Metabolism of diazepam in dogs: transformation to oxazepam

Xenobiotic metabolism by cultured primary porcine hepatocytes

Considering the large yield of viable cells comparable to human liver, primary porcine hepatocytes offer a valuable resource for constructing a bioartificial liver device. In this study, the ability of cultured primary porcine hepatocytes to detoxify xenobiotics has been examined using various known substrates of cytochrome P450 isoenzymes and UDP-glucuronosyltransferases. Present investigation demonstrated the stability of the isoenzymes responsible for the metabolism of diazepam in native state and stabilization of other isoenzymes, as judged by ethoxycoumarin o-dealkylase (ECOD), ethoxyresorufin o-dealkylase (EROD), benzyloxyresorufin o-dealkylase (BROD), and pentoxyresorufin o-dealkylase (PROD) activities following induction in culture environment, for a period of 8 days. Resorufin O-dealkylase activities were found to be the most unstable and deteriorated within first 5 days in culture. These activities were restored following induction with 3-methylcholanthrene (3-MC) or sodium phenobarbital (PB) to 20-fold of 1 activity for EROD, and 60 and 174% of day 1 activity for PROD and BROD on day 8, respectively. Metabolism of methoxyresorufin was most strikingly increased following induction with 3-MC to approximately 60-fold of day 1 activity, on day 8. UDP-glucuronosyltransferase-dependent glucuronidation of phenol red, however, stayed intact during the course of our study without induction. Our study indicated that porcine hepatocytes in vitro maintain many important liver-specific functions including detoxification (steady state and inducibility).

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.

Comparative drug metabolism of diazepam in hepatocytes isolated from man, rat, monkey and dog

Diazepam (DZ) was used as a substrate in drug metabolism studies to characterise the differences in metabolite profiles in hepatocytes isolated from four species: Wistar rat, cynomolgus monkey, beagle dog and man. Hepatocytes were incubated with DZ (20 microM) for 180 min at 3 hr post isolation in culture, and the disappearance of parent compound and appearance of its metabolites determined. DZ disappearance was found to be monoexponential in rat, monkey and human cells, but that DZ disappearance in dog hepatocytes was best described by a two compartment process. There were considerable differences in both the rates of formation and the profiles of metabolites produced from DZ in each species. Drug metabolism of DZ was determined in five human hepatocyte preparations. The rates of formation of both the major metabolites, temezepam (TEM) and nordiazepam (NOR) were highly variable between samples, and oxazepam (OX) was detected in only three of the preparations. There was no evidence of further metabolism of these metabolites, and the profiles were comparable with in vivo findings. In a single case, human hepatocytes were cultured for five days, and DZ was used as substrate to characterise the changes in drug metabolising activities. There was a rapid loss in the production of OX in the initial 24 hr, and a complete loss of 3-hydroxylation activities in the succeeding 120 hr. N-demethylation activities, however, were well maintained, and the appearance of NOR declined to 47% of initial rate. The hepatocytes of all species were found to produce NOR and TEM as metabolites; NOR representing the principal metabolite in the dog, monkey and human cells. In the dog, TEM was found only as a minor metabolite. OX was a significant metabolite in the monkey and a minor metabolite in the dog and human hepatocytes, but was not detected in rat cultures. The principal metabolite in rat cells was 4'-hydroxy diazepam, which was rapidly further metabolised to its glucuronide. The drug metabolising activities of the hepatocyte cultures towards DZ were comparable with the drug metabolism of DZ found in vivo in each species. These findings substantiate hepatocytes as an in vitro model of hepatic metabolism.

The effects of benzodiazepines upon the fidelity of mitotic cell division in cultured Chinese hamster cells

4 benzodiazepine sedatives, namely diazepam, medazepam, midazolam and bromazepam were investigated for their effects upon the fidelity of cell division in both low passage number and immortalised Chinese hamster cell lines. The study revealed substantial differences in the effect of these structurally related drugs upon mitosis, which may reflect different mechanisms of action of the drugs in cultured cells. Diazepam and medazepam exposure of immortal and low passage number cells resulted in the formation of monopolar mitotic spindles and subsequent metaphase arrest. The production of these spindles may be explained by the inhibition or centriole separation . In contrast, midazolam and bromazepam failed to produce observable changes in spindle structure. All 4 benzodiazepines produced significant toxicity in low passage number cells whereas, immortalised cells were more resistant to their toxic effects. They all induced metaphase chromosome dislocations in immortalised cells, whereas only diazepam and medazepam produced such effects in the low passage number cell line. In general, immortal cells appeared to be less sensitive to the toxic effects of benzodiazepines than the low passage number cells.

Biotransformations and plasma-level curves of chiral 1,4-benzodiazepine-2-ones

Biotransformations of chiral 1,4-benzodiazepine-2-ones, (S)- and (R)-1 (7-chloro-1,3-dihydro-3 (S and R)-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one) in untreated and phenobarbital-pretreated rats were investigated. In urine, a 4'-oxygenated metabolite (compound 2) was identified as the biotransformation product from both enantiomers, (S)-2 being present in much higher amounts than (R)-2. Unchanged parent compounds were not found in urine. In plasma, 3'- and 4'-oxygenated metabolites were identified after administration of (S)-1 and (R)-1, respectively. The metabolite possessing an R-configuration was present in much lower amounts. The maximum concentrations of (R)-1 in plasma, following a single dose, was about 6 time as high as the maximum plasma concentration of (S)-1. Faster biotransformation and elimination of (S)-1 is assumed to be the explanation of these findings.

Double-blind crossover study of the efficacy and acceptability of oxazepam Expidet tablets compared to placebo in patients undergoing gynaecological surgery

In a double-blind crossover trial, the hypnotic efficacy and acceptability of oxazepam Expidet, a fast-dissolving tablet, was compared to placebo in patients undergoing minor gynaecological surgery. Patients received 30 mg oxazepam Expidet or placebo the night before their operation and the alternate medication the night after. A sleep questionnaire was completed the morning after both nights and acceptability was assessed the morning after the second night. Data were available for analysis on seventy-two patients aged 18-50 years. There was a significant improvement in sleep onset and quality and less awakenings after oxazepam compared to placebo (p less than or equal to 0.01). There was no significant difference in the occurrence or type of dreams, or morning-after symptoms. There was a significant preference for oxazepam compared to placebo and for the fast-dissolving Expidet form compared to conventional tablets or capsules (p less than or equal to 0.01). There were no adverse reactions in the oxazepam group. It was concluded that oxazepam Expidet was an effective and acceptable hypnotic in this group of patients.

Analysis of the 1,4-benzodiazepines by methods based on hydrolysis

The analytical applications of the hydrolysis of 1,4-benzodiazepines to the corresponding benzophenone derivatives are reviewed according to the analytical methods used for their final determination. The scope and limitations of the individual methods for the hydrolysis products are discussed: Colour reactions, photometry, fluorimetry, thin-layer chromatography, gas chromatography and high-performance liquid chromatography. Published data on the kinetic parameters and mechanisms are summarized in an attempt to explain the problems involved in exploiting this reaction for analytical applications.

Comparative metabolic study of nimetazepam and its desmethyl derivative (nitrazepam) in dogs

1. Blood levels of nimetazepam after oral administration to dogs were relatively low at early periods after dosage and reached peak levels (7-7-7-9 mug equiv./ml) after 8 h. The time course of blood levels was similar after oral administration of its desmethyl derivative (nitrazepam) to dogs. Blood levels of the latter, however, were low compared with nimetazepam and reached a peak (5-2-6-3 mug equiv./ml) after 4 h. 2. Recoveries of nimetazepam in urine and faeces were 46 and 52% of the dose for 0-24 h, 27 and 34% for 24-48 h and 4 and 6% for 48-72 h, while those of its desmethyl derivative (nitrazepam) were 63 and 71% for 0-24 h, 12 and 21% for 24-48 h and 2 and 3% for 48-72 h. 3. At least four kinds of reaction were involved in the biotransformation of nimetazepam and its desmethyl derivative (nitrazepam): (i) demethylation at N-1 (ii) hydroxylation at C-3, (iii) subsequent glucuronic acid conjugation of 3-hydroxy derivatives and (iv) reduction of the nitro group at C-7 to an amino group. Reaction (i) proceeded very rapidly in dogs, so that the blood metabolites of nimetazepam were closely similar to those of nitrazepam. For both drugs, the major blood metabolite was nitrazepam. Reaction (ii) was rapidly followed by reaction (iii), and glucuronides were predominantly excreted in urine. Reaction (iv) as well as reaction (iii) are important in the excretion of both drugs. The subsequent acetylation of 7-amino group, however, did not occur in dogs as it did in mice and rats.