Pharmacokinetic Herb-Drug Interactions of Xiang-Sha-Liu-Jun-Zi-Tang and Paclitaxel in Male Sprague Dawley Rats and Its Influence on Enzyme Kinetics in Human Liver Microsomes.

Paclitaxel is a prescribed anticancer drug used to treat various cancers. It is a substrate of cytochrome P-450 (CYP-450) enzymes. Despite its efficacy, paclitaxel has severe side effects. Herbal medicines are commonly used to treat the side effects of chemotherapy. They can be administered before, during, and after chemotherapy. Xiang-Sha-Liu-Jun-Zi Tang (XSLJZT) is a herbal formula commonly used in breast cancer patients. The main purpose of this study was to assess the pharmacokinetic (PK) influence of XSLJZT on paclitaxel PK parameters, determine its effect on CYP-450 enzyme expression, and evaluate its effect on enzyme activity. Sprague Dawley rats were classified into pretreatment and co-treatment groups, where XSLJZT was pre-administered for 3, 5, and 7 days and co-administered 2 h before paclitaxel administration. The rat liver tissues and Hep-G2 cells were used to determine the effects of XSLJZT on CYP3A1/2 and CYP3A4 enzymes respectively. Western blot analysis was used to detect changes in the CYP3A1/2 and CYP3A4 enzymes expression. The influence of XSLJZT on enzyme activity was evaluated using human liver microsomes, and a liquid chromatography-tandem mass spectrometric system was developed to monitor paclitaxel levels in rat plasma. Results demonstrated that XSLJZT increased the area under the concentration versus time curve (AUC) for paclitaxel in pretreatment groups by 2-, 3-, and 4-fold after 3, 5, and 7 days, respectively. In contrast, no significant change in the AUC was observed in the co-treatment group. However, the half-life was prolonged in all groups from 17.11 min to a maximum of 37.56 min. XSLJZT inhibited CYP3A1/2 expression in the rat liver tissues and CYP3A4 enzymes in Hep-G2 cells in a time-dependent manner, with the highest inhibition observed after 7 days of pretreatment in rat liver tissues. In the enzyme kinetics study, XSLJZT inhibited enzyme activity in a competitive dose-dependent manner. In conclusion, there is a potential interaction between XSLJZT and paclitaxel at different co-treatment and pretreatment time points.

Effect of catechin and commercial preparation of green tea essence on the pharmacokinetics of l-dopa in rabbits.

The aim of this study was to investigate drug interactions of L-dopa/carbidopa with catechin and green tea essence in rabbits following the simultaneous administration via an intramuscular injection of catechin or via an intragastric route for green tea essence with L-dopa/carbidopa. The results indicated that catechin at doses of 10, 20 and 50 mg/kg increased the area under the plasma concentration-time curve from time zero to the time of the last quantifiable concentration (AUC0-t ) of L-dopa by about 69, 78 and 42%, respectively. The metabolic ratios of the AUC0-t for 3-O-methyldopa (3-OMD)/L-dopa significantly decreased by about 56, 68 and 76% (P < 0.05), respectively. In addition, a single dose of 5/1.25 mg/kg L-dopa/carbidopa was co-administrated with 150 mg/kg green tea essence via an intragastric route with an oral-gastric tube. Comparing the related pharmacokinetic parameters of L-dopa, the clearance and metabolic ratio of L-dopa decreased by 20 and 19% (P < 0.05), respectively. In conclusion, catechin and green tea essence can significantly affect the metabolism of L-dopa by the catechol-O-methyltransferase (COMT) metabolic pathway. Catechin can enhance L-dopa bioavailability, and both catechin and green tea essence decreased 3-OMD formation. Therefore, catechin and green tea essence may increase L-dopa efficacy for Parkinson's disease treatment.

Association between acid-suppressive drug use and atopic dermatitis in patients with upper gastrointestinal diseases: A population-based retrospective cohort study.

WHAT IS KNOWN AND OBJECTIVE: Proton-pump inhibitors (PPIs) and histamine-2-receptor antagonists (H2RAs) are two of the most widely used acid-suppressive drugs (ASDs). Some studies have reported that prenatal ASD exposure may increase the risk of asthma and other allergic diseases. This study investigated the effects of ASDs on the risk of atopic dermatitis in patients with upper gastrointestinal diseases. METHODS: This population-based retrospective cohort study used data of 289,850 patients with at least two diagnoses of upper gastrointestinal diseases (UGIDs) between 1 January 2001 and 31 December 2005, from Taiwan's National Health Insurance Research Database. The AD risks among ASD users and nonusers were compared. Differences in sociodemographic characteristics and potential covariates were examined. AD hazard ratios were estimated, and groups were compared using Cox proportional hazards regression analysis after adjustment for age, sex and other covariates. RESULTS AND DISCUSSION: In total, 109,980 patients were included. The adjusted hazard ratio (HR) of AD risk in ASD users relative to that in nonusers was 1.52 (95% confidence interval [CI]: 1.40-1.64, p < 0.001). For a dose-effect sub-analysis, patients were divided into four groups based on their defined daily dose. ASDs dose-dependently affected the AD risk (p for trend <0.01). Furthermore, the adjusted HR of the AD risk among ASD nonusers was 2.30 (95% CI: 2.06-2.57) relative to that in the comparison group (ASD nonusers without UGIDs). Among patients with UGIDs, ASD users had a higher AD risk than ASD nonusers. A subgroup analysis revealed only H2RA use was associated with an increased AD risk (adjusted HR 1.70, 95% CI: 1.53-1.89, p < 0.001). WHAT IS NEW AND CONCLUSIONS: These results indicate that the use of H2RAs was associated with an increased risk of AD among patients with UGIDs, and the increase in risk appeared to be dose-dependent. ASDs should be used only in situations where clear clinical benefits can be obtained.

Dose-dependent pharmacokinetics and tentative identification of urine metabolites from an isosteviol derivative with anti-hepatitis B activity in rats.

Compound 1 (ent-16-oxobeyeran-19-N-methylureido) is a semisynthetic isosteviol derivative that shows anti-hepatitis B virus activity in Huh7 cells by affecting viral DNA transcription and the Toll-like receptor 2/nuclear factor-κB signaling pathway. Thus, the pharmacokinetics and metabolite identification were studied as part of the discovery and development process of compound 1. The pharmacokinetics was evaluated after administration to rats at an intravenous dose of 2 mg/kg, and oral doses of 2, 5 and 10 mg/kg. Plasma concentrations were determined using LC-MS/MS. Moreover, urine samples from rats dosed at 10 mg/kg were scanned for metabolites using UPLC-QTOF-MS/MS. Results for the intravenously administered dose of 2 mg/kg showed that the area under the concentration-time curve was 65,223.31 ± 4269.80 ng min/mL, and the systemic clearance was 0.031 ± 0.0021 L/min. Oral pharmacokinetic parameters were dose-dependent, showing nonproportional increases in the oral AUCs with respective values of 4371.62 ± 3084.81, 22,472.75 ± 9103.33 and 135,141.83 ± 38,934.03 ng min/mL for 2, 5 and 10 mg/kg. The bioavailability was low at 1.5% for 2 mg/kg dose, and at 1.1% for both 5 and 10 mg/kg doses. Metabolites excreted in the urine indicate possible N-oxidation and glucuronide conjugation.

Development and validation of an LC-MS/MS method for quantification of NC-8 in rat plasma and its application to pharmacokinetic studies.

ent-16-Oxobeyeran-19-N-methylureido (NC-8) is a recently synthesized derivative of isosteviol that showed anti-hepatitis B virus (HBV) activity by disturbing replication and gene expression of the HBV and by inhibiting the host toll-like receptor 2/nuclear factor-κB signaling pathway. To study its pharmacokinetics as a part of the drug development process, a highly sensitive, rapid, and reliable liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed and validated for determining NC-8 in rat plasma. After protein precipitation extraction, the chromatographic separation of the analyte and internal standard (IS; diclofenac sodium) was performed on a reverse-phase Luna C18 column coupled with a Quattro Ultima triple quadruple mass spectrometer in the multiple-reaction monitoring mode using the transitions, m/z 347.31 â†’ 75.09 for NC-8 and m/z 295.89 â†’ 214.06 for the IS. The lower limit of quantitation was 0.5 ng/mL. The linear scope of the standard curve was between 0.5 and 500 ng/mL. Both the precision (coefficient of variation; %) and accuracy (relative error; %) were within acceptable criteria of <15%. Recoveries ranged from 104% to 113.4%, and the matrix effects (absolute) were non-significant (CV ≤ 6%). The validated method was successfully applied to investigate the pharmacokinetics of NC-8 in male Sprague-Dawley rats. The present methodology provides an analytical means to better understand the preliminary pharmacokinetics of NC-8 for investigations on further drug development.

Pharmacokinetics of dinalbuphine sebacate and nalbuphine in human after intramuscular injection of dinalbuphine sebacate in an extended-release formulation.

Nalbuphine is a semi-synthetic opioid indicated for the relief of moderate to severe pain. Its short half-life requires frequent injections in clinical practice, resulting in a greater incidence of adverse events. A prodrug of nalbuphine has been developed, dinalbuphine sebacate (DNS), dissolved in a simple oil-based injectable formulation, which could deliver and maintain an effective blood level of nalbuphine. An open-label, prospective, two-period study was performed in healthy volunteers to verify the extended blood concentration profile of nalbuphine. Twelve healthy Taiwanese were randomized to receive an intramuscular injection of 20 mg nalbuphine HCl and 150 mg DNS sequentially with a washout period of 5 days. To prevent DNS hydrolysis during sample analysis, the effect of four esterase inhibitors was evaluated in the quantitation of DNS in human whole blood and thenoyltrifluoroacetone was chosen. The bioavailability of nalbuphine from intramuscularly injected DNS relative to that from nalbuphine HCl was 85.4%. The mean absorption time of nalbuphine from DNS was 145.2 h. It took approximately 6 days for the complete release of DNS into the blood stream where DNS was rapidly hydrolysed to nalbuphine; suggesting a single injection of 150 mg DNS in our extended-release formulation could provide long-lasting pain relief.

Differential changes in the pharmacokinetics of statins in collagen-induced arthritis rats.

The elevated systemic levels of cytokines in rheumatoid arthritis (RA) can change the expression of metabolic enzymes and transporters. Given that statins are lipid-lowering agents frequently used in RA patients with concurrent cardiovascular diseases, the objective of the present study was to investigate the impacts of RA on the pharmacokinetics of statins of different disposition properties in rats with collagen-induced arthritis (CIA). The expression of metabolic enzymes and transporters in tissues of CIA rats were analyzed by RT-qPCR. Statins were given to CIA rats and controls through different routes, respectively. Blood samples were collected and analyzed by UPLC/MS/MS. Isolated microsomes and hepatocytes were used to determine the metabolic and uptake clearance of statins. The results showed that, compared with controls, the mRNA levels of intestinal Cyp3a1 and hepatic Cyp2c6, Cyp2c7, Cyp3a1, Oatp1a1, Oatp1b2, Oatp1a4, and Mrp2 were markedly decreased in the CIA rats. The maximal metabolic activities of Cyp2c and Cyp3a were reduced in liver microsomes of CIA rats. When given orally or injected through hepatic portal vein, the systemic levels of fluvastatin, simvastatin, and atorvastatin, but not of rosuvastatin and pravastatin, were increased in CIA rats. The metabolic clearance of simvastatin and hepatic uptake clearance of fluvastatin and atorvastatin were decreased in CIA rats. These findings suggest that the changes in the expression of enzymes and/or transporters in CIA rats differentially affect the pharmacokinetics of statins.

Allopurinol, benzbromarone and risk of coronary heart disease in gout patients: A population-based study.

BACKGROUND: The effect of gout on the risk of developing coronary artery disease (CAD) is uncertain. Some studies have found that gout is a risk factor for acute myocardial infarction. This study examined the changes in risk of CAD in gout patients taking allopurinol and/or benzbromarone, and analyzed the dose-response relationship of both drugs with CAD incidence. METHODS: The medical records of one million subjects from 2000 to 2011 were provided by the Taiwan National Health Insurance Research Database. Cox proportional hazard ratio was used to compare the risk of CAD in gout patients taking allopurinol or/and benzbromarone with those taking neither drug. Hazard ratios (HR) were adjusted for possible confounding factors, including age, gender, hypertension, hyperlipidemia, diabetes mellitus, chronic kidney disease, and relevant medications. RESULTS: Of 8047 gout patients, 1422 were treated with allopurinol (Group A), 4141 with benzbromarone (Group B), and 2484 with both drugs (Group A/B) during the follow-up period. Our results showed the incidence of CAD after adjusting for covariates for Group A, Group B, and Group A/B did not significantly differ from the comparison group. However, after adjustment for covariates in dose-response analyses, treatment with over 270 defined daily doses (DDDs) of allopurinol, and over 360 DDDs of benzbromarone, was associated with a significantly reduced risk of CAD. CONCLUSION: We found that the use of allopurinol and benzbromarone, whether alone or in combination, had a linear dose-response relationship between the numbers of defined daily doses and the risk of CAD, especially in higher DDDs.

The use of proton pump inhibitors decreases the risk of diabetes mellitus in patients with upper gastrointestinal disease: A population-based retrospective cohort study.

OBJECTIVES: The aim of this study was to investigate the effects of proton pump inhibitors (PPIs) on the risk of diabetes mellitus (DM) among patients with upper gastrointestinal disease (UGID). METHODS: This was a retrospective cohort study with a follow-up period of 5 years. We identified 388,098 patients who were diagnosed with UGID between 2000 and 2006 from the Longitudinal Health Insurance Database of the Taiwan National Health Insurance program. We used Cox proportional hazard ratio (HR) to compare the risk of DM between UGID patients received PPIs and those did not receive PPIs. HRs were adjusted for possible confounders, including age, sex, hypertension, gout and/or hyperuricemia, coronary artery disease, stroke, pancreatitis, hyperlipidemia, obesity, H2-blocker use, and clozapine or olanzapine use. The dose-related effects of PPIs on the risk of DM were evaluated according to the defined daily dose (DDD). RESULTS: The adjusted HR was 0.80 (95% CI, 0.73-0.88) for the study group (UGID patients with PPIs) compared with comparison group I (UGID patients without PPIs). Among patients who used PPIs, those older than 60 years of age had a lower risk of DM (HR, 0.73; 95% CI, 0.63-0.83) than those younger than 40 years. Additionally, the effect of PPIs was significantly dose-dependent (P for trend <0.001). Patients with UGID who received >540 DDDs of PPIs exhibited the greatest reduction in the risk of DM. CONCLUSIONS: Our results demonstrated a decreased risk of DM in UGID patients who used PPIs; the risk appeared to be significantly dose-dependent.

Effects of metformin dose on cancer risk reduction in patients with type 2 diabetes mellitus: a 6-year follow-up study.

STUDY OBJECTIVE: To explore the effects of metformin dose on cancer risk reduction in patients with type 2 diabetes. DESIGN: Population-based cohort study. DATA SOURCE: National Health Insurance program Longitudinal Health Insurance Database. PATIENTS: A total of 65,754 age- and gender-matched patients without diabetes and no previous cancer diagnosis were extracted from the database. MEASUREMENTS AND MAIN RESULTS: We compared cancer risk among the subjects who had no diabetes, had type 2 diabetes but were not on diabetes drugs, used metformin only, used antidiabetic drugs other than metformin, or used metformin in combination with other antidiabetic drugs. Our results revealed dose-dependent effects of metformin on cancer risk and cancer onset times. A significant decrease in cancer risk was found in the monotherapy group who received more than 360 defined daily doses (DDDs) of metformin (hazard ratio [HR] 0.40, 95% confidence interval [CI] 0.24-0.66). The greatest decrease in cancer risk was observed in patients who took more than 1080 DDDs (HR 0.27, 95% CI 0.09-0.84). Significantly greater dose-dependent effects were seen in patients who used metformin in combination with other antidiabetic drugs. CONCLUSION: The magnitude of cancer risk reduction and prolonged cancer onset times produced by metformin in patients with type 2 diabetes depended on the dose of metformin, regardless of whether metformin was used alone or combined with other antidiabetic drugs.

Improved dissolution rate and oral bioavailability of lovastatin in red yeast rice products.

Lovastatin, categorized as a class II compound according to the Biopharmaceutics Classification System, is mainly responsible for the blood cholesterol lowering effect of red yeast rice (RYR). The aim of this study was to compare the dissolution rate, physical state, and oral bioavailability of lovastatin in three RYR products (LipoCol Forte, Cholestin, or Xuezhikang) to those of two lovastatin tablets (Mevacor or Lovasta). The results showed that the dissolution rate of lovastatin in various dissolution media in the registered RYR products was faster and higher than that of lovastatin in lovastatin tablets. Powder X-ray diffraction and differential scanning calorimetry patterns showed that the crystallinity of lovastatin was reduced in RYR products. In human studies, the AUC and Cmax values for both lovastatin and its active metabolite, lovastatin acid, were significantly higher in volunteers receiving LipoCol Forte capsules or powder than in those receiving lovastatin tablets or powder. In addition, shorter and less variable Tmax values were observed in volunteers taking LipoCol Forte than in those taking lovastatin tablets. These findings suggest that the oral bioavailability of lovastatin is significantly improved in RYR products as a result of a higher dissolution rate and reduced crystallinity.

Interaction between Red Yeast Rice and CYP450 Enzymes/P-Glycoprotein and Its Implication for the Clinical Pharmacokinetics of Lovastatin.

Red yeast rice (RYR) can reduce cholesterol through its active component, lovastatin. This study was to investigate the pharmacokinetic properties of lovastatin in RYR products and potential RYR-drug interactions. Extracts of three registered RYR products (LipoCol Forte, Cholestin, and Xuezhikang) were more effective than pure lovastatin in inhibiting the activities of cytochrome P450 enzymes and P-glycoprotein. Among CYP450 enzymes, RYR showed the highest inhibition on CYP1A2 and CYP2C19, with comparable inhibitory potencies to the corresponding typical inhibitors. In healthy volunteers taking the RYR product LipoCol Forte, the pharmacokinetic properties of lovastatin and lovastatin acid were linear in the dose range of 1 to 4 capsules taken as a single dose and no significant accumulation was observed after multiple dosing. Concomitant use of one LipoCol Forte capsule with nifedipine did not change the pharmacokinetics of nifedipine. Yet, concomitant use of gemfibrozil with LipoCol Forte resulted in a significant increase in the plasma concentration of lovastatin acid. These findings suggest that the use of RYR products may not have effects on the pharmacokinetics of concomitant comedications despite their effects to inhibit the activities of CYP450 enzymes and P-gp, whereas gemfibrozil affects the pharmacokinetics of lovastatin acid when used concomitantly with RYR products.

Differential inhibitory effects of proton pump inhibitors on the metabolism and antiplatelet activities of clopidogrel and prasugrel.

The interaction between proton pump inhibitors (PPIs) and clopidogrel/prasugrel was investigated. The IC50 values of omeprazole, esomeprazole, lansoprazole, pantoprazole and rabeprazole on the metabolic ratios of 2-oxo-clopidogrel/clopidogrel, H4 (the active metabolite of clopidogrel)/2-oxo-clopidogrel and R-138727 (the active metabolite of prasugrel)/prasugrel thiolactone in human liver microsomes were determined. The antiplatelet activities of clopidogrel and prasugrel were measured with or without PPIs. As a result, most PPIs (except for pantoprazole) inhibited the formation of 2-oxo-clopidogrel with IC50 values of 20-32 µm and inhibited the formation of H4 with IC50 values of 6-20 µm. PPIs inhibited the formation of R-138727 with IC50 values of 9-25 µm. Among the tested PPIs, omeprazole exhibited the highest inhibitory potency on the formation of H4. Omeprazole, esomeprazole and rabeprazole exhibited the highest inhibitory potencies on the formation of R-138727. For platelet aggregation, omeprazole and lansoprazole show higher inhibitory effects on the antiplatelet activity of clopidogrel. On the other hand, omeprazole, esomeprazole and rabeprazole significantly decreased the antiplatelet activity of prasugrel thiolactone. These data indicate that PPIs differ in their effects of inhibiting the metabolism and antiplatelet activities of clopidogrel and prasugrel.

Caffeic acid improves the bioavailability of L-dopa in rabbit plasma.

The impacts of caffeic acid (3,4-dihydroxycinnamic acid, CA) on the pharmacokinetics of levodopa (L-dopa) were studied in rabbits. A single dose of 5/1.25 mg kg(-1) L-dopa/carbidopa was administered alone or was co-administered with three different doses of caffeic acid (2.5, 5, and 10 mg kg(-1)), or a single dose of 5 mg kg(-1) caffeic acid was administered alone via an intramuscular route to six rabbits each in a crossover treatment protocol. Plasma levels of L-dopa, 3-O-methyldopa (3-OMD), caffeic acid, and ferulic acid were determined and subsequently used to calculate their pharmacokinetic parameters. The results indicated that caffeic acid administered at a dose of 10 mg kg(-1) decreased about 22% of the peripheral formation of 3-OMD and about 31% of the C(max) of 3-OMD. In addition, the metabolic ratios (MR, AUC of 3-OMD/AUC of L-dopa) decreased by about 22%. Results also indicated that caffeic acid significantly decreased the proportion of 3-OMD (p < 0.05). In contrast, the parameters of neither caffeic acid nor ferulic acid were significantly affected by L-dopa/carbidopa. In conclusion, caffeic acid at a dose of 10 mg kg(-1) can significantly affect the COMT metabolic pathway of L-dopa.

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

AIMS: The aim was to explore the role of CYP2C19 polymorphism in short-term rabeprazole-based triple therapy against Helicobacter pylori infection. METHODS: Patients with H. pylori infection were tested for CYP2C19 genotype as poor metabolizers (PMs) or extensive metabolizers (EMs, homozygous EM or heterozygous EM) and given rabeprazole for 7 days. Antibiotics (clarithromycin and amoxicillin) were given on days 1-4, days 4-7, or days 1-7. A direct link model with an effect compartment was used in the population pharmacokinetic-pharmacodynamic analysis. The status of H. pylori infection was evaluated. RESULTS: Rabeprazole clearance was lower in CYP2C19 PMs than in EMs (with average values of 10.7 vs. 16.8 l h(-1) in PMs and EMs, respectively), resulting in higher plasma levels in the former group. The values of EC(50) and k(eo) of gastrin response increased with multiple doses of rabeprazole. The k(eo) values were lower in CYP2C19 PMs than in EMs on day 1 (0.012 vs. 0.017 x 10(-4) l min(-1)), and higher than in EMs on day 4 (0.804 vs. 0.169 x 10(-4) l min(-1)) of rabeprazole treatment. The predicted gastrin-time profile showed a higher response in CYP2C19 PMs than in EMs on days 4 and 7. Helicobacter pylori was eradicated in all CYP2C19 PMs except in one patient infected by a resistant strain. In contrast, in CYP2C19 EMs the eradication rates ranged from 58 to 85%. CONCLUSIONS: CYP2C19 genotypes play a role in H. pylori eradication therapy. Rabeprazole-based short-term triple therapy may be applicable in CYP2C19 PMs for H. pylori eradication.

Pharmacokinetics of nifedipine in Taiwanese.

To elucidate the pharmacokinetics of nifedipine in Taiwanese, a retrospective review of nifedipine bioequivalence studies completed in Taiwan in the past 5 years was conducted. A total of 198 healthy male volunteers were given a single dose of a 10 mg Adalat capsule as a reference drug after overnight fasting. Pharmacokinetic parameters derived from Adalat administration were calculated by non-compartmental analysis with the WinNonlin program. After oral administration of an immediate-release dosage form of a 10 mg nifedipine capsule to Taiwan residents, a skewed distribution with no clear evidence of bimodality of pharmacokinetic parameters was observed. The mean Cmax was 143.12+/-53.48 ng/ml, the mean AUC was 293.77+/-115.62 ng.h/ml, the mean T1/2 was 3.08+/-1.61 h, and the median value of Tmax was 0.61 h. Compared with other published studies, the Cmax and AUC of nifedipine after 10 mg administration were significantly higher in Taiwanese than in British and American subjects. However, the Cmax and AUC were similar to those of Indian and Mexican subjects. According to the antimode of AUC distribution of 22.5 ng.h/ml/mg proposed by Kleinbloesem, 69.7% of Taiwanese can be categorized as slow metabolizers. Based on the results in this study, the majority of Taiwanese show lower activity of nifedipine metabolism.

Time-dependent amplified pharmacokinetic and pharmacodynamic responses of rabeprazole in cytochrome P450 2C19 poor metabolizers.

STUDY OBJECTIVES: To determine the pharmacokinetic and pharmacodynamic rationale for the optimum regimen of rabeprazole in the treatment of Helicobacter pylori infection in patients who are cytochrome P450 (CYP) 2C19 poor metabolizers or extensive metabolizers. DESIGN: Prospective, multiple-dose pharmacokinetic and pharmacodynamic study. SETTING: University-affiliated medical center in Taiwan. SUBJECTS: Twelve healthy volunteers (aged 20-30 yrs) who were identified as CYP2C19 poor metabolizers (six subjects) or extensive metabolizers (six). INTERVENTION: Each subject received rabeprazole 20 mg twice/day for 3 consecutive days and once/day on the fourth day. MEASUREMENTS AND MAIN RESULTS: Pharmacokinetic and pharmacodynamic parameters were compared between CYP2C19 poor and extensive metabolizers on day 1 and day 4 of dosing. The mean +/- SD values of area under the concentration-time curve of rabeprazole and rabeprazole thioether were significantly higher in poor metabolizers than in extensive metabolizers on day 1 (5357 +/- 883 vs 1131 +/- 512 ng x hr/ml and 1703 +/- 432 vs 561 +/- 358 ng x hr/ml, respectively; p<0.001) and on day 4 (5601 +/- 669 vs 1619 +/- 778 ng x hr/ml and 1914 +/- 378 vs 511 +/- 360 ng x hr/ml, respectively; p<0.001). However, no significant difference was noted between day 1 and day 4 of dosing within the same genotype groups. Only CYP2C19 poor metabolizers had significantly higher plasma gastrin levels on day 4 compared with those levels on day 1 (p<0.05). The pharmacokinetic-pharmacodynamic relationship of rabeprazole appears to be time dependent. CONCLUSION: The pharmacokinetic and pharmacodynamic data suggest that CYP2C19 poor metabolizers might be subject to advantageous conditions, especially after day 4, for treating H. pylori infection with rabeprazole.