QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) All Versions of this Article: dmd.104.000216v1 32/11/1287    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Sanchez, R. I. Articles by Huskey, S.-E. W. Search for Related Content PubMed PubMed Citation Articles by Sanchez, R. I. Articles by Huskey, S.-E. W.

CYTOCHROME P450 3A4 IS THE MAJOR ENZYME INVOLVED IN THE METABOLISM OF THE SUBSTANCE P RECEPTOR ANTAGONIST APREPITANT

Department of Drug Metabolism, Merck Research Laboratories, Rahway, New Jersey (R.I.S., R.W.W., D.J.N., R.B., S.-H.L.C., D.C.E., S.W.H.); and Department of Drug Metabolism, Merck Research Laboratories West Point, Pennsylvania (P.L.)

(Received April 13, 2004; accepted August 5, 2004)

	Abstract

Top Abstract Materials and Methods Results Discussion References

 
The contribution of human cytochrome P450 (P450) isoforms to the metabolism of aprepitant in humans was investigated using recombinant P450s and inhibition studies. In addition, aprepitant was evaluated as an inhibitor of human P450s. Metabolism of aprepitant by microsomes prepared from baculovirus-expressed human P450s was observed only when CYP1A2, CYP2C19, or CYP3A4 was present in the expression system. Incubation with CYP1A2 and CYP2C19 yielded only products of O-dealkylation, whereas CYP3A4 catalyzed both N- and O-dealkylation reactions. The metabolism of aprepitant by human liver microsomes was inhibited completely by ketoconazole or troleandomycin. No inhibition was observed with other P450 isoform-selective inhibitors. Aprepitant was evaluated also as a P450 inhibitor in human liver microsomes. No significant inhibition of CYP1A2, CYP2B6, CYP2C8, CYP2D6, and CYP2E1 was observed in experiments with isoform-specific substrates (IC₅₀ > 70 µM). Aprepitant was a moderate inhibitor of CYP3A4, with K_i values of 10 µM for the 1'- and 4-hydroxylation of midazolam, and the N-demethylation of diltiazem, respectively. Aprepitant was a very weak inhibitor of CYP2C9 and CYP2C19, with K_i values of 108 and 66 µM for the 7-hydroxylation of warfarin and the 4'-hydroxylation of S-mephenytoin, respectively. Collectively, these results indicated that aprepitant is both a substrate and a moderate inhibitor of CYP3A4.

In drug-drug interaction studies, it was observed that coadministration with aprepitant resulted in increases in the area under the plasma concentration versus time curve (AUC) for dexamethasone and methylprednisolone (McCrea et al., 2003). When the standard dexamethasone regimen (20 mg on day 1 and 12 mg on days 2–5) was given concomitantly with aprepitant, dexamethasone AUC_{0–24 h} increased 2-fold on both day 1 and day 5 compared with the standard dexamethasone regimen alone. When a modified dexamethasone regimen (12 mg on day 1 and 4 mg on days 2 and 5) was given concomitantly with aprepitant, the dexamethasone AUC_{0–24 h} also increased, making it similar to that of the standard regimen alone. When 125 mg of methylprednisolone i.v. on day 1 and 40 mg p.o. on days 2 and 3 was given with aprepitant, the AUC of methylprednisolone increased approximately 30% on day 1 (after i.v. administration) and 2-fold on day 3 (after oral administration). Aprepitant had no effect on either ondansetron (i.v.) or granisetron (p.o.) pharmacokinetics (Blum et al., 2003). Dexamethasone, methylprednisolone, and granisetron are metabolized by CYP3A4 (Glynn et al., 1986; Bloomer et al., 1994; Gentile et al., 1996; Varis et al., 1998), whereas ondansetron is metabolized by multiple P450 isoforms, including CYP1A2, CYP2D6, and CYP3A4 (Fischer et al., 1994; Dixon et al., 1995).

Furthermore, clinical drug interaction studies indicated that administration of aprepitant at two different dosing regimens for 5 days altered the pharmacokinetics of the CYP3A4 probe substrate midazolam, when administered on days 1 and 5 of aprepitant therapy. The pharmacokinetic changes included 2.3- and 1.5-fold increases in midazolam AUC and maximum observed plasma concentration, respectively (Majumdar et al., 2003). Collectively, these results suggested that aprepitant is a moderate inhibitor of CYP3A4.

Other clinical drug interaction studies conducted with aprepitant suggest that it is not an inhibitor of CYP2C9 or CYP2D6 [EMEND (aprepitant) capsules product information; Merck & Co. Inc., White House Station NJ, 2003]. Moreover, when a single 125-mg dose of aprepitant was administered on day 5 of a 10-day regimen of 600 mg/day ketoconazole, a strong inhibitor of CYP3A4, the AUC of aprepitant increased approximately 5-fold [EMEND (aprepitant) capsules product information; Merck & Co. Inc., White House Station NJ, 2003], suggesting that aprepitant is a substrate of CYP3A4.

The metabolic pathways of aprepitant have been established in vivo (Huskey et al., 2004). Briefly, two oxidative pathways have been identified, namely, N- and O-dealkylation, and incubation of aprepitant in human liver microsomes allowed the identification of the major P450 isoforms involved in the catalysis of several intermediate reactions in these pathways. The experiments presented in this paper were aimed at the identification of the major P450 isoforms involved in the metabolism of aprepitant in human liver and the evaluation of this drug as a potential P450 inhibitor.

	Materials and Methods

Top Abstract Materials and Methods Results Discussion References

 
Chemicals. All chemicals were of the highest analytical purity available. Bufuralol, 1'-hydroxybufuralol, furafylline, R,S- and S-warfarin, 7-hydroxy-warfarin, S-mephenytoin, 4-hydroxy-mephenytoin, and 6-hydroxychlorzoxazone were purchased from BD Gentest (Woburn, MA). Aprepitant, M-1, M-2, M-3, and M-4 were synthesized by Merck Basic Chemistry (Rahway, NJ). [Morpholine-2-¹⁴C]aprepitant (specific activity 29.8 µCi/mg) and [4-fluorophenyl-3-³H]aprepitant (specific activity 11.62 mCi/mg) were prepared by the Merck Labeled Compound Synthesis Group (Rahway, NJ). Midazolam maleate, 1'-hydroxymidazolam, 4-hydroxymidazolam, and desmethyl-diltiazem were provided by the Merck Labeled Compound Synthesis Group. All other chemicals were purchased from Sigma-Aldrich (St. Louis, MO).

Preparation of Liver Microsomes from Humans. Microsomal fractions were prepared from frozen livers from human subjects (International Institute for the Advancement of Medicine, Exton, PA) according to a published procedure (Huskey et al., 1995). Protein concentration was determined using the BCA method (Pierce Chemical, Rockford, IL) according to the manufacturer's recommendations. The P450 content was determined as described previously (Omura and Sato, 1964).

Incubation Conditions. All incubations contained 100 mM phosphate buffer, pH 7.4 and an NADPH-regenerating system consisting of 5 mM glucose 6-phosphate, 1 mM NADP, and 0.7 IU/ml glucose-6-phosphate dehydrogenase. All reactions were initiated by addition of NADP. Substrates and inhibitors were prepared in methanol or acetonitrile so that each reaction contained <2% solvent.

Incubations with Recombinant P450s. The reaction mixtures (200 µl) contained 10 µM [¹⁴C]aprepitant, and microsomes prepared from baculovirus-infected Sf-21 cells expressing recombinant P450 isoforms (20 or 30 pmol; CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, or CYP3A4). The reactions proceeded for 30 min at 37°C and were terminated by the addition of 200 µl of methanol. The resulting suspensions were centrifuged and aliquots (200 µl) of the supernatants were analyzed by HPLC as described below. Identification of reaction products was based on similarity of retention time and MS/MS fragmentation pattern to those of synthetic standards as described elsewhere (Huskey et al., 2004).

Enzyme Kinetics Studies. Varying concentrations of [³H]aprepitant (1- 40µM) were incubated with a pool of liver microsomes from three human subjects. Reactions proceeded for 20 min in the presence of 1 mg/ml microsomal protein and were quenched with 4 volumes of acetonitrile. After centrifugation, the supernatants were transferred to clean tubes and evaporated to dryness under N₂. The residues were reconstituted in 200 µl of 1:1 methanol/water and aliquots of 100 µl were analyzed by HPLC as described under "HPLC Methods". Rates of metabolism were calculated from the peak areas of aprepitant as % of total radioactivity in the radiochromatograms.

Inhibition of aprepitant metabolism. The reaction mixtures (500 µl) containing [³H]aprepitant, (10 µM) and human liver microsomes (3 different preparations, 1 mg/ml) were incubated for 30 min in the presence of furafylline (25 µM), sulfaphenazole (1 µM), quinidine (1 µM), 4-methylpyrazole (100 µM), ketoconazole (1 µM) or troleandomycin (TAO, 25 µM). The reactions were terminated and processed as described above for HPLC analysis (see "HPLC Methods"). The extent of inhibition was determined from a comparison of turnover in the presence of an inhibitor to a control reaction run simultaneously with solvent vehicle only.

Determination of the IC₅₀ for the Inhibition of P450-Mediated Reactions by Aprepitant. Concentrations of substrates used in these experiments were kept near or below their K_m (K_m values for bupropion and paclitaxel (Taxol) were determined in the pool of microsomes used for these experiments as 14.4 and 98 µM, respectively; bufuralol, chlorzoxazone, and testosterone concentrations were used based on literature values). For phenacetin and tolbutamide, concentrations of 100 µM were used based on a report by Von Moltke et al. (2001).

The reaction mixtures (500 µl except for paclitaxel and bupropion, which were done in 200 µl) containing phenacetin (100 µM), bupropion (100 µM), paclitaxel (15 µM), tolbutamide (100 µM), bufuralol (10 µM), chlorzoxazone (100 µM), or testosterone (10 µM), and various concentrations of aprepitant (1–100 µM) and human liver microsomes (0.25–1 mg/ml to obtain substrate turnovers of <15%) were incubated at 37°C for 20 min. The reactions (phenacetin, bufuralol, chlorzoxazone, testosterone) were quenched by the addition of 50 µl of methanol containing 1% (v/v) trifluoroacetic acid (TFA), 50 µl of 50% (v/v) TFA in water (tolbutamide), or 4 volumes of acetonitrile (bupropion, paclitaxel). The samples (phenacetin, bufuralol, tolbutamide, chlorzoxazone, and testosterone) were centrifuged and aliquots were analyzed by HPLC as described under "HPLC Methods". After addition of internal standard (see Table 2) and centrifugation at 1000g for 10 min, 500-µl aliquots of bupropion or paclitaxel reactions were dried under N₂ and reconstituted in 100 µl of 30% (v/v) acetonitrile in water. Aliquots of 20 µl were analyzed by LC-MS/MS (see "LC-MS/MS Methods").

Determination of K_i for the Inhibition of P450-Specific Reactions by Aprepitant. Midazolam. The reaction mixtures (250 µl) containing midazolam (2–250 µM), aprepitant (3–48 µM), and pooled human liver microsomes (n = 10, 0.5 mg/ml) were incubated at 37°C for 5 min. The reactions were quenched by addition of 4 volumes of acetonitrile and 10 µlofa250 µM solution of the internal standard. After centrifugation, aliquots (20 µl) of the supernatant were analyzed by LC-MS/MS (see Table 2). Concentrations of the metabolites were determined from standard curves constructed over the range of 0.1 to 10 µM for 1'-hydroxymidazolam and 0.05 to 10 µM for 4-hydroxymidazolam.

Diltiazem. Reaction mixtures (250 µl) containing diltiazem (5–200 µM), aprepitant (3–48 µM), and pooled human liver microsomes (n = 10, 1 mg/ml) were incubated at 37°C for 10 min. Quenching and addition of internal standard was done as described for midazolam. After centrifugation, aliquots (20 µl) of the supernatant were analyzed by LC-MS/MS (see Table 2). N-Desmethyl diltiazem was quantified from standard curves constructed over the range of 0.5 to 30 µM.

R,S-Warfarin. R,S-Warfarin (5–200 µM) was incubated for 30 min at 37°C in the presence of various concentrations of aprepitant (10–400 µM) and 2 mg/ml microsomal protein (pool of 10 preparations) The reactions (500 µl) were quenched by addition of 10 µl of 70% perchloric acid, and after centrifugation, aliquots (50 µl) were analyzed by fluorescence detection (Table 1). Reaction rates were calculated from metabolite concentrations extrapolated from standard curves constructed over the range of 1 to 10 pmol.

S-Mephenytoin. Reactions (200 µl) containing 10 to 200 µM S-mephenytoin, various concentrations of aprepitant (10–80 µM), and 1 mg/ml pooled human liver microsomes were incubated for 30 min at 37°C. The reactions were quenched by addition of 4 volumes of acetonitrile, and 10 µl of a 20 µg/ml solution of 5-(4'-hydroxyphenyl)-5-phenylhydantoin (HPPH) was added as internal standard. Aliquots (20 µl) were analyzed by LC-MS/MS. The concentrations of 4-hydroxymephenytoin were determined by extrapolation from a standard curve constructed over the range of 1 to 26 µM.

HPLC Methods. The HPLC systems used for analysis (Shimadzu Scientific Instruments Inc., Columbia, MD) consisted of two pumps (LC10ADvp), a controller (SCL10Avp), an autosampler (SIL-10A), a UV detector (SPD-10AVvp), and/or a fluorometer (model RF-10AxL).

Aprepitant. The separation of aprepitant from its metabolites was accomplished on a Zorbax RX-C8 analytical column (5 µm, 4.6 x 250 mm; Agilent Technologies, Palo Alto, CA) using a linear gradient from 35 to 80% B in 40 min at a flow rate of 1 ml/min. The mobile phase consisted of solvent A (10 mM ammonium acetate in water) and solvent B [10 mM ammonium acetate in 9:1 (v/v) acetonitrile/methanol]. Radioactive aprepitant and its metabolites were monitored using an on-line radiometric detector (IN/US Systems Inc., Tampa, FL) and Ultima-Flow M (PerkinElmer Life and Analytical Sciences, Boston, MA) as scintillant at a flow rate of 3 ml/min.

Metabolism of P450 Probes. HPLC separations were performed on an SB-C8 analytical column (5 µm, 4.6 x 75 mm; Agilent Technologies) using the mobile phase described above. Analytes were eluted using 10-min gradients at a flow rate of 2 ml/min. Details for these methods are described in Table 1.

LC-MS/MS Methods. All methods were developed on a PerkinElmer HPLC apparatus linked to a triple quadrupole mass spectrometer (Applied Biosystems/MDS Sciex, Foster City, CA) with an atmospheric pressure chemical ionization source in the positive ion mode. Metabolites were quantified by multiple reaction monitoring (MRM). LC conditions as well as analyte and internal standard transitions monitored are described in Table 2.

Kinetic Calculations. Kinetic constants for the inhibition of specific P450 isoform-mediated reactions were calculated using KaleidaGraph software (Abelbeck/Synergy, Reading PA). Apparent K_m values were calculated using the Michaelis-Menten equation: v = V_max x S/(K_m + S).

For inhibition studies, replots of apparent K_m or apparent K_m/V_max (competitive or noncompetitive) versus concentrations of aprepitant were fitted to a linear regression where the intercept and slope represent K_m and K_m/K_i (competitive), or K_m/V_max and K_m/(V_max x K_i) (noncompetitive), respectively.

IC₅₀ values were calculated according to the equation: V/V_o = 1/(IC₅₀ + S), where V represents an array of the rates of the reaction measured in the presence of various concentrations of inhibitor, V_o represents the rate of the reaction in the absence of inhibitor, and S represents a selected concentration of the substrate.

	Results

Top Abstract Materials and Methods Results Discussion References

 
Metabolism of Aprepitant by Recombinant P450s. CYP3A4 catalyzed the N-dealkylation reaction of aprepitant to the primary metabolite M-1 and the subsequent oxidation of M-1 to the imine M-2. The presence of metabolites M-3 and M-4 in incubations of aprepitant with CYP3A4 (Fig. 1) indicated that this enzyme also catalyzed the O-dealkylation of aprepitant. CYP1A2 and CYP2C19 catalyzed the O-dealkylation of aprepitant to M-3 and M-4 (Fig. 1). The pathways for aprepitant metabolism are outlined in Fig. 2.

View larger version (21K): [in this window] [in a new window]   FIG. 1. Radiochromatograms displaying the metabolism of [14C]aprepitant by recombinant human P450 enzymes.

View larger version (14K): [in this window] [in a new window]   FIG. 2. The routes of aprepitant metabolism catalyzed by recombinant human P450 enzymes. Details on the structural identification of metabolites depicted here are reported elsewhere (Huskey et al., 2004)

Kinetics for the Metabolism of Aprepitant in Human Liver Microsomes. Incubation of aprepitant with a pool of human liver microsomes in the presence of the NADPH-generating system resulted in the formation of the metabolites described above (data not shown), with profiles similar to those obtained for CYP3A4 (Fig. 1, panel C). The metabolism of aprepitant (measured as parent disappearance), followed single-site Michaelis-Menten kinetics. An apparent K_m of 8.9 ± 1.3 µM and V_max of 127 ± 6 pmol/mg/min were obtained. Based on these results, subsequent studies were performed using a 10 µM concentration of aprepitant.

Inhibition of the Metabolism of Aprepitant by Isoform-Selective Inhibitors. The effect of several isoform-selective inhibitors (Newton et al., 1995) on the metabolism of [³H]aprepitant was examined in three preparations of human liver microsomes. The metabolism of [³H]aprepitant was inhibited >98% by the CYP3A inhibitors ketoconazole (1 µM) and TAO (25 µM), which suggested that CYP3A4 was responsible, primarily, for the metabolism of [³H]aprepitant in liver fractions (Fig. 3). Other selective inhibitors had no significant effect (<10% inhibition) on the metabolism of aprepitant in microsomal incubations.

View larger version (13K): [in this window] [in a new window]   FIG. 3. Inhibition of the metabolism of [14C]aprepitant by P450 isoform-selective inhibitors. Bars represent averages ± S.E. of measurements done using liver microsome preparations from three different subjects. For inhibition with furafylline and TAO (mechanism-based inhibitors), samples were preincubated with the inhibitors for 30 min before addition of aprepitant. A concentration of aprepitant of 10 µM was chosen based on its Km in human liver microsomes (8.9 ± 1.3 µM).

Effect of aprepitant on the metabolism of specific P450 substrates by human liver microsomes. The effect of aprepitant on several metabolic conversions mediated by P450 isoforms was studied. Aprepitant showed moderate inhibition on the conversion of testosterone to its 6ß-hydroxylated metabolite, but exhibited very little inhibitory effect on the activities of CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2D6 and CYP2E1 (Table 3). In vitro drug-interaction studies were performed to evaluate the potential of aprepitant to interact with drugs that are commonly used as probe substrates of specific P450 isoforms. Midazolam (CYP3A4), diltiazem (CYP3A4), RS-warfarin (CYP2C9) and S-mephenytoin (CYP2C19) were used as substrates in these studies. The K_i values of aprepitant on the metabolic reactions of midazolam (hydroxylation) or diltiazem (N-demethylation), were estimated to be approximately 10 µM (Table 4), consistent with results obtained for testosterone 6ß-hydroxylation (IC₅₀ = 6.3 ± 2.8 µM at 10 µM testosterone). These results show no substrate-specific differences in inhibition (Kenworthy et al., 1999). In addition, aprepitant showed weak inhibition of (RS)-warfarin 7-hydroxylation and S-mephenytoin 4'-hydroxylation with Ki values >50 µM (Table 4).

	Discussion

Top Abstract Materials and Methods Results Discussion References

 
Aprepitant is metabolized extensively by the N- and O-dealkylation pathways (Huskey et al., 2004). Studies in animals indicated that the products derived from the initial N-dealkylation and subsequent reactions were eliminated in feces or further metabolized by either conjugation or oxidation, while products of O-dealkylation were readily eliminated in urine (Huskey et al., 2004). Similar results were obtained when [¹⁴C]aprepitant was administered to human subjects (Huskey et al., unpublished data).

Results presented here showed that the O-dealkylation of aprepitant was catalyzed by recombinant CYP1A2, CYP2C19, and CYP3A4, whereas the N-dealkylation pathway resulted primarily from CYP3A4 activity. However, our results indicated that CYP3A4 represents the major contributor to the metabolism of aprepitant in human liver. This was evidenced by the ability of CYP3A4 to catalyze both metabolic pathways of aprepitant and the complete inhibition observed in human liver microsomes when ketoconazole or TAO was used as inhibitor (Fig. 3). These results are likely a reflection of the low levels of CYP1A2 and CYP2C19 in human liver relative to CYP3A4 (Rodrigues, 1999).

Aprepitant undergoes monophasic kinetics in human liver microsomes, and its K_m approaches 10 µM. Furthermore, aprepitant was a moderate inhibitor of CYP3A4, with a K_i of approximately 10 µM for two CYP3A4 probes, midazolam and diltiazem (IC₅₀ for 10 µM testosterone = 6 µM).

At the dosing regimen used for aprepitant administration to CINV patients (i.e., 120 mg on day 1 and 80 mg on days 2–5), maximal concentrations of aprepitant in plasma are approximately 1.5 µM (Constanzer et al., 2004). Under this regimen, clinical drug interaction studies showed a moderate inhibitory effect on CYP3A4 (Majumdar et al., 2003; McCrea et al., 2003) but not on CYP2D6, CYP2C9, or CP2C19 substrates [EMEND (aprepitant) capsules product information; Merck & Co. Inc., White House Station NJ, 2003]. Thus, the in vitro phenotyping and inhibition studies appropriately assessed the moderate drug-drug interaction potential of the compound and helped to understand the clinical observations.

In conclusion, the data presented here support the results obtained from clinical studies, in which aprepitant, administered at the dosing regimens recommended for the treatment of CINV in conjunction with other drugs that are CYP3A4 substrates, led to increased plasma levels of those drugs. Thus, aprepitant should be used with caution when given concomitantly with drugs, including chemotherapeutic agents, that are primarily metabolized by CYP3A4. Increases in plasma concentrations of drugs that are metabolized by CYP3A4 may occur when coadministering these agents with aprepitant.

Interaction of aprepitant with drugs that are substrates of P450 isoforms other than CYP3A4 is unlikely to involve inhibition of their metabolism. For example, a modest, transient inductive effect on tolbutamide metabolism occurred when this drug was administered on days 4 or 8 after a 3-day aprepitant CINV therapy, but disappeared by day 15 (Shadle et al., 2004). A similar effect was observed in the same study when patients were administered intravenous midazolam after aprepitant treatment. The modest inductive effect on CYP2C9 is not likely to be clinically relevant for most CYP2C9 substrates, but it could be important for drugs with a low therapeutic index, such as warfarin. On the other hand, given that the inductive effect on midazolam was weak, it is unlikely that it would significantly affect the pharmacokinetics of chemotherapeutic agents administered within 12 days after completion of the aprepitant regimen for prevention of CINV.

	Acknowledgments

 
We thank Dr. Ronald Franklin, Dr. Anup Majumdar, and Dr. Jacqueline McCrea for helpful discussions during the preparation of the manuscript.

	Footnotes

 
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.

doi:10.1124/dmd.104.000216.

ABBREVIATIONS: CINV, chemotherapy-induced nausea and vomiting; AUC, area under the plasma concentration versus time curve; HPPH, 5-(4'-hydroxyphenyl)-5-phenylhydantoin; P450, cytochrome P450; TAO, troleandomycin; HPLC, high-performance liquid chromatography; LC-MS/MS, liquid chromatography-tandem mass spectrometry; TFA, trifluoroacetic acid; MRM, multiple reaction monitoring.

Address correspondence to: Dr. Rosa I. Sanchez, Department of Drug Metabolism, Merck Research Laboratories, P.O. Box 2000, Rahway, NJ 07065. E-mail: rosa_sanchez{at}merck.com

	References

Top Abstract Materials and Methods Results Discussion References

 


Bloomer JC, Baldwin SJ, Smith GJ, Ayrton AD, Clarke SE, and Chenery RJ (1994) Characterisation of the cytochrome P450 enzymes involved in the in vitro metabolism of granisetron. Br J Clin Pharmacol 38: 557-566.[Medline]

Blum RA, Majumdar A, McCrea J, Busillo J, Orlowski LH, Panebianco D, Hesney M, Petty KJ, Goldberg MR, Murphy MG, et al. (2003) Effects of aprepitant on the pharmacokinetics of ondansetron and granisetron in healthy subjects. Clin Ther 25: 1407-1419.[CrossRef][Medline]

Campos D, Pereira JR, Reinhardt RR, Carracedo C, Poli S, Vogel C, Martinez-Cedillo J, Erazo A, Wittreich J, Eriksson LO, et al. (2001) Prevention of cisplatin-induced emesis by the oral neurokinin-1 antagonist, MK-869, in combination with granisetron and dexamethasone or with dexamethasone alone. J Clin Oncol 19: 1759-1767.[Abstract/Free Full Text]

Constanzer ML, Chavez-Eng CM, Dru J, Kline WF, and Matuszewski BK (2004) Determination of a novel substance P inhibitor in human plasma by high-performance liquid chromatography with atmospheric pressure chemical ionization mass spectrometric detection using single and triple quadrupole detectors. J Chromatogr B Anal Technol Biomed Life Sci 807: 243-250.

Dixon CM, Colthup PV, Serabjit-Singh CJ, Kerr BM, Boehlert CC, Park GR, and Tarbit MH (1995) Multiple forms of cytochrome P450 are involved in the metabolism of ondansetron in humans. Drug Metab Dispos 23: 1225-1230.[Abstract]

Fischer V, Vickers AE, Heitz F, Mahadevan S, Baldeck JP, Minery P, and Tynes R (1994) The polymorphic cytochrome P-4502D6 is involved in the metabolism of both 5-hydroxytryptamine antagonists, tropisetron and ondansetron. Drug Metab Dispos 22: 269-274.[Abstract]

Gentile DM, Tomlinson ES, Maggs JL, Park BK, and Back DJ (1996) Dexamethasone metabolism by human liver in vitro. Metabolite identification and inhibition of 6-hydroxylation. J Pharmacol Exp Ther 277: 105-112.[Abstract/Free Full Text]

Glynn AM, Slaughter RL, Brass C, D'Ambrosio R, and Jusko WJ (1986) Effects of ketoconazole on methylprednisolone pharmacokinetics and cortisol secretion. Clin Pharmacol Ther 39: 654-659.[Medline]

Gralla RJ, Osoba D, Kris MG, Kirkbride P, Hesketh PJ, Chinnery LW, Clark-Snow R, Gill DP, Groshen S, Grunberg S, et al. (1999) Recommendations for the use of antiemetics: evidence-based, clinical practice guidelines. American Society of Clinical Oncology. J Clin Oncol 17: 2971-2994.[Free Full Text]

Huskey SW, Dean DC, Miller RR, Rasmusson GH, and Chiu SH (1995) Identification of human cytochrome P450 isoforms responsible for the in vitro oxidative metabolism of finasteride. Drug Metab Dispos 23: 1126-1135.[Abstract]

Huskey SE, Dean BJ, Doss GA, Wang Z, Hop CECA, Anari MR, Finke PE, Robichaud AJ, Zhang M, Wang B, et al. (2004) The metabolic disposition of aprepitant, a substance P receptor antagonist, in rats and dogs. Drug Metab Dispos 32: 246-258.[Abstract/Free Full Text]

Kenworthy KE, Bloomer JC, Clarke SE, and Houston JB (1999) CYP3A4 drug interactions: correlation of 10 in vitro probe substrates. J Clin Pharmacol 48: 716-727.

Majumdar AK, McCrea JB, Panebianco DL, Hesney M, Dru J, Constanzer M, Goldberg MR, Murphy G, Gottesdiener KM, Lines CR, et al. (2003) Effects of aprepitant on cytochrome P450 3A4 activity using midazolam as a probe. Clin Pharmacol Ther 74: 150-156.[CrossRef][Medline]

McCrea JB, Majumdar AK, Goldberg MR, Iwamoto M, Gargano C, Panebianco DL, Hesney M, Lines CR, Petty KJ, Deutsch PJ, et al. (2003) Effects of the neurokinin1 receptor antagonist aprepitant on the pharmacokinetics of dexamethasone and methylprednisolone. Clin Pharmacol Ther 74: 17-24.[CrossRef][Medline]

Navari RM, Reinhardt RR, Gralla RJ, Kris MG, Hesketh PJ, Khojasteh A, Kindler H, Grote TH, Pendergrass K, Grunberg SM, et al. (1999) Reduction of cisplatin-induced emesis by a selective neurokinin-1-receptor antagonist. L-754,030. Antiemetic Trials Group. N Engl J Med 340: 190-195.[Abstract/Free Full Text]

Newton DJ, Wang RW, and Lu AY (1995) Cytochrome P450 inhibitors. Evaluation of specificities in the in vitro metabolism of therapeutic agents by human liver microsomes. Drug Metab Dispos 23: 154-158.[Abstract]

Omura T and Sato R (1964) The carbon-monoxide binding pigment of liver microsomes. J Biol Chem 239: 2370-2378.[Free Full Text]

Rodrigues AD (1999) Integrated cytochrome P450 reaction phenotyping: attempting to bridge the gap between cDNA-expressed cytochromes P450 and native human liver microsomes. Biochem Pharmacol 57: 465-480.[CrossRef][Medline]

Roila F, Del Favero A, Gralla RJ, and Tonato M (1998) Prevention of chemotherapy- and radiotherapy-induced emesis: results of the Perugia consensus conference. Ann Oncol 9: 818-819.

Shadle CR, Lee Y, Majumdar AK, Petty KJ, Gargano C, Bradstreet TE, Evans JK, and Blum RA (2004) Evaluation of potential inductive effects of aprepitant on cytochrome P450 3A4 and 2C9 activity. J Clin Pharmacol 44: 215-223.[Abstract/Free Full Text]

Varis T, Kaukonen KM, Kivisto KT, and Neuvonen PJ (1998) Plasma concentrations and effects of oral methylprednisolone are considerably increased by itraconazole. Clin Pharmacol Ther 64: 363-368.[CrossRef][Medline]

Von Moltke LL, Greenblatt DL, Giancarlo GM, Granda BW, Harmatz JS, and Shader RI (2001) Escitalopram (S-citalopram) and its metabolites in vitro: cytochromes mediating biotransformation, inhibitory effects and comparison to R-citalopram. Drug Metab Dispos 29: 1102-1109.[Abstract/Free Full Text]

This article has been cited by other articles:

				R. B Ibrahim, M. H Abidi, L. J Ayash, S. M Cronin, C. Cadotte, J. Mulawa, P. A Jacobson, D. W Smith, J. P Uberti, and D. J Edwards Effect of aprepitant on intravenous tacrolimus disposition in reduced intensity hematopoietic stem cell transplantation Journal of Oncology Pharmacy Practice, September 1, 2008; 14(3): 113 - 121. [Abstract] [PDF]

				P. J. Hesketh Chemotherapy-Induced Nausea and Vomiting N. Engl. J. Med., June 5, 2008; 358(23): 2482 - 2494. [Full Text] [PDF]

				A. K. Majumdar, K. X. Yan, D. V. Selverian, S. Barlas, M. Constanzer, J. Dru, J. B. McCrea, T. Ahmed, G. S. Frick, W. K. Kraft, et al. Effect of Aprepitant on the Pharmacokinetics of Intravenous Midazolam J. Clin. Pharmacol., June 1, 2007; 47(6): 744 - 750. [Abstract] [Full Text] [PDF]

				G. H. Wynn, N. B. Sandson, and K. L. Cozza Gastrointestinal Medications Psychosomatics, February 1, 2007; 48(1): 79 - 85. [Abstract] [Full Text] [PDF]

				S. Ekins, S. Andreyev, A. Ryabov, E. Kirillov, E. A. Rakhmatulin, S. Sorokina, A. Bugrim, and T. Nikolskaya A COMBINED APPROACH TO DRUG METABOLISM AND TOXICITY ASSESSMENT Drug Metab. Dispos., March 1, 2006; 34(3): 495 - 503. [Abstract] [Full Text] [PDF]

				A. K. Majumdar, L. Howard, M. R. Goldberg, L. Hickey, M. Constanzer, P. L. Rothenberg, T. M. Crumley, D. Panebianco, T. E. Bradstreet, A. J. Bergman, et al. Pharmacokinetics of aprepitant after single and multiple oral doses in healthy volunteers. J. Clin. Pharmacol., March 1, 2006; 46(3): 291 - 300. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) All Versions of this Article: dmd.104.000216v1 32/11/1287    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Sanchez, R. I. Articles by Huskey, S.-E. W. Search for Related Content PubMed PubMed Citation Articles by Sanchez, R. I. Articles by Huskey, S.-E. W.