone on performance or subjective state was seen. Zimelidine showed no discernible interaction with the effects of temazepam as assessed by subjective reports, by psychomotor tests, or by pharmacokinetic analysis.

Clinical pharmacokinetics of the newer benzodiazepines

New benzodiazepine derivatives continue to be developed and introduced into clinical use. The pharmacokinetic properties of these newer drugs can best be understood by their categorisation according to range of elimination half-life and pathway of metabolism (oxidation versus conjugation). Clobazam and halazepam are long half-life (and therefore accumulating) anxiolytics metabolised by oxidation. Alprazolam and clotiazepam also are oxidised compounds but have short to intermediate half-life values and therefore produce considerably less accumulation. Temazepam and lormetazepam are hypnotic agents with intermediate half-lives but metabolised by conjugation. The most unique of the newer benzodiazepines are the ultra-short half-life (oxidised) compounds midazolam, triazolam and brotizolam, which are essentially non-accumulating during multiple dosage.

Pharmacokinetic properties of benzodiazepine hypnotics

The kinetic properties of three benzodiazepine hypnotics are reviewed. Flurazepam serves as a precursor for at least two rapidly appearing and rapidly cleared metabolites that may contribute to sleep induction and are nonaccumulating. The final metabolite of flurazepam (N-desalkylflurazepam), however, has a long half-life and accumulates during repeated dosage. Temazepam has a relatively slow rate of absorption and an intermediate half-life in the range of 10 to 20 hours. Triazolam has an intermediate rate of absorption; due to its ultrashort half-life (1.5 to 5 hours), triazolam is a non-accumulating hypnotic. Taken together with sleep laboratory studies and clinical trials, knowledge of the kinetic profile of benzodiazepine hypnotics can assist in evaluating their clinical benefits and disadvantages.

Enterohepatic circulation of radioactivity following an oral dose of [14C]temazepam in the rat

The enterohepatic circulation of radioactive material after administering [14C]temazepam was evaluated in three sets of male Wistar strain rats connected in pairs by bile duct-duodenum cannulae. After a single oral dose (10 mg kg-1) to the donor rat, the excretion of radioactivity in the urine and faeces of both rats and in the bile of the recipient rat was determined. Mean total recovery of the administered radioactivity was 92.2%. Based on the amount remaining in the donor rat (gastrointestinal tract and faeces), 81.7% of the dose was absorbed by the donor. The total amount recovered from the recipient, 69.4% of original dose (85.1% of donor's absorbed dose), represented the amount excreted in the donor's bile. Similarly, 54.1% of the original dose (77.9% of the transferred biliary excretion from donor) was reabsorbed by the recipient, and the biliary excretion from this animal (45.9% original dose) accounted for 86.% of the amount reabsorbed.

Biliary excretion of [14C]temazepam and its metabolites in the rat

The excretion of temazepam and its N-desmethyl metabolite, oxazepam, and their respective O-conjugates was examined following a single intravenous dose of [14C]temazepam to two groups of bile fistula rats, with and without bile replenishment to the animals via duodenal cannulae. During an 8-hr collection period, the two groups produced virtually identical bile volumes, and there were no significant differences between them in the amount of total radioactivity, free temazepam, or the identified metabolites in the bile, as determined by TLC and liquid scintillation counting. Elimination of the radioactive dose was rapid during 0-8 hr, with a half-life of approximately 1 hr. Approximately 85-90% of the administered radioactivity was recovered in the bile: less than 1% as free temazepam, 3% as oxazepam, and approximately 10% as their O-conjugates.