(-)-N-3-Benzylphenobarbital Is Superior to Omeprazole and (+)-N-3-Benzylnirvanol as a CYP2C19 Inhibitor in Suspended Human Hepatocytes.

Early assessment of metabolism pathways of new chemical entities guides the understanding of drug-drug interactions. Selective enzyme inhibitors are indispensable in CYP reaction phenotyping. The most commonly applied CYP2C19 inhibitor, omeprazole, lacks selectivity. Two promising alternatives, (+)-N-3-benzylnirvanol and (-)-N-3-benzylphenobarbital, are already used as CYP2C19 inhibitors in some in vitro studies with suspended human hepatocytes. However, a full validation proving their suitability in terms of CYP and non-CYP selectivity has not been presented in literature. The present study provides a thorough comparison between omeprazole, (+)-N-3-benzylnirvanol, and (-)-N-3-benzylphenobarbital in terms of potency and selectivity and shows the superiority of (-)-N-3-benzylphenobarbital as a CYP2C19 inhibitor in suspended human hepatocytes. Furthermore, we evaluated the application of (-)-N-3-benzylphenobarbital to predict the in vivo contribution of CYP2C19 to drug metabolism [fraction metabolized (fm) of CYP2C19, fmCYP2C19]. A set of 10 clinically used CYP2C19 substrates with reported in vivo fmCYP2C19 data was evaluated. fmCYP2C19, which was predicted using data from suspended human hepatocyte incubations, underestimated the in vivo fmCYP2C19 The use of a different hepatocyte batch with a different CYP3A4/CYP2C19 activity ratio showed the impact of intrinsic CYP activities on the determination of fmCYP2C19 Overall, this study confirms the selective CYP2C19 inhibition by (-)-N-3-benzylphenobarbital over other CYP isoforms (CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2D6, and CYP3A4) and clinically relevant non-CYP enzymes [aldehyde oxidase, flavin-containing monooxygenase 3, N-acetyltransferase 2, uridine diphosphate glucuronosyltransferase (UGT) 1A1, UGT1A4, UGT2B7, UGT2B15] in suspended human hepatocytes. (-)-N-3-benzylphenobarbital is therefore the preferred CYP2C19 inhibitor to assess fmCYP2C19 in suspended human hepatocytes in comparison with omeprazole and (+)-N-3-benzylnirvanol. SIGNIFICANCE STATEMENT: (-)-N-3-Benzylphenobarbital is a more potent and selective inhibitor of CYP2C19 in suspended human hepatocytes than omeprazole and (+)-N-3-benzylnirvanol. (-)-N-3-Benzylphenobarbital can be used to predict the fraction metabolized by CYP2C19 in suspended human hepatocytes.

Clinical implications of trials investigating drug-drug interactions between cannabidiol and enzyme inducers or inhibitors or common antiseizure drugs.

Highly purified cannabidiol (CBD) has demonstrated efficacy with an acceptable safety profile in patients with Lennox-Gastaut syndrome or Dravet syndrome in randomized, double-blind, add-on, controlled phase 3 trials. It is important to consider the possibility of drug-drug interactions (DDIs). Here, we review six trials of CBD (Epidiolex/Epidyolex; 100 mg/mL oral solution) in healthy volunteers or patients with epilepsy, which investigated potential interactions between CBD and enzymes involved in drug metabolism of common antiseizure drugs (ASDs). CBD did not affect CYP3A4 activity. Induction of CYP3A4 and CYP2C19 led to small reductions in exposure to CBD and its major metabolites. Inhibition of CYP3A4 activity did not affect CBD exposure and caused small increases in exposure to CBD metabolites. Inhibition of CYP2C19 activity led to a small increase in exposure to CBD and small decreases in exposure to CBD metabolites. One potentially clinically important DDI was identified: combination of CBD and clobazam (CLB) did not affect CBD or CLB exposure, but increased exposure to major metabolites of both compounds. Reduction of CLB dose may be considered if adverse reactions known to occur with CLB are experienced when it is coadministered with CBD. There was a small increase of exposure to stiripentol (STP) when coadministered with CBD. STP had no effect on CBD exposure but led to minor decreases in exposure to CBD metabolites. Combination of CBD and valproate (VPA) did not cause clinically important changes in the pharmacokinetics of either drug, or 2-propyl-4-pentenoic acid. Concomitant VPA caused small increases in exposure to CBD metabolites. Dose adjustments are not likely to be necessary when CBD is combined with STP or VPA. The safety results from these trials were consistent with the known safety profile of CBD. These trials indicate an overall low potential for DDIs between CBD and other ASDs, except for CLB.

Population pharmacokinetics of the MEK inhibitor selumetinib and its active N-desmethyl metabolite: data from 10 phase I trials.

AIMS: The aims of the study were to characterize the pharmacokinetics (PK) of selumetinib (AZD6244; ARRY-142886), a mitogen-activated protein kinase kinase (MEK) 1/2 inhibitor in clinical development for various indications, and its N-desmethyl metabolite in healthy volunteers, and evaluate clinically important covariates. METHODS: A pooled-population PK analysis was performed using a nonlinear mixed-effects approach with plasma concentration data from 346 subjects who received single oral doses of selumetinib 20-75 mg across 10 phase I studies. Absolute bioavailability was determined using intravenous [14 C] selumetinib. RESULTS: A two-compartment linear model with sequential zero-first order absorption and a lag time for the zero-order process was described for selumetinib PK. N-desmethyl metabolite disposition was described by a single compartment with linear elimination, without back transformation. The parent-only and joint models generally described pooled data adequately. For the median subject, not taking interacting drugs, estimates for clearance (CL) and central volume of distribution (V2) for selumetinib in the final joint model were 12.7 l h-1 and 35.6 l, respectively. Food effects, comedication with itraconazole [a cytochrome P450 (CYP) 3A4 inhibitor], fluconazole (a CYP2C19 inhibitor) and rifampicin (a CYP3A4 inducer) and formulation effects were incorporated into the base model a priori. Race and hepatic function were also influential in the PK model. Additional covariates affecting selumetinib disposition identified from covariate analysis were age on V2, bilirubin on CL, and weight on CL and V2. CONCLUSIONS: Analysis confirmed previous clinical pharmacology study findings of drug-drug interactions and food effects, with additional covariates that influence selumetinib and N-desmethyl selumetinib PK identified. Dose modifications based on these additional covariates were not considered necessary.

Impact of Drug Interactions on Clobazam and N-Desmethylclobazam Concentrations in Pediatric Patients With Epilepsy.

BACKGROUND: Clobazam (CLB) is approved as adjunctive treatment for seizures associated with Lennox-Gastaut syndrome in patients aged 2 years and older. It is converted to an active metabolite N-desmethylclobazam (NCLB) by CYP3A4, which is then broken down to an inactive metabolite by CYP2C19. This study characterizes the impact of CYP3A4 and CYP2C19 drug interactions on CLB and NCLB serum concentrations (Cp) and concentration/dose (Cp/D) ratios in pediatric patients with epilepsy. METHODS: This was a retrospective chart review including patients older than 1 month, who received CLB between April 2012 and March 2017. Extracted data included patient demographics, CLB daily dose, CLB and NCLB Cp, calculated CLB and NCLB Cp/Cp and Cp/D ratios, and all concomitant drugs. RESULTS: The study included 995 CLB concentration sets from 302 patients (median age 7.6 years and range 0.2-40.1 years). Pharmacokinetic variability was extensive, as seen by widespread ranges of CLB and NCLB Cp, NCLB/CLB Cp ratio, and 3 Cp/D ratios (CLB, NCLB, and CLB + NCLB). Comedications, described as CYP3A4 inducers and/or CYP2C19 inhibitors (carbamazepine, eslicarbazepine, felbamate, (fos)phenytoin, oxcarbazepine, pentobarbital, phenobarbital, rufinamide, and topiramate), generally increased NCLB/CLB Cp ratio (267%-400%), NCLB Cp/D ratio (167%-202%), and CLB + NCLB Cp/D ratio (142%-185%) and decreased CLB Cp/D ratio (47%-76%) compared with a group of concentration sets in patients receiving only neutral comedications (P < 0.025 for all comparisons). Older age was associated with higher Cp/D ratios (mg/kg), indicative of decreased clearance. CONCLUSIONS: Pharmacokinetic variability of CLB in pediatric patients is extensive, and it is influenced by drug-drug interactions and age. Therapeutic drug monitoring of CLB and active metabolite NCLB with calculation of various Cp/Cp and Cp/D ratios can provide useful insight into CLB pharmacokinetics and help differentiate between causes of variability.

Substantial Impairment of Voriconazole Clearance by High-Dose Meropenem in a Patient With Renal Failure.

A critically ill patient with multiple postoperative infections repeatedly required profound voriconazole dose reductions whenever high-dose meropenem was added. Subsequent in vitro assessment confirmed inhibition of cytochrome P450 (CYP) 2C19 and CYP3A4 by meropenem, suggesting that during meropenem treatment, narrow therapeutic index drugs metabolized by these CYPs require close monitoring.

Synthesis and pharmacological evaluation of glycine amide derivatives as novel vascular adhesion protein-1 inhibitors without CYP3A4 and CYP2C19 inhibition.

Vascular adhesion protein-1 (VAP-1) is a promising therapeutic target for the treatment of diabetic nephropathy. Here, we conducted optimization studies of our lead compound 1, which we previously reported as a novel VAP-1 inhibitor, to enhance the inhibition of human VAP-1 and to reduce CYP3A4 and CYP2C19 inhibition. As a result, we identified 3-chloro-4-{4-[5-(3-{[glycyl(methyl)amino]methyl}phenyl)pyrimidin-2-yl]piperazin-1-yl}benzoic acid (17h) as a novel orally active VAP-1 inhibitor, with 14-fold increased human VAP-1 inhibitory activity compared to 1, without CYP3A4 and CYP2C19 inhibition. Oral administration of 17h significantly inhibited the progression of proteinuria in streptozotocin (STZ) induced diabetic rats at 0.3 and 1mg/kg, suggesting that this compound has potential to be a therapeutic agent for the treatment of diabetic nephropathy.

Effects of cytochrome P450 (CYP3A4 and CYP2C19) inhibition and induction on the exposure of selumetinib, a MEK1/2 inhibitor, in healthy subjects: results from two clinical trials.

PURPOSE: Two phase I, open-label trials in healthy subjects assessed whether co-administration with CYP3A4/CYP2C19 inhibitors, itraconazole/fluconazole (study A), or CYP3A4 inducer, rifampicin (study B), affects the exposure, safety/tolerability and pharmacokinetics of selumetinib and its metabolite N-desmethyl selumetinib. METHODS: In study A (n = 26), subjects received a single dose of selumetinib 25 mg and, after 4 days of washout, were randomized to treatment 1 (itraconazole 200 mg twice daily on days 1-11) or treatment 2 (fluconazole 400 mg on day 1 then 200 mg/day on days 2-11) plus co-administration of single-dose selumetinib 25 mg on day 8 (selumetinib staggered 4 h after itraconazole/fluconazole dose); Twenty-one days after discharge/washout, subjects received the alternate treatment. In study B (n = 22), subjects received a single dose of selumetinib 75 mg (day 1) then rifampicin 600 mg/day (days 4-14) plus a single dose of selumetinib 75 mg on day 12. Pharmacokinetic analysis and safety assessments were performed. RESULTS: Selumetinib co-administered with itraconazole, fluconazole (selumetinib staggered 4 h after itraconazole/fluconazole dose), or rifampicin was well tolerated. Selumetinib exposure was higher when co-administered with itraconazole or fluconazole (area under the plasma concentration-time curve (AUC) increased by 49 and 53%, respectively; maximum plasma concentration (C max) increased by 19 and 26%, respectively) but lower when co-dosed with rifampicin (AUC and C max decreased by 51 and 26%, respectively) versus selumetinib dosed alone. Co-administration with itraconazole or rifampicin decreased N-desmethyl selumetinib AUC(0-t) (11 and 55%, respectively), and C max (25 and 18%, respectively), with fluconazole, AUC(0-t) increased by 40%, but there was no effect on C max. CONCLUSIONS: Co-administration of CYP3A4/CYP2C19 inhibitors will likely increase exposure to selumetinib, while CYP3A4 inducers will likely reduce its exposure.

Effects of Dual-Dose Clopidogrel, Clopidogrel Combined with Tongxinluo Capsule, and Ticagrelor on Patients with Coronary Heart Disease and CYP2C19*2 Gene Mutation After Percutaneous Coronary Interventions (PCI).

BACKGROUND In recent years, genetic factors have attracted research interest as important predisposing factors for cardiovascular susceptibility. This study aimed to investigate the influences of dual-dose clopidogrel, clopidogrel combined with tongxinluo, and ticagrelor on the platelet activity and MACE events of patients with CYP2C19*2 gene function deficiency and poor clopidogrel response after PCI. MATERIAL AND METHODS We selected 458 patients with coronary heart disease undergoing PCI, and the genotype of CYP2C19*2 was detected by TaqMan real-time PCR. We finally enrolled 212 patients and divided them into 4 groups: a standard anti-platelet group of 46 patients, a clopidogrel double-dose group of 50 cases, a clopidogrel combined with tongxinluo group of 59 cases, and a ticagrelor group of 57. The platelet inhibition rate was detected by TEG. We analyzed and compared differences in platelet activity and the occurrence of MACE events in these 4 groups at different follow-up times. RESULTS The results showed that inhibition of platelet aggregation was better in the double-dose clopidogrel group, the clopidogrel combined with tongxinluo group, and the ticagrelor group than in the regular-dose clopidogrel group, and ticagrelor was the best. We also found that the total incidence of MACE was much lower in the double-dose clopidogrel group, the clopidogrel combined with tongxinluo group, and the ticagrelor group, while the incidence of hemorrhage in the ticagrelor group was higher. CONCLUSIONS Adjusting the dose or combining with other drugs improves the efficacy of anti-platelet therapy and reduces the incidence of ischemic events after PCI.

Use of Human Plasma Samples to Identify Circulating Drug Metabolites that Inhibit Cytochrome P450 Enzymes.

Drug interactions elicited through inhibition of cytochrome P450 (P450) enzymes are important in pharmacotherapy. Recently, greater attention has been focused on not only parent drugs inhibiting P450 enzymes but also on possible inhibition of these enzymes by circulating metabolites. In this report, an ex vivo method whereby the potential for circulating metabolites to be inhibitors of P450 enzymes is described. To test this method, seven drugs and their known plasma metabolites were added to control human plasma at concentrations previously reported to occur in humans after administration of the parent drug. A volume of plasma for each drug based on the known inhibitory potency and time-averaged concentration of the parent drug was extracted and fractionated by high-pressure liquid chromatography-mass spectrometry, and the fractions were tested for inhibition of six human P450 enzyme activities (CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP3A4). Observation of inhibition in fractions that correspond to the retention times of metabolites indicates that the metabolite has the potential to contribute to P450 inhibition in vivo. Using this approach, norfluoxetine, hydroxyitraconazole, desmethyldiltiazem, desacetyldiltiazem, desethylamiodarone, hydroxybupropion, erythro-dihydrobupropion, and threo-dihydrobupropion were identified as circulating metabolites that inhibit P450 activities at a similar or greater extent as the parent drug. A decision tree is presented outlining how this method can be used to determine when a deeper investigation of the P450 inhibition properties of a drug metabolite is warranted.

Time-Dependent Inhibition of CYP2C19 by Isoquinoline Alkaloids: In Vitro and In Silico Analysis.

The cytochrome P450 2C19 (CYP2C19) enzyme plays an important role in the metabolism of many commonly used drugs. Relatively little is known about CYP2C19 inhibitors, including compounds of natural origin, which could inhibit CYP2C19, potentially causing clinically relevant metabolism-based drug interactions. We evaluated a series (N = 49) of structurally related plant isoquinoline alkaloids for their abilities to interact with CYP2C19 enzyme using in vitro and in silico methods. We examined several common active alkaloids found in herbal products such as apomorphine, berberine, noscapine, and papaverine, as well as the previously identified mechanism-based inactivators bulbocapnine, canadine, and protopine. The IC50 values of the alkaloids ranged from 0.11 to 210 µM, and 42 of the alkaloids were confirmed to be time-dependent inhibitors of CYP2C19. Molecular docking and three-dimensional quantitative structure-activity relationship analysis revealed key interactions of the potent inhibitors with the enzyme active site. We constructed a comparative molecular field analysis model that was able to predict the inhibitory potency of a series of independent test molecules. This study revealed that many of these isoquinoline alkaloids do have the potential to cause clinically relevant drug interactions. These results highlight the need for studying more profoundly the potential interactions between drugs and herbal products. When further refined, in silico methods can be useful in the high-throughput prediction of P450 inhibitory potential of pharmaceutical compounds.

Physiologically based pharmacokinetic modeling for sequential metabolism: effect of CYP2C19 genetic polymorphism on clopidogrel and clopidogrel active metabolite pharmacokinetics.

Clopidogrel is a prodrug that needs to be converted to its active metabolite (clopi-H4) in two sequential cytochrome P450 (P450)-dependent steps. In the present study, a dynamic physiologically based pharmacokinetic (PBPK) model was developed in Simcyp for clopidogrel and clopi-H4 using a specific sequential metabolite module in four populations with phenotypically different CYP2C19 activity (poor, intermediate, extensive, and ultrarapid metabolizers) receiving a loading dose of 300 mg followed by a maintenance dose of 75 mg. This model was validated using several approaches. First, a comparison of predicted-to-observed area under the curve (AUC)0-24 obtained from a randomized crossover study conducted in four balanced CYP2C19-phenotype metabolizer groups was performed using a visual predictive check method. Second, the interindividual and intertrial variability (on the basis of AUC0-24 comparisons) between the predicted trials and the observed trial of individuals, for each phenotypic group, were compared. Finally, a further validation, on the basis of drug-drug-interaction prediction, was performed by comparing observed values of clopidogrel and clopi-H4 with or without dronedarone (moderate CYP3A4 inhibitor) coadministration using a previously developed and validated physiologically based PBPK dronedarone model. The PBPK model was well validated for both clopidogrel and its active metabolite clopi-H4, in each CYP2C19-phenotypic group, whatever the treatment period (300-mg loading dose and 75-mg last maintenance dose). This is the first study proposing a full dynamic PBPK model able to accurately predict simultaneously the pharmacokinetics of the parent drug and of its primary and secondary metabolites in populations with genetically different activity for a metabolizing enzyme.

Effects of capsicine on rat cytochrome P450 isoforms CYP1A2, CYP2C19, and CYP3A4.

Due to the frequent consumption of capsaicin (CAP) and its current therapeutic application, the correct assessment of this compound is important from a public health standpoint. The purpose of this study was to find out whether CAP affects rat cytochrome P450 (CYP) enzymes (CYP1A2, CYP2C19, and CYP3A4) by using cocktail probe drugs in vivo. A cocktail solution at a dose of 5 mL/kg, which contained phenacetin (15 mg/kg), omeprazole (15 mg/kg), and midazolam (10 mg/kg), was given orally to rats treated for 7 d with oral administration of CAP. Blood samples were collected at a series of time-points and the concentrations of probe drugs in plasma were determined by HPLC-MS. The results showed that treatment with multiple doses of CAP had no significant effect on rat CYP1A2. However, CAP had a significant inhibitory effect on CYP2C19 and an inductive effect on CYP3A4. Therefore, caution is needed when CAP is co-administered with some CYP substrates clinically because of potential drug-CAP interactions.

Phenoconversion Due to Drug-Drug Interactions in CYP2C19 Genotyped Healthy Volunteers.

To compensate for drug response variability, drug metabolism phenotypes are determined based on the results of genetic testing, and if necessary, drug dosages are adjusted. In some cases, discrepancies between predicted and observed phenotypes (phenoconversion) may occur due to drug-drug interactions caused by concomitant medications. We conducted a prospective, exploratory study to evaluate the risk of CYP2C19 phenoconversion in genotyped healthy volunteers exposed to CYP2C19 inhibitors. Three groups of volunteers were enrolled: CYP2C19 g-RM, g-NM, and g-IM (g- for genetically predicted). All volunteers received as CYP2C19 phenotyping substrate 10 mg omeprazole (OME) alone at the control session and in co-administration with CYP2C19 inhibitors: voriconazole 400 mg and fluvoxamine 50 mg in second and third study sessions, respectively. Phenoconversion occurred in over 80% of healthy volunteers, with variations among genotypic groups, revealing distinct proportions in response to fluvoxamine and voriconazole. Statistically significant differences were observed in mean metabolic ratios between CYP2C19 intermediate metabolizers (g-IMs) with *1/*2 and *2/*17 genotypes, with the *2/*17 group exhibiting lower ratios, and distinctions were noted between genotypic groups, emphasizing the impact of genetic variations on drug metabolism. When reclassified according to CYP2C19 baseline-measured phenotype into p-RM, p-NM, and p-IM (p- for measured phenotype), we observed 100% phenoconversion of p-RMs and a significant phenotype switch in p-NMs, p-IMs, and p-PMs after fluvoxamine and voriconazole, and complete phenoconversion of p-IMs to p-PMs on both inhibitors, emphasizing the impact of genetic variations on the vulnerability to CYP2C19 phenoconversion and the importance of considering both genotyping and phenotyping in predicting drug response.

Advancements in physiologically based pharmacokinetic modeling for fedratinib: updating dose guidance in the presence of a dual inhibitor of CYP3A4 and CYP2C19.

PURPOSE: A physiologically based pharmacokinetic (PBPK) model for fedratinib was updated and revalidated to bridge a gap between the observed drug-drug interaction (DDI) of a single sub-efficacious dose in healthy participants and the potential DDI in patients with cancer at steady state. The study aimed to establish an appropriate dose for fedratinib in patients coadministered with dual CYP3A4 and CYP2C19 inhibitors, providing quantitative evidence to inform dosing guidance. METHODS: The original minimal PBPK model was developed using Simcyp® Simulator v17. The model was updated by substituting a single distribution rate (Qsac) with 2 separate rates (CLin/CLout) and transitioning to v20. Model parameter updates were further informed with 3 clinical studies, and 3 more studies served as independent validation data. The validated model was applied to simulate potential DDIs between fedratinib and a known dual inhibitor of CYP3A4 and CYP2C19 (fluconazole). RESULTS: Coadministration of fedratinib with fluconazole in patients was predicted to increase fedratinib exposure by < 2-fold in all simulated scenarios. For patients with cancer receiving the approved dose of fedratinib 400 mg once daily along with fluconazole 200 mg daily, the model predicted an approximate 50% increase in fedratinib exposure at steady state. CONCLUSIONS: The updated PBPK model improved description of the observed pharmacokinetics and predicted a low risk of clinically significant DDIs between fedratinib and fluconazole. The quantitative evidence serves as a primary foundation for providing dose guidance in clinical practice for the coadministration of fedratinib with dual CYP3A4 and CYP2C19 inhibitors.

Prediction of cytochromes P450 3A and 2C19 modulation by both inflammation and drug interactions using physiologically based pharmacokinetics.

Xenobiotics can interact with cytochromes P450 (CYPs), resulting in drug-drug interactions, but CYPs can also contribute to drug-disease interactions, especially in the case of inflammation, which downregulates CYP activities through pretranscriptional and posttranscriptional mechanisms. Interleukin-6 (IL-6), a key proinflammatory cytokine, is mainly responsible for this effect. The aim of our study was to develop a physiologically based pharmacokinetic (PBPK) model to foresee the impact of elevated IL-6 levels in combination with drug interactions with esomeprazole on CYP3A and CYP2C19. Data from a cohort of elective hip surgery patients whose CYP3A and CYP2C19 activities were measured before and after surgery were used to validate the accurate prediction of the developed models. Successive steps were to fit models for IL-6, esomeprazole, and omeprazole and its metabolite from the literature and to validate them. The models for midazolam and its metabolite were obtained from the literature. When appropriate, a correction factor was applied to convert drug concentrations from whole blood to plasma. Mean ratios between simulated and observed areas under the curve for omeprazole/5-hydroxy omeprazole, esomeprazole, and IL-6 were 1.53, 1.06, and 0.69, respectively, indicating an accurate prediction of the developed models. The impact of IL-6 and esomeprazole on the exposure to CYP3A and CYP2C19 probe substrates and respective metabolites were correctly predicted. Indeed, the ratio between predicted and observed mean concentrations were <2 for all observations (ranging from 0.51 to 1.7). The impact of IL-6 and esomeprazole on CYP3A and CYP2C19 activities after a hip surgery were correctly predicted with the developed PBPK models.

Inhibition of cytochrome P450 enzymes and uridine 5'-diphospho-glucuronosyltransferases by vicagrel in human liver microsomes: A prediction of potential drug-drug interactions.

Vicagrel, an antiplatelet drug candidate targeting platelet P2Y12 receptor and has finished its phase II clinical trial. The inhibition of six major cytochrome P450 enzymes (P450) (CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP3A4) and six UDP-glucuronosyltransferases (UGT) (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, and UGT2B7) by vicagrel was evaluated using pooled human liver microsomes and specific probe substrates. Physiology-based pharmacokinetic (PBPK) simulation was further applied to predict the in vivo drug-drug interaction (DDI) potential between vicagrel and bupropion as well as S-mephenytoin. The results suggested that vicagrel inhibited CYP2B6 and CYP2C19 potently with apparent IC50 values of 1.6 and 2.0 µM, respectively. In terms of mode of reversible inhibition, vicagrel exhibited mixed-type inhibition of CYP2B6-catalyzed bupropion hydroxylation and noncompetitive inhibition of CYP2C19-mediated S-mephenytoin 4'-hydroxylation with Ki values of 0.19 µM and 1.2 µM, respectively. Vicagrel displayed profound time-dependent inhibition towards CYP2B6 with maximal rate constant of inactivation (kinact) and half-maximal inactivator concentration (KI) values of 0.062 min-1 and 1.52 µM, respectively. No time-dependent inhibition by vicagrel was noted for CYP2C19. For UGT, negligible to moderate inhibition by vicagrel was observed with IC50 values of >50.0, >50.0, 28.2, 8.7, >50.0 and 28.2 µM for UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9 and UGT2B7, respectively. In terms of mode of reversible inhibition, vicagrel exhibited mixed-type inhibition of UGT1A6-catalyzed N-Acetylserotonin ß-D-glucuronidation with a Ki value of 5.6 µM. No time-dependent inhibition by vicagrel was noted for UGT1A6. PBPK simulation indicated that neither altered AUC nor Cmax of bupropion and S-mephenytoin was observed in the presence of vicagrel. Our study provides inhibitory constants for future DDI prediction between vicagrel and drug substrates of CYP2B6, CYP2C19 and UGT1A6. In addition, our simulation suggests the lack of clinically important DDI between vicagrel and bupropion or S-mephenytoin.

Clopidogrel Dosing: Current Successes and Emerging Factors for Further Consideration.

This review aimed to evaluate the clinical success of clopidogrel dosing based on CYP2C19 genotype and to identify the relevant additional factors that may be useful for consideration by the clinician when dosing individuals with clopidogrel. The results indicated that genotype-guided dosing in individuals with acute coronary syndrome undergoing percutaneous coronary intervention is frequently practiced, although the advantages remain controversial. Demographic factors, such as age, ethnicity, and some comorbidities, such as diabetes mellitus, can potentially contribute to further refinement of clopidogrel dosage but additional clinical studies to guide these practices are required. Drugs that are CYP2C19 or CYP3A4 inhibitors may reduce the effectiveness of clopidogrel and should be carefully considered during co-administration. In particular, as stated in the clopidogrel label, concomitant use with strong or moderate CYP2C19 inhibitors, such as omeprazole, should be avoided. Increased exposure and response to clopidogrel has been observed in smokers. Noteworthy, a very recent study has shown that smoking cessation in clopidogrel patients may result in reduced response and carries the risk of high on-clopidogrel platelet reactivity. Recent studies have shown clinically significant increases in exposure to CYP2C8 substrates (repaglinide, dasabuvir, and desloratadine) and a CYP2B6 substrate (s-sibutramine) following co-administration with clopidogrel, indicating that therapeutic strategies with clopidogrel should avoid these drugs.

Enantioselective inhibition of human CYP2C19 by the chiral pesticide ethofumesate: Prediction of pesticide-drug interactions in humans.

Ethofumesate is a chiral herbicide that may display enantioselective behavior in humans. For this reason, the enantioselective potential of ethofumesate and its main metabolite ethofumesate-2-hydroxy to cause pesticide-drug interactions on cytochrome P450 forms (CYPs) has been evaluated by using human liver microsomes. Among the evaluated CYPs, CYP2C19 had its activity decreased by the ethofumesate racemic mixture (rac-ETO), (+)-ethofumesate ((+)-ETO), and (-)-ethofumesate ((-)-ETO). CYP2C19 inhibition was not time-dependent, but a strong inhibition potential was observed for rac-ETO (IC50 = 5 ± 1 µmol L-1), (+)-ETO (IC50 = 1.6 ± 0.4 µmol L-1), and (-)-ETO (IC50 = 1.8 ± 0.4 µmol L-1). The reversible inhibition mechanism was competitive, and the inhibition constant (Ki) values for rac-ETO (2.6 ± 0.4 µmol L-1), (+)-ETO (1.5 ± 0.2 µmol L-1), and (-)-ETO (0.7 ± 0.1 µmol L-1) were comparable to the Ki values of strong CYP2C19 inhibitors. Inhibition of CYP2C19 by ethofumesate was enantioselective, being almost twice higher for (-)-ETO than for (+)-ETO, which indicates that this enantiomer may be a more potent inhibitor of this CYP form. For an in vitro-in vivo correlation, the Food and Drug Administration's (FDA) guideline on the assessment of drug-drug interactions used in the early stages of drug development was used. The FDA's R1 values were estimated on the basis of the obtained ethofumesate Ki and distribution volume, metabolism, unbound plasma fraction, gastrointestinal and dermal absorption data available in the literature. The correlation revealed that ethofumesate probably inhibits CYP2C19 in vivo for both chronic (oral) and occupational (dermal) exposure scenarios.

The Molecular and Enzyme Kinetic Basis for Altered Activity of Three Cytochrome P450 2C19 Variants Found in the Chinese Population.

BACKGROUND: There is a large inter-individual variation in cytochrome P450 2C19 (CYP2C19) activity. The variability can be caused by the genetic polymorphism of CYP2C19 gene. This study aimed to investigate the molecular and kinetics basis for activity changes in three alleles including CYP2C19*23, CYP2C19*24 and CYP2C19*25found in the Chinese population. METHODS: The three variants expressed by bacteria were investigated using substrate (omeprazole and 3- cyano-7-ethoxycoumarin[CEC]) and inhibitor (ketoconazole, fluoxetine, sertraline and loratadine) probes in enzyme assays along with molecular docking. RESULTS: All alleles exhibited very low enzyme activity and affinity towards omeprazole and CEC (6.1% or less in intrinsic clearance). The inhibition studies with the four inhibitors, however, suggested that mutations in different variants have a tendency to cause enhanced binding (reduced IC50 values). The enhanced binding could partially be explained by the lower polar solvent accessible surface area of the inhibitors relative to the substrates. Molecular docking indicated that G91R, R335Q and F448L, the unique mutations in the alleles, have caused slight alteration in the substrate access channel morphology and a more compact active site cavity hence affecting ligand access and binding. It is likely that these structural alterations in CYP2C19 proteins have caused ligand-specific alteration in catalytic and inhibitory specificities as observed in the in vitro assays. CONCLUSION: This study indicates that CYP2C19 variant selectivity for ligands was not solely governed by mutation-induced modifications in the active site architecture, but the intrinsic properties of the probe compounds also played a vital role.

Effect of High-Dose Esomeprazole on CYP1A2, CYP2C19, and CYP3A4 Activities in Humans: Evidence for Substantial and Long-lasting Inhibition of CYP2C19.

In vitro, esomeprazole is a time-dependent inhibitor of CYP2C19. Additionally, racemic omeprazole induces CYP1A2 and omeprazole and its metabolites inhibit CYP3A4 in vitro. In this 5-phase study, 10 healthy volunteers ingested 20 mg pantoprazole, 0.5 mg midazolam, and 50 mg caffeine as respective index substrates for CYP2C19, 3A4, and 1A2 before and 1, 25, 49 (pantoprazole only), and 73 hours after an 8-day pretreatment with 80 mg esomeprazole twice daily. The area under the plasma concentration-time curve (AUC) of R-pantoprazole increased 4.92-fold (90% confidence interval (CI) 3.55-6.82), 2.31-fold (90% CI 1.85-2.88), and 1.33-fold (90% CI 1.06-1.68) at the 1-hour, 25-hour, and 73-hour phases, respectively, consistent with a substantial and persistent inhibition of CYP2C19. The AUC of midazolam increased up to 1.44-fold (90% CI 1.22-1.72) and the paraxanthine/caffeine metabolic ratio up to 1.19-fold (90% CI 1.04-1.36), when the index substrates were taken 1 hour after esomeprazole. Based on the recovery of R-pantoprazole oral clearance, the turnover half-life of CYP2C19 was estimated to average 53 hours. Pharmacokinetic simulation based on the observed concentrations of esomeprazole and its metabolites as well as their published CYP2C19 inhibitory constants was well in line with the observed changes in R-pantoprazole pharmacokinetics during the course of the study. Extrapolations assuming linear pharmacokinetics of esomeprazole suggested weak to moderate inhibition at 20 and 40 mg twice daily dosing. In conclusion, high-dose esomeprazole can cause strong inhibition of CYP2C19, but only weakly inhibits CYP3A4 and leads to minor induction of CYP1A2. The enzymatic activity of CYP2C19 recovers gradually in ~ 3-4 days after discontinuation of esomeprazole treatment.