Simultaneous determination of diazepam and its metabolites N-desmethyldiazepam, oxydiazepam and oxazepam in plasma and urine of man and dog by means of high-performance liquid chromatography

Vree, T. B.; Baars, A. M.; Hekster, Y.A.; Kleijn, Eppo van der; O'Reilly, W.J.

doi:10.1016/s0378-4347(00)81842-3

Cited by 62 publications

(30 citation statements)

References 19 publications

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“…High midazolam f m,in vivo values have been observed in excretion studies (0.99) (Smith et al, 1981), and values Ͼ0.90 have typically been used for human DDI extrapolations. In dogs, no unchanged drug was observed in urine (Vree et al, 1981), and no reports of fecal excretion could be found. As a result, only f m,in vivo ϭ 1 was evaluated for midazolam.…”

Section: Methodsmentioning

confidence: 88%

Current Cytochrome P450 Phenotyping Methods Applied to Metabolic Drug-Drug Interaction Prediction in Dogs

Mills

Zaya²,

Walters³

et al. 2009

Drug Metab Dispos

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ABSTRACT:Recombinant cytochrome P450 (P450) phenotyping, different approaches for estimating fraction metabolized (f m ), and multiple measures of in vivo inhibitor exposure were tested for their ability to predict drug interaction magnitude in dogs. In previous reports, midazolam-ketoconazole interaction studies in dogs have been attributed to inhibition of CYP3A pathways. However, in vitro phenotyping studies demonstrated higher apparent intrinsic clearances (CL int,app ) of midazolam with canine CYP2B11 and CYP2C21. Application of activity correction factors and isoform hepatic abundance to liver microsome CL int,app values further implicated CYP2B11 (f m > 0.89) as the dog enzyme responsible for midazolam-and temazepam-ketoconazole interactions in vivo. Mean area under the curve (AUC) in the presence of the inhibitor/AUC ratios from intravenous and oral midazolam interaction studies were predicted well with unbound K i and estimates of unbound hepatic inlet inhibitor concentrations and intestinal metabolism using the AUC-competitive inhibitor relationship. No interactions were observed in vivo with bufuralol, although significant interactions with bufuralol were predicted with fluoxetine via CYP2D and CYP2C pathways (>2.45-fold) but not with clomipramine (<2-fold). The minor caffeine-fluvoxamine interaction (1.78-fold) was slightly higher than predicted values based on determination of a moderate f m value for CYP1A1, although CYP1A2 may also be involved in caffeine metabolism. The findings suggest promise for in vitro approaches to drug interaction assessment in dogs, but they also highlight the need to identify improved substrate and inhibitor probes for canine P450s.Metabolism-mediated drug interactions are an important consideration during preclinical drug lead optimization. Inhibitors of drugmetabolizing enzymes such as cytochromes P450 (P450) may be capable of decreasing the clearance of coadministered drugs when their clearance is metabolic. Therefore, it is important to evaluate new chemical entities as substrates and inhibitors of P450. To speed up this evaluation process, in vitro-in vivo extrapolation methods aimed at predicting metabolic drug interactions have continued to evolve. For instance, the choice of inhibition values (e.g., K i versus unbound K i ) (Brown et al., 2006), inhibitor absorption rates (Kanamitsu et al., 2000;Brown et al., 2005), P450 induction , and the choice of in vivo concentrations of P450 inhibitors (Brown et al., 2005;Obach et al., 2005) have all been studied with respect to in vitro-based drug-drug interaction (DDI) predictions. Irreversible enzyme inhibition mechanisms, although recognized for some time, have increasingly been added to in vitro-based drug interaction extrapolation methods with assumptions about the turnover rates of P450 isoforms (Mayhew et al., 2000;Venkatakrishnan and Obach, 2007). Several of these in vitro findings or approaches have even been integrated into several commercial software packages as biology continues to advance toward more physiolog...

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Section: Methodsmentioning

confidence: 88%

Current Cytochrome P450 Phenotyping Methods Applied to Metabolic Drug-Drug Interaction Prediction in Dogs

Mills

Zaya²,

Walters³

et al. 2009

Drug Metab Dispos

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“…Because MDZ is hydroxylated at the 1'-and the 4-position to a different degree e.g. in rat.man and dog (9,12,22), the total MDZ hydroxylation was used. Rat hepatocytes showed a steady decline in CYP3A activity to 30% of the initial value after 72 hours in culture (Table V).…”

Section: Resultsmentioning

confidence: 99%

“…Moreover, dog and man eliminate midazolam in a comparable way i.e. the parent drug and its hydroxylated metabolites (12).…”

Section: Introductionmentioning

confidence: 99%

Comparison of the stability of some major cytochrome P450 and conjugation reactions in rat, dog and human hepatocyte monolayers

Ubeaud

Schiller

Hurbin

et al. 2001

Eur. J. Drug Metab. Pharmacokinet.

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The stability of four major cytochrome P450 isoenzymes (CYPIA, CYP2B, CYP2E1 and CYP3A) and of two phase II conjugation enzymes (glucuronyl- and sulfotransferases) was investigated in primary cultures of rat, dog and human hepatocytes in the same conditions. 7-ethoxyresorufin deethylation (EROD), 7-methoxycoumarin demethylation (MCOD), chlorzoxazone (CLOX) 6-hydroxylation, 1'- and 4-hydroxylation of midazolam (MDZ), and p-nitrophenol glucuronidation and sulfation, were used respectively. The EROD activity was stable over 72 hours in rat and dog and only 48 hours in human hepatocytes. The MCOD activity was also stable in rat but decreased in dog by 30% within 72 hours The CLOX hydroxylase activity was most stable in human whereas in rat and dog it fell down to 30% within 72 and 24 hours, respectively. The MDZ hydroxylase activity showed the same unstability profile in the three species investigated. Both conjugation reactions were either stable or showed an increase by up to 60-70% in all three species over 72 hours. The enzymes tested showed different stabilities in rat, dog and human hepatocytes over 72 hours, thus demonstrating the limitations of hepatocyte monolayers as models for metabolic investigations and emphasising the need for validation/characterization studies before routine use.

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“…17], Nevertheless, several groups [6,7] have not detected the unconjugated metabo lite in plasma from subjects receiving MDZ, although Ueizmann and Ziegler [6] did find trace amounts of unconjugated 4-OH-MDZ in the urine of subjects given MDZ.…”

Section: Discussionmentioning

confidence: 99%

“…1) is an imidazo benzodiazepine used as a premedication and induction agent for anesthesia, and as a hyp notic for the treatment of sleep disorders [1][2][3][4][5]. The major metabolic pathway for MDZ in humans involves hydroxylation at the 1-po sition, yielding 1 -hydroxymidazolam (1-OH-MDZ; alternatively named 1-hydroxyme thyl midazolam) which in turn is conjugated and excreted in the urine as a glucuronide [6][7][8][9] (fig. 1).…”

mentioning

confidence: 99%

Quantitation by Gas Chromatography of the 1- and 4-Hydroxy Metabolites of Midazolam in Human Plasma

1984

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The imidazobenzodiazepine midazolam (MDZ), along with its 1 -hydroxy and 4-hydroxy metabolites (1-OH-MDZ, 4-OH-MDZ) can be simultaneously quantitated by electron capture gas-liquid chromatography. After addition of diazepam as internal standard, alkalinized plasma samples are extracted into benzene-isoamyl alcohol. The organic extract is separated, evaporated to dryness, reconstituted, and chromatographed using 3% SP-2250 as the liquid phase. The indentity of 4-OH-MDZ, not previously detected in human plasma in unconjugated form, was verified by negative-ion chemical ionization mass spectroscopy. After single oral doses of MDZ administered to humans, concentrations of MDZ and 1-OH-MDZ (alternatively named 1-hydroxymethyl midazolam) were similar, and both compounds were eliminated from plasma in parallel. Concentrations of 4-OH-MDZ were considerably lower, but this metabolite was also eliminated in parallel with the parent compound.

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Simultaneous determination of diazepam and its metabolites N-desmethyldiazepam, oxydiazepam and oxazepam in plasma and urine of man and dog by means of high-performance liquid chromatography

Cited by 62 publications

References 19 publications

Current Cytochrome P450 Phenotyping Methods Applied to Metabolic Drug-Drug Interaction Prediction in Dogs

Current Cytochrome P450 Phenotyping Methods Applied to Metabolic Drug-Drug Interaction Prediction in Dogs

Comparison of the stability of some major cytochrome P450 and conjugation reactions in rat, dog and human hepatocyte monolayers

Quantitation by Gas Chromatography of the 1- and 4-Hydroxy Metabolites of Midazolam in Human Plasma

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