Effect of omeprazole 10 mg on intragastric pH in three different CYP2C19 genotypes, compared with omeprazole 20 mg and lafutidine 20 mg, a new H2-receptor antagonist

Assessing and mitigating pH-mediated DDI risks in drug development - formulation approaches and clinical considerations

pH-mediated drug-drug interactions (DDI) is a prevalent DDI in drug development, especially for weak base compounds with highly pH-dependent solubility. FDA has released a guidance on the evaluation of pH-mediated DDI assessments using in vitro testing and clinical studies. Currently, there is no common practice of ways of testing across the academia and industry. The development of biopredictive method and physiologically-based biopharmaceutics modeling (PBBM) approaches to assess acid-reducing agent (ARA)-DDI have been proven with accurate prediction and could decrease drug development burden, inform clinical design and potentially waive clinical studies. Formulation strategies and careful clinical design could help mitigate the pH-mediated DDI to avoid more clinical studies and label restrictions, ultimately benefiting the patient. In this review paper, a detailed introduction on biorelevant dissolution testing, preclinical and clinical study requirement and PBPK modeling approaches to assess ARA-DDI are described. An improved decision tree for pH-mediated DDI is proposed. Potential mitigations including clinical or formulation strategies are discussed.

Prediction of Omeprazole Pharmacokinetics and its Inhibition on Gastric Acid Secretion in Humans Using Physiologically Based Pharmacokinetic-Pharmacodynamic Model Characterizing CYP2C19 Polymorphisms

PURPOSE

To develop a whole physiologically based pharmacokinetic-pharmacodynamic (PBPK-PD) model to describe the pharmacokinetics and anti-gastric acid secretion of omeprazole in CYP2C19 extensive metabolizers (EMs), intermediate metabolizers (IMs), poor metabolizers (PMs) and ultrarapid metabolizers (UMs) following oral or intravenous administration.

METHODS

A PBPK/PD model was built using Phoenix WinNolin software. Omeprazole was mainly metabolized by CYP2C19 and CYP3A4 and the CYP2C19 polymorphism was incorporated using in vitro data. We described the PD by using a turn-over model with parameter estimates from dogs and the effect of a meal on the acid secretion was also implemented. The model predictions were compared to 53 sets of clinical data.

RESULTS

Predictions of omeprazole plasma concentration (72.2%) and 24 h stomach pH after administration (85%) were within 0.5-2.0-fold of the observed values, indicating that the PBPK-PD model was successfully developed. Sensitivity analysis demonstrated that the contributions of the tested factors to the plasma concentration of omeprazole were Vmax,2C19 ≈ Papp > Vmax,3A4 > Kti, and contributions to its pharmacodynamic were Vmax,2C19 > kome > kms > Papp > Vmax,3A4. The simulations showed that while the initial omeprazole dose in UMs, EMs, and IMs increased 7.5-, 3- and 1.25-fold compared to those of PMs, the therapeutic effect was similar.

CONCLUSIONS

The successful establishment of this PBPK-PD model highlights that pharmacokinetic and pharmacodynamic profiles of drugs can be predicted using preclinical data. The PBPK-PD model also provided a feasible alternative to empirical guidance for the recommended doses of omeprazole.

A Pharmacogenetics-Based Approach to Managing Gastroesophageal Reflux Disease: Current Perspectives and Future Steps

Proton pump inhibitors (PPIs) are commonly used medications to treat acid-related conditions, including gastro-esophageal reflux disease (GERD). Gastroenterology guidelines mention the importance of CYP2C19 in PPI metabolism and the influence of CYP2C19 genetic variations on variable responses to PPIs, but do not currently recommend the genotyping of CYP2C19 prior to prescribing PPIs. There are strong data to support the influence of CYP2C19 genetic variations on the pharmacokinetics of PPIs and clinical outcomes. Existing pharmacogenetic guideline recommendations for dose increases focus on H. pylori and erosive esophagitis indications, but PPIs are also the main therapy for treating GERD. Recent data suggest GERD patients being treated with a PPI may also benefit from genotype-guided dosing. We summarize the literature supporting this contention and highlight future directions for improved management of patients with GERD through precision medicine approaches.

Effects of CYP2C19 genetic polymorphisms on the cure rates of H. pylori in patients treated with the proton pump inhibitors: An updated meta-analysis

Background: The cure rates of Helicobacter pylori (H. pylori) treatment using a proton pump inhibitor (PPI) are gradually decreasing due to antibiotic resistance, poor compliance, high gastric acidity, and cytochrome P450 2C19 (CYP2C19) polymorphism, and the effects of PPI depend on metabolic enzymes, cytochrome P450 enzymes. The aim of this meta-analysis was to determine whether CYP2C19 polymorphisms affect H. pylori cure rates in patients treated with different proton pump inhibitors (PPIs) according to stratified analysis.

Materials and methods: The literature was searched with the key words “H. pylori” and “CYP2C19” in PubMed, CNKI, and Wanfang up to 31 May 2022, and the studies were limited to clinical observational or randomized controlled trials (RCTs). Finally, seven RCTs and 29 clinical observational studies met the inclusion criteria and were used for the meta-analysis via STATA version 16.

Results: The cure rates were significantly different between genotypes of homozygous extensive metabolizers (EM) and poor metabolizers (PM) (OR = 0.58, 95% CI: 0.47–0.71) and between EM and heterozygous extensive metabolizers (IM) (OR = 0.71, 95% CI: 0.59–0.86), but not between IM and PM. Moreover, there was a significantly lower H. pylori cure rate in EM subjects than that in IM subjects when treated with omeprazole (66.4% vs. 84.1%), lansoprazole (76.1% vs. 85.6%), but not rabeprazole, esomeprazole, or pantoprazole. In addition, there was a significantly lower H. pylori cure rate in EM subjects than that in IM subjects when treated with a PPIs for 7 days (77.4% vs. 82.1%), but not 14 days (85.4% vs. 90.0%).

Conclusion: Carriers of CYP2C19 loss-of-function variant alleles (IM and PM) exhibit a significantly greater cure rate of H. pylori than noncarriers (EM) regardless of other factors (84.7% vs. 79.2%). In addition, pantoprazole- and rabeprazole-based quadruple therapy for H. pylori treatment is less dependent on the CYP2C19 genotype and should be prioritized in Asian populations with H. pylori.

The role of vonoprazan in patients with erosive esophagitis

Acid suppression is the primary therapy for erosive esophagitis (EE). Although proton pump inhibitors (PPIs) are considered as the first-line medication for EE, 10-20% of patients with Los Angeles C and D grade EE do not gain complete mucosal healing and symptom control despite 8-week double-dose PPI treatment. Vonoprazan is a novel potassium-competitive acid blocker (P-CAB), which blocks the H+, K+-adenosine triphosphatase enzymes in a K+-competitive and reversible manner. Vonoprazan exhibits different pharmacological and pharmacokinetic profiles from conventional PPIs, and has a rapid, potent and sustained acid inhibitory effect. In this review, we summarized and discussed current evidence regarding the role of vonoprazan in terms of mucosal healing, maintaining remission and symptom relief for the management of EE, including the initial and maintenance treatment of EE, as well as for PPI-resistant EE patients. Safety concerns and cost-effectiveness analysis of vonoprazan were also mentioned in the article. As a potent and well-tolerated acid blocker, vonoprazan has the potential to become a novel option for the management of EE.

Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2C19 and Proton Pump Inhibitor Dosing

Proton pump inhibitors (PPIs) are widely used for acid suppression in the treatment and prevention of many conditions, including gastroesophageal reflux disease, gastric and duodenal ulcers, erosive esophagitis, Helicobacter pylori infection, and pathological hypersecretory conditions. Most PPIs are metabolized primarily by cytochrome P450 2C19 (CYP2C19) into inactive metabolites, and CYP2C19 genotype has been linked to PPI exposure, efficacy, and adverse effects. We summarize the evidence from the literature and provide therapeutic recommendations for PPI prescribing based on CYP2C19 genotype (updates at www.cpicpgx.org). The potential benefits of using CYP2C19 genotype data to guide PPI therapy include (i) identifying patients with genotypes predictive of lower plasma exposure and prescribing them a higher dose that will increase the likelihood of efficacy, and (ii) identifying patients on chronic therapy with genotypes predictive of higher plasma exposure and prescribing them a decreased dose to minimize the risk of toxicity that is associated with long-term PPI use, particularly at higher plasma concentrations.

New Guidance on Cytochrome P450 2C19 Phenotype-based Use of Proton Pump Inhibitors

Since the approval of the first proton pump inhibitor (PPI) in 1989, our knowledge regarding this class of medications has further developed. An increasing amount of data now supports the association between cytochrome P450 2C19 (CYP2C19) phenotype and PPI safety and efficacy. This includes pediatric studies, such as those published here and in other pediatric journals within the past year. Moreover, the most recent pediatric Helicobacter pylori guidelines stated that using the PPIs that are less dependent on CYP2C19 for inactivation may be preferred for H pylori eradication among populations that are more likely to have rapid clearance of CYP2C19-metabolized PPIs. Conversely, pantoprazole package insert recommends a dose reduction in known pediatric CYP2C19 poor metabolizers (PMs), citing a 6-fold increase in serum concentrations compared with normal metabolizers (NMs). The purpose of this communication is to introduce a recently published Clinical Pharmacogenetics Implementation Consortium (CPIC) guideline for CYP2C19 and PPI dosing.

Analysis of the CYP2C19 genetic polymorphism in Han and Uyghur patients with cardiovascular and cerebrovascular diseases in the Kashi area of Xinjiang

BACKGROUND

The aim of this study was to analyze the CYP2C19 genetic polymorphism among Han and Uyghur patients with cardiovascular and cerebrovascular diseases in the Kashi area of Xinjiang.

MATERIAL/METHODS

We enrolled 1020 patients with cardiovascular and cerebrovascular diseases, including 220 Han subjects and 800 Uyghur subjects. We used the gene chip method to detect polymorphisms in CYP2C19. The allele frequencies of CYP2C19 and the metabolic phenotype frequencies were then compared between the 2 ethnic groups.

RESULTS

The frequency of CYP2C19 *1 was 0.6454 in Han subjects and 0.7869 in Uyghur subjects, and the difference was statistically significant (P<0.05). The frequency of CYP2C19 *2 was 0.3273 in Han subjects and 0.1837 in Uyghur subjects (P<0.05). The frequency of the homozygous extensive metabolizer phenotype was 42.72% and 62.13% in Han and Uyghur subjects, respectively (P<0.01). The frequency of the heterozygous extensive metabolizer phenotype was 43.64% and 33.13% in Han and Uyghur subjects, respectively (P<0.01). The frequency of poor metabolizers in Han and Uyghur subjects was 13.64% and 4.76%, respectively (P<0.01).

CONCLUSIONS

Among patients with cardiovascular and cerebrovascular diseases located in the Kashgar Prefecture of Xinjiang, there is a differential distribution of CYP2C19 genotypes between the Han and Uyghur populations. Uyghur patients showed higher frequencies of extensive metabolizer genotypes than Han patients, while Han patients showed higher frequencies of poor metabolizer genotypes than Uyghur patients.

Antiplatelet drug interactions with proton pump inhibitors

INTRODUCTION

Non-aspirin antiplatelet agents (e.g., clopidogrel, prasugrel, ticagrelor) are commonly prescribed for the prevention of recurrent cardiovascular events among patients with acute coronary syndromes (ACS) and/or those undergoing percutaneous coronary intervention (PCI). In addition, combination therapy with proton pump inhibitors (PPIs) is often recommended to attenuate gastrointestinal bleeding risk, particularly during dual antiplatelet therapy (DAPT) with clopidogrel and aspirin. Importantly, a pharmacological interaction between clopidogrel and some PPIs has been proposed based on mutual CYP450-dependent metabolism, but available evidence is inconsistent.

AREAS COVERED

This article provides an overview of the currently approved antiplatelet agents and PPIs, including their metabolic pathways. Additionally, the CYP450 isoenzyme at the center of the drug interaction, CYP2C19, is described in detail, and the available evidence on both the potential pharmacological interaction and influence on clinical outcomes are summarized and evaluated.

EXPERT OPINION

Although concomitant DAPT and PPI use reduces clopidogrel active metabolite levels and ex vivo-measured platelet inhibition, the influence of the drug interaction on clinical outcomes has been conflicting and largely reported from non-randomized observational studies. Despite this inconsistency, a clinically important interaction cannot be definitively excluded, particularly among patient subgroups with higher overall cardiovascular risk and potentially among CYP2C19 loss-of-function allele carriers.

Intravenous proton pump inhibitors for peptic ulcer bleeding: Clinical benefits and limits

Peptic ulcer bleeding is a common disease and recurrent bleeding is an independent risk factor of mortality. Infusion with proton pump inhibitors (PPIs) prevents recurrent bleeding after successful endoscopic therapy. A gastric acidic environment of less than pH 5.4 alters coagulation function and activates pepsin to disaggregate platelet plugs. Gastric acid is secreted by H⁺, K⁺-ATPase, naming the proton pump. This update review focuses on the mechanism and the role of PPIs in the clinical management of patients with peptic ulcer bleeding. An intravenous omeprazole bolus followed by high-dose continuous infusion for 72 h after successful endoscopic therapy can prevent the recurrent bleeding. In the Asian, however, the infusion dosage can possibly be diminished whilst preserving favorable control of the intragastric pH and thereby still decreasing rates of recurrent bleeding. Irrespective of the infusion dosage of PPIs, rates of recurrent bleeding remain high in patients with co-morbidities. Because recurrent peptic ulcer bleeding may be prolonged in those with co-morbidities, a low-dose infusion of IV PPIs for up to 7-day may result in better control of recurrent bleeding of peptic ulcers. Due to the inter-patient variability in CYP2C19 genotypes, the infusion form of new generation PPIs, such as esomeprazole, should be promising for the prevention of recurrent bleeding. This article offers a comprehensive review of clinical practice, highlighting the indication, the optimal dosage, the duration, and the potential limitation of PPIs infusion for peptic ulcer bleeding.

An open-label, randomized, cross-over bioequivalence study of lafutidine 10 mg under fasting condition

AIM: To assess the relative bioavailability and pharmacokinetic properties of two formulations (test and reference) of Lafutidine 10 mg.

METHODS: The study was performed as an open label, randomized, two-way, two-period, two-treatment, single dose cross-over bioequivalence study, under non-fed condition to compare the pharmacokinetic profiles of the lafutidine formulation manufactured by Emcure Pharmaceuticals Ltd., India using an indigenously developed active pharmaceutical ingredient (API) and the commercially available Stogra^® formulation, of UCB Japan Co., Ltd., Japan. The two treatments were separated by a wash-out period of 5 d. After an overnight fasting period of 10 h, the subjects were administered either the test or the reference medication as per the randomization schedule. Blood samples were collected at intervals up to 24 h, as per the approved protocol. Concentrations of lafutidine in plasma were analyzed by a validated liquid chromatography/tandem mass spectrometry (LC/MS/MS) method, and a non-compartmental model was used for pharmacokinetic analysis. The pharmacokinetic parameters were subjected to a 4-way ANOVA accounting for sequence, subjects, period and treatment. Statistical significance was evaluated at 95% confidence level (P ≥ 0.05).

RESULTS: The mean (± SD) values of the pharmacokinetic parameters (test vs reference) were C_max (265.15 ± 49.84 ng/mL vs 246.79 ± 29.30 ng/mL, P < 0.05), Area under the curve (AUC)_(0-t) (1033.13 ± 298.74 ng.h/mL vs 952.93 ± 244.07 ng.h/mL, P < 0.05), AUC_(0-∞) (1047.61 ± 301.22 ng.h/mL vs 964.21 ± 246.45 ng.h/mL, P < 0.05), and t_½(1.92 ± 0.94 h vs 2.05 ± 1.01 h, P < 0.05). The 90% confidence intervals (CI) for the test/reference ratio of mean C_max, AUC_(0-t), and AUC_(0-∞) were within the acceptable range of 80.00 to 125.00. The mean times (± SD) to attain maximal plasma concentration (t_max) of lafutidine were 0.95 ± 0.24 h vs 1.01 ± 0.29 h (P < 0.05) for the test and the reference formulations respectively. Both the formulations were well tolerated.

CONCLUSION: In summary, this study has demonstrated the bioequivalence of the two formulations of lafutidine 10 mg. Hence it can be concluded that the two formulations can be used interchangeably in clinical settings.

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.

Effects of acid antisecretory drugs on mucus barrier of the rat against 5-fluorouracil-induced gastrointestinal mucositis

OBJECTIVE

Acid antisecretory agents are used for the prophylaxis of cancer chemotherapy (CT)-induced gastrointestinal (GI) mucositis. Although these drugs seem to be clinically beneficial, data on their effects on the GI mucosal defense during CT treatment are scant. The objective of this study was to compare the effects of omeprazole, lansoprazole, and lafutidine on mucin, a major mucus component, during 5-fluorouracil (5-FU) treatment, as a CT regimen.

MATERIAL AND METHODS

Rats, weighing approximately 230 g, were divided into five groups. The control group was administered 0.5% carboxymethylcellulose orally once daily for 5 days. The second, third, fourth, and fifth groups were treated with 5-FU (50 mg/kg), 5-FU plus omeprazole (10 mg/kg), 5-FU plus lansoprazole (10 mg/kg), and 5-FU plus lafutidine (30 mg/kg) in the same way, respectively. The rats were sacrificed on the sixth day, and their stomachs and small intestines were removed. Using anti-mucin monoclonal antibodies, we compared the immunoreactivity in different areas of the rats' GI tracts as well as the mucin content.

RESULTS

Body-weight decreased in rats in the 5-FU group. Lafutidine, but neither omeprazole nor lansoprazole, inhibited the 5-FU-induced weight loss. Mucosal damage and reduced mucin content in stomach and small intestine were observed in rats receiving 5-FU alone. In the stomach, all antisecretory drugs caused the protective effects against 5-FU-induced mucosal injury and alleviation of the decreased mucin accumulation. In the jejunum and ileum, lafutidine, but neither omeprazole nor lansoprazole, ameliorated the 5-FU-induced mucosal damage and decreased mucin accumulation.

CONCLUSION

Lafutidine could offer the possibility of more effective prevention of CT-induced mucositis through the activation of GI mucus cells.

Effects of CYP2C19 genetic polymorphism on the pharmacokinetics and pharmacodynamics of omeprazole in Chinese people

BACKGROUND

To investigate whether the pharmacodynamics and pharmacokinetics of omeprazole (OPZ) are dependent of the CYP2C19 genotype status in Chinese people.

METHODS

Eighteen healthy subjects were voluntary to participate in the study, whose CYP2C19 genotype status were determined by polymerase chain reaction-restriction fragment length polymorphism method. There were six homozygous extensive metabolizers, six heterozygous extensive metabolizers and six poor metabolizers (PMs). All subjects were Helicobacter pylori-negative, determined by serology method and (13)C-urea breath test. After d1 and d8 orally received OPZ 20 mg once daily in the morning, intragastric pH values were monitored for 24 h by Digitrapper pH. Meanwhile, blood samples were collected at various time-points until 24 h after administration. The serum concentrations of OPZ were measured by liquid chromatography.

RESULTS

After single or repeated doses, the PMs showed a significantly higher mean area under the serum concentration-time curves (AUC) values than that observed in the homozygous extensive metabolizers or the heterozygous extensive metabolizers, with a relative ratio of 1.0 : 1.1 : 4.2 and 1.0 : 1.3 : 3.3 (homozygous extensive metabolizers:heterozygous extensive metabolizers:poor metabolizers), respectively. After a single dose of OPZ, significant differences in intragastric pH median, pH > 3 holding time and pH > 4 holding time were observed among the three groups. After repeated doses, the PMs showed a significantly higher intragastric pH values than that observed in the homozygous extensive metabolizers or the heterozygous extensive metabolizers.

CONCLUSION

The pharmacodynamic effects of OPZ and its pharmacokinetics depend on the CYP2C19 genotype status in Chinese people.

Effects of a novel histamine H2-receptor antagonist, lafutidine, on the mucus barrier of human gastric mucosa

BACKGROUND AND AIM

Lafutidine is a novel histamine H(2)-receptor antagonist used primarily as an antisecretory agent in Japan. Previous human studies have not assessed its gastroprotective effects. The purpose of the present study was to determine the effects of lafutidine on the human gastric mucus layer using both histological and biochemical methods.

METHODS

Of the 14 patients scheduled for gastrectomy who consented to participate, seven were given 14 days of lafutidine 20 mg/day (lafutidine group) and the others received no medication (control group). The surface mucus gel layer in Carnoy-fixed tissue sections was examined immunohistochemically. Both the thickness of the mucus layer and its mucin content were measured in gastric corpus mucosa.

RESULTS

There was no detectable difference between the groups in the grade of gastritis or the immunohistochemical staining characteristics. The laminated structure of the surface mucus gel layer was retained after administration of lafutidine and it was thicker than the layer in the control group. The surface layer in the lafutidine group had three-fold more mucin than that in the control group. There was no difference between the two groups in the mucin content of the deep mucosa.

CONCLUSION

Lafutidine, given at clinical dosages, not only inhibits acid secretion but also strengthens the mucus barrier of the human gastric mucosa.

Acid-suppressive effects of various regimens of omeprazole in Helicobacter pylori-negative CYP2C19 homozygous extensive metabolizers: which regimen has the strongest effect?

To achieve more potent and long-lasting acid suppression, omeprazole was administered for 7 days in 5 regimens: 10, 20, and 40 mg once daily (od), and 10 and 20 mg twice daily (bid), in 7 healthy Helicobacter pylori-negative CYP2C19 homozygous extensive metabolizers, and intragastric pH was continuously measured. The median intragastric pH and percent time pH > 4.0 for 24 hours increased dose dependently with 10, 20, and 40 mg od. Ten and 20 mg bid wre comparable to 20 and 40 mg od, respectively. Concerning percent time pH > 4.0 in the nighttime (20:00-8:00 hours), 20 mg bid was significantly superior to 40 mg od (P < .05). In 4 of the 5 regimens, all 7 subjects had nocturnal acid breakthrough, whereas with 20 mg bid it occurred in only 3. We concluded that, considering nighttime acid suppression, omeprazole 20 mg bid had the strongest effect.

Pharmacokinetic and Pharmacodynamic Properties of Lafutidine after Postprandial Oral Administration in Healthy Subjects: Comparison with Famotidine

Lafutidine, a histamine H(2)-receptor antagonist, inhibits gastric acid secretion during the daytime, however, the relationship between the plasma concentration and the drug response remains unclear. The aim of this study was to compare the pharmacokinetic and pharmacodynamic properties of lafutidine and famotidine following postprandial oral administration. After a lafutidine tablet (10 mg), famotidine tablet (20 mg), or water only (control) was administered, blood samples were taken and intragastric pH was measured. The plasma concentrations of lafutidine and famotidine were determined by HPLC, and the median intragastric pH values per 30 min were used as the degrees of gastric acid suppression. Data were analyzed based on a one-compartment pharmacokinetic model and a sigmoid E(max) pharmacodynamic model. Lafutidine plasma concentrations rapidly increased after administration; famotidine required some time to increase the plasma concentrations, requiring an absorption lag time in the pharmacokinetic model. Between the plasma concentration and DeltapH (the difference in intragastric pH by the drug vs. control), lafutidine showed an anticlockwise hysteresis loop which indicated equilibration delay between the plasma concentration and effect site, requiring an effect site compartment in the pharmacodynamic model; famotidine showed more parallel relationship. These results indicated that the pharmacokinetic and pharmacodynamic properties of lafutidine after postprandial oral administration were different from those of famotidine at least 4.5 h after dosing.

Effect of CYP2C19*17 gene variant on Helicobacter pylori eradication in peptic ulcer patients

OBJECTIVE

Eradication of Helicobacter pylori is an important treatment strategy in peptic ulcer patients. Current regimens of eradication consist of proton pump inhibitor (PPI) and two antibiotics. The principal enzyme involved in PPIs metabolism is CYP2C19, which exhibits an interindividual variability of activity, mainly due to genetic polymorphism. Two alleles (CYP2C19*2 and CYP2C19*3), responsible for slow PPIs metabolism, were previously associated with higher efficacy of eradication. Recently, a novel CYP2C19 gene variant (CYP2C19*17), associated with faster metabolism of CYP2C19 substrates, was described. In the present study, a potential association between CYP2C19*17 allele and lower H. pylori eradication efficacy was tested in a group of peptic ulcer patients.

METHODS

A total of 125 peptic ulcer patients, positive for H. pylori infection, were treated with triple therapy (pantoprazole+amoxicillin+metronidazole). Subsequently, the patients were divided into two groups (group 1 - success, and group 2 - failure of eradication after therapy) and genotyped for the presence of CYP2C19 variant alleles (*2, *3, and *17).

RESULTS

Frequency of CYP2C19 alleles in two groups of patients were: 56.4 versus 65 (p=0.060) for *1, 15.4 versus 5.3 (p=0.015) for *2, and 28.2 versus 25.5 (p=0.663) for *17 allele, respectively. CYP2C19*3 was not detected in the evaluated population. No significant differences in frequency nor distribution of *17 allele were found between two groups of patients. CYP2C19*2 allele was associated with successful H. pylori eradication (p<0.02), *2 allele carriers were found to be over 4-times more prone to the treatment compared to *1/*1 homozygotes (OR=4.2, p=0.015).

CONCLUSION

Our results suggest that, contrary to CYP2C19*2, CYP2C19*17 allele has no impact on efficacy of H. pylori eradication in peptic ulcer patients treated with pantoprazole.

Lafutidine, a newly developed antiulcer drug, elevates postprandial intragastric pH and increases plasma calcitonin gene-related peptide and somatostatin concentrations in humans: comparisons with famotidine

Lafutidine, a newly developed histamine H(2)-receptor antagonist, inhibits daytime (i.e., postprandial) as well as nighttime gastric acid secretion in clinical studies. It also has gastroprotective activity that particularly affects mucosal blood flow in rats. This study focused on the efficacy of lafutidine on plasma concentrations of gastrointestinal peptides in humans. Six healthy male volunteers aged 23-32 years without Helicobacter pylori infection were orally administered either 10 mg lafutidine, 20 mg famotidine, or water only (control) 30 min after a standard meal (650 kcal). Plasma concentrations of lafutidine and famotidine were highest from 90 to 150 min after administration. Intragastric pH was elevated after both lafutidine and famotidine compared with the control. Plasma concentrations of calcitonin gene-related peptide (CGRP) and somatostatin were significantly increased after lafutidine at 60 and 90 min. We concluded that lafutidine increases plasma concentrations of CGRP and somatostatin in humans, which may result in inhibition of postprandial acid secretion and gastroprotective activity.

Acid-suppressive efficacy of a reduced dosage of rabeprazole: comparison of 10 mg twice daily rabeprazole with 20 mg twice daily rabeprazole, 30 mg twice daily lansoprazole, and 20 mg twice daily omeprazole by 24-hr intragastric pH-metry

Rabeprazole achieves more potent acid suppression than other proton pump inhibitors. Therefore it is administered at reduced as well as high dosages in eradication therapy for Helicobacter pylori; however, there is incomplete assessment of the efficacy of a reduced dosage of rabeprazole as might be employed in therapy. In this study, we evaluated acid-suppressive efficacy of a reduced dosage of rabeprazole on day 7 by 24-hr pH-metry in 10 healthy male cytochrome P-450 2C19 extensive metabolizers without Helicobacterpylori infection and compared the results with those of high dosages of rabeprazole, lansoprazole, and omeprazole. Median intragastric pH value, pH >3 holding time ratio (pH>3HT), pH>4HT, pH>5HT, pH>6HT, and pH>7HT for 24 hr with rabeprazole, 10 mg twice daily, were not significantly different from those of rabeprazole, 20 mg twice daily, lansoprazole, 30 mg twice daily, and omeprazole, 20 mg twice daily. In conclusion, for acid-suppressive efficacy, a reduced dosage of rabeprazole is comparable to high dosages of rabeprazole, lansoprazole, and omeprazole.

Effect of CYP2C19 and MDR1 polymorphisms on cure rate in patients with acid-related disorders with Helicobacter pylori infection

A proton pump inhibitor (PPI) plus two antibiotics (amoxicillin and either clarithromycin or metronidazole) are recommended for treatment of acid-related disorders with Helicobacter pylori (H. pylori) infection. The aim of this pharmacogenetic study was to evaluate the efficacy of triple therapy with PPIs on eradication of H. pylori infection in relation to cytochrome P450 2C19 (CYP2C19) and P-glycoprotein (MDR1) gene polymorphisms. The retrospective study involved 70 Polish Caucasian patients with H. pylori infection, diagnosed and treated with one of the two different triple therapy regimens [omeprazole, amoxicillin, and clarithromycin (OAC) or pantoprazole, amoxicillin, and metronidazole (PAM)]. Using genomic DNA, CYP2C19 (*2 and *3) and C3435T MDR1 alleles were determined by means of polymerase chain reaction-restriction fragment length polymorphism assays. A significantly higher prevalence (P<0.05) of heterozygous extensive metabolizers (hetEM) with CYP2C19*1/*2 genotype (32.4% versus 8.3%) and homozygous with 3435TT MDR1 genotype (38.2% versus 13.9%) was found in patients cured after the first cycle of triple therapy than in patients with failure of eradication after the first cycle. CYP2C19*1/*2 and 3435TT MDR1 genotypes as well as PAM regimen of treatment were also predictive of successful eradication of H. pylori infection after the first cycle of triple therapy at univariate/multivariate logistic regression analysis. This pharmacogenetic study on the influence of different CYP2C19 and C3435T MDR1 genotypes on H. pylori eradication suggests that CYP2C19 and MDR1 polymorphisms may be independent predictable determinants of the efficacy of triple therapy including PPI. The PAM regimen of treatment seems to be more effective after the first cycle of the therapy than the OAC regimen.

CYP2C19Polymorphism and Proton Pump Inhibitors

Proton pump inhibitors such as omeprazole (esomeprazole), lansoprazole, pantoprazole and rabeprazole are eliminated by the hepatic route and the polymorphic CYP2C19 is mainly involved in their metabolism. In different populations three phenotypes have been identified: extensive metabolizers, poor metabolizers and individuals carrying one wild type and one mutant allele (het extensive metabolizers). Systemic exposure to the proton pump inhibitors as expressed by the AUC (area under the plasma level time profiles) is 5-12-times higher in poor metabolizers than in extensive metabolizers. As the pharmacodynamic response (elevation of intragastric pH) to the proton pump inhibitors is related directly to their AUC, a much higher pH can be monitored over 24 hr in poor metabolizers than in extensive metabolizers. Furthermore, clinical efficacy of all proton pump inhibitors depend on maintaining intragastric pH above certain threshold levels and significantly higher eradication rates of Helicobacter pylori have been observed in patients of the poor metabolizers and het extensive metabolizers phenotype if compared to extensive metabolizers. Likewise, limited data suggest that proton pump inhibitors-induced healing rates in gastro-oesophageal reflux disease are apparently higher in poor metabolizers/het extensive metabolizers than in extensive metabolizers of CYP2C19. Therefore initial genotyping for this enzyme and higher dosage in extensive metabolizers is likely to improve the clinical efficacy of proton pump inhibitors.