Cytochrome P450 Enzymes CYP2C19 Research Articles

A Review on the Pharmacokinetics and Toxicological Profile of Rabeprazole

Rabeprazole, a proton pump inhibitor, is used for individuals with ulcers. The prodrug is transformed into an active sulphenamide form by the acidic conditions present in the parietal cells. Rabeprazole inhibits the H+K+ ATPase of the gastric cells, leading to a decrease in the generation of stomach acid in both normal and stimulated situations. The present review was based on the pharmacokinetics and toxicological profile of Rabeprazole. Once absorbed into the body, approximately 96.3–97% of rabeprazole is bound to plasma proteins. In humans, the half-life of rabeprazole is approximately one hour. The peak concentration of rabeprazole in human plasma following a single oral dose does not appear until around 3.5 hours later. Rabeprazole is metabolised mostly by the liver. Once the liver has metabolised the medicine, 90% of it will be excreted via the kidneys. The elimination fraction is 10%. Rabeprazole is mostly metabolised by the cytochrome P450 enzymes CYP2C19 and CYP3A4. . It concluded that in the human pylorus, it decreased muscular tone, maximal contraction values, and contraction frequencies. When diclofenac sodium SR, glucosamine, diacerein, calcium, and vitamin D preparations were administered in addition to rabeprazole, the patients experienced GI bleeding, fatty liver grade 1, mild epigastric discomfort, black stools, and decreased haemoglobin content.

Abstract 12412: In Silico Evaluation of Dosing Regimens to Accommodate Coadministration of Mavacamten With Strong Inhibitors of Cytochrome P450 3A4 and Moderate Inhibitors of Cytochrome P450 2C19 in Patients With Obstructive Hypertrophic Cardiomyopathy

Background: Mavacamten is primarily metabolized by cytochrome P450 enzymes CYP2C19 and CYP3A4 and coadministration with strong CYP3A4 or moderate CYP2C19 inhibitors is contraindicated in patients with obstructive hypertrophic cardiomyopathy (HCM) in the US prescribing information (USPI). Aim: To assess the safety and efficacy of accommodating coadministration of mavacamten with strong CYP3A4 and moderate CYP2C19 inhibitors via simulations. Methods: Simulations of 5000 virtual patients with obstructive HCM uniformly distributed by CYP2C19 metabolizer phenotypes were performed using population pharmacokinetic and pharmacodynamic models. The USPI posology and variations were simulated to evaluate if short term (1 week) and long term (chronic) coadministration of CYP3A4 or CYP2C19 inhibitors could be accommodated. Analogous to USPI posology development, comparisons were made by evaluating proportions of patients with left ventricular ejection fraction [LVEF] < 50% (safety) and Valsalva left ventricular outflow tract gradient [VLVOTg] < 30 mmHg (efficacy). Results: When initiating mavacamten with a CYP3A4 inhibitor, a posology using 2.5 mg starting dose, with coadministration stopped if LVEF < 50% at 2.5 mg, resulted in a similar peak proportion of CYP2C19 poor metabolizers with LVEF < 50% (5.7%) and LVEF < 40% (0.9%) compared to the USPI (2.7% and 0.3% respectively; Table ). When initiating mavacamten with a CYP2C19 inhibitor, a 2.5 mg starting dose resulted in a similar peak proportion of LVEF < 50% in CYP2C19 ultrarapid metabolizers to USPI. Optimal efficacy was achieved; in some patients, this was delayed owing to dose reduction. Interruption of mavacamten during short term administration of inhibitors transiently increased VLVOTg for the duration of interruption, with no effect on LVEF. Conclusion: Coadministration of mavacamten with CYP3A4 or CYP2C19 inhibitors could be accommodated within the titration scheme with dose interruption or down titration.

Bosentan effect on Teneligliptin’s Antidiabetic effect in Animal Model

Due to a variety of comorbidities, Patients with type 2 diabetes usually require a multifaceted approach to therapy. A large number of medications taken at the same time increase the risk of undesirable drug effects or drug interactions in the patient. It's vital to think about cytochrome P-450 (CYP) enzyme interactions while using a multifactorial pharmacotherapy approach. The cytochrome P450 enzymes CYP2C9 and CYP3A4 metabolize bosentan in the liver similarly, teneligliptin is metabolized by flavin-containing monooxygenase 3 (FMO3) and cytochrome P450 (CYP) 3A4. This study was conducted to investigate a possible pharmacokinetic interaction between bosentan and teneligliptin. Interaction of teneligliptin, the known dipeptidyl peptidase-4 inhibitors or gliptins anti diabetic drugs with bosentan, a pulmonary antihypertensive agent, in healthy and alloxan-induced diabetic rats, was tested. Blood samples were taken from rats at various intervals up to 24 hours and blood glucose levels were calculated. The parameters considered for the analysis of the effect on teneligliptin induced hypoglycemia were the onset of hypoglycemia (duration required to reduce blood glucose level by 15% - 20%), duration of hypoglycemia (duration of time in which more than 15 % -20 % decrease in blood glucose level is managed to maintained), and peak hypoglycemia. In both healthy albino rats and diabetic rats, a single dose of bosentan did not affect blood glucose levels. These results suggest that bosentan has no hypoglycemic effect, implying that the drug-drug interaction with teneligliptin is of the pharmacokinetic kind.

Pharmacogenetic Dose Modeling Based on CYP2C19 Allelic Phenotypes.

Pharmacogenetic variability in drug metabolism leads to patient vulnerability to side effects and to therapeutic failure. Our purpose was to introduce a systematic statistical methodology to estimate quantitative dose adjustments based on pharmacokinetic differences in pharmacogenetic subgroups, addressing the concerns of sparse data, incomplete information on phenotypic groups, and heterogeneity of study design. Data on psychotropic drugs metabolized by the cytochrome P450 enzyme CYP2C19 were used as a case study. CYP2C19 activity scores were estimated, while statistically assessing the influence of methodological differences between studies, and used to estimate dose adjustments in genotypic groups. Modeling effects of activity scores in each substance as a population led to prudential predictions of adjustments when few data were available ('shrinkage'). The best results were obtained with the regularized horseshoe, an innovative Bayesian approach to estimate coefficients viewed as a sample from two populations. This approach was compared to modeling the population of substance as normally distributed, to a more traditional "fixed effects" approach, and to dose adjustments based on weighted means, as in current practice. Modeling strategies were able to assess the influence of study parameters and deliver adjustment levels when necessary, extrapolated to all phenotype groups, as well as their level of uncertainty. In addition, the horseshoe reacted sensitively to small study sizes, and provided conservative estimates of required adjustments.

Loss of function polymorphisms in SLCO1B1 (c.521T>C, rs4149056) and ABCG2 (c.421C>A, rs2231142) genes are associated with adverse events of rosuvastatin: a case-control study.

The study aims to evaluate relationship between polymorphisms associated with a reduced function of two transporter proteins resulting in increased exposure to rosuvastatin - organic anion transporter 1B1 (OATP1B1) (SLCO1B1 c.521T>C) and ATP binding cassette subfamily G member 2 (ABCG2) (ABCG2 c.421C>A) and occurrence of rosuvastatin related myotoxicity/hepatotoxicity. In a case-control study, cases (rosuvastatin treated patients developing myotoxicity or hepatotoxicity) and controls (concurrent rosuvastatin treated patients free of adverse events) were prospectively recruited over a 2 year period in a single tertiary center specialized in treatment of metabolic disorders. Subjects were evaluated for clinical, comorbidity, and comedication characteristics and for genotype predicted metabolizing phenotypes regarding cytochrome P450 enzymes CYP2C9 and CYP2C19. Standard regression analysis and analysis in matched sets of cases and controls (optimal full matching) were undertaken by fitting frequentist and Bayesian models (covariates/matching variables: age, sex, diabetes, liver/renal disease, hypertension, CYP2C9 and C19 phenotype, use of CYP or transporter inhibitors, non evaluated transporter genotype). A total of 88 cases (81 with myotoxicity, 6 with hepatotoxicity, 1 with both) and 129 controls were recruited. Odds of variant SLCO1B1 c.521T>C allele were 2.2-2.5 times higher in cases than in controls (OR = 2.45, 95% CI 1.34-4.48; Bayesian OR = 2.59, 95% CrI 1.42-4.90 in regression analysis; OR = 2.20, 1.10-4.42; Bayesian OR = 2.26, 1.28-4.41 in matched analysis). Odds of variant ABCG2 c.421C>A allele were 2.1-2.3 times higher in cases than in controls (OR = 2.24, 1.04-4.83; Bayesian OR = 2.35, 1.09-4.31 in regression analysis; OR = 2.10, 0.83-5.31; Bayesian OR = 2.17, 1.07-4.35 in matched analysis). Loss of function polymorphisms in SLCO1B1 c.521T>C and ABCG2 c.421C>A genes are associated with the presence of rosuvastatin related myotoxicity and/or hepatotoxicity.

CYP2C9 polymorphisms in epilepsy: influence on phenytoin treatment.

Phenytoin (PHT) is an antiepileptic drug widely used in the treatment of focal epilepsy and status epilepticus, and effective in controlling focal seizures with and without tonic–clonic generalization and status epilepticus. The metabolization of PHT is carried out by two oxidative cytochrome P450 enzymes CYP2C9 and CYP2C19; 90% of this metabolization is done by CYP2C9 and the remaining 10% by CYP2C19. Genetic polymorphism of CYP2C9 may reduce the metabolism of PHT by 25–50% in patients with variants *2 and *3 compared to those with wild-type variant *1. The frequency distribution of CYP2C9 polymorphism alleles in patients with epilepsy around the world ranges from 4.5 to 13.6%, being less frequent in African-Americans and Asians. PHT has a narrow therapeutic range and a nonlinear pharmacokinetic profile; hence, its poor metabolization has significant clinical implications as it causes more frequent and more serious adverse effects requiring discontinuation of treatment, even if it had been effective. There is evidence that polymorphisms of CYP2C9 and the use of PHT are associated with an increase in the frequency of some side effects, such as cerebellar atrophy, gingival hypertrophy or acute cutaneous reactions. The presence of HLA-B*15:02 and CYP2C9 *2 or *3 in the same patient increases the risk of Stevens–Johnson syndrome and toxic epidermal necrolysis; hence, PHT should not be prescribed in these patients. In patients with CYP2C9 *1/*2 or *1/*3 alleles (intermediate metabolizers), the usual PHT maintenance dose (5–10 mg/kg/day) must be reduced by 25%, and in those with CYP2C9 *2/*2, *2/*3 or *3/*3 alleles (poor metabolizers), the dose must be reduced by 50%. It is controversial whether CYP2C9 genotyping should be done before starting PHT treatment. In this paper, we aim to review the influence of CYP2C9 polymorphism on the metabolization of PHT and the clinical implications of poor metabolization in the treatment of epilepsies.

Rapid screening for targeted genetic variants via high-resolution melting curve analysis.

Current methods for the detection of single nucleotide polymorphisms (SNPs) associated with aberrant drug-metabolizing enzyme function are hindered by long turnaround times and specialized techniques and instrumentation. In this study, we describe the development and validation of a high-resolution melting (HRM) curve assay for the rapid screening of variant genotypes for targeted genetic polymorphisms in the cytochrome P450 enzymes CYP2C9, CYP2C19, and CYP3A5. Sequence-specific primers were custom-designed to flank nine SNPs within the genetic regions of aforementioned drug metabolizing enzymes. PCR amplification was performed followed by amplicon denaturation by precise temperature ramping in order to distinguish genotypes by melting temperature (Tm). A standardized software algorithm was used to assign amplicons as 'reference' or 'variant' as compared to duplicate reference sequence DNA controls for each SNP. Intra-assay (n=5) precision of Tms for all SNPs was ≤0.19%, while inter-assay (n=20) precision ranged from 0.04% to 0.21%. When compared to a reference method of Sanger sequencing, the HRM assay produced no false negative results, and overcall frequency ranged from 0% to 26%, depending on the SNP. Furthermore, HRM genotyping displayed accuracy over input DNA concentrations ranging from 10 to 200 ng/μL. The presented assay provides a rapid method for the screening for genetic variants in targeted CYP450 regions with a result of 'reference' or 'variant' available within 2 h from receipt of extracted DNA. The method can serve as a screening approach to rapidly identify individuals with variant sequences who should be further investigated by reflexed confirmatory testing for aberrant cytochrome P450 enzymatic activity. Rapid knowledge of variant status may aid in the avoidance of adverse clinical events by allowing for dosing of normal metabolizer patients immediately while identifying the need to wait for confirmatory testing in those patients who are likely to possess pharmacogenetically-relevant variants.

Pharmacogenomics of anti-platelet therapy: how much evidence is enough for clinical implementation?

Pharmacogenomics, the study of the genomics of drug response and adverse effects, holds great promise for more effective individualized (personalized) medicine. Recent evidence supports a role of loss-of-function variants in the cytochrome P450 enzyme CYP2C19 as a determinant of clopidogrel response. Those who carry loss-of-function variants do not metabolize clopidogrel, a prodrug, into its active form resulting in decreased inhibition of platelet function and a higher likelihood of recurrent cardiovascular events. Despite a large body of evidence supporting clinical utility, adoption of anti-platelet pharmacogenetics into clinical practice has been slow. In this review, we summarize the pharmacokinetic, pharmacodynamics, and clinical evidence, identify gaps in knowledge and other barriers that appear to be slowing adoption, and describe CYP2C19 pharmacogenetics implementation projects currently underway. Only when we surmount these barriers will the astute clinician be able to use pharmacogenetic information in conjunction with the history, physical exam, and other medical tests and information to choose the most efficacious anti-platelet therapy for each individual patient.

Trend of medicine of the 21st century

Until today, traditional clinical diagnosis and disease management was focused on the individual patient’s clinical symptoms and signs, medical and family history, data from laboratory and imaging evaluation that led to diagnose and treatment of illnesses. This is often a reactive approach to treatment, i.e., treatment starts after the symptoms and signs appear. Advances in medical genetics have enabled a more detailed understanding of the impact of genetics in diseases. It was the main reason for developing a so called personalized medicine. Large collaborative research projects (for example, the Human genome project) have laid the groundwork for the understanding of the roles of genes in human development and physiology. Even that revealed single nucleotide polymorphisms that pointed to some of the genetic variabilities between individuals. Important biological functions: growth, death, cellular movement and localization, differentiation, etc. are controlled by a process called signal transduction. This process is nearly entirely epi-genetic and governed by protein enzyme activity. Diseases such as cancer, based on genomic mutations, are functionally manifest as dysfunctional protein signal transduction. Historically, the pharmaceutical industry has developed medications based on empiric observations and more recently, on known disease mechanisms. For example, medications for diabetes aim to improve insulin release from the pancreas and the sensitivity of the muscle cells and fat tissues on the effect of insulin. Drugs for high cholesterol, affect the absorption, metabolism, and generation of cholesterol. It means that medications are developed based on mechanisms of disease that have been extensively studied over the past century. We hope that recent advancements in the genetic etiologies of common diseases will improve pharmaceutical development. Today we discovered that information about a patient’s proteomic, genetic and metabolic profile could be used to tailor medical care to that individual’s needs. One idea of this medical model is the development of diagnostics, whereby molecular assays that measure levels of proteins, genes or specific mutations are used to provide a specific therapy for an individual’s condition by stratifying disease status, selecting the proper medication and tailoring dosages to that patient’s specific needs. Besides that, many scientists and practitioners estimate that such methods might be used to assess a patient’s risk factor for a number of conditions and tailor individual preventative treatments such as nutritional immunology approaches. Contemporary potential applications of personalized medicine include pharmacogenetics, pharmacometabolomics and cancer management. Examples of pharmacogenetics include: Genotyping for single nucleotide polymorphisms in genes involved in the action and metabolism of warfarin. This medication is used clinically as an anticoagulant but requires periodic monitoring and is associated with adverse side effects. Recently, genetic variants in the gene encoding Cytochrome P450 enzyme CYP2C9, which metabolizes warfarin 1, and the Vitamin K epoxide reductase gene (VKORC1), a target of coumarins2, have led to commercially-available testing that enables more accurate dosing based on algorithms that take into account the age, gender, weight, and genotype of an individual. Examples of personalized cancer management include: Testing for disease-causing mutations in the BRCA1 and BRCA2genes, which are implicated in familial breast and ovarian cancer syndromes. Discovery of a disease-causing mutation in a family can inform “at-risk” individuals as to whether they are at higher risk for cancer and may prompt individualized prophylactic therapy including mastectomy and removal of the ovaries. More detailed molecular stratification of breast tumors may pave the way for future tailored treatments3. Targeted therapy is used for medications’ designing which targets epidermal grow factor receptors (EGFR) in a subset of patients with Non-Small Cell Lung Cancer (NSCLC). For example, Tyrosine kinase inhibitors such as erlotinib and gefitinib have been developed to treat NSCLC, where the mutation of the epidermal growth factor receptor gene (exon 19 - 21) in lung cancer cells was detected. These medications specifically inhibit the intracellular domain of this receptor, this way making blockade of intracellular signal transduction cascade which is responsible for cellular proliferation, invasion, metastasis, angiogenesis and inhibition of apoptosis. In the future, tissue-derived molecular information might be combined with an individual’s personal medical history, family history, data from imaging, and other laboratory tests to develop more effective treatments for a wider variety of conditions.

Clopidogrel and CYP2C19 Testing: Ready for Clinical Prime Time?

Effective platelet inhibition has become a cornerstone in the management of patients with acute coronary syndromes (ACSs).4 The addition of clopidogrel, a blocker of the ADP platelet receptor, to aspirin therapy significantly reduces major cardiovascular events in ACS patients and reduces the frequency of percutaneous coronary intervention (PCI) with stent implantation. As PCI became the dominant approach for myocardial revascularization, clopidogrel use grew steadily, and clopidogrel is now the second most highly prescribed medicine in the US. Even though clopidogrel was approved for use in 1997, its mechanism of action continues to be progressively understood. The response to clopidogrel is highly variable among patients. Patients with low or incomplete platelet inhibition (so-called high residual on-clopidogrel platelet reactivity) are at a greater risk of cardiovascular events (1). Multiple mechanisms have been proposed for the variable response to clopidogrel. Pharmacokinetic and pharmacodynamic analyses have established that a substantial portion of the variation in platelet response is explained by the variability in plasma concentrations of the active metabolite of clopidogrel (2–4). Clopidogrel is a prodrug that requires bioactivation to achieve its antiplatelet efficacy. Only 15% of the prodrug is available for transformation to the active agent; the remaining 85% is hydrolyzed by esterases into inactive forms. The cytochrome P450 enzyme CYP2C19 contributes an estimated 21% to the generation of the active metabolite (5). Like many other members of the cytochrome P450 gene superfamily, the CYP2C19 (cytochrome P450, family 2, subfamily C, polypeptide 19) gene is highly polymorphic, with >25 variant alleles known. The most common CYP2C19 loss-of-function allele is * 2 (c.681G>A; rs4244285), with allele frequencies of approximately 15% in Caucasians and Africans, and 29%–35% in Asians. Carriers of two * 2 alleles are defined as poor metabolizers, whereas carriers of only one * 2 allele are defined as intermediate …

Association between CYP2C19*17 and metabolism of amitriptyline, citalopram and clomipramine in Dutch hospitalized patients

Polymorphisms in genes coding for drug metabolizing enzymes, such as the cytochrome P450 enzymes CYP2C19 and CYP2D6, can lead to therapy failure and side effects. In earlier studies, the novel variant CYP2C19*17 increased metabolism of several CYP2C19 substrates. The objective of this study was to evaluate the impact of CYP2C19*17 on the metabolism of amitriptyline (AT), citalopram (CIT), and clomipramine (CLOM). Six-hundred and seventy-eight patients were included in this study, based on availability of DNA and serum levels of parent drug and main metabolite. We investigated the relationship between CYP2C19 genotypes and metabolic parameters, including serum levels corrected for dose and metabolic ratio (MR). The CYP2C19*17 allele was significantly associated with decreased MR for CIT (CYP2C19*1/*17 mean MR=2.3, compared with CYP2C19*1/*1 mean MR=2.8) and AT (CYP2C19*17/*17 mean MR=0.8, compared with CYP2C19*1/*1 mean MR=3.7 in the CYP2D6*1/*1 subgroup). Furthermore, significant association of CYP2D6 genotype with AT, CIT, and CLOM metabolism was observed. No clear correlation was found between CYP2C19 genotype and CLOM metabolism. This study confirms the increased activity of the CYP2C19*17 allele and shows increased metabolism of drugs that are metabolized by CYP2C19, including AT and CIT. However, the clinical relevance of CYP2C19*17 is probably limited for AT, CIT, and CLOM.

Fluconazole-induced intoxication with phenytoin in a patient with ultra-high activity of CYP2C9

The cytochrome P450 enzyme CYP2C9 metabolizes several important drugs, such as warfarin and oral antidiabetic drugs. The enzyme is polymorphic, and all known alleles, for example, CYP2C9*2 and*3, give decreased activity. Ultra-high activity of the enzyme has not yet been reported. We present a patient with Behçet's disease who required treatment with high doses of phenytoin. When fluconazole, a potent inhibitor of CYP2C9, was added to the treatment regimen, the patient developed ataxia, tremor, fatigue, slurred speech and somnolence, indicating phenytoin intoxication. On suspicion of ultra-high activity of CYP2C9, a phenotyping test for CYP2C9 with losartan was performed. The patient was shown to have a higher activity of CYP2C9 than any of the 190 healthy Swedish Caucasians used as controls. Our finding of an ultrarapid metabolism of losartan and phenytoin may apply to other CYP2C9 substrates, where inhibition of CYP2C9 may cause severe adverse drug reactions.

Pharmacogenetic Testing for Clopidogrel Using the Rapid INFINITI Analyzer: A Dose-Escalation Study

Our aim was to assess whether a higher clopidogrel maintenance dose has a greater antiplatelet effect in CYP2C19*2 allele carriers compared with noncarriers. Clopidogrel is a prodrug that is biotransformed by the cytochrome P450 enzymes CYP2C19, 2C9, and 3A4, 2B6, 1A2. The CYPC219*2 loss of function variant has been associated with a reduced antiplatelet response to clopidogrel and a 3-fold risk of stent thrombosis. Forty patients on standard maintenance dosage clopidogrel (75 mg), for 9.4 +/- 9.2 weeks, were enrolled into a dose escalation study. Platelet function was assessed at baseline and after 1 week of 150 mg once daily using the VerifyNow platelet function analyzer (Accumetrics Ltd., San Diego, California). Genomic DNA was hybridized to a BioFilmChip microarray on the INFINITI analyzer (AutoGenomics Inc., Carlsbad, California) and analyzed for the CYP19*2, *4, *17, and CYP2C9*2, *3 polymorphisms. Platelet inhibition increased over 1 week, mean +8.6 +/- 13.5% (p = 0.0003). Carriers of the CYP2C19*2 allele had significantly reduced platelet inhibition at baseline (median 18%, range 0% to 72%) compared with wildtype (wt) (median 59%, range 11% to 95%, p = 0.01) and at 1 week (p = 0.03). CYP2C19*2 allele carriers had an increase in platelet inhibition of (mean +9 +/- 11%, p = 0.03) and reduction in platelet reactivity (mean -26 +/- 38 platelet response unit, p = 0.04) with a higher dose. Together CYP2C19*2 and CYP2C9*3 loss of function carriers had a greater change in platelet inhibition with 150 mg daily than wt/wt (+10.9% vs. +0.7%, p = 0.04). Increasing the dose of clopidogrel in patients with nonresponder polymorphisms can increase antiplatelet response. Personalizing clopidogrel dosing using pharmacogenomics may be an effective method of optimizing treatment.

Cytochrome P450 2C19 inhibitory activity of common berry constituents

The cytochrome P450 enzyme CYP2C19 is involved in the metabolism of many commonly prescribed drugs, including proton pump inhibitors, antiepileptics and antidepressants. CYP2C19 inhibitors from food and food supplements may augment the toxicity of these agents and lead to noncompliance with treatment. The present investigation addresses CYP2C19 inhibition by 18 berry constituents using a chemiluminescent assay. Test compounds displayed inhibitory properties in a concentration-dependent fashion, with IC(50) values ranging from 20.2 microM up to >316 microM. In the order of decreasing effect size, anthocyanidins were followed by anthocyanidin-monoglycosides and procyanidins. Anthocyanidin-diglucosides exhibited weak and biphasic effects. When compared with the CYP2C19 inhibitor fluvoxamine, the flavonoids under study were 50- to 750-fold less potent. It is concluded that the above natural substances are moderate to poor inhibitors of CYP2C19 in vitro.

T1085 Effect of CYP2C19 Genotype On Control of Gastric Acidity with Rabeprazole and Esomeprazole After Single and Repeated Oral Administration

Introduction: Esomeprazole (eso) and rabeprazole (rabe) are metabolized in the liver. Genetic polymorphism of the cytochrome P-450 enzyme CYP2C19 determines fast (homozygous extensive metabolizers, wt/wt), intermediate (heterozygous extensive metabolizers, wt/∗2 or wt/∗3) and slow (poor metabolizers, ∗2/∗2, ∗3/∗3 or ∗2/∗3) or rapid (wt/∗17 or ∗17/∗17) metabolism of proton pump inhibitors (PPIs). In the Caucasian population 60% has the wt/ wt genotype, 30-40% is wt/∗2 and 2-5% ∗2/∗2. Aim: To investigate the impact of CYP2C19 genotype on control of gastric acidity (median pH and % of time pH

Lopinavir/Ritonavir Induces the Hepatic Activity of Cytochrome P450 Enzymes CYP2C9, CYP2C19, and CYP1A2 But Inhibits the Hepatic and Intestinal Activity of CYP3A as Measured by a Phenotyping Drug Cocktail in Healthy Volunteers

The effect of lopinavir/ritonavir (LPV/r) administration on cytochrome P450 (CYP) enzyme activity was quantified using a phenotyping biomarker cocktail. Changes in CYP2C9, CYP2C19, CYP3A, CYP1A2, N-acetyltransferase-2 (NAT-2), and xanthine oxidase (XO) activities were evaluated using warfarin (WARF) + vitamin K, omeprazole (OMP), intravenous (IV) and oral (PO) midazolam (MDZ), and caffeine (CAF). : Open-label, multiple-dose, pharmacokinetic study in healthy volunteers. Subjects (n = 14) simultaneously received PO WARF 10 mg, vitamin K 10 mg, OMP 40 mg, CAF 2 mg/kg, and IV MDZ 0.025 mg/kg on days (D) 1 and 14, and PO MDZ 5 mg on D2 and D15. LPV/r (400/100 mg twice daily) was administered on D4-17. CYP2C9 and CYP2C19 activities were quantified by S-WARF AUC0-inf and OMP/5-hydroxy OMP ratio, respectively. CYP1A2, NAT-2, and XO activities were quantified by urinary CAF metabolite ratios. Hepatic and intestinal + hepatic CYP3A activities were quantified by IV (CL) and PO (CL/F) MDZ clearance, respectively. After LPV/r therapy, CYP2C9, CYP2C19, and CYP1A2 activity increased by 29%, 100%, and 43% (P = 0.001, 0.046, and 0.001), respectively. No changes were seen in NAT-2 or XO activity. Hepatic and intestinal + hepatic CYP3A activity decreased by 77% (P < 0.001) and 92% (P = 0.001), respectively. LPV/r therapy results in modest induction of CYP1A2 and CYP2C9 and potent induction of CYP2C19 activity. Increasing doses of concomitant medications metabolized by these enzymes may be necessary. LPV/r inhibited intestinal CYP3A to a greater extent than hepatic CYP3A activity. Doses of concomitant CYP3A substrates should be reduced when combined with LPV/r, although intravenously administered compounds may require less of a relative dose reduction than orally administered compounds.

Pharmacokinetic interaction between bosentan and the oral contraceptives norethisterone and ethinyl estradiol

Bosentan has been shown in vitro and in vivo to induce the cytochrome P450 enzymes CYP2C9 and CYP3A4. The present study was conducted to investigate the effect of bosentan on the pharmacokinetics of a combined oral contraceptive. In a randomized, 2-way crossover study, 20 healthy female subjects received Treatments A and B. Treatment A consisted of a single dose of OrthoNovum containing 1 mg norethisterone (norethindrone) and 35 microg ethinyl estradiol. Treatment B consisted of bosentan, 125 mg b.i.d. for 7 days plus concomitant norethisterone and ethinyl estradiol on Day 7. Plasma concentrations of norethisterone and ethinyl estradiol were measured on days of oral contraceptive administration. In the absence of bosentan, the pharmacokinetics of norethisterone and ethinyl estradiol were characterized by Cmax and AUC0-infinity values (95% CI) of 9.8 (8.1, 11.9) ng/ml and 72.9 (57.0, 93.1) ng x h/ml, and 53.0 (47.0, 59.9) pg/ml and 758 (655, 878) pg x h/ml, respectively. Concomitant bosentan did not affect the Cmax but significantly decreased the AUC of norethisterone and ethinyl estradiol by 13.7% (-23.5, -2.6) and 31.0% (-40.5,-20.2), respectively. The maximum decrease in AUC of norethisterone and ethinyl estradiol in an individual subject was 56% and 66%, respectively. Bosentan decreases the AUC of norethisterone and ethinyl estradiol in healthy female subjects. In patients treated with bosentan, reduced efficacy of hormonal contraceptives should be considered.

Quantification of mephenytoin and its metabolites 4'-hydroxymephenytoin and nirvanol in human urine using a simple sample processing method.

A reliable and easy to use liquid chromatography/tandem mass spectrometry (LC/MS/MS) method without the use of sample extraction was developed for the simultaneous quantification of urinary concentrations of mephenytoin, a standard phenotyping substrate for the cytochrome P450 enzyme CYP2C19, and its phase I metabolites 4'-hydroxymephenytoin and nirvanol. Fifty microL of urine were diluted with a buffered beta-glucuronidase solution and incubated at 37 degrees C for 6 h followed by addition of methanol, containing the internal standard 4'-methoxymephenytoin. The chromatographic separation was achieved using a 100 x 3 mm, 5 micro Thermo Electron Aquasil C18 column with a gradient flow, increasing the organic fraction (acetonitrile/methanol 50:50) of the mobile phase from 10 to 90%. Quantification by triple-stage mass spectrometry (TSQ Quantum, Thermo Electron) was accomplished by negative electrospray ionization in the selected reaction monitoring mode. Linearity was observed for all substances in the concentration range 15-10 000 ng/mL. The lower limit of quantification (LLOQ) was 20 ng/mL for 4'-hydroxymephenytoin and 30 ng/mL for nirvanol and mephenytoin, respectively. Intra- and inter-day inaccuracy did not exceed 9.5% for all substances from LLOQ to 10 000 ng/mL. Intra- and inter-day precision were in the range of 0.8-10.5%. The method was validated according to international ICH and FDA guidelines and successfully applied for phenotyping of Caucasian male volunteers who received an oral dose of 50 mg mephenytoin.

Warfarin sensitivity related to CYP2C9, CYP3A5, ABCB1 (MDR1) and other factors

The required dose of the oral anticoagulant warfarin varies greatly, and overdosing often leads to bleeding. Warfarin is metabolised by cytochrome P450 enzymes CYP2C9, CYP1A2 and CYP3A. The target cell level of warfarin may be dependent on the efflux pump P-glycoprotein, encoded by the adenosine triphosphate-binding cassette gene ABCB1 (multidrug resistance gene 1). Genetic variability in CYP2C9, CYP3A5 and ABCB1 was analysed in 201 stable warfarin-treated patients using solid-phase minisequencing, pyrosequencing and SNaPshot. CYP2C9 variants, age, weight, concurrent drug treatment and indication for treatment significantly influenced warfarin dosing in these patients, explaining 29% of the variation in dose. CYP3A5 did not affect warfarin dosing. An ABCB1 haplotype containing the exon 26 3435T variant was over-represented among low-dose patients. Thirty-six patients with serious bleeding complications had higher prothrombin time international normalised ratios than 189 warfarin-treated patients without serious bleeding, but there were no significant differences in CYP2C9, CYP3A5 or ABCB1 genotypes and allelic variants.

Pharmacokinetics of diclofenac and inhibition of cyclooxygenases 1 and 2: no relationship to the CYP2C9 genetic polymorphism in humans.

The cytochrome P450 enzyme CYP2C9 catalyses the 4'-hydroxylation of the nonsteroidal analgesic drug diclofenac in humans. We studied the influences of the known amino acid variants, CYP2C9*2 (Arg144Cys) and CYP2C9*3 (Ile359Leu), on diclofenac pharmacokinetics after a 50-mg oral dose of diclofenac in healthy volunteers. As a surrogate marker of diclofenac activity, the ex vivo formation of prostaglandin E2 and thromboxane B2, which reflects COX-2 and COX-1 activity, was measured. Genotyping was performed in 516 healthy volunteers to obtain 20 participants with all allelic combinations of the two CYP2C9 variants Arg144Cys (*2) and Ile359Leu (*3). Diclofenac and 4'-hydroxydiclofenac were quantified in plasma by reversed phase h.p.l.c. after oral intake of 50 mg diclofenac. Concentrations of thromboxane B2 (TxB2) and prostaglandin E2 (PGE2) were measured by immunoassays. There was no evidence of impaired metabolism of oral diclofenac in heterozygous and homozygous carriers of the CYP2C9 alleles *2 and *3 compared with the wild type (mean CL/F (95% CI) 20.5 (11, 30) l h-1 for *1/*1, 29.9 (19, 40) l h-1 for *1/*2, 30.0 (4, 56) l h-1 for *2/*2, 22.6 (12, 33) l h-1 for *1/*3, 23.5 (11, 37) l h-1 for *3/*3 and 37.3 (-15, 89) l h-1 in *2/*3). Furthermore, plasma concentrations of the metabolite 4'-hydroxydiclofenac were not lower in carriers of the CYP2C9 low-activity alleles *2 and *3 compared with carriers of the CYP2C9*1/*1 genotype. Marked diclofenac mediated inhibition of COX-1- and COX-2 activity was detected in all individuals independent of CYP2C9 genotype. Polymorphisms of the CYP2C9 gene had no discernible effect on the pharmacokinetics and pharmacodynamics of diclofenac. The question of whether enzymes other than CYP2C9 play a major role in diclofenac 4'-hydroxylation in vivo or whether 4'-hydroxylation is not a rate-limiting step in diclofenac elimination in vivo, or whether the effect of the CYP2C9 polymorphisms is substrate-dependent, needs further investigation.