CYP2C19Polymorphism and Proton Pump Inhibitors

Effects of Esomeprazole on the Pharmacokinetics of Lapatinib in Breast Cancer Patients

The aqueous solubility of lapatinib declines significantly at pH >4, suggesting that its bioavailability might be lowered by acid-reducing drugs. A study was therefore conducted to assess the effects of esomeprazole on lapatinib pharmacokinetics (PK). Women with metastatic human epidermal growth factor receptor 2 positive (HER2(+) ) breast cancer were enrolled. Patients received 1,250 mg lapatinib once daily (QD) in the morning on Days 1-7 (Period 1) and Days 8-14 (Period 2) with 40 mg esomeprazole QD at bedtime 3 hours after dinner on Days 8-14. Lapatinib PK sampling occurred during the 24-hour steady-state dosing intervals on Day 7 (lapatinib alone) and Day 14 (lapatinib with esomeprazole). Esomeprazole treatment resulted in decreased lapatinib bioavailability (mean 26%, range 6-49%) that was inversely associated with patient age as a significant covariate.

Randomized trial comparing rabeprazole- versus lansoprazole-based Helicobacter pylori eradication regimens

Different types of proton pump inhibitor (PPI)-based triple therapies could result in different Helicobacter pylori eradication rates. This study aimed to compare the efficacy and safety of rabeprazole- and lansoprazole-based triple therapies in primary treatment of H. pylori infection. From September 2005 to July 2008, 426 H. pylori-infected patients were randomly assigned to receive a 7-day eradication therapy with either rabeprazole 20mgbid (RAC group, n=222) or lansoprazole 30mgbid (LAC group, n=228) in combination with amoxicillin 1gbid and clarithromycin 500mgbid. The patients received follow-up esophagogastroduodenoscopy (EGD) and/or (13)C-urea breath test 12-16 weeks later to define H. pylori status. Their personal and medical history, compliance and side effects were obtained by using a standardized questionnaire. Intention-to-treat analysis revealed that the eradication rate was 87.84% in the RAC group and 85.96% in the LAC group (p=0.56). All patients returned for assessment of compliance (100% in the LAC group vs. 99.50% in the RAC group; p=0.32) and adverse events (7.20% in the RAC group vs. 5.70% in the LAC group, p=0.51). Univariate analysis suggested that patients with nonsteroid anti-inflammatory agent (NSAID) use had lower eradication rates than those without (76.71% vs. 88.74%; p=0.006). Our results showed that efficacy and safety were similar in rabeprazole- and lansoprazole-based primary therapies. The influence of NSAID usage on H. pylori eradication needs to be further investigated.

The pharmacokinetics of ilaprazole for gastro-esophageal reflux treatment

INTRODUCTION

Approximately 20% of the Western population is affected by gastro-esophageal reflux disease (GERD). To date, proton pump inhibitors (PPIs) represent the mainstay of GERD medical treatment. However, despite their undoubted benefit, about 40% of GERD patients display an inadequate response to these drugs. Recently, a new PPI, ilaprazole , at oral doses of 10 mg has shown higher suppression of gastric acid secretion, more prolonged plasma half-life, and similar safety compared to 20 mg omeprazole.

AREAS COVERED

This review provides an update on the following points: pharmacokinetic profile and metabolism of ilaprazole in relation to its pharmacodynamic properties; comparative data on the pharmacokinetics and pharmacodynamics of ilaprazole with currently available PPIs; and implications for studies on the therapeutic efficacy of ilaprazole in GERD.

EXPERT OPINION

Different studies show that ilaprazole, a benzimidazole derivative, has an extended plasma half-life in comparison with all other approved PPIs. In addition, ilaprazole metabolism is not significantly influenced by CYP2C19, compared to the available PPIs. Furthermore, the pharmacological characteristics of ilaprazole confer theoretical advantages that are expected to translate into an improved acid control, particularly at night time. However, studies comparing the clinical pharmacokinetics and pharmacodynamics of ilaprazole with those of second-generation PPIs are insufficient. Moreover, further investigations assessing the efficacy of ilaprazole in the management of GERD are required. In healthy volunteers, as well as in patients with gastric or duodenal ulcers, ilaprazole has not shown clinically relevant changes in hematology and biochemistry testing, nor significant treatment-related adverse symptoms.

Efficacy and safety of proton pump inhibitors in the management of pediatric gastroesophageal reflux disease

Proton pump inhibitors (PPIs) are commonly prescribed to infants and children for managing gastroesophageal reflux disease (GERD). Recently published literature illustrates conflicting evidence on the efficacy of PPIs in infants and children. Randomized controlled trials and systematic reviews have demonstrated a lack of efficacy of PPIs, specifically in young infants. Furthermore, emerging evidence also suggests that PPIs are not as benign as once thought, with newer data implicating a potential association of PPIs with an increased risk of respiratory tract infections, gastrointestinal infections, bone fractures, hypomagnesemia, and the occurrence of rebound hyperacidity after discontinuation of PPI therapy. To summarize the emerging data in children, we reviewed the literature to assess the efficacy and safety of PPIs in managing pediatric GERD. Despite conflicting evidence on the efficacy of PPIs, most studies in children demonstrated some benefit when compared with placebo. With respect to the safety of PPIs in children, only a few small studies and case reports indicated a potential association of PPIs with an increased risk of respiratory tract or gastrointestinal infections, bone fractures, and hypomagnesemia; however, many of those studies had their own limitations. From the review, it is clear that further well-designed trials and observational studies are needed to shed more light on the efficacy and safety of PPIs in the pediatric population.

Gastric acid, calcium absorption, and their impact on bone health

Calcium balance is essential for a multitude of physiological processes, ranging from cell signaling to maintenance of bone health. Adequate intestinal absorption of calcium is a major factor for maintaining systemic calcium homeostasis. Recent observations indicate that a reduction of gastric acidity may impair effective calcium uptake through the intestine. This article reviews the physiology of gastric acid secretion, intestinal calcium absorption, and their respective neuroendocrine regulation and explores the physiological basis of a potential link between these individual systems.

Cytochrome P450 enzymes in drug metabolism: regulation of gene expression, enzyme activities, and impact of genetic variation

Cytochromes P450 (CYP) are a major source of variability in drug pharmacokinetics and response. Of 57 putatively functional human CYPs only about a dozen enzymes, belonging to the CYP1, 2, and 3 families, are responsible for the biotransformation of most foreign substances including 70-80% of all drugs in clinical use. The highest expressed forms in liver are CYPs 3A4, 2C9, 2C8, 2E1, and 1A2, while 2A6, 2D6, 2B6, 2C19 and 3A5 are less abundant and CYPs 2J2, 1A1, and 1B1 are mainly expressed extrahepatically. Expression of each CYP is influenced by a unique combination of mechanisms and factors including genetic polymorphisms, induction by xenobiotics, regulation by cytokines, hormones and during disease states, as well as sex, age, and others. Multiallelic genetic polymorphisms, which strongly depend on ethnicity, play a major role for the function of CYPs 2D6, 2C19, 2C9, 2B6, 3A5 and 2A6, and lead to distinct pharmacogenetic phenotypes termed as poor, intermediate, extensive, and ultrarapid metabolizers. For these CYPs, the evidence for clinical significance regarding adverse drug reactions (ADRs), drug efficacy and dose requirement is rapidly growing. Polymorphisms in CYPs 1A1, 1A2, 2C8, 2E1, 2J2, and 3A4 are generally less predictive, but new data on CYP3A4 show that predictive variants exist and that additional variants in regulatory genes or in NADPH:cytochrome P450 oxidoreductase (POR) can have an influence. Here we review the recent progress on drug metabolism activity profiles, interindividual variability and regulation of expression, and the functional and clinical impact of genetic variation in drug metabolizing P450s.

Pharmacokinetics and pharmacodynamics of the proton pump inhibitors

Proton pump inhibitor (PPI) is a prodrug which is activated by acid. Activated PPI binds covalently to the gastric H⁺, K⁺-ATPase via disulfide bond. Cys813 is the primary site responsible for the inhibition of acid pump enzyme, where PPIs bind. Omeprazole was the first PPI introduced in market, followed by pantoprazole, lansoprazole and rabeprazole. Though these PPIs share the core structures benzimidazole and pyridine, their pharmacokinetics and pharmacodynamics are a little different. Several factors must be considered in understanding the pharmacodynamics of PPIs, including: accumulation of PPI in the parietal cell, the proportion of the pump enzyme located at the canaliculus, de novo synthesis of new pump enzyme, metabolism of PPI, amounts of covalent binding of PPI in the parietal cell, and the stability of PPI binding. PPIs have about 1hour of elimination half-life. Area under the plasmic concentration curve and the intragastric pH profile are very good indicators for evaluating PPI efficacy. Though CYP2C19 and CYP3A4 polymorphism are major components of PPI metabolism, the pharmacokinetics and pharmacodynamics of racemic mixture of PPIs depend on the CYP2C19 genotype status. S-omeprazole is relatively insensitive to CYP2C19, so better control of the intragastric pH is achieved. Similarly, R-lansoprazole was developed in order to increase the drug activity. Delayed-release formulation resulted in a longer duration of effective concentration of R-lansoprazole in blood, in addition to metabolic advantage. Thus, dexlansoprazole showed best control of the intragastric pH among the present PPIs. Overall, PPIs made significant progress in the management of acid-related diseases and improved health-related quality of life.

Efficacy of esomeprazole in treating acid-related diseases in Japanese populations

Esomeprazole (Nexium(®); AstraZeneca), the S-isomer of omeprazole, is the first proton pump inhibitor (PPI) to be developed as an optical isomer. Compared with omeprazole, esomeprazole has an improved pharmacokinetic profile with regards to CYP2C19 (S-mephenytoin 4'-hydroxylase) genotype, showing increased systemic exposure and less interindividual variability. Further, esomeprazole is a more potent acid inhibitor than other currently available PPIs and is therefore used as a first-line drug for acid-related diseases. While esomeprazole has been available in a number of countries worldwide, the compound only received authorized permission to be marketed in Japan in September 2011. The standard esomeprazole dose in Japan for the treatment of peptic ulcers and gastroesophageal reflux disease (GERD) is 20 mg. Other advised dosages are 10 mg for nonerosive reflux disease and 20 mg twice-daily dosing for eradication of Helicobacter pylori. In Japanese, the effective rate of esomeprazole 20 mg during 24 weeks for GERD patients is 92.0% (88.0%-96.0%), while the prevention of peptic ulcer development using 20 mg for 24 weeks in patients treated with nonsteroidal anti-inflammatory drugs is 96.0% (92.8%-99.1%). Although clinical data are limited, the usefulness of esomeprazole is expected in Japanese subjects given the reduced prevalence of CYP2C19 rapid metabolizers in Japan compared with Western countries.

The role of pharmacogenetics in nonmalignant gastrointestinal diseases

Genetic variation influences the absorption and efflux of drugs in the intestine, the metabolism of drugs in the liver and the effects of these drugs on their target proteins. Indeed, variations in genes whose products have a role in the pathophysiology of nonmalignant gastrointestinal diseases, such as IBD, have been shown to affect the response of patients to therapy. This Review provides an overview of pharmacogenetics in the management of nonmalignant gastrointestinal diseases on the basis of data from clinical trials. Genetic variants that have the greatest effect on the management of patients with IBD involve the metabolism of thiopurines. Variation in drug metabolism by cytochrome P450 enzymes also requires attention so as to avoid drug interactions in patients receiving tricyclic antidepressants and PPIs. Few genotyping tests are currently used in the clinical management of patients with nonmalignant gastrointestinal diseases, owing to a lack of data from clinical trials showing their effectiveness in predicting nonresponse or adverse outcomes. However, pharmacogenetics could have a beneficial role in enabling pharmacotherapy for nonmalignant gastrointestinal diseases to be targeted to the individual patient.

Ilaprazole, a new proton pump inhibitor, is primarily metabolized to ilaprazole sulfone by CYP3A4 and 3A5

Ilaprazole is a new proton pump inhibitor, designed for treatment of gastric ulcers, and developed by Il-Yang Pharmaceutical Co (Seoul, Korea). It is extensively metabolised to the major metabolite ilaprazole sulfone. In the present study, several in vitro approaches were used to identify the cytochrome P450 (CYP) enzymes responsible for ilaprazole sulfone formation. Concentrations of ilaprazole sulfone were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Incubation of ilaprazole with cDNA-expressed recombinant CYPs indicated that CYP3A was the major enzyme that catalyses ilaprozole to ilaprazole sulfone. This reaction was inhibited significantly by ketoconazole, a CYP3A inhibitor, and azamulin, a mechanism-based inhibitor of CYP3A, while no substantial effect was observed using selective inhibitors for eight other P450s (CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP2E1). In addition, the formation of ilaprazole sulfone correlated well with CYP3A-catalysed testosterone 6β-hydroxylation and midazolam 1'-hydroxylation in 20 different human liver microsome panels. The intrinsic clearance of the formation of ilaprazole sulfone by CYP3A4 was 16-fold higher than that by CYP3A5. Collectively, these results indicate that the formation of the major metabolite of ilaprazole, ilaprazole sulfone, is predominantly catalysed by CYP3A4/5.

Omeprazole inhibits proliferation and modulates autophagy in pancreatic cancer cells

BACKGROUND

Omeprazole has recently been described as a modulator of tumour chemoresistance, although its underlying molecular mechanisms remain controversial. Since pancreatic tumours are highly chemoresistant, a logical step would be to investigate the pharmacodynamic, morphological and biochemical effects of omeprazole on pancreatic cancer cell lines.

METHODOLOGY/PRINCIPAL FINDINGS

Dose-effect curves of omeprazole, pantoprazole, gemcitabine, 5-fluorouracil and the combinations of omeprazole and 5-fluorouracil or gemcitabine were generated for the pancreatic cancer cell lines MiaPaCa-2, ASPC-1, Colo357, PancTu-1, Panc1 and Panc89. They revealed that omeprazole inhibited proliferation at probably non-toxic concentrations and reversed the hormesis phenomena of 5-fluorouracil. Electron microscopy showed that omeprazole led to accumulation of phagophores and early autophagosomes in ASPC-1 and MiaPaCa-2 cells. Signal changes indicating inhibited proliferation and programmed cell death were found by proton NMR spectroscopy of both cell lines when treated with omeprazole which was identified intracellularly. Omeprazole modulates the lysosomal transport pathway as shown by Western blot analysis of the expression of LAMP-1, Cathepsin-D and β-COP in lysosome- and Golgi complex containing cell fractions. Acridine orange staining revealed that the pump function of the vATPase was not specifically inhibited by omeprazole. Gene expression of the autophagy-related LC3 gene as well as of Bad, Mdr-1, Atg12 and the vATPase was analysed after treatment of cells with 5-fluorouracil and omeprazole and confirmed the above mentioned results.

CONCLUSIONS

We hypothesise that omeprazole interacts with the regulatory functions of the vATPase without inhibiting its pump function. A modulation of the lysosomal transport pathway and autophagy is caused in pancreatic cancer cells leading to programmed cell death. This may circumvent common resistance mechanisms of pancreatic cancer. Since omeprazole use has already been established in clinical practice these results could lead to new clinical applications.

Proton pump inhibitors, genetic polymorphisms and response to clopidogrel therapy

Clopidogrel has become part of the mainstay of therapy for acute coronary syndromes and in patients post stenting. Clopidogrel is a pro drug and is metabolised by liver enzymes, particularly CYP2C19, into its active form. A considerable proportion of patients have a poor response to clopidogrel and this may be due to several factors. Genetic polymorphisms involved in clopidogrel's absorption, metabolism and activity at the platelet may interfere with its antiplatelet actions. Further, proton pump inhibitors (PPI) may interfere with clopidogrel's actions by functionally reducing the ability of CYP2C19 to convert clopidogrel to its active metabolite. By attenuating clopidogrel's actions, both polymorphisms and drug interactions may increase the risk of thrombotic events during clopidogrel therapy. This review will explore the current evidence relating to the association between PPIs, genetic polymorphisms and poor response to clopidogrel. Routine genetic testing cannot be recommended for patients receiving dual antiplatelet therapy (DAPT). However, it may have a role for patients with an episode of stent thrombosis, prior to planned high-risk stenting or major bleeding. Regarding concomitant clopidogrel and PPI therapy, it is recommended that only patients with previous gastrointestinal (GI) bleeding or multiple risk factors for GI bleeding should be prescribed gastroprotection. This is due to the uncertainty surrounding the clinical significance of this interaction given the discordant biochemical and clinical data, conflicting results from observational studies and the limitations of the COGENT study. Pantoprazole seems least likely to interact with clopidogrel and most suitable for use in patients receiving DAPT.

Influence of CYP2C9 and CYP2C19 genetic polymorphisms on pharmacokinetics and pharmacodynamics of gliclazide in healthy Chinese Han volunteers

BACKGROUND AND OBJECTIVE

CYP2C9 is the major contributor to gliclazide metabolic clearance in vitro, while the pharmacokinetics of gliclazide modified release are affected mainly by CYP2C19 genetic polymorphisms in vivo. This study aims to investigate the influence of CYP2C9 and CYP2C19 genetic polymorphisms on the pharmacokinetics and pharmacodynamics of gliclazide in healthy Chinese Han volunteers.

METHODS

Eighteen healthy Han subjects with various combinations of CYP2C9 and CYP2C19 genotypes received 80 mg gliclazide. Plasma gliclazide concentrations were measured by a liquid chromatography-tandem mass spectrometry method for 84 h and plasma glucose and insulin levels were measured up to 15 h post-dose.

RESULTS AND DISCUSSION

There was no difference in either pharmacokinetic and or pharmacodynamic parameters of gliclazide when group A (CYP2C9*1/*1, CYP2C19 extensive metabolizers) was compared with group B (CYP2C9*1/*3, CYP2C19 *1/*1). When group C (CYP2C9*1/*1 and CYP2C19 poor metabolizers) was compared with group A, the AUC(0-∞) and C(max) in group C were significantly higher [83.94 ± 40.41 vs. 16.39 ± 5.10 μg·h/mL (P = 0.000) and 1.50 ± 0.85 vs. 0.45 ± 0.18 μg/mL (P = 0.000)], and the oral clearance was significantly lower [1.17 ± 0.63 vs. 5.38 ± 1.86 L/h (P = 0.000)]. The half-life of gliclazide was also significantly prolonged in group C subjects when compared with that of group A (33.47 ± 12.39 vs. 19.34 ± 10.45 h), but the difference was not significant (P = 0.052). The increase in serum glucose level at 11 h after dosing (ΔC(glu11)) in group C was significantly higher than that of group A (-1.08 ± 0.42 vs. 0.22 ± 1.01 mmol/L, P = 0.022). The corresponding insulin levels showed no difference between the two groups.

CONCLUSION

CYP2C9*3 was not associated with any change in the disposition of gliclazide. CYP2C19 polymorphisms appear to exert the dominant influence on the pharmacokinetics of gliclazide in healthy Chinese Han subjects, and may also affect the observed pharmacodynamics of the drug as a result.

Effect of CYP2C19 genotypes on the pharmacokinetic/pharmacodynamic relationship of rabeprazole after a single oral dose in healthy Chinese volunteers

AIMS

To explore the pharmacokinetic/pharmacodynamic relationship of rabeprazole and the role of CYP2C19 genotypes after a single oral dose in healthy Chinese volunteers by a population approach.

METHODS

Plasma concentration time profile data and intragastric pH values of 19 genotyped healthy male adults after a single oral dose of rabeprazole in an open label randomized fashion were used for this population analysis. Simulation technology was performed to examine the rabeprazole response in subjects with different CYP2C19 genotypes to further investigate the effect of acid inhibition.

RESULTS

The pharmacokinetics of rabeprazole was characterized by a two-compartment model with first order absorption and with an absorption lag-time. The results show that clearance of rabeprazole was affected by CYP2C19 genotypes (average clearances of homEM, hetEM, and PM were 13.9, 11.5, and 8.74 L·h(-1) respectively). An effect compartment with a sigmoidal Emax model was considered more rational for analyzing the relationship between rabeprazole concentrations and intragastric pH values. Simulated results suggest that rabeprazole 20 mg once daily for PMs is sufficient, but might be administered more frequently for other genotypes in treating gastro-esophageal reflux disease.

CONCLUSION

The CYP2C19 genotype played a considerable role in the pharmacokinetic characteristics of rabeprazole, and this might need to be taken into account for clinical use.

Rabeprazole can overcome the impact of CYP2C19 polymorphism on quadruple therapy

OBJECTIVES

The prospective study was designed to clarify the impact of CYP2C19 on quadruple therapies and survey the efficacies of rabeprazole-based quadruple therapy for Helicobacter pylori infection after failure of standard triple therapies.

PATIENTS AND METHODS

From January 2007 to March 2009, 1055 H. pylori-infected patients received standard triple regimens (proton-pump inhibitor (PPI), clarithromycin, and amoxicillin). Helicobacter pylori eradication was achieved in 865 (81.9%) subjects. One hundred ninety eradication-failure patients were enrolled and randomly assigned to receive a 7-day eradication therapy. Ninety-six patients were treated with esomeprazole-based quadruple rescue therapies (EB), while 94 patients were treated with rabeprazole-based quadruple rescue therapies (RB). Follow-up endoscopy was done 16 weeks later to assess the treatment response. Patients' responses, CYP2C19 genotypes, and antibiotics resistances were also examined.

RESULTS

Intention-to-treat analysis revealed that RB had better eradication rates than EB (EB: 72.9%; 95% CI: 64.9-80.9% and RB: 78.7%; 95% CI 72.5-84.9%) (p value = .543). Per-protocol results were EB = 75.3%; 95% CI: 70.3-80.3% and RB = 85.1%; 95% CI: 80.6-89.6% (p value = .0401). Both regimens had similar compliance (p value = 0.155) and adverse events (p value = 0.219). We also surveyed those patients without resistance of any antibiotics. RB still showed better outcome than EB. Our data showed that esomeprazole-based regimen and CYP2C19 Hom EM genotype were important predictors for eradication failure.

CONCLUSIONS

In quadruple therapy, rabeprazole-based regimens had better efficacy than esomeprazole-based regimens. CYP2C19 polymorphism also played an important role in quadruple therapy. It seems advisable to change PPI to rabeprazole in second-line quadruple therapy.

Platelet pharmacogenomics

Platelet responsiveness to conventional antiplatelet therapy underlies a high interindividual variability influenced by various factors. For instance, antiplatelet therapy does not curtail the expected effects in a relevant number of patients as demonstrated by the occurrence of repeated cardiovascular events including stent thrombosis and/or by inadequate platelet inhibition measured by in vitro platelet function assays. Besides non-genetic factors such as age, gender, liver and renal function and co-medication, considerable variation of antiplatelet drug responsiveness can be attributed to genetic factors including polymorphisms and genetic variants of platelet surface proteins and drug metabolizing enzymes. Nowadays, platelet pharmacogenomics has started a new field with the goal to link genetic information of various drug targets to interindividual variability of drug response. Evolving data from large cohort studies suggest a promising role for pharmacogenomics in the context of antiplatelet therapy. Additionally, with the revolution of low cost and high-throughput genotyping techniques, genetic testing has become affordable for clinical application and individualization of therapy. However, a key issue to define the future role of pharmacogenomics will rely on the benefit and the timeliness of implementing the genetic information into therapeutic decision. Hence, it warrants further investigations to document the prognostic effects of therapeutic alterations in distinct genotypes. Concerning the safety profile of emerging antiplatelet and antithrombotic drugs in certain risk groups it would be fatal to individualize treatment barely on behalf of an atherothrombotic genotype. In contrast, individual risk assessment combining non-genetic information and pharmacogenetic analysis represents a reasonable concept. Here, we provide a review on current data describing the role of pharmacogenomics in the field of antiplatelet drug treatment in cardiovascular patients with future directions.

Influence of CYP2C19 on the relationship between pharmacokinetics and intragastric pH of omeprazole administered by successive intravenous infusions in Chinese healthy volunteers

OBJECTIVES

To explore the effect of cytochrome P450 2C19 (CYP2C19) polymorphisms on the relationship between the pharmacokinetics and pharmacodynamics of omeprazole administered by intravenous successive infusions in Chinese healthy volunteers.

METHODS

A total of 21 subjects [7 homozygous extensive metabolizers (homEMs), 9 heterozygous extensive metabolizers (hetEMs), 5 poor metabolizers (PMs)] received a 5-day course of omeprazole (40 mg) administered as a single dose daily during a 30-min period. Plasma concentrations were monitored by sampling at very short intervals for the first 8.5 h post-omeprazole administration and at 24 h post-administration, and intragastric pH was recorded on days 1 and 5.

RESULTS

After a single dose, both the area under the plasma concentration-time curve (AUC) and peak concentration (C(max)) were higher in PMs than in EMs. Both the mean half-life (t((1/2))) and total clearance in PMs were significantly higher and lower than those in homEMs and EMs, respectively. Mean AUC and C(max) ratios in homEMs, hetEMs, and PMs were 1.0:1.1:1.4 and 1.0:1.0:1.1, respectively. Relative to the values determined after a single dose in EMs, after repeated doses, the intragastric pH, AUC, C(max), and t((1/2)) had increased significantly, while the total clearance had decreased significantly. Mean AUC and C(max) ratios in homEMs, hetEMs, and PMs were 1.4:1.4:1.5 and 1.2:1.2:1.3, respectively, compared to those of a single dose. The mean intragastric pH was significantly higher in PMs than in EMs after the fifth dose.

CONCLUSIONS

There is a relationship between the pharmacokinetics and pharmacodynamics of omeprazole, with the latter depending in part on the duration of administration as evidenced by a higher AUC or C(max) and intragastric pH resulting from repeated dosing.

Efficacy and pharmacokinetics of pantoprazole in alpacas

BACKGROUND

Despite frequent clinical use, information about the pharmacokinetics and efficacy of pantoprazole in camelids is not available.

OBJECTIVES

To examine the pharmacokinetics of both IV and SC pantoprazole and to determine whether pantoprazole administration would increase 3rd compartment pH in alpacas.

ANIMALS

Six healthy adult alpacas.

METHODS

Alpacas were fitted with a 3rd compartment cannula for measuring gastric pH. After recovery, alpacas received 1 mg/kg pantoprazole IV, q24h for 3 days or 2 mg/kg SC q24h for 3 days. Alpacas received both IV and SC pantoprazole, with a minimum of 3 weeks between treatments. Third compartment pH was recorded and plasma samples were taken for pharmacokinetic analysis.

RESULTS

Pantoprazole induced a slow but sustained increase in 3rd compartment pH when given by both the IV and SC routes. Third compartment pH was significantly increased as compared with baseline values (1.81+/-0.7; mean+/-SD) at 24 (2.47+/-0.8), 48 (3.53+/-1.0) and 72 hours (4.03+/-1.3) after daily IV administration of pantoprazole. Third compartment pH increased from 1.73+/-0.6 at baseline to 3.05+/-1.1, 4.02+/-1.4, and 3.61+/-1.6 at 24, 48, and 72 hours after SC administration, respectively. Pharmacokinetic analysis demonstrated that pantoprazole had a short elimination half-life (0.47+0.06 h) and a high clearance rate (12.2+/-2.9 mL/kg/min) after both IV and SC administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Based on the results of this study, pantoprazole represents a safe and effective drug for increasing 3rd compartment pH in camelids. Either IV or SC administration is likely to be an effective treatment for gastric ulcers.

CYP2C19 genotypes in the pharmacokinetics/pharmacodynamics of proton pump inhibitor-based therapy of Helicobacter pylori infection

IMPORTANCE OF THE FIELD

Proton pump inhibitors (PPIs) are potent gastric acid inhibitors. Therapies with a PPI and antibiotics are used to cure Helicobacter pylori (H. pylori) infection, which is closely related to many gastrointestinal diseases. Most PPIs are mainly metabolized by cytochrome 2C19 (CYP2C19). The genetic polymorphisms of CYP2C19 may lead to the differences in pharmacokinetics (PK), pharmacodynamics (PD) and clinical efficacy of PPIs.

AREAS COVERED IN THIS REVIEW

The roles of PPIs on the eradication of H. pylori are summarized. The impact f CYP2C19 polymorphism on the PK and PD of PPIs is addressed and related to the present status of therapy for H. pylori infection. The opinions on the strategy of PPIs-based therapies of H. pylori infection are provided.

WHAT THE READER WILL GAIN

Update the factors that may influence the PPIs-based therapies of H. pylori infection.

TAKE HOME MESSAGE

The eradication rates of H. pylori infection are significantly different between patients who are CYP2C19 extensive metabolizers and poor metabolizers, partly because of the differences in the PK and PD of PPIs. Nonetheless, the differences can be improved by adjusting the regimens of PPIs and using antibiotics that have less H. pylori-resistance.

Effects of genetic variation at the CYP2C19/CYP2C9 locus on pharmacokinetics of chlorcycloguanil in adult Gambians

AIMS

Antimalarial biguanides are metabolized by CYP2C19, thus genetic variation at the CYP2C locus might affect pharmacokinetics and so treatment outcome for malaria.

MATERIALS & METHODS

Polymorphisms in CYP2C19 and CYP2C9 in 43 adult Gambians treated with chlorproguanil/dapsone for uncomplicated malaria were assessed. Chlorcycloguanil pharmacokinetics were measured and associations with CYP2C19 and CYP2C9 alleles and CYP2C19 metabolizer groups investigated.

RESULTS

All CYP2C19/CYP2C9 alleles obeyed Hardy-Weinberg equilibrium. There were 15 CYP2C19/2C9 haplotypes with a common haplotype frequency of 0.23. Participants with the CYP2C19*17 allele had higher chlorcycloguanil area under the concentration versus curve at 24 h (AUC(0-24)) than those without (geometric means: 317 vs 216 ng.h/ml; ratio of geometric means: 1.46; 95% CI: 1.03 to 2.09; p = 0.0363) and higher C(max) (geometric mean ratio: 1.52; 95% CI: 1.13 to 2.05; p = 0.0071).

CONCLUSION

CYP2C19*17 determines antimalarial biguanide metabolic profile at the CYP2C19/CYP2C9 locus.

A comparative study of proton-pump inhibitor tests for Chinese reflux patients in relation to the CYP2C19 genotypes

BACKGROUND

The proton-pump inhibitor (PPI) test has been proposed as a valuable tool for diagnosing gastroesophageal reflux disease in Western populations.

GOALS

We aim to compare the diagnostic accuracy of the PPI test using rabeprazole and pantoprazole in a Chinese population with a higher prevalence of poor PPI metabolization.

STUDY

After diagnostic endoscopy, patients with gastroesophageal reflux disease symptoms were randomly assigned to a 2-week test with rabeprazole (20 mg b.i.d.) or pantoprazole (40 mg b.i.d.). Therapeutic response was assessed with a 5-grade daily record. Genotypes of cytochrome P450 (CYP) 2C19 polymorphism were determined.

RESULTS

Of the 178 patients who completed the study, 92 (51.7%) had erosive esophagitis and 78 (48.3%) were endoscopy-negative reflux disease. On the basis of 50% reduction of symptoms, there was a nonsignificant difference of diagnostic performances between rabeprazole and pantoprazole. For the CYP2C19 genotypes, 138 (87.3%) were determined to be extensive metabolizers (EMs) and 20 (12.7%) were poor metabolizers (PMs). When comparing the EMs and PMs, the diagnostic specificity in the prediction of erosive esophagitis was higher in the EMs (57.6% vs. 20.0%, P=0.040), as was the accuracy (74.6% vs. 50.0%, P=0.023). There were no differences in the sensitivity, positive predictive value, or negative predictive value.

CONCLUSIONS

CYP2C19 genotypic polymorphism was related to a higher possibility of false-positive results for patients who metabolized PPI poorly. High-dose rabeprazole and pantoprazole showed a similar diagnostic performance.

AJG series: molecular biology for clinicians

Pharmacogenetics is an evolving field that provides the link between an individual's genetic code and drug metabolism and drug response. This field offers the great promise of individualized medication selection and optimized dosage to maximize treatment response and to minimize adverse side effects. As our understanding of the role of the effects of genetic variants on drug metabolism and body drug processing grows, so does our ability to educate and inform our patients about expected treatment response to the medications being prescribed to them. This brief review will provide an overview of genetics, pharmacogenetics, and current and future examples of genetic variants predicting drug response in gastrointestinal disease, and the limitations and the promise of this exciting and developing field.

Pharmacokinetics and drug metabolism in the elderly

Aging involves progressive impairments in the functional reserve of multiple organs, which might also affect drug metabolism and pharmacokinetics. In addition, the elderly population will develop multiple diseases and, consequently, often has to take several drugs. As the hepatic first-pass effect of highly cleared drugs could be reduced (due to decreases in liver mass and perfusion), the bioavailability of some drugs can be increased in the elderly. Significant changes in body composition occur with advancing age. Lipophilic drugs may have an increased volume of distribution (Vd) with a prolonged half-life, and water-soluble drugs tend to have a smaller Vd. In the elderly, hepatic drug clearance of some drugs can be reduced by up to 30% and CYP-mediated phase I reactions are more likely to be impaired than phase II metabolism, which is relatively preserved in the elderly. Concerning the most important CYP3A4 studies with human liver microsomes and clinical studies with the validated probe, midazolam, it is indicated that there are no significant differences in CYP3A4 activity between young and old populations. Finally, renal excretion is decreased (up to 50%) in about two thirds of elderly subjects, but confounding factors such as hypertension and coronary heart disease account also for a decline in kidney function. In conclusion, age-related physiological and pharmacokinetic changes as well as the presence of comorbidity and polypharmacy will complicate drug therapy in the elderly.

The transcriptional regulation of the human CYP2C genes

In humans, four members of the CYP2C subfamily (CYP2C8, CYP2C9, CYP2C18, and CYP2C19) metabolize more than 20% of all therapeutic drugs as well as a number of endogenous compounds. The CYP2C enzymes are found predominantly in the liver, where they comprise approximately 20% of the total cytochrome P450. A variety of xenobiotics such as phenobarbital, rifampicin, and hyperforin have been shown to induce the transcriptional expression of CYP2C genes in primary human hepatocytes and to increase the metabolism of CYP2C substrates in vivo in man. This induction can result in drug-drug interactions, drug tolerance, and therapeutic failure. Several drug-activated nuclear receptors including CAR, PXR, VDR, and GR recognize drug responsive elements within the 5' flanking promoter region of CYP2C genes to mediate the transcriptional upregulation of these genes in response to xenobiotics and steroids. Other nuclear receptors and transcriptional factors including HNF4alpha, HNF3gamma, C/EBPalpha and more recently RORs, have been reported to regulate the constitutive expression of CYP2C genes in liver. The maximum transcriptional induction of CYP2C genes appears to be achieved through a coordinative cross-talk between drug responsive nuclear receptors, hepatic factors, and coactivators. The transcriptional regulatory mechanisms of the expression of CYP2C genes in extrahepatic tissues has received less study, but these may be altered by perturbations from pathological conditions such as ischemia as well as some of the receptors mentioned above.

Pharmacokinetic- pharmacodynamic analysis of the role of CYP2C19 genotypes in short-term rabeprazole-based triple therapy against Helicobacter pylori

AIMS

The aim was to explore the role of CYP2C19 polymorphism in short-term rabeprazole-based triple therapy against Helicobacter pylori infection.

METHODS

Patients with H. pylori infection were tested for CYP2C19 genotype as poor metabolizers (PMs) or extensive metabolizers (EMs, homozygous EM or heterozygous EM) and given rabeprazole for 7 days. Antibiotics (clarithromycin and amoxicillin) were given on days 1-4, days 4-7, or days 1-7. A direct link model with an effect compartment was used in the population pharmacokinetic-pharmacodynamic analysis. The status of H. pylori infection was evaluated.

RESULTS

Rabeprazole clearance was lower in CYP2C19 PMs than in EMs (with average values of 10.7 vs. 16.8 l h(-1) in PMs and EMs, respectively), resulting in higher plasma levels in the former group. The values of EC(50) and k(eo) of gastrin response increased with multiple doses of rabeprazole. The k(eo) values were lower in CYP2C19 PMs than in EMs on day 1 (0.012 vs. 0.017 x 10(-4) l min(-1)), and higher than in EMs on day 4 (0.804 vs. 0.169 x 10(-4) l min(-1)) of rabeprazole treatment. The predicted gastrin-time profile showed a higher response in CYP2C19 PMs than in EMs on days 4 and 7. Helicobacter pylori was eradicated in all CYP2C19 PMs except in one patient infected by a resistant strain. In contrast, in CYP2C19 EMs the eradication rates ranged from 58 to 85%.

CONCLUSIONS

CYP2C19 genotypes play a role in H. pylori eradication therapy. Rabeprazole-based short-term triple therapy may be applicable in CYP2C19 PMs for H. pylori eradication.

Identification and molecular characterization of triple- and quadruple-resistant Helicobacter pylori clinical isolates in Germany

OBJECTIVES

The aim of this study was to estimate the frequency of triple- and quadruple-resistant Helicobacter pylori isolated in Germany, to characterize those isolates molecular genetically and to identify risk factors for the development of multiresistance.

METHODS

Antimicrobial susceptibility to metronidazole, clarithromycin, amoxicillin, tetracycline, ciprofloxacin/levofloxacin and rifampicin in 1118 clinical isolates obtained between July 2006 and December 2007 was tested by the Etest method. For patients harbouring triple- or quadruple-resistant strains (n = 169), data on prior eradication therapies and underlying diseases were collected and evaluated. A select number of quadruple- and triple-resistant strains were examined for resistance-mediating mutations in their 23S rRNA, 16S rRNA, gyrA and rpoB genes, respectively.

RESULTS

From 1118 clinical isolates, 13.4% (n = 150) showed phenotypic resistance to metronidazole, clarithromycin and quinolones and 0.9% (n = 10) to metronidazole, clarithromycin and rifampicin; one isolate exhibited resistance to clarithromycin, quinolones and rifampicin. In eight isolates (0.7%), we detected phenotypic quadruple resistance to metronidazole, clarithromycin, quinolones and rifampicin or tetracycline. Triple- and quadruple-resistant strains harboured resistance-associated mutations in their 23S rRNA, 16S rRNA, gyrA or rpoB genes and were nearly exclusively isolated from patients who had already been unsuccessfully treated on multiple occasions.

CONCLUSIONS

We show that more than 15% of H. pylori strains isolated from routine samples in the German National Reference Centre are resistant to three or more antimicrobials and identified prior unsuccessful eradication therapies as a key factor for the development of multiresistance. Our data emphasize the need for further comprehensive surveillance studies monitoring the role of treatment regimens in antimicrobial resistance in H. pylori.

Need for reassessment of reported CYP2C19 allele frequencies in various populations in view of CYP2C19*17 discovery: the case of Greece

Introduction: CYP2C19*17 is a novel variant allele causing ultrarapid metabolism of CYP2C19 substrates. In the present study we investigated the CYP2C19*17 allelic frequency and recalculated previously reported frequencies of the CYP2C19*1/*1 genotype and of all genotype-derived phenotypes for CYP2C19 in the Greek population. Materials & methods: A total of 283 nonrelated healthy Greek ethnic subjects that had already been genotyped for CYP2C19*2 and *3 alleles as well as for CYP2D6 and CYP2C9 variant alleles participated in the study. The CYP2C19*17 allele was genotyped by the PCR-RFLP method. Results: The CYP2C19*17 allele frequency was 19.61%. The prevalence of CYP2C19*17 carriers in the Greek population was estimated at 31.80%, while the frequency of CYP2C19*1/*1 genotype was recalculated to 44.17% from 75.97% in our previous study. Several subjects possessing both CYP2C19*17 and variant alleles of CYP2D6 and CYP2C9 were also identified. Discussion & conclusion: The CYP2C19*17 allele is present in Greeks at a high frequency similar to that found in other European populations of Caucasian origin. Our study highlights the need of reassessing and updating CYP2C19 allelic frequencies in various populations in view of the major role that CYP2C19*17 may have in predicting the clinical outcome of drugs metabolized by CYP2C19.

Relative potency of proton-pump inhibitors-comparison of effects on intragastric pH

AIM

Comparative potency of proton-pump inhibitors (PPIs) is an important clinical issue. Most available trials have compared the different PPIs at one or a few selected specific dosages, making it difficult to derive quantitative equivalence dosages. Here we derived PPI dose equivalents based on a comprehensive assessment of dose-dependent effects on intragastric pH.

METHODS

All available clinical studies reporting the effects of PPIs on mean 24-h intragastric pH were sought from electronic databases including Medline. Studies included were restricted to those targeting the Caucasian population, and healthy volunteers or gastroesophageal reflux disease (GERD) patients. The dose-effect relationships for mean 24-h intragastric pH and for percentage of time with pH > 4 in 24 h were analyzed for each PPI using pharmacodynamic modeling with NONMEM and a model integrating all available data.

RESULTS

Fifty-seven studies fulfilled the inclusion criteria. Based on the mean 24-h gastric pH, the relative potencies of the five PPIs compared to omeprazole were 0.23, 0.90, 1.00, 1.60, and 1.82 for pantoprazole, lansoprazole, omeprazole, esomeprazole, and rabeprazole, respectively. Compared with healthy volunteers, patients with GERD needed a 1.9-fold higher dose and Helicobacter pylori-positive individuals needed only about 20% of the dose to achieve a given increase in mean 24-h intragastric pH.

CONCLUSION

The present meta-analysis provides quantitative estimates on clinical potency of individual PPIs that may be helpful when switching between PPIs and for assessing the cost-effectiveness of specific PPIs. However, our estimates must be viewed with caution because only a limited dose range has been tested and not exactly the same study conditions were applied for the different substances.

CYP2C19 and nongenetic factors predict poor responsiveness to clopidogrel loading dose after coronary stent implantation

Aims: To investigate an association of responsiveness to clopidogrel loading dose with genotypes of cytochrome P450 (CYP) 2C19, other CYP isozymes and nongenetic factors in patients with coronary artery disease. Materials & methods: Genotyping for CYP2C19 (*2, *3 and *17), CYP3A4*1B and CYP3A5*3 variants was performed in patients (n = 237) who underwent percutaneous coronary intervention. Adenosine diphosphate-induced platelet aggregation was determined after first administration of 600 mg clopidogrel. Results: CYP2C19*2 carriers showed significantly increased residual platelet aggregation (RPA) (OR: 4.6; 95% CI: 2.5–8.7; p < 0.0001) compared with noncarriers. All other polymorphisms had no influence on RPA. For the development of a risk score for better prediction of RPA, CYP2C19*2 genotype and previously identified nongenetic risk factors (age >65 years, Type 2 diabetes mellitus, decreased left ventricular function, renal failure and acute coronary syndrome) were analyzed. Multivariable logistic regression analysis showed a significant correlation of the nongenetic factors (χ 2  = 5.32; p = 0.021) and CYP2C19*2 (χ 2  = 21.31; p < 0.0001) with high RPA, and an even higher association for the combination of both (χ 2  = 25.85; p < 0.0001). Conclusions: Prediction of responsiveness after clopidogrel loading dose may substantially be improved by adding CYP2C19*2 genotype to nongenetic risk factors.

Proton pump inhibitors: an update of their clinical use and pharmacokinetics

BACKGROUND

Proton pump inhibitors (PPIs) represent drugs of first choice for treating peptic ulcer, Helicobacter pylori infection, gastrooesophageal reflux disease, nonsteroidal anti-inflammatory drug (NSAID)-induced gastrointestinal lesions (complications), and Zollinger-Ellison syndrome.

RESULTS

The available agents (omeprazole/esomeprazole, lansoprazole, pantoprazole, and rabeprazole) differ somewhat in their pharmacokinetic properties (e.g., time-/dose-dependent bioavailability, metabolic pattern, interaction potential, genetic variability). For all PPIs, there is a clear relationship between drug exposure (area under the plasma concentration/time curve) and the pharmacodynamic response (inhibition of acid secretion). Furthermore, clinical outcome (e.g., healing and eradication rates) depends on maintaining intragastric pH values above certain threshold levels. Thus, any changes in drug disposition will subsequently be translated directly into clinical efficiency so that extensive metabolizers of CYP2C19 will demonstrate a higher rate of therapeutic nonresponse.

CONCLUSIONS

This update of pharmacokinetic, pharmacodynamic, and clinical data will provide the necessary guide by which to select between the various PPIs that differ-based on pharmacodynamic assessments-in their relative potencies (e.g., higher doses are needed for pantoprazole and lansoprazole compared with rabeprazole). Despite their well-documented clinical efficacy and safety, there is still a certain number of patients who are refractory to treatment with PPIs (nonresponder), which will leave sufficient space for future drug development and clinical research.

Pharmacokinetics/genotype associations for major cytochrome P450 enzymes in native and first- and third-generation Japanese populations: comparison with Korean, Chinese, and Caucasian populations

Application of foreign clinical data across geographic regions can accelerate drug development. Drug disposition can be variable, and identification of factors influencing responsible pharmacokinetic/pharmacogenomic approaches could facilitate the universal application of foreign data and reduce the total amount of phase III clinical trials evaluating risks in different populations. Our objective was to establish and compare genotype (major cytochrome P450 (CYP) enzymes)/phenotype associations for Japanese (native and first- and third-generation Japanese living abroad), Caucasian, Chinese, and Korean populations using a standard drug panel. The mean metabolic ratios (MRs) for the four ethnic groups were similar except for a lower activity of CYP2D6 in Caucasians and CYP2C19 in Asians. Genotype, not ethnicity, impacted the MR for CYP2C9, CYP2C19, and CYP2D6; neither affected CYP1A2, CYP2E1, and CYP3A4/5 activities. We conclude that equivalent plasma drug concentrations and metabolic profiles can be expected for native Japanese, first- and third-generation Japanese, Koreans, and Chinese for compounds handled through these six CYP enzymes.

Increased omeprazole metabolism in carriers of the CYP2C19*17 allele; a pharmacokinetic study in healthy volunteers

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

The only existing study of CYP2C19*17-associated alterations in drug pharmacokinetics was retrospective and compared probe drug metabolic ratios. The CYP2C19*17 allele had been associated with a two- and fourfold decrease in omeprazole and S/R-mephenytoin metabolic ratios.

WHAT THIS STUDY ADDS

This study characterized the single-dose pharmacokinetics of omeprazole, along with the 5-hydroxy and sulphone metabolites, in CYP2C19*17/*17 and CYP2C19*1/*1 subjects. The observed differences in omeprazole AUC(infinity) suggest that the CYP2C19*17 allele is an important explanatory factor behind individual cases of therapeutic failure. AIMS To investigate the influence of the CYP2C19*17 allele on the pharmacokinetics of omeprazole, a commonly used CYP2C19 probe drug, in healthy volunteers.

METHODS

In a single-dose pharmacokinetic study, 17 healthy White volunteers genotyped as either CYP2C19*17/*17 or CYP2C19*1/*1 received an oral dose of 40 mg of omeprazole. Plasma was sampled for up to 10 h postdose, followed by quantification of omeprazole, 5-hydroxy omeprazole and omeprazole sulphone by high-performance liquid chromatography.

RESULTS

The mean omeprazole AUC(infinity) of 1973 h nmol l(-1) in CYP2C19*17/*17 subjects was 2.1-fold lower [95% confidence interval (CI) 1.1, 3.3] than in CYP2C19*1/*1 subjects (4151 h nmol l(-1), P = 0.04). A similar trend was observed for the sulphone metabolite with the CYP2C19*17/*17 group having a mean AUC(infinity) of 1083 h nmol l(-1), 3.1-fold lower (95% CI 1.2, 5.5) than the CYP2C19*1/*1 group (3343 h nmol l(-1), P = 0.03). A pronounced correlation (r(2) = 0.95, P < 0.0001) was seen in the intraindividual omeprazole AUC(infinity) and omeprazole sulphone AUC(infinity) values.

CONCLUSIONS

The pharmacokinetics of omeprazole and omeprazole sulphone differ significantly between homozygous CYP2C19*17 and CYP2C19*1 subjects. For clinically important drugs that are metabolized predominantly by CYP2C19, the CYP2C19*17 allele might be associated with subtherapeutic drug exposure.

Pharmacokinetics of the new proton pump inhibitor ilaprazole in Chinese healthy subjects in relation to CYP3A5 and CYP2C19 genotypes

BACKGROUND

PPIs are widely used in peptic diseases, and this paper is to investigate the kinetic characteristics of a new PPI ilaprazole in Chinese healthy subjects and the association with CYP3A5 and CYP2C19 polymorphisms.

METHODS

21 subjects were selected and treated with 10mg ilaprazole according to their CYP3A5*3 genotypes (including 7 of CYP3A5*1/*1, 7 of *1/*3, and 7 of *3/*3). The plasma concentrations of ilaprazole and its metabolites were monitored by LC-MS/MS method.

RESULTS

The C(max), AUC((0-6)), AUC((0-48)) and AUC((0-infinity)) of ilaprazole were all significantly different across the 3 CYP3A5 genotypes (including 4 of CYP3A5*1/*1, 4 of *1/*3, 3 of *3/*3; P<0.05) in CYP2C19 wild-type subjects (CYP2C19 wt/wts), similar variety of C(max) and AUC((0-6)) among CYP3A5 genotypes (including 3 of CYP3A5*1/*1, 3 of *1/*3, 4 of *3/*3; P<0.05) were also observed in CYP2C19 heterozygous subjects (CYP2C19 wt/mts). The sulfoxidation metabolic index (measure of collective CYP3A activity) indicates that the CYP3A5*1/*1, (high-expressers), *1/*3, (low-expressers), and *3/*3 (no-expressers) groups have medium, lowest and highest activities on ilaprazole metabolism, inconsistent with genotype-based CYP3A5 enzymatic activity. Further analysis showed no correlation between ilaprazole metabolism and CYP2C19 genotypes, evidenced by that the AUC((0-infinity)) of ilaprazole from either CYP3A5*1/*1 or CYP3A5*1/*3 groups was much higher in CYP2C19 wt/wts (n=4) than that in CYP2C19 wt/mts (n=3) (P<0.001), but the C(max) and AUC((0-6)) of ilaprazole from CYP3A5*3/*3 groups, were significantly lower in CYP2C19 wt/wts (n=3) compared to CYP2C19 wt/mts (n=4) (P<0.01).

CONCLUSIONS

There was no demonstrated relationship between ilaprazole metabolism and CYP3A5 polymorphisms.

Limited frequency of the CYP2C19*17 allele and its minor role in a Japanese population

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

A novel CYP2C19 gene variant, CYP2C19*17, is associated with increased metabolic activity. Ethnic differences in the frequency of the variant allele have been reported. However, the frequency of the CYP2C19*17 allele has not been studied in the Japanese population.

WHAT THIS STUDY ADDS

In a population of 265 healthy Japanese subjects, a low frequency (1.3%) of the CYP2C19*17 allele was observed. The limited frequency of the *17 allele and the absence of a subject homozygous for *17 indicated that CYP2C19*17 would play a minor role in a Japanese population.

AIMS

We investigated the CYP2C19*17 allelic frequency in Japanese subjects, and evaluated whether CYP2C19*17 is an important determinant of interindividual variability of CYP2C19 activity.

METHODS

We enrolled 265 subjects to determine their CYP2C19 genotype and plasma metabolic ratio following a single dose of 40 mg omeprazole.

RESULTS

Seven subjects heterozygous for CYP2C19*17 and no *17/*17 subjects resulted in the CYP2C19*17 frequency being 1.3%. These heterozygotes had moderate metabolic activities when compared with the metabolic ratio of the other subjects.

CONCLUSIONS

The low frequency of CYP2C19*17 and the absence of *17/*17 indicates that CYP2C19*17 plays a minor role in the Japanese population.

Pharmacogenomics in gastrointestinal disorders

It is anticipated that unraveling the human genome will have a direct impact on the management of specific diseases. Variations or mutations in genes involved in drug metabolism or disease pathophysiology in gastroenterology and hepatology are expected to have effect on response to therapy. The spectrum of diseases is vast. Thus, we focus this review on clinical pharmacogenetics of inflammatory bowel disease, Helicobacter pylori infections, gastroesophageal reflux disease, irritable bowel syndrome, liver transplantation, and colon cancer. Although only a few genotyping tests are used regularly in clinical practice, we anticipate that in the future there will be more routine use of many of the tests described in this review.

Treatment strategy to eradicate Helicobacter pylori infection: impact of pharmacogenomics-based acid inhibition regimen and alternative antibiotics

The eradication rates of Helicobacter pylori by the triple therapy consisting of a proton pump inhibitor (PPI) and two antimicrobial agents are mainly influenced by bacterial susceptibility to antimicrobial agents and magnitude of acid inhibition during the treatment with a PPI. Acid inhibition during the treatment is affected by the dosing schemes of acid inhibitory drugs (i.e., PPI), genotypes of drug-metabolizing enzymes (i.e., CYP450 2C19), drug transporters (i.e., multi-drug resistant transporter-1) and inflammatory cytokines (i.e., IL-1 beta). Modification of dosing schedules of a PPI, such as frequent PPI dosing and concomitant dosing with a histamine 2-receptor antagonist, could overcome these genetics-related differences in therapeutic effectiveness. For attaining higher eradication rates, the tailored regimen based on the relevant pharmacogenomics is preferable.

Influence of cytochrome P450 2C19 genetic polymorphism and dosage of rabeprazole on accuracy of proton-pump inhibitor testing in Chinese patients with gastroesophageal reflux disease

BACKGROUND AND AIM

To evaluate the optimal dosage of rabeprazole for proton-pump inhibitor (PPI) testing of gastroesophageal reflux disease (GERD) and to test the influence of cytochrome P450 (CYP) 2C19 polymorphism in a population with a high prevalence of people who metabolize PPI poorly.

METHODS

In this randomized, open-label trial, patients with symptoms suggestive of GERD were randomized to receive a 2-week test with 20- or 40-mg rabeprazole after diagnostic endoscopy. Symptom response was assessed with a four-grade daily record; in addition, DNA from peripheral blood leukocytes was genotyped for CYP2C19 polymorphism with the polymerase chain reaction-restriction fragment length polymorphism technique.

RESULTS

Of the 164 patients who completed the study, 69 (42.1%) were endoscopically positive for esophagitis; the remaining 95 (57.9%) were diagnosed with endoscopy-negative reflux disease. Based on the best cut-off value for 50% symptom reduction, the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy for detecting erosive esophagitis were 68%, 70%, 66%, 72%, and 69%, respectively, for the 20-mg regimen, and 84%, 71%, 64%, 88%, and 76%, respectively, for the 40-mg regimen, a non-significant difference. Regarding the genotype, 60 (39%) patients had two wild-type alleles, 63 (40.9%) had one variant allele, and 31 (20.1%) had two variant CYP2C19 alleles. The presence of a variant allele did not alter the diagnostic efficacy of PPI testing.

CONCLUSIONS

Both dose levels of rabeprazole proved efficacious in the diagnosis of GERD. Various measures of test accuracy were unrelated to the status of the CYP2C19 genotype.

The clinical role of genetic polymorphisms in drug-metabolizing enzymes

For most drug-metabolizing enzymes (DMEs), the functional consequences of genetic polymorphisms have been examined. Variants leading to reduced or increased enzymatic activity as compared to the wild-type alleles have been identified. This review tries to define potential fields in the therapy of major medical conditions where genotyping (or phenotyping) of genetically polymorphic DMEs might be beneficial for drug safety or therapeutic outcome. The possible application of genotyping is discussed for depression, cardiovascular diseases and thromboembolic disorders, gastric ulcer, malignant diseases and tuberculosis. Some drugs used for relief of these ailments are metabolized with participation of genetically polymorphic DMEs including CYP2D6, CYP2C9, CYP2C19, thiopurine-S-methyltransferase, dihydropyrimidine dehydrogenase, uridine diphosphate glucuronosyltransferase and N-acetyltransferase type 2. Current evidence suggests that taking genetically determined metabolic capacities of DMEs into account has the potential to improve individual risk/benefit relationship. However, more prospective studies with clinical endpoints are needed before the paradigm of 'personalized medicine' based on DME variants can be established.

Treatment and dosing of Helicobacter pylori infection: when pharmacology meets clinic

Helicobacter pylori infection is a major cause of diseases located in the upper gastrointestinal tract. Successful eradication of the bacteria may improve H. pylori-related symptomatic complaints in functional dyspepsia, cure peptic ulcer disease and prevent gastric cancer. As vaccines are not available, the search for the optimal drug regimen has dominated the last decade. Today, most countries prefer a 7- to 10-day regimen containing a proton pump inhibitor, clarithromycin and amoxicillin as first-line treatment. An alternative (or second-line) treatment contains a proton pump inhibitor, bismuth, tetracycline and metronidazole. This review also highlights the impact of new drugs, new drug combinations, and their optimal dosing required to maximise clinical outcome.

Gastrointestinal medications

Medications to address gastrointestinal disorders are among the most commonly dispensed somatic medications. The authors examine proton pump inhibitors, H(2) blockers, 5-HT(3) receptor-antagonists, and a few other drugs that are used to address this domain of medical concerns. The metabolic pathways, interactions with the P-glycoprotein transporter, and capabilities of inhibiting or inducing metabolic enzymes are elucidated for each drug. Specific drug-drug interactions with each agent are also detailed, including both psychotropic and non-psychotropic agents. Also, the article explores how different genotypic variants for specific cytochrome P450 enzymes have an impact on the effectiveness and likelihood of drug-drug interactions relating to specific gastro-intestinal medications.

Liquid chromatographic–mass spectrometry analysis and pharmacokinetic studies of a novel rabeprazole formulation, sterile powder for injection, in dogs and rats

Rabeprazole is among the most potent proton pump inhibitors (PPI) identified to date and it has been demonstrated that it is effective in such diseases as gastroesophageal reflux disease (GERD), duodenal ulcer and gastric ulcer. There is currently interest in developing a new formulation: rabeprazole sterile powder for injection (RSPI). This investigation was conducted to evaluate the preclinical pharmacokinetics of RSPI in rats and at the same time a comparative study was carried out in dogs between RSPI and Pariet tablets using liquid chromatographic-mass spectrometry analysis. The liquid chromatographic-mass spectrometry method was first conducted and validated as being specific, and having accuracy, precision, sensitivity and a satisfactory recovery. After intravenous administration of RSPI (i.v.: 2, 6 and 18 mg/kg) to rats, no significant dose-dependency was found in the CL (4.20-5.72 l/h/kg), V(area) (d) (0.94-1.32 l/kg), dose-normalized AUC (197.20-245.82 microg/l*h based on 1 mg/kg) and t(1/2) (p>0.05). In the dog, a randomized, open-label, crossover experiment was carried out to show that the mean area under the plasma concentration-time curve (AUC(0-infinity)) after i.v. administration of RSPI was at least four times larger than that following oral administration of Pariet tablet at an equivalent dose but the elimination half-life of these two formulation was similar (p>0.05). The results showed that the pharmacokinetics of RSPI was linear (r(2) = 0.98) in the dose range 2-18 mg/kg and the RSPI had a much higher AUC(0-infinity) and similar t(1/2) values compared with the enteric-coated tablet.

Clinical application of pharmacogenetics in gastrointestinal diseases

As knowledge of the human genome grows, there will be a direct impact on the management of specific diseases. Within gastroenterology and hepatology, there has been a change in the understanding of how variations or mutations in genes involved in drug metabolism or disease pathophysiology affect response to therapy. This review discusses the application of clinical pharmacogenetics to the following diseases and disorders: inflammatory bowel disease, Helicobacter pylori infections, gastroesophageal reflux disease, irritable bowel syndrome, functional dyspepsia, liver transplantation and colon cancer. Although only a few genotyping tests are regularly used in clinical practice, it is anticipated that studies will propel the routine use of many of the tests described in this review, in the future.

Genetic variation at the CYP2C locus and its association with torsemide biotransformation

In 97 unselected volunteers and two additional homozygous carriers of CYP2C9(*)3, we investigated the oral clearance of torsemide in relation to 37 polymorphisms at the CYP2C gene locus. Torsemide total oral clearance was linearly associated with the number of CYP2C9(*)3 alleles (geometric mean: 59, 40 and 20 ml/min in carriers of no, one and two alleles) and so were the methyl- and ring-hydroxylation but not the carboxylation clearance. Haplotypes including the CYP2C9(*)3 allele were similarly associated with the clearances but no other variant and no haplotype not including the CYP2C9(*)3 variant. The extended haplotype length (EHL) of the CYP2C9 haplotypes was positively associated with higher activity of the gene product. Torsemide total oral clearance was predictable with r(2)=82.1% using plasma concentrations at 0.5, 1, 2 and 24 h. In conclusion, torsemide's biotransformation strongly depended on the CYP2C9(*)3 variant but no other. Higher clearance CYP2C9 haplotypes appear to be evolutionarily selected.