Cytochrome P450 Substrates Research Articles

Modulation of Hepatic Cytochrome P450 Enzymes by Curcumin and its Pharmacokinetic Consequences in Sprague-dawley Rats.

Background:Curcumin (CUR) is a polyphenolic component derived from an herbal remedy and dietary spice turmeric (Curcuma longa).Objective:The aim of this study was to investigate inhibitory effects of CUR on in vitro cytochrome P450 (CYP) activity and in vivo pharmacokinetic consequences of single CUR dose in rats.Materials and Methods:An in vitro CYP inhibition study in rat liver microsomes (RLM) was conducted using probe substrates for CYPs. Then, an in vivo pharmacokinetics of intravenous buspirone (BUS), a probe substrate for CYP3A, was studied with the concurrent administration of oral CUR in rats.Results:In the in vitro CYP inhibition study, CUR inhibited the CYP3A-mediated metabolism of testosterone (TES) with a half maximal inhibitory concentration of 11.0 ± 3.3 μM. However, the impact of a single oral CUR dose on the pharmacokinetics of BUS in rats is limited, showing that CUR cannot function as an inhibitor for CYP3A-mediated drug metabolism in vivo.Conclusion:To the best of our knowledge, our results are the first reported data regarding the inhibition of in vitro CYP3A-mediated metabolism of TES and the in vivo impact of a single CUR dose on the pharmacokinetics of BUS in rats. Further study is required to draw a confirmative conclusion on whether CUR can be a clinically relevant CYP3A4 inhibitor.SUMMARY CUR can inhibit the in vitro CYP3A-mediated metabolism of TES in RLM. However, the impact of a single oral CUR dose on the pharmacokinetics of BUS in rats is limited, showing that CUR cannot function as an inhibitor for CYP3A-mediated drug metabolism in vivo.

Species Differences in the Pharmacokinetic Parameters of Cytochrome P450 Probe Substrates between Experimental Animals, such as Mice, Rats, Dogs, Monkeys, and Microminipigs, and Humans

To clarify species differences in the pharmacokinetic parameters of cytochrome P450 (CYP) activities between humans and experimental animals, we assessed several CYP activities in mice, rats, dogs, monkeys, and microminipigs, using the simultaneous administration of typical human CYP substrates, such as caffeine (human CYP1A2 substrate), losartan (CYP2C9), omeprazole (CYP2C19), dextromethorphan (CYP2D6), and midazolam (CYP3A), to these animals. The intrinsic clearance (CLint) of these 5 substrates was also examined using the liver microsomes of humans and the experimental animals. The high bioavailabilities (BAs) and low CLint values of caffeine in the experimental animals were similar to those in humans. Mice and monkeys had lower BAs and higher CLint values of losartan than those in humans. Mice, rats, and monkeys had lower BAs and higher CLint values of omeprazole than those in humans. The lowest BAs of dextromethorphan were observed in monkeys and microminipigs, and only the CLint in dogs was similar to that in humans. The BA of midazolam in microminipigs only was similar to that in humans, while the CLint values in the other animals were similar to that in humans. These results indicated that in vitro and in vivo experimental data obtained using multiple animals including microminipigs are useful for predicting human pharmacokinetics.

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Objectives Preeclampsia (PreE) is thought to originate from an impaired vascular remodeling of the placental spiral arteries. Recent data suggests a possible role of cytochromeP450 (CYP450) vasoactive eicosanoids in the etiology of the disease. We tested the hypothesis that alterations in the profile of arachidonic acid (AA) metabolites of the CYP450 pathway may contribute to the impaired vascular remodeling in preeclampsia. Methods Proliferation of BeWo cells, an in vivo model of trophoblast syncytialisation, was measured in the presence of 20-HETE, the major CYP450 metabolite, and 17-ODYA, a mechanism-based suicide substrate CYP450 inhibitor, in order to determine the proliferative actions of 20-HETE. In addition, microsomes were isolated from placental vessels of normal pregnant (NP) and PreE women and CYP450 enzyme activity was determined by HPLC/mass spectrometry. Results Incubation of BeWo cells with 10 nM, 100 nM, and 1 μ M of 20-HETE displayed a dose-dependent increase in cell proliferation with an approximate 40% increase at 1 μ M, while inhibition of 20-HETE with 17-ODYA (10 μ M) displayed a 40% decrease in BeWo cell proliferation. Placental vascular microsomes isolated from PreE women displayed a significant increase in 20-HETE production relative to NP women. 15-HETE, 12-HETE, and total HETE production were also increased in PreE compared to NP. Conclusions Increases in 20-HETE production promote, while inhibition of 20-HETE reduces proliferation of trophoblasts in vitro. Increases in the production of an endogenous inhibitor of 20-HETE, such as15-HETE, may contribute to the reduced trophoblast invasion and impaired vascular remodeling seen in PreE. Disclosures N. Lee: None. S. Spencer: None. B.B. LaMarca: None. S. Murphy: None.

Effect of kanglaite on rat cytochrome P450

Context: Kanglaite (KLT) is an oily substance extracted from Coix lacryma-jobi Linn. (Cramineae) and has been proved to significantly improve the life span and quality of life of patients, when combined with chemotherapy, radiotherapy, or surgery.Objective: The purpose of this study was to find out whether KLT influences the effect on rat cytochrome P450 (CYP) enzymes (CYP1A2, CYP2B6, CYP2C9, CYP2C19, and CYP3A4) by using cocktail probe drugs in vivo.Materials and methods: A cocktail solution at a dose of 5 mL/kg, which contained phenacetin (20 mg/kg), bupropion (20 mg/kg), tolbutamide (5 mg/kg), omeprazole (20 mg/kg), and midazolam (10 mg/kg), was given as oral administration to rats treated with 7 d intraperitoneal injection of KLT. Blood samples were collected at a series of time-points and the concentrations of probe drugs in plasma were determined by HPLC-MS/MS. The corresponding pharmacokinetic parameters were calculated by the software of DAS 2.0 (SPPS Inc., Chicago, IL).Results: In the experiment, there was a statistically significant difference in the t1/2, Cmax, AUC(0–∞), and CL for phenacetin, bupropion, tolbutamide, omeprazole, and midazolam. Our study showed that treatment with multiple doses of KLT had induction effect on rat CYP1A2, while CYP2B6, CYP2C9, CYP2C19, and CYP3A4 enzyme activities had been inhibited after multiple doses of KLT treatment.Conclusions: KLT can either induce or inhibit activities of CYP. Therefore, caution is needed when KLT is co-administration with some CYP substrates in clinic, which may result in herb–drug interactions.

Review of current chemoinformatic tools for modeling important aspects of CYPs-mediated drug metabolism. Integrating metabolism data with other biological profiles to enhance drug discovery.

The study of the metabolism of xenobiotics by the human body is an essential stage in the complex and expensive process of drug discovery, being one of the main causes of disapproval and/or withdrawal of drugs. Regarding this, enzymes known as cytochromes P450 (CYPs) play a very decisive role in the biotransformation of many chemicals. For this reason, the use of chemoinformatics to predict and /or analyze from different points of view CYPs-mediated drug metabolism, can help to reduce time and financial resources. This work is focused on the most remarkable advances in the last 5 years of the chemoinformatics tools towards the virtual analysis of CYPsmediated drug metabolism. First, a brief section is dedicated to the applicability of chemoinformatics in different areas associated with drug metabolism. Then, both the models for prediction of CYPs substrates and those allowing the assessment of sites of metabolism (SOM) are discussed. At the same time, the principal limitations of the current chemoinformatic tools are pointed out. Finally, and taking into account that metabolism is an essential step in the whole process of designing any drug, we introduce here as a case of study, the first multitasking model for quantitative-structure biological effect relationships (mtk-QSBER). The purpose of this model is to integrate different types of biological profiles such as ADMET (absorption, distribution, metabolism, excretion, toxicity) profiles and antistaphylococci activities. The mtk-QSBER model was created by employing a heterogeneous dataset of more than 66000 cases tested in 6510 different experimental conditions. The model displayed a total accuracy higher than 94%. To the best of our knowledge, this is the first attempt to complement metabolism assays with other relevant biological data in order to speed up the discovery of efficacious antistaphylococci agents.

Evaluation of the Potential for Pharmacokinetic Drug–Drug Interaction Between Armodafinil and Carbamazepine in Healthy Adults

PurposePolypharmacy is common in psychiatry practice and can lead to an increased risk of drug interactions. Armodafinil, a wakefulness-promoting agent, has been studied as adjunctive therapy for the treatment of major depressive episodes associated with bipolar I disorder. Armodafinil and the mood stabilizer carbamazepine are both inducers of and substrates for cytochrome P450 (CYP3A4). This study was designed to evaluate the bidirectional carbamazepine–armodafinil pharmacokinetic drug–drug interaction. MethodsThis was an open-label, single-center study conducted in healthy adult men. Subjects assigned to group 1 received a dose of carbamazepine (200 mg) alone and a dose after pretreatment with daily dosing of armodafinil (titrated to 250 mg/d). Subjects assigned to group 2 received a dose of armodafinil (250 mg) alone and a dose after pretreatment with carbamazepine BID (titrated to 400 mg/d). Pharmacokinetic parameters for carbamazepine, armodafinil, and their major circulating metabolites were determined when dosed alone and after pretreatment with the other drug. The safety and tolerability of armodafinil and carbamazepine were also assessed throughout the study. FindingsEighty-one subjects enrolled in the study (group 1 = 40; group 2 = 41), of whom 79 (group 1 = 40; group 2 = 39) were evaluable for pharmacokinetic analysis and 80 (group 1 = 40; group 2 = 40) were evaluable for safety analysis. In group 1, pretreatment with armodafinil reduced systemic exposure to carbamazepine by 12% for Cmax and 25% for AUC (based on comparison of geometric means). Similarly, in group 2, pretreatment with carbamazepine reduced systemic exposure to armodafinil by 11% for Cmax and 37% for AUC. Systemic exposure to the metabolites of these agents that are formed via CYP3A4 were increased after pretreatment in each group. There were no new or unexpected adverse events. ImplicationsSystemic exposure to both carbamazepine and armodafinil was reduced after pretreatment with the other drug; systemic exposure to the metabolites of each drug, which are formed via CYP3A4, was increased. These changes were consistent with the induction of CYP3A4. Both drugs were generally safe and well tolerated alone and in combination under the conditions studied. Dose adjustment may be required when initiating or discontinuing armodafinil and carbamazepine cotherapy.

Effects of selected xenobiotics on hepatic and plasmatic biomarkers in juveniles of Solea senegalensis

In recent years, Solea senegalensis has increasingly been used in pollution monitoring studies. In order to assess its response to some particular widespread pollutants, juveniles of S. senegalensis were administered an intraperitoneal injection of the model aryl hydrocarbon receptor agonist β-naphtoflavone (βNF) and chemicals of environmental concern, such as the fungicide ketoconazole (KETO), the lipid regulator gemfibrozil (GEM), the surfactant nonylphenol (NP) and the synthetic hormone ethinylestradiol (EE2). Two days after injection, the effect of these chemicals was followed up as alterations of hepatic microsomal activities of the cytochrome P450 (CYPs) and associated reductases, carboxylesterases (CbEs) and the conjugation enzyme uridine diphosphate glucuronyltransferase (UDPGT). In the cytosolic fraction of the liver, the effect on CbEs, glutathione S-transferase (GST) and antioxidant activities was also considered. Alterations on the endocrine reproductive system were evaluated by plasma levels of vitellogenin (VTG) and the sex steroids estradiol (E2), testosterone (T), 11-ketotestosterone (11KT) and the progestin 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-P). Injection with the model compound βNF induced the hydrolysis rate of the seven CYP substrates assayed. The xenobiotic GEM induced three CYP-related activities (e.g. ECOD) and UDPGT, but depressed antioxidant defenses. EE2 induced four CYPs, more significantly ECOD and BFCOD activities. The xenoestrogens NP and EE2 altered the activities of CbE in microsomes and catalase, and were the only treatments that induced de novo VTG synthesis. In addition, the progestin 17,20β-P, was induced in NP-injected fish. None of the treatments caused statistically significant effects on steroid plasma levels. In conclusion, the CYP substrates assayed responded specifically to treatments and juveniles of S. senegalensis appear good candidates for assessing xenobiotics exposure.

Pharmacokinetic and pharmacogenetic analysis of tacrolimus in pediatric liver transplant patients in the early post-liver transplantation period

Objective: Tacrolimus is characterized by a restricted therapeutic index, a high inter- and intra-individual pharmacokinetic variability and a series of severe adverse effects. It is a substrate of cytochrome p-450 (CYP) 3A enzyme and of the drug transporter ABCB1.

ABT-450: a novel protease inhibitor for the treatment of hepatitis C virus infection.

About 2.3% of the world's population is infected with hepatitis C virus (HCV) and patients have a high risk of developing liver cirrhosis and its complications. Current therapeutic strategies are based on a combination of pegylatedinterferon, ribavirin and (only for patients with genotype 1 infection) a protease inhibitor (boceprevir or telaprevir). Consequently, all these combinations have the limitations of interferon. In fact, they are contraindicated in decompensated disease and in subjects with severe comorbidities, and are associated with a high rate of side effects. Moreover, they are poorly effective in advanced disease. As complete viral eradication is associated with improved disease-free survival, several molecules are under clinical development for their potential to overcome the drawbacks of currently available treatments. This review focuses on the pharmacodynamics, pharmacokinetics, safety and tolerability of ABT-450, a potent inhibitor of non-structural 3 protease. ABT-450 is a substrate of cytochrome P450; hence its co-administration with ritonavir, a cytochrome P450 inhibitor, dramatically increases the plasma concentration and half-life of ABT-450 and allows once-daily administration. Given in monotherapy for 3 days at different doses, ABT-450 causes a mean maximum viral decline of about 4 logs. Interestingly, high doses of ABT-450 are associated with a reduced and delayed development of resistance-conferring mutations. Given in combination with other direct antiviral drugs, the sustained response rate reaches 90-95% in both naïve and treatment-experienced genotype 1 patients, and tolerability is good. In conclusion, ABT-450 is an excellent component of interferon-free combinations for the treatment of chronic HCV infection.

Biological products for the treatment of psoriasis: therapeutic targets, pharmacodynamics and disease-drug-drug interaction implications.

Psoriasis is a chronic inflammatory skin disease condition that involves altered expression of a broad spectrum of proinflammatory cytokines which are associated with activation of T cells and proliferation of keratinocytes. Currently approved biological products for psoriasis treatment fall into two main classes: cytokine modulators and biologics targeting T cells. In psoriatic patients, elevated levels of proinflammatory cytokines are observed. Elevated proinflammatory cytokines can suppress some cytochrome P450 (CYP) enzymes, and the treatment of psoriasis with biological products can reduce proinflammatory cytokine levels. Therefore, the exposure of CYP substrate drugs is anticipated to be affected by the psoriasis disease resulting in a higher exposure than in healthy state (named disease-drug interaction) as well as by the biological treatments due to disease improvements resulting in a decrease in exposure (named disease-drug-drug interaction, disease-DDI). However, the quantitative impact on CYP substrate exposure due to disease or due to treatment with biological products remains to be evaluated. The objective of the current review is to provide an overview of the therapeutic targets and cytokine-related pharmacodynamic effects of biological products in psoriasis treatment with a particular focus on their implications for disease-DDI. The clinical study design considerations for psoriasis disease-DDI evaluation are also discussed.

Inhibition of human drug-metabolising cytochrome P450 and UDP-glucuronosyltransferase enzyme activities in vitro by uremic toxins

To investigate the potential inhibitory effects of uremic toxins on the major human hepatic drug-metabolising cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT) enzymes in vitro. Benzyl alcohol, p-cresol, indoxyl sulfate, hippuric acid and a combination of the four uremic toxins were co-incubated with human liver microsomes and selective probe substrates for the major human drug-metabolising CYP and UGT enzymes. The percentage of enzyme inhibition was calculated by measuring the rates of probe metabolite formation in the absence and presence of the uremic toxins. Kinetics studies were conducted to evaluate the K i values and mechanism(s) of the inhibition of CYP2E1, CYP3A4, UGT1A1 and UGT1A9 by p-cresol. The individual uremic toxins inhibited CYP and UGT enzymes to a variable extent. p-Cresol was the most potent individual inhibitor, producing >50% inhibition of CYP2E1, CYP3A4, UGT1A1, UGT1A9 and UGT2B7 at a concentration of 100 μM. The greatest inhibition was observed with UGT1A9. p-Cresol was shown to be an uncompetitive inhibitor of UGT1A9, with unbound K i values of 9.1 and 2.5 μM in the absence and presence of bovine serum albumin (BSA), respectively. K i values for p-cresol inhibition of human liver microsomal CYP2E1, CYP3A4 and UGT1A1 ranged from 43 to 89 μM. A combination of the four uremic toxins produced >50% decreases in the activities of CYP1A2, CYP2C9, CYP2E1, CYP3A4, UGT1A1, UGT1A9 and UGT2B7. Uremic toxins may contribute to decreases in drug hepatic clearance in individuals with kidney disease by inhibition of hepatic drug-metabolising enzymes.

Aldrin epoxidation in flathead mullet (Mugil cephalus): possible involvement of CYP1A and CYP3A.

The primary objective of this study was to determine specific cytochrome P450 isozyme(s) involved in the metabolism of aldrin to its toxic metabolite dieldrin in flathead mullet (Mugil cephalus) liver microsomes. To identify the cytochrome P450 isozyme responsible for the aldrin metabolism in mullet liver, the effects of mammalian-specific cytochrome P450 inhibitors and substrates were determined in the epoxidation reaction of aldrin. CYP3A-related inhibitors, ketoconazole, SKF-525A, and cimetidine, inhibited the metabolism of aldrin. The contribution of CYP1A to the aldrin metabolism was shown by the inhibition of 7-ethoxyresorufin-O-deethylase activity in the presence of aldrin. The results indicate that CY1A and CYP3A are the cytochrome P450s involved in aldrin epoxidase activity in mullet. In addition, the suitability of aldrin epoxidase activity for monitoring of environmental pollution was also assessed in the fish samples caught from four different locations of the West Black Sea coast of Turkey.

In Vitro and In Vivo Evaluation of the Effect of Puerarin on Hepatic Cytochrome P450-Mediated Drug Metabolism

Puerarin (8-β-D-glucopyranosyl-7-hydroxy-3-(4-hydroxyphenyl)-4H-1-benzopyran-4-one) is a major pharmacological component of Puerariae Radix, the root of Pueraria lobata. We investigated the effect of puerarin on hepatic cytochrome P450-mediated drug metabolism in rats and humans. The in vitro cytochrome P450 inhibitory effect of puerarin in human and rat liver microsomes was evaluated using the following model cytochrome P450 substrates: phenacetin for CYP1A, diclofenac for CYP2C, dextromethorphan for CYP2D, and testosterone for CYP3A. The in vivo pharmacokinetics of intravenous and oral buspirone, a probe substrate for CYP3A, was studied with single simultaneous intravenous coadministration of puerarin in rats. In the in vitro cytochrome P450 inhibition study, the rate of disappearance of testosterone was significantly reduced in the presence of 10 µM PU, while that of other cytochrome P450 substrates was not significantly affected in both human and rat liver microsomes, suggesting that puerarin inhibits the in vitro hepatic CYP3A-mediated metabolism in the human and rat systems (IC50 = 15.5 ± 3.9 µM). After intravenous administration of buspirone with single simultaneous coadministration of intravenous puerarin at a dose of 10 mg/kg in rats, the total area under the plasma concentration-time curve from time zero to time infinity was increased while time-averaged total body clearance decreased. When buspirone was orally administered in rats with the 10 mg/kg intravenous puerarin coadministration, both total area under the plasma concentration-time curve from time zero to time infinity and the extent of absolute oral bioavailability were significantly increased. Therefore, results of the in vitro microsomal and in vivo pharmacokinetic studies suggest the possible inhibition of hepatic CYP3A-mediated drug metabolism by puerarin administration, potentially leading to metabolism-mediated herb-drug interactions with clinical significance.

The prevalence of co-prescription of clinically relevant CYP enzyme inhibitor and substrate drugs in community-dwelling elderly Australians

The elderly are at increased risk of adverse effects resulting from drug interactions due to decreased drug clearance and polypharmacy. This study examines the prevalence of the co-administration of clinically relevant cytochrome P450 (CYP) enzyme inhibitors with drugs that are substrates for these enzymes, in the community-dwelling elderly in Australia. Participants aged 75years or older (n=1045) were recruited via their general practitioners at four Australian sites (Newcastle, Sydney, Melbourne and Adelaide). A research nurse visited the home of each patient to compile a list of all prescription medications (including doses) currently used by the patient, and to complete assessments for depression, quality of life and cognitive status. The medication data were searched for the co-prescription of clinically relevant CYP inhibitor and corresponding substrate drugs. Potentially inappropriate CYP inhibitor-substrate combinations were found in 6·2% (65/1045) of patients. These patients were on significantly more medications (6·1±3·0 vs. 3·9±2·5; P=0·001) and had a significantly lower physical quality of life (P=0·047) than those who were not on any CYP inhibitor-substrate combinations. The most commonly prescribed inhibitor-substrate combinations involved the CYP 3A4 inhibitors, diltiazem and verapamil, with the substrates simvastatin or atorvastatin. Only 1 of 41 patients on a CYP3A4 inhibitor and a statin was prescribed a non-CYP 3A4 metabolized statin. Metoprolol was another substrate commonly co-prescribed with a CYP2D6 inhibitor. In many cases, the risks and benefits of potential interactions may have been considered by the GP as the prescribed doses of both the inhibitor and substrate were relatively low. There were, however, some notable exceptions, also involving the substrates simvastatin, atorvastatin and metoprolol. There were no GP factors that were associated with co-prescription of CYP inhibitors and substrates. There is not a particular GP demographic that should be targeted for education regarding CYP interactions, but a focus on particular medications such as the statins may reduce the potential for clinically significant drug-drug interactions. As CYP drug-drug interactions are more common in patients on higher number of medications, particular vigilance is required at the time of prescribing and dispensing medications for elderly patients with multiple conditions.

Impact of 17-alpha-hydroxyprogesterone caproate on cytochrome P450s in primary cultures of human hepatocytes

The aim of this study was to examine the effects of 17-alpha-hydroxyprogesterone caproate (17OHP-C) on the activity and expression of several common hepatic cytochrome P450 (CYP) enzymes. Primary human hepatocytes were pretreated with vehicle or 17OHP-C (0.1 and 1 μmol/L) for 72 hours, then incubated for 1 hour with a cocktail of CYP substrates. The activity of various CYP enzymes was determined by measuring the formation of the metabolites of specific CYP substrates, using liquid chromatography-tandem mass spectrometry. The messenger RNA expression of various CYP enzymes was determined by real-time polymerase chain reaction. In primary cultures of human hepatocytes, 17OHP-C minimally altered the activity or messenger RNA levels of CYP1A2, CYP2C9, CYP2D6, and CYP3A. However, 17OHP-C at 1 μmol/L increased CYP2C19 activity by 2.8-fold (P < .01) and CYP2C19 expression by 2.4-fold (P < .001), compared with vehicle-treated cells. A strong positive correlation between activity and expression of CYP2C19 was also observed (r= 0.9, P < .001). The activity and expression of hepatic CYP2C19 was significantly increased by 17OHP-C in primary cultures of human hepatocytes. This suggests that exposure to medications that are metabolized by CYP2C19 may be decreased in pregnant patients receiving 17OHP-C. Metabolism of substrates of CYP1A2, CYP2C9, CYP2D6, and CYP3A are not expected to be altered in patients receiving 17OHP-C.

Effects of dietary sodium butyrate on hepatic biotransformation and pharmacokinetics of erythromycin in chickens

Butyrate, a commonly applied feed additive in poultry nutrition, can modify the expression of certain genes, including those encoding cytochrome P450 (CYP) enzymes. In comparative in vitro and in vivo experiments, the effect of butyrate on hepatic CYP genes was examined in primary cultures of chicken hepatocytes and in liver samples of chickens collected from animals that had been given butyrate as a feed additive. Moreover, the effect of butyrate on the biotransformation of erythromycin, a marker substance for the activity of enzymes of the CYP3A family, was investigated in vitro and in vivo. Butyrate increased the expression of the avian-specific CYP2H1 both in vitro and in vivo. In contrast, the avian CYP3A37 expression was decreased in hepatocytes following butyrate exposure, but not in the in vivo model. CYP1A was suppressed by butyrate in the in vitro experiments, and overexpressed in vivo in butyrate-fed animals. The concomitant incubation of hepatocytes with butyrate and erythromycin led to an increased CYP2H1 expression and a less pronounced inhibition of CYP3A37. In in vivo pharmacokinetic experiments, butyrate-fed animals given a single i.m. injection of erythromycin, a slower absorption phase (longer T(half-abs) and delayed T(max)) but a rapid elimination phase of this marker substrate was observed. Although these measurable differences were detected in the pharmacokinetics of erythromycin, it is unlikely that a concomitant application of sodium butyrate with erythromycin or other CYP substrates will cause clinically significant feed-drug interaction in chickens.

PS-052 Incidence and description of interactions between Imatinib and other drugs in patients with Chronic Myeloid Leukaemia

BackgroundImatinib, a tyrosine kinase inhibitor (TKI), is a substrate and inhibitor of cytochrome P450, therefore imatinib can be affected by concomitant drugs or a change in the concentration of other...

Simultaneous and comprehensive in vivo analysis of cytochrome P450 activity by using a cocktail approach in rats

A cocktail approach can detect the activities of multiple cytochrome P450 (CYP) isoforms following the administration of multiple CYP-specific substrates in a single experiment. This study aimed to develop a simultaneous and comprehensive in vivo analysis of CYP activity in rats. The rats received an oral administration of losartan (10 mg/kg) and omeprazole (40 mg/kg). Caffeine (1 mg/kg), dextromethorphan (10 mg/kg) and midazolam (10 mg/kg) were administered 15 min later. In the drug-interaction phase, the rats were treated orally with dexamethasone (80 mg/kg) 24 h before, or with ketoconazole (10 mg/kg), fluvoxamine (100 mg kg) or fluconazole (10 mg/kg) 1 h before the administration of cocktail drugs. The concentrations of the drugs and their metabolites were determined by LC/MS/MS. Plasma concentrations of five CYP substrates and their metabolites were simultaneously evaluated after the oral drug administration. Fluvoxamine and fluconazole significantly increased the Cmax and AUC of caffeine, and the AUC of omeprazole and midazolam. Dexamethasone significantly increased Cmax and AUC of losartan, while it decreased the Cmax of midazolam. Ketoconazole showed no significant effect on the pharmacokinetic parameters of the tested drugs. In conclusion, a cocktail approach was developed for simultaneous and comprehensive analysis of the activities of multiple CYP isoforms in rats. In this approach, the effects of inhibitors and an inducer of various CYP isoforms were examined. Although further studies are necessary to predict the effects in humans, this approach may be expected to serve as a convenient method for detecting drug-drug interactions in rats.

Two-way interaction study between ritonavirboosted danoprevir, a potent HCV protease inhibitor, and ketoconazole in healthy subjects

Danoprevir is a potent, highly selective, macrocyclic, orally bioavailable inhibitor of the hepatitis C virus protease, and a substrate of cytochrome P450 (CYP) 3A. It is co-administered with low-dose ritonavir, a potent CYP3A inhibitor, to enhance danoprevir pharmacokinetics. Ketoconazole is a substrate for and potent selective inhibitor of CYP3A. In this open-label, 3-period study, the 2-way interaction potential between ritonavir-boosted danoprevir (danoprevir/r) and ketoconazole was investigated in 18 healthy subjects. Subjects initially received ketoconazole 200 mg q24h for 4 days (Period 1) followed by a 7-day washout period. Danoprevir/r 100/100 mg q12h was then given for 10 days (Period 2) followed by a further 4 days of danoprevir/r 100/100 mg q12h plus ketoconazole 200 mg q24h (Period 3). Serial blood samples were collected for the determination of danoprevir, ritonavir and/or ketoconazole plasma concentrations, and calculation of pharmacokinetic parameters. Safety and tolerability were monitored throughout the study. Co-administration of ketoconazole with danoprevir/r modestly increased the danoprevir AUCτ by 1.44-fold, with no effect on danoprevir Cmax. Co-administration of danoprevir/r with ketoconazole substantially increased ketoconazole AUCτ and Cmax by 3.71-fold and 1.73-fold, respectively. Danoprevir/r was well tolerated when administered alone or with ketoconazole. These results indicate that the effect of potent CYP3A inhibitors, such as ketoconazole, on danoprevir/r pharmacokinetics is not likely to be clinically relevant.

Simultaneous LC-MS/MS Analysis of the Plasma Concentrations of a Cocktail of 5 Cytochrome P450 Substrate Drugs and Their Metabolites

A "cocktail" approach, which involves simultaneous administration of multiple CYP-specific probes, concurrently detects the activity of multiple CYP enzymes. We developed and validated a rapid and selective LC-MS/MS method for determining the plasma concentrations of 5 CYP probe drugs and metabolites (caffeine/paraxanthine, CYP1A2 substrate; losartan/losartan carboxylic acid (E3174), CYP2C9 substrate; omeprazole/5-hydroxyomeprazole, CYP2C19 substrate; dextromethorphan/dextrorphan, CYP2D6 substrate; and midazolam/1'-hydroxymidazolam, CYP3A4 substrate) by single-step extraction, followed by a single LC-MS/MS run. An Ostro™ 96-well plate was used for extraction of CYP substrates and metabolites from human plasma and urine. Following optimization of the chromatographic conditions, all the peaks were well separated, and retention times ranged between 4.4 and 11.7 min. The total run time for a single injection was within 13 min. The accuracy and precision values suggested that the assay had high accuracy and reliability in plasma and urine samples. No significant matrix interference was observed. To demonstrate the efficacy of this method, plasma and urine concentrations of 5 CYP probe substrates and their metabolites were determined after simultaneous oral administration of 5 drugs to 4 healthy volunteers. All the substrates and metabolites were detected over an 8 h period, and the plasma concentrations of each substrate at 8 h after administration were above the lower limit of quantification. Urine concentrations of drugs and their metabolic ratio were evaluated after the administration. In conclusion, the advantage of our cocktail approach is that it enables in vivo assessment of the activity of various drug-metabolizing enzymes in a single assay.