CYP2C19 genotype and pharmacokinetics of three proton pump inhibitors in healthy subjects

Exploring the impact of ethnicity on drug pharmacokinetics using PBPK models: A case study with lansoprazole in Japanese subjects

AIMS

The aim of this study is to demonstrate the use of PBPK modelling to explore the impact of ethnic differences on drug PK.

METHODS

A PBPK model developed for lansoprazole was used to predict the clinical PK of lansoprazole in Japanese subjects by incorporating the physiological parameters of a Japanese population into the model. Further verification of the developed Japanese population with clinical studies involving eight other CYP substrates-omeprazole, ticlopidine, alprazolam, midazolam, nifedipine, cinacalcet, paroxetine and dextromethorphan-was also carried out.

RESULTS

The PK of lansoprazole in both Caucasian and Japanese subjects was well predicted by the model as the observed data were within the 5th and 95th percentiles across all the clinical studies. In age- and sex-matched simulations in both the Caucasian and Japanese populations, the predicted PK (mean ± SD) of a single oral dose of 30-mg lansoprazole was higher in the Japanese population in all cases, with more than twofold higher AUC of 5.98 ± 6.43 mg/L.h (95% CI: 4.72, 7.24) vs. 2.46 ± 2.45 mg/L.h (95% CI: 1.98, 2.94) in one scenario. In addition, in two out of the nine clinical DDIs of lansoprazole and the additional CYP substrates simulated using the Japanese population, the predicted DDI in Japanese was more than 1.25-fold that in Caucasians, indicating an increased DDI liability.

CONCLUSIONS

By accounting for various physiological parameters that characterize a population in a PBPK model, the impact of the different identified interethnic differences on the drug's PK can be explored, which can inform the adoption of drugs from one region to another.

Synthesis, antioxidant activity, antimicrobial efficacy and molecular docking studies of 4-chloro-2-(1-(4-methoxyphenyl)-4,5-diphenyl-1H-imidazol-2-yl)phenol and its transition metal complexes

Herein, a one-pot synthesis of tetra-substituted imidazole, 4-chloro-2-(1-(4-methoxyphenyl)-4,5-diphenyl-1H-imidazol-2-yl)phenol (HL), is reported by the reaction of benzil, 5-bromosalicylaldehyde, ammonium acetate and anisidine. The synthesized imidazole was reacted with salts of 1st row transition metals (Co(ii), Ni(ii), Cu(ii), Mn(ii) and Zn(ii)) to obtain metal complexes. The structure of the compounds was confirmed using various spectroscopic and analytical techniques. HL, which is crystalline, was characterized by SC-XRD. Subsequently, the synthesized compounds were evaluated for their antioxidant and antimicrobial activities. Antimicrobial studies revealed the more noxious nature of metal complexes compared to ligand against various strains of bacteria and fungi. Molecular docking results based on the binding energy values also supported the experimental results of the antioxidant activities of the compounds. HL was found to be a better antioxidant than metal complexes. For a better insight into the structure, computational studies of the compounds were also carried out. A clear intra-molecular charge transfer was perceived in the ligand and its metal complexes. The transfer integral values for holes (36.48 meV) were found to be higher than the electron transfer integrals (24.76 meV), which indicated that the ligand would be a better hole transporter. According to the frontier molecular orbitals of the dimer, the charge transfer within the molecule is found from monomer 1 to 2.

Pharmacokinetics and bioequivalence evaluation of omeprazole and sodium bicarbonate dry suspensions in healthy Chinese volunteers

Omeprazole and sodium bicarbonate dry suspension are effective treatments for acid-related disorders. This study compared the bioequivalence and safety of the two formulations of omeprazole and sodium bicarbonate powder and assessed how CYP2C19 gene polymorphisms affect pharmacokinetics (PK). A single-center, randomized, single-dose, 2-sequence and 2-period crossover method was performed in forty healthy Chinese subjects. Blood samples were collected after a single dose for PK (AUC0-∞, AUC0-t, and Cmax) analysis. The concentrations of Omeprazole in human plasma were determined by HPLC-MS/MS. Besides, the gene polymorphisms of CYP2C19 were assessed by Sanger sequencing. The geometric mean ratios (90% confidence interval) [GMR (95% CI)] of Test/Reference preparation for Cmax: 95.2% (88.48%, 102.43%), AUC0-t: 97.47% (94.4%, 101.02%), AUC0-∞: 97.68% (94.27%, 101.21%) were within the range of 80.00-125.00%. The non-parametric test showed no statistical difference in Tmax between the two groups (p > 0.05). All drugs were well tolerated, no severe adverse reactions occurred, and no significant differences in adverse events between the two drugs. For CYP2C19 gene polymorphisms, the results showed that of 40 subjects, 12 subjects were extensive metabolizers, 24 were intermediate metabolizers, and 4 were poor metabolizers, the frequency of metabolic genotypes were 30%, 60%, and 10%. And the allele distributions for CYP2C19 were *1, *2, and *3 at 60%, 38.75%, and 1.25%. Both the CYP2C19 alleles and metabolic genotypes were consistent with other studies in Chinese. The results of PK parameters showed that different genotypes of CYP2C19 lead to significant differences in t1/2, AUC0-t, AUC0-∞ and Cmax, but no significant differences in Tmax in each group. At the same time, we confirmed that the PK parameters of the test and reference had no differences between the males and females. This study has shown that the pharmacokinetic parameters of the two formulations are not significantly different, which showed bioequivalence and exemplary safety. CYP2C19 gene polymorphism significantly differed in the PK parameters of omeprazole sodium bicarbonate powder.

Performance Verification of CYP2C19 Enzyme Abundance Polymorphism Settings within the Simcyp Simulator v21

Physiologically based pharmacokinetic (PBPK) modeling has a number of applications, including assessing drug−drug interactions (DDIs) in polymorphic populations, and should be iteratively refined as science progresses. The Simcyp Simulator is annually updated and version 21 included updates to hepatic and intestinal CYP2C19 enzyme abundance, including addition of intermediate and rapid metabolizer phenotypes and changes to the ultra-rapid metabolizer enzyme abundance, with implications for population clearance and DDI predictions. This work details verification of the updates with sensitive CYP2C19 substrates, omeprazole and lansoprazole, using available clinical data from literature. Multiple assessments were performed, including recovery of areas under the concentration-time curve (AUC) and Cmax from compiled datasets for each drug, recovery of victim DDI ratios with CYP2C19 and/or CYP3A4 inhibition and recovery of relative exposure between phenotypes. Simulated data were within respective acceptance criteria for >80% of omeprazole AUC values, >70% of lansoprazole AUC and Cmax, >60% of AUC and Cmax DDI ratios and >80% of exposure ratios between different phenotypes. Recovery of omeprazole Cmax was lower (>50−70% within 2-fold) and possibly attributed to the variety of formulations used in the clinical dataset. Overall, the results demonstrated that the updated data used to parameterize CYP2C19 phenotypes reasonably described the pharmacokinetics of omeprazole and lansoprazole in genotyped or phenotyped individuals.

A Decade of Pharmacogenetic Studies in Jordan: A Systemic Review

The aim of this study was to perform a systematic overview of the pharmacogenetic studies conducted in Jordan. A structured search of Medline was conducted for articles over the last decade (January 2010-July 2020). Studies were classified by design, sample size, drug-gene combination, and the significance of the results. Thirty-two studies met the criteria for review. Most pharmacogenomic studies had a case-only design (n = 23). Only five studies included >500 participants. The total number of genetic variants in all studies was one hundred fifteen, which were found in forty genes, including dynamic (n = 27), and kinetic (n = 9) genes. The most commonly studied drugs were within the hematology and cardiology therapeutic areas and included statins, warfarin, aspirin, and clopidogrel. Most studies (n = 18) reported results with mixed p values [<0.05 and >0.05]. Pharmacogenomic research in Jordan is still in its infancy and is limited mainly to replication attempts. The need for standardization is imperative, especially in developing countries with scarce funding resources.

Clinical treatment for hepatitis C reverses CYP2C19 inhibition

AIMS

Infection by the hepatitis C virus (HCV) generates inflammatory response selectively modulating cytochrome P450 protein (CYP) activities. This study assessed the effect of chronic hepatitis C on CYP2C19 activity in patients with HCV.

METHODS

Patients with HCV infection (n = 23) at different fibrosis stages were allocated into groups 1 (F0/F1 and F2, mild to moderate fibrosis) and 2 (F3 and F4, advanced fibrosis stages). Phase 1 was conducted before the treatment with direct-acting antivirals (DAAs) and phase 2 after the sustained virological response. Participants were administered 2 mg of a single oral dose of omeprazole (OME) as probe drug in both phases. Metabolic ratios (MRs) (plasma samples collected at 4 h after OME administration) were calculated by dividing plasma concentrations of 5-hydroxyomeprazole by OME.

RESULTS

The MRs for group 1 were 0.45 (0.34-0.60, 90% confidence interval) and 0.69 (0.50-0.96) for phases 1 and 2, respectively, while the MRs for group 2 were 0.25 (0.21-0.31) and 0.41 (0.30-0.56) for phases 1 and 2, respectively. MRs were different (P < .05) between phases 1 and 2 for both groups, as well as between groups 1 and 2 in phase 1, but not in phase 2 (P > .05).

CONCLUSIONS

Both groups presented different MRs before and after treatment with DAAs, evidencing that CYP2C19 inhibition during inflammation was at least partially reversed after DAA treatment. Groups 1 and 2 were also found to be different in phase 1 but not phase 2, showing that CYP2C19 metabolic activity does not differ between groups after DAA treatment.

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

Early assessment of metabolism pathways of new chemical entities guides the understanding of drug-drug interactions. Selective enzyme inhibitors are indispensable in CYP reaction phenotyping. The most commonly applied CYP2C19 inhibitor, omeprazole, lacks selectivity. Two promising alternatives, (+)-N-3-benzylnirvanol and (-)-N-3-benzylphenobarbital, are already used as CYP2C19 inhibitors in some in vitro studies with suspended human hepatocytes. However, a full validation proving their suitability in terms of CYP and non-CYP selectivity has not been presented in literature. The present study provides a thorough comparison between omeprazole, (+)-N-3-benzylnirvanol, and (-)-N-3-benzylphenobarbital in terms of potency and selectivity and shows the superiority of (-)-N-3-benzylphenobarbital as a CYP2C19 inhibitor in suspended human hepatocytes. Furthermore, we evaluated the application of (-)-N-3-benzylphenobarbital to predict the in vivo contribution of CYP2C19 to drug metabolism [fraction metabolized (fm) of CYP2C19, fm_CYP2C19]. A set of 10 clinically used CYP2C19 substrates with reported in vivo fm_CYP2C19 data was evaluated. fm_CYP2C19, which was predicted using data from suspended human hepatocyte incubations, underestimated the in vivo fm_CYP2C19 The use of a different hepatocyte batch with a different CYP3A4/CYP2C19 activity ratio showed the impact of intrinsic CYP activities on the determination of fm_CYP2C19 Overall, this study confirms the selective CYP2C19 inhibition by (-)-N-3-benzylphenobarbital over other CYP isoforms (CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2D6, and CYP3A4) and clinically relevant non-CYP enzymes [aldehyde oxidase, flavin-containing monooxygenase 3, N-acetyltransferase 2, uridine diphosphate glucuronosyltransferase (UGT) 1A1, UGT1A4, UGT2B7, UGT2B15] in suspended human hepatocytes. (-)-N-3-benzylphenobarbital is therefore the preferred CYP2C19 inhibitor to assess fm_CYP2C19 in suspended human hepatocytes in comparison with omeprazole and (+)-N-3-benzylnirvanol. SIGNIFICANCE STATEMENT: (-)-N-3-Benzylphenobarbital is a more potent and selective inhibitor of CYP2C19 in suspended human hepatocytes than omeprazole and (+)-N-3-benzylnirvanol. (-)-N-3-Benzylphenobarbital can be used to predict the fraction metabolized by CYP2C19 in suspended human hepatocytes.

A Retrospective Evaluation of Allometry, Population Pharmacokinetics, and Physiologically-Based Pharmacokinetics for Pediatric Dosing Using Clearance as a Surrogate

Physiologically-based pharmacokinetic models are increasingly applied for pediatric dose selection along with traditional methods such as allometry and population pharmacokinetic models. We report a retrospective evaluation of the three methods. Pediatric population pharmacokinetic models sourced from literature for a subset of eight compounds were used to predict clearances for children < 2 years when they were within the modeled age range (interpolation, N = 11) or including those outside the modeled age range (interpolation and extrapolation, N = 18). Pediatric/adult clearance ratios were evaluated with a strict performance criterion of 0.8-1.25 and with twofold criteria. For children > 2 years, 58-75% of the clinical studies (N = 10) met the strict criteria, and > 80% of the clinical studies were predicted within twofold by all three methods. For children < 2 years, physiologically-based pharmacokinetic, allometry with age-dependent exponents, and pediatric population pharmacokinetic models predict 54%, 82%, and 64% within twofold of the observed, respectively.

Evaluation of Omeprazole Limited Sampling Strategies to Estimate Constitutive Cytochrome P450 2C19 Activity in Healthy Adults

BACKGROUND

Limited sampling strategy (LSS) is a validated method to estimate pharmacokinetic (PK) parameters from a reduced number of samples. Omeprazole is used to phenotype in vivo cytochrome P450 (CYP) 2C19 activity. This study examined an LSS using 2 estimation methods to determine apparent oral clearance (CL/F) and thus CYP2C19 activity.

METHODS

Data from 7 previously published studies included healthy subjects receiving a single, oral dose of omeprazole with intensive PK sampling. CL/F was estimated using noncompartmental analysis (NCA) and population PK modeling. LSS was simulated by selecting the 1, 2, 4, and/or 6-hour postdose time points. Linear regression was performed to assess whether CL/F estimated from limited sampling could accurately predict CL/F from the full PK profile.

RESULTS

Median CL/F was 23.7 L/h by NCA and 19.3 L/h by population PK modeling. In comparing the LSS NCA estimated versus observed CL/F, all evaluated linear regression models had unacceptable coefficients of determination (r, range: 0.14-0.81). With the population PK approach, 737 plasma concentrations (n = 71) and CYP2C19 genotype data were described with a 1-compartment structural model with mixed zero and first-order absorption and lag time. In comparing the population PK LSS estimated versus observed CL/F, all evaluated linear regression models had unacceptable r (range: 0.02-0.74). Post hoc comparison of CYP2C19 poor metabolizers versus CYP2C19 extensive metabolizers resulted in significantly lower CL/F in poor metabolizers versus extensive metabolizers.

CONCLUSIONS

Omeprazole LSS performed poorly in estimating CL/F using 2 separate estimation approaches and does not seem to be a suitable method for determining CYP2C19 activity.

Developmental pharmacogenetics of CYP2C19 in neonates and young infants: omeprazole as a probe drug

AIMS

Although substantial progress has been made in understanding of ontogeny of drug metabolism, there is still a gap of knowledge in developmental pharmacogenetics in neonates. We hypothesized that both age and pharmacogenetics might explain the developmental pattern of CYP2C19. We conducted a population pharmacokinetic-pharmacogenetic study to quantify the developmental pharmacogenetics of CYP2C19 in neonates and young infants using omeprazole as a probe drug.

METHODS

Pharmacokinetic samples were collected from 51 Caucasian neonates and young infants, who were receiving omeprazole treatment. Population pharmacokinetic-pharmacogenetic analysis of omeprazole and its metabolites was performed using NONMEM.

RESULTS

Data fitted a one-compartment parent and metabolite model with first-order absorption and elimination. CYP2C19 and CYP3A4 are predominantly involved in the metabolism of omeprazole despite their relatively low activities compared to adults. The clearance of omeprazole converted to 5-hydroxy-omeprazole (CL_OMZ-M1 ) increases with postnatal age. In CYP2C19 poor and intermediate metabolizers, model-predicted CL_OMZ-M1 are 12.5% (5-95% percentile: 3-14.9%) and 44.9% (5-95% percentile: 29.9-72.6%) of the value in extensive/ultrarapid metabolizer, respectively. Model-predicted absorption rate constant of omeprazole is 6.93 (5-95% percentile: 3.01-14.61) times higher in ABCB1 homozygous mutant patients, 1.86 (5-95% percentile: 0.86-3.47) times higher in ABCB1 heterozygous patients than that in ABCB1 homozygous wild-type patients.

CONCLUSIONS

Developmental pharmacogenetics of CYP2C19 was quantitatively described in neonates and young infants using omeprazole as a probe drug. Our findings emphasize the importance of semiphysiological developmental pharmacokinetic modelling approach when evaluating developmental pharmacogenetics of drugs with multiple routes of biotransformation.

Predictive Performance of Physiologically Based Pharmacokinetic (PBPK) Modeling of Drugs Extensively Metabolized by Major Cytochrome P450s in Children

The accuracy of physiologically based pharmacokinetic (PBPK) model prediction in children, especially those younger than 2 years old, has not been systematically evaluated. The aim of this study was to characterize the pediatric predictive performance of the PBPK approach for 10 drugs extensively metabolized by CYP1A2 (theophylline), CYP2C8 (desloratidine, montelukast), CYP2C9 (diclofenac), CYP2C19 (esomeprazole, lansoprazole), CYP2D6 (tramadol), and CYP3A4 (itraconazole, ondansetron, sufentanil). Model performance in children was evaluated by comparing simulated plasma concentration-time profiles with observed clinical results for each drug and age group. PBPK models reasonably predicted the pharmacokinetics of desloratadine, diclofenac, itraconazole, lansoprazole, montelukast, ondansetron, sufentanil, theophylline, and tramadol across all age groups. Collectively, 58 out of 67 predictions were within 2-fold and 43 out of 67 predictions within 1.5-fold of observed values. Developed PBPK models can reasonably predict exposure in children age 1 month and older for an array of predominantly CYP metabolized drugs.

Molecular genetic predictors of resistance to anti-Helicobacter pylori therapy

In current clinical practice, there is no optimal empirical therapy for Helicobacter pylori (H. pylori) infection and there is a progressive decrease in the efficiency of classical eradication therapy (ET) regimens. The variability in the efficiency of ET in a specific patient is largely due to the heterogeneous molecular genetic mechanisms underlying the resistance of the microorganism to the components of the treatment regimens. The basis of the mechanisms for antibiotic resistance in H. pylori is mainly the point mutations in some genes, which determine alterations in the mechanisms of action of drugs, such as clarithromycin (domain V of 23S rRNA), metronidazole (rdxA, frxA), amoxicillin (pbp1A), tetracycline (16S rRNA), and levofloxacin (gyrA). The predictors of resistance to ET are also the CagA-negative status of the microorganism and the presence of the vacA s2 allele. There are a number of host genetic determinants (the CYP2C19 genotype (*1/*1, *1/*17, *17/*17) and the MDR1 3435 T/T genotype (in an Asian population)) that reduce the efficiency of ET, by altering the pharmacokinetics of proton pump inhibitors. In addition, the IL-1β-511 C/C polymorphism that affects gastric acid secretion is a predictor of the inefficiency of ET.

Influence of Proton Pump Inhibitors on Mycophenolic Acid Pharmacokinetics in Patients With Renal Transplantation and the Relationship With Cytochrome 2C19 Gene Polymorphism

BACKGROUND

Most patients have serious digestive complications after renal transplantation. Therefore, it is important to protect gastrointestinal function to improve the survival rate of transplant patients. Proton pump inhibitors (PPIs) such as lansoprazole and rabeprazole are widely administered to renal transplant patients with mycophenolic acid (MPA) in the perioperative period. PPIs are metabolized by cytochrome (CYP) 2C19 enzymes. Mycophenolate sodium (MYF) and mycophenolate mofetil (MMF) have been used in immunosuppression. Clinically relevant drug-drug interactions have been described between immunosuppressive drugs. In the present study, we investigated the drug interaction between MPA and lansoparazole or rabeprazole and the impact of CYP2C19 polymorphisms on these drug interactions after renal transplantation.

MATERIALS AND METHODS

A total of 125 renal transplant patients taking MPA derivatives between 2012 and 2016 were included in this study. The 125 patients were divided into 6 groups: MMF/tacrolimus/steroid together with lansoprazole or rabeprazole; MYF/tacrolimus/steroid together with lansoprazole or rabeprazole and without PPI. The single nucleotide polymorphisms of CYP2C19 were determined by the polymerase chain reaction-restriction fragment length polymorphism. Plasma concentrations of MPA were measured by cloned enzyme donor immunoassay. Clinical parameters such as incidence of delayed graft function and acute rejection, the rate of change of serum creatinine, toxicity, and gastrointestinal adverse effects were analyzed retrospectively.

RESULTS

The mean concentrations of MPA in the MYF group were higher than those in the MMF group. The mean dose-adjusted blood concentration of MPA coadministered with lansoprazole was lower than that of MPA with rabeprazole or without PPI in MMF and MYF groups (P < .05). In patients with the CYP2C19*2/*2 genotype, the mean concentrations of MMF with lansoprazole were significantly lower than those with rabeprazole with MMF or without PPI (P < .05). Gastrointestinal side effects were significantly higher in MMF with lansoprazole group than in MYF with lansoprazole group (P < .05). However, no differences were found according to genotype distribution in all groups (P > .05).

CONCLUSION

Polymorphisms in CYP2C19 are related to the metabolic oxidation of drugs to varying degrees. Both genetic and clinical factors in pharmacokinetics may help to make further progress toward individualized therapy to yield maximum efficacy with minimal side effects.

The role of acid inhibition in Helicobacter pylori eradication

Infection of the stomach by the gastric pathogen Helicobacter pylori results in chronic active gastritis and leads to the development of gastric and duodenal ulcer disease and gastric adenocarcinoma. Eradication of H. pylori infection improves or resolves the associated pathology. Current treatments of H. pylori infection rely on acid suppression in combination with at least two antibiotics. The role of acid suppression in eradication therapy has been variously attributed to antibacterial activity of proton pump inhibitors directly or through inhibition of urease activity or increased stability and activity of antibiotics. Here we discuss the effect of acid suppression on enhanced replicative capacity of H. pylori to permit the bactericidal activity of growth-dependent antibiotics. The future of eradication therapy will rely on improvement of acid inhibition along with current antibiotics or the development of novel compounds targeting the organism's ability to survive in acid.

Evaluation of the relationship between polymorphisms in CYP2C19 and the pharmacokinetics of omeprazole, pantoprazole and rabeprazole

AIM

To evaluate the possible association between polymorphisms in CYP2C19 and the pharmacokinetics of omeprazole, rabeprazole and pantoprazole.

MATERIALS & METHODS

151 healthy volunteers were evaluated for polymorphisms in the CYP2C19 gene using real-time polymerase chain reaction. Plasma concentrations were measured using high-performance liquid chromatography coupled to mass spectrometry.

RESULTS

Carriers of the *2 allele displayed poor metabolism for all the PPIs studied (around 50% decrease in clearance). Subjects with the *17 allele showed a light increase in clearance compared with *1/*1 (not significant).

CONCLUSION

CYP2C19*2 is associated with decreased clearance of all the PPIs, that could be associated with higher drug efficacy. CYP2C19*17 could increase clearance of these drugs, although the effect seems small.

Hydroxylation index of omeprazole in relation to CYP2C19 polymorphism and sex in a healthy Iranian population

BACKGROUND

Polymorphism of CYP2C19 gene is one of the important factors in pharmacokinetics of CYP2C19 substrates. Omeprazole is a proton pump inhibitor which is mainly metabolized by cytochrome P450 2C19 (CYP2C19). The aim of present study was to assess omeprazole hydroxylation index as a measure of CYP2C19 activity considering new variant allele (CYP2C19*17) in Iranian population and also to see if this activity is sex dependent.

METHODS

One hundred and eighty healthy unrelated Iranian individuals attended in this study. Blood samples for genotyping and phenotyping were collected 3 hours after administration of 20 mg omeprazole orally. Genotyping of 2C19 variant alleles *2, *3 and *17 was performed by using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and semi-nested PCR methods. Plasma concentrations of omeprazole and hydroxyomeprazole were determined by high performance liquid chromatography (HPLC) technique and hydxroxylation index (HI) (omeprazole/ hydroxyomeprazole) was calculated.

RESULTS

The CYP2C19*17 was the most common variant allele in the studied population (21.6%). Genotype frequencies of CYP2C19*17*17, *1*17, and *2*17 were 5.5%, 28.8% and 3.3% respectively. The lowest and the highest median omeprazole HI was observed in *17*17 and *2*2 genotypes respectively (0.36 vs. 13.09). The median HI of omeprazole in subjects homozygous for CYP2C19*1 was 2.16-fold higher than individuals homozygous for CYP2C19*17 (P < 0.001) and the median HI of CYP2C19*1*17 genotype was 1.98-fold higher than CYP2C19 *17*17 subjects (P < 0.001). However, subjects with CYP2C19*2*17 (median HI: 1.74) and CYP2C19*1*2 (median HI: 1.98) genotypes and also CYP2C19*1*17 (median HI: 0.71) and CYP2C19*1*1 (mean HI: 0.78) did not show any significantly different enzyme activity. In addition, no statistically significant difference was found between women and men in distribution of CYP2C19 genotypes. Furthermore, the hydroxylation index of Omeprazole was not different between women and men in the studied population.

CONCLUSION

Our data point out the importance of CYP2C19*2 and CYP2C19*17 variant alleles in metabolism of omeprazole and therefore CYP2C19 activity. Regarding the high frequency of CYP2C19*17 in Iranian population, the importance of this new variant allele in metabolism of CYP2C19 substrates shall be considered.

Prediction of inter-individual variability in the pharmacokinetics of CYP2C19 substrates in humans

Significant inter-individual variability of exposure for CYP2C19 substrates may be only partly due to genetic polymorphism. Therefore, the in vivo inter-individual variability in hepatic intrinsic clearance (CL(int,h)) of CYP2C19 substrates was estimated from reported AUC values using Monte Carlo simulations. The coefficient of variation (CV) for CL(int,h) in poor metabolizers (PM) expected from genotypes CYP2C19*2/*2, CYP2C19*3/*3 or CYP2C19*2/*3 was estimated as 25.8% from the CV for AUC of omeprazole in PMs. With this, CVs of CL(int,h) in extensive metabolizers (EM: CYP2C19*1/*1), intermediate metabolizers (IM: CYP2C19*1/*2 or *3) and ultra-rapid metabolizers (UM), CYP2C19*17/*17 and *1/*17, were estimated as 66.0%, 55.8%, 6.8% and 48.0%, respectively. To validate these CVs, variability in the AUC of CYP2C19 substrates lansoprazole and rabeprazole, partially metabolized by CYP3A4 in EMs and IMs, were simulated using the CV in CL(int,h) for CYP2C19 EMs and IMs and 33% of the CV previously reported for CYP3A4. Published values were within 2.5-97.5 percentile range of simulated CVs for the AUC. Furthermore, simulated CVs for the AUC of omeprazole and lansoprazole in ungenotyped populations were comparable with published values. Thus, estimated CL(int,h) variability can predict variability in the AUC of drugs metabolized not only by CYP2C19 but also by multiple enzymes.

Therapeutic management of uncomplicated gastroesophageal reflux disease in france in 2005: Potential cost savings of omeprazole substitution

BACKGROUND

Proton pump inhibitors (PPIs) cost the French health care system >€1 billion in 2005, and ~50% of PPI prescriptions were for the treatment of gastroesophageal reflux disease (GERD).

OBJECTIVES

This study aimed to describe the current use of PPIs for GERD, to estimate the total annual costs of treatment, and to evaluate the economic impact of the various possible substitutions among PPIs available for this indication in France.

METHODS

Data from a sample of patients aged ≥20 years who visited their general practitioner (GP) at least once in 2005 for uncomplicated, symptomatic GERD were retrieved from the Thales database (a group of 1200 representative GPs connected to a computerized network). Costs of the prescriptions presented for reimbursement and costs of those reimbursed by the French health care insurance system were analyzed. We then evaluated the economic consequences of replacing full-dose generic omeprazole (after substitution from brand-name omeprazole by the pharmacists) with other compounds that are indicated for mild symptoms at half dose (ie, lansoprazole 15 mg, pantoprazole 20 mg, rabeprazole 10 mg, and esomeprazole 20 mg). The results were adjusted to account for the proportions of patients who had full health care coverage and the treatment duration as reported in the database. RESULTS are presented from the perspective of the French health care insurance system.

RESULTS

In 2005, a total of 122,571 patients (mean age, 55.7 years; 45.5% men; 13.8% with a history of at least 1 gastrointestinal disorder) met the inclusion criteria. Extrapolated to the French population, this sample corresponded to ≈5.7 million people (ie, 13% of the adult population who visited a GP during the year). PPIs were prescribed as first-line treatment for GERD in 84.1% of the consultations (14.3% in association with other antiulcer drugs). Omeprazole, as a proprietary or generic drug, was prescribed most often (78.9%) and at full dose (20 mg), while other compounds (lansoprazole, pantoprazole, rabeprazole, and esomeprazole) were prescribed at half dose in 64.3% of cases. The extrapolated annual cost of PPIs reimbursed for this indication was €465.02 million at a mean reimbursement level of 72.7%. Brand-name omeprazole still accounted for ≈11% of the total cost reimbursed. Complete replacement of brand-name omeprazole with its generic counterpart would have reduced costs by €18.35 million (a decrease of 4.3% in the total reimbursed expenditure). The switch from generic full-dose omeprazole to a half dose of other PPIs would have allowed further savings ranging from €2.59 million (with lansoprazole) to €13.19 million (with pantoprazole).

CONCLUSION

In accordance with recent recommendations for the treatment of uncomplicated GERD and based on the 2006 PPI pricing, switching from branded full-dose omeprazole to generic omeprazole or to the use of half doses of other PPIs may allow cost savings in France.

Genetic Polymorphisms of Cytochrome P450 Enzymes and the Effect on Interindividual, Pharmacokinetic Variability in Extensive Metabolizers

Genetic polymorphisms of cytochrome P450 (CYP) enzymes are one of the factors that contribute to the pharmacokinetic (PK) variability of drugs. PK variability is observed in the bimodal distribution between extensive metabolizers (EMs) and poor metabolizers (PMs). PK variability may also exist between individuals genotyped as homozygous EMs and heterozygous EMs. This may carry implications for drug dosing and drug response (e.g., risk of therapeutic failure or drug toxicity). Studies have reported significant PK differences between homozygous and heterozygous EMs. Some literature suggests that this distinction may be of clinical relevance. Due to study design limitations and data that are either sparse or conflicting, generalizations regarding the potential impact of the CYP genotype, within EMs, are difficult. Optimally designed clinical trials are needed. This review evaluates the potential impact of CYP genetic polymorphisms on interindividual PK variability of drugs within an EM population.

Polymorphisms and the Pocketbook: The Cost-Effectiveness of Cytochrome P450 2C19 Genotyping in the Eradication ofHelicobacter pyloriInfection Associated with Duodenal Ulcer

The clinical outcome of duodenal ulcer treated with proton pump inhibitor (PPI)-based, anti-Helicobacter pylori (H.p.) regimens varies according to cytochrome P450 2C19 (CYP2C19) genotype. CYP2C19 genotypes differ markedly in peoples of Pacific Rim descent compared with another ethnicity. The authors sought to determine the specific impact that these factors have on the cost-effectiveness of duodenal ulcer management. Their model consisted of two patient cohorts with Helicobacter pylori and duodenal ulcer, trichotomized into CYP2C19 homozygous extensive metabolizers (EMs), heterozygous EMs, and poor metabolizers (PMs), altering the anti-H.p. regimen in the genotyped cohort only. The authors took the perspective of a third-party payer, and the denominator was ulcer episode prevented. In the reference case, the use of CYP2C19 genotyping prior to initiating anti-H.p. therapy was dominant (costs were saved with each ulcer episode prevented) in all geographic regions of the United States. The subsequent break-even analysis showed a range of 89.20 dollars to 118.96 dollars--from Hawaii to the Midwest, respectively--required to eliminate the cost-savings from each genotype test performed. Using probabilities most unfavorable to genotyping, the variation of peoples with Pacific Rim origins from 0% to 100% altered the cost-effectiveness from 495 dollars to 2125 dollars per ulcer event prevented, respectively. The results suggest that treatment decisions for H.p. infection that are based on a patient's CYP2C19 genotype decreases expenses for health plans implementing testing. This analysis provides an economic basis to support recent calls to expand this technology into routine clinical care to prevent toxicity of narrow therapeutic index drugs.

In vivo quantitative prediction of the effect of gene polymorphisms and drug interactions on drug exposure for CYP2C19 substrates

We present a unified quantitative approach to predict the in vivo alteration in drug exposure caused by either cytochrome P450 (CYP) gene polymorphisms or CYP-mediated drug-drug interactions (DDI). An application to drugs metabolized by CYP2C19 is presented. The metrics used is the ratio of altered drug area under the curve (AUC) to the AUC in extensive metabolizers with no mutation or no interaction. Data from 42 pharmacokinetic studies performed in CYP2C19 genetic subgroups and 18 DDI studies were used to estimate model parameters and predicted AUC ratios by using Bayesian approach. Pharmacogenetic information was used to estimate a parameter of the model which was then used to predict DDI. The method adequately predicted the AUC ratios published in the literature, with mean errors of -0.15 and -0.62 and mean absolute errors of 0.62 and 1.05 for genotype and DDI data, respectively. The approach provides quantitative prediction of the effect of five genotype variants and 10 inhibitors on the exposure to 25 CYP2C19 substrates, including a number of unobserved cases. A quantitative approach for predicting the effect of gene polymorphisms and drug interactions on drug exposure has been successfully applied for CYP2C19 substrates. This study shows that pharmacogenetic information can be used to predict DDI. This may have important implications for the development of personalized medicine and drug development.

Pharmacokinetics of lansoprazole and its main metabolites after single and multiple intravenous doses in healthy Chinese subjects

The aim of the study was to evaluate and compare the pharmacokinetics of lansoprazole (LPZ) and its main metabolites, 5'-hydroxy lansoprazole (HLPZ) and lansoprazole sulfone (LPZS), after single and multiple intravenous (i.v.) doses of LPZ in healthy Chinese subjects. Twelve subjects (six males and six females) were given a single dose of LPZ by i.v. infusion on day 1, and multiple doses from day 2 to day 6. Blood samples were collected at designated time points for analysis of plasma concentrations of LPZ, HLPZ and LPZS by an LC-MS/MS method. LPZ was generally well tolerated in healthy Chinese subjects. After single and multiple i.v. doses of 30 mg LPZ, the C max values of LPZ, HLPZ and LPZS were 1490 ± 290 and 1450 ± 280, 175 ± 71 and 154 ± 56, and 51.3 ± 82.9 and 74.1 ± 158.7 ng/mL, with the AUC0-t values 3280 ± 2550 and 4260 ± 3880, 381 ± 128 and 389 ± 111, and 389 ± 1204 and 700 ± 2255 ng h/mL, respectively. The t 1/2 and CL values of LPZ after single and multiple i.v. doses were 1.48 ± 1.03 and 2.19 ± 1.03 h, and 11.67 ± 4.49 and 9.56 ± 4.08 L/h, respectively. Compared with the pharmacokinetics of LPZ after a single dose, t 1/2 increased markedly, CL decreased significantly and AUC increased by over 20 % after multiple doses. The results indicated that there was drug accumulation of LPZ after multiple i.v. doses, and there was no gender-related difference in pharmacokinetics of LPZ and its two metabolites.

Impact of genetic polymorphisms in CYP2C9 and CYP2C19 on the pharmacokinetics of clinically used drugs

Human cytochrome P450 (CYP) is a superfamily of hemoproteins which oxidize a number of endogenous compounds and xenobiotics. The human CYP2C subfamily consists of four members: CYP2C8, CYP2C9, CYP2C18 and CYP2C19. CYP2C9 and CYP2C19 are important drug-metabolizing enzymes and together metabolize approximately 20% of therapeutically used drugs. Forty-two allelic variants for CYP2C9 and 34 for CYP2C19 have been reported. The frequencies of these variants show marked inter-ethnic variation. The functional consequences of genetic polymorphisms have been examined, and many studies have shown the clinical importance of these polymorphisms. Current evidence suggests that taking the genetically determined metabolic capacity of CYP2C9 and CYP2C19 into account has the potential to improve individual risk/benefit relationships. However, more prospective studies with clinical endpoints are needed before the paradigm of "personalized medicine" based on the variants can be established. This review summarizes the currently available important information on this topic.

Clinical Application of Pharmacogenomics

The purpose of this review is to discuss the clinical application of pharmacogenomics for select drug therapies (eg, proton pump inhibitors [PPIs], codeine, and carbamazepine) and to highlight limitations and challenges that preclude implementation of pharmacogenomics into clinical practice. Genetic polymorphisms of cytochrome P450 (CYP) enzymes and the presence of the human leukocyte antigen ( HLA) -B*1502 allele influence drug disposition and/or response. A portion of PPI pharmacokinetic and pharmacodynamic variability can be explained by CYP2C19 genotype. However, conflicting evidence exists related to Helicobacter pylori cure rates based on CYP2C19 genotype. For codeine, adverse drug reactions in neonates through breast-feeding from CYP2D6 ultra-rapid metabolizers have been reported. However, there is lack of conclusive evidence regarding the overall influence of CYP2D6 polymorphisms on codeine efficacy and toxicity. Although CYP2C19 and CYP2D6 genotyping tests are available, clinical utility remains low. The presence of the HLA-B*1502 allele is associated with carbamazepine-induced Stevens-Johnson syndrome (SJS) and/or toxic epidermal necrolysis (TEN). Pharmacogenomic testing is required prior to initiating carbamazepine in high-risk patients. Lack of sufficient resources, provider knowledge, and ethical, legal, and social issues are several limitations and challenges to implementing pharmacogenomic testing in clinical practice.

Omeprazole limited sampling strategies to predict area under the concentration-time curve ratios: implications for cytochrome P450 2C19 and 3A phenotyping

PURPOSE

To develop a limited sampling strategy (LSS) to predict area under the concentration-time curve (AUC) ratios of omeprazole (AUC(OPZ)) to its metabolites 5-hydroxyomeprazole (AUC(5OH)) and omeprazole sulfone (AUC(SUL)) as phenotyping parameters for cytochrome P450 (CYP) 2C19 and 3A.

METHODS

Data were obtained from 37 (4 women) Caucasian, Chinese, and Korean healthy adults from three published studies. The AUC(OPZ), AUC(5OH), and AUC(SUL) were calculated via noncompartmental analysis. Observed AUC(OPZ, OBS)/AUC(5OH, OBS) and AUC(OPZ, OBS)/AUC(SUL, OBS) were determined. Plasma concentrations of omeprazole, 5-hydroxyomeprazole, and omeprazole sulfone at 1, 1.5, 2, 3, 4, 6, and 8 h post-dose were used to generate limited sampling strategy (LSS) models to predict AUC(OPZ,PRE)/AUC(5OH,PRE) and AUC(OPZ,PRE/)AUC(SUL,PRE). Bias and precision were assessed via percentage mean prediction error (%MPE) and percentage mean absolute error (%MAE), with acceptable limits being <15%.

RESULTS

For CYP2C19, the AUC(OPZ,OBS)/AUC(5OH,OBS) was [mean ± standard deviation (SD)] 2.10 ± 1.63. Five LSS models of AUC(OPZ,PRE)/AUC(5OH,PRE) were generated, but none met the bias or precision criteria. Upon stratification by CYP2C19 genotype and ethnicity, a three-timepoint (at 1, 2, and 4 h) LSS model accurately predicted AUC(OPZ)/AUC(5OH) in Caucasian CYP2C19*1/*1 subjects. For CYP3A, AUC(OPZ,OBS)/AUC(SUL,OBS) (mean ± SD) was 1.79 ± 0.67. All LSS models had unacceptable %MAE, even when stratified by CYP2C19 genotype and ethnicity.

CONCLUSIONS

A LSS model to predict AUC(OPZ)/AUC(5OH), and thus CYP2C19 activity, was generated for Caucasian CYP2C19*1/*1 subjects. However, additional model validation is needed prior to general use. LSS models to predict AUC(OPZ)/AUC(SUL), and thus CYP3A activity, were not possible, even upon stratification by CYP2C19 genotype and ethnicity.

Clinical usefulness of limited sampling strategies for estimating AUC of proton pump inhibitors

Cytochrome P450 (CYP) 2C19 (CYP2C19) genotype is regarded as a useful tool to predict area under the blood concentration-time curve (AUC) of proton pump inhibitors (PPIs). In our results, however, CYP2C19 genotypes had no influence on AUC of all PPIs during fluvoxamine treatment. These findings suggest that CYP2C19 genotyping is not always a good indicator for estimating AUC of PPIs. Limited sampling strategies (LSS) were developed to estimate AUC simply and accurately. It is important to minimize the number of blood samples because of patient's acceptance. This article reviewed the usefulness of LSS for estimating AUC of three PPIs (omeprazole: OPZ, lansoprazole: LPZ and rabeprazole: RPZ). The best prediction formulas in each PPI were AUC(OPZ)=9.24 x C(6h)+2638.03, AUC(LPZ)=12.32 x C(6h)+3276.09 and AUC(RPZ)=1.39 x C(3h)+7.17 x C(6h)+344.14, respectively. In order to optimize the sampling strategy of LPZ, we tried to establish LSS for LPZ using a time point within 3 hours through the property of pharmacokinetics of its enantiomers. The best prediction formula using the fewest sampling points (one point) was AUC(racemic LPZ)=6.5 x C(3h) of (R)-LPZ+13.7 x C(3h) of (S)-LPZ-9917.3 x G1-14387.2×G2+7103.6 (G1: homozygous extensive metabolizer is 1 and the other genotypes are 0; G2: heterozygous extensive metabolizer is 1 and the other genotypes are 0). Those strategies, plasma concentration monitoring at one or two time-points, might be more suitable for AUC estimation than reference to CYP2C19 genotypes, particularly in the case of coadministration of CYP mediators.

Study of the pharmacokinetics and intragastric pH of rabeprazole given as successive intravenous infusion to healthy Chinese volunteers

OBJECTIVES

To investigate the pharmacokinetics and pharmacodynamics of rabeprazole (RPZ) given as successive intravenous infusion to healthy Chinese volunteers.

METHODS

A total of 63 subjects (33 males and 30 females) were recruited at four research centers and given a 5-day therapeutic course of RPZ (10, 20, or 40 mg) administered as single daily doses during a 30-min period. Plasma concentrations were monitored by sampling at very short intervals for the first 330, 360, or 420 min post-RPZ administration. Intragastric pH was recorded 24 h post-RPZ administration on day 1 and day 5.

RESULTS

After receiving a single and repeated doses of RPZ, the area under the plasma concentration-time curve (AUC(0-τ)) was 51.9 ± 22.1, 96.7 ± 27.6, and 188.4 ± 65.8 mg·min/L on day 1 and 59.3 ± 23.9, 106.7 ± 27.8, and 200.3 ± 79.0 mg·min/L on day 5 for the low-, middle-, and high-dose groups, respectively. The corresponding peak concentrations (C(max)) were 0.64 ± 0.11, 1.30 ± 0.26, and 2.6 ± 0.54 μg/mL on day 1 and 0.76 ± 0.15, 1.39 ± 0.25, and 2.91 ± 0.53 μg/mL on day 5, respectively. Although the mean AUC and C(max) values increased from a single dose to repeated doses in the three groups, the difference was not significant. The mean AUC((0, τ)) and C(max) ratios of repeated dose to single dose were 1.14, 1.10, and 1.06 on day 1 and 1.19, 1.07, and 1.12 on day 5 for the low-, middle-, and high-dose groups, respectively. After administration of a single dose, the 24-h pH value was significantly higher in the high-dose group than in the low-dose group. After repeated doses, significant increases in pH were observed in the low-, middle-, and high-dose groups; however, the between-group differences were not statistically significant.

CONCLUSIONS

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

The effect of CYP2C19 activity on pharmacokinetics of lansoprazole and its active metabolites in healthy subjects

CONTEXT

Lansoprazole is a gastric proton-pump inhibitor and has been demonstrated to be effective in the treatment of various peptic diseases. The effects of CYP2C19 activity on the pharmacokinetics of lansoprazole and its active metabolites in Chinese subjects have not previously been evaluated.

OBJECTIVE

The study aimed to evaluate the effects of CYP2C19 activity in healthy Chinese volunteers.

MATERIALS AND METHODS

Twenty-two healthy volunteers were recruited for an open trial and received a single dose of 30 mg lansoprazole. Using a validated LC-MS/MS method, we measured the plasma concentrations of lansoprazole, 5-hydroxylansoprazole, and lansoprazole sulfone. The genotype of CYP2C19 was identified by polymerase chain reaction (PCR) analysis of single nucleotide polymorphisms (SNPs). Subjects were genotypically classified into the following three groups on the basis of PCR-SNP analysis for CYP2C19: homozygous EM (hmEM) group, heterozygous EM (htEM) group, and PM group. To test differences in pharmacokinetic parameters among the three groups, analysis of variance (ANOVA) after log-transformation of data was used.

RESULTS AND CONCLUSION

Our results indicated that there were significant differences (p < 0.001) between the hmEM and PM groups, between the htEM and PM groups, and between the hmEM and htEM groups in C(max), AUC(0-t), and AUC(0-inf) of lansoprazole and lansoprazole sulfone. There were also significant differences (p < 0.001) between the hmEM and PM groups, and between the htEM and PM groups in C(max) of 5-hydroxylansoprazole.

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.

Transfer and distribution of amoxicillin in the rat gastric mucosa and gastric juice and the effects of rabeprazole

AIM

To investigate the distribution of amoxicillin in the gastric juice and gastric mucosa of rats and to investigate the effects of proton pump inhibitor rabeprazole on amoxicillin concentrations in various compartments.

METHODS

One hundred and sixty anesthetized rats were divided into five groups, and given intravenously different doses of amoxicillin or amoxicillin and rabeprazole. The pH value and volume of gastric juice was aspirated were measured and separated gastric mucosa was homogenized. The concentrations of amoxicillin in the plasma, gastric juice and gastric mucosa were measured by high performance liquid chromatography (HPLC).

RESULTS

The maximum concentrations of amoxicillin in gastric juice and gastric mucosa were significantly lower than those in plasma (P<0.001). Concentrations in the glandular stomach mucosa were higher than those in the forestomach mucosa. Rabeprazole did not significantly change the pharmacokinetic parameters of amoxicillin in the plasma and did not alter gastric antibiotic clearance or the gastric transfer fraction of amoxicillin in gastric juice. However, rabeprazole did increase the amoxicillin concentration and pH value in gastric juice and reduced the volume of the gastric juice.

CONCLUSION

Amoxicillin could penetrate the gastric mucosa and achieve therapeutic concentrations at the target site after transfer from the blood to the stomach. Rabeprazole increased the amoxicillin concentration in gastric juice by decreasing the gastric juice volume but did not affect its concentration in blood or gastric mucosa.

Advances in clinical research on the interaction between proton pump inhibitors and clopidogrel

As a new antiplatelet drug, clopidogrel is the cornerstone of drug treatment for coronary artery disease. However, clinical use of clopidogrel frequently leads to gastrointestinal injury or increases the risk of gastrointestinal bleeding. To prevent clopidogrel-associated gastrointestinal injury, concomitant proton pump inhibitors (PPIs) have been used widely in clinical practice. However, recent studies show that treatment with clopidogrel plus PPIs can increase the incidence of adverse cardiovascular events. Despite being controversial, this finding has attracted wide attention from clinicians. This article will review the recent advances in clinical research on the interaction between proton pump inhibitors and clopidogrel.

Proton pump inhibitor and clopidogrel interaction: fact or fiction?

Current consensus recommendations state that patients prescribed clopidogrel plus aspirin should receive a proton pump inhibitor (PPI) to reduce gastrointestinal bleeding. Clopidogrel is converted to its active metabolite by cytochrome P450 (CYP) enzymes. Clopidogrel users with decreased CYP2C19 function have less inhibition of platelet aggregation and increased cardiovascular (CV) events. As PPI metabolism also involves CYP2C19, it was hypothesized that competition by PPIs might interfere with clopidogrel's action. Omeprazole, but not other PPIs, worsens surrogate markers of clopidogrel efficacy. Some (but not all) observational studies show that clopidogrel users prescribed PPIs have increased risks of CV events (hazard/odds ratios=1.25-1.5). When effect sizes are small to moderate (relative risks<1.5-2.0), however, it is only possible to conclude whether statistical associations are valid in randomized trials. A randomized trial of omeprazole vs. placebo in clopidogrel users showed no difference in CV events (hazard ratio=1.02,0.70-1.51). Thus, current evidence does not justify a conclusion that PPIs are associated with CV events among clopidogrel users, let alone a judgment of causality. Nonetheless, positive results from some observational studies and biological plausibility have led some health-care providers to accept that PPIs reduce clopidogrel's efficacy. The US Food and Drug Administration (FDA) recommends that "concomitant use of drugs that inhibit CYP2C19 (e.g., omeprazole) should be discouraged." As the presence of PPIs and clopidogrel in plasma is short lived, separation by 12-20 h should in theory prevent competitive inhibition of CYP metabolism and minimize any potential, though unproven, clinical interaction. PPI may be given before breakfast and clopidogrel at bedtime, or PPI may be taken before dinner and clopidogrel at lunchtime.

CYP2C19 haplotypes in Koreans as a marker of enzyme activity evaluated with omeprazole

BACKGROUND AND OBJECTIVE

CYP2C19 is clinically important in Korea because of the relatively high incidence of poor metabolizers in the population. To fully understand the genetic mechanism of the CYP2C19 defect in poor metabolizers, all variants need to be studied simultaneously. The aim of this study was to investigate the usefulness of CYP2C19 haplotypes as a marker of CYP2C19 enzyme activity in Koreans.

METHODS

We analysed the single nucleotide polymorphisms and haplotypes of the CYP2C19 gene in 150 healthy Koreans and found three major (frequency > 0.1) haplotypes (H1, H2 and H3). One oral dose of 40 mg omeprazole (Losec) was administered to 30 subjects grouped as H1/H1, H2/H2, H1/H2, H1/H3 and H2/H3. The pharmacokinetics of omeprazole and its metabolites, 5-hydroxyomeprazole and omeprazole sulphone, in those groups was analysed.

RESULTS AND DISCUSSION

The area under the plasma concentration-time curve (AUC(0-->infinity)) and elimination half-life (T(1/2)) of omeprazole were significantly greater in the H2/H2 and H2/H3 groups than in the H1/H1 group (P < 0.05), whereas the metabolic ratios of omeprazole to 5-hydroxyomeprazole were also markedly higher.

CONCLUSION

Although a specific SNP of CYP2C19 may be predictive of enzyme activity, haplotyping is more reliable for identifying poor metabolizers in populations with variant alleles other than CYP2C19*2 and *3 alleles.

Potential of genetic translational research in gastroenterology

The concept that genetic variation underlies inter-individual differences in drug response and contributes to the risk of developing common, complex disorders is expanding rapidly. Consequently the interest in genetic translational research has increased. Polymorphic DNA markers, either microsatellites or single nucleotide polymorphisms (SNPs), are used to assess genetic identities and track genetic differences between individuals. Given their abundance and stability, SNPs hold great promise as markers for mapping disease susceptibility loci for common, complex disorders by association studies. For this purpose the development of inexpensive, accurate, high-throughput methods for scoring large numbers of SNPs from hundreds of patients and controls is critical. Furthermore, gene expression profiling using DNA microarrays is likely to become a useful diagnostic tool enabling classification of disease phenotype based on molecular basis of disease pathogenesis, revealing information that cannot be obtained by histological assessment. Moreover, identification of differentially expressed genes in affected versus control tissue or over time in affected tissue will lead to better understanding of the mechanisms underlying disease and ultimately to the development of more effective drug therapies. To illustrate the potential of genetic translational research, several examples in the field of gastroenterology are described.

Rabeprazole: a pharmacologic and clinical review for acid-related disorders

Rabeprazole is a proton pump inhibitor that can be used in the treatment of acid-peptic-related disorders (gastroesophageal reflux disease [GERD], duodenal ulcer, gastric ulcer, gastric acid hypersecretory syndromes) and Helicobacter pylori. Pharmacodynamic data has demonstrated that rabeprazole, with a high pKa of approximately 5.0, can be activated at a higher pH than other proton pump inhibitors. This possibly results in faster onset of action. Owing to its non-enzymatic pathway of metabolism, rabeprazole is also less influenced by genetic polymorphisms of the CYP2C19, which others proton pump inhibitors are dependent on. In a 2-week, placebo-controlled trial, rabeprazole was both rapid and effective in relieving heartburn on day 1 of therapy and improved other GERD-related symptoms including regurgitation, belching, bloating, early satiety and nausea. For oesophageal reflux disease without erosions both 10 and 20 mg of rabeprazole are equivalent and better than placebo at 2 and 4 weeks. An on-demand approach to non-erosive reflux disease with 10 mg of rabeprazole has also been documented as superior to placebo. Some success in the treatment of extra-oesophageal manifestations of GERD, such as asthma and chronic laryngitis, has also been achieved with rabeprazole. Overall, rabeprazole with very few side effects is a safe and efficacious medication for acid suppression therapy.

Blood concentration of pantoprazole sodium is significantly high in hepatogenic peptic ulcer patients, especially those with a poor CYP2C19 metabolism

OBJECTIVE

To determine the plasma concentration of pantoprazole sodium by high performance liquid chromatography and its distribution in patients with different CYP2C19 genotypes in an attempt to provide experimental data for the clinical dosage adjustment of the drug.

METHODS

Patients with liver disease and associated peptic ulcer were genotyped according to their CYP2C19 wild-type sequences and mutations in CYP2C19m1 and CYP2C19m2 by the principles of the American Surgical Association using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The plasma concentration of pantoprazole sodium was detected after oral administration of the enteric-coated capsules in all patients. Included in the present study were 21 patients with primary liver cancer complicated by pathogenic peptic ulcers (confirmed by endoscopy), 22 patients with fatty liver and 25 healthy volunteers between January 2006 and October 2007. The subjects were administered orally with pantoprazole sodium at 40 mg/day for 1 week consecutively. The drug concentration was detected at 24 h and 1 week after drug administration by drawing 3.0 mL blood from the cubital vein.

RESULTS

The plasma concentration of pantoprazole sodium was related to the CYP2C19 enzyme type. The plasma concentration of extensive metabolizers (EM) was lower than that of poor metabolizers (PM) in the healthy control group at day 7 of drug administration. Regardless of PM or EM, the plasma concentration of pantoprazole sodium in primary liver cancer patients was higher than that in fatty liver patients, and even higher than that in healthy controls (P < 0.05).

CONCLUSION

These results suggest that CYP2C19 activity is inversely correlated with the severity of liver disease, especially in PM patients.

Age-dependent pharmacokinetics of lansoprazole in neonates and infants

BACKGROUND

Evidence suggests that age may affect the pharmacokinetics of lansoprazole in pediatric patients, but little information is available in neonates and infants.

OBJECTIVE

To determine the pharmacokinetics of lansoprazole in neonates and infants <1 year of age with gastroesophageal reflux disease (GERD)-associated symptoms.

METHODS

Two single- and repeated-dose, randomized, open-label, multicenter studies were conducted. Studies involved a pretreatment period of 7 or 14 days, a dose administration period of 5 days, and a follow-up period of 30 days for adverse events collection. The studies were conducted in both hospital and private clinic settings. The studies were performed in 24 neonates (aged <or=28 days) and 24 infants (aged >28 days, but <1 year) with GERD-associated symptoms diagnosed by medical history and the clinical judgment of the treating physician. Participants received lansoprazole 0.5 or 1.0 mg/kg/day (neonates) or 1.0 or 2.0 mg/kg/day (infants) for 5 days. Plasma pharmacokinetic parameters on dose administration day 1 were calculated, and plasma concentrations on day 5 were obtained.

RESULTS

The pharmacokinetics of lansoprazole were approximately dose proportional. After a single dose in neonates, the mean maximum plasma concentrations (C(max)) were 831 and 1672 ng/mL, and the mean area under the plasma concentration-time curve (AUC) values were 5086 and 9372 ng . h/mL for lansoprazole doses of 0.5 and 1.0 mg/kg, respectively. The time to C(max) (t(max)) [3.1 hours] and harmonic mean terminal elimination half-life (t((1/2))) [2.8 hours] were slightly longer in neonates receiving 0.5 mg/kg than the t(max) (2.6 hours) and t((1/2)) (2.0 hours) values observed in neonates receiving 1.0 mg/kg. Mean oral clearance (CL/F) was identical for the two doses (0.16 L/h/kg). After a single 1.0 or 2.0 mg/kg dose in infants, the lansoprazole C(max) values were 959 and 2087 ng/mL and the mean AUC values were approximately 2203 and 5794 ng . h/mL, respectively. The mean t(max) and mean t((1/2)) were 1.8 hours and 0.8 hours, respectively, for both doses (1.0 or 2.0 mg/kg), while mean CL/F was 0.71 and 0.61 L/h/kg, respectively. In both patient groups, mean plasma concentrations on day 5 were similar to day 1 concentrations. No clinically meaningful accumulation was observed following 5 days' dose administration. Plots of lansoprazole pharmacokinetics against chronologic age showed that dose-normalized C(max), t((1/2)), and AUC were two, three, and five times higher, respectively, in study participants aged <or=10 weeks than in study participants aged >10 weeks-1 year. Lansoprazole was well tolerated in all patients.

CONCLUSIONS

The pharmacokinetics of lansoprazole in pediatric patients are age dependent, with those aged <or=10 weeks showing higher plasma exposure and lower plasma clearance than those aged >10 weeks-1 year. Thus, pediatric patients aged <or=10 weeks require a lower dose of lansoprazole than pediatric patients aged >10 weeks to achieve similar plasma exposure.

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.

Comparison of enantioselective disposition of rabeprazole versus lansoprazole in renal-transplant recipients who are CYP2C19 extensive metabolizers

The purpose of this study was to investigate the comparative pharmacokinetics of rabeprazole and lansoprazole enantiomers in renal-transplant recipients on tacrolimus who were CYP2C19 extensive metabolizers. Sixteen Japanese patients were randomly assigned after renal transplantation to receive repeated doses of one of the following two regimens for 28 days; tacrolimus, mycophenolate mofetil and prednisolone together with either 20mg of racemic rabeprazole (n=8) or 30 mg of racemic lansoprazole (n=8). The mean Cmax and AUC0-24 of (R)-lansoprazole compared to (S)-lansoprazole in renal transplant recipients were 12-fold (954+/-522 vs. 167+/-137 ngml(-1), respectively) and 6.9-fold (4787+/-3454 vs. 451+/-354 nghml(-1), respectively) greater, and its elimination half-life was 2.1-fold (2.3+/-1.0 vs. 1.2+/-0.6h, respectively) longer. In contrast, although the elimination half-life of (R)-rabeprazole was significantly longer than that of the (S)-enantiomer (2.1+/-0.5 vs. 1.3+/-0.9h, respectively; P<0.05), there was no difference in Cmax between the (R)- and (S)-enantiomer (186+/-40 vs. 200+/-92 ngml(-1), respectively). In conclusion, in renal-transplant recipients who are CYP2C19 extensive metabolizers, there is less stereoselective difference in the pharmacokinetic disposition between the (R)- and (S)-enantiomers of rabeprazole than those of lansoprazole.

Endoscopic analysis of gastric ulcer after one week's treatment with omeprazole and rabeprazole in relation to CYP2C19 genotype

In Japanese healthy CYP2C19 extensive metabolizers, rabeprazole 10 mg shows a faster onset of action and stronger inhibition of acid secretion than does omeprazole 20 mg on the first 3 days of administration. We evaluated gastric ulcer improvement after 1 week's treatment with rabeprazole or omeprazole in relation to CYP2C19 polymorphism. A 6-mm rubber disc was placed temporarily at the side of the ulcer for measurement of the ulcer area. The improvement ratios of ulcer area in homozygous extensive metabolizers (homoEMs), heterozygous extensive metabolizers (heteroEMs) and poor metabolizers (PMs) treated with rabeprazole 10 mg were 60.8, 65.0 and 55.3%, respectively, and these values are not significantly different. Corresponding values with omeprazole 20 mg were 46.3, 61.7 and 63.2%, respectively, and the value of homoEMs was significantly smaller than that of heteroEMs. The improvement ratios with rabeprazole in homoEMs and heteroEMs were significantly greater than that with omeprazole in homoEMs.