Determination of diazepam and its metabolites by high-performance liquid chromatography and thin-layer chromatography

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.

A selective fluorimetric method for the determination of some 1,4-benzodiazepine drugs containing a hydroxyl group at C-3

A highly selective and sensitive fluorimetric method was developed for the determination of four 1,4-benzodiazepine drugs containing a hydroxyl group at carbon 3, namely oxazepam, lorazepam, cinolazepam and temazepam. The method is highly specific because other benzodiazepinee lacking the hydroxyl group at C-3 do not react similarly and hence do not interfere. The proposed method involves reduction of the target compound using Zno/HCl at room temperature with the formation of a highly fluorescent derivative within 15 min. The different experimental parameters were carefully studied and incorporated into the procedure. Under the described conditions, the proposed method is applicable over the concentration range of 0.1-1.2 micrograms ml-1 for both temazepam and cinolazepam, and 0.2-2.5 and 1-8 micrograms ml-1 for oxazepam and lorazepam respectively. The recoveries of the title compounds from spiked urine ranged from 90.0 to 92.0% and for serum from 94.1 to 95.4% with a limit of detection (S/N = 2) of 4 ng ml-1 for all drugs. The mechanism of the fluorimetric reaction is discussed.

Analysis of oxazepam in urine using solid-phase extraction and high-performance liquid chromatography with fluorescence detection by post-column derivatization

A reversed-phase high-performance liquid chromatographic method for oxazepam in human urine samples has been developed. The sample preparation consists of an enzymatic hydrolysis with beta-glucuronidase, followed by a solid-phase extraction process using Bond-Elut C2 cartridges. The mobile phase used was a methanol-water (60:40, v/v) mixture at a flow-rate of 0.50 ml/min. The column was a 3.5 cm x 4.6 mm I.D. C18 reversed-phase column. The detection system was based on a fluorescence post-column derivatization of oxazepam in mixtures of methanol and acetic acid. A linear range from 0.01 to 1 micrograms/ml of urine and a limit of detection of 4 ng/ml of urine were attained. Within-day recoveries and reproducibilities from urine samples spiked with 0.2 and 0.02 microgram/ml oxazepam were 97.9 and 95.0 and 2.1 and 9.4%, respectively.

Characterization of specific cytochrome P450 enzymes responsible for the metabolism of diazepam in hepatic microsomes of adult male rats

The role of several P450 enzymes in the metabolism of diazepam (DZ) has been investigated. Hepatic microsomes of adult male rats were pretreated with antisera raised against the P450s CYP3A2, 2B1, 2C6, 2C11, 2D1 and 2E1, and their influence on the subsequent metabolism of DZ was determined by simultaneously measuring the changes in the relative rates of formation of its metabolites. Several forms of P450 were found to be positively involved in DZ metabolism. Antisera of the "male-specific" P450 enzyme CYP2C11 partially inhibited both DZ N-demethylase and C3 hydroxylase activities (60%) which resulted in decreased formations of N-desmethyl-DZ (NDZ) and 3-hydroxy-DZ (3HDZ), respectively. In a reconstitution experiment with the purified enzyme, CYP2C11 predominantly catalysed the formation of NDZ from DZ. Antisera of a further male-specific P450 CYP3A2 strongly inhibited (95%) the C3 hydroxylase of DZ and thus 3HDZ formation. A corresponding reconstitution experiment with this same P450 enzyme gave 3HDZ as principal product. CYP2D1 antisera inhibited the aromatic hydroxylation of DZ (98%) and subsequent formation of 4'-hydroxy-DZ (4'HDZ). This enzyme was also observed to inhibit DZ N-demethylase activity (60%). A reconstitution experiment with pure CYP2D1 catalysed the formation of both 4'HDZ and NDZ.

The screening of selected microorganisms for use as models of mammalian drug metabolism

Fifty fungi and two Streptomyces species were screened for their ability to metabolise the probe substrates aminopyrine, diazepam, testosterone, theophylline and warfarin. The metabolism of the 14C-labelled substrates by whole growing cells was compared with that by rat liver microsomes using TLC-autoradiography. Testosterone, warfarin and diazepam were readily metabolised by most microorganisms, and aminopyrine and theophylline were only metabolised by a few. A relationship between substrate lipophilicity and number of microorganisms able to biotransform the substrate was observed, lipophilic substrates being favoured for metabolism, analagous to mammalian cytochrome P-450. A wide variety of metabolites were produced by the screened cultures, with a significant number co-chromatographing with mammalian metabolites. Most microorganisms appeared to exhibit cytochrome P-450-type oxidative reactions such as hydroxylation and N-demethylation, similar to mammalian hepatic microsomal cytochrome P-450 systems.

Chromatography of benzodiazepines

An overview of methods for the determination of benzodiazepines in biological media, based on the application of chromatographic techniques, is presented. A general discussion of the techniques in terms of stability, selectivity, validation, standardization, detection and sensitivity is given. No single technique can be claimed as the method of choice for benzodiazepines. Gas chromatography with electron-capture detection has some strong claims and shows generally good sensitivity and reproducibility. High-performance liquid chromatographic equipment is readily available in most laboratories. The ultimate choice of an assay method for benzodiazepines will be determined by the clinical application (routine monitoring, pharmacokinetics, overdose, forensic medicine) and by the characteristics of the benzodiazepine, the expertise of the analyst, the equipment available, the desired sensitivity and specificity and the time involved in method development or adaptation and validation.

Physiological modeling of drug and metabolite: disposition of oxazepam and oxazepam glucuronides in the recirculating perfused mouse liver preparation

The disposition of tracer doses of 3H-oxazepam was studied in the recirculating perfused mouse liver preparation. 3H-Oxazepam was biotransformed primarily to the diastereomeric 3H-oxazepam glucuronides, which either effluxed into the circulation or underwent biliary excretion. Three additional, unknown metabolites constituted a small fraction (5-10%) of the total radioactivity recovered in bile (7% of dose); no other metabolite was detected in perfusate. A physiologically based model, comprising the reservoir, liver blood and tissue, and bile, was fitted to reservoir concentrations of 3H-oxazepam and 3H-oxazepam glucuronides, and the cumulative amount excreted into bile. The model allowed for consideration of elimination pathways other than glucuronidation and the presence of a transport barrier for the oxazepam glucuronides across the hepatocyte membrane. The fitted results suggest a slight barrier existing for the transport of metabolites across the sinusoidal membrane, inasmuch as the transmembrane clearance was comparable to liver blood flow rate. Upon further comparison of estimates of formation, biliary, and transmembrane clearances for the oxazepam glucuronides, the rate-limiting step in the overall (biliary) clearance appears to be a poor capacity for biliary excretion. The influence of the cumulative volume loss that a recirculating perfused organ system incurs upon repeated sampling was discussed, and a compartmental method of correcting the observed concentrations of drug and generated metabolite was presented.

Analysis of benzodiazepines and tricyclic antidepressants in serum using a common solid-phase clean-up and a common mobile phase

A single, rapid and specific solid-phase clean-up procedure was developed for the analysis of benzodiazepines and tricyclic antidepressants using a carefully selected wash step and specific sequential elution. Benzodiazepines were eluted from the solid-phase column using as mixture of water-methanol-acetonitrile (2:3:3) followed by the elution of tricyclic antidepressants with methanol containing 0.6% diethylamine. A 30% solution of acetonitrile in phosphate buffer containing dimethyloctylamine was used as a common isocratic mobile phase for the analysis of benzodiazepines and tricyclic antidepressants on a reversed-phase column and detection was carried out at 242 nm. The sensitivity limit of the assay for benzodiazepines and tricyclic antidepressants was 25 ng/ml in serum with recoveries of 95-105% for benzodiazepines and 76-95% for tricyclic antidepressants. The results were linear for benzodiazepines over the range 50-2000 ng/ml and for tricyclic antidepressants over the range 25-500 ng/ml. Analysis for benzodiazepines and tricyclic antidepressants gave good precision, with a coefficient of variation of less than 5.0%. The method described here will be suitable for use in a clinical setting, where there is a concomitant use of benzodiazepines and tricyclic antidepressants.

Suppression of pentylenetetrazol-elicited seizure activity by intraosseous lorazepam in pigs

Use of the intraosseous (i.o.) route as an alternative venous access for drug administration has increased. This study examined the efficacy of i.o. lorazepam (LZP) in suppressing pentylenetetrazol (PTZ)-induced seizure activity in pigs. Domestic swine (13-20 kg) were prepared for recordings of arterial blood pressure, EEG, and electrocortical activity. Seizure activity was induced by PTZ (100 mg/kg i.v.). Sixty seconds after onset of seizure activity, animals either received no drug (control) or LZP (1.0 mg/kg) administered i.v. or i.o. via an 18- or 13-gauge spinal needle inserted in the right proximal tibia. Both i.o. and i.v. LZP significantly suppressed the duration of seizure activity (DSA) (s/min interval) within 1 min following drug administration: DSA control, 46.2 +/- 3.6; i.v. LZP, 25.0 +/- 5.1; i.o. (18-gauge) LZP, 27.6 +/- 6.0; i.o. (13-gauge) LZP, 24.0 +/- 2.4. Seizure activity was essentially abolished at 1 min following LZP infusion. In addition, both i.v. and i.o. LZP did not have significant effects on the basal heart rate and mean arterial blood pressure. The data demonstrate that in swine (1) the i.o. route is an effective alternative venous access for LZP administration, and (2) the size of spinal needles does not affect the antiepileptic efficacy of i.o. infusion of LZP.